design and development of hydraulic fixture for · pdf filedesign and development of hydraulic...

204

Int. J. Mech. Eng. & Rob. Res. 2014 Shailesh S Pachbhai and Laukik P Raut, 2014

ISSN 2278 – 0149 www.ijmerr.com

Vol. 3, No. 3, July, 2014

© 2014 IJMERR. All Rights Reserved

Research Paper

DESIGN AND DEVELOPMENT OF HYDRAULIC FIXTURE

FOR MACHINING HYDRAULIC LIFT HOUSING

Shailesh S Pachbhai1* and Laukik P Raut2

*Corresponding Author: Shailesh S Pachbhai � [email protected]

In machining fixtures, minimizing workpiece deformation due to clamping and cutting forces isessential to maintain the machining accuracy. The recent trends in industry are towards adoptingthe hydraulic techniques, because it save time generates accuracy and it is having some flexibility.Hydraulic Fixture is major application in the field of designing, where in several software’s areavailable for the purpose of design. Hydraulic lift housing is engine part of an agricultural tractorwhich plays an important role in application of lifting trolley of tractor and machining of hydrauliclift housing is a important task. Loading and unloading of workpiece in manual clamping is timeconsuming process, so reducing machining time, set up time etc is a main aim of process. Thejob having cylindrical shape, this is a challenging task for design engineer, hence hydraulicfixture design is incorporated in manufacturing industry. Except toggle clamp, no other option isavailable to hold cylindrical object, hence special type of fixture is design for this case, whichcan be used for machining of hydraulic lift housing, Fixture reduces operation time, increasesproductivity, and best quality of operation is possible. The project deals with the designing ofdifferent parts of fixture assembly, 3D modeling by using Pro-E WILDFIRE 5.0, finite elementanalysis of hydraulic lift housing by using ANSYS software.

Keywords: Fixture, Accuracy, Clamping, Toggle clamp

INTRODUCTION

Background and Context

A fixture is a device used to locate, clampand support a workpiece during machining,assembly or inspection. The most importantcriteria’s for fixturing are workpiece stability,position accuracy and workpiece defor-mation. A good fixture design is one that

1 M.Tech. (CAD/CAM), G. H. Raisoni College of Engineering, Nagpur.2 Assistant Professor, G. H. Raisoni College of Engineering, Nagpur.

minimizes workpiece geometric error.Workpiece location principles are defined interms of 3-2-1 fixturing which is widely usedworkpiece location method for prismaticparts. Force analysis is concerned withchecking whether the forces applied by thefixture and clamping are sufficient to maintainstatic equilibrium (E Caillaudli D et al., 1995).

205


Fixtures must correctly locate a work piecein a given orientation with respect to a cuttingtool or measuring device, or with respect toanother component, as for instance inassembly or welding. Such location must beinvariant in the sense that the devices mustclamp and secure the workpiece in thatlocation for the particular processingoperation. There are many standard workholding devices such as jaw chucks, machinevises, drill chucks, collets, etc. which arewidely used in workshops and are usuallykept in stock for general applications. Fixturesare normally designed for a definite operationto process a specific workpiece and aredesigned and manufactured individually(Kailing LI, et al., 2006).

Importance of Fixtures in

Manufacturing

The use of fixtures has two fold benefits. Iteliminates individual marking, positioning andfrequent checking before machiningoperation starts, thereby resulting in conside-rable saving in set-up time. In addition, theusage of work holding devices saves operatorlabor through simplifying locating andclamping tasks and makes possible thereplacement of skilled workforce with semi-skilled labor, hence effecting substantialsaving in labor cost which also translates intoenhanced production rate. Furthermore, theuse of well-structured fixtures with higherlocating and clamping rigidity would allow forincrease in cutting speeds and feeds, therebyreducing tm, hence improving productionrate. Besides improving the productivity interms of the rate of production, there are alsoother benefits accrued through the use offixtures, they are:

Increases machining accuracy because ofprecise location with fixtures,

Decreases expenditure on quality controlof machined parts as fixtures facilitate uniformquality in manufacturing, Widens thetechnology capacity of machine tools andincreases the versatility of machiningoperations to be performed, Either fully orpartly automates the machine tool (Yun-HuiLiu, 2004).

What is Hydraulic Fixture?

A clamping system that uses high-pressureliquids to power clamps and hold a work piecein place. Hydraulically clamped fixtures havemany advantages over manually clampedfixtures. In most cases, these benefits reducecosts for manufacturers allowing them tojustify the initial investment for a hydraulicclamping system. Hydraulic clamping ena-bles manufacturers to put more intelligenceinto the fixture eliminating human error andproducing a more stable, predictable proce-sses no matter who the operator is or whatproduction shift your machine runs.

Advantages of Hydraulic Fixture

1) More Productivity: More parts will fitwithin machine envelope due to the highclamp forces generated with smallhydraulic components.

2) Consistent Clamping Forces: Everycycle, parts are clamped with the sameclamping force, eliminating variables andimproving process stability.

3) Repeatable Clamp Location: Everycycle, parts are clamped in the samelocation eliminating the variability in partdeflection from clamping forces.

206


4) Eliminates Human Error: Assurancethat every clamp will be actuated withevery cycle, eliminating human error andmissed steps.

5) Faster: Load and unload times and moreproductivity when cycle times areoperator dependant.

6) Ergonomic Efficiency: Allows operatorsto be consistently more productive withless effort.

7) Improved Part Stability: Hydraulic worksupports can be used to support the partand/or dampen machining forces withoutdistorting the work piece. Manual worksupports are easily ignored, distort thepart and cause miss-loads.

8) Flexibility: Sophisticated clampingsequences can be developed with “live”hydraulic systems. Clamping can besequenced automatically during themachining cycle to provide clearance forcutting tools, to remove forces for finishcuts of close tolerance features, retainparts for robotic loading, reduce cycletimes and improve productivity.

Problem Identification

With the advent of VMC machiningtechnology and the capability of multi axismachines to perform several operations andreduce the number of set-ups, the fixturedesign task has been somewhat simplifiedin terms of the number of fixtures which wouldneed to be designed. However, there is aneed to address the faster response andshorter lead-time required in designing andconstructing new fixtures (Jose F Hurtadoand Shreyes N Melkote, 2001).

Problems Occurring in Existing Fixture are

• Fixture setup is done manually due tothis cycle time is more.

• Overtightning or loosening of screwleads to machining defects.

• Product quality is not obtained as perspecification.

• Sometimes rejection rate is observed.

• Manual clamping leads to accidents.

• More hectic to operator to load andunload.

As solution to this problem greatly helpsthe industries to increase their productivity,this problem is needed to be solved to meetthe current trends of designing andmanufacturing. Solution to this problemrequires hydraulic fixture in modellingsoftware’s which are now a day’s back boneof all design and manufacturing industries(Dan Ding Guoliang et al., 2002).

REVIEW OF LITERATURE

The main purpose of literature reviews thatdiscussion on important point regardingmatter of fixture which is represented bydifferent researcher:

Principles of Locations

Guohua Qin et al., (2006), focuses on thefixture clamping sequence. It consists of twoparts:

a. For the first time he evaluated varyingcontact forces and workpiece positionerrors in each clamping step by solving anonlinear mathematical programmingproblem. This is done by minimizing thetotal complementary energy of theworkpiece-fixture system. The prediction

207


proves to be rigorous and reasonable aftercomparing with experimental data andreferenced results.

b. The optimal clamping sequence isidentified based on the deflections of theworkpiece and minimum position error.Finally, to predict the contact forces andto optimize the clamping sequence threeexamples are discussed.

First mathematical modeling for clampingsequence is done then he determined thecontact forces in clamping sequence asshown in Figure 1. After that he optimized ofclamping sequence for higher stiffnessworkpiece and low stiffness workpiece. Hefound that with the use of optimal clampingsequence, good agreements are achievedbetween predicted results and experimentaldata and the workpiece machining quality canbe improved.

Design Consideration in Fixtures

The importance of fixture design automationis emphasized by Djordje Vukelic (MichaelStampfer, 2008). General structure of the

automated design system shown in Figure 2with a highlight on the fixture design systemsand their main characteristics.

Figure 1: Scheme of 3-2-1 Fixture Setup(Guohua Qin, Weihong, Zhang Min Wan, 2006)

It also shows a structure and a part ofoutput results of the automated modularfixture design system. The expert systemshave been mostly used for the generation ofpartial fixture solutions, i.e. for the selectionof locating and clamping elements.

Shrikant et al., (2013), discussed variousdesign and analysis methods in the contextof to improve the life of fixture; different fixturegeometries are compared experimentally andare selected. The proposed eccentric shaftfixture will fulfilled researcher Productiontarget and enhanced the efficiency, fixturereduces operation time and increasesproductivity, high quality of operation.

Clamping Approach

J Cecil proposed an innovative clampingdesign approach is described in the contextof fixture design activities. The clampingdesign approach involves identification ofclamping surfaces and clamp points on agiven workpiece. This approach can beapplied in conjunction with a locator designapproach to hold and support the workpiece

Figure 2: Layout of Working(Michael Stampfer, 2008)

208


during machining and to position theworkpiece correctly with respect to the cuttingtool. Detailed steps are given for automatedclamp design. Geometric reasoning techni-ques are used to determine feasible clampfaces and positions. The required inputsinclude CAD model specifications, featuresidentified on the finished workpiece, locatorpoints and elements.

Figure 3: Fixture Design for theSample Part (J Cecil, 2008)

Hydraulic System

This paper proposes a polynomial fit basedsimulation method to build nonlinear modelin hydraulic actuator control system. Thismethod is used to simulate two kinds oftypical hydraulic actuator control system.Contrastively, a simulation with traditionallinear model is also executed. Through

comparison among the result of two kinds ofsimulation and the test data, it is proved thatthis polynomial fit based method is moreaccurate than the traditional method and itcan perform more effectively for fault detec-tion in hydraulic actuator control system.

Shop air is just used for boosting .In additionelectric booster and hydraulic pump are usedto air- operated booster system. Hydraulicpump is used for larger applications.Accumulator is installed between clamps andpower source which maintain the necessarypressure when power is disconnected.

DEVELOPMENT OF FIXTURE

FOR HYDRAULIC LIFT HOUSING

Fixtures accurately locate and secure a partduring machining operations such that thepart can be manufactured to design specifi-cations. To reduce design costs associatedwith fixturing, various clamping methods havebeen developed through the years to assistthe fixture designer (E Caillaudli D et al.,1995).

For making a fixture following steps involvedare

• Analytical design for fixture.

• 3-D modeling in PRO - ENGINEERWildfire 5.0

Figure 4: Configuration of Hydraulic ActuatorControl System (Wang Jinyong, 2012)

209


• Assembly

• Analysis by using ANSYS.

Existing Fixture

Figure 5 shows the existing CAD model offixture which is used for machining of hydra-ulic lift housing.

In this fixture clamping is done manuallyso there is extra time loss for loading andunloading operation. To avoid this problemthere is necessity to develop new design toimprove the productivity.

Type of Machine

Vertical machining centre is used to performoperation on hydraulic lift housing. Themachining is to done on the upper surface ofthe workpiece. VMC provides the featuresand performance needed making it the bestinvestment we’ve ever considered, andproviding more utility, flexibility, andproductivity. Basically operations such asdrilling, reaming and chamfering takes placeon workpiece. Drilling is a cutting process thatuses a drill bit to cut or enlarge a hole of

circular cross-section in solid materials. Indrilling operation, hole created from 18mmto 26 mm from upper surface of workpiece.Following are the machining parameters fordrilling:

• Spindle speed 500 rpmo Feed 0.15 mm/rev

• Radial depth 18 mm

• Projection length 90 mm

The process of using a multi-point tool tosmooth the interior surface of a hole is calledas reaming. Following are the machiningparameters for reaming:

• Reamer diameter 26 mm

• Number of flute 4

• Spindle speed 120 rpm

• Feed 0.25 mm/rev

• Radial depth 26 mm

• Projection length 90 mm

DESIGN OF PARTS OF FIXTURE

The design of fixture parts includesconsideration of material of fixture and afterthat analytical design of parts such as designof base plate, locating pins and clamp iscarried out.

Criteria for Material Selection of Fixture

Mechanical Properties

The material must possess a certain strengthand stiffness. Selected materials areexamined for strength and stiffness values,and then potential materials are furtherinspected for other desired properties.

Wear of Materials

Wear is a problem when the materials arecontacting each other in a product. So it must

Figure 5: CAD Model of CompleteFixture Assembly

210


be ensured that the selected materials havesufficient wear resistance.

Corrosion

The importance of material selection inengineering is clearly visible in corrosiveenvironments. Also it is an importantengineering design criterion for designs opento the environment for a longer period of time.Some materials are very likely to be corrodedin the service depending on the serviceenvironment. Metals like iron are heavilyprone to corrosion if it not prepared to resistcorrosion. Therefore it must be assured thatthe material is capable of being employedfor the particular design before selecting it.Painting or any other surface coating method,cathodic protection, etc. are possible waysto minimize the effect and increase theservice life.

Ability to Manufacture

The material is well capable of using for thedesign, it may be difficult to manufacture. Thisis particularly applicable in mechanicalengineering design. If this selection criteriais neglected the manufacture process mightbe very costly making it unprofitable as acommercial product. So before selecting thematerials this fact also must be considered.

Cost

Cost is a critical fact to consider whenselecting materials for a certain design formost products because they are facing asevere competition in the market. So you maysee that most of the metal or other valuablematerials are replaced by plastics in most ofthe designs which they are applicable suchas mechanical engineering designs. The costfactor can be neglected when performance

is given the top priority. When estimatingcosts, all the associated cost factors mustbe considered to get a more reasonablevalue. It may involve the transportation,processing, etc. costs.

Design of Base Plate

While designing base plate total length shouldbe considered.

Base plate length (l) = 300 mmBase plate width (b) = 300 mmBase plate height (h) = 30 mm

Design of Clamp

Clamping mostly depends on cutting forces

FHC X RHCClamping force = —————— = 200 N

RS

Figure 6: Clamp of Fixture

211


Where, FHC- holding force

Cylinder bore size = 25 mm

Piston area = 0.785 d²

= 506.4506 sq. mm

Cylinder force= 111.20 N

Therefore, the required cylinder output forceis 12 bar.

Calculations for Existing Fixture

Followings are the data available from thecompany

1) Time Required

Total number of shifts = 3

There are 3 Shift of 8 hours each.

Total working time in a shift is 7 hr 30 min i.e450 min (30 minutes utilized in lunch break).

Total number of finished part in each shift =32

Processing time = machining time + loading/unloading time + part travel time (from palletto fixture or vice versa)

Machining time = 11.36 min

Loading time = 1.20 min

Unloading time = 1 min

Part travel time = 10 sec

Therefore, Processing time = 14.06 min

2) Cost of Operation

Cost of finished product = Rs. 345/- part

Cost of finished product/shift = Rs. 11040/-

Cost of finished product /day = Rs. 33120/-

There are 26 days of working in one month

Therefore,

Annual production cost of finished product =Rs. 10333440/-

3) Machine Utilization

A measure (usually expressed as a percent-age) of how intensively a resources is beingused to produce a good or service (J Cecil,2008).

Capacity = 3*8*1*6

= 144 machine hours

Hours available - hours downMachine Utilization = —————————————— x 100

Hours available

= 91.66%

Calculations for New Proposed

Fixture

1) Time Required

Total processing time includes machiningtime, clamp actuation/de-actuation time andpart travel time.

According to standard specification of cylin-der, clamping will actuate in 5 sec.

Therefore,

Processing time = machining time + clampacting time + part travel time

v machining time = 11.36 min

clamp acting time = 0.10 min

part travel time = 0.10 min

Total number of finished parts per shift = 39

2) Cost of Operation

Cost of finished product per day = Rs.40365/-

Annual cost of finished part = Rs.1,25,93880/-

Annual increase in production cost of finishedpart = Rs.22,60,440/-

3) Machine Utilization Hours available - hours down

Machine Utilization = —————————————— x 100 Hours available

212


Machine hours = 144

Hours down = 9.5

Analysis of Fixture

Figure 7: Minimum and Maximum VonMisses Stress or (Equivalent Tensile Stress)

Figure 7 shows a stress distribution acrossthe fixture A force of 200N is applied on threepoints where clamping force acting on it. Afteranalysis it is observe that, von missesstresses is comparatively lower than standardvalues and hence, we can conclude thatdesign is safe.

RESULTS

Figure 8 shows the fixture with hydraulicattachments it includes a component suchas base plate, cylinder, hoses, rubber padetc.

Table 1: Comparative Analysis

Parameter

Finished part/shift

Production cost offinished part

Machine utilization

Processing time

Existing Fixture

32 parts

Rs.1,03,33440/-

91.66%

14.06 min

Proposed Fixture

39 parts

Rs.1,25,93880/-

93.40%

11.56 min

Figure 8: Hydraulic Fixture Assembly

Hydraulic clampings are actuated by cylin-ders, clamping fixtures is clamping nut attach-ed to cylinder ram. When pressurized fluidpulls ram and clamps against workpiece,toggle clamps operate through a linkagesystem of levers and pivots. The fixed-lengthlevers, connected by pivoting pins, apply theaction and clamping force. The toggle actionhas a lock point which fixes and stops linkage.Once in the lock position, the clamp does notunlock unless the linkage is moved/released.

CONCLUSION

• The proposed fixture will not onlyprovides the repeatability and highproductivity, but also offers a solution,which reduces workpiece distortion dueto clamping and machining forces.

• All the values of deformation and vonmisses stress calculated with ANSYSsoftware is comparatively lower thanstandard values and hence, we canconclude that design is safe.

• As per calculations, the proposedfixtures have a direct impact on productquality, productivity and cost.

213


• The person from industry will definatelysatisfied with the performance of fixturefor machining hydraulic lift housingbecause of more benefits compared toconventional process with accuracy andrepeatability on vertical machiningcenter (VMC).

REFERENCES

1. Dan Ding Guoliang et al., (2002), “FixtureLayout Design for Curved Work Pieces”,Proceedings of the 2002 IEEEInternational Conference on Robotics 8Automation Washington, DC.

2. E Caillaudli D et al., (1995), “ConcurrentEngineering: An Expert System forFixture Design”, IEEE.

3. en.wikipedia.org/wiki/Fixture_(tool

4. Guohua Qin, Weihong and Zhang MinWan (2006), “Analysis and OptimalDesign of Fixture Clamping Sequence”,ASME for Publication in the Journal ofManufacturing Science and Engineering.

5. h t tp : / /www.dmtworkhold ing.com/hydraulicworkholdingfixtures

6. J Cecil (2008), “A Clamping DesignApproach for Automated Fixture Design”,International Journal of AdvanceManufacturing Technology, Vol. 18, pp.784-789.

7. Jose F Hurtado and Shreyes N Melkote(2001), “Effect of Fixture Design Variableson Fixture-Work piece Conformability andStatic Stability”, 2001 IEEHASMEInternational Conference on AdvancedIntelligent Mechatronic Proceedings,COW Italy.

8. Kailing Li et al., (2006), “Development ofan Intelligent Jig and Fixture DesignSystem”, School of MechanicalEngineering, Shandong University73,Jingshi Road, Jinan, Shandong, P RChina, 250061b School of MechanicalEngineering, Weifang University.

9. Michael Stampfer (2008), “AutomatedSetup and Fixture Planning System forBox-shaped Parts”, International Journalof Advance Manufacturing Technology,Vol. 45, pp. 540-552.

10. Shailesh S Pachbhai and Laukik P Raut(2014), “A Review on Design of Fixtures”,International Journal of EngineeringResearch and General Science, Vol. 2,No. 2, ISSN, pp. 2091-2730.

11. Shrikant V Peshawar and Laukik P Raut(2013), “Design and Development ofFixture for Eccentric Shaft: A Review”,International Journal of EngineeringResearch and Applications (IJERA)ISSN: 2248-9622, Vol. 3, No. 1.

12. Shrikant V Peshatwar and Laukik P Raut(2014), “Computer-Aided Fixture Design:A Review”, International Journal ofAdvanced Engineering Research andTechnology, Vol. 2, No. 1, ISSN, pp. 2348-8190.

13. WANG Jinyong (2012), “The Applicationof a Polynomial Fit Based SimulationMethod in Hydraulic Actuator ControlSystem”, IEEE, 978-1-4673-0311-8/12.

14. Weifang Chen, et al., (2007), “A DualOptimization Model of Fixture Design forthe Thinwalled Work Piece”, IEEE.

214


15. Yan Zhuang and Ken Goldberg (1997),“Design Rules for Tolerance-Insensitiveand Multipurpose Fixture”, ICAR 91Monterey, CA.

16. Yiming (Kevin) Rong and Xingsen (Corry)Li (1997), “Locating Method AnalysisBased Rapid Fixture ConfigurationDesign”, Intelligent Design andManufacturing, ASME WAM, PED, Vol.64, No. 1, pp. 15-28, pp. 43-66.

17. Yun-Hui Liu (2004), “Optimal FixtureLayout Design for 3-D Work Pieces”,Proceedings of the 2004 IEEEInternational Conference on Robotics 8Automation New Orleans, LA.

18. Zhang Yuru and Peng Gaoliang (2005),“Development of an Integrated Systemfor Setup Planning and Fixture Design inCAPP”, International Conference onAdvanced Intelligent MechatronicsMonterey, California, USA, pp. 24-28.

design and development of hydraulic fixture for · pdf filedesign and development of hydraulic...

Documents