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Copyright 2006 John Wiley & Sons, Inc.Beni Asllani
University of Tennessee at Chattanooga
Operations Management - 5thEdition
Chapter 4 Supplement
Roberta Russell & Bernard W. Taylor, III
Acceptance Sampling
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Lecture Outline
Single-Sample Attribute Plan
Operating Characteristic Curve
Developing a Sampling Plan with Excel
Average Outgoing Quality
Double - and Multiple-Sampling Plans
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Acceptance Sampling
Accepting or rejecting a productionlot based on the number of defects
in a sample Not consistent with TQM or Zero
Defects philosophy producer and customer agree on the
number of acceptable defects a means of identifying not preventing
poor quality percent of defective parts versus PPM
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SingleSample
Attribute Plan
Single sampling plan
N= lot size
n= sample size (random)
c= acceptance number
d= number of defective items in sample
If d c, accept lot; else reject
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Producers and
Consumers Risk AQL or acceptable quality level
proportion defect the customer will accept a
given lot LTPD or lot tolerance percent defective
limit on the number of defectives thecustomer will accept
or producers risk probability of rejecting a good lot or consumers risk
probability of accepting a bad lot
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Producers and
Consumers Risk (cont.)
Sampling Errors
GoodLot
Bad
Lot
Accept Reject
No Error Type I ErrorProducer Risk
Type II Error
Consumers RiskNo Error
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Operating Characteristic
(OC) Curve shows probability of accepting lots of
different quality levels for a specific
sampling plan assists management to discriminate
between good and bad lots
exact shape and location of the curve is
defined by the sample size (n) andacceptance level (c) for the samplingplan
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OC Curve (cont.)
OC curve forn
andc
Proportion defectiveAQL LTPD
Probabilityofaccep
tance,
Pa
= 0.10
= 0.051.00
0.80
0.60
0.40
0.20
|0.02
|
0.04
|
0.06
|
0.08
|
0.10
|
0.12
|
0.14
|
0.16
|
0.18
|
0.20
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Developing a Sampling Plan
with Excel
ABC Company produces mugs inlots of 10,000. Performancemeasures for quality of mugs sentto stores call for a producers riskof 0.05 with an AQL of 1%defective and a consumers risk of0.10 with a LTPD of 5% defective.What size sample and whatacceptance number should ABCuse to achieve performancemeasures called for in the sampling
plan?
N = 10,000 n = ?
= 0.05 c = ? = 0.10
AQL = 1%
LTPD = 5%
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Sampling Plan and OC Curve
Input
Use Poisson
distribution functionto calculate PAs
Use chart wizard to
graph OC
Use Solver to find
values forn and c
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Average Outgoing
Quality (AOQ)
Expected number of defective
items that will pass on tocustomer with a sampling plan
Average outgoing quality limit
(AOQL) maximum point on the curve
worst level of outgoing quality
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AOQ Curve
AOQL 1.39%
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Double Sampling Plans
Take small initial sample If # defective < lower limit, accept
If # defective > upper limit, reject If # defective between limits, take second
sample
Accept or reject based on 2 samples
Less costly than single-sampling plans
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Multiple Sampling Plans
Uses smaller sample sizes
Take initial sample If # defective < lower limit, accept
If # defective > upper limit, reject
If # defective between limits, resample
Continue sampling until accept or rejectlot based on all sample data
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Copyright 2006 John Wiley & Sons, Inc.
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