Assy-for-gutowski 1© Daniel E Whitney9/6/2006Mechanical Assembly• Goals of this class:– Explain the basics of assembly as a manufacturing process– Show some examples– Explain Design for Assembly• Not included: (take 2.875)– Design processes for creating assemblies– Computer representations of assemblies– The “reach” of assembly into company operating processes and strategies– Relationship to modularity and product architectureAssy-for-gutowski 2© Daniel E Whitney9/6/2006Historical Aspects of Assembly• All assembly was manual until about 50 years ago• Little scientific knowledge existed about what happens during assembly operations: people “just do it”• All fabrication techniques have been mechanized for 100 to 5000 years and a lot is known about them• Assembly included fitting, adjustment, and selection until the 1830s• Technology and methods to create interchangeable parts evolved during 1765-1900• Mass production requires interchangeable parts• Interchangeable parts enable use of low skill assemblers• Supply chain implementation of manufacturing requires interchangeable partsAssy-for-gutowski 3© Daniel E Whitney9/6/2006Interchangeable Parts Enable Mass ConsumptionParts InterchangeAssembly Is quick andeasyLow skillPeople Can do itLots of AssembliesGet madeThey are cheapLots of People canAfford themThere is High demandLots of AssembliesGet soldThey are cheapEveryoneMakesmoneyIncludingThe Assemblers Investmentin Tools andKnowledgeInvestmentin equipmentAnd designAssy-for-gutowski 4© Daniel E Whitney9/6/2006Technical Aspects• Assembly creates product functions or sub-functions• Results of assembly can be tested– Results of fabrication can be inspected but not tested• Assembly requires coordination of many parts, tools, fixtures, packages, people, companies• Assembly step times are short compared to manufacturing process step times– Non-assembly actions take proportionately much more time– Time is needed to move the assembly from one station to the nextor to change tools– People and space are needed for incoming parts and outgoing boxesAssy-for-gutowski 5© Daniel E Whitney9/6/2006“Chain of Delivery” of QualityHood(Ford-Chicago)Inner Fenders(Budd-Philadelphia)Body Frame(Ford LAP)Radiator Support(DECO)Assembly Fixture for Fender:Fixture Vendor ACowl Top(Hawthorne)ContactChainAssembly Tooling (TESCO)Fender(Part:Budd-ShelbyvilleChecking fixture: M&M)Fender Skin(Budd-Shelbyville)Reinforcements(Wise, Metalform)CustomerFeature:Hood Fit toFenderFixture Vendor C)Check Fixture Vendor D)Parts Vendor BFixture Vendor FPart Vendor AClosure Panel Check Fixture: Fixture Vendor GAssembly Fixture for Hood: Fixture Vendor AN. Soman, M. ChangOrganizationalBoundaryPart Vendor CStructural Check Fixture:Fixture Vendor ED-pillar Assembly Station:Fixture Vendor BPART COUNT: 9PART SOURCES: 7TOOL COUNT: 5TOOL SOURCES: 4CHECK FIXTURE COUNT: 2CHECK FIXTURE SOURCES: 2DISPERSAL INDEX: 81%Assy-for-gutowski 6© Daniel E Whitney9/6/2006More Technical Aspects of Assembly• Three methods are used– Manual (always involved for large items; almost always involved for small items)– Specialized equipment (used only for small items made in high volumes - units/year in the millions)– Robots (used for small and medium sized items)• Low volume ~ big items: planes, ships• High volume ~ small items: cigarettes, small toys• Takt time for 777 airplane: 3 days• Takt time for Ford or GM car: 59 seconds• Takt time for a cigarette: 10 msAssy-for-gutowski 7© Daniel E Whitney9/6/2006Assy-for-gutowski 8© Daniel E Whitney9/6/2006Assy-for-gutowski 9© Daniel E Whitney9/6/2006Typical Cam-operated Assembly MachineMultiple identical base modules bolted together as neededCams cut by NC to do the necessary operationsSynchronous parts transportSynchronous parts transportAssy-for-gutowski 10© Daniel E Whitney9/6/2006Typical Dial MachineAssy-for-gutowski 11© Daniel E Whitney9/6/2006Machine Makes Washer TubsAssy-for-gutowski 12© Daniel E Whitney9/6/2006Typical Small Parts Assembly MachineAssy-for-gutowski 13© Daniel E Whitney9/6/2006Economic Aspects• Assembly employs more people than any other phase of manufacturing• Short assembly takt times mean that cost of assembly is a small fraction of manufacturing cost• Each technical kind of assembly has its own economic featuresAssy-for-gutowski 14© Daniel E Whitney9/6/2006Unit Cost Example - 2Unit Assembly Cost by Three Methods00.20.40.60.811.21.41.61.820 100000 200000 300000 400000 500000 600000Annual VolumeUnit CostMANUAL $/UNITFIXED $/UNITFLEX $/UNITfAC=0.38T=2sLH=$15/hrS$=50000$/tool = $10000N = 10 parts/unitw = 0.25 workers/staAssy-for-gutowski 15© Daniel E Whitney9/6/2006Operational Organization of Assembly• One person or station does all assembly operations• Subassemblies are made and flow into a final assembly process• Assembly is done in a small area by a team where each member does many operations• Assembly is done on a long line where each person does a small amount• As production rates and volumes rise, the line becomes the only efficient wayAssy-for-gutowski 16© Daniel E Whitney9/6/2006Operational Aspects - Line Balancing• Different operations take different lengths of time• When only one or a few ops are done at each station, large differences in station time can result• Slow stations make fast stations wait• Sometimes a different sequence will have better balance• Sometimes, extra stations in parallel are provided• Queues can build up behind slow stations• Fast stations can become starved• “A cycle lost on the bottleneck station is a cycle lost forever”Assy-for-gutowski 17© Daniel E Whitney9/6/2006Assembly sequence options• Typical products have hundreds or thousands of feasible assembly sequences• Different sequences enable options for– Line balancing– In-line repair– Equipment feasibility– Human performance and fatigue– Product qualityAssy-for-gutowski 18© Daniel E Whitney9/6/2006Two Alternator SequencesREAR HOUSINGSHAFT/ROTORBEARINGFRONT HOUSINGBEARING SPACERFANFAN SPACERPULLEYLOCKWASHERNUTMAIN ASSEMBLYFIXTUREASSEMBLYSEQUENCE #1BEARINGRETAINERSUBASSEMBLYFIXTUREMAIN ASSEMBLYFIXTURE #1MAIN ASSEMBLYFIXTURE #2ASSEMBLY SEQUENCE #2Assy-for-gutowski 19© Daniel E Whitney9/6/2006Two More Alternator SequencesMAIN ASSEMBLYFIXTURESUBASSEMBLYFIXTUREASSEMBLYSEQUENCE #3IntendedActualASSEMBLY SEQUENCE #4MAIN ASSEMBLYFIXTUREAssy-for-gutowski 20© Daniel E
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