a - (casting, welding & foundry)

National Conference on Recent Innovations in Production Engineering RIPE - 2010, MIT Campus - Anna University Chennai

A - 1

RADIOGRAPHY TEST ON AA 7075 ALUMINIUM ALLOY GTAW AND

GMAW WELDMENTS

Sivashanmugam1. M, Manoharan. N2, Ravikumar. S3

1. Research Scholar, Sathyabama University, Chennai-119, e-mail: [email protected] 2. Vice Chancellor, Sathyabama University, Chennai – 600 119, India, E-mail: [email protected] 3. Lecturer, Department of Mechanical & Production, Sathyabama University, Chennai – 600 119, India, [email protected].

Abstract: NDT- Non Destructive Testing’s are inspections, checks and surveys carried out by means of methods that do not alter the material and do not require the destruction or removal of test samples from the concerned structure. The main feature of this kind of tests is the possibility to check the concerned parts without interfering with the tested material. On-destructive tests are thus a crucial tool for the product final check. As for safety parts, the check by means of non-destructive test also ensures the product conformity. Aluminum and its alloys have been used in recent times due to their light weight, moderate strength and good corrosion resistance aluminum alloy- AA 7075 has been researched upon especially as a potential candidate for aircraft material. This alloy is difficult to weld using conventional welding techniques like GMAW and GTAW. An attempt has been made in this paper to weld 7075 alloy using GTAW and GMAW with argon as a shielding gas. Mechanical properties of the joint like tensile strength, Hardness and impact strength have been reported. Radiography is widely used in crack detection and other defects inspection. Liquid Penetrate testing, Ultrasonic testing, Eddy current inspection etc. are the various NDT techniques used in industries for final inspection.

Key words: GTAW, GMAW, Radiography, defects detection

1. INTRODUCTION Radiographic Testing (RT), or industrial radiography, is a nondestructive testing (NDT) method of inspecting materials for hidden flaws by using the ability of short wavelength electromagnetic radiation (high energy photons) to penetrate various materials. Either an X-ray machine or a radioactive source (Ir-192, Co-60, or in rare cases Cs-137) can be used as a source of photons. Neutron radiographic testing (NR) is a variant of radiographic testing which uses neutrons instead of photons to penetrate materials. This can see very different things from X-rays, because neutrons can pass with ease through lead and steel but are stopped by plastics, water and oils. Since the amount of radiation emerging from the opposite side of the material can be detected and measured, variations in this amount (or intensity) of radiation are used to determine thickness or composition of material [1]. Penetrating radiations are those restricted to that part of the electromagnetic spectrum of wavelength less than about 10 nanometers. Radiography is one of the most useful of the non-destructive tests which can be applied for assessing the quality of welded joints. Radiography can detect flaws or Discontinuities in welds such as Cold Lap, Porosity, and Slag Inclusions. Incomplete Penetration or Lack of Penetration (LOP), incomplete fusion, internal concavity or Suck Back. Internal & External Undercut Offset or Mismatch, Inadequate & Excess Weld Reinforcement and Cracks [2]. Radiography technique is based upon exposing the components to short wavelength radiations in the form of X-rays of wavelength less than 0.001x10-

8 cm to about 40x10-8 cm from a suitable source. The portion of the weldment where defects are suspected is exposed to X-rays emitted from the X-ray tube [3]. During exposure X-rays penetrate the welded object and thus affect the x-ray film.

mailto:[email protected]




A - 2

1.1 Heat-treatable and Non-heat-treatable alloy Heat-treatable alloys: 2000, 6000, 7000 & 8000 Non-heat-treatable alloys: 1000, 3000, 4000 &5000 1.1.1 Non-Heat-Treatable Alloys The initial strength of alloys in this group depends upon the hardening effect of elements such as manganese, silicon, iron, and magnesium, alone or in various combinations. The non-heat-treatable alloys are usually designated as, in 1,000, 3,000, 4,000 or 5,000 series. Since these alloys are work-hardenable, further strengthening is made possible by various degrees of cold working, denoted by the "H" series of tempers. Alloys containing appreciable amounts of magnesium when supplied in strain-hardened tempers are usually given a final elevated temperature treatment called normalizing to ensure stability of properties.[4] 1.1.2 Heat-Treatable Alloys Heat-treatable alloys are 2000, 6000, 7000 & 8000 in series. The initial strength of alloys in this group is enhanced by the addition of alloying elements such as copper, magnesium, zinc and silicon. Since these elements single or in various combinations show increasing solid solubility in aluminum with increasing temperature, it is possible to subject them to thermal treatments which will impart pronounced strengthening. Precipitation hardening is commonly used to process copper alloys and other non-ferrous metals for commercial use .The examples of aluminum –copper alloys, copper-beryllium, copper –tin, magnesium- aluminum and some ferrous alloys [5].

Table: 1Base metal AA7075 chemical composition and microstructure investigation

1.1.2 Digital Radiography Digital image processing involves manipulating one or more digital images Operations of practical importance on a single image involve artifact suppression, gray-scale manipulations, distortion corrections, and edge enhancement. Important techniques involving two or more images are (time difference) subtraction, dual energy cancellation of bone or soft tissue structures, and the extraction of flow or organ function parameters. The processing of a single image can be classified as a point operation, a local operation or a global operation. A point operation uses a single point (pixel) of the initial or input image to obtain the corresponding point of the final or output image. A local or neighborhood operation uses several pixels in a limited area of the input image to obtain a point in the processed or final image [6].

Fig.1 Base metal microstructure

Fig.1 refers the microstructure which has revealed spheroidal particles of Mg2Zn2 (black) and light grey particles of FeAl3 present in the aluminium solid solution. Fig.2 shows the Microstructure has revealed Interdendritic eutectic with light grey particles of FeAl3 present in the solid solution [7].

200 X


A - 3

Fig.2 welded zone microstructure

Fig.3 Heat affected zone (HAZ)

Fig.3 refers the HAZ microstructure shows the elongated grains with grain boundary eutectic and light grey particles of Al3 present in the aluminum solid solution. Fig.4 shows the tungsten inclusions in the micrograph with irregularly shaped lower density spots randomly located in the weld image.

Fig.4 - Irregularly shaped lower density spots randomly located in the weld image

The TIG & MIG weldments are radio graphically tested with VIDISCO (fox – Rayzor) Machine for various intensities with time were taken the following set value (100/40,100/35,100/30). By using 10-16-AL pentameter it is low range thickness we observed 3 wire lines of sensitivity in digital graphs through necked eye [8].

Fig.5 GTAW-X-ray (VIDISCO)

200 X

200 X


A - 4

Fig.6 GTAW-X-ray (VIDISCO)

Fig.7 GMAW- X-ray (VIDISCO)

5.0 CONCLUSION The experimental TIG & MIG weldments are tested by means of digital radiography with different intensity and time. The observed images are in fig.5, 6 & 7 shows the defect of porosity and cluster porosity in both the weldments, and if the experimental parameters are optimized the defect can be nullified. 6.0 REFERENCES 1. Thwarter, “Recently developed solutions for aerospace applications,” Materials Science Forum, Vol.519-

521, 2006, pp. 1271–1278. 2. Saqib sadiq, Future prospects for space materials, Quality Assurance and materials Research Division,

Pakistan space and upper Atmosphere research. 3. Aircraft materials and process, M.George 4. A Method for studying Weld Fusion Boundary Microstructure Evolution in Aluminum Alloys By Kostrivas and J.C.Lippold (Supplement to the welding journal January 2000 5. Studies on friction stir welded AA 7075 Aluminium Alloy, K.Srinivasa Rao et al,Vol 57,No 6 , December 2004, pp.659-663. 6. Gas tungsten arc welded AA 2219 Alloy using scandium containing fillers- mechanical and Corrosion behavior, S.R.Koteswararao, G.Madhusudhan Reddy,K.Srinivasa Rao, P.Srinivasa Rao vol.57, October 2004, pp.451-459. 7. Mechanical and microstructural behavior of 2024-7075 aluminium alloy sheets joined by friction stir Welding P.Cavaliere, R.nobile, F.W.panella, A.Squillace, International journal of machine tools and Manufacture, 46,(2006),pp.588-594. 8. Aluminum information at aircraft spruce.com .accessed, October 13, 2006.Effect of welding processes on Tensile properties of AA6061 aluminum alloy joints A.K.Elongovan K.Lakshminarayanan&V. Balasubramanian.


A - 5

CONTINUOUS CONTROL OF THE THICKNESS DISTRIBUTION IN

SUPERPLASTIC FORMING PROCESS

G. KUMARESAN1, S. DINESH KUMAR2, K. KALAICHELVAN3

1. Teaching Research Associate, 2. PG Student 3. Assistant Professor, MIT Anna University, Department of Production Technology Chennai e-mail:[email protected]

Abstract:Superplasticity in materials is characterized by large neck-free elongation under low flow stress when they are formed at temperature exceeding about one half of the melting point. In superplastic forming, the controlling of the thickness distribution is a very important problem. Sheets formed under this technique obtain variation thickness. It leads to the degradation of the mechanical properties of the formed parts. In this work eutectic Pb-Sn superplastic sheet materials were considered. Cast sheet blanks were thermomechanically treated to obtain superplastic properties. The complex shape (combination of the rectangular with dome shape) was identified. As the forming height increases, the thickness decreases in the formed components. The proximity sensor was used to indicate the dynamic height variation of the formed component. Based on the height variation of the formed component, the bulging pressure was controlled. Instead of the constant bulge pressure method, the continuous control of the bulging pressure according to the bulge height variation, the variation in thickness distribution of the formed component was controlled. Key word: Superplastic forming, uniform thickness, proximity sensor.

1.INTRODUCTION Super Plastic Forming (SPF) is a manufacturing process whereby certain material under the correct conditions of temperature and strain rate exhibit a large elongation without failure, while requiring low forming pressure and no heat treatment. This phenomenon has been observed for a wide range of materials including metallic alloys (such as titanium, aluminium alloys, ceramics, composites and minerals) [1-3].In practice, superplastic forming are summarized as a grain size less than 10µm,low strain rate of less than 10-3s-1 and at temperatures of ≥ 0.5Tm,where Tm is the melting point of the material. The main application fields of this process are automobile and aircraft industries because of its superior characteristics, such as lightweight, low cost and short fabrication time. The problems related with non- uniform thickness distribution and cavitation often occur during Superplastic forming [4-5]. It leads to a degradation of the mechanical properties of the super plastically formed parts. In the current study, an investigation of the effect of variable pressure method on the superplastic forming behavior of a eutectic pb-sn sheet material is presented. 2. EXPERIMENTAL WORK 2.1.Experimental Setup The process setup consist of a air compressor with tank, thermocouple to measure the die temperature. The forming chamber consist of top and bottom dies. Recess is provided in bottom die to hold sheet blank. The Top die is a complex shape(Combination of the rectangular with the Dome shape).The entire die arrangements where placed in a furnace and the die temperature was controlled by temperature controller. The compressed air fed to the forming chamber as shown in fig.1.

mailto:e-mail:[email protected]


A - 6

Fig 1. Experimental setup

2.2.Material Preparation The Material selected for this work is eutectic lead and tin composition. The pb 61.9 and sn 38.1 alloy was prepared by melting one-hour 184°C and cast into a mould of the dimension 100mm X 92mm X 5mm.The sheets are prepared to a thickness of 1mm by Thermo-mechanical treatments for required grain-size. Finally the circular sheet with a thickness of 1mm and an effective diameter of 90mm were prepared. 2.3.Experimental Procedure The Experimental work was divided into two segments. In the first segment, two samples namely I and II were considered .In the next segment, three samples namely, samples A,B &C were considered. In the first Segment for sample I a constant forming pressure of 0.3 Mpa were chosen and for sample II two different forming pressure of 0.3 Mpa (up to first 8mm formation)and 0.2 Mpa (up to next 8mm formation) were chosen and the forming temperature of 100°C was selected. The eutectic pb-sn sheet samples I and II were superplastically formed in the die setup as shown in fig1.The superplastically formed part was taken out of the die setup and the thickness distribution was measured. In the second segment for sample A, a constant forming pressure of 0.3 Mpa were chosen and for sample B two different forming pressure of 0.3 Mpa (up to first 8mm formation)and 0.2 Mpa (up to next 8mm formation) were chosen. For sample C three different forming pressure of 0.3 Mpa (up to first 8mm formation) and 0.2 Mpa (up to next 4mm formation)and 0.1 Mpa (up to last 4mm formation) were chosen and the forming temperature of 100°C was selected. The eutectic pb-sn sheet samples A,B and C were superplastically formed in the die setup as shown in fig 1.The superplastically formed part was taken out of the die setup and the thickness distribution was measured. 3.RESULTS AND DISCUSSION In the First segment the sample I that was formed under high pressure(0.3 Mpa) took less forming time and the thickness distribution were not good compared with the sample II that was formed under two stages. In the first stage the sample II was formed under high pressure (0.3 Mpa) up to first 8mm of the die cavity. In the next stage the sample II was formed under low pressure (0.2 Mpa) up to the remaining 8mm of the die cavity. In the second segment the sample A that was formed under high pressure(0.3 Mpa) took less forming time and the thickness distribution were not good compared with the sample B and C. The sample B was formed under two stages. In the first stage the sample B was formed under high pressure (0.3 Mpa)up to the first 8mm of the die cavity, In the next stage the sample B was formed under low pressure (0.2 Mpa) up to the remaining 8mm of the die cavity. The Sample C was formed under three stages. In the first stage the sample C was formed under high pressure (0.3 Mpa) up to the first 8mm of the die cavity, In the next stage the sample C was formed under low pressure (0.2 Mpa) up to the next 4mm of the die cavity. In the third stage the sample C was formed


A - 7

under very low pressure(0.1 Mpa) up to last 4mm in the die cavity. The thickness distribution were good in sample C compared with sample A and B. In dynamic control pressure method ,the pressure was controlled continuously according to the component height, the proximity sensor was used to indicate the dynamic height variation of the formed component. Instead of the constant pressure method, the dynamic control pressure method was used for getting uniform thickness distribution throughout the formed component.

Fig.2 Formed component

Fig.3 Different position of thickness measurement in the formed component.

Table 1 Segment 1

SEGMENT 1 SAMPLE 1 SAMPLE 2

POSITION THICKNESS(µm) POSITION THICKNESS (µm) 1 1 000 1 1000 2 690 2 690 3 620 3 680 4 700 4 720 5 730 5 725 6 610 6 675 7 730 7 720 8 700 8 720 9 620 9 700 10 690 10 680


A - 8

Table 2 Segment 2

SEGMENT 2 SAMPLE A SAMPLE B SAMPLE C

POSITION THICKNESS (µm)



1 1000 1 1000 1 1000 2 650 2 710 2 710 3 640 3 670 3 690 4 740 4 730 4 720 5 640 5 670 5 760 6 600 6 640 6 670 7 640 7 680 7 780 8 740 8 740 8 680 9 610 9 640 9 670 10 640 10 710 10 720

4. CONCLUSION In order to have uniform thickness distribution, with considerable amount of deformation, the continuous control of superplastic forming process gives significant results in thin sheet superplasitc forming. In this test, two things were absorbed, In slow pressure the thickness distribution and dome height are favorable and in high pressure they are not favorable, but the forming time is reduced. An experiment was conducted based upon variable pressure method, according to the component height variation to achieve the uniform thickness distribution with minimum forming time. 5. REFERENCES 1. Young-Seon Lee,Sang-Yong Lee,Jung-Hwan Lee,(2001), “A Study on the process to control the cavity and

the thickness distribution of superplastically formed parts”, The international journal of Materials processing technology, Vol 112,pp 114-120.

2. Yenihayat O.F ,Mimaroglu A and Unal H,(2005), “Modelling and tracing the super plastic deformation process of 7075aluminium alloy sheet: use of finite element technique”, The international journal of Materials and Design, Vol26, pp73-78.

3. Kalaichelvan.K, Sivaramakrishnan.R, Dinakaran.D, Joseph Stanley.A,(2005), “Cavity Minimization and Uniformity studies on Superplastic forming of thin eutectic Pb-Sn sheet by optimum loading and performing”, The International Journal of Materials processing Technology, Vol 162-163,pp 519-523.

4. Senthil Kumar V.S, Viswanathan.D, Natarajan.S,(2006), “Theoretical prediction and FEM analysis of superplastic forming of AA7475 aluminium alloy in a Hemisperical Die”,The International Journal of Materials processing Technology, Vol 173,pp 247-251.

5. Padmanabhan k.A.,(1980), Superplasticity, Springer-Verlag Berlin Heidelberg New York.


A - 9

EXPERIMENTAL INVESTIGATIONS ON SQUEEZE CASTING OF

METAL MATRIX COMPOSITES (A356 Al alloy +SiC)

P.Senthilkumar1, Dr. M.Jayaraman2

1. Final M.E (CAD/CAM) 2. Professor & Head, Department of Mechatronics Engineering, Kongu Engineering College, Erode, email: [email protected]

ABSTRACT: Squeeze casting is a hybrid metal forming process combining features of both casting and forging in one operation. An attempt was made to prepare solid cylindrical components of (A356 +SiC) aluminum alloy through squeeze casting The objective is to investigate the effect of process parameters on the mechanical and metallurgical properties exhibited by the castings produced though squeeze casting process . A set of trials are conducted based on parameters settings suggested in Taguchi’s offline quality control concept. The experimental results indicate that the squeeze pressure and the die-preheating temperature, pouring temperature, Duration of pressure application were the parameters making significant contribution toward improvement in mechanical properties of squeeze cast (A356 +sic) aluminum alloy. Keywords: Squeeze casting, Taguchi method, Tensilestrength, microhardness

1. INTRODUCTION

Metal matrix composite materials are advanced materials, which combine tough metallic matrix with a ceramic. Metal matrix composites show advantages in a great number of specific applications (aircraft, automobile, machines) due to their high specific strength and stiffness, wear resistance and dimensional stability(1). Conventional casting process cannot produce parts as strong as forged parts. Squeeze casting accounts for 15 to 40% improvement of the mechanical properties than gravity die casting (2). This study investigated the effects of squeeze parameters on the properties of squeeze castings and the optimum parameters for producing squeeze castings from Al-Si alloy. Squeeze casting is a very important manufacturing process that combines the advantages of forging and casting and is used for the production of a wide range of products from monolithic alloys and metal-matrix composites parts. It also compared the properties of the squeeze castings with those of chill castings (3).

The use of reinforcement among others a good understanding of the effects of process parameters is essential as the structure and properties of alloys can be optimised without the use of expensive alloying elements or nucleating agents It was found that the SiC particles acted as substrates for heterogeneous nucleation of Si crystals in one of the cast composites(4). This observation can also be explained by the thermal lag model proposed. The microstructure and fracture behavior of the composites were examined The Taguchi approach enables a comprehensive understanding of the individual and combined from a minimum number of simulation trials (5). This technique is multi – step process which follow a certain sequence for the experiments to yield an improved understanding of product or process performance (6).Though several works applying Taguchi methods on die cast components have been reported in literature, it appears that very limited works have been carried out for squeeze cast components. On considering the importance of aluminum alloys, the main objective of the research was to apply Taguchi method to find the optimal set of control parameters for squeeze casting of (A356+ SiC) aluminum alloy.



A - 10

2. SQUEEZE CASTING – PROCESS OUTLINE

Squeeze casting process, is based on the pressurized solidification of the molten metal in re-usable dies, and involves the following steps: 1.Preheating of the die and the punch. 2.Pouring molten metal into the die cavity. 3.Application of squeeze pressure and allowing for solidification. 4.Ejection of solidified casting Table 1 Control factors and levels

Factor notation

Control factor

Level 1 Level 2 Level 3

A Squeeze pressure(MPa) 4 8 12 B Pouring temperature(°C) 800 850 900 C Duration of pressure application(sec) 20 40 60 D Die preheating temperature(°C) 80 160 250

3 .TAGUCHI METHOD Taguchi method is an efficient problem-solving tool, which can upgrade/improve the performance of the product process, design, and system with a significant slash in experimental time and cost this technique determines the most influential parameter on the output response for the significant improvement in the overall performance. Table 2 Experimental observations

Exp. no A B C D Tensile strength MPa

Hardness BHN

1 4 800 20 80 220 70 2 4 850 40 160 223 84 3 4 900 60 250 216 93 4 8 800 60 160 210 88 5 8 850 20 250 228 95 6 8 900 40 80 236 80 7 12 800 40 250 230 94 8 12 850 60 80 240 95 9 12 900 20 160 234 82

Exp. no – Experiment number .A – Squeeze pressure (MPa), B – pouring temperature (°C), C – Duration of pressure application (Sec), D- die-preheating temperature (°C). Table 3 S/N ratio for tensile strength and hardness

EXP NO

A B C D S/N Ratio Tensile strength

S/N Ratio (Hardness Hv)

1 1 1 1 1 47.8260 38.8378 2 1 2 2 2 47.4782 38.6226 3 1 3 3 3 46.9565 38.3333 4 2 1 3 2 48.5652 39.7927 5 2 2 1 3 48.3043 39.4827 6 2 3 2 1 48.7297 39.3396 7 3 1 2 3 48.8918 39.8113 8 3 2 3 1 48.8945 39.8113 9 3 3 1 2 47.9130 39.6792

In order to observe the influencing degree of process parameters in squeeze casting, four parameters namely squeeze pressure, pouring temperature, duration of pressure application and die preheating temperature each at three levels were considered and are listed in Table 1. Maintaining these processing parameters as constants enabled us to study the effect of squeeze pressure, die preheat temperature, and duration of pressure application. The total degrees of freedom for four parameters in each of three levels were 6. A three level L9 34 orthogonal array with nine experimental runs was selected (degrees of freedom = 9-1 = 8). Table 4 Pareto ANOVA for three level factors

Factors A B C D Total 1 ΣA1 ΣB1 ΣC1 ΣD1

2 ΣA2 ΣB2 ΣC2 ΣD2

Sum at factor level

3 ΣA3 ΣB3 ΣC3 ΣD3

T

Sum of squares of differences SA SB SC SD ST Degrees of freedom 2 2 2 2 8 (contribution ratio)/100 SA/ST SB/ST SC/ST SD/ST 1


A - 11

T = ΣA1 + ΣA2 +ΣA3 SA = (ΣA1 - ΣA2)2 + (ΣA1 - ΣA3)2 + (ΣA2 - ΣA3)2 SB = (ΣB1 - ΣB2)2 + (ΣB1 - ΣB3)2 + (ΣB2 - ΣB3)2 SC = (ΣC1 - ΣC2)2 + (ΣC1 - ΣC3)2 + (ΣC2 - ΣC3)2 SD = (ΣD1 - ΣD2)2 + (ΣD1 - ΣD3)2 + (ΣD2 - ΣD3)2 ST = SA + AB + SC + SD 4. EXPERIMENTAL PROCEDURE

A 25 tone hydraulic press was modified to apply pressure during solidification of the aluminum alloy. The (A356+ SiC) aluminum alloy was melted and the die was preheated using a stirrer Casting furnace. The experimental set-up is shown in Fig. 1. Two trial castings were made as per the data sheet of L9 (34) orthogonal array. Tensile strength and hardness specimens were machined from these castings and the obtained values are tabulated in Table 2.

Fig. 1 Experimental set-up 5. RESULTS AND DISCUSSION The squeeze cast process parameters, namely squeeze pressure (A), pouring temperature (B) and duration of pressure application (C) and die preheating temperature (d) were assigned to the 1st, 2nd, 3nd and 4th columns of L9 34 array, respectively.. The S/N ratios were computed for tensile strength and hardness in each of the nine trial conditions and their values are given in Table3. Table 5 Pareto ANOVA for tensile strength

Factors A B C D Total 1 142.2607 143.5992 144.0433 144.1526 2 145.5992 145.283 145.0997 143.9564

Sum at factor level

3 145.6993 144.677 144.4162 145.4502

433.5592

Sum of squares of differences

22.9796 7.6484 1.7221 3.9536 36.3037

Degrees of freedom 2 2 2 2 8 Contribution ratio 63.30 21.07 4.74 10.89 100 Optimum level A3 B2 C2 D3

From Table (5), it can be seen that the third level of factor (A) give the highest summation squeeze pressure of 12MPa (A3). The highest summation for factor (B) is at the second level pouring temperature of 850°c (B2) and the highest summation for factor(C) is at the second level duration of pressure application 40 s (C2) and the highest summation for factor (B) is at the third level die preheating temperature of 250°C (D3). These predicted parameters are not used in the composite preparation which indicated in table (2). We conducted an experiment at the predicted parameters (A = 12 MPa, B = 850°c and C = 40 s, D=250°C), and tested the resulted specimen by tensile. These levels were found to improve tensile strength and hardness. It must be noted that the above combination of factor levels A3, B2, C2, D3 are not among the nine combinations tested for the experimentation. This was expected because of the multifactor nature of the experimental design employed.(9 from 33=27 possible combinations). The resulted tensile strength was 256 MPa which is greater than the tensile strength values in table (3). These results have proved the success of Taguchi method in the prediction of the optimum parameters for higher tensile strength In table (6) it can be seen that the highest summation is at A3 (squeeze pressure of 12MPa e), B2 (pouring temperature of 850°c), and C2 (duration of pressure application 40 s), and D4 (die preheating temperature of 250°C). The predicted parameters for giving the highest hardness by Taguchi method is already used in our experiments and it gave the highest hardness. This also proves the success of Taguchi method


A - 12

Table 6 Pareto ANOVA for hardness

Factors A B C D Total 1 115.7937 117.9276 117.7735 117.9997 2 118.615 118.4418 117. 9997 117.6273

Sum at factor level

3 119.0128 117.3521 117.9483 119.0945

338.0996

Sum of squares of differences

18.4806 2.0328 0.0843 3.4899 24.0876

Degrees of freedom 2 2 2 2 8 Contribution ratio 76.72 8.44 0.34 14.50 100 Optimum level A3 B2 C2 D3

6. CONCLUSIONS Squeeze cast technology has the potential to play an important role in the near future for improving the quality of the engineering components. This paper has reported a research in which Taguchi's off – line quality control method was applied to determine the optimal process parameters which maximize the mechanical properties of A356+SiC al alloy composites. For this purpose, concepts like orthogonal array, S/N ratio and ANOVA were employed. After determining the optimum process parameters one confirmation experiment was conducted. In light of our analysis the following conclusions were drawn: The optimum level of process parameters to obtain good mechanical properties of squeeze cast components of A356+SIC aluminum alloy are a squeeze pressure of 12 MPa and pouring temperature of 850°c and duration of pressure application 40 s, die preheating temperature of 250°C.Taguchi method has proved its success in prediction the optimum parameters to reach the best properties.

REFERENCES 1. Surappa.M.K.(2003) ‘Aluminium matrix composites: Challenges and opportunities’ Journal of

Sadhana,Vol.28 parts 1&2 pp . 319-334. 2. Vijian.P. Arunachalam.V.P. (2007) ’Optimization Of squeeze casting process parameters using Taguchi

analysis’ Int J Adv Manufacturing Technology Vol 33 pp. 1122–1127. 3. Raji.A and Khan.R.H. (2006) ‘Effects of Pouring Temperature and Squeeze Pressure on Al-8%SAlloy

Squeeze Cast Parts’ pp. 229-237 4. Zhou.W, Xu.Z.M (1997)’Casting of SiC Reinforced Metal Matrix Composites’ Journal of Materials

Processing Technology Vol 63 pp. 358-363 5. Shang-Nan Choua, Jow-Lay Huanga, Ding-Fwu Lii b, Horng- HwaLu(2006)‘The mechanical properties of

Al2O3/aluminum alloy A356composite manufactured by squeeze casting’ Journal of Alloys and Compounds Vol 419, pp. 98–102

6. Osama S. Muhammed , Haitham R. Saleh & Hussam L. Alwan (2009) ‘Using of Taguchi Method to Optimize the Casting of Al–Si /Al2O3 Composites’ Journal of Eng and Technology Vol 27.

National Conference on Recent Innovations in Production Engineering, RIPE – 2010, MIT Campus – Anna University Chennai

A-13

RISK ANALYSIS OF PRESSURE VESSEL DUE TO WELD FRACTURE

S.Sathiya moorthy1, Dr.K.Kalaichelvan2, Dr.K.Balaji rao3, Dr.A.Rajadurai4

1. MIT Anna University Department of Production Technology,Chennai E-mail: [email protected] 2. MIT Anna University Department of Production Technology,Chennai E-mail: [email protected] 3. Structural Engineering Research Centre Department of Risk and Reliability,Chennai E-mail: [email protected]

Abstract: The main aim of this project is to identify the procedure commonly used to design pressure vessel. From the literature review it has been found that two design codes namely ASME and European code are popularly used for design the design of pressure vessel. The project presents first the consideration in the design towards identification of critical components. This is followed by a critical evaluation of design process in ASME. The critical evaluation would be useful in setting up the safety margin equation required for carrying out reliability analysis. From the review it is also noted that application of fracture mechanics concepts are gaining important in the design of welds of pressure vessel. The brittle fracture model by European standard EN 13445 is found to be suitable for the reliable design of pressure vessels. The supremacy of EN 13445 is due to the incorporation of various factors such as crack geometry, primary and secondary stresses, relation between fracture toughness and impact toughness, influence of strain rate on fracture toughness and safety margin. PV Elite software is used to analyze the pressure vessel to calculate the thickness, maximum allowable pressure and stress and minimum design temperature. These values are carried out to ANSYS software to probabilistic analysis. Key words: Pressure vessel, Stress, Weld, Brittle failure, reliability

1. INTRODUCTION

A pressure vessel is a closed container designed to hold gases or liquids at a pressure different from the ambient pressure. The pressure differential is potentially dangerous and many fatal accidents have occurred in the history of their development and operation. Consequently, their design, manufacture, and operation are regulated by engineering authorities backed up by laws. For these reasons, the definition of a pressure vessel varies from country to country, but involves parameters such as maximum safe operating pressure and temperature. The fracture toughness values measured on the single edge bending [SE (B)] specimens with both orientations follow the course of the master curve. Nearly all values lie within the fracture toughness curves for 2% and 98% fracture probability. There is a strong variation of the reference temperature T0 through the thickness of the welding seam, which can be explained by micro structural differences. The scatter is more pronounced for the TS SE (B) specimens. It can be shown that specimens with TL and TS orientation in the welding seam have a differentiating and integrating behavior, respectively. High strength steels have wide application in engineering structures. Their performance to cost ratio makes these steels very competitive. In the past the use of high strength steels in pressure vessels has been fairly limited. One concern has been that the risk for brittle failure could be unacceptably high. This is reflected in





A-14

the design of pressure vessel, where the strength exceeding the certain pressure value. To improve the design procedures against brittle failures, in this project deals with the design of a pressure vessel. Type of the material used, weld characteristics and the design process are studied in detail, while designing the pressure vessel and analysis the pressure vessel using PV Elite and ANSYS software for probabilistic analysis against the brittle fracture.

2. DESIGN OF PRESSURE VESSEL

Pressure vessels have been designed with standard code books like ASME boiler and pressure vessel, European standard and Indian boiler standard. They have different type of design methods. They are

1. Working stress method 2. Limit analysis method 3. PSF method

In ASME standard the pressure vessels have designed with working stress method because the safety of weld zone against weld fracture is very high compared with other design methods. So identified the critical components in the typical pressure vessel and designed the pressure vessel with ASME standard by working stress method. Shell, head, weld joints, nozzle and gaskets identified as the major component in the pressure vessel. 3. DESIGN FACTORS OF PRESSURE VESSEL While designing the pressure vessel, some of the most critical factors are taken into account to design the pressure vessel. They are Material requirement thickness, Material selection, Strength, Fracture toughness, Corrosion allowance, Stress, Maximum allowable stress, Internal and External pressure, Temperature, Weld method (Types & categories)

The material requirement thickness, pressure and stress values are calculated from the Table 1.

Table 1 ASME code equations

In pressure vessel, ASME standard materials are used to manufacture both shell and heads. Most of the time the shell and head materials are same. But some cases it varies due to some working pressure condition. The materials are grouped based on common fracture toughness properties. Lower strength grades of same specifications have better fracture toughness and normalization improves fracture toughness. In this project we select the SA 516 Grade 55,60,65,70 materials. This material contains C-Mn-Si composition. The material would have negligible toughness in which case the weld would fracture through thickness. The reactors may have been subjected to stresses greater than those considered here. The cracks will likely continue growing and linking around the circumference. The stress intensity values for the cracks to link around the manhole circumference are greater than those for the crack to propagate through the thickness.


A-15

The stresses are also induced some crack growth in a pressure vessel. So the every material is having some maximum stress value to resist the fracture during the pressurized condition. The allowable stresses for all permissible materials of construction are provided in the ASME Code Book listed below.

Table 2 Maximum Allowable Stress

SA516 Gr 60 Gr65 Gr70

Tensile Strength (MPa) 415-550 450-585 485-620

Yield Strength (MPa) 220 240 260

4. BRITTLE FRACTURE MODEL FOR PRESSURE VESSEL 4.1 Basic Assumptions in the Model 4.1.1 Crack geometry For linear elastic component behavior (linear elastic fracture mechanics) the stress intensity factor of a component is calculated from

( )WcaaYK applI ,2,∏= σ (1) where KI is the stress intensity factor, sappl the component stress perpendicular to the crack, a the crack depth of the design crack, 2c the crack length of the design crack, W the component width and Y a geometrical correction factor, which is taken from handbooks. An elliptical surface crack with a/c=0.4 is assumed in the same way as in the model for EN 13445, which corresponds to a value of =1.001 for this geometry. In a crack depth of a=t/4 is the starting point, where t is the gauge thickness. This is a reasonable assumption for thicker gauges since such large cracks should easily be detected during non-destructive testing. 4.1.2 Primary and Secondary Stresses The background to the basic assumptions in the model on stress levels will only be summarized briefly here since a more detailed account can be found elsewhere. The applied stress in Eq. (4.1) has contributions from primary and secondary stresses. The maximum primary (hoop) stress allowed is

=

m

nomm

s

nomelprim f

Rf

R ,, ,minσ (2)

Where ReL,nom and Rm,nom are the nominal yield and tensile strength. The safety factors in general take the values fs=1.5 and fm=2.4. The maximum secondary stress value at As welded condition

shiftnomels

AW Rf

σσ +

−= ,sec,

11 (3)

The primary and secondary stresses are used to calculate the stress intensity factor. The total stress intensity factor KI is given as the sum of a contribution from the primary stresses, KI

p, and a contribution from the secondary stresses, Ks

I. V is applied to KsI to account for plasticity effects.

SI

PII KKK += (4)


A-16

4.1.3 Relation between Fracture Toughness and Impact Toughness The temperature dependence of the fracture toughness can be expressed as

41

41

27

11ln25

5218exp771120

−

×

+−

++=feff

JDc PB

TTK (5)

TD is the test temperature, T27J is the impact transition temperature at 27 J, Beff the effective thickness (=total crack front length in mm), and pf the failure probability. Eq. (5) also gives the thickness correction to Kc and the relation between the impact transition temperature and the fracture toughness. Using this relation, the minimum design temperature is calculated to avoid the brittle fracture failure in the pressure vessel. 5. CONCLUSION In this project, identified the reliable procedure to design pressure vessel according to ASME boiler and pressure vessel and design towards identification of pressure vessel components. The critical evaluation of design process in ASME using with material requirement thickness, material selection, strength, fracture toughness, corrosion allowance, maximum allowable stress, internal and external pressure and temperature. From the brittle fracture model, calculated the minimum design temperature against brittle fracture. PV Elite pressure vessel analysis software results compared with this brittle fracture model. 6. REFERENCES

1. ASME Boiler and Pressure vessel code book (2007), Vol. 2. 2. Bouchard P.J., Goldthorpe M.R., Prottey P, (2001), “Integral and local damage fracture analyses for a

pump casing containing large weld repairs”, Journal of Pressure Vessels Piping, Vol.78, pp 295-305. 3. Giovanola J.H and Kirkpatrik S.W, (1999), “Fracture of geometrically scaled, notched three points bend

bars of high strength steel”, Journal of Engg Fracture mechanics”, Vol.62, pp 291-310. 4. Jovanovic A, (2001), “Risk based inspection and maintenance in power and process plants in europe”,

Paper 10, MPA-Safe Workshop, Vol.226, pp 165-182. 5. Mayer K.H, Heinruch D, Prestel W, Gnirss G, (1993), “Investigation by non destructive inspection to

determine the size of natural defects in large forgings of turbo generators”, Journal of Nuclear engineering, Vol.144, pp 155-170.

6. Raju I.S and Newman J.C.J, (1982), “Stress intensity factors for internal and external surface cracks in cylindrical vessels”, Journal of pressure vessel Technology, Vol. 104, pp 293-298.

7. Rolf sandstorm and peter langenberg, (2004), “New brittle fracture model for the European pressure vessel standard”, Journal of Pressure Vessel and Piping, Vol. 817, pp 837-845.


A-17

MONITORING AND DYNAMIC CONTROL OF PRESSURE IN

SUPERPLASTIC FORMING PROCESS

S.Dinesh Kumar1, G.Kumaresan2, K.Kalaichelvan3

1. P.G Student, MIT Anna University Department of Production Technology,Chennai e-mail: [email protected] 2. T.R.A, MIT Anna University Department of Production Technology,Chennai e-mail: [email protected] 3. Asst.Proffessor, MIT Anna University Department of Production Technology,Chennai e-mail: [email protected]

Abstract: Superplasticity is the process of deformation of metals that is capable of producing neck free elongations of 100%-5000% under certain condition. The variation in thickness distribution in the formed component is one of the major defects in superplastic forming. To achieve the superplastic behavior, the material is subjected to thermomechanical treatment to increase its ductility. Initially the sheets were cut into circular bank. The forming process was conducted at constant temperature by varying pressure for complex shape. As the forming height increases, the thickness decreases in the formed component. A sensor is used to detect the height of the formed component and the output signal will be sent to the PC through the Data Acquisition Card. The program to receive the signal from sensor and to control the strain rate is to be programmed with visual C++. Based on the value of sensor, the compressed air is applied to die and controlled by the stepper motor. Hence in this work, the forming parameters can be controlled at any time to minimize the variation in the thickness distribution. Keyword: Superplastic Forming, Proximity Sensor, Data Acquisition System

1. INTRODUCTION

Superplasticity is a term used to indicate the exceptional ductility that certain metals can exhibit when deformed under proper conditions [5]. For a superplastic metal that is tensile tested under proper conditions of temperature, the observed ductility is seen to vary substantially with strain rate. The constitutive equation of superplastic materials, which defines the relationship between the flow stress, s, the strain, e, and the strain rate, έ, is

σ = kεn έm (1) Where K is the strength coefficient, n the strain hardening index and m the strain-rate sensitivity index.

The uniform thickness distribution plays the important role in the mechanical strength of the formed component. Hence it becomes necessary to control the thickness variation of the superplastic formed component. The component for superplastic forming is modeled using suitable parameters. The component is a combination of rectangular box [1] and a dome shape [2] and the parameters varies with respect to the shape.

2. EXPERIMENTAL SETUP

The experimental setup for this work is shown in Fig.1. Here the Die is placed in the furnace in which the compressed air from the compressor is sent through the base of the Die. The strain rate for the superplastic forming is produced by the compressor.





A-18

Fig.1. Experimental Setup

2.1 Sensor

The Sensor that is used for the detection of the range of the sheet metal forming in the Die is LVDT.

The strength of the LVDT sensor's principle is that there is no electrical contact across the transducer position sensing element which for the user of the sensor means clean data, infinite resolution and a very long life. Since an LVDT operates on electromagnetic coupling principles in a friction-free structure, it can measure infinitesimally small changes in position. As the sheet metal moves upward in the Die, the LVDT will sense the distance moved by the sheet within the Die.

2.2 Data Acquisition System

Today, most scientists and engineers use personal computers (PCs) with PCI, PXI, Compact PCI, PCMCIA, USB, FireWire, parallel, or serial ports for data acquisition in laboratory research, test and measurement, and industrial automation. The visual C++ software is used to control the Data Acquisition Card to receive the signal from the sensor and to send the signal from PC to stepper motor for controlling the forming process. The system interface of the Sensor, PC and Stepper motor through the Data Acquisition Card [3] is shown in Fig.2.

Fig.2. DAC System Interface

3. Formed Component The component chosen for the superplastic forming is AA2024 aluminum alloy. The forming parameters

used for the superplastic forming to identify the variation in thickness distribution of the 1 mm thickness


A-19

sheet are a constant temperature of 5000C and a constant forming pressure of 4 Bar. The formed component is shown in Fig.3.

Fig.3. Formed Component

4. Dynamic Control

The Superplastic forming process can be dynamically controlled by varying the strain rate with respect to the height of the component that is forming inside the Die. The initial strain rate should be higher and succeeding strain rate with respect to the increase in the height of the forming sheet should be gradually reduced after every succession. The varying strain rate is been shown in the Fig.4.

Fig.4. Strain rate control

5. Results and Discussion

The superplastic forming parameters for modelling the complex shape was studied and a Die for the complex shape was modelled. The alloy which is suitable for superplastic forming is been used for forming in the modelled Die. The Thickness Distribution of the Formed Component is shown in the Fig.5.


A-20

Fig.5. Thickness Distribution of the Formed Component

Since the uniform thickness plays the major role in the formed component, a LVDT is used to measure the forming sheet dynamically and the strain rate is controlled with respect to the LVDT feedback by controlling the pressure with the stepper motor. Hence the variation in the thickness distribution of the superplastic forming will be minimized.

6. Reference 1. Bimal Roy and Chandra N., (1989), Computational Modeling of Superplastic Sheet Metal Forming

Process, Proceedings IEEE System Theory, pp 209-214. 2. V.S. Senthil Kumar, D. Viswanathan, and S. Natarajan., (2006), Theoretical prediction and FEM

analysis of superplastic forming of AA7475 aluminum alloy in a hemispherical die, Journal of Materials Processing Technology 173 pp 247–251.

3. Agoston Katalin, (2006), Data Acquisition for Pressure Monitoring and Control in Distributed Systems, IEEE International Conference on Automation, Quality and Testing, Robotics, Vol. 2, pp 157-160.

4. Fadi K. ABU-Farha and Marwan K. Khraisheh, (2007), On the high temperature testing of superplastic materials, JMEP Vol. 16 Number 2, pp 142-149.

5. ASM Handbook, Forming and Forging, Vol. 14, pp 1875-1937.


A-21

EXPERIMENTAL INVESTIGATION ON MECHANICAL PROPERTIES

OF FRICTION STIR WELDING AND SUERPLASTIC FORMING OF

ALUMINIUM ALLOY- 6061

Srikarthikeyan.S 1 Ganesh.P 2, 1. P.G Student, MIT Anna University, Department of Production Technology, Chennai, email: [email protected],[email protected] 2. Lecturer , MIT Anna University, Department of Production Technology, Chennai, email: [email protected]

ABSTRACT : Friction stir welding is completely solid state joining process where the resulting weld metal characteristics remain unchanged as far as possible. The post weld FSW process produces minimal distortion, increased ductility, increased hardness and produce equiaxed recrystallized grains of quiet uniform size in the stirred zone which improves the superplasticity of the material. Superplasticity is the ability of materials to undergo extensive tensile plastic deformation under specific conditions. It is influenced by micro structural features, such as cavities and grain size, which is responsible for strength, ductility, toughness, corrosion resistance, and heat resistance. Grain size also has a significant influence on the strain rate and temperature during the superplastic deformation process. Therefore combination of FSW/SPF will leads to higher strain rate at optimum temperature. Therefore this research work is done to evaluate the performance of as weld friction stir welding and superplastic formed Aluminum alloy sheet. The improvements in superplasticity due to friction stir welding will be predicted by forming as weld aluminium sheet and comparing with forming as fabricated aluminium alloy sheet. Keywords: Frictions stir welding, Superplastic forming, thin sheets, FSW Tool design

1. INTRODUCTION

Friction-stir welding (FSW) is a solid-state joining process used for applications where the original metal characteristics must remain unchanged as far as possible. This process is primarily used on aluminum, and most often on large pieces which cannot be easily heat treated .It was invented and experimentally proved by Wayne Thomas and a team of his colleagues at The Welding Institute UK in December 1991. A method of solid phase welding, which permits a wide range of parts and geometries to be welded in friction stir welding (FSW).Friction stir welding is a relatively simple process as shown in Figure 1 and a specially shaped cylindrical tool, made from material that have a hard and wear resistant relative to the material being welded, is rotated and plunged into the abutting edges of the aluminium parts to be joined. After entry of the screw thread probe to almost the thickness of the material and to allow the tool shoulder to just penetrate into the aluminium plate, the rotating tool is transitioned along the joint line. The length of the pin is slightly less than the weld depth required and the tool shoulder should be in intimate contact with the work surface. The pin is then moved against the Work and the rotating tool develops frictional heating with the material, causing it to plasticize and flow from the front of the tool to the back where it cools and consolidates to produce a high integrity weld, in the solid phase. The two parameters have considerable importance and must be chosen with care to ensure a successful and efficient welding cycle. The relationship between the welding speeds and the heat input during welding is complex but, in general, it can be said that increasing the rotation speed or decreasing the traverse speed will result in a hotter weld. In order to produce a successful weld it is necessary that the material

mailto:[email protected],[email protected]



A-22

surrounding the tool is hot enough to enable the extensive plastic flow required and minimize the forces acting on the tool. If the material is too cool then voids or other flaws may be present in the stir zone and in extreme cases the tool may break. At the other end of the scale excessively high heat input may determine the final properties of the weld. Theoretically, this could even result in defects due to the liquation of low-melting-point phases (similar to liquation cracking in fusion welds). These competing demands lead onto the concept of a ‘processing window’: the range of processing parameters that will produce a good quality weld. Within this window the resulting weld will have a sufficiently high heat input to ensure adequate material plasticity but not so high that the weld properties are excessively reduced. 1.1 Step Involved In Friction Stir Welding Process

1) Tool used in friction stir welding process rotates about its own axis. 2) Tool pin plunges into the abutting edges of the material to be joined due to the frictional heat

between the tool pin and material. 3) Tool shoulder contacts the material and plasticizes the material due to frictional heat between the

shoulder and material. 4) The above steps involved in friction stir welding process are explained in the figures shown below.

Fig.1. steps involved in friction stir welding process

2. SUPERPLASTIC FORMING PROCESS Superplastic materials are a unique class of polycrystalline solids that have the ability to undergo very large, uniform tensile elongations prior to failure. Elongations in excess of 200%usually indicate superplasticity. The low flow stresses and high sensitivity of flow stress to strain rate are the main aspects of superplastic deformation. Fine and equiaxed grain size, forming temperature greater than half the absolute melting temperature of the material, and controlled strain rate, are the main requirements for superplasticity. The optimum value of strain rate varies with the type of material, but is usually very low. Superplastic forming (SPF) is a near net-shape forming process which offers many advantages over conventional forming operations including low forming pressure due to low flow stress, lower die cost, greater design flexibility, and the ability to shape hard metals and form complex shapes. However, low production rate due to slow forming process and limited predictive capabilities due to lack of accurate constitutive models for superplastic deformation, are the main obstacles to the widespread use of SPF. This factor has restricted the growth of applications of Superplastic alloy to low volume production industries like the aerospace industry. 3. EXPERIMENTAL WORK Aluminium alloy 6061 is selected for this project work. For performing the FSW process the process parameters required are downward force, tool traverse feed and tool rotational speed are selected and applied on the AA6061 to get the perfect weld. The material was subjected to various mechanical tests in order to analyse the improvement in mechanical properties on the material due to the FSW process. In order to identify the improvements in mechanical properties the mechanical test such as tensile test, hardness test are carried out before and after FSW process. The mechanical properties such as ultimate tensile strength, yield strength, ductility are evaluated by performing the tensile test and hardness test. The microstructure of both the base material and welded component also identified with the help of the optical microscope and scanning electron microscope. The creep test is also performed in the AA6061 to determine the strain rate of the material. As the various mechanical test mentioned above are performed which provide the information about improvement in mechanical properties due to FSW will enhance the superplasticity of the material. Therefore this research work is carried out in two phases. In first phase the mechanical test such as tensile test is carried out in the AA6061 to evaluate the mechanical properties such as ultimate tensile strength, yield strength and percentage elongation of the component. The microstructure of the base material has been taken by optical microscope. The tool material for welding AA6061 is identified and the tool with required geometry is machined for this material. In second phase friction stir welding on AA6061 is done and various mechanical tests will be done to evaluate whether the FSW increases the superplasticity of the material. The superplastic behaviour of the FSW material will be


A-23

evaluated by forming the material. The improvements in superplasticity due to friction stir welding will be predicted by forming as weld aluminium sheet and comparing with as fabricated aluminium alloy sheet. 3.1 Friction Stir Welding of Alminium Alloy 6061 For friction stir welding of aluminium alloy cylindrical profile pin is selected. The cylindrical tool is made up of M2 High Speed Steel which is selected to weld the base material, which is to be tempered and hardened to 50 HRC. The tool material composition is shown in below

Table 1: Tool material composition

For hardening the tool it is subjected to heat treatment process such as stress reliving process and tempering process. The process is carried out in muffle furnace and vertical chamber furnace. The machined tool contains some stress due to the machining process therefore the tool is subjected to stress relieving process. It is carried out by loading the tool in vertical furnace chamber at a temperature of 650 degree Celsius and holding the temperature up to one hour. The tool is Furnace cooled up to 450 degree Celsius through air. The tool is hardened using Muffle Furnace (MF).It is loaded at temperature of 900 degree Celsius and temperature increased to 1150 degree Celsius and the Holding temperature was up to thirty minutes and then Cooled in oil. The tempering process was conducted using Vertical Force Chamber Furnace (VFC).the tool is loaded at temperature of 550 degree Celsius and holding temperature was up to two hour and the tool is cooled through air. Thus the following process is carried out to hardening the tool to 50 HRC.

Fig.2. (a) Vertical force chamber furnace (b) Muffle Furnace

Fig.3. M2 HSS tool for friction stir welding process. Fig.4. Friction stir welding on AA6061 at 710 RPM

Therefore friction stir welding of aluminium alloy is performed using the above designed tool .Trial welding is performed on the aluminium sheets at 500 RPM. The friction stir welding also conducted at 700 and 1000 RPM. Thus friction stir welding on aluminium alloy was conducted using M2 HSS tool at various RPM. The various welding speeds are carried out and the resulting weld are shown in the figure 4,5. The friction stir welding parameters used for welding AA6061 are shown in the table below.

Fig.5. Friction stir welding on AA6061 at 1000 RPM. Table 2. Friction stir welding parameters

Material C Cr W Mo V Fe M2 0.85 4.0 6.0 5.0 2.0 Remaining

Process parameter Values Rotational speed(rpm) 1000,700,500 Welding speed(mm/min) 0.5-1.25 Pin length(mm) 5.5 Shoulder diameter(mm),D 18 Pin diameter (mm),d 6 D/d ratio 3.0


A-24

After friction stir welding process the component is subjected to Superplastic forming process. As the sheet has a thickness of 6mm it is machined to a thickness of 1.5 mm. For machining the sheet it is subjected to wire cutting process (EDM). As the component which is to be formed is of circular shape it is machined to a diameter of 72.5mm. The circular section which is obtained from friction stir welded component is shown in the figure below.

Fig 6. Sheet for superplastic forming from friction stir welded component. 3.2 Tensile test results Tensile properties such as tensile strength and percentage of elongation have been evaluated for aluminum alloy 6061 and the mechanical properties such as tensile strength, proof stress and percentage of elongation have been evaluated for the comparison of mechanical properties after friction stir welding process. The tested specimens are showed in figure and results are tabulated in table.

Table 4 Mechanical Properties From Tensile Test

Properties Composition Tensile strength(Mpa) 162.56 Elongation (%) 15.6% Youngs Modulus(Mpa) 49516 Yield stress(Mpa) 144.640

Thus mechanical properties have been obtained and it will be compared with the same component after friction stir welding process. 4. CONCLUSION The formability time will be estimated for the as fabricated component and compared by forming the friction stir welded (as welded) component and estimating its formability time. The advantage of superplastic forming on the friction stir welding process also be evaluated by performing the mechanical test such as tensile test, creep test and microscopic view of the component before and after friction stir welding process. 5. REFERENCES

1. Elangovan K (2008), ‘Influences of tool pin profile and welding speed on the formation of friction stir

processing zone in AA2219 aluminum alloy’, Journal of materials processing technology 200, page 163–175

2. D.G.Sanders (2007) ‘Characterization of Superplastically Formed Friction Stir Weld in Titanium 6AL-4V’.

3. H.G.Salem (2003) ‘Structural Evolution and Superplastic Formability of Friction Stir Welded AA 2095 Sheets’.ASM international.

4. R.A.Vasin (1998) ‘Method to determine the strain rate sensitivity of a superplastic material from the initial slopes of its stress-strain curves’.Iinstitute of metal superplasticity problems’

5. Rajiv S. Mishra (2001) ‘Processing Commercial Aluminum Alloys for High Strain Rate Superplasticity’. 6. Rodrigues D M (2009), ‘Influence of friction stir welding parameters on the micro structural and

mechanical properties of AA 6016-T4 thin welds’.

National Conference on Recent Innovations in Production Engineering

RIPE - 2010, MIT Campus - Anna University Chennai

A-25

Study on work Hardening Behavior and Establishment of

Constitutive Relationship model based on artificial neural network

(ANN) of Aluminium Alloys during cold Forming Process

M.Duraisamy 1 and Dr.R.Parameshwaran 2 1. PG Scholar Kongu Engineering College Department of Mechanical Engineering Perundurai, e-mail:[email protected]

Abstract: Work hardening is produced by metal forming processes that induce plastic deformation to exact a shape change. A compressive experiment was studied to acquire flow stress at different deformation temperatures, strain rates and strains. The artificial neural network with the error back propagation (BP) algorithms was used to establish constitutive model of aluminum alloys (4043, 5182&RR58) based on the experiment data. The ultimate goal is to predicting the flow stresses when the process controls variables are given as inputs. Flow stresses of the material under various thermodynamic conditions are predicted by the neural network model, and the predicted results correspond with the experimental results. A knowledge-based constitutive relation model is developed. Microstructure study is done to the deformation materials. Keywords: Work hardening, constitutive model, aluminum alloy, Microstructure.

1. INTRODUCTION

1.1. Cold Working

Cold working of metals results in an increase in the strength and hardness and decrease in ductility. When cold working is excessive, the metal will fracture before reaching the desired shape and size. Therefore, in order to avoid such difficulties, clod working operations are usually carried out in several steps, with intermediate annealing operations introduced to soften the cold worked metal and restore the ductility. This sequence of repeated cold working and annealing is frequently called the cold work anneal cycle. Deformation using cold working results in, Higher stiffness, and strength, but Reduced malleability and ductility of the metal, Anisotropy ,Better accuracy and surface finish, Strain hardening increases strength and hardness, Grain flow during deformation provides directional properties, No heating is needed.

1.2. Constitutive Equations

Constitutive equation describes the relations between stress and strain in terms of the variables of strain rate and temperature. The simple power law relationship (eq.1) and its variants are elementary forms of a constitutive equation.

σ = kεn (1) where, n is the strain-hardening exponent and k is the strength coefficient. Yet another form of constitutive relations developed for computer representation of high-temperature deformation is called MATMOD. A much simpler but useful relation describes the combined temperature and strain-rate dependence of flow stress.

σ = f (z) (2) z = έе ∆H/RT

where ∆H is activation energy, J mol-1, that is related to the activation energy, Q is. the quantity, Z is called the Zener-Hollomon parameter. It may also be referred to as a temperature-modified strain rate.




A-26

2. EXPERIMENTAL

2.1. Experimental Data

The upset forging experiment was used for experiment. The available experimental data is shown in table below

Table 1 Experimental Data at strain 0.4

Temperature K

Strain rate /s

Flow stress(4043) MPa

Flow stress(RR58) MPa

Flow stress(5182) MPa

300 0.02 142 298 254 350 0.02 132 265 225 400 0.02 124 222 203 450 0.02 110 190 195 500 0.02 90 160 176 300 0.2 155 356 320 350 0.2 151 320 300 400 0.2 136 270 256 450 0.2 125 248 224 500 0.2 98 196 186 300 8 186 390 324 350 8 180 304 310 400 8 167 284 304 450 8 162 278 288 500 8 150 256 264

2.2. Artificial Neural Network Model Multi-layer feed-forward neural network is also called BP (Back Propagation) neural network. The standard feed-forward neural network is formed by three layers (input, output, hidden) of neurons, as shown in Fig. 1. In this model, the input layer includes three nodes representing three input parameters έ, ε and T, and the output layer includes only one node representing one output parameter σ, while the number of hidden layer nodes depends on the training process. Such neural network has the following characteristics: no feedback connection between different layers; no connection between neurons within a layer; there are connections only between the adjacent neurons. Sigmoid function is used as the incentive function of the neurons in the hidden layer and linear function as the incentive function of the neuron in the output layer. The output value of the jth neuron from the pth training sample is given below.

Opj = f (Netj) =1/1 + exp [- (Σwijxj + θij)] (3)

Where Netj is the jth neural element input in the hidden layer; θj is the threshold of the unit in the hidden layer; wij is the connection weight between the input layer and the hidden layer. By modifying the connection weight among different layers and the threshold among different neurons, modeling of the complex nonlinear object can be achieved. As to every input pattern p, if the initial weight of the network has been set randomly, the error Ep between the output value of network and desired output value exists. Here, the objective function for training is as follows:

(4) = E ( wij , wjk ,θj ,θk)

where ypj is the desired output of the jth output unit in the pth learning sample; Opj is the actual output of pth learning specimen's jth neural elements; M is the number of training samples; N is the number of output nodes of the network; θi is the threshold of hidden layer; θk is the threshold of output layer; wjk is the connection weight between hidden layer and output layer. The maximum gradient descent algorithm is used to make the weight vary in the direction of antigradient of the error function.



A-27

Fig.1. Schematic diagram of a multilayer feed-forward neural network

3. RESULTS AND DISCUSSION

Results of the neural network are compared with the experimental data for validation of the neural network. Two types of graph are drawn; in the first type, the graph is drawn between temperatures, stain rate, strain and flow stress. In the second type, the graph is drawn between temperature and flow stress for different strain rate and compared with the experimental data. The graph indicates the error between outputs from the neural network and the experimental data are very less of about 7 percent. So, we can rely on the artificial neural network for predicting the flow stress.

Table 2 Comparison between Predicted Ann Model Data and Experimental Data

Temperature K

Strain rate /s

Flow stress(4043)

MPa

Predicted Flow stress(4043)

MPa

Error %

300 0.02 142 142.56 0.3

350 0.02 132 131.59 0.3

400 0.02 124 122.87 1

450 0.02 110 108.85 1.1

500 0.02 90 91.74 1.9

300 0.2 155 156.41 1

350 0.2 151 150.74 2.1

400 0.2 136 135.21 1.2

450 0.2 125 123.94 1.1

500 0.2 98 99.14 2.3

300 8 186 187.74 1.3

350 8 180 180.87 0.4

400 8 167 168.01 1.1

450 8 162 161.13 2

500 8 150 149.27 0.9



A-28

Fig.2 Comparison between Predicted Ann Model Fig.3 Temperature Vs Flow stress, at

Data and Experimental Data (4043 Alloy) strain rate 0.02/s

Fig.4 Temperature Vs Flow stress, at Fig.5 Temperature Vs Flow stress, at

strain rate 0.2/s strain rate 8/s

4. CONCLUSIONS The graph indicates the error between outputs from the neural network and the experimental data are very less of about 7 percent. So, we can rely on the artificial neural network for predicting the flow stress. Future research can be extended by developing the software for all materials. Since manufacturing design is becoming largely automated through use of CAD modelers, adding intelligence in the form of knowledge based systems and neural network is synergistic. The designer need not search a catalog of applicable features and attributes, and apply them consistently.

5. REFERENCES

1. Lin.Q.Q, Peng.Du, zhu Yuan.Z, (2005), “Establishment of constitutive relationship model for 2519 aluminum

alloy based on BP Artificial Neural Network”, journal of materials engineering, vol.12, No.4, pp.380-385. 2. Abhijit.B, Myrjam.W, (2004), “Prediction of cold rolling texture of steels using an Artificial Neural Network”,

journal of Material Science and Technology, vol.No.19, pp.256-260. 3. Luis E. Z, Sergio M.D, (2009), “Qualitative behavior rules for the cold rolling process extracted from trained

ANN via the FCANN method”, journal of Material Science and Technology,vol.No.22,pp.718-731. 4. Li.M.Q, Aiming.X, Xiaoli.L, (2005),”Adaptive Constitutive Model of the Ti-6.29Al-2.71Mo-1.42Cr Alloy in

High-Temperature Deformation”, journal of materials engineering and performance, vol.No.15, pp.9-12. 5. Wang.M, Chunlei.G, (2005),”Deformation Behavior of 6063 Aluminum Alloy during High-Speed

Compression”, journal of Materials Science and Engineering, vol.20, No.3, pp.40-43. 6. V.Strizhalo, S. Novogrudskii, (2007), “Cold Hardening of Steels under conditions of inhomogeneous stress

and action of electric current pulses”, journal of Materials Science and Engineering, vol.8, No.3, pp.343-343.


A-29

FABRICATION OF ALUMINUM CAST ALLOY/ FLY ASH METAL

MATRIX COMPOSITE USING SQUEEZE CASTING METHOD

P.Suya prem anand1, T.V.Moorthy2, A. Suresh babu3, J.Udaya prakash4 S.Vetrivel5

1. PG Student 2. Professor and Head 3. Lecturer 4. TRA 5. Professional Assistant, Department of Manufacturing Engineering, College of Engineering

Guindy, Anna University Chennai. e-mail: [email protected]

Abstract: In the present experimental investigation, Aluminium cast alloy having 7% of silicon as matrix material and reinforcement as 5, 10 and 15% fly ash composites was fabricated using Squeeze casting process. Mechanical sieve shaker was used to sieve different sizes of fly ash particles. The particle size ranges from 75 to 150µm were used to fabricate 10% Aluminium cast alloy /fly ash MMC and also sizes varied from 150 to 212µm were used to fabricate 15% Aluminium cast alloy/fly ash MMC. The micro structural characteristics of different compositions of fly ash particles were viewed through SEM (Scanning Electron Microscope). This reveals whether the fly ash particles were distributed uniformly in the aluminium metal matrix composites. The distributions of fly ash particle were based on the number of variables generally controls the quality of castings.

Key words: Squeeze casting, MMC, SEM (Scanning Electron Microscope).

1. INTRODUCTION

Discontinuously reinforced MMC are much less expensive to fabricate than continuously reinforced composites. The properties of discontinuously reinforcement (MMC) are nearly isotropic, where the properties of continuously reinforcement (MMC) are highly anisotropic. Fly ash particles are discontinuous dispersions material used in this metal matrix composites. They are available at low cost and have low density reinforcement available in large quantities as a waste by product of thermal power plant. Here the fly ash particles were obtained from Tuticorin Thermal Power Plant. Addition of fly ash particles improves the wear resistance, damping properties, hardness and stiffness and reduces the density of Al alloys. Stir Casting was a liquid state method of fabricating composite materials, in which a dispersed phase (ceramic particles or short fibers) was mixed with a molten metal by means of mechanical stirring. Stir Casting was the simplest and the most cost effective method of fabrication in liquid state method. The liquid composite material is then cast by conventional casting methods and also be processed by conventional metal forming technologies [7].Earlier studies were shown that the Al 356 cast alloy and its composite reinforcement with 15% fly ash were fabricated by different stir casting methods. They compare the three different fabrication processes such as Liquid stir casting, compo casting and squeeze casting process. The separation of fly ash particle and dispersion are more effective in compo casting method than in all other processes due to the shearing of fly ash particles. Finally they resulted that squeeze casting was the best method for the distribution of fly ash particle followed by compo casting and liquid stir casting [2]. Rohatgi has reported that the addition of fly ash particles to the aluminium alloy significantly increases its abrasive wear resistance.Aluminium was an important material for tribological application because of its low density and high thermal conductivity. The most important application of Al – MMC was being used in automotive brake rotor materials. In such application, the Aluminium metal matrix



A-30

composites slides against a semi metallic phenolic pad, which was commercially used in vehicles. Metal matrix composites exhibit better wear resistance compared to the unreinforced alloys. 2. MATERIALS 2.1 Matrix Material

A356 cast aluminum alloy having 7% silicon was chosen as the matrix alloy with fly ash particles varied as (Non uniform, 75-150 µm and 150-212 µm ) as the reinforcement. In liquid metal stir casting, the addition of fly ash particle into molten metal and pouring of composite melt into the die are carried out in a fully liquid state. The melting point of Al alloy ranges from 560-615ºC and it has good castability and weldability. The chemical composition of Al alloy was listed in table 1. Table 1: Chemical composition of Aluminium alloy in weight percentage Si Fe Cu Mn Mg Zn Al 6.74 0.21 0.01 0.01 0.34 0.01 Bal 2.2 Reinforcement Material

The particle size of fly ash particles was estimated by using SEM (Scanning Electron Microscope) and sieve analysis were performed to collect different sized particles. The fly ash particles are spherical in shape, most of the fly ash mainly consists of solid particles but smaller amount of partially solid or hollow spherical particles were also seen. As a result of the preheating of fly ash particulates to 600◦C prior to the addition in the superheated liquid metallic melt and addition of magnesium during stirring of metallic melt and fly ash particulates mixture. Table 2: Chemical composition of fly ash particles in weight percentage

Figure .1. SEM image of fly ash particles having non uniform particle size 3. EXPERIMENTAL PROCEDURE

The fly ash particles collected from the source are preheated to 100º C by using muffle furnace and it was allowed to pass through different standardized sieve size ranges in micron level. A mechanical Sieve shaker has been used to determine the particle size distribution of the coarse and fine fly ash particles. The fabrication of Aluminium metal matrix composite used in the present study was carried out by using squeeze casting method. Aluminium cast alloy having 7% Silicon in the form of ingots were melted to the desired temperature of above 850ºC in a graphite crucibles under a cover of flux in order to minimize the oxidation of molten metal. For each melting process 2 kg of Aluminium alloy was used and the fly ash particles are preheated to around 750ºC were then added to the molten metal. The mixture was stirred continuously by using a mechanical stirrer.

Figure .2. Stirrer setup with induction furnace Figure .3. Hydraulic press setup for squeeze casting

The stirring time was maintained between 5-10min at a drive speed of 350 to 400 rpm before stirring

small amount of magnesium was added to improve the wettability of fly ash particles. The metal with the reinforced particulates were poured into the dried, lubricated rectangular mould of size 165*100*80 mm. The pouring temperature was maintained at 800 to 850ºC. Squeeze casting consist of pouring liquid metal into a preheated, lubricated die and forging the metal while it solidifies. The load was applied shortly after the metal

Al2O3

SiO2

Fe2O3

TiO2

LOI

Carbon content

30.40%

58.41%

8.44%

2.75%

1.6%

1.9%


A-31

begins to freeze and was maintained until the entire casting has solidified. Casting ejection and handling are done in the same way as in closed die forging. The high pressure applied normally varies from 5 to 15 Mpa. 4. RESULT AND DISCUSSION The mechanical properties such as microhardness and density of Aluminium metal matrix composites were detected. Micro hardness of Al-MMC was determined using Vickers hardness test. Here the load applied to the composites material as 500gm. Results shows considerable increase in microhardness as the percentage of fly ash particles increases from 5 to 15.The comparison of mechanical properties of Aluminium metal matrix composites for both Fly ash and SiC reinforcement were performed in the previous study. So that tensile property has been enhanced for Alumina and SiC. While that for fly ash it has been reduced. Table 4: Density of Aluminium/fly ash Metal matrix Composites

Figure 5: Hardness of Aluminium/fly ash MMC

The presence of eutectic silicon around solid fly ash particles was more than that around hollow cenosphere particle. The infiltration of Aluminium matrix alloy into the hollow space of a broken cenospherical particle occurs. The major constituents of fly ash include SiO2, Al2O3 and Fe2O3. While the minor one are Na2O, CaO and ZnO. These constituents react with Al and Mg present in the molten matrix alloy.

Fig .6. SEM of Solid Fly ash particle Fig .7 10% fly ash composites Figure .8

Fig .7 shows the 10% fly ash composites uniformly distributed with the matrix alloy having size range from 75 to 150µm. Cenospheres are hard, hollow, free flowing, microspheres found in fly ash The volume fraction of 5% fly ash particle were distributed uniformly with the matrix alloy but the particle size range from 0.5 to 850µm are shown in Fig .8. Fly ash particle are generally in the form of solid spheres known as precipitator fly ash or in the form of hollow spheres termed as cenosphere fly ash. 4.1 Parameters affecting squeeze casting

The parameters which are used to control the quality of squeeze castings are discussed during experimental procedure but the failure of such parameters will be resulted in the following defects. Oxide inclusions occur, when cleaning of molten metal was not handled in proper way. Preventing the inclusion of foreign particles into the molten metal will be helpful to avoid oxide inclusions.

(a) (b)

Figure .9. (a) VMS image of Agglomerated particles (b) VMS image of porosity formed

Aluminium Metal matrix composites

Density (g/cm2)

5% Aluminium/Fly ash 2.129 10% Aluminium/Fly ash 1.972 15% Aluminium/Fly ash 1.86


A-32

Fig .9. (b) Shows the video measuring system image of the formation of porosity resulted due to the insufficient pressure applied during squeeze casting process. When the pressure exceeds the normal level, it will be resulted in the formation of cracks. Porosity was eliminated by increasing the pressure applied to the molten metal. Air or gas from the melt was trapped below the surface during the die filling process resulted in the formation of blisters on the surface of composite materials. Methods involved to avoid such defects include degassing the melt and preheating the handling transfer equipment.

(a) (b)

Figure .10. (a) VMS image of Crack formed during Squeeze casting (b) VMS image of overlapping Fig.10.(b)Shows the formation of overlapping during squeeze casting process. cold lapping was

caused, when pouring the molten metal over the previously solidified layers with incomplete bonding between the two layers. It was necessary to increase the pouring temperature or the die temperature. 5. CONCLUSION 1. The hardness of composites material improved based on the percentage of increase of fly ash particle added

to the matrix alloy. 2. The drastic variation among hardness shows the particle are not uniformly distributed for 15% volume

fraction but it was resulted in the formation of agglomerates. 3. The density of fly ash particle reduces the density of matrix alloy and resulted to the performance of

reduction in density, when the percentage of fly ash particle increases. 4. The dispersion of fly ash particles are observed to be uniformly distributed in Aluminium metal matrix

composites having 10% volume fraction of fly ash. 5. The size ranges from (75 to 150µm) were observed to be most suited for reinforcement process; since they

are uniformly distributed along with the matrix alloy materials. 6. Most of the important parameters of squeeze casting process are discussed and the defects responsible for

the failure of squeeze casting process are identified. 6. REFERENCES 1. Sudarshan, and Surappa M.K. (2008) ‘Dry sliding wear of fly ash particle reinforced A356 Al

composite’, composite science and technology, Vol.265, pp.349-360. 2. Rajan T.P.D, Pillai R.M., Pai B.C.,Satyanarayana K.G. and Rohatgi P.K. (2007) ‘Fabrication and

characterization of Al-7Si-0.35 Mg/fly ash metal matrix composites processed by different stir casting routes’, composite science and technology,Vol.67, pp.3367-3377.

3. RamChandra M. and Rradakrishna K. (2005) ‘Synthesis – microstructure-mechanical properties-wear and corrosion behavior of an Al-Si (12%)- fly ash metal matrix composite’, Journal of material science, Vol.40, pp.5989-5997.

4. Subramanian c. (1992) ‘Some consideration towards the design of a wear resistant aluminium alloy’, Journal of material science (wear), Vol.155, pp. 193-205.

5. Mahapatra S.S. and Amar Patnaik. (2009) ‘Study on mechanical and erosion wear behavior of hybrid composite using experimental design’, Materials and Design, Vol.30, pp. 2791-280


A-33

WETTABILITY S TUDIES ON Al-S iC METAL MATRIX COMPOSITES

L.POOVAZHAGAN1, K.KALAICHELVAN2

1. Lecturer, Department of Marine Engineering, Sri Venketeswara College of Engineering,

Pennalur, Sriperumbudur, Chennai-602 105, E-mail- [email protected]. 2. Assistant Professor, Department of Production Technology, Madras Institute of Technology, Anna

University, Chrompet, Chennai.

ABS TRACT: Many researchers have been carried out in Al Metal Matrix Composite (MMC) synthesis using conventional stir casting technique. The major problems encountered while processing ceramic reinforced MMCs using stir casting are wettability between ceramic and matrix, uniform distribution of particles and porosity in the solidified material. This paper reviews the various process parameters such as Mg addition, coating of particles, heat treatment of particles, different stirring conditions, SiC particle size and volume percentage to improve the wettability and uniform particle distribution in the stir casting of Al-SiC MMCs. The wettability is measured by two dimensional area fraction methods and validated by optical and SEM images. Keywo rds : Wettability, Stir Casting, Metal Matrix Composites, Process Parameters

1. INTRODUCTION 1.1 Metal Matrix Composites Composite is a multiphase material formed from a combination of materials which differ in composition or form, remain bonded together, and retain their identities and properties. A metal matrix composite (MMC) combines into a single material a metallic base with a reinforcing constituent, which is usually a ceramic. Combining the metallic properties such as good ductility and toughness of the matrix with ceramic properties such as high strength, hardness and elastic modulus of the reinforcement, the composites exhibiting high toughness, specific strength and stiffness and good wear resistance can be obtained. MMCs can also have low thermal and electrical conductivity and low sensitivity to temperature variation. Consequently, they have extensitive interest from defense, aerospace and automotive industries and have become very promising materials for structural applications as well. Aluminum metal matrix composites (AMMC) are appealing because of their low density and high specific stiffness. In addition, the ceramic-particle reinforcement significantly increases wear resistance. Nevertheless, high cost relative to conventional aluminum alloys has prevented widespread industrial applications. Two primary factors account for the high cost of metal matrix composites. The first factor is the raw material cost of both the aluminum matrix material and the ceramic reinforcement particles. The second factor leading to higher cost is related to the fabrication process. If these two factors could be controlled and reduced, then a wider range of applications becomes possible. 1.2 Stir Casting Metal Matrix Composites are produced by different processing routes like Liquid State Processing, Solid-State Processing and Vapor State Processing. Liquid state fabrication of particulate reinforced metal matrix composites (PMMCs) involves incorporation of dispersed phase into a molten matrix metal, followed by its solidification. Among the available liquid state processing stir casting is the most economical way of manufacturing PMMCs. Stir casting is a liquid state method of composite materials fabrication, in which a dispersed phase (ceramic particles) is mixed with a molten matrix metal by means of mechanical stirring.



A-34

Conventional stir-casting technology has been employed for producing PMMCs for decades. In order to provide high level of mechanical properties of the composite, good interfacial bonding (wetting) between the dispersed phase and the liquid matrix should be obtained. [9, 10] 2. WETTABILITY – BASICS In preparing metal matrix composites by the stir casting method, there are several factors that need considerable attention, including the difficulty of achieving a uniform distribution of the reinforcement material; wettability between the two main substances; porosity in the cast metal matrix composites; and chemical reactions between the reinforcement material and the matrix alloy. In order to achieve the optimum properties of the metal matrix composite, the distribution of the reinforcement material in the matrix alloy must be uniform, and the wettability or bonding between these substances should be optimized. The porosity levels need to be minimized, and chemical reactions between the reinforcement materials and the matrix alloy must be avoided Wettability is defined as the ability of the liquid surface to spread on a solid surface and represents the extent of intimate contact between the liquid and solid [8]. Good wetting between solid ceramic phase and molten Al alloy is an essential condition for the generation of satisfactory bond between these two elements during casting. The mechanical properties of MMCs are controlled to a large extent by the structure and properties of the reinforcement-metal interface. Strong interface permits transfer and distribution of load from matrix to reinforcement resulting in increased elastic modulus and strength. Molten Al has high oxygen affinity, at 4000C a 50 nm thick layer is formed on Al alloy in 4 hours. Experimental results show that it is very difficult to avoid oxide formation in Al Previous experimental results shows that Mg addition, coating of particles, heat treatment of particles, reduced solidification time, optimum stirring speed and time enhances the wettability. The formation of melt oxide layer, contaminated particles, reduced particle size and increased volume percentage are detrimental to wetting. . In this paper, the problem associated with the wettability between molten Al and SiC particles and the factors influencing wettability are discussed. [2, 3, 4] 2.1.1 Effect of Mg addition Alloying elements reduces the surface tension of the melt by reducing the solid liquid interfacial energy or inducing wettability by chemical reaction. The following alloying elements are tested by various authors Magnesium, Zirconium, Titanium, calcium, Lanthanum, Bismuth, Lead, Ti and Copper [7, 8]. Among the various alloying element tested, addition of Mg gives the better wettability. Mg is a powerful surfactant. Surfactants are wetting agents that lower the surface tension of liquid Al and allow easier spreading of liquid over solid and reduce the solid-liquid interfacial energy. Mg also acts as a powerful scavenger of oxygen. Mg reacts with oxygen present on the surface of the particles and thinning the gas layers. Experimental results show that adding 1 % Mg gives the effective wetting to Al-SiC composites. Increasing Mg weight % increases the tendency towards agglomeration or clustering. Adding more than 1 % Mg increases the viscosity Al-matrix alloy. Increase in viscosity makes it more difficult to get uniform SiC distribution. Adding 3 % Mg to Al-Si alloy forms Mg2Al8 phase which has low melting point and detrimental to the mechanical properties of MMCs. Less than 1 % Mg not influencing the uniform particle distribution. [4, 7, 8] 2.1.2 Particle Coating Non-metallic particles are very difficult to wet liquid metal. Coating the particles with wettable metal improves wetting. Mutual solubility or formation of inter metallic compounds induces highest wettability. Coating methods for SiC particles includes CVD, PVD, Electroplating, Cementation, Plasma Spraying and Sol-Gel. The following metals are tested as coating elements; Nickel, Copper and Chromium. Nickel coating is most widely used for Al-SiC MMCs. The following problems are still unsolved in this method, interaction of coating elements with liquid metal during stirring, influence of these elements on solidification microstructure and mechanical properties of composites. [7, 8] 2.1.3 Particle Treatment Heating the SiC particles to 9000 C alters the surface composition due to the formation of an oxide layer. Particle oxide layer and clean particles improves wetting. Ultrasonic techniques, Etching and Heating in suitable atmosphere are used to clean the particles. [7, 8] 2.1.4 Different Stirring Conditions


A-35

Previous results showed that stirring is essential for any incorporation particles to occur. The novel two steps mixing give good wettability [1, 8]. When there were no stirring particles simply floating on the top of the melted alloy, irrespective of the presence of magnesium or heat treatment of particles. With stirring in fully liquid condition poor wetting was observed. During stirring some of the particles tended to float on the surface of the melt, and others accumulated at the base of the crucible. This occurred irrespective of the speed of stirring. After pouring it was found that most of the particles still accumulated at the bottom of the crucible. Stirring continuously while the slurry becomes semi solid from a liquid condition gave good wettability. In a semi-solid state, primary α-Al phase exists so SiC particles are mechanically entrapped and prevented from agglomeration. This process can also help to trap SiC particles and stop them from settling, thus helping to achieve good wettability. Decreasing the cooling time helps to trap more SiC particles. Decreasing cooling time increases the volume fraction of primary α-Al, improving the possibility to trap more particles into the matrix [7]. The second step of stirring is important in order to disperse the particles throughout the matrix. This is because the particles which are already incorporated into the matrix during semi-solid stirring will tend to the bottom of the molten matrix during soaking in fully liquid state. Increasing the mixing times promotes metal-ceramic bonding. 2.1.5 SiC particle size and Volume percentage The tendency to incorporate the SiC into the matrix alloy reduced with the increase of volume fraction of SiC. The reason is by increasing the volume fraction of SiC particles, the viscosity of the slurry is increased, thus creating greater difficulty and less chance for more particles to be embedded into the melt. The attainment of complete wetting becomes is more difficult to achieve as particle size decreases. The smaller particles are also more difficult to disperse because of their inherently greater surface area. These finely divided powders show an increasing tendency to agglomerate or clump together [8]. 2.1.6 Measuring Wettability The percentage of SiC incorporated within the solidified composite is an indicative of the wettability. Two dimensional area measurements are used to measure wettability. Using a micrograph of a section through a composite, the total area of SiC as compared to the total micrograph area is taken to indicate the percentage of SiC content. If the area of the SiC particles fully occupies the square, the wettability is 100 % [7, 8]. The optical and SEM images are taken to validate the wettability. Figure 1 explains the graphical method used to measure percentage wetting. If the area of the SiC particles fully occupies the square, that means the wettability is 100 %.

Fig.2, Microstructure of Al-10% SiCp MMC fabricated at 500 rpm a) 5 min stirring b) 10 min stirring c) 15 min stirring. More stirring time less tendency towards clustering (1) 3. CONCLUSION This paper reviewed the various process parameters which promotes wettability of SiC particles by molten Al alloy and also reviewed the parameters which are detrimental to wettability. Previous results show that mechanical stirring is necessary to promote wetting and uniform particle distribution. Stirring while the slurry is solidifying improves the incorporation of particles into the matrix alloy. Decreasing the solidifying time improves the wetting. Magnesium addition enhances the wettability, however increasing the content above 1 wt. %, increases the viscosity of slurry to the detriment of particle distribution. Increasing the volume percentage of SiC particles decreases the wettability. Use of heat treated particles also improves the wetting and particle distribution. The presence of oxide layer on the melt surface creates a resistance to reinforcement particle penetration. The smaller particles are more difficult to disperse because of their inherently greater surface area.

Fig: 1, Graphical method used to measure percentage wetting.


A-36

4. RFERENCES 1. S.Balasivanantha Brabhu et al (2006), Influence of stirring speed and stirring time on distribution of

particles in cast MMCs, Journal of Material processing Technology, vol 171, pp 268-273. 2. N.Aniban et al (2002), An analysis of impeller parameters for Al-MMC synthesis, Materials and Design,

vol 23, pp 553-556. 3. J.Hashim et al (2002), Particle distribution in cast MMC-Part I, Journal of material processing technology,

vol 123, pp 251-257. 4. E.Candan et al (2002), The effect of alloying elements to aluminum on the wettability of Al-SiC system,

Turkish Journal of Engineering & Environmental Science, vol 26, pp 1-5. 5. A.Ourdjini et al (2001), Settling of SiC particles in cast MMCs, Journal of Material Casting processing

Technology, vol 116, pp 72-76. 6. J.Hashim (2001), The production of cast MMCs by a modified stir casting method, Journal Technology, vol

35A, pp 9-20. 7. J.Hashim et al (2001), Wettability of SiC particles by molten Al-alloy, vol 119, pp 324-328. 8. J.Hashim et al (2001), The enhancement of wettability of SiC particles in cast Al-matrix composites, vol

119, pp 329-335. 9. J.Hashim et al (1999), MMC-Production by stir casting method, Journal of material processing technology,

vol 92-93, pp 1-7. 10. W.Zhou et al (1997), Casting of SiC reinforced Metal Matrix Composites, Journal of Material processing

Technology, vol 63, pp 358-363.


A - 37

EFFECT OF SLOW COOLING AFTER SINTERING ON POROSITY

AND MICRO HARDNESS OF ELEMENTAL 6061al ALLOY IN P/M

PROCESS

S. Solay Anand 1, B. Mohan 2, T.R. Parthasarathy 3

1. Department of Mechanical Engineering, Adhiparasakthi Engg. College, Melmaruvathur 2. MIT Anna University, Department of Production Technology, Chennai, e-mail: [email protected] 3. MetMech Engineers, Chennai, e-mail:[email protected]

Abstract: The usage of aluminium in lieu of ferrous components in automotives helps to lower the weight of vehicle. The major drawback in the commercially available press sintered aluminium alloy is porosity which is mainly depending on the P/M process parameters such as compaction pressure, sintering temperature and cooling temperature after sintering. In this work it is demonstrated that slow cooling to 200°C from a high sintering temperature of 600°C reduces porosity in 6061Al alloy powder compacts. The compacts are warm compacted at 150MPa. Two different particle sizes 165µm and 45µm of aluminium powder is used to compare the porosity level at different cooling temperatures. Key words: Particle size, cooling rate, precipitation.

1. INTRODUCTION Due to revolution in automobile industry towards light weight metals, there is a particular interest in aluminium matrix composites [Polmear, 1995, Slavinch, 2002], especially through powder metallurgy (P/M), as it is a means by which complex, net shape, light weight components can be produced cost effectively [Schaffer,2000]. The main drawback in P/M components is porosity. Porosity in sintered alloys is consequent of (a) primary pores carried over from green state and arising from the removal of the lubricant wax which are not entirely eliminated by shrinkage phenomena; (b) secondary pores generated by the diffusion of alloying elements into the major phase, leaving residual porosity located at the sites of the original alloy particles; (c) bubbles generated by the vaporization of a volatile phase. In the early works by Schaffer et. al. [Lumely et.al, 1996, Lumely et.al, 1998] on various aluminium alloy powder compacts it is clearly shown that the progression of sintering and the final porosity in the system is also dependant on the process variables such as additive particle size, heating rate and the final sintering temperature.

Traditionally aluminium powder products where thought difficult to sinter and their properties deemed poor. Recent research works [Sercombe, et.al, 1999] on the sintering response of press and sintered Al 4.4Cu-0.8Si-0.5Mg powders through addition of trace amounts tin showed marked improvement in strength and density.




A - 38

(a)

Current commercial aluminium powder metallurgy alloys are based on the wrought 6XXX series (Al-Mg-Si) and 2xxx series (Al-Cu-Mg) of alloys, where as little research has been conducted using elemental powders. This work was therefore undertaken to ascertain whether data on solution heat treatment of elemental 6061Al P/M alloy has any adverse effect on slow cooling from sintering temperature. The levels of porosity on variation of grain size of aluminium powders during slow cooling from sintering temperature were also examined.

2. EXPERIMENTAL METHODS An elemental 6061Al alloy is taken for this experimental study and its composition is shown in table.1. Two different particle sizes of aluminium powders of 165µm and 45µm is selected for this study. The prepared alloy mixture is weighed out to an accuracy of 0.01g for each specimen of size 70 x 50 x 10 mm. The powder was warm compacted at 150MPa in a rectangular die with die temperature as 150°C and plunger temperature as 170°C, in an uniaxial hydraulic press of 100Tonnes capacity to give rectangular specimens of size 70 x 50 x 10mm. Paraffin wax is used as die wall lubricant during each compact. Dewaxing and sintering process is carried out in a high purity nitrogen atmosphere (dew point < -60°C). Green bars were dewaxed at 300°C for 20min and sintered for 60min at 600°C. After sintering the bars are furnace cooled to 500°C, 400°C, 300°C and 200°C and air cooled. All these samples were solution heat treated at 530°C for 90min, water quenched and precipitate hardened at 170°C for 6hrs. Both heating and cooling rate are at 15°C/min. Specimens were prepared and tested for Vicker’s micro hardness at 0.5Kg load. % of volume porosity is found out in polished specimens at various regions according to ASTM B276 standards by using dewinter software coupled online with optical microscope.

Table 1 Composition of 6061 Al alloy (all in wt %) investigated in the present work

Mg Si Cu Fe Zn Sn Mn Al as measured 1.2 0.6 0.3 0.7 0.25 0.3 0.3 Bal 3. RESULTS AND DISCUSSION The effects of different cooling temperature after sintering on porosity and micro hardness have been discussed below. 3.1 Effects of Porosity

The porosity for sintered and solution heat treated specimens at various cooling temperature is shown in Fig.1. Decrease in porosity level for solution heat treated specimens as compared to sintered specimens is due to the densification of precipitates (mainlyCuAl2 and MgSi2) around the pores during solution heat treatment. Porosity level for 45µm aluminium particle size is apparently equal to 4.23vol% and that for 165µm aluminium particle size porosity is apparently equal to 7.43vol%. This variation in porosity level may be related to compressibility [Medhi Rahimian, et. al, 2009] which is good for 45 µm when compared to 165µm. The reduction in porosity in solution heat treated samples is due to the densification of the phases formed

(b)


A - 39

(a)

Fig.1 Effect of slow cooling after sintering at different temperature on porosity level of 6061 Al alloy as sintered and as solution heat treated (a) aluminium particle size of 165µm (b)aluminium particle size of 45µm during sintering around the pores during solution heat treatment process and is clearly shown in Fig.2, 3. Comparing Fig.1, 2, 3, 4 it is clear that as porosity level decreases due to slow cooling rate after sintering and solution heat treatment process, correspondingly the micro hardness value increases. Similar case was noted in the work [Kent et. al, 2005] age hardening of sintered Al-Cu-Mg-Si-Sn alloy systems. Precipitation induced densification observed here is also similar to the work [Lumley et. al, 2006] on precipitation induced densification in a sintered Al-Zn-Mg-Cu alloy.

Fig.2. Optical microstructure of 6061 Al alloy at a cooling temperature 400°C after sintering for aluminium particle size of 165µm (a) as sintered and (b) as solution heat treated.

Fig.3. Optical microstructure of 6061 Al alloy at a cooling temperature 400°C after sintering for aluminium particle size of 45µm (a) as sintered and (b) as solution heat treated. 3.2 Effects of Micro Hardness Fig.4 Effect of slow cooling after sintering at different temperature on micro hardness of 6061 Al alloy as sintered and as solution heat treated (a) aluminium particle size of 165µm

(b)

(a) (bCuAl2 phases formed during sintering

Mg2Si Phases formed

Phase desifies after SHT

CuAl2 phases formed during sintering

Mg2Si Phases formed during sintering

Phase desifies after SHT

(a) (b


A - 40

(b)aluminium particle size of 45µm The effect of micro hardness for aluminium particle size of 165µm and 45µm on different cooling temperature after sintering and as solution heat treated is shown in Fig.4. The hardness value increases for both as sintered and as solution heat treated as the cooling temperature decreases to 200°C and reaches a value of HV0.5 ~ 40(for 165µm) and ~50(for 45µm) as solution heat treated. The increase in hardness value on slow cooling after sintering is mainly due to the precipitation of various phases formed along the pores [Kent et.al.2005]. From the microstructure shown in Fig 2,3 it is clear that porosity does not affect the kinetics of precipitation. The time taken to achieve peak hardness increased at low cooling temperature because the rate of precipitation is largely controlled by diffusion of solute elements which is highly dependent on cooling temperature [Martin,1998]. The time taken to reach peak hardness was similar to those observed in near dense wrought 2014 alloys [Bonfield,1976, Dutta, et. al. 1994]. 4. CONCLUSIONS The following points have been concluded from the work. 1. Slow cooling after sintering reduces porosity level due to densification of various phases formed. 2. By lowering the particle size of aluminium powders from 165 µm to 45 µm the micro hardness value

increases to about 10% which is mainly due to compressibility of fine aluminium particles. 3. Pores are mainly formed around the alloying elements which forms phases during sintering and these

phases formed densifies during solution heat treatment and filling of pores takes place. 4. For both grain sizes micro hardness is inversely related to porosity level 5. Compaction pressure required for obtaining the density is minimum (150MPa) for warm compaction when

compared to cold compaction (300MPa). REFERENCES 1. I.J.Polmear, Light Alloys-Metallurgy of the Light metals, third ed., Arnold, London.1995. 2. D.Slavnich, (2002), “Electric and Hybrid Vechile” Journal of Automobile Engg., Vol 27, pp52 – 60. 3. G.B.Schaffer, Mater. Forum 24(2000) 109 – 125 4. R.N.Lumley, G.B. Schaffer, (1996) “Surface oxide and the role of magnesium in liquid phase sintering”

Scripta Mater. Vol 35, pp 589 - 595 5. R.N.Lumley, G.B. Schaffer, (1998) “The effect of additive particle size on sintered Al-Cu alloys" Scripta

Mater. Vol.39, pp1089-1094 6. T.B.Sercombe, G.B.Schaffer, (1999) “Statistical experimental design of Al–Cu–Mg–Si P/M alloys” Journal

of Mater. Science and Engg. A Vol.268 pp32 – 39 7. J.W.Martin, Precipitation Hardening second ed., Oxford 1998. 8. W.Bonfield, P.K Datta,(1976)” Precipitation hardening in Al–Cu–Si–Mg alloy at 130–220 °C” Journal of

Mater. Sci. Vol.11,pp1661 – 1666 9. L.Dutta, C.P Harper, G.Dutta, (1994) “The control of grain size and distribution of particles in a (6061

alloym/(Al2O3)P composite by solutionizing treatment” Journal of Metallurgical and Materials Transactions A Vol.25 pp1591 – 1602

10. D. Kent, G.B Schaffer, J.Drennan, (2005) “Age hardening of a sintered Al-Cu-Mg-Si-(Sn) alloy”Journal of Mater. Sci Engg A Vol.405 pp65 – 73.

11. R.N Lumely, G.B.Schaffer, (2006) “Precipitation induced densification in a sintered Al-Zn-Mg-Cu alloy” Journal of Script Mater. Vol.55, pp 207 – 210.

12. Mehdi Rahimian, Naser Ehsania, Nader Parvin, Hamid reza Baharvandi, (2009), “The effect of particle size, sintering temperature and sintering time on the properties of Al–Al2O3 composites, made by powder metallurgy” Journal of Material Processing Technology, Vol209, pp5387 – 5393.


A - 41

STUDY ON WELDING OF AISI 301 STAINLESS STEEL WITH

IRS M-41/97 CORTEN STEEL

G.Thirukumaran 1, A. Rajadurai 2 and M.V.Venkatesan 3

1. P.G.Student,Department of Production Technology, Anna University Chennai, MIT Campus. e-mail: [email protected] 2. Professor, Department of Production Technology, Anna University Chennai, MIT Campus 3. Instructor, Technical Training Centre, Integral Coach Factory, Chennai-38.

Abstract: Integral Coach Factory (ICF), Chennai-38 has been involved in manufacturing of steel body railway coaches since 1955. Carbon steel and stainless steels are used for rail coach building. Rail coach parts are fabricated by welding process. Welding is associated with heating and cooling. Due to non-uniform cooling, it results in weldment distortion. Various methods are used to control distortion. Selection of suitable process parameters is one among them. In this study, the effect of process parameters on bowing distortion of dissimilar metal joints was studied. The process parameters such as current, voltage and type of shielding gas were varied. Corten steel (IRS M41/97) and Austenitic stainless steel (AISI 301) was joined by Flux cored arc welding process. CO2 100% and Ar 80% & CO2 20% gas mixtures were used as additional shielding gases to weld the test plates. It was observed that bowing distortion decreased with increase in current, for both shielding gases. No major slag inclusions were found during X-Ray radiograph test. Ferrite content found to increase with increase in current. Key words: Flux cored Arc Welding, Austenitic Stainless steel, CO2 shielding gas.

1.0 INTRODUCTION 1.1 General Information

Integral coach factory (ICF) has been manufacturing various types of railway passenger coaches. Welding plays a major role in fabrication of rail coaches and many types of welding process are being used. Various parts of a coach such as Roof, Side wall, End wall, Under frame and various other parts are integrated by welding process.

1.2 Significance of the Study

Gas Tungsten Arc Welding (GTAW) is the most suitable process for joining stainless steel plates [1]. But, the process is slow with lower deposition rates when compared with GMAW, FCAW processes. Due to its lack of deposition rate, in ICF, FCAW process with higher deposition rates of 5.8 kg/hr for 1.2mm wire is used for welding similar and dissimilar combination of metals. CO2 gas and Argon mixture gas are used as supportive gas in FCAW process.

2.0 OBJECTIVES

The specific objective of the present study on “Study on Welding of AISI 301 Stainless Steel with IRS M-41/97 CORTEN Steel” is to, investigate the effect of process parameters on mechanical, metallurgical properties in weldment of AISI 301 Stainless Steel with CORTEN steel.



A - 42

3.0 MATERIALS AND METHODS

The composition of base metals such as AISI 301stainless steel, CORTEN steel and filler metal AWS

309LT-1 are stated in Table 1 Table 1 Chemical Composition of Base Metals & Electrode

Wt. % Material C Cr Ni Cu Mn Si P S Mo

IRS M41-97 (Base metal CORTEN steel) 0.1 0.35-

0.8 0.2 - 0.47

0.3 - 0.8

0.25 -

0.45

0.28-

0.72

0.075 -0.14 0.03 0.05

AISI 301 (Base metal stainless steel) 0.15 16-18 6-8 Nil 2.0 1.0 0.045 0.03 Nil

AWS 309 LT-1 (Electrode) 0.04 22-25 12-14 0.5 0.5-

2.5 1.0 0.04 0.03 0.5

3.1 Welding Procedure

The Stainless steel and CORTEN steel specimens were sheared to the size of 250 x 125 x 2mm taking rolling direction into consideration. These specimens were properly cleaned and edges were de-burred. The plates were set at 1.2 mm apart as root gap and tack welded on both ends. The selected process parameters, process variables and design matrix are listed in Table 2, 3 & 4

Table 3 Process variables and their levels Table 2 Welding Process Parameters with CO2 as supportive shielding gas Table 4 Design Matrix

Process FCAW Parameters Unit Level-1

Level+1

Specimen No. I V

Root gap 1.2 mm I- Current Amp 70 80 1 -1 -1 Gas flow rate 10 L/min V-Voltage Volts 20 24 2 +1 -1 Joint design Square butt 3 -1 +1 Technique Fore hand 4 +1 +1 Thickness 2.0 mm

Welding position Down hand

Weld specimens with Argon mixture (Ar 80% + CO2 20%) as shielding gas were prepared as per the above

design matrix. But, the resultant weld bead was not satisfactory and the base metal got burn through. It may be due to additional heat input caused due to the ionization of Argon gas. Therefore, weld trials were carried out at different current and voltage levels. The new current levels are 60 to 70 Amps and new voltage levels are 18 to 20 Volts and the corresponding process variables and design matrix are listed in Table 5&6 Table 5 Process variables and their levels with Argon mixture (Ar 80%+ CO2 20% as shielding gas) Table 6 Design Matrix

Parameters Unit Level -1 Level +1 Specimen No. I V I- Current Amp 60 70 5 -1 -1 V-Voltage Volts 18 20 6 +1 -1 7 -1 +1

8 +1 +1

3.2 Inspection and Analysis

Visual, X-ray, Bowing distortion tests and Ferrite content were done to analyse the effect of current and voltage on Distortion, Weld quality and Penetration of the weldment.


A - 43

4.0 RESULTS 4.1 Visual Inspection

The specimen welded without any shielding gas, resulted in porosity, poor weld bead profile and incomplete penetration throughout the weldment. Whereas, by using CO2 and Argon mixture as additional shielding gas, the resulting weldment had good weld bead and good penetration in all the eight specimens. 4.2 X-Ray Radiograph Test

X-Ray radiography indicated that, there was no major defect observed in specimens welded using shielding gas, whereas specimens welded without shielding gas, resulted in porosity.

4.3 Distortion Test

The presence of bowing distortion in the welded plates were measured by using a Profile tracer [2] shown

in Fig.1

Fig.1 Schematic Diagram of Bowing Distortion

The bowing distortion was traced on both sides of the weldment. The measured peak value of the bowing

distortion of both stainless steel and CORTEN steel metals are listed in Table 7 and shown in Fig.2&3

Table 7 Results of bowing distortion tests

Specimen No. Current ( I ) Amp

Voltage (V)

Volts

Travel speed

(mm/min)

Bowing distortion on SS side (mm)

Bowing distortion on CORTEN steel side (mm)

1 70 20 294 4.52 4.12 2 80 20 300 4.22 3.10 3 70 24 357 5.32 4.38 4 80 24 395 4.72 3.24 5 60 18 190 5.50 5.38 6 70 18 200 4.54 3.72 7 60 20 210 5.48 4.80 8 70 20 220 4.80 3.94

At 20 Volts (CO2)

4.224.52

4.12 3.1

0

1

2

3

4

5

70 80

Current (Amp)

Bow

ing

Dis

tort

ion

(mm

)

sscorten

At 24 Volts (CO2)

4.72

3.24

5.32

4.38

0

1

2

3

4

5

6

70 80

Current (Amp)

Bow

ing

Dis

tort

ion

(mm

)

sscorten

Fig.2 Influence of Current over Bowing distortion (CO2)

At 18 Volts (Ar 80% + CO2 20%)

4.54

3.72

5.5

5.38

0

1

2

3

4

5

6

60 70

Current (Amp)

Bow

ing

Dist

ortio

n (m

m)

sscorten

At 20 Volts (Ar 80% + CO2 20% )

4.85.48

4.8

3.94

0

1

2

3

4

5

6

60 70

Current (Amp)

Bow

ing

Dis

torti

on (m

m)

sscorten


A - 44

Fig.3 Influence of Current over Bowing distortion (Ar 80% + CO2 20%) From the results it is inferred that, as the Current increases bowing distortion decreases. Bowing distortion

in Stainless steel side is high compared with CORTEN steel side, due to difference in co-efficient of thermal expansion of the base metals.

4.4 Ferrite Content Test

The Ferrite content in percentage (Fe %) is measured using Feritscope MP30 E-S (with RS 232 interface) manufactured by M/s Fischer India. Readings were taken at eight locations on the length of the weldment and their average percentage of Ferrite content is shown in Table 8

Table 8 Ferrite content in the Weldment of Specimens

Specimen No. Average Ferrite content in %

1 3.60 2 3.70 3 3.90 4 4.27 5 4.00 6 4.50 7 4.70 8 4.82

The results show that, the Ferrite content increases, as the current, voltage and travel speed increases. This

could be attributed to the suppression of transformation of ferrite into austenite during fast cooling [3].

In this study, an attempt was made to study the effect of various process parameters such as Current, Voltage and Shielding gas on Distortion, Bead quality and Ferrite content in welding of AISI 301 stainless steel with IRS M-41/97 CORTEN steel. FCAW process was employed and the conclusions are as follows

1. Welding of AISI stainless steel with CORTEN steel without shielding resulted in poor bead quality,

porosity and incomplete penetration. 2. Welding with CO2 and Argon mixture as additional shielding gas improves penetration and removes

porosity and thus resulting in good weldment. 3. No major slag inclusion and defects are present in the weldment as evident in the X-ray radiological

examination. 4. Bowing distortion in Stainless steel side is high compared with CORTEN steel side when the current is

increased due to difference in co-efficient of thermal expansion. 5. The Ferrite content in the weldment increases as the current, voltage and the travel speed increases.

REFERENCES: 1. Larry Jeffus (2004), “Welding principles and application”, Thomas Delmar learning, U.S.A 2. Venkatesan.M.V, Murugan.N, and Prasad.B.M (2009), “Study on measurement of bowing distortion of

stainless steel sheets joined by FCAW” Proceeding of the National Welding seminar, IIW India. 3. Vitek.J.M and David.S.A (2001) “Improved models for predicting Ferrite content in stainless steels”

http://www.ornl.gov/~webworks/cppr/y2001/pres/111655.pdf

http://www.ornl.gov/~webworks/cppr/y2001/pres/111655.pdf

National Conference on Recent Innovations in Production Engineering, RIPE - 2010, MIT Campus - Anna University Chennai

A - 45

CORROSION AS AN WELD QUALITY INDICATOR IN Ti6Al4V

ALLOY WELDMENTS

V.K.Bupesh Raja1, K.PalaniKumar2 and N.Manoharan3

1. Research Scholar, Department of Mechanical and Production Engineering, Sathyabama University, Chennai-600 119, India.

2. Principal, Sai Ram Institute of Technology, Chennai, India.

3. Vice Chancellor, Sathyabama University, Chennai-600 119, India. e-mail: [email protected].

Abstract: The Ti6Al4V alloy is the military grade titanium alloy known as Grade 5 titanium alloy. It is immune to corrosion due to its ability to form a passive oxide layer. In this investigation the corrosion rate was taken as an index to study the quality of welds. During the welding process the atmospheric gases contaminate the weld pool resulting in an increase in the corrosion. The 3mm thick plates of Ti6Al4V alloy were square butt-welded using gas tungsten arc welding (GTAW) process with argon gas shielding. The corrosion studies were done using potentiodynamic polarization technique, with non-deaerated 3.5% NaCl solution of pH 7. The LBW weldments showed an increase in the corrosion rate when compared with the GTAW weldments. Key words: Titanium Alloy, Ti6Al4V, Gas Tungsten Arc Welding (GTAW), Corrosion rate, Pitting

1. INTRODUCTION

The Ti6Al4V titanium alloy designated as ASTM B265 Grade5 is the most commonly used among the 39 Grades of titanium alloys [1]. The Ti6Al4V is considered as the military grade of titanium. Due to its corrosion resistance it is widely used in fabricating chemical processing equipments and in highly corrosive environments. Pitting corrosion is the localized corrosion resulting in the appearance of holes on the metal surface. Even though pitting causes minimal loss of metal, pitting leads to perforation, causing loss of functionality reliability of the equipments and components. Therefore the study of pitting corrosion has been done in this investigation [2]. In this investigation the GTAW was done to study the effect of the process on the pitting corrosion of Ti6Al4V alloy. Argon gas was used to shield and purge the weldment to produce defect and contamination free weldments. 2. MATERIALS AND WELDING PROCESS

The square butt joints were autogenously fabricated from cold rolled, annealed plates of Ti6Al4V of size (50 x 125 x 3mm), along the rolling direction. The composition of the base metal was determined using a vacuum optical emission spectrometer (SPECTRO-LAB, Germany). Table. 1.

Table. 1: Chemical Composition (wt %) of the base metal



A - 46

The GTAW was done manually with highly skilled welder, using Easy Weld SSR 400/600, 3 phase, 415 V ± 10%, 50 Hz Ac equipment. The GTAW process was done autogenously without filler wire with a root gap of 1.6 mm. Proper care was taken to prevent any contamination, distortions and embrittlement, by using 99.9% pure argon with top and bottom purging and suitable clamping. The frequency of the GTAW was kept constant as 6 HZ. The weld bead, quality of weld and full penetration was achieved by selecting suitable welding parameters. Table. 2

Table. 2: GTAW Parameters

3. WELD QUALITY INDICATOR

The Ti6Al4V alloy is immune to corrosion. Titanium has good corrosion resistance due to the

formation of passive oxide film of TiO2 spontaneously at room temperature. The oxide film is very stable, continuous and highly adherent protective film. The oxide film may comprise of a mixture of titanium oxides like TiO2, Ti2O3 and TiO [3]. Generally the colour of the weld surface is observed to indicate the quality of the weldment. In this investigation along with weld surface colour, the corrosion rate was considered for checking the purity and quality of the weldments. The increase in corrosion rate indicates the contamination of the hot weld pool from atmospheric gases caused by insufficient argon shielding and impurities. Therefore the corrosion rate was taken as the weld quality indicator in this investigation. 4. CORROSION TEST

The as-welded corrosion test specimens of size 10 x 40 mm were polished to mirror finish according to the metallographic procedures. The corrosion analysis were done taking the top surface of the welded surface as the area of interest (AOI), instead of the cross section, since it is the surface exposed more to the environment [4]. In the area of interest a 4 mm diameter circular area of the weld region was exposed to the electrolyte by coating the other surfaces with acid resistant lacquer. Fig.1.

Fig.1: Corrosion specimen

The potentiodynamic polarization studies of the GTAW weldment was done using ACM GILL AC Potentiostat, an ASTM standard cell and personal computer. A non-deaerated 3.5% NaCl solution of pH 7 was used for conducting the polarization studies. The polarization studies yielded the potentiodynamic curves shown in Fig 2. The pitting corrosion was detected by morphological analysis of the surface using optical microscope METAVIS 1000[5, 6, 7, 8, 9] Fig.3.


A - 47

Fig.2: Potentiodynamic polarization curves of GTAW weldment.

Fig.3: Weld surface after corrosion test of GTAW weldment.

20µ


A - 48

5. RESULT AND DISCUSSIONS The morphological analysis of the surface was done using optical microscope. The corrosion was very

negligible, limited to small pits. The corrosion is very minimal and the visibility of the corrosion products is very less due to the white and transparent nature of the oxides. The pitting corrosion rate of GTAW process is 0.45 mils/year which within permissible limits. This shows that the GTAW process shall not affect the corrosion resistance of the Ti6Al4V alloy if suitable argon gas shielding and safety precautions are adopted.

6. CONCLUSIONS

The Ti6Al4V alloy being immune to corrosion in normal conditions tends to corrode when subjected to high temperature. The high temperature prevailing during the GTAW process causes the weld pool to react with the atmospheric gases resulting in the Ti6Al4V alloy becoming vulnerable to corrosion. Effect of Gas Tungsten Arc Welding (GTAW) on Corrosion of Ti6Al4V Alloy was studied. The corrosion tests were conducted in non-deaerated 3.5% NaCl solution of pH 7.The fusion zone of the GTAW welded Ti6Al4V showed very few pits having a pitting corrosion rate of 0.45 mils/year, which is within the permissible values. 7. ACKNOWLEDGEMENTS

The authors would like to thank the Head of the Department of Manufacturing Engineering, Annamalai University, Annamalai Nagar, Tamil Nadu and Dr.V.Balasubramanian, Centre for Materials Joining Research, Department of Manufacturing Engineering, Annamalai University, Annamalai Nagar, Tamil Nadu and Dr.K.Shanmugam of Manufacturing Engineering, Annamalai University, Annamalai Nagar, Tamil Nadu for extending the facilities of Materials Testing Laboratory to carryout this investigation. 8. REFERENCES

1. Designation: B 265–06b, “Standard Specification for Titanium Alloy Strip”, Sheet and Plate, ASTM

International, United States. 2. Mars G. Fontana, Norbert D.Greene, (1978), “Corrosion Engineering”, Second edition, McGRAW-Hill

Book Company. 3. J.R.Davis, Davis and Associates, (2003), “Alloying – Understanding the Basics”, ASM International,

USA, pp. 425. 4. F. Zucchi, G. Trabanelli, V. Grassi, (2001), Pitting and stress corrosion cracking resistance of friction stir

welded AA 5083, Materials and Corrosion, Volume 52, Issue 11, pp. 853 – 859. 5. Stefano Maggiolino, Chiara Schmid, (2008), “Corrosion resistance in FSW and in MIG welding

techniques of AA6XXX”, Journal of Materials Processing Technology, 197, pp. 237-240. 6. Hasan Guleryuz, Huseyin, Cimenoglu, (2004), “Effect of thermal oxidation on corrosion and corrosion-

wear behaviour of a Ti-6Al-4V alloy”, Biomaterials, 25, pp. 3325-3333. 7. F.Karimzadeh, M.Heidarbeigy, A.Saatchi, (2008), “Effect of heat treatment on corrosion behaviour of

Ti-6Al-4V alloy weldments”, Journal of Materials Processing Technology, Volume 206, Issues 1-3, pp. 388-394.

8. M.Balasubramanian, V.Jayabalan, V.Balasubramanian, (November, 2008), “Optimizing pulsed current parameters to minimize corrosion rate in gas tungsten arc welded titanium alloy”, International Journal of Advanced Manufacturing Technology, Volume 39, Numbers 5-6, pp. 474-481

9. M.Balasubramanian, V.Jayabalan, V.Balasubramanian, “Effect of pulsed gas tungsten arc welding on corrosion behaviour of Ti-6Al-4V titanium alloy”, (2008), Materials & Design, Volume 29, Issue 7, pp. 1359-1363.


A - 49

EFFECT OF PROCESS PARAMETERS IN FRICTION STIR WELDING

OF AA1100 and AA2024-AA7075 DISSIMILAR ALUMINIUM ALLOYS

T.Ganesh1 , N.Srirangarajalu2 ,M.R.Thansekhar3 ,A.Rajadurai4

1. PG S tudent, Department of Production Technology, MIT Campus, Anna University Chennai. 2. Lecturer, Department of Production Technology, MIT Campus, Anna Unive rsity Chenna i. 3. Professor, Depa rtment of Mechanical Enginee ring, SS N College of Enginee ring, Chenna i. 4. Professor, Depa rtment of Production Technology, MIT Campus, Anna Unive rsity Chenna i.

Abstract: Friction s tir welding was invented at Welding institute , United Kingdom in the yea r 1991 and ha s e ve r s ince been proved to be one of the best solid s ta te joining me thods for mate rials such a s a luminium and magne sium. Some of the aluminium alloys which a re not weldable (Al-Cu, Al-Zn-Mg a lloy) by fusion welding techniques, which produce defects and reduce the mechanical propertie s on the weld nugge t could be we lded using friction stir we lding (FS W) succes sfully with excellent joint efficiencies . However effect of the proces s pa rame te rs on the propertie s of weldment have not been inve stiga ted fully. In this s tudy friction s tir welding of dissimila r a luminium a lloys AA2024-AA7075 is se lected for investiga tion. The welding proces s were conducted on varying the we lding proces s parame ters such a s Tool rota tion spee d (RPM), Welding speed (mm/min), Downward force (kN) and Tool pin profiles. The prope rtie s such a s de fects , hardness, tensile and bend behavior on welded plate s were studied and compared with the base me ta l.

Key Words: Friction s tir welding, Tool rotation speed (RP M), Welding speed (mm/min), Down ward force (kN), Tool pin profile , Aluminium a lloy 2024 and 7075.

1. INTRODUCTION Friction stir welding is a relatively simple process as shown in Figure 1. A specially shaped tool, made from material that have a hard and wear resistant relative to the material being welded, is rotated and plunged into the abutting edges of the parts to be joined. After entry of the tool probe to almost the thickness of the material and to allow the tool shoulder to just penetrate into the plate, the rotating tool is transitioned along the joint line. The rotating tool develops frictional heating of the material, causing it to plasticize and flow from the front of the tool to the back where it cools and consolidates to produce a high integrity weld, in the solid phase. This advanced technology is capable to weld aluminium alloys difficult to be welded with traditional fusion techniques (the 2XXX series alloys show limited weldability, whilst 7XXX series largely employed in aerospace applications are also claimed to be not easily welded). Dendrite structure occurs in the fusion zone due to conventional TIG and laser welding, leading to a drastic decrease of the mechanical behaviour.

Figure 1: Schematic Diagram of Friction Stir Welding


A - 50

Table1: Chemical Composition Material Si Fe Cu Mn Mg Zn Al AA2024 0.103 0.136 4.416 0.535 1.646 0.011 Remainder

2. EXPERIMENTAL PROCEDURE The welding trials were conducted using Friction Stir Welding (FSW) on AA2024 and AA7075. Base material chemical compositions were tested using Optical Emission Spectrometer and given in Table 1. Tool geometry is the most influential aspect of the process development. It plays a critical role in material flow and in turn governs the traverse rate at which friction stir welding can be conducted. The tool consists of a shoulder and pin. In the initial stage of tool plunge, the heating results primarily from the friction between pin and work piece. The tool is plunged till the shoulder touches the work piece. The friction between shoulder and work piece results in heating. The shoulder also provides confinement for the heated volume of material. The second function of tool is to stir and move the material. Threaded tool pin profiles produce defect free weld joints and improve the mechanical properties [1]. The tool pin profiles used in these experiments are straight cylindrical, straight cylindrical with thread and taper cylindrical with thread as shown in Figure 2. The tool is made up of M2 high speed steel and which was tempered and hardened to 50 HRC. The tool dimensions are shank length and dia 70 mm and 20mm respectively, shoulder length and dia 10mm and 18mm respectively, pin length and dia 4.5mm and 6mm respectively and thread pitch is 0.5mm. The ratio between shoulder dia and pin dia is 3 [2, 5].

(a) Straight cylindrical threaded (b) Taper cylindrical threaded

Figure 2: Tool Pin profiles The weld trials were conducted using Friction Stir Welding (FSW) on commercial aluminium, AA2024 and AA7075. The base material is cut to the size of length 200mm, width 100mm and thickness 5mm. In these experiments the process parameters used are given in Table 2.

Table2: Process parameters Tool Pin profile Tool rotation speed

(RPM) Downward force (kN) Welding speed (mm/min)

Straight cylindrical 600,800,1000,1200 1.5 62.5 Straight cylindrical threaded 800 1.5 62.5 Taper cylindrical threaded 800 1.5 62.5

X-Ray radiographic inspection was carried out on the welded plates using Radiographic unit operated at 85 kV, 5 mA and exposure of 1 min. To determine the quality of the weldment. Hardness was tested using Vickers Micro hardness testing machine. Diamond Intender was used and 0.05 kg load were given. The tensile specimens were cut as per the ASTM E-1251. The bend specimens were cut as per the ASTM B-557 size. Mandrel base has radius of 4-times of thickness of plate and 180 degrees of bend angle. Both tensile and bend tests were performed at Computer Controlled AUTO Make Universal Testing Machine. Bend tests were performed on both face and root side of the welds. Face and root bend tests are used as an important test to understand about the ductility and toughness of friction stir welds. 3. RESULTS AND DISCUSSION The welding trials were conducted using Friction Stir Welding (FSW) on commercial aluminium, AA2024 and AA7075. Commercial aluminium butt welded plates are shown in Figure 3.a and 3.b and dissimilar aluminium alloy butt welded plates are shown in Figure 3.c and 3.d. No visible defects were found in the weldments.

Material Si Fe Cu Mn Mg Zn Cr Al AA7075 0.062 0.186 1.445 0.019 2.55 5.602 0.195 Remainder


A - 51

(a) (b) (c) (d)

Figure 3: (a) & (b) commercial aluminium butt welded plate (c) & (d) dissimilar aluminium alloy butt welded plate 3.1 Radiography test X-Ray radiographs indicated a good quality weld with out any pores and discontinuities at weldment. This conforms defect free weldment irrespective to tool rotation speed for the commercial aluminium AA1100. But dissimilar aluminium alloy AA2024-AA7075 weld plates shows the lack of penetration at the weldment respective to 800 RPM tool rotation speed. The reasons may be insufficient downward force or tool rotation speed or welding speed.

3.2 Hardness test The hardness at the weldment is less compared to the base metal and may be due to the annealing effects while welding. The hardness of the base materials and the welded plates are given in the Table 3.

Table 3: Micro Hardness

Combination Tool pin profile Tool rotation speed (RPM) Hardness(VHN)

AA1100 (Base material) -- -- 130

AA2024 (Base material) -- -- 141 AA7075 (Base material) -- -- 174

AA1100-AA1100 Straight cylindrical 600 101 AA1100-AA1100 Straight cylindrical 800 100 AA1100-AA1100 Straight cylindrical 1000 99 AA1100-AA1100 Straight cylindrical 1200 99 AA2024-AA7075 Straight cylindrical threaded 800 90 AA2024-AA7075 Taper cylindrical threaded 800 90

3.3 Tensile Properties

Tensile properties such as tensile strength and percentage of elongation have been evaluated for welded plates and compared with base metal. In tensile specimens the necking region occurred at thermo-mechanically affected zone (TMAZ) The tensile strength at the weldment is marginally decreased and percentage of elongation is largely decreased compared to the base metal [3]. But as the tool rotation speed increased the tensile properties are marginally increased at the weldment are given in the Table 4. We are obtaining the joint efficiency 92-96%.

Table 4: Tensile Properties Combination Tool rotation

speed (RPM) 0.2% proof stress(MPa)

Tensile Strength (MPa)

Elongation (%) Joint efficiency (%)

AA1100 (Base material) ---- 104 110 42 --- AA1100-AA1100 600 93 101 21 92.1 AA1100-AA1100 800 101 106 25.2 95.3

3.4 Bend Test

Both face bend and root bend tests were performed on the bend test welded specimens which is shown in Figure 4. Most of the welds are of good ductility, allowing for very high bend angles and no cracks were observed [4]. Such ductility is a well known characteristic of the AA1100. Bend test results are given in Table 5.The above result conforms that weld specimens passes the bend test and allowing for very high bend angles and no cracks were observed in weld nugget

Table 5: Bend Test Results

Combination Tool rotation speed (RPM) Root bend Face bend AA1100-AA1100 600 No cracks observed No cracks observed AA1100-AA1100 800 Cracks observed after 90 degree bend No cracks observed


A - 52

(a) AA1100-AA1100 (ST) Root and Face Bend Specimens (b) AA1100-AA1100 (TT) Root and Face Bend Specimens Figure 4: Bend Tested Weld Specimens 4. CONCLUSION 1. Quality welds could be obtained with the tool rotation speeds of 600, 800, 1000, 1200 RPM. No defect

occurred at the weldment irrespective to tool rotation speed for AA1100. Lack of penetration defect occurred in dissimilar aluminium alloys.

2. Hardness is decreased at the weldment compared to the base metal due to annealing effects. 3. The tensile strength is reduced by only about 10% and the percentage elongation reduced almost half 4. compared to the base metal and the joint efficiency 92-96% for AA1100. 5. As the tool rotation speed increased the tensile properties are marginally increased. 6. The welded specimens passed both root and face bend test allowing for very high bend angles and no

cracks were observed in welded regions for AA1100. 7. For AA1100, Straight Cylinder Tool gives quality weld at RPMs above 800. REFERENCES 1. Bahemmat P (2008), ‘Experimental study on the effect of rotational speed and tool pin profile on aa2024

aluminium friction stir welded butt joints’. 2. Balasubramanian V (2008), ‘Influences of tool pin profile and tool shoulder diameter on the formation of

friction stir processing zone in AA6061 aluminium alloy’, Materials and Design 29, page 362–373. 3. Cavaliere P (2005), ‘Mechanical and micro structural behaviors of 2024–7075 aluminium alloy sheets

joined by friction stir welding’, International Journal of Machine Tools & Manufacture. 4. Chunlin Dong (2009), ‘Microstructure and mechanical properties of friction stir welded joints in 2219-T6

aluminum alloy’, Materials and Design 30, page 3460–3467. 5. Padmanaban G (2009), ‘Selection of FSW tool pin profile, shoulder diameter and material for joining

AZ31B magnesium alloy – An experimental approach’, Materials and Design 30, page 2647–2656.


A - 53

INVESTIGATIONS ON FIRST MODE OF METAL TRANSFER DURING

FRICTION STIR PROCESSING IN CAST ALUMINUM A319 ALLOY

L.Karthikeyan1, S.Muthukrishnan2, V.S.Senthilkumar3, L.Karunamoorthy4

1. Ph.D. Research Scholar, Department of Mechanical Engineering, College of Engineering Guindy Campus, Anna University Chennai, Chennai- 600025. Email: [email protected]

2. Project fellow, Department of Mechanical Engineering, College of Engineering Guindy Campus, Anna University Chennai, Chennai- 600025. Email: [email protected]

3. Assistant Professor, Department of Mechanical Engineering, College of Engineering Guindy Campus, Anna University Chennai, Chennai- 600025. Email: [email protected]

4. Professor and Head, Central Workshop, Department of Mechanical Engineering, College of Engineering Guindy Campus, Anna University Chennai, Chennai- 600025. Email: [email protected]

ABSTRACT: Friction stir processing (FSP) is a recent solid state processing technique that utilizes a non consumable rotating cylindrical tool to generate frictional heat and local plastic deformation at any selected processing location. FSP can eliminate casting defects and refine microstructures, thereby improving the tensile properties. During FSP the metal flow takes places by two modes of metal transfer. The first mode of metal transfer takes place layer by layer and is caused by the shearing action of the tool shoulder, whereas the second mode is caused by the extrusion of the plasticized metal around the pin.

The aim of the present study is to quantitatively determine the amount of metal transferred by the first mode during friction stir processing of cast Al alloys A319 at three different feed rates viz., 22.2 mm/min, 40.2 mm/min and 75 mm/min and at different speeds viz., 800, 1000, 1200, 1400, 1600 rpm. On processing, the tensile properties showed remarkable improvement over parent metal. This improvement in tensile properties was found to be in direct correlation with the first mode of metal transfer. The observations made are listed in detail and pictorially represented.

Key words: Friction stir processing, Metal flow, Grain structure, First mode of metal transfer.

1.0 INTRODUCTION

Cast aluminum- silicon A319 alloy is generally used in the automotive industry in the manufacturing of parts such as brake cylinders, crank case, gear boxes, cylinder heads, engine blocks etc., where moderate mechanical properties and good corrosion resistance are required [1]. However these alloys portray porosity and inter-dendritic regions which cause low performance due to degradation in the mechanical properties. FSP is a recently evolving technique which selectively modifies the microstructure in specific areas resulting in the closure of porosity and improvement in local mechanical properties [2-4]. During FSP, a non-consumable tool comprising a shoulder and pin rubs against the work material and produces enormous frictional heat. The heat, combined with deformation by the stirring action of tool pin and pressure due to tool shoulder, produces a defect-free, recrystallized, fine-grained microstructure. Material flow in friction stir processing is characterized by two modes of transfer. The first mode of metal transfer occurs due to the frictional heat generated between the tool shoulder and the plate and takes place as layer-by-layer deposition of metal one over the other. The second mode of metal transfer occurs by the extrusion of metal around the tool pin, when it reaches a state of sufficient plasticity. Muthukumaran et al [5, 6] has established that the first mode of metal transfer plays a major role in influencing the mechanical properties during friction stir process. The first and second modes of metal transfer






A - 54

are clearly visible in all the fracture samples, though they are not too distinct in macrostructure of most processed samples. This investigation aims to understand the correlation between the first mode of metal transfer during friction stir processing and the various tensile properties of cast aluminum alloy A319.

2.0 EXPERIMENTAL

Cast aluminum A319 alloy with the composition (in weight %): Al-5.2 Si-2.51 Cu was sand cast and cut into rectangular pieces of 200mm X 50mm X 10mm. A special purpose friction stir welding machine with a maximum force of 25kN, tool rotational speed of 3000 rpm and power of 15 HP was used. The work material was fixed with respect to the FSP tool. A high carbon steel tool was used for friction stir processing. The threads on the pin were right handed with a pitch of 1 mm. Three feed rates viz., 22.2 mm/min, 40.2 mm/min, 75 mm/min and five tool rotational speeds viz., 800 rpm, 1000 rpm, 1200 rpm, 1400 rpm and 1600 rpm were employed for friction stir processing. The tensile specimens were extracted in the longitudinal direction parallel to the direction of processing for all parametric combinations. The tensile specimens were prepared as per American Society for Testing and Materials (ASTM) standards B557M. The tensile tested specimens were used for fracture image analysis. The first mode of metal transfer was identified visually by the grain size, which is characterized by a fine grain structure. The images of the fractured faces of the sample were captured using an optical microscope at low magnification (10X) to identify and distinguish the two modes of metal transfer and contour plotted using MATLAB (v7.0) software. The various steps involved in the contour plotting of the fracture surfaces of the tensile tested specimens are listed below.

1. The preliminary pre processing stage consists of applying filtering techniques to eliminate the noise from the acquired images thereby sharpening the image. 2. Next a portion of the original image is cropped to select the region of interest. 3. Then the cropped image is converted into an 8-bit gray scale intensity image for further analysis. 4. The gray level image is equalized to improve its contrast by histogram equalization techniques. 5. Finally contouring of the gray level image is done to display a contour plot of the data and extract the prominent features from the image. A contour is defined as a path in an image along which the image intensity values are assumed to be constant. Based on this contour plot, the region representing the first and second modes of metal transfer can be identified. 6. Grids are made on the processed images to facilitate quantitative measurement of the first mode of metal transfer. The percentage of first mode of metal transfer was computed using the following relation:

% First mode = plotcontour theof area Total

modefirst in the ed transferrmetal ofAmount

= plotcontour in grids ofnumber Total

modefirst in the grids ofNumber

The relationship existing between the first mode metal transfer and various tensile properties were developed using a statistical software SPSS (v17.0). 3.0 RESULTS AND DISCUSSION 3.1 Effect of rotational speed on first mode metal transfer

The images of the tensile fractured surface of specimen and the corresponding contour plots are shown in Fig. 1. The region representing the first mode metal transfer is differentiated with a contour.

Fig. 1 First mode metal transfer analysis of FSP specimen at a feed rate of 75 mm/min

a. Optical micrograph of metal transfer at a tool rotational speed of 1400 rpm b. Contour plot of metal transfer at a tool rotational speed of 1400 rpm

The relationship between the first mode metal transfer and the process parameters is shown in the Fig. 2. The results indicate that the first mode metal transfer increases with rotational speed till 1200 rpm. This can be attributed to the high temperatures the material is exposed to with higher tool rotational speeds and the resultant reasonably fine recrystallized grains obtained. Owing to the frictional heat during FSP material flow


A - 55

caused by the stirring action of the pin takes place along with a severe plastic deformation. This is responsible for the grain refinement and dynamic recrystallization present. However at higher than the optimum tool rotational speeds a reduction in the first mode metal transfer occurs due to very high frictional heat input and thereby resulting in a turbulent plastic flow.

3.2 Effect of first mode metal transfer on ultimate tensile strength

Fig. 3 shows the relationship between the first mode of metal transfer and the ultimate tensile strength. It can be seen that the ultimate tensile strength increases with the first mode metal transfer. The material extruded by the pin is compacted due to the compressive load by the tool shoulder offered during the first mode metal transfer. It offers solidity to the process zone and hence increase in the first mode metal transfer is found to improve the tensile properties. In addition, the grain refinement during FSP results in the closure of casting porosity and produces a homogenized microstructure. This converts the as-cast material into a near-wrought condition. This homogenized and refined microstructure along with the reduced porosity results in improved tensile properties.

Fig. 2 Effect of friction stir processing parameters Fig. 3 Relationship between first mode of metal transfer and on first mode of metal transfer ultimate tensile strength

3.3 Effect of first mode metal transfer on yield strength

Response of yield strength to the variations in the first mode meal transfer is displayed in the Fig.4. The same reasons attributed to the increases in the tensile strength with tool rotational speed can be given here too. On the whole increase in the yield strength can be due to the reduced strain localizations in consequence of the uniform microstructure following friction stir processing.

Fig. 4 Relationship between first mode of metal transfer and yield strength

3.4 Correlation between first mode metal transfer and tensile properties

In use of the multi-variable linear regression analysis, the correlation between first mode metal transfer and tensile properties in friction stir processing was obtained.

a) Ultimate tensile strength 912.02R1MT079.694.17UTS =ε++=σ (1)

b) Yield strength 78.02R1MT692.491.27YS =ε++=σ (2) This good correlation indicates that first mode metal transfer plays a major role in influencing the

mechanical properties.From the tables and graphs, it can be observed that first mode of metal transfer has an influence over the mechanical properties of the processed material and this agrees with the previously reported results [5-7].


A - 56

4.0 CONCLUSIONS From this study on first mode of metal transfer and its influence of tensile properties the following

conclusions could be drawn.

Ø The two modes of metal transfer are distinct in the fractured surface. Ø Friction stir processed plates that exhibit better yield and tensile strengths are characterized by a higher

percentage of metal transfer indicating a linear relationship between them. Ø The percent first mode metal transfer increases distinctly with tool rotational speed and it is ascertained that

for the friction stir processing, the optimum tool rotational speed is 1200 rpm for all feed rates. Ø The variation in the process parameters such as tool rotation and traverse speed produces different thermal

profiles. So any change in the process parameters affects the tensile properties. Ø A good correlation between first mode metal transfer and tensile properties was established using multi-

variable linear regression. This indicates that first mode metal transfer plays a major role in influencing the mechanical properties.

5.0 REFERENCES 1. Tavitas-Medrano F. J. , Gruzleski J. E., Samuel F. H., Valtierra S. , Doty H. W.. (2008), Effect of Mg

and Sr-modification on the mechanical properties of 319-type aluminum cast alloys subjected to artificial aging. Materials Science & Engineering A, Vol. 480 pp 356-364.

2. Santelia M.L., Engstrom T., Storjohann D., Pan T. Y. (2005), Effects of friction stir processing on mechanical properties of the cast aluminum alloys A319 and A356. Scipta Materialia, Vol. 53 pp 201–206.

3. P. Caveliere, A. Squillace. (2005), High temperature deformation of friction stir processed 7075 aluminum alloy. Materials Characterization Vol.55, pp 136–142.

4. Nakata K., Kim Y.G., Fujii H., Tsumura T., Komazaki T.. (2006), Improvement of mechanical properties of aluminum die casting alloy by multi-pass friction stir processing. Materials Science and Engineering A Vol.437, pp 274–280.

5. Preetish Sinha, Muthukumaran, S., Mukherjee, S.K., (2008), Analysis of first mode of metal transfer in friction stir welded plates by image processing technique” Journal of material processing technology. Vol.197, pp 17-21.

6. Muthukumaran, S., Mukherjee, S.K. (2006), Two modes of metal flow phenomenon in friction stir welding process, Sci. Technol. Weld. Join. Vol.11, pp 337-340.

7. Karthikeyan L., Senthilkumar V.S., Balasubramanian V., Arul S. (2010). Analysis of First Mode Metal Transfer in A413 Cast Aluminum Alloy during Friction Stir Processing. Materials letters Vol. 64 pp 301-304.

Acknowledgements The authors gratefully acknowledge University Grants Commission (UGC), Delhi, India for its financial support through the grant UGC F.No.33-402/2007 (SR) towards carrying out this research. The authors are grateful to the Department of Manufacturing Engineering, Annamalai University, Annamalai Nagar, India for extending the facilities of Metal Joining Laboratory to carry out this investigation. The help of Professor (Dr.) V. Balasubramanian, Center for Materials Joining and Research, Department of Manufacturing Engineering, Annamalai University is highly appreciated.


A - 57

SQUEEZE CASTING - A NOVEL METAL PROCESSING TECHNIQUE:

AN OVERVIEW

M .Thirumal Azhagan1, Dr. B. Mohan2, K.G. Ashok3

1. Lecturer,MIT, Anna University Chennai, Department of Production Technology, Email: [email protected]

2. Assistant Professor, MIT, Anna University Chennai, Department of Production Technology, Email: [email protected]

3. P.G. Student, MIT, Anna University Chennai, Department of Production Technology, Email: [email protected]

Abstract: Squeeze Casting is a metal processing technique which combines the features of both casting and forging in one operation. The automotive and aerospace industries are the main driving force behind the advent of squeeze casting as this process produces components with improved mechanical properties. Squeeze casting is the process in which the molten metal is solidified under the application of pressure within the die. The time required for solidification is substantially reduced due to enhanced heat transfer at the mould surfaces under high pressure. The solidification time is estimated by varying heat transfer coefficient. Higher heat transfer coefficient is interpreted as a consequence of higher applied pressure. Key words: Squeeze casting, solidification, mechanical properties

1. INTRODUCTION

The most economical process of making metallic components is by casting in which the liquid metal is directly poured in the mould cavity of required shape and size with or without pressure. The main draw backs of casting process are the formation of casting defects such as porosity, segregation, hot tears etc. In order to compensate the limitations of casting process, several new casting techniques have been developed. Squeeze casting is one of such new casting techniques developed which has got great potential to fabricate components with improved mechanical properties having high integrity with very low defects. The automotive and aerospace industries have been main driving force behind the squeeze casting process. Squeeze casting has been used for wide range of metals ranging from the lowest melting point alloy to very high melting point alloys. Squeeze casting is an advanced manufacturing process where molten metal is subjected to high applied pressure during cooling and solidification. The advantages of the squeeze cast products are mainly nil gas porosity or shrinkage porosity, better mechanical properties and reduced metal wastage. It has been reported that the mechanical properties of a squeeze cast item can be as good as wrought products of similar composition. In squeeze casting, the applied pressure plays a very important role. The main advantage of the deployment of high pressure is that it enhances the heat transfer coefficient by several orders of magnitude. This enhancement is realized due to the establishment of direct contact between the liquid metal and the die wall. Owing to the high heat flux at the boundaries, the solidification is quickly achieved. Solidification and heat transfer are the very important aspects of the microstructure.





A - 58

Fig. 1. Classifications of the Squeeze Casting Process 2. The Casting Process outline Two basic forms of the process may be distinguished, depending on whether the pressure is applied directly on to the solidifying cast product via an upper or male die (punch) or the applied pressure is exerted through an intermediate feeding system as schematically shown in Fig 2: (i) the direct squeeze casting mode, and (ii) the indirect squeeze casting mode. For the direct mode, two further forms may be distinguished based on liquid metal displacement initiated by the punch movement: (i) without metal movement, and (ii) with metal movement. As illustrated in Fig.3. the first form is suitable for ingot type components where there is no metal movement, while the second type involving metal movement, also known as the backward process, is more versatile and can be used to cast a wide range of shaped components.

Fig. 2. Schematic Diagram to illustrate the Direct and Indirect Modes of the Squeeze Casting Process

Fig 3. Schematic Diagram to show Two Forms of the Direct Squeeze Casting Process


A - 59

3. Steps involved in squeeze casting The process of squeeze casting involves the following steps:

1. The metal is melted in a furnace 2. The die set is pre heated to a temperature range of 300°C

3. The molten metal is poured in to the die cavity; the punch is placed in the hydraulic press. 4. The pressure is applied over the molten metal by means of punch until the solidification is complete. 5. The punch is with drawn and the component is ejected.

4. Elements of Squeeze Casting 4.1 The Die The most crucial aspect in permanent mould castings such as die-casting or squeeze casting is the die itself and very importantly the design of the die including the selection of suitable die material, the manufacturing process, appropriate heat treatment and the maintenance practice plays a vital role. Squeeze casting dies are exposed to severe thermal and mechanical cyclic loading, which may cause thermal fatigue, cracking, erosion, corrosion, and indentation. Currently H11/H13 tool steel is a widely used material for the constructions of die. 4.2 Type of Equipment A variety of squeeze casting machines are in use in various parts of the world. They are either designed by the researchers themselves the so-called home-made, or manufactured by machine tools companies on a mass production basis. The direct SC-machines are simple and straightforward but the indirect ones generally fall into the following categories of: (i) vertical die closing and injection, (ii) horizontal die closing and injection, (iii) horizontal disclosing and vertical injection, and (iv) vertical die closing and horizontal injection 4.3 Pressure applying duration

Although squeeze casting is regarded as the pressurization of molten alloy, it may also be used for shaping semi-solids and, therefore, a further classification are :(I) before the beginning of crystallization, and (ii) after the beginning of crystallization, which may also be described as semi-solid pressing.

4.4 Process Parameters

The most important process parameter is the alloy itself. The composition and physical characteristics of the alloy are of important due to their direct effects on the die life. These include the melting temperature, and thermal conductivity of the alloy together with the combined effect of the heat-transfer coefficient and soldering onto the die material. Furthermore, the alloy dictates the selection of casting parameters such as die temperature, which has direct consequence on the die life. Therefore, squeeze casting is usually employed for low melting temperature alloys of aluminium and magnesium. In addition to the composition of a casting alloy, which determines its freezing range and affects the quality of finished components, the casting parameters should also be controlled very closely to achieve a sound casting. The most dominant process parameters are die temperature and pouring temperature, and superheat, although the level of applied pressure is also important. Since the metal is cast under pressure, the inherent cast ability of the alloy is of little or no concern. The die temperature is usually held at between 200oC and 300oC for aluminium and magnesium alloys, whilst the applied pressure varies between 50 and 150 Mpa. The lubrication medium, i.e., the die coat, is usually graphite based. Heat-transfer coefficients are extremely high due to the casting metal being pressed against the die wall.

5. CONCLUSION

The squeeze casting process has been proven to be an ideal way to produce near-net shape high quality engineering components, especially for the automotive industry in both conventionally cast and wrought-alloy compositions. Squeeze casting is one of such new casting techniques developed which has got great potential to fabricate components with improved mechanical properties having high integrity with very low defects. Squeeze casting has been used for wide range of metals ranging from the lowest melting point alloy to very high melting point alloys. The process is most suitable for opening up new possibilities for the productions of castings that are subjected to high service stresses.


A - 60

6. REFERENCES 1. P. Vijian , V.P. Arunachalam, (2005) “Experimental study of squeeze casting of gunmetal”, Journal of

Materials Processing Technology 170 32–36 2. P. Vijian , V.P. Arunachalam, (2006), “Optimization of squeeze cast parameters of LM6 aluminium

alloy for surface roughness using Taguchi method” Journal of Materials Processing Technology 180, 161–166

3. Ghomashchi M.R. Vikhrov A. (2000) “Squeeze casting: an overview”, Journal of Materials Processing Technology, 101 pp.165-170.

4. Himadri Chattopadhyay (2007) “Simulation of transport processes in squeeze casting” Journal of Materials Processing Technology, 186, pp.174–178

5. Raji A. and Khan R. H. (2008) “Effects of Pouring Temperature and Squeeze Pressure on Squeeze Cast Parts” Paper No.75-122. AFS Transactions 83: 755-60

6. Roland Lewis W. Eligiusz Postek W. (2005) “A finite element model of the squeeze casting process” Finite Elements Analysis and Design, Vol. 34 No. 2, pp. 193-209.

7. Janusz krawczyk and Piotr bała (2004) “Effect of heat treatment on properties of hot work tool steel” Vol.20 pp.145-156

8. Minaie B. K.A. Stelson K.A. (2003) “Analysis of flow patterns and solidification phenomena in the die casting process” ASME Trans.113


A - 61

OPTIM IZATION OF PROCESS PARAMETERS OF PLASMA ARC WELDING FOR ENGINE VALVE MANUFACTURING

Mr.JOTHILINGAM.A1, PRADEEPKUMAR.D 2

1. Assistant Professor 2. PG Student, Department of Production Technology, MIT Campus, Anna University Chennai, email: [email protected]

ABSTRACT: The neck of the engine valve is subjected to more wear than the other surfaces so that it is coated with satellite F powder. But this coating has blow holes and porosity which was identified in penetration test. In order to reduce these we are going to optimize the process parameters of plasma transferred arc welding by doing so we can able to reduce the productivity of the engine valve. Taguchi's method for parameter design, Design of experiments and Analysis of variance are going to be employed for finding the optimum parameters. In this work the coating of satellite F powder will be carried out in plasma transferred arc welding. The optimum process parameters are going to be determined.

1. INTRODUCTION

Plasma transferred arc (PTA) welded coatings are used to improve surface properties of mechanical parts. Advantages are the high reliability of the process and the low dilution of substrate and coating material. Processing of surfaces by PTA welding is restricted at the time to flat horizontal position. Furthermore, industry is interested in the development of strategies for coating with PTA in constraint position as complex three-dimensional (3D) parts could be then easily processed as well. Under commercial aspects, the process design can be optimized to increase process efficiency and to reduce heat input during the welding process. Process optimization involves the determination of guidelines for PTA welding in constraint positions as well. Modeling the process gives an alternative to reduce the experimental effort to optimize the welding process. Results of simulation studies of the PTA welding process are given in the present work. It will be shown that coating conditions can be optimized by varying plasma gas flow, heat input and heat flow, process speed, or powder injection with regard to welding in constraint positions. The defined controlling of the PTA welding allows modification of process management with less experimental effort and to develop coating strategies for processing in different positions. In experimental investigations, the developed coating strategies are confirmed by producing PTA coatings in constraint position as well as complex 3D parts. Processing of surfaces by PTA welding is restricted at the time to flat horizontal position. This means that damaged parts have to be dismounted to be processed. Furthermore, industry is interested in the development of strategies for PTA coating in constraint positions as complex three-dimensional (3D) parts could be easily processed as well. Process modeling is an important tool to develop process strategies for PTA coating in constraint positions and to generate complex geometries, as the influence of the process parameters (plasma power, gun position, injection conditions, and substrate) and the material on the heat input and the coating geometry can be specified. The objective of this work is to study the plasma arc welding and find the optimum parameters using design of experiments 2. WELDING

Welding is the process of joining of two metals. This can be carried out by means of melting the metals. This process can be used for several applications. Our study is about the plasma arc welding.



A - 62

3.1 INTRODUCTION OF PLASMA ARC WELDING

Arc is a temporary state of gas. The gas get ionized after the passage of electric current through it and become a conductor of electricity. In ionized state gas atoms breaks into electrons and ions and the system contains ions electrons and highly excited atoms. 3.2 DEFINITION Plasma arc welding is an arc welding process wherein coalescence is produced by heat obtained from a constricted arc set up between a tungsten/alloy tungsten electrode and the water cooled nozzle(non transferred) or up between a tungsten/alloy tungsten electrode and the job(transferred). The process employs two inert gases one forms the arc plasma and second shields the arc plasma. There are two types of plasma arc welding. They are non transferred arc and transferred arc. Our study is on transferred arc welding. In this the tungsten electrode act as cathode and the work piece act as anode. 3.3 EXPERIMENTAL SET UP In the PTA process two independent arcs are used. A pilot arc is formed between a nonconsumable tungsten electrode (cathode) and copper plasma nozzle with an inner diameter of 2 mm (anode) in the welding torch. A plasma gas (Ar, He, Ar/He, or Ar/H2 mixture) flows coaxially to the tungsten electrode in the copper nozzle and is ionized by the applied arc energy. A second arc (transferred or plasma arc) is then established between the tungsten electrode and the workpiece. The resulting temperature in the transferred arc is between 10,000 and 15,000 °C. There is no direct contact between the copper plasma nozzle and the workpiece, and no arc is burning. The energy released by the arc is influenced by arc current and length. Powder is fed into the plasma through injection nozzles and is subsequently heated by the arc. Shielding gas for protecting the area around the plasma from oxidation is fed through a large outer nozzle. Figure 1 shows the principle of the plasma transferred arc process. Main parameters of the PTA process are the current of the pilot and the transferred arc, the flow rate of the plasma, the shielding, and the powder carrier gas . The gas flow rate and the gas type have a significant influence on the heating and melting of the coating material during the PTA process. Additionally, the powder feed rate and the process velocity influence the resulting properties of the coating

Fig 3.1 Plasma Arc Welding 4.1 DESIGN OF EXPERIMENTS

Orthogonal Arrays (OA) allow us to conduct statistically designed experiments involving a large number of factors using only a limited number of trials that is practically feasible. The work on construction of Orthogonal Arrays for reducing run-size of an experiment started way back in 1947 in Indian Statistical Institute, Calcutta. However, the credit for popularizing the use of OA’s for industrial experimentation goes primarily to Dr.G. Taguchi of Japan. Dr.Taguchi has developed a set of Orthogonal Arrays and the associated


A - 63

linear graphs and given us a battery of methods for obtaining experimental design to suit one’s requirements. There are other OA’s (like Plackett Burman designs) which are similar to those developed by Taguchi. However, here we shall discuss only the arrays and methods of Taguchi. The following table gives the model experiment.

Experiment No.

Column / factors 1(A) 2(B) 3(C) 4(D) Response

1 1 1 1 1 Y1

2 1 2 2 2 Y2

3 1 3 3 3 Y3

4 2 1 2 3 Y4

5 2 2 3 1 Y5

6 2 3 1 2 Y6

7 3 1 3 2 Y7

8 3 2 1 3 Y8

9 3 3 2 1 Y9

Table 4.1 Model Experiment

5.1 EXPERIMENTAL ANALYSIS The experimental evaluations are going to be carried out in plasma transferred arc welding technique. The coating of stellite F powder in the valve will be carried out. The main input parameters are angle, speed, current and powder feed rate. The performance which we measured are porosity, thickness of coating and hardness of the material. 5.2 MATERIAL COMPOSITION The plasma transferred arc deposition of stellite F will be carried out in engine valve seats made of X45CrSi93 martensitic steel. The composition of the valve material and the stellite powder are given in the following tables. Nominal chemical composition of base material (X45CrSi)

elements C Si Mn Cr Ni P S Weight% 0.45 3.00 0.80 9.00 0.50 0.04 0.03 Table 5.1 Chemical Composition of X45CrSi Nominal chemical composition of Stellite F Element Cr W Mo C Fe Ni Si Mn Co Weight% 25 12.30 1 1.75 3 22 2 1 Balance Table 5.2 Chemical Composition of Stellite F

5.3 CONTROL FACTORS The control factors that we are considered are plasma gas flow rate, powder gas feed rate, temperature and current. The performance that we measured are penetration, thickness and hardness.The levels of the parameters are plasma gas flow rate:1.2 LPM, 2.2 LPM, 2.8 LPM powder gas feed rate:1.2 LPM, 2.2 LPM, 2.8 LPM, temperature: 60°, 80°, 100, current intensity:84A, 92A, 100A. 6. EXPERIMENTAL OBSERVATIONS


A - 64

The experiment is carried in plasma transferred arc welding. The observations for the various performance namely penetration , thickness and hardness on varying levels of cutting parameters are recorded for an orthogonal array which minimizes the number of experimental evaluations to 9 experiments. The following data gives the experimental data.

Sl No. PGFR LPM

PDFGR LPM

CURRENT A

TEMP deg

Penetration mm

Hardness HRC

Thickness mm

1 1.2 1.2 84 60 1.1 30 1.6 2 1.2 2.2 92 80 1.15 36 1.49 3 1.2 2.8 100 100 1.18 42 2.2 4 2.2 1.2 100 80 1.2 32 1.23 5 2.2 2.2 84 100 1.23 38 1.1 6 2.2 2.8 92 60 1.25 33 1.70 7 2.8 1.2 92 60 1.34 33 2.15 8 2.8 2.2 100 100 1.45 40 1.32 9 2.8 2.8 84 80 1.50 34 1.7

The optimum process parameters are calculated by finding the signal to noise ratio for the output parameters and graphs are plotted between process parameters and mean s/n ratio. 6. CONCLUSION The process of plasma transferred arc welding which was applied in coating of stellite F powder in the neck of the engine valve has been studied. The effect of process parameters namely plasma gas flow rate, powder gas feed rate, current intensity and temperature and performance measures like penetration, thickness and hardness during coating were analyzed. By finding the response table and by plotting the response graph the optimum parameters will be identified. 7. REFERNCES 1. GAO Zhonglin et al., (2008) “Modeling of arc force in plasma arc welding”, Tianjin University and Springer Verlag 2. Samotugin.S.S et al., (2003) “Optimising the design of plasma torches for surface hardening of materials”,

Welding International. 3. M.G.Sharapov(2003) “Optimisation of gas shielding in plasma welding”, Welding International 4. Sharapov.M.G and Shvedikov.V.M(2004) “The efficiency of gas jet shielding in argon-arc welding”,

Welding International. 5. Sundaraiyah.B and Bala Srinivasan.P(2008) “Optimization of process parameters for deposition of Stellite

on X45CrSi93 steel by plasma transferred arc technique”, Elsevier Materials and Design 6. Wilden.J et al (2006) “Plasma Transferred Arc Welding—Modeling and Experimental Optimization”, ASM

International 7. Book reference: Ronald E.Walpole(2004) “Probability and Statistics”, Pearson Education.


A-65

DELAMINATION ANALYSIS OF FIBER REINFORCED

POLYMER COMPOSITE LAMINATES

K.S ASHRAFF ALI *1, A. AROCKIA JULIAS 2, Dr. S.S.M.ABDUL MAJEED 3

1. PG student, M.E (CAD)B.S.Abdur Rahman Crescent Engineering College

[email protected]

2. Assistant Professor,B.S.Abdur Rahman Crescent Engineering College [email protected] 3. ProfessorB.S.Abdur Rahman Crescent Engineering College [email protected]

Abstract: Delamination is one of the predominant forms of failure in laminated composites due to the lack of reinforcement in the thickness direction. In this work mode-I delamination failure is analyzed using double cantilever beam (DCB) test. The DCB test has been conducted for glass fiber laminates with different orientation. The laminates are manufactured by hand layup technique as per ASTM standard D 5528-01 and strain energy release rate GIc for different combinations are calculated. Finite Element Analysis (FEA) of DCB test has been done using ANSYS software. The fracture toughness obtained by FEA is compared with the experimental results.

Keywords: Delamination, Opening mode, GIc, DCB, ANSYS

1. INTRODUCTION

Composite is defined as the sum of matrix and reinforcement where two are more different materials are combined together. Materials like vinyl ester, epoxy & polyester are used as matrix. The reinforcement materials are glass, carbon, aramid & graphite. Fiber reinforced polymer composites materials are widely used in aerospace, automobile, infrastructure & aircraft application. Most of the failures occur due to delamination in FRP composites.

The composite structures are in the form of layers or laminates. In these laminates one of the most common failures is delamination. In such cases, layered composites suffer severally by delamination cracking because of poor interlaminar fracture resistance. The evaluation and propagation of inter laminar damage leads to laminate separation. A quite typical structural failure mode is called as delamination. Delamination may be introduced by the external loading as in static bending, compression or tension in cyclic fatigue or by impact loads, during manufacture or service life condition.

ASTM standard D 5528-01 is used for delamination test [1]. This test method describes the determination of

the Mode I (opening) interlaminar fracture toughness. GIc of continuous fiber-reinforced composite materials are calculated using the double cantilever beam (DCB) test. The main objective of this work is to analyze and test the mechanical properties and delamintion behavior of unidirectional glass fiber reinforced polymer (FRP) composite with different Orientation. Influence of in-fiber orientation on Mode I interlaminar fracture toughness of glass/polyester composites is done by “S.Solaimurugan, R.velmurugan” [2]. Opening mode interlaminar fracture toughness of interply hybrid composite materials is studied by “Stun-Fa Hwang, Bon-cherg shen” [3].





A-66

2. LAMINATE PREPARATION

The laminate preparation as shown in fig. 1 in which Glass is used as the reinforcement, epoxy is used as the matrix. Fiber in the form of mat is prepared for the required dimensions. Resin and hardener were mixed with the ratio of 1:10 and mats are arranged to required orientation. This method commonly uses a specimen in which an initial crack is created by inserting a thin Teflon film (typically 0.013 mm thick) at the midplane before molding. Hand lay-up technique is used for laminate preparation and allowed for curing in atmospheric condition (2 days).

Fig.1. Laminate preparation. 3. SPECIMEN PREPARATION

Specimens is 125 mm (5.0 in.) long and nominally from 20 to 25 mm (0.8 to 1.0 in.) wide. The laminate thickness shall normally be between 3 and 5 mm (0.12 and 0.2 in.) as per ASTM dimension D 5528-01as shown in fig 2. The variation in thickness for any given specimen shall not exceed 0.1 mm. The initial delamination length is measured from the load line to the end of the panel insert. Hinged metal tabs are bonded at the delaminated end of the specimen.

Fig.2. Specimen preparation.


A-67

4. TEST METHOD

The DCB test is used for determining the strain energy release rate GIc for delamination growth under Mode I loading. The DCB shown in Fig.3 consists of a rectangular, uniform thickness, unidirectional laminated composite specimen containing a non adhesive insert on the midplane that serves as a delamination initiator. Opening forces are applied to the DCB specimen by means of loading blocks (Fig. 3) bonded to one end of the specimen. The ends of the DCB are opened by controlling either the opening displacement or the crosshead movement, while the load and delamination length are recorded. Test is conducted in the UTM Instron machine.

Fig.3. Double cantilever test. 5. CALCULATION

Modified Beam Theory (MBT) Method is used for calculating GIc. The strain energy release rate GIc for various tested specimen can be calculated by the curve between load and crack opening displacement. The locations of instantaneous front are marked for different intervals of delamination growth. The Mode I critical strain energy release rate was calculated using (MBT) method as given in equation (1). The values are given in Table 1.

(1)

Where: P = load

= load point displacement b = specimen width a = delamination length.

Table 1 Critical energy release rate of unstitched laminates

Crack length (mm)

35 40 45 50 55 60

Load (N) 150.5 110.6 95.5 83.2 76 70 Load point deflection (mm)

3.3 4.5 6.57 8.2 10.2 12.8

∆ 0.23 0.36 0.47 0.60 0.72 0.85


A-68

GIc ( J/m2 ) 3107 2910 2443 2109 1767 1424 6. FINITE ELEMENT ANALYSIS USING ANSYS

Finite element analysis of delamination test has been done using the virtual crack closure technique. The FEA is modeled as per ASTM standard D 5528-01. The material properties and meshing is defined for glass fiber. The load is applied on one end and another end is arrested. The fracture toughness obtained by FEA is compared with the experimental results.

Fig.4. Delamination analysis 7. RESULT

The GIc valve is calculated using the MBT method. The valve obtained from experiment for 0º& 90º

orientation (cross ply) is reported in table (1). The GIc of the specimen increases with increase in orientation angle. Delamination has been done using the virtual crack closure technique and compared with the experimental results.

8. REFERENCE

1 ASTM standard designation D 5528-01. 2 S.Solaimurugan, R.velmurugan, 2008, “Influence of in-fiber orientation on mode 1 interlaminar

fracture toughness of stitched glass/polyester composites”. Composite science and technology, pp1752-1782

3 Stun-Fa Hwang, Bon-cherg shen, 1999, “Opening mode interlaminar fracture toughness of interply hybrid composite materials”. Composite science and technology, pp 1861-1869

4 P.K. Mallick- “Fiber reinforced composite materials, manufacturing, and design”. 5 Bhagwan D.Agarwal- “Analysis and performance of fiber composite”. 6 Prasanthakumar- “Mechanics of facture”.

a - (casting, welding & foundry)

Documents