NOKIAProcessCapabi最新培训课件.pptx

Process Capability(Cp/Cpk/Pp/Ppk)Global Training MaterialGlobal Training MaterialCreator :Global Mechanics Process ManagerFunction :MechanicsApprover :Gary Bradley/Global Process TeamDocument ID :DMT00018-ENVersion/Status:V.1.0/ApprovedLocation :Notes:NMP DOCMANR4 PCP PC Process Library DocManChange History:IssueDateHandled ByComments1.021st Dec01Jim Christy&Sren LundsfrydApproved for Global UseNOTE All comments and improvements should be addressed to the creator of this document.培训专用ContentsSectionHeading/DescriptionPage1Variation,Tolerances and Dimensional Control42Population,Sample and Normal Distribution153Cp and Cpk Concept284Use of the NMP Data Collection Spreadsheet445Confidence of Cpk52培训专用Process Capability-Evaluating Manufacturing VariationAcknowledgementsBenny Matthiassen(NMP CMT,Copenhagen,Denmark)Frank Adler(NMP Alliance,Dallas,USA)Joni Laakso(NMP R&D,Salo,Finland)Jim Christy(NMP SRC,Southwood,UK)培训专用Section 1Variation,Tolerances and Dimensional Control培训专用Two Types of Product CharacteristicsVariable:A characteristic measured in physical units,e.g.millimetres,volts,amps,decibel and seconds.ONOFFAttribute:A characteristic that by comparison to some standard is judged“good”or“bad”,e.g.free from scratches(visual quality).In this training we deal with variables only培训专用The Sources of Process/System VariationMethodsOperatorsCustomer SatisfactionMaterialEnvironmentEquipmentProcess培训专用Two Types of ProcessesAll processes have:Natural(random)variability=due to common causesStable Process:A process in which variation in outcomes arises only from common causesUnstable Process:A process in which variation is a result of both common and special causesUSLLSLnominal valueDefectUSLLSLnominal value Unnatural variability=due to special causes培训专用Shewhart(1931)Shewhart(1931)The Two Causes of VariationCommon Causes:Causes that are implemented in the process due to the design of the process,and affect all outcomes of the processIdentifying these types of causes requires methods such as Design of Experiment(DOE),etc.Special Causes:Causes that are not present in the process all the time and do not affect all outcomes,but arise because of specific circumstancesSpecial causes can be identified using Statistical Process Control(SPC)USLLSLNominalvalueDefectUSLLSLnominal value培训专用TolerancesLSL(lower specification limit)10,7USL(upper specification limit)10,9Acceptable partRejected PartRejected ProductNominal10,80,1Rejected PartA tolerance is a allowed maximum variation of a dimension.培训专用Measurement ReportIn most cases we measure only one part per cavity for measurement report培训专用Example of Capability Analysis DataFor some critical dimensions we need to measure more than 1 partFor capability data we usually measure 5 pcs 2 times/hour=100 pcs(but sampling plan needs to be made on the basis of production quantity,run duration and cycle time)培训专用Process Capability-What is it?Process Capability is a measure of the inherent capability of a manufacturing process to be able to consistently produce components that meet the required design specificationsProcess Capability is designated by Cp and CpkProcess Performance is a measure of the performance of a process to be able to consistently produce components that meet the required design specifications.Process Performance includes special causes of variation not present in Process CapabilityProcess Performance is designated Pp and Ppk培训专用Why Make Process Capability StudiesLSL(lower specification limit)10,7USL(upper specification limit)10,9Nominal10,80,1This part is within spec.The tool would be approved if only this part was measuredThese parts are out of spec and could be approved if only one good part was measuredA process capability study would reveal that the tool should not be acceptedWhen a dimension needs to be kept properly within spec,we must study the process capability.but still this is no guarantee for the actual performance of the process as it is only an initial capability study培训专用 E1.5 E1 E2 E3 E4 E5The Nokia Process Verification ProcessBlack diamonds to be fixed by E3(often a change of a white diamond)Proposal for black diamonds to be discussed with Supplier.Max:105,85Ongoing Process Control(SPC)Tolerances applied to drawingType 1 Functional Characteristics-1 part/cavity measured for measurement reportWhite diamonds(s)to be agreedWhite diamonds(s)to be discussed with supplier10 parts/cavity measured for measurement reportCapability study:Requirement:Cp and Cpk 1.67 by E3.Quantities to be agreed with supplier.Minimum 5 parts pr 1/2 hour in 10 hours measured for each cavity=100 parts.Can vary depending on tool capacity,e.g.stamped parts(see DMY00019-EN)培训专用Section 2.Population,Sample and Normal Distribution培训专用The Bell Shaped(Normal)DistributionSymmetrical shape with a peak in the middle of the range of the data.Indicates that the input variables(Xs)to the process are randomly influenced.培训专用“Population Parameters”=Population mean=Population standard deviationPopulation versus SamplePopulationAn entire group of objects that have been made or will be made containing a characteristic of interestSampleThe group of objects actually measured in a statistical studyA sample is usually a subset of the population of interestPopulationSample“Sample Statistics”x=Sample means=Sample standard deviation培训专用The Normal Distribution培训专用What Measurements Can Be Used to Describe a Process or System?Example:x1 =5x2 =7x3 =4x4 =2x5 =6mean(average)or describes the location of the distribution(m),a measure of central tendency,is the mean or average of all values in the population.When only a sample of the population is being described,mean is more properly denoted as (x-bar):培训专用Example:x1 =5x2 =7x3 =4x4 =2x5 =6The most simple measure of variability is the range.The range of a sample is defined by as the difference between the largest and the smallest observation from samples in a sub-group,e.g.5 consecutive parts from the manufacturing process.What Measurements Can Be Used to Describe Process variation?培训专用sST-often notated as or sigma,is another measure of dispersion or variability and stands for“short-term standard deviation”,which measures the variability of a process or system using“rational”sub-grouping.where is the range of subgroup j,N the number of subgroups,and d2*depends on the number N of subgroups and the size n of a subgroup(see next slide)What Measurements Can Be Used to Describe Process variation?培训专用d2*values for SSTWhere:N=no.of sub-groups,n=no.of samples in each sub-groupd d2 2*d d2 2Typical:N=20&n=5培训专用 x x3 3 x x2 2 x x1 1 x x1010 x x_ _t tExample:What Measurements Can Be Used to Describe Process variation?培训专用The Difference Between SST and sLT!meanTimeDimensionShort term Standard DeviationLong term Standard DeviationSubgroup size n=5Number of subgroups N=7TRENDSubgroup No.1培训专用The difference between the standard deviations sLT and sST gives an indication of how much better one can do when using appropriate production control,like Statistical Process Control(SPC).Short-term standard deviation:Long-term standard deviation :The difference between sST and sLT培训专用The difference between sST and sLTThe difference between sLT and sST is only in the way that the standard deviation is calculatedsLT is always the same or larger than sSTIf sLT equals sST,then the process control over the longer-term is the same as the short-term,and the process would not benefit from SPCIf sLT is larger than sST,then the process has lost control over the longer-term,and the process would benefit from SPCThe reliability of sLT is improved if the data is taken over a longer period of time.Alternatively sLT can be calculated on several occasions separated by time and the results compared to see whether sLT is stable培训专用Exercise 1:Sample Distributions1.In Excel file Data exercise 1.xls you find 100 measurements being the result of a capability study.The specification for the dimension is 15,16,01 2.How well does the sample population fit the specification,e.g.should we expect any parts outside spec?3.Mention possible consequences of having a part outside spec.4.Mention possible causes of variation for parts.5.Calculate the sample mean and sample standard deviation for the 100 measurements.Use the average and stdev functions Excel.培训专用Section 3.Cp and Cpk Concept培训专用Defining Cp and PpSample meanProcess variation 6*s USL-LSLLSL USLNominal dimThe tolerance area divided by the total process variation,irrespective of process centring.培训专用Defining Cpk and PpkSample meanProcess variation 3sProcess variation 3sMean-LSLUSL-MeanLSL USLNominal dimCpk and Ppk Indexes account also for process centring.培训专用What is the Difference Between Cp and Cpk?The Cp index only accounts for process variabilityThe Cpk Index accounts for process variability and centering of the process mean to the design nominal Therefore,Cp CpkNOTE:Same applies also for Pp and PpkCp=Cpk(both low)LSLUSLMean=NominalReject partsReject partsCp high,Cpk low Process should be optimized!NominalLSLMeanUSLReject parts培训专用What Do These Indexes Tell Us?Simple numerical values to describe the quality of the process The higher the number the betterRequirement for Cp and Cpk is 1.67 min.Recommendation for Pp and Ppk is 1.33 min.This leaves us some space for the variation,i.e.a safety marginAre we able to improve our process by using SPC?If index is low,following things should be given a thought:Is the product design OK?Are tolerance limits set correctly?Too tight?Is the process capable of producing good quality products?Process variation?DOE required?Is the measuring system capable?(See Gage R&R)培训专用Cpk-With a 2-sigma safety margin-3 sST+3 sSTLCLUCLLSLUSLMean value=Nominal value or TargetRequirement for Cp and Cpk is 1.67 min.1.67 is a ratio of=5/3 or 10/6.6*standard deviation10*standard deviation2*standard deviation2*standard deviation培训专用Cpk=1.67 the process is CAPABLECpk=2.0 the process has reached Six Sigma level培训专用What Do These Indexes Tell Us?If Cp=Cpk,If Pp=Ppk,If Cpk Cp,If Ppk Pp,If Cp=Pp,If Cpk=Ppk,If Pp Cp,If Ppk Cpk,then process is affected by special causes.Investigate X-bar/R-chart for out-of-control conditions.SPC may be effective then process is not affected by special causes during the study run.SPC would not be effective in this case then process perfectly centred then process not centred(check process mean against design nominal)培训专用Cp and Cpk Indices and Defects(both tails of the normal distribution)(both tails of the normal distribution)Pp=Ppk=1,33 63 ppm defects=0,006%Cp=Cpk=1,67 0,6 ppm defects=0,00006%Note:Ppm reject rates calculated from Cp&Cpk are based on the short term variation which may not represent the long term reject rate 培训专用The Effects of Cpk and Cp on FFR培训专用Exercise 2:Cp and CpkCalculate Cp and Cpk for the 100 measurements in the file Data exercise 1.xlsDetermine the approximate Cp and Cpk for the 4 sample populations on the following pageShould actions be made to improve these processes.If yes,which?培训专用Estimate Cp and Cpk?The width of the normal distributions shown include 3*sLSLUSLA)LSLUSLB)LSLUSLC)USLLSLD)培训专用Estimate Cp and Cpk?-A)LSLUSLA)Mean and nominalUSL-LSL6*sUSL-MeanMean-LSL3*s培训专用Estimate Cp and Cpk?-B)LSLUSLB)NominalMeanUSL-LSL6*sUSL-MeanMean-LSL3*s培训专用Estimate Cp and Cpk?-C)LSLUSLC)NominalMeanUSL-LSL6*sUSL-MeanMean-LSL3*s培训专用Estimate Cp and Cpk?-DUSLLSLD)NominalMeanUSL-LSL6*sUSL-MeanMean-LSL3*s培训专用Section 4.Use of the NMP Data Collection Spreadsheet培训专用Example of how to Collect Data 1.Run in and stabilise process2.Note the main parameters for reference3.When the process is stable run the tool for 10 hours3.Take 5 parts out from each cavity every half hour and mark them with time,date and cavity.Total 20 sets of 5 parts from each cavity must be made,or according to agreement.4.After the last sample lot note the main process parameters for reference5.Measure and record the main functional characteristics(white diamonds)6.Fill data into the NMP data collection spreadsheet7.Analyse!See DMY 00019-ENClassification and Marking of Functional CharacteristicsTimeDimensionSubgroup size n=5Number of subgroups N=200,5 hours between samples takenNote:For clarity,only 6 subgroups are shown培训专用Data Collection Sheet(DMM00024-EN-5.0)培训专用Data Collection Sheet(DMM00024-EN-5.0)培训专用Graphical Presentation:HistogramWhat kind of distribution?Location versus tolerance area Width(deviation)Example:Cp2.59 Pp1.86Cpk0.88 Ppk0.63培训专用Graphical Presentation:X-bar and R-ChartX-Bar ChartR-Chart培训专用Graphical Presentation-Time Series PlotSomething happened here!培训专用Exercise 3:Cpk Data SpreadsheetOpen spreadsheet Data exercice 3.xls.Dim 13 is identical to the data from the previous exercises.Verify the results from the previous exercises for dimension 13.Analyse the remaining data sets an comment the process,should any actions be made?Remember to create and look at the charts.培训专用Section 5.Confidence of Cpk培训专用Confidence of CpkCpk values are not definite numbers as they are based on relatively small samples of a population.The 95%confidence interval determines the interval which includes the true Cpk value with a probability of 95%,i.e.there is a probability of 5%that Cpk is either lower or higher than this confidence interval.95%confidence intervalActual cpkCpk upper confidence limitCpk lower confidence limit培训专用Confidence of CpkSmall sample sizes gives wide confidence intervals培训专用Cpk Confidence Limits with a sample size of 100 and a nominal Cpk of 1.67培训专用演讲完毕，谢谢观看！培训专用内容总结Process Capability(Cp/Cpk/Pp/Ppk)Global Training Material。IssueDateHandled ByComments。Pp=Ppk=1,33。Cp=Cpk=1,67。Example:Cp2.59Pp1.86。Cpk0.88Ppk0.63培训专用