生产过程控制教材课件.pptx

1、1 NOKIA 2001 T0001801.PPT/21-Dec-2001/Jim ChristyCompany Confidential生产过程控制教材生产过程控制教材2 NOKIA 2001 T0001801.PPT/21-Dec-2001/Jim ChristyCompany ConfidentialSectionHeading/DescriptionPage1Variation,Tolerances and Dimensional Control42Population,Sample and Normal Distribution153Cp and Cpk Concept284Use

2、of the NMP Data Collection Spreadsheet445Confidence of Cpk523 NOKIA 2001 T0001801.PPT/21-Dec-2001/Jim ChristyCompany ConfidentialAcknowledgementsBenny Matthiassen(NMP CMT,Copenhagen,Denmark)Frank Adler(NMP Alliance,Dallas,USA)Joni Laakso(NMP R&D,Salo,Finland)Jim Christy(NMP SRC,Southwood,UK)4 NOKIA

3、2001 T0001801.PPT/21-Dec-2001/Jim ChristyCompany ConfidentialVariation,Tolerances and Dimensional Control5 NOKIA 2001 T0001801.PPT/21-Dec-2001/Jim ChristyCompany ConfidentialVariable:A characteristic measured in physical units,e.g.millimetres,volts,amps,decibel and seconds.ONOFFAttribute:A character

4、istic 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 only6 NOKIA 2001 T0001801.PPT/21-Dec-2001/Jim ChristyCompany ConfidentialMethodsOperatorsCustomer SatisfactionMaterialEnvironmentEquipmentProcess7 NOKIA 20

5、01 T0001801.PPT/21-Dec-2001/Jim ChristyCompany ConfidentialTwo Types of Processes All processes have:Natural(random)variability=due to common causes Stable Process:A process in which variation in outcomes arises only from common causes Unstable Process:A process in which variation is a result of bot

6、h common and special causesUSLLSLnominal valueDefectUSLLSLnominal value Unnatural variability=due to special causes8 NOKIA 2001 T0001801.PPT/21-Dec-2001/Jim ChristyCompany Confidential Common Causes:Causes that are implemented in the process due to the design of the process,and affect all outcomes o

7、f 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 Pr

8、ocess Control(SPC)USLLSLNominalvalueDefectUSLLSLnominal value9 NOKIA 2001 T0001801.PPT/21-Dec-2001/Jim ChristyCompany ConfidentialTolerancesLSL(lower specification limit)10,7USL(upper specification limit)10,9Acceptable partRejected PartRejected ProductNominal10,80,1Rejected PartA tolerance is a allo

9、wed maximum variation of a dimension.10 NOKIA 2001 T0001801.PPT/21-Dec-2001/Jim ChristyCompany ConfidentialMeasurement ReportIn most cases we measure only one part per cavity for measurement report11 NOKIA 2001 T0001801.PPT/21-Dec-2001/Jim ChristyCompany ConfidentialExample of Capability Analysis Da

10、ta For some critical dimensions we need to measure more than 1 part For 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)12 NOKIA 2001 T0001801.PPT/21-Dec-2001/Jim ChristyCompany Confident

11、ialProcess 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 specifications Process Capability is designated by Cp and Cpk Process Performance is a measure of the per

12、formance 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 Capability Process Performance is designated Pp and Ppk13 NOKIA 2001 T0001801.PPT/21-Dec-2001/Jim ChristyCo

13、mpany ConfidentialWhy 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 measure

14、dA 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 study14 NOKIA 2001 T00

15、01801.PPT/21-Dec-2001/Jim ChristyCompany Confidential 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 draw

16、ingType 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

17、 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)15 NOKIA 2001 T0001801.PPT/21-Dec-2001/Jim ChristyCompany Confidential16 NOKIA 2001 T0001801.PPT/21-Dec-2001/Jim ChristyCompany Confidential Symmetrical shape wit

18、h a peak in the middle of the range of the data.Indicates that the input variables(Xs)to the process are randomly influenced.17 NOKIA 2001 T0001801.PPT/21-Dec-2001/Jim ChristyCompany Confidential“Population Parameters”=Population mean=Population standard deviationPopulation versus SamplePopulation A

19、n entire group of objects that have been made or will be made containing a characteristic of interestSample The group of objects actually measured in a statistical study A sample is usually a subset of the population of interestPopulationSample“Sample Statistics”x=Sample means=Sample standard deviat

20、ion18 NOKIA 2001 T0001801.PPT/21-Dec-2001/Jim ChristyCompany ConfidentialThe Normal Distribution19 NOKIA 2001 T0001801.PPT/21-Dec-2001/Jim ChristyCompany ConfidentialExample:x1 =5x2 =7x3 =4x4 =2x5 =6 mean(average)or describes the location of the distribution (m),a measure of central tendency,is the

21、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):20 NOKIA 2001 T0001801.PPT/21-Dec-2001/Jim ChristyCompany ConfidentialExample:x1 =5x2 =7x3 =4x4 =2x5 =6The most simple measure of variability is the range.

22、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.21 NOKIA 2001 T0001801.PPT/21-Dec-2001/Jim ChristyCompany ConfidentialsST-often notated as or sigma,is another mea

23、sure 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 ne

24、xt slide)22 NOKIA 2001 T0001801.PPT/21-Dec-2001/Jim ChristyCompany ConfidentialWhere:N=no.of sub-groups,n=no.of samples in each sub-groupTypical:N=20&n=523 NOKIA 2001 T0001801.PPT/21-Dec-2001/Jim ChristyCompany Confidential Example:24 NOKIA 2001 T0001801.PPT/21-Dec-2001/Jim ChristyCompany Confidenti

25、almeanTimeDimensionShort term Standard DeviationLong term Standard DeviationSubgroup size n=5Number of subgroups N=7TRENDSubgroup No.125 NOKIA 2001 T0001801.PPT/21-Dec-2001/Jim ChristyCompany ConfidentialThe difference between the standard deviations sLT and sST gives an indication of how much bette

26、r one can do when using appropriate production control,like Statistical Process Control(SPC).Short-term standard deviation:Long-term standard deviation26 NOKIA 2001 T0001801.PPT/21-Dec-2001/Jim ChristyCompany ConfidentialThe difference between sLT and sST is only in the way that the standard deviati

27、on 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 bene

28、fit 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 stable27 NOKIA 2001 T0001801.PPT/21-Dec-2001/Jim ChristyCompany Confidential1.In

29、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 out

30、side 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.28 NOKIA 2001 T0001801.PPT/21-Dec-2001/Jim ChristyCompany Confidential29 NOKIA 2001 T0001801.PPT/21-Dec-2001/Jim Chr

31、istyCompany ConfidentialDefining Cp and PpSample meanProcess variation 6*s USL-LSLLSL USLNominal dimThe tolerance area divided by the total process variation,irrespective of process centring.30 NOKIA 2001 T0001801.PPT/21-Dec-2001/Jim ChristyCompany ConfidentialDefining Cpk and PpkSample meanProcess

32、variation 3sProcess variation 3sMean-LSLUSL-MeanLSL USLNominal dimCpk and Ppk Indexes account also for process centring.31 NOKIA 2001 T0001801.PPT/21-Dec-2001/Jim ChristyCompany ConfidentialWhat is the Difference Between Cp and Cpk?The Cp index only accounts for process variability The Cpk Index acc

33、ounts for process variability and centering of the process mean to the design nominal Therefore,Cp Cpk NOTE:Same applies also for Pp and PpkCp=Cpk(both low)LSLUSLMean=NominalReject partsReject partsCp high,Cpk low Process should be optimized!NominalLSLMeanUSLReject parts32 NOKIA 2001 T0001801.PPT/21

34、-Dec-2001/Jim ChristyCompany ConfidentialSimple 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 impro

35、ve 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)33 NOKIA

36、 2001 T0001801.PPT/21-Dec-2001/Jim ChristyCompany Confidential-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 deviation34 NOKIA 2001 T0001801.PPT/21

37、-Dec-2001/Jim ChristyCompany ConfidentialCpk=1.67 the process is CAPABLECpk=2.0 the process has reached Six Sigma level35 NOKIA 2001 T0001801.PPT/21-Dec-2001/Jim ChristyCompany ConfidentialIf 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 spe

38、cial 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)36 NO

39、KIA 2001 T0001801.PPT/21-Dec-2001/Jim ChristyCompany ConfidentialCp and Cpk Indices and Defects(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

40、represent the long term reject rate 37 NOKIA 2001 T0001801.PPT/21-Dec-2001/Jim ChristyCompany ConfidentialThe Effects of Cpk and Cp on FFR38 NOKIA 2001 T0001801.PPT/21-Dec-2001/Jim ChristyCompany Confidential Calculate Cp and Cpk for the 100 measurements in the file Data exercise 1.xls Determine the

41、 approximate Cp and Cpk for the 4 sample populations on the following page Should actions be made to improve these processes.If yes,which?39 NOKIA 2001 T0001801.PPT/21-Dec-2001/Jim ChristyCompany ConfidentialEstimate Cp and Cpk?The width of the normal distributions shown include 3*sLSLUSLA)LSLUSLB)L

42、SLUSLC)USLLSLD)40 NOKIA 2001 T0001801.PPT/21-Dec-2001/Jim ChristyCompany ConfidentialEstimate Cp and Cpk?-A)LSLUSLA)Mean and nominalUSL-LSL6*sUSL-MeanMean-LSL3*s41 NOKIA 2001 T0001801.PPT/21-Dec-2001/Jim ChristyCompany ConfidentialEstimate Cp and Cpk?-B)LSLUSLB)NominalMeanUSL-LSL6*sUSL-MeanMean-LSL3

43、*s42 NOKIA 2001 T0001801.PPT/21-Dec-2001/Jim ChristyCompany ConfidentialEstimate Cp and Cpk?-C)LSLUSLC)NominalMeanUSL-LSL6*sUSL-MeanMean-LSL3*s43 NOKIA 2001 T0001801.PPT/21-Dec-2001/Jim ChristyCompany ConfidentialEstimate Cp and Cpk?-DUSLLSLD)NominalMeanUSL-LSL6*sUSL-MeanMean-LSL3*s44 NOKIA 2001 T00

44、01801.PPT/21-Dec-2001/Jim ChristyCompany Confidential45 NOKIA 2001 T0001801.PPT/21-Dec-2001/Jim ChristyCompany Confidential1.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 a

45、nd 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 coll

46、ection 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 shown46 NOKIA 2001 T0001801.PPT/21-Dec-2001/Jim ChristyCompany Confidential47

47、 NOKIA 2001 T0001801.PPT/21-Dec-2001/Jim ChristyCompany Confidential48 NOKIA 2001 T0001801.PPT/21-Dec-2001/Jim ChristyCompany ConfidentialGraphical Presentation:Histogram What kind of distribution?Location versus tolerance area Width(deviation)Example:Cp2.59Pp1.86Cpk0.88Ppk0.6349 NOKIA 2001 T0001801

48、.PPT/21-Dec-2001/Jim ChristyCompany ConfidentialGraphical Presentation:X-bar and R-ChartX-Bar ChartR-Chart50 NOKIA 2001 T0001801.PPT/21-Dec-2001/Jim ChristyCompany ConfidentialGraphical Presentation-Time Series PlotSomething happened here!51 NOKIA 2001 T0001801.PPT/21-Dec-2001/Jim ChristyCompany Con

49、fidential Open 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.52 NO

50、KIA 2001 T0001801.PPT/21-Dec-2001/Jim ChristyCompany Confidential53 NOKIA 2001 T0001801.PPT/21-Dec-2001/Jim ChristyCompany Confidential Cpk 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