11Assembly and Joining2ManufactureUnit ManufacturingProcessesUnit ManufacturingProcessesAssembly and JoiningAssembly and JoiningMarketResearchFactory, Systems & Enterprise•Welding•Bolting•Bonding•Soldering•Machining•Injection molding•Rapid prototyping•Stamping•Chemical vapor depositionConceptualDesignDesign forManufacture3Impact of Design on Product CostThe majority of cost commitment is made early in the product design cycle.Cost inPercentConceptionValidationDevelopmentProductionOperationTimeSource:British Aerospace100010203040506070809085%95%5%20%CommittedSpent4Cost of Design ChangesCONCEPTDESIGNX10XTOOLINGTESTING100X1000XRELEASE10,000X25“The best design is thesimplest one that works”Albert Einstein6Assembly and Joining• Assembly as a mfg process– Process components– Cost, Quality, Rate and Flexibility• Specific joining processes– Mechanical– Adhesives– Solder and brazing– Cold welding– Fusion welding7Assembly statistics8Justifying the need/type of assembly•For assembly– Can’t be made in one piece– Functional (bushings, bearings)– Manufacturability– Repair and maintenance– Transport: Does it fit in a plane?•Against assembly– Defects that occur at interfaces– Loss of stiffness– Time & effort– Labor costs–Size39Rough assembly process diagramMaterial / partsFeeding OrientationStoragePresent&fixtureManipulationTransportJoiningCuringtimePosttreatmentJoiningprocessPresent&fixtureInspectionMaterial / parts10Manual vs Automatic AssemblyManual assembly•Dexterity• Time (small run, urgent)• ComplexityAutomatic assembly• Precision• Load•TimeWhat is important• Minimize parts• Ergonomics•Cost• Training• Reliability11PART TRANSPORT, ORIENATION AND FEEDING12Part handling and feeding Moving parts between processing stations Control amount delivered Control spacing and frequency of delivery Robust with respect to tangling and jamming413Part transport: Overheadhttp://www.tegopi.pt/pt/novidades/images/25-10-2000.jpghttp://accosystems.com/autoclient%20(2).jpg14Part transport: Conveyorhttp://www.ssiconveyors.com/pics/ http://www.ssiconveyors.com/pics/ 15Part transport: Transfer line16AGVPallet load / unload mechanismWorkpiecePalletSafeguards against collision517Part feeding and orientation18Part feeding and orientation19Part feeding and orientation20Part feeding and orientation621Guidelines to Good Design-for-Assembly Minimize the number of parts Design assembly process in a layered fashion Consider ease of part handling Utilize optimum attachment methods Consider ease of alignment and insertion Avoid design features that require adjustments22DFA - Example0.10.20.30.40.50.60.70.80.91.0024842Annual production volumes :robotic - 200,000automatic - 2,400,000Assembly cost ($)Number of partsMinimize the number of parts23Minimize the number of partsDFA - Example24Design assembly process in a layered fashionDFA - Example725Consider ease of part handlingDFA - Example26Consider ease of part handlingDFA - Example27Utilize optimum attachment methodsDFA - Example28Utilize optimum attachment methods102030 405010020002468box-end wrenchopen-end wrenchSocket ratchet wrenchNut driverClearance, mmRun down time / rev, sClearanceClearanceHex-nut driverSocket ratchet wrenchBox-end wrenchOpen-end wrenchDFA - Example829Utilize optimum attachment methodsDFA - Example30Utilize optimum attachment methodsDFA - Example31Consider ease of alignment and insertion Design parts to maintain locationDFA - Example32Consider ease of alignment and insertion Mating parts should be easy to align and insertDFA - Example933Consider ease of alignment and insertionDFA - Example34Avoid design features that require adjustmentsDFA - Example35Avoid restricted visionDFA - Example36Avoid obstructed accessDFA - Example1037Joining Assembly cost often account for more than 50% Joining processes High scrap cost Failure spot38Joining processes/types39Selection Criteria Geometry Material type Value of end product Size of product run Availability of joining method40MECHANICAL JOINING1141Mechanical Fastening Any shape and material Semi-permanent Least expensive for low volume (standardized) Problems: strength, seal, extra part, assembly, loosen42Fasteners• Bolts/screws– Good for disassembly and reassembly– Cross threading can be a problem• Rivets– Used when disassembly is not required• Dowel pins• Cotter pins• Snap fits43Elastic AveragingNon-DeterministicPinned JointsNo Unique PositionExact constraintKinematic ConstraintCommon alignment mechanismsContaminants: SensitiveLoad capacity: HighWear in: LongExact constraint: NoCost: $$$Complexity: SimpleCommon: YesRepeatability ~ 5 micronafter wear inContaminants: InsensitiveLoad capacity: Low - HighWear in: NoExact constraint: NoCost: $ <-> $$$Complexity: SimpleCommon: YesRepeatability ~ 25 micronat bestContaminants: InsensitiveLoad capacity: Low - HighWear in: ShortExact constraint: YesCost: $$Complexity: ModerateCommon: NoRepeatability ~ ¼ micronis commonRelative cost:$ = low cost$$ = moderate cost$$$ = expensive44Embossing and hemming• Embossed protrusions– Plastic deformation / interference– Appliances– Automotive–Furniture• Hemming– Bend edge of one component over another– Automobile doors1245Press fits()()()⎥⎦⎤⎢⎣⎡−⋅⋅−⋅−⋅⋅=ioiorrRrRRrREp22222222δroRriinsertinsertxRpF⋅⋅⋅⋅⋅=πµ2TRthermal∆⋅⋅=αδδ = radial interference α = Coefficient of thermal expansionE = Young’s modulus ∆T = Temperature changep = interface pressureInsertion force for press fit0500100015002000250030000.00 0.05 0.10 0.15 0.20 0.25Press Depth, inPress Force, lbf46ADHESIVEJOINING47Example – Adhesive Bonding48Adhesive joining• Advantages– Different materials, Easily automated, Damp /seal• Limitations– Time, Preparation/curing, Loading• Important properties/characteristics of adhesives– Strength, Chemically inert, Compatibility1349Adhesive Bonding Quick, non-invasive, inexpensive Low stress Variety of materials Seal Low part count Temperature-limited Long set time Surface preparation Reliability/disassembly Best for components with high surface to volume ratio50Stefan Equationuyrah/2h/2F⎥⎥⎦⎤⎢⎢⎣⎡−=2241143ifhhaFtµπ51What does Stephan equation