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Acceptance Sampling Prepared by Anthony Lizza Penn State University.

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1 Acceptance Sampling Prepared by Anthony Lizza Penn State University

2 What will be covered? What is acceptance sampling?What is acceptance sampling? How/When would you use it in your organization?How/When would you use it in your organization? Acceptance sampling explained.Acceptance sampling explained. How acceptance sampling works.How acceptance sampling works. An exercise.An exercise. SummarySummary

3 What is acceptance sampling? Acceptance SamplingAcceptance Sampling –Statistical quality control technique, where a random sample is taken from a lot, and upon the results of the sample taken the lot will either be rejected or accepted.

4 What is acceptance sampling? Accept LotAccept Lot –Ready for customers Reject LotReject Lot –Not suitable for customers Statistical Process Control(SPC)Statistical Process Control(SPC) –Sample and determine if in acceptable limits

5 What is acceptance sampling? PurposesPurposes –Determine the quality level of an incoming shipment or, at the end production –Ensure that the quality level is within the level that has been predetermined

6 What is acceptance sampling? Can be either 100% inspection, or a few items of a lot.Can be either 100% inspection, or a few items of a lot. Complete inspectionComplete inspection –Inspecting each item produced to see if each item meets the level desired –Used when defective items would be very detrimental in some way

7 Acceptance Sampling method

8 What is acceptance sampling? Problems with 100% inspectionProblems with 100% inspection –Very expensive –When product must be destroyed to test –Inspection must be very tedious so defective items do not slip through inspection

9 How/When would you use it? Acceptance sampling advantagesAcceptance sampling advantages –Less handling damages –Fewer inspectors to put on payroll –100% inspection costs are to high –100% testing would take to long

10 How/When would you use it? Acceptance sampling disadvantagesAcceptance sampling disadvantages –Risk included in chance of bad lot “acceptance” and good lot “rejection” –Sample taken provides less information than 100% inspection

11 How/When would you use it? Between your organization and outside worldBetween your organization and outside world Samples taken run through “filter,” either passing or rejecting itSamples taken run through “filter,” either passing or rejecting it –Also filter from suppliers to you

12 How/When you would use it? When products in use could be damaged easilyWhen products in use could be damaged easily When using new suppliersWhen using new suppliers When new products producedWhen new products produced When current supplier in questionWhen current supplier in question Testing whole lot could be harmfulTesting whole lot could be harmful

13 How/When you would use it? Determine how many units, n, to sample from an lotDetermine how many units, n, to sample from an lot Determine maximum number of defective items, c, that can be found before the lot is rejectedDetermine maximum number of defective items, c, that can be found before the lot is rejected

14 Acceptance sampling explained Acceptable Quality levels(AQL)Acceptable Quality levels(AQL) –Number of defect percentage allowed in a lot which can still be considered accepted(Type I error) Lot Tolerance Percent Defective(LTPD)Lot Tolerance Percent Defective(LTPD) –Amount of defects that will come with a lot of goods(Type II error)

15 Acceptance sampling explained Sampling PlanSampling Plan –Forms after n and c values have been found Producers riskProducers risk –Risk associated with a lot of acceptable quality rejected

16 Acceptance sampling explained Consumers riskConsumers risk –Receive shipment, assume good quality, actually bad quality AlphaAlpha –Type I error(producers risk) BetaBeta –Type II error(consumers risk)

17 Acceptance sampling explained N –Sample size taken for your sampling plan C –Where rejections would occur when defects exceeded this percent

18 Acceptance sampling explained Operating characteristics curve(OC)Operating characteristics curve(OC) –A graph, displaying standards at which shipments would be accepted FirstFirst –Determine AQL, a, LTPD, b, –Take LTPD/AQL, this gives you the n(AQL)

19 Acceptance sampling explained Reference n(AQL) in the tableReference n(AQL) in the table –C will be given as well when referencing the table NextNext –N(AQL/AQL)=n-sample size –C= reject if more percent defects more The equations can be tricky but the exercise later will helpThe equations can be tricky but the exercise later will help

20 How acceptance sampling works Two classifications of acceptance plansTwo classifications of acceptance plans –Attributes(“go no-go”) –Variables

21 How acceptance sampling works Attributes(“go no-go”)Attributes(“go no-go”) –Defectives-product acceptability across range –Defects-number of defects per unit Variable(continuous)Variable(continuous) –Usually measured by mean and standard deviation

22 How acceptance sampling works RememberRemember –You are not measuring the quality of the lot, but, you are to sentence the lot to either reject or accept it

23 An Exercise Determine theDetermine the –AQL, a, LTPD, B? –Reference table provided- c LTPD/ AQL nAQLc nAQL

24 An Exercise cont. Assume a manufacturer purchases wire from an outside vendor. The wire vendor has an accepted quality level of 1% and accepts a 5% risk of rejecting lots below this level. The manufacturer considers lots with 3% defectives to be unacceptable and assumes a 10% risk of accepting a defective lot. Develop a sample plan for the manufacturer to be followed by the inspection personnelAssume a manufacturer purchases wire from an outside vendor. The wire vendor has an accepted quality level of 1% and accepts a 5% risk of rejecting lots below this level. The manufacturer considers lots with 3% defectives to be unacceptable and assumes a 10% risk of accepting a defective lot. Develop a sample plan for the manufacturer to be followed by the inspection personnel

25 Summary Acceptance sampling is used by organizations to determine if there process’s are running within a controlled limit and to see if they should reject or accept lotsAcceptance sampling is used by organizations to determine if there process’s are running within a controlled limit and to see if they should reject or accept lots

26 Summary There are many basic terms you need to know to be able to understand acceptance samplingThere are many basic terms you need to know to be able to understand acceptance sampling –SPC, Accepts Lot, Reject Lot, Complete Inspection, AQL, LTPD, Sampling Plans, Producers Risk, Consumers Risk, Alpha, Beta, Defect, Defectives, Attributes, Variables.

27 Summary Advantages/Disadvantages of acceptance samplingAdvantages/Disadvantages of acceptance sampling Purpose of acceptance samplingPurpose of acceptance sampling When to use acceptance samplingWhen to use acceptance sampling Equations involvedEquations involved ExerciseExercise –Notes pages have many beneficial hints and help better relate the material, the answer to the exercise is also located on a the notes page of the exercise.

28 Bibliography (Foster, S.Thomas: “Managing Quality-An Integrative Approach:pgs :copyright 2001)(Foster, S.Thomas: “Managing Quality-An Integrative Approach:pgs :copyright 2001) “Quality Control in Furniture Manufacturing”:Internet ions/library/quality/qc40.htn“Quality Control in Furniture Manufacturing”:Internet ions/library/quality/qc40.htn ions/library/quality/qc40.htn ions/library/quality/qc40.htn

29 Bibliography “Process Analysis”:Internet ook/stprocan.html“Process Analysis”:Internet ook/stprocan.html ook/stprocan.html ook/stprocan.html “Quality Control”: Internet ontrol.html“Quality Control”: Internet ontrol.html ontrol.html ontrol.html


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