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1 Prepared by Anthony Lizza Penn State University Acceptance SamplingPrepared byAnthony LizzaPenn State University
2 What will be covered? What is acceptance sampling? How/When would you use it in your organization?Acceptance sampling explained.How acceptance sampling works.An exercise.SummaryYou will be informed with the general knowledge to better understand and implement acceptance sampling into your organization.
3 What is acceptance 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.In general, acceptance sampling is an approach to test the conformance of the products you have produced. You can either test a few items or every item in the lot.(LOT)-is the entire batch, group of items produced.
4 What is acceptance sampling? Accept LotReady for customersReject LotNot suitable for customersStatistical Process Control(SPC)Sample and determine if in acceptable limits(LOT)-entire batch, group of items produced.
5 What is acceptance sampling? PurposesDetermine the quality level of an incoming shipment or, at the end productionEnsure that the quality level is within the level that has been predeterminedRemember your main purpose is to sentence the lot basically to life or death. You will reject or accept it but not measure the quality of the product.
6 What is acceptance sampling? Can be either 100% inspection, or a few items of a lot.Complete inspectionInspecting each item produced to see if each item meets the level desiredUsed when defective items would be very detrimental in some wayCertain situations will tend to favor different sampling methods.
8 What is acceptance sampling? Problems with 100% inspectionVery expensiveWhen product must be destroyed to testInspection must be very tedious so defective items do not slip through inspectionAcceptance sampling is very favorable when weighing out the advantages and disadvantages associated with complete inspection. However, certain situations favor different approaches as stated earlier.
9 How/When would you use it? Acceptance sampling advantagesLess handling damagesFewer inspectors to put on payroll100% inspection costs are to high100% testing would take to longThe how and when slides will begin to show you and give you a respect towards the different approaches, not only to show you how and when to implement, but also why you should.
10 How/When would you use it? Acceptance sampling disadvantagesRisk included in chance of bad lot “acceptance” and good lot “rejection”Sample taken provides less information than 100% inspectionThe disadvantages show shy acceptance sampling could be bad. You may be confused right now about what method to implement. You must choose which one would fit proportionately with your organizations procedures.
11 How/When would you use it? Between your organization and outside worldSamples taken run through “filter,” either passing or rejecting itAlso filter from suppliers to youFilter is a way of preventing defects from being issued to customers, and defects coming to you from suppliers.
12 How/When you would use it? When products in use could be damaged easilyWhen using new suppliersWhen new products producedWhen current supplier in questionTesting whole lot could be harmfulThese are a few situations in which your organization would find it worthy of using the acceptance sampling approach.
13 How/When you would use it? Determine how many units, n, to sample from an lotDetermine maximum number of defective items, c, that can be found before the lot is rejectedNow you will begin to understand the variables and there meaning when doing the equating during the acceptance sampling process.
14 Acceptance sampling explained 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)Amount of defects that will come with a lot of goods(Type II error)These are more terms you need to know when equating, Type I and II errors are explained in the next couple slides.
15 Acceptance sampling explained Sampling PlanForms after n and c values have been foundProducers riskRisk associated with a lot of acceptable quality rejectedMore basically producers risk is the chance of the suppliers shipment being rejected by the organization when the shipment is good.Consumers risk is the risk involved when sending products to consumers and assume the lot to be good, but it’s not.
16 Acceptance sampling explained Consumers riskReceive shipment, assume good quality, actually bad qualityAlphaType I error(producers risk)BetaType II error(consumers risk)
17 Acceptance sampling explained Sample size taken for your sampling planCWhere rejections would occur when defects exceeded this percentN is the number of products sampled.C is where you would reject a lot if percentage of defects surpassed it.OC is the graph showing the point where the lot would be accepted to.
18 Acceptance sampling explained Operating characteristics curve(OC)A graph, displaying standards at which shipments would be acceptedFirstDetermine AQL, a, LTPD, b,Take LTPD/AQL, this gives you the n(AQL)
19 Acceptance sampling explained Reference n(AQL) in the tableC will be given as well when referencing the tableNextN(AQL/AQL)=n-sample sizeC= reject if more percent defects moreThe equations can be tricky but the exercise later will helpHow to begin equating.
20 How acceptance sampling works Two classifications of acceptance plansAttributes(“go no-go”)VariablesAcceptance Plans-attributesvariables
21 How acceptance sampling works Attributes(“go no-go”)Defectives-product acceptability across rangeDefects-number of defects per unitVariable(continuous)Usually measured by mean and standard deviationDifference between defect and defectiveness in attributes.Definitions of attributes and variables.
22 How acceptance sampling works RememberYou are not measuring the quality of the lot, but, you are to sentence the lot to either reject or accept itNOT MEASURING QUALITY, REJECTING OR ACCEPTING A LOT DEPENDING ON CERTAIN CIRCUMSTANCES.
23 An Exercise Determine the AQL, a, LTPD, B? Reference table provided- c LTPD/ AQLnAQL44.890.05253.5492.613110.946.035563.2063.28626.509.081872.9573.98134.8901.36682.7684.69544.0571.97092.6185.426Remember the equations from earlier.Answer and method:LTPD/AQL=.03/.01=3 - these numbers were provided in the problem, the vendor has a 1% acceptable quality level and the manufacturer considers 3% defectives unacceptable.N(AQL)=3.286 – you have to find the number closest rounded to three fro the previous equation.C=6, from tableN(AQL)= 3.286/.01= 328.6, 329-round upThis means that you would take a random sample of 329 units for the specific lot and reject it if more than 6 units were defective.
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 personnel
25 SummaryAcceptance 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 SummaryThere are many basic terms you need to know to be able to understand acceptance samplingSPC, 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 sampling Purpose of acceptance samplingWhen to use acceptance samplingEquations involvedExerciseNotes 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)“Quality Control in Furniture Manufacturing”:Internet
29 Bibliography“Process Analysis”:Internet“Quality Control”: Internet
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