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MIT 2 810 - Mechanical Assembly Systems

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Mechanical Assembly SystemsComplicated products require more assembly…..PowerPoint PresentationTo solve this problem Ford developed the moving assembly lineSee GM front end assemblyRequirements;Time Estimation for AssemblyHandling IssuesB-D Manual handling chartInsertion IssuesSlide 11Slide 12Slide 13B-D Manual insertion chart AB-D Manual insertion chart BPneumatic Piston Sub-AssemblyDistribution of Assembly operation timesErgonomics and Cycle TimeBoothroyd/Dewhurst Design RulesRules to reduce part countSlide 21Re-designSlide 23Slide 24See master mechanic electric screw driverSlide 26Boothroyd/Dewhurst Economic Assessment ChartEconomic AnalysisSee IBM ProprinterClassificationAutomatic assembly machinesRules for design for high speed-automatic assemblySlide 33Pick and Place Chip AssemblyRobot AssemblyRules for design for Robot assemblyPart mating behaviorRemote Compliance CenterSlide 39Kinematic Coupling 6 degrees of freedom require 6 points of restraintSlide 41Polaroid Case Study (Ref. Ulrich et al. Management Science/ Vol 39, No. 4 April 1993)Design for Disassembly ref BrasBut often only a small amount of disassembly takes place before shreddingChain of Delivery of QualitySummaryReferencesMechanical Assembly Systems2.810 Fall 2002Professor Tim GutowskiBody Drop, Ford Motor Company, Highland Park, 1913Ref: “From the American System to Mass Production, 1800-1932” by David A. Hounshell, John Hopkins Press, 1984Complicated products require more assembly…..which can then become a bottleneckModel T Ford >1,000 partsLPCHPCFan caseHPTLPTexhaustcasediffusergearbox>10,000 parts> 100,000 partsPratt & Whitney JT9DBoeing 747To solve this problem Ford developed the moving assembly lineStatic bench assemblyMoving assemblylineSee GM front end assemblyRequirements;1. Work design (balance steps, ergonomics)2. Designs that work (DFA)3. Interchangeable partsJohn Hall’s breech designdemonstrated interchageabilityAt Harper’s Ferrry in 1827Time Estimation for Assembly1. Handling1. pick up2. orient2. Insertion1. location (obstructed view? Self locating?)2. hold down and resistance3. securing methodSymmetryHandling Issues0 180 180 90 360 3600 0 90 180 0 360Size Fragile/SharpNest/TangleSlippery/FlexibleB-D Manual handling chartInsertion IssuesObstructed Access/ViewAlignmentInsertion ForceB/D chart 2-2 first &secondB-D Manual insertion chart1 – screw(2) (steel) not easy to align2 – cover(steel) not easy to align – assembly worker’s fingers must be used to align edges3 – spring(steel) (closed ends) subject to continuous cycling and must be spring steel4 – piston stop(plastic) edge is chamfered for ease of alignment5 – piston(aluminum) obstructed access for insertion of spindle into bottom of bore6 – main block(plastic) depth of bore is 28mm with small through hole for piston spindlePneumatic Piston Sub-AssemblyB-D Manual handling chartpistonscrews coverspringB-D Manual insertion chart AcoverpistonspringB-D Manual insertion chart BscrewsPneumatic Piston Sub-Assembly1 2 3 4 5 6 7 8 9Name of AssemblyPart I.D. No.number of times the operation is carried out consecutivelytwo-digit manual handling codemanual handling time per parttwo-digit manual insertion codemanual insertion time per partoperation time, seconds (2)*[(4)+(6)]operation cost, cents 0.4*(7)figures for estimation of theoretical minimum partsPNEUMATIC PISTON6 1 30 1.95 00 1.50 3.45 1.38 1MAIN BLOCK5 1 10 1.50 10 4.00 5.50 2.20 1PISTON4 1 10 1.50 00 1.50 3.00 1.20 1PISTON STOP3 1 05 1.84 00 1.50 3.34 1.34 1SPRING2 1 23 2.36 08 6.50 8.86 3.54 0COVER1 2 11 1.80 39 8.00 19.60 7.84 0SCREW43.75 17.50 4 design efficiency 0.27TM CM NM = (3*NM)/TMDistribution of Assembly operation times 0 3 4 5 6 8 91234Time bins (sec)Occurrences7 10Ergonomics and Cycle TimeBoothroyd/Dewhurst Design Rules1. Reduce part count and part types2. Strive to eliminate adjustments3. Design parts to be self-aligning and self-locating4. Ensure adequate access and unrestricted vision5. Ensure the ease of handling of parts from bulk6. Minimize the need for reorientations during assembly7. Design parts that cannot be installed incorrectly8. Maximize part symmetry if possible or make parts obviously asymmetricalRules to reduce part count1. During operation of the product, does the part move relative to all other parts already assembled?Only gross motion should be considered – small motions that can be accommodated by elastic hinges, for example, are not sufficient for a positive answer2. Must the part be of a different material than or be isolated from all other parts already assembled?Only fundamental reasons concerned with material properties are acceptable3. Must the part be separate from all other parts already assembled because otherwise necessary assembly or disassembly of other separate parts would be impossible?1 – snap on cover and stop (plastic)2 – spring(steel)3 – piston (aluminum)4 – main block (plastic)Redesign: Pneumatic Piston Sub-AssemblyRe-design1 2 3 4 5 6 7 8 9Name of AssemblyPart I.D. No.number of times the operation is carried out consecutivelytwo-digit manual handling codemanual handling time per parttwo-digit manual insertion codemanual insertion time per partoperation time, seconds (2)*[(4)+(6)]operation cost, cents 0.4*(7)figures for estimation of theoretical minimum partsPNEUMATIC PISTON (re-design)4 1 30 1.95 00 1.50 3.45 1.38 1MAIN BLOCK3 1 10 1.50 00 1.50 3.00 1.20 1PISTON1 1 05 1.84 00 1.50 3.34 1.34 1SPRING2 1 10 1.50 30 2.00 3.50 1.40 1COVER & STOP13.29 5.32 4 design efficiency 0.90TM CM NM = (3*NM)/TMDistribution of Assembly operation times 0 1 2 3 4 5 61234Time bins (sec)Occurrences7WORKER #2WORKER #3WORKER #4 WORKER #5WiresS o l d e r i n gI r o nGB3WiresGB3W O R K E R # 7W O R K E R # 6E l e c . S c r e wD r i v e rW O R K E R # 8S c r e wF C 1F C 1S c r e wI n s p e c t i o nT o o lT r a n s p o r t t oP a c k a g i n gS h i p p i n gT r a n s p o r t t oP a c k a g i n gS h i p p i n gG l u eG l u eF C 2F C 2B C 3B C 3B C 1B C 2B C 1B C 2B C 4B C 4S c r e wE l e c . S c r e wD r i v e rB C 5 F C 7 F C 8 F C 9 F C 1 0F C 6F C 3F C 4F C 5Manual Assembly SystemsBenchLineSee master mechanic electric screw driverDistribution of Assembly operation times 0 5 10 15 20 25 302468101214Time bins (sec)OccurrencesBoothroyd/Dewhurst Economic Assessment ChartVA = annual production volume measured in thousandsNA = number of parts in the assemblyNT = total number of parts from which various


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MIT 2 810 - Mechanical Assembly Systems

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