This paper discussed the relationship between design for modularity and maintenance in order to extend product

life. Modularization can be described as an engineering approach to simplify component or product configuration as functional independence it creates

Abdullah, Ahmad Baharuddin

Mohd Ripin, Zaidi

Yusoff, M. S.

English

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Integration of design for modularity and design for assembly to enhanceproduct maintainabilityA. B. Abdullah*, M. S. Yusoff and Z. M. RipinSchool Of Mechanical Engineering, Universiti Sains Malaysia Engineering Campus14300 Nibong Tebal, Pulau Pinang, Malaysiae-mail: mebaha@eng.usm.my*ABSTRACT()This paper discussed the relationship between design for modularity and maintenance in order to extend productlife. Modularization can be described as an engineering approach to simplify component or productconfiguration as functional independence it creates. This loose interaction characteristic makes the maintenanceprocess easier. In this preliminary study, experiment is conducted to measure the maintainability in term ofmaintenance time. A case study of drum brake is carried out to clarify this work. At this stage, a survey and timestudy have been conducted and the result is presented.Keywords: Maintainability, modularity, assembly digraph, assembly type, accessibilityCharacteristic Design For Design ForAssembly Modularity(DFA) (DFMo)1- Standardize to Standardize andStandardize reduce part use common partsPart variety. and materials.2- Reduce Simplify the ModularizePart design and multiple parts intoreduce the singlenumber of subassemblies.part.3- Insertion Insert new part Design for ease ofPart into an assembly.assembly fromabove.4- Analyze each Design for partsOrientation part for ease of orientation andhandling. handling.5- Assembly Provide Building in self-alignment fastening features.features.Product design and assembly type will affect themaintainability efficiency; this is why companies arestruggling to achieved not only the best design butalso provide a maintenance-friendly features thatcould increase their product performance. Proper andsimpler maintenances can extend product life-cycle.There are many approach have been taken such asDesign for Maintainability, Life-Cycle Cost (LeC),Design for Serviceability and many more. Inmaintenance time to repair (TTR) is very crucial and itdepends mainly on the product/system configurations.By simplifying the product configuration, repair andmaintenance can be accomplish in shorter timeModularity is believed capable to makes maintenancesimpler due to functional independence created in theproduct configuration [1].The paper is organized as the following steps.It begins with introduction and then the result of thecustomer survey result is tabulated. Furthermore themethodology used is presented. A time study is alsoconducted. Result is then discussed and the paper ends 3. RELATED WORKSwith conclusion.1. INTRODUCTION2. DESIGN FOR MODULARITY AND DESIGNFOR ASSEMBLEDesign for Assembly have similarcharacteristic in nature to Design for Modularity,where they try to achieve the highest level ofsimplification and standardization in product design.There several similarity features that DFA and DFMohave as summarized in Table 1.Table I Similarity between DFA and DFMoIn maintainability analysis, disassembly andreassembly is the most critical factor [3]. Balanchardet al. [4] and Cunningham and Cox [5] include timetaken in disassembly, assembly, localization andisolation of least replacement of components. Thereare several quantitative measure used in determiningmaintenance efficiency. Maintainability can bemeasured based on time consume in completing thetask or mean time to repair (MTTR) and maintenanceactivity time as claimed by Utez [2). Ehud et al. [6)measure disassembly using difficulty rating, whereaccessibility, position, force, additional time andspecial problems is interpreted based on difficulty of·263 -~ Proceedings ofthe 1st IntematioTUlI Conference & 7th AUN/SEED-Net.1.'11" Fieldwise Seminar on Manufacturing and Material Processing()disassembly task. Cost of assembly/disassembly iscritical only in selection of appropriate tools [7].Meanwhile Tsai et al. [8] introduce modularityoperations and considering reliability and maintenancecost as a measure. They also list five problems thatshould be considered in maintainability analysis,which are disassembly sequence, selection of tools,time required for disassembly and human factor issuessuch as accessibility and visibility. Clark and Parsch[9] and Parsch and Ruff [10] taken diagnosabilityaspect as main consideration in determiningmaintainability, while Wani and Gandhi [11] considertribology aspect. Maintainability also should consideroptimal resources such as personnel and supportequipment [12]. A maintainability software namedRelex, use the same approach where measured time isthe major output.4. METHODOLOGYThis study involves development of MaintainabilityIndex Template (MIT) based on several establishedformulas. By implementing the characteristics andguideline given by the developed approach namedDesign for Assembly (DFA) and Design forModularity (DFMo), the formulas are developed.5. CASE STUDYFor this work, a case study of rear motorcyclebrake system is used. For that purpose, severalexperiments have been conducted to determine meantime by involving operator with different backgroundfrom beginner with no experience to expert whomdealing with the job daily. From the observations,indicates that time needed is between 1 to 5 minutes asshown in Table 3. The objective of the experiment isto establish a standard time for maintaining thetargeted parts for this case, brake shoe. Figure 4 showthe model that been used for the experiment.Table 3 Experimental ResultOperator Level Avera~e Time, tavaBeginner 5 min 6 sec.Intermediate 2 min 22 sec.Expert 1 min 15 sec.- 264-Figure 4 Rear brake assemblyEach steps involve in disassembly process arerecorded. Figure 5 shows the disassembly steps. Afterthat, the disassembly digraph is constructed todemonstrate the disassembly process. Figure 8 depictsthe disassembly digraph. The disassembly processstarts by unscrewing the nut from the shaft (part no.2). The numbers represent the components as listed inFigure 5 and the arrows demonstrate the sequence ofdisassembly process till the targeted parts is achieved.Time is taken after the brake shoes are disassembled.As a result from the simulation, the average time isabout 2 to 5 minutes for disassembling the parts tillaccessing the brake shoe as simplified in Table 2.Figure 5 Brake shoes disassembly process5.1 Maintainability Index CalculationThe maintainability index is calculated basedon the assembly characteristics and the componentsfeatures. For example the harder component to beaccess whether the component is located inside othercomponents or it is blocked by other components, thelower maintainability index. Here the most importantfactor are the assembly type and location of thecomponents. So that formula have been derived asshown in Figure 6 [13].A. B. Abdullah et al.,Integration ofdesign for nwdularity and designfor assembly to enhance product maintainability, 263-267Figure 6 Formulas used in maintainability index calculationWhere;Table 4()MT = Maintenance Frequency (Rare = I, Seldom = 2,Frequent = 3, Most Frequent = 4)CP = Critical Path, ( i = 1, 2 n)AS. = Assembly Score for assembly n=iAN = Assembly NumberCn = Total Number of Components in the ProductCcp = Total Number of Components in the PathIn determining the component maintenance frequency.as survey have been conducted and as a result, most ofthe customer claimed that the most frequent (every 4-6months) is the brake shoe which is about 71.5% asshown in Table 4. From here. quantitative weightageis given as 1 to 4.Component # PercentageRespondentBrake Shoe 25 71.5%Brake 1 2.8%LininqSprinq 5 14.3%Paddle 2 5.7%Brake Rod 2 5.7%After that, based on the formula, the maintainabilityindex of the selected case study is determined. Table 5shows the result of the rear drum brake assemblymaintainability index.Table 5 Result from the calculationRear Brake Drum Assembly# Component Frequency, Mr Critical Path, Cp As. Score. Ar Maint. Index1 Axle Rear Wheel 1 1 14 0.072 Rear Brake Panel Side Collar 1 2 18 0.063 Rear Brake Panel Component 1 3 22 0.054 Shoe Brake Component 4 4 26 0.155 Spring Brake Shoe 3 5 30 0.106 Rear Brake Cam 1 6 34 0.037 Dust Seal Brake Cam 2 5 30 0.078 Rear Brake Indicator 1 3 22 0.059 Bolt Flange 6x28 2 3 22 0.0910 Nut Hexal!:on 6mm 2 1 14 0.1413 Bolt Flange 6x32 2 5 42 0.0514 Nut Flange 6mm 2 1 14 0.1415 Rear Brake Arms 1 2 18 0.0616 Nut Hexagon 8mm 2 1 14 0.1418 Rubber Stopper Arm Wheel 2 3 18 0.1119 Bolt Brake Stopper 2 5 36 0.0620 Rear Brake Rod 1 4 26 0.0421 Nut Brake Road Adjustable 2 1 14 0.1422 Joint Brake Arms 1 2 18 0.0623 Spring Brake Rod 2 3 22 0.09Total = 1.68- 265-~ Proceedings ofthe 1st lnterr~tionalConference & 7th AUNISEED-Net...., Fieldwise Seminar on Manufacturing and Material Processing(J6. MAINTAINABILITY INDEX TEMPLATETo assist in the product maintainabilitycalculation, a template using Microsoft Excel havebeen developed. The user could display the result aftercompleting the steps involve. The steps are;Step 1: Identify number of componentsStep 2: Determine the type/number of assembly foreach of the componentsStep 3: Established the critical pathStep 4: Construct the assembly/disassembly digraphStep 5: Calculate the maintainability indexSchematic DiagramFigure 7 A template used in automating maintainability index calculationREFERENCES7. CONCLUSIONThe study indicated that maintainability depends onthe component accessibility, location of the targetedcomponents and the skill of the operator. The lesserworkload requires in accessing the component, thebetter maintainability. Moreover the higher level ofskill of the operator, the faster maintenance can bedone. The development of the Maintainability IndexTemplate could help in determining maintenanceefficiency of the product.AcknowledgementThe authors would like to thank the School ofMechanical Engineering and Universiti SainsMalaysia for their cooperation and fund provided(NC 6035101).- 266-[1] Gershenson, J.K. and Prasad, G.J (1997),Product Modularity and its effect on Service andMaintenance, Proc. of the 1997 Maintenance andReliability Conference, Knoxville, Tennessee.[2] Utez, H., (1983), Maintainability of ProductionSystem, Maintenance Management International, pp.455-68.[3] Cunningham, C.E. and Cox, W., (1972), AppliedMaintainability Engineering, Wiley and Sons, NewYork.[4] Vujesovic, R., Raskar, R., Yeturkuri, N.V.,Jothishankar, M.e. and Juang, S-H., (1995),Simulation, Animation and Analysis of DesignDisassembly for Maintainability Analysis, Int. J.Production Research, vol. 33, no. I, pp. 2999-3022.[5] Balanchard. B. S., Verma, D. and Peterson, E. L,(1995), Maintainability, John Wiley and Sons, NewYork.[6] Ehud,K., Brent, B. and Antony, P., (1996),Methodology to Evaluate Ease of Disassembly for- - --- -- - -- -- ---- ------------- -- ---A. B. Abdullah et al.,lntegration ofdesign for modularity and designfor assembly to enhance product maintainability, 263-267()Product Recycling, lIE Transactions, vol. 28, no. 28,pp. 837-845.[7] Vujosevic, R. (1995), Maintainability Analysisin Concurrent Engineering of Mechanical System,CERA, vol. 3, no. 1, pp. 61-73.[8] Tsai, Y. T., Wang, K.S. and Lo, S.P. (2003), AStudy of Modularity Operation of Systems Based onMaintenance Consideration. J. Eng. Design, vol. 14,no. I, pp. 41-56.[9] Clark, G.E. and Paasch, R. K., (1996),Diagnostic Modeling and Diagnosability Evaluationof Mechanical Systems, J. Mech. Design, vol. 118, no.1, pp. 425-431.[10] Paasch, R.K. and Ruff, D.N. (1997), Evaluationof Failure Diagnosis in Conceptual Design ofMechanical System, J. Mech. Design, vol. 119, no. 1,pp.57-67.- 267-[11] Wani, M.F. and Gandhi, O. P., (2002),Maintainability Design and Evaluation of MechanicalSystems Based on Tribology, Reliability Eng. andSystem Safety, vol. 77, pp. 181-188.[12] Wani, M.F. and Gandhi, O. P., (1999),Development of Maintainability Index for MechanicalSystems, Reliability Eng. and System Safety, vol. 65,pp. 259-270.[13] Abdullah, A. B. and Ripin, Z. M., (2005),Kaedah Pengukuran Indek Keboleh-Se1enggaraanProduk Atau Sistem Berdasarkan KriteriaPemasangan, Jumal Teknologi (A), Bit 42, pp. 91-106.[14] Crow, K., Design for Manufacturabilitydownload from http://www.npd-solutions.comldfm.html[15]http://www.relexsoftware.comlproducts

Integration Of Design For Modularity And Design For Assembly To Enhance Product Maintainability.

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Integration Of Design For Modularity And Design For Assembly To Enhance Product Maintainability.

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