ToleranceManagement(公差管理).ppt

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1、Tolerance Management31 July, 2002Agilent RestrictedContents Tolerance Synthesis Tolerance Allocation Total Tolerance ManagementTolerance Management31 July, 2002Agilent RestrictedTolerance Synthesis Synthesis or allocation? Tolerance analysis methodWC (Worst Case)RSS(Root Sum Squares)Monte Carlo (Sim

2、ulation method) Worst case method or statistical method? How? When?Tolerance Management31 July, 2002Agilent RestrictedSynthesis Vs. AllocationTolerance Management31 July, 2002Agilent RestrictedAnalysis method Worst Case RSS(Root Sum Squares)112233| (Sensitivity)asmasmiTfTfTfTTaccumulated tolerancefp

3、artial derivative222112233()()() (Sensitivity)asmasmiTfTfTfTTaccumulated tolerancefpartial derivativeTolerance Management31 July, 2002Agilent RestrictedSensitivity analysis What is Sensitivity?123123123123( ,) * * * , sensitivitiesxxxxxxyf x x xdyfdxfdxfdxffand fareTolerance Management31 July, 2002A

4、gilent RestrictedSensitivity Example2222222Measure L and h to get radius RR()( )2824()48LRhLhRhLLhdRdldhhhDifferent variation have different influence to final assembly.During design phase we need to optimize sensitivities of components to make the product more robustTolerance Management31 July, 200

5、2Agilent RestrictedWorst Case Vs. Statistical Tolerance10.03Case study4 blocks assemblyBlock length=1 0.03Assembly requirement: 4 0.1 (3.94.1)10.03 10.03 10.03 10.03?Tolerance Management31 July, 2002Agilent RestrictedWorst-Case Tolerance = 4*0.03 = 0.012 Block length = 4 0.012 (3.884.12) Result: Out

6、 of requirement!Tolerance Management31 July, 2002Agilent RestrictedStatistical Case Statistical Tolerance Tolerance 3.944.06 12341234222222221.00 1.00 1.00 1.004.000.010.010.010.010.0230.06ddddkddddkkktttttTolerance Management31 July, 2002Agilent RestrictedExtreme Case When block is in 0.976 0.06,us

7、ing statistical tolerance could cause:Block length: 3.904 0.12,Out of toleranceTolerance Management31 July, 2002Agilent RestrictedApplicationStatistical Tolerance only can be used when tolerance distribution is centered WC:Safe,critical application,expensive RSS Statistical :Inexpensive, but should

8、meet assumption (centered distribution),need good supplier management(Supplier should follow statistical tolerancing)Tolerance Management31 July, 2002Agilent RestrictedTolerance AllocationPopular MethodEqual Tolerance Equal tolerances are assigned to all components (Bad practice)Equal precision All

9、parts in an assembly have the same precision (manufacturing difficulty)Weighted precision All parts are set the same precision initially,use different weight to optimize tolerance allocationTolerance Management31 July, 2002Agilent RestrictedProportional ScalingProcedure:1.Assigning reasonable tolera

10、nce based on process or design guidelines2. All tolerances are summed to see if they meet the specified tolerance.3.If not, all tolerance are scaled by a constant proportionality factor.Tolerance Management31 July, 2002Agilent RestrictedIllustration of Proportional ScalingTolerance Management31 July

11、, 2002Agilent RestrictedPractical ProblemDimValueTolerance DesignFixedA Retaining Ring0.05050.0015B8.000?C bearing0.50930.0025D0.400?E7.711?F0.400?G bearing0.50930.0025Required clearance:0.020 0.015Tolerance Management31 July, 2002Agilent RestrictedDimValueTolerance DesignFixedA Retaining Ring0.0505

12、0.0015B8.0000.008C bearing0.50930.0025D0.4000.002E7.7110.006F0.4000.002G bearing0.50930.0025Initial SettingTolerance Management31 July, 2002Agilent RestrictedProportional Scaling Worst-CaseTSUM = + TA + TB + TC + TD + TE + TF + TG= + .0015 + .008 + .0025 + .002 + .006 + .002 + .0025= .0245 (too larg

13、e) ProportionalTASM = .015 = .0015 +.0025 +.0025 + P* (.008 + .002 + .006 + .002)P = .47222TB = .47222 (.008) = .00378TE = .47222 (.006) = .00283TD = .47222 (.002) = .00094 TF = .47222 (.002) = .00094DimValueTolerance DesignFixedA Retaining Ring0.05050.0015B8.0000.00378C bearing0.50930.0025D0.4000.0

14、0094E7.7110.00283F0.4000.00094G bearing0.50930.0025Tolerance Management31 July, 2002Agilent RestrictedStatistical AllocationDimValueTolerance DesignFixedA Retaining Ring0.05050.0015B8.0000.012C bearing0.50930.0025D0.4000.0028E7.7110.084F0.4000.028G bearing0.50930.002522222222ASMT = .015 = .0015 +.00

15、25 +.0025 + P * (.008 + .002 + .006 + .002 )1.40P Statistical methodTolerance Management31 July, 2002Agilent RestrictedAllocation by Weight FactorsBased on machining difficulty,different weight can be assign to a tolerance of a part to optimizeFor example, B,D, E, F are assigned 10,20,10,20 as weigh

16、t.Tolerance Management31 July, 2002Agilent RestrictedWorst CaseDimValueTolerance DesignFixedA Retaining Ring0.05050.0015B8.0000.00309C bearing0.50930.0025D0.4000.00155E7.7110.00232F0.4000.00155G bearing0.50930.0025iiiASMBEDT = PWTT = .015 = .0015 +.0025 +.0025 +P (10/60)(.008) + (20/60)(.002) + (10/

17、60)(.006) + (20/60)(.002)P = 2.31818T = 2.31818(10/60)(.008) = .00309 T = 2.31818(10/60)(.006) = .00232T = 2.318F18(20/60)(.002) = .00155 T = 2.31818(20/60)(.002) = .00155Tolerance Management31 July, 2002Agilent RestrictedStatisticalDimValueTolerance DesignFixedA Retaining Ring0.05050.0015B8.0000.01

18、010C bearing0.50930.0025D0.4000.00505E7.7110.00757F0.4000.00505G bearing0.50930.0025iii222222222222222AASMBBCDDEEFFGBEDFT = PWTT= T+ P W T + T + P W T+ P W T + P W T + TP = 7.57238T = (7.57238)(10/60)(.008) = .01010 T = (7.57238)(10/60)(.006) = .00757T = (7.57238)(20/60)(.002) = .00505 T = (7.57238)

19、(20/60)(.002) = .00505Tolerance Management31 July, 2002Agilent RestrictedComparisonTolerance Management31 July, 2002Agilent RestrictedTolerance for coupling Dimensional tolerance Geometrical tolerance Synthesis of dimensional tolerance and geometrical toleranceWhen feature of size has been assign di

20、mensional tolerance and geometrical tolerance, the total tolerance of mating is different from conventional mating tolerance.Tolerance Management31 July, 2002Agilent RestrictedExample-linkage mechanismTolerance Management31 July, 2002Agilent RestrictedCalculationMinimal Gap = VC hole- VCshaft =30-30

21、=0.0Maximum Gap = LMS hole LMS Shaft= 30.5-29.5 = 1.0Maximum displacement = RC hole LMS shaft = 31.0-29.5 = 1.5Tolerance Management31 July, 2002Agilent RestrictedValidation in sub-assembly 2 mode:VC(virtual condition) mode and RC(resultant condition) For critical dimension chain,all coupling should

22、be validated at virtual condition and resultant condition( Two extreme condition)This process can expose design error in embodiment designTolerance Management31 July, 2002Agilent RestrictedCommon problems in tolerance managementConception: Feasibility analysis Lack of general knowledge and understan

23、ding Difficult to represent GD&T tolerances in tolerance chain calculationsDetail Design: Difficult to make a cost efficient tolerance allocation Difficult to represent GD&T tolerances in tolerance chain calculations The tolerance standard is erroneously applied, resulting in inconsistent requiremen

24、tsManufacturing: The tolerance standard is erroneously applied, resulting in inconsistent requirementsDrawings are misinterpreted which gives errors in manufacturing and verification Inspection: The measurements are erroneously performed Inconsistent use of datumConceptionDesignDetail DesignManufact

25、uring Dev.InspectionTotal Tolerance ManagementTolerance Management31 July, 2002Agilent RestrictedWarranty Failure or In-house failure?A product passing final test doesnt mean it is of high quality,especially those products pass final test just at the end of tolerance zone.it will short the product l

26、ife, increase warranty cost.1.DesignTolerances are assigned to each component at a balanced justification.2.ManufacturingProcess Capability is maintained,manufacturing equipments dont “eat” too much tolerance,Reduce possibility of process failureHow to evaluate a good tolerance managementTolerance M

27、anagement31 July, 2002Agilent RestrictedSome Statistics terms Mean Standard deviation123n123nmean group of parts, their actual dimensions are measured d ,d ,d ,.d ,its average value (mean)d +d +d +dd = An2222123()()().()1meanmeanmeannmeanddddddddnTolerance Management31 July, 2002Agilent RestrictedPr

28、ocess Capability Cp Cpk6 Tolerance LimitL - Lower Tolerance Limit-Standard DeviationULCpUUpper| - |(1) k=()2norminal value (Soecification)CpkCpk whereULmean Tolerance Management31 July, 2002Agilent RestrictedExplanationCp1.0Process is too bad1.0Cp1.33Good1.33Cp= 2.0 and Cpk=1.5 imply 6 SIGMA quality

29、 (3.4ppm defective,)Tolerance Management31 July, 2002Agilent RestrictedBest Practice Motorola 6 Sigma Taguchis MethodConceptionDesignParameterDesignToleranceDesignTolerance Management31 July, 2002Agilent RestrictedVariations causing component failure 5M1EMan, Method,Machine & Measuring Tool,Material

30、, Environment Variations in different product phasePhaseDesignComponentAssemblyVariationDesign is not robust, too sensible to variationMachine precisionProcess variationManufacturing processFixture precisionAssembly processCalibration tool precision Process variationResultTolerance is too tight, hig

31、h manufacturing cost.High defect on arrival, scrap rate is too highDOA,High Failure Rate,Shorten product lifeTolerance Management31 July, 2002Agilent RestrictedDesignManufacturingInspectionVendor ManagementFixture DevelopmentAssembly Process DevelopmentCalibration Process DevelopmentTolerance Manage

32、ment Activities in Different PhaseTolerance Management31 July, 2002Agilent RestrictedDesign PhaseRobust designSensitivity analysis and optimizationManufacturing method?Balance between assembly tolerance and component toleranceBuild high precision or manufacturing high precision?Fixture and compliant

33、 assembly can ensure tight tolerance.Example:Injector Back plateAssembly tolerance or calibrated tolerance?If a product has high repeatability,product can be calibrated to home point,avoiding high manufacturing cost.Example: Tray and injectorTolerance Management31 July, 2002Agilent RestrictedSeneiti

34、vityAnalysisParameterOptimizationSubassemblyToleranceClearance forcouplingDimension andTolerance formating partsValidationEntry oftoleranceFlowchart for designerFlowchart for designerTolerance Management31 July, 2002Agilent RestrictedManufacturing Fixture designUse correct positioning method,Try not

35、 to widen tolerance zone or reduce tolerance zone Assembly processReduce operator influence in process variationAdd test process for each sub-assembly Preventive Maintenance Prevent equipment from malfunction Be prepared rather than fire-fighterTolerance Management31 July, 2002Agilent RestrictedSamp

36、ling Common Problem: When problem occurs, we know there are something wrong Sampling Everything can go wrong,be proactive! Sample method? Have vendor to sample parts and submit a sampling report to consumer. 100% incoming inspection is not encouraged Consumer develops a sampling plan: N,n,A,R N - lo

37、t size n-sample size, A-accept size, R Reject size. Tolerance Management31 July, 2002Agilent RestrictedSampling Sample period Critical part Non-Critical Part Reject methodThe best way is to reject all parts to vendor at vendors expense Advantages:Push vendors improve quality Vendor understand what is wrong Reduce impact to production lineDisadvantages: Impact on-time-delivery 结束结束