Reconfiguration of a Milling Machine to achieve Friction Stir Welds

Akinlabi Esther Titilayo1, a, Madyira Daniel Makundwaneyi2, b

and Akinlabi Stephen Akinwale3, c 1Senior Lecturer, Department of Mechanical Engineering Science, University of Johannesburg,

P. O. Box 524, Auckland Park Kingsway Campus, Auckland Park, Johannesburg, South Africa. 2006.

2Lecturer, Department of Mechanical Engineering Science, University of Johannesburg, P. O. Box

524, Auckland Park Kingsway Campus, Auckland Park, Johannesburg, South Africa. 2006.

3Doctorate Candidate, Department of Mechanical Engineering Science, University of Johannesburg, P. O. Box 524, Auckland Park Kingsway Campus, Auckland Park, Johannesburg, South Africa.

2006.

aetakinlabi@uj.ac.za,

bdmadyira@uj.ac.za,

csaakinlabi@uj.ac.za

Keywords:Friction stir processing,Friction stir welding, Milling machine,Reconfiguration.

Abstract.This paper reports on the reconfiguration of a milling machine to produce friction stir welds

of aluminium and copper and friction stir processing of 6086 aluminium alloy. Friction stir welding

tools were designed and manufactured from tool steel. The tools were inserted into the chuck of the

milling machine. A backing plate was also specially designed and manufacturedfrom mild steel to

protect the milling machine table and was placed on the bed with the use of T-nuts. The plates were

secured firmly on the backing plate with the use of specially designed clamping fixtures. The varied

welding speeds and the rotational speeds were achieved using the control system on the vertical

milling machine. The reconfigured milling machine was successfully employed to produce friction

stir processing of aluminium and friction stir welds of aluminium and copper. An optimum joint

strength of 74% was achieved.

Introduction

Manufacturing system consists of people, machines, tools, materials and information, which are

related to each other to produce a value-added product. Reconfigurable Manufacturing System

became necessary in order for manufacturing systems to be more responsive, this means adapting the

manufacturing system to market conditions [1]. Reconfigurable systems are focused on achieving

responsiveness to a customer need and achieving it at a low cost and at a rapid time. Manufacturing

systems that use reconfigurable components offer a much greater benefit to manufacturers than

traditional manufacturing systems. These include adjustable rates of productivity and flexibility,

along with new tools for designing systems and getting production up and running are a characteristic

of reconfiguration design that improves the time-to-market and provide production at precisely the

quantities needed, and at the lowest possible cost. Responsiveness is an attribute enabling

manufacturing systems to quickly launch new products on existing systems and to react rapidly and

cost-effectively to: market changes, customers orders, government regulations and system failures.

Market changes include: changes in product demand, changes in current products and introducing

new products. A cost-effective response to market changes requires a new manufacturing approach

that is able to react to changes quickly and efficiently. This is achieved by designing systems

according to two principles. The first one is a design of a system and its machines for adjustable

structure that enables scalability in response to market demands and system or machine adaptability to

new products. Structure may be adjusted at the system level and at the machine level. The second one

is a design of a manufacturing system around the part family, with the customized flexibility required

for producing all parts of this part family, this reduces the system cost [2]. The need and rationale for

Applied Mechanics and Materials Vol. 232 (2012) pp 86-91 (2012) Trans Tech Publications, Switzerlanddoi:10.4028/www.scientific.net/AMM.232.86

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reconfigurable manufacturing systems arises from unpredictable market changes that are occurring

with increasing pace and increasing demand for portable manufacturing systems for research and

development purposes. Some of the market changes include - increasing frequency in introduction of

new products, changes in parts of existing products, large fluctuation in product demand and mix,

changes in government policy and regulations, and changes in process technology [2]. Consequently,

the concept of reconfiguration of manufacturing systems and design of machine tools has been

investigated by many researchers [2-8] for reasons such as making the design of the new

reconfigurable machine tool to configure existing modules for execution of specific tasks and also a

new design that illustrates the ideas of reconfigurable science [3].Furthermore, Mpofu et al[4]

reported that with the concept of reconfiguration of machine tools, the product life cost of the modular

machine will be reduced since the time of developing new concept will be shorter because some basic

machine modules remain the same while some selected components of the assembly has to be

redesigned to meet customers specific new requirements.As a result of the challenges of

globalization of the manufacturing environment such as uncertainties and turbulences of customers

requirements and manufacturing resources, Bi[5] reported that reconfiguration of manufacturing

system will also be an effective way to increase the competitiveness and adaptability of

manufacturing systems. It was also identified that new methodologies and technologies were also

developed to support reconfigurable manufacturing system; one of such was reported by Xinget al[6].

They applied artificial intelligence to designing and analysis of a reconfigurable cellular

manufacturing system. The emphasis of this investigation was to develop a dynamic and logical

clustering of some manufacturing resources, driven by specific customers orders, aiming at optimally

fulfilling customers orders along with other reconfigurable manufacturing cells in a reconfigurable

cellular manufacturing system. Minton and Mynors [7] were first among other researchers that

documented the investigation of utilizing engineering workshop equipment for friction stir welding.

They successfully described a method to determine if a conventional milling machine is capable of

being used to produce friction stir welds. This was tested by producing welds of same thickness from

6.3 mm and 4.6 mm 6082T6 aluminium sheets.The result demonstrated that a conventional milling

machine can perform friction stir welding and reasonable welds were produced using a relatively stout

tool to join 6.3 mm thick 6082-T6 aluminium and lesser quality welds were produced when joining

4.6 mm thick 6082-T6 aluminium. This paper reports the reconfiguration of a vertical milling

machine to produce both friction stir processing of aluminium and friction stir butt welds of

aluminium and copper.

Experimental procedure

A Model YS5BS with Syntec PC Based Controller vertical milling machine was reconfigured to

performthe Fiction Stir Processing (FSP) of aluminium and Friction Stir Welding(FSW) of

aluminium and copper in butt joint configurations. It is a variable speed bed type milling machine

with a robust solid cast bed, power feed on the x, y and z axes and equipped with a 4 kW motor. The

spindle speed on the milling machine can be varied from 70 to 4200 rpm. A backing plate was

specially designed, manufactured and bolted to the bed with the use of T-nuts. The backing plate and

the clamping fixtures were machined by Sheaf Precision Engineering, Johannesburg, South Africa.

The experimental set up for the assembly of the backing plate and the clamping fixtures are shown in

Fig.1. Other drawings related to the backing plate and the clamping systems are presented in the

Appendix.

Applied Mechanics and Materials Vol. 232 87

Fig.1: Assembly drawing of backing plates, clamping fixtures and aluminium and copper sheets

The tool employed was a 5mm long threaded pin with 18mm concave shoulder, machined from

H13 tool steel and hardened to 52HRC.The Friction stir welding tools were manufacturedby

Grip-Tech (Pty) Ltd Johannesburg South Africa. The FSW tool was inserted into the chuck of the

milling machine to produce the welds. The schematic diagram of the FSW tool used in this research

work is presented in Fig. 2.

Fig. 2: FSW tool - Threaded pin and concave shoulder [9].

The FSW of aluminium and copper were produced on 600 mm x 120 mm x 3mm thick sheets of

6084 - T6Aluminium Alloy (AA) and C1000 copper (Cu) and the dimensions of the friction stir

processed aluminium sheets were 600 mm x 220 mm x 3 mm thick sheets.The aluminium and copper

sheets to be friction stir processed and/or welded were abutted and clampedonthe backing plate which

was bolted directly to the bed of the milling machine. The surfaces of both sheets were cleaned with

acetone before the welding procedure. The welding speeds and the rotational speeds were achieved

using the control system and the panel. The rotational speeds of 600, 900 and 1200 rpm and feed rates

at 50, 150 and 250 mm/min were chosen to represent low, medium and high settings respectively.

Other parameters such as the tool tilt angle, the plunge depth and dwell time were kept constant at 20,

2.90 mm and 2 seconds respectively. The tensile samples were tested in accordance with ASTM E-8.

A servo-hydraulic Instron 8801tensile testing machine was used to conduct the tests. An extension

rate of 5 mm/min and a gauge length of 50 mm were used.

88 Mechanical and Aerospace Engineering

Results and Discussion

Macro appearance

The surface and the root appearances of a typical friction stir processed sheet is presented in Fig 3

(a) and (b).

Fig. 3(a): Surface appearance of friction stir processed the aluminium alloy sheet produced at 2500

rpm and 50 mm/min

Fig. 3(b): Root appearance of friction stir processed the aluminium alloy sheetproduced at 2500 rpm

and 50 mm/min

The surface and root appearances of a typical friction stir weld of aluminium and copper is

presented in Figure 4(a) and (b).

Fig. 4(a): Surface appearance of friction stir weld of aluminium and copper sheet produced at 950 rpm

and 150 mm/min

Fig. 4(b): Root appearance of friction stir weld of aluminium and copper sheetproduced at 950 rpm

and 150 mm/min

Visual inspection of the weld top surfaces indicates a good top surface appearance without defect

and the deformation at the root indicate effective plunging of the tool during the welding process.

Tensile Test

The tensile test results of the parent material and a sample processed at 2500 rpm and 50 mm/min are

presented in Table 1. The average Ultimate Tensile Strength (UTS) and the Standard Deviation (s) of

the three samples tested are also presented.

Table 1: Tensile test results of the parent material and the processed sample

Ultimate Tensile Strength

(MPa)

Mean UTS

(MPa)

Standard

deviations (MPa)

T1 T2 T3

Parent

material 80.2 81.6 85.3 82.4 2.6

FSP 56.4 61.1 64.4 60.6 4.0

Applied Mechanics and Materials Vol. 232 89

The data label T1, T2 and T3 represent the first, second and the third tensile sample taken from the

parent plate and the FSP sheet. Based on the Standard Deviation, s, there was minor variation in the

data, hence the welds were cpnsistent. The tensile curves of the friction stir processed aluminium

alloy sheet are presented in Fig.5.

Fig. 5: Stress/Strain curves of FSP of the aluminium alloy sheet produced at 2500 rpm and 50

mm/min

It was observed that the tensile samples exhibited a ductile behaviour which is an indication of

plastic deformation that has occured during the friction stir processing.

Conclusion

A vertical milling machine was successfully reconfigured and utilized to produce friction stir

processing of aluminium and friction stir welds of aluminium and copper. FSW tools, backing plate

and the clamping system were machined and optimized in this research work. Further research work

is ongoing to incorporate temperature measurements and measurement of the forces acting during the

process.

Acknowledgement

The authors will like to thank Tool quip, Johannesburg, South Africa for the opportunity to use their

milling machine for this research work to produce the samples and the University of Johannesburg

Research Committee for the grant to conduct this research.

Appendix

90 Mechanical and Aerospace Engineering

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