acceptance sampling prepared by anthony lizza penn state university

Acceptance SamplingAcceptance Sampling

Prepared byPrepared by

Anthony LizzaAnthony Lizza

Penn State UniversityPenn State University

What will be covered?What will be covered?

• What is acceptance sampling?What is acceptance sampling?• How/When would you use it in your How/When would you use it in your

organization?organization?• Acceptance sampling explained.Acceptance sampling explained.• How acceptance sampling works.How acceptance sampling works.• An exercise.An exercise.• SummarySummary

What is acceptance What is acceptance sampling?sampling?

• Acceptance SamplingAcceptance Sampling– Statistical quality control technique, Statistical quality control technique,

where a random sample is taken from where a random sample is taken from a lot, and upon the results of the a lot, and upon the results of the sample taken the lot will either be sample taken the lot will either be rejected or accepted.rejected or accepted.


• Accept LotAccept Lot– Ready for customersReady for customers

• Reject LotReject Lot– Not suitable for customersNot suitable for customers

• Statistical Process Control(SPC)Statistical Process Control(SPC)– Sample and determine if in Sample and determine if in

acceptable limitsacceptable limits


• PurposesPurposes– Determine the quality level of an Determine the quality level of an

incoming shipment or, at the end incoming shipment or, at the end productionproduction

– Ensure that the quality level is within Ensure that the quality level is within the level that has been predeterminedthe level that has been predetermined


• Can be either 100% inspection, or Can be either 100% inspection, or a few items of a lot.a few items of a lot.

• Complete inspectionComplete inspection– Inspecting each item produced to see Inspecting each item produced to see

if each item meets the level desiredif each item meets the level desired– Used when defective items would be Used when defective items would be

very detrimental in some wayvery detrimental in some way

Acceptance Sampling Acceptance Sampling methodmethod

A C C E P T A N C E S A M P L IN G

A C C E P T L O T

R E T U R N L O T T O S U P P L IE R 1 0 0 % IN S P E C T IO N

D E C IS IO N

R E JE C T L O T S A M P LE A G A IN

D E C IS IO N

IN S P E C T S A M P LET yp e tit le h e re

T A K E S A M P LE


• Problems with 100% inspectionProblems with 100% inspection– Very expensiveVery expensive– When product must be destroyed to When product must be destroyed to

testtest– Inspection must be very tedious so Inspection must be very tedious so

defective items do not slip through defective items do not slip through inspectioninspection

How/When would you use How/When would you use it?it?

• Acceptance sampling advantagesAcceptance sampling advantages– Less handling damagesLess handling damages– Fewer inspectors to put on payrollFewer inspectors to put on payroll– 100% inspection costs are to high100% inspection costs are to high– 100% testing would take to long100% testing would take to long


• Acceptance sampling Acceptance sampling disadvantagesdisadvantages– Risk included in chance of bad lot Risk included in chance of bad lot

“acceptance” and good lot “rejection”“acceptance” and good lot “rejection”– Sample taken provides less Sample taken provides less

information than 100% inspectioninformation than 100% inspection


• Between your organization and Between your organization and outside worldoutside world

• Samples taken run through “filter,” Samples taken run through “filter,” either passing or rejecting iteither passing or rejecting it– Also filter from suppliers to youAlso filter from suppliers to you

How/When you would use How/When you would use it?it?

• When products in use could be When products in use could be damaged easilydamaged 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

How/When you would use How/When you would use it?it?

• Determine how many units, n, to Determine how many units, n, to sample from an lotsample from an lot

• Determine maximum number of Determine maximum number of defective items, c, that can be defective items, c, that can be found before the lot is rejectedfound before the lot is rejected

Acceptance sampling Acceptance sampling explainedexplained

• Acceptable Quality levels(AQL)Acceptable Quality levels(AQL)– Number of defect percentage allowed Number of defect percentage allowed

in a lot which can still be considered in a lot which can still be considered accepted(Type I error)accepted(Type I error)

• Lot Tolerance Percent Lot Tolerance Percent Defective(LTPD)Defective(LTPD)– Amount of defects that will come with Amount of defects that will come with

a lot of goods(Type II error)a lot of goods(Type II error)


• Sampling PlanSampling Plan– Forms after n and c values have been Forms after n and c values have been

foundfound

• Producers riskProducers risk– Risk associated with a lot of Risk associated with a lot of

acceptable quality rejectedacceptable quality rejected


• Consumers riskConsumers risk– Receive shipment, assume good Receive shipment, assume good

quality, actually bad qualityquality, actually bad quality

• AlphaAlpha– Type I error(producers risk)Type I error(producers risk)

• BetaBeta– Type II error(consumers risk)Type II error(consumers risk)


• NN– Sample size taken for your sampling Sample size taken for your sampling

planplan

• CC– Where rejections would occur when Where rejections would occur when

defects exceeded this percentdefects exceeded this percent


• Operating characteristics Operating characteristics curve(OC)curve(OC)– A graph, displaying standards at A graph, displaying standards at

which shipments would be acceptedwhich shipments would be accepted• FirstFirst

– Determine AQL, a, LTPD, b, Determine AQL, a, LTPD, b, – Take LTPD/AQL, this gives you the Take LTPD/AQL, this gives you the

n(AQL)n(AQL)


• Reference n(AQL) in the tableReference n(AQL) in the table– C will be given as well when referencing the C will be given as well when referencing the

tabletable

• NextNext– N(AQL/AQL)=n-sample sizeN(AQL/AQL)=n-sample size– C= reject if more percent defects moreC= reject if more percent defects more

• The equations can be tricky but the The equations can be tricky but the exercise later will helpexercise later will help

How acceptance sampling How acceptance sampling worksworks

• Two classifications of acceptance Two classifications of acceptance plansplans– Attributes(“go no-go”)Attributes(“go no-go”)– VariablesVariables


• Attributes(“go no-go”)Attributes(“go no-go”)– Defectives-product acceptability Defectives-product acceptability

across rangeacross range– Defects-number of defects per unitDefects-number of defects per unit

• Variable(continuous)Variable(continuous)– Usually measured by mean and Usually measured by mean and

standard deviationstandard deviation


• RememberRemember– You are not measuring the quality of You are not measuring the quality of

the lot, but, you are to sentence the the lot, but, you are to sentence the lot to either reject or accept itlot to either reject or accept it

An Exercise An Exercise

• Determine the Determine the – AQL, a, LTPD, B?AQL, a, LTPD, B?– Reference table provided-Reference table provided-

cc LTPD/ LTPD/ AQLAQL

nAQLnAQL cc LTPD/ LTPD/ AQLAQL

nAQLnAQL

00 44.89044.890 .052.052 55 3.5493.549 2.6132.613

11 10.94610.946 .0355.0355 66 3.2063.206 3.2863.286

22 6.5096.509 .0818.0818 77 2.9572.957 3.9813.981

33 4.8904.890 1.3661.366 88 2.7682.768 4.6954.695

44 4.0574.057 1.9701.970 99 2.6182.618 5.4265.426

An Exercise cont.An Exercise cont.

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

SummarySummary

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

SummarySummary

• There are many basic terms you need to There are many basic terms you need to know to be able to understand know to be able to understand acceptance samplingacceptance sampling– SPC, Accepts Lot, Reject Lot, Complete SPC, Accepts Lot, Reject Lot, Complete

Inspection, AQL, LTPD, Sampling Plans, Inspection, AQL, LTPD, Sampling Plans, Producers Risk, Consumers Risk, Alpha, Producers Risk, Consumers Risk, Alpha, Beta, Defect, Defectives, Attributes, Beta, Defect, Defectives, Attributes, Variables.Variables.

SummarySummary

• Advantages/Disadvantages of Advantages/Disadvantages of acceptance samplingacceptance 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 Notes pages have many beneficial hints and help better relate the material, the answer help better relate the material, the answer to the exercise is also located on a the notes to the exercise is also located on a the notes page of the exercise.page of the exercise.

BibliographyBibliography

• (Foster, S.Thomas: “Managing (Foster, S.Thomas: “Managing Quality-An Integrative Quality-An Integrative Approach:pgs. 263-274:copyright Approach:pgs. 263-274:copyright 2001)2001)

• ““Quality Control in Furniture Quality Control in Furniture Manufacturing”:Internet Manufacturing”:Internet http://www.mtc.com.my/publicationhttp://www.mtc.com.my/publications/library/quality/qc40.htns/library/quality/qc40.htn

BibliographyBibliography

• ““Process Analysis”:Internet Process Analysis”:Internet http://www.statsofinc.com/textbookhttp://www.statsofinc.com/textbook/stprocan.html/stprocan.html

• ““Quality Control”: Internet Quality Control”: Internet http://www.ms.ic.ac.uk/jeb/or/qconthttp://www.ms.ic.ac.uk/jeb/or/qcontrol.htmlrol.html

acceptance sampling prepared by anthony lizza penn state university

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