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10S. Acceptance Sampling. Learning Objectives. Explain the purpose of acceptance sampling Contrast acceptance sampling and process control Compare and contrast single- and multiple-sampling plans Determine the average outgoing quality of inspected lots. Acceptance Sampling. - PowerPoint PPT PresentationTRANSCRIPT
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Copyright © 2014 by McGraw-Hill Education (Asia). All rights reserved.
10S10S
Acceptance Sampling
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10S-2
Learning ObjectivesLearning Objectives
Explain the purpose of acceptance sampling Contrast acceptance sampling and process
control Compare and contrast single- and multiple-
sampling plans Determine the average outgoing quality of
inspected lots
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10S-3
Acceptance SamplingAcceptance Sampling
Acceptance sampling: Form of inspection applied to lots or batches of items before or after a process, to judge conformance with predetermined standards
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10S-4
Acceptance SamplingAcceptance Sampling
Acceptance sampling is most useful when A large number of items must be processed in a
short time The cost consequences of passing defects are
low Destructive testing is required Fatigue or boredom leads to inspection errors
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10S-5
Sampling PlansSampling Plans
Plans that specify lot size, sample size, number of samples, and acceptance/rejection criteria
Types of plans: Single-sampling
Double-sampling
Multiple-sampling
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10S-6
Operating Characteristic CurveOperating Characteristic Curve
Operating Characteristic (OC) Curve: Probability curve that shows the probabilities of accepting lots with various fractions defective.
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10S-7
Typical OC CurveTypical OC Curve
00.10.20.30.40.50.60.70.80.9
1
0 .05 .10 .15 .20 .25
Pro
bab
ilit
y of
acc
epti
ng
lot
Lot quality (fraction defective)
3%
Figure 10S.1
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10S-8
Decision CriteriaDecision Criteria
0
1.00P
rob
abil
ity
of a
ccep
tin
g lo
t
Lot quality (fraction defective)
“Good” “Bad”
Ideal
Not verydiscriminating
Figure 10S.2
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10S-9
Sampling TermsSampling Terms
Acceptance quality level (AQL): the percentage of defects at which consumers are willing to accept lots as “good”
Lot tolerance percent defective (LTPD): the upper limit on the percentage of defects that a consumer is willing to accept
Consumer’s risk: the probability that a lot containing defectives exceeding the LTPD will be accepted
Producer’s risk: the probability that a lot containing the acceptable quality level will be rejected
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10S-10
Consumer’s and Producer’s RiskConsumer’s and Producer’s Risk
00.10.20.30.40.50.60.70.80.9
1
0 .05 .10 .15 .20 .25
Pro
bab
ilit
y of
acc
epti
ng
lot
Lot quality (fraction defective)
= .10
= .10
“Good”
AQL
“Bad”Indifferent
LTPD
Figure 10S.3
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10S-11
QC Curve for n = 10, c = 1QC Curve for n = 10, c = 1Figure 10S.4
00.10.20.30.40.50.60.70.80.9
1
0 .10 .20 .30 .40 .50
Pro
bab
ilit
y of
acc
epta
nce
Fraction defective in lot
.9139
.7361
.5443
.3758
.2440.1493
.0860
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10S-12
Average QualityAverage Quality
Average outgoing quality (AOQ): Average of inspected lots (100%) and uninspected lots
AOQ Pac pN n
N
Pac = Probability of accepting lotp = Fraction defectiveN = Lot sizen = Sample size
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10S-13
Example 10S-2: AOQExample 10S-2: AOQ
0 00.05 0.0460.1 0.074
0.15 0.0820.2 0.075
0.25 0.0610.3 0.045
0.35 0.030.4 0.019
00.010.02
0.030.040.050.06
0.070.080.09
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4
Approximate AOQL = .082
AO
Q (
Fra
ctio
n d
efec
tive
ou
t)
Incoming fraction defective