NOTES 9 - Acceptance Sampling cbu main c

Acceptance Sampling
Acceptance Sampling

Lecture Outline
Lecture Outline
 Single-Sample Attribute Plan
Single-Sample Attribute Plan
 Operating Characteristic Curve
Operating Characteristic Curve
 Developing a Sampling Plan with Excel
Developing a Sampling Plan with Excel
 Average Outgoing Quality
Average Outgoing Quality
 Double - and Multiple-Sampling Plans
Double - and Multiple-Sampling Plans

Acceptance Sampling
Acceptance Sampling
 Accepting or rejecting a production
Accepting or rejecting a production
lot based on the number of defects
lot based on the number of defects
in a sample
in a sample
 Not consistent with TQM or Zero
Not consistent with TQM or Zero
Defects philosophy
Defects philosophy

producer and customer agree on the
producer and customer agree on the
number of acceptable defects
number of acceptable defects

a means of identifying not preventing
a means of identifying not preventing
poor quality
poor quality

percent of defective parts versus PPM
percent of defective parts versus PPM

Single–Sample
Single–Sample
Attribute Plan
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

Producer’s and
Producer’s and
Consumer’s Risk
Consumer’s Risk
 AQL or acceptable quality level
AQL or acceptable quality level

proportion defect the customer will accept a
proportion defect the customer will accept a
given lot
given lot
 LTPD or lot tolerance percent defective
LTPD or lot tolerance percent defective

limit on the number of defectives the
limit on the number of defectives the
customer will accept
customer will accept
 
 or producer’s risk
or producer’s risk

probability of rejecting a good lot
probability of rejecting a good lot
 β
β or consumer’s risk
or consumer’s risk

probability of accepting a bad lot
probability of accepting a bad lot

Producer’s and
Producer’s and
Consumer’s Risk (cont.)
Consumer’s Risk (cont.)
Sampling Errors
Good
Lot
Good
Lot
Bad
Lot
Bad
Lot
Accept
Accept Reject
Reject
No Error
Type I Error
Producer’ Risk
Type II Error
Consumer’s Risk
No Error

Operating Characteristic
Operating Characteristic
(OC) Curve
(OC) Curve
 shows probability of accepting lots of
shows probability of accepting lots of
different quality levels for a specific
different quality levels for a specific
sampling plan
sampling plan
 assists management to discriminate
assists management to discriminate
between good and bad lots
between good and bad lots
 exact shape and location of the curve is
exact shape and location of the curve is
defined by the sample size (
defined by the sample size (n
n) and
) and
acceptance level (
acceptance level (c
c) for the sampling
) for the sampling
plan
plan

OC Curve (cont.)
OC Curve (cont.)
OC curve for
OC curve for n
n and
and c
c
Proportion defective
Proportion defective
AQL
AQL LTPD
LTPD
Probability
of
acceptance,
Probability
of
acceptance,
Pa
Pa

 = 0.10
= 0.10

 = 0.05
= 0.05
1.00
1.00 –
0.80
0.80 –
0.60
0.60 –
0.40
0.40 –
0.20
0.20 –
–
|
0.02
0.02
|
0.04
0.04
|
0.06
0.06
|
0.08
0.08
|
0.10
0.10
|
0.12
0.12
|
0.14
0.14
|
0.16
0.16
|
0.18
0.18
|
0.20
0.20

Developing a Sampling Plan
Developing a Sampling Plan
with Excel
with Excel
ABC Company produces mugs in
lots of 10,000. Performance
measures for quality of mugs sent
to stores call for a producer’s risk
of 0.05 with an AQL of 1%
defective and a consumer’s risk of
0.10 with a LTPD of 5% defective.
What size sample and what
acceptance number should ABC
use to achieve performance
measures called for in the
sampling plan?
N = 10,000 n = ?
α = 0.05 c = ?
β = 0.10
AQL = 1%
LTPD = 5%

Sampling Plan and OC Curve
Sampling Plan and OC Curve
Input
Use Poisson
distribution function
to calculate PAs
Use chart wizard to
graph OC
Use Solver to find
values for n and c

Average Outgoing
Average Outgoing
Quality (AOQ)
Quality (AOQ)
 Expected number of defective
Expected number of defective
items that will pass on to
items that will pass on to
customer with a sampling plan
customer with a sampling plan
 Average outgoing quality limit
Average outgoing quality limit
(AOQL)
(AOQL)

maximum point on the curve
maximum point on the curve

worst level of outgoing quality
worst level of outgoing quality

AOQ Curve
AOQ Curve
AOQL 1.39%

Double Sampling Plans
Double Sampling Plans
 Take small initial sample
Take small initial sample

If # defective < lower limit, accept

If # defective > upper limit, reject

If # defective between limits, take second
If # defective between limits, take second
sample
sample
 Accept or reject based on 2 samples
Accept or reject based on 2 samples
 Less costly than single-sampling plans
Less costly than single-sampling plans

Multiple Sampling Plans
Multiple Sampling Plans
 Uses smaller sample sizes
Uses smaller sample sizes
 Take initial sample
Take initial sample



If # defective between limits, resample
If # defective between limits, resample
 Continue sampling until accept or reject
Continue sampling until accept or reject
lot based on all sample data
lot based on all sample data

NOTES 9 - Acceptance Sampling cbu main c

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NOTES 9 - Acceptance Sampling cbu main c