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Continuous
ProductionAcceptance Sampling
for Attributes
Continuous Sampling Plan
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T opic Outcome:
At the end of this topic, students will be able to:Identify and use various types of continuous samplingplan.
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T opic Outline:Introduction
CSP-1CSP-2MIL-STD-1235B
CSP-1,
CSP-2,CSP-F,CSP-T,CSP-V
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An Introduction
In cases where production is continuouscontinuous , the formationof inspection lots for lot-by-lot inspection is somewhatartificial.
Continuous sampling plans is used it is not necessary not necessary
to accumulate a lot before making decisionto accumulate a lot before making decision & theproduction organization can deliver product more rapidlyand less storage space is required.
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Prerequisites for application of singlesingle- -level continuouslevel continuous
sampling plansampling plan :
Inspection must involve moving product (product isflowing past an inspection station via conveyor belt or straight-line system)
Rapid 100% inspection must be feasible.
Inspection must be relatively easy.
Product must be homogeneous.
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Basic concept of continuous sampling plan.
100% Inspection
If stated number of units (clearance number, i)Is free from nonconformities
Sampling Inspection
A specific number of nonconformingunits are found
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This concept was first developed by H.H. Dodge (1943)CSP-1, with two additional plans,CSP-2 and CSP-3.
They are categorized as single-level plans.
Multilevel continuous plans G. Licherman and H.Soloman(1955).
MIL-STD-1235 (ORD) superseded MIL-STD-1235A(MU) (1974) MIL-STD-1235B (1981).
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CSP-1The plan operates as follows:
Inspector inspects 100% of the units
When i consecutive units are found free of nonconformities concerned
Inspector inspects is released from100% inspection.
Sampling inspector inspects a fraction, f,of the units.
Sample units are selected in a random
manner.When Sampling Inspector finds 1 of the
nonconformities concerned
START
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Two terms need to be clarified:Clearance number (i) number of conforming units in
100% inspection.Sampling frequency (f) Ratio of units inspected tothe total units passing an inspection station duringperiods of sampling inspection.
f=1/50 1 sampling inspection is made for every 50 units of product.CSP-1 plans are indexed by AOQL.For a particular AOQL, there are different combinations of iand f.Table 10-11
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Q & AOne plan for an AOQL of 0.79 is i=59 and f=1/3.
Interpretation: Sampling inspection of 1 out of every 3products is instigated after 59 consecutive products arefree of nonconformities. Sampling continuous until anonconformity is found, at which time 100% inspection isreinstated.
Along with AOQL of 0.79, there are others combination of iand f.Refers to Table 10-11: as f value decreases (lessprotection), the i value increases.Consideration of choosing i and f values:
Quality protection & amount of production per shift.
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CSP-2It is a modification of CSP-1.
No requirement of 100% inspection when a nonconformitiesis found. Unless a second nonconformities is found in thenext i or fewer sample units.Purpose of this plan : To provide protection against theoccurrence of an isolated nonconformity that would initiate areturn to 100% inspection.It is indexed by AOQL.Having different combinations of i and f (Table 10-14).
AOQL=2.90 I=59,f=1/15Sampling inspection of 1 out of every 15 continues after onenonconformity is found. If a second nonconformity is found inthe next 59 sample units, 100% inspection is invoked. If asecond nonconformity does not occur, sampling continuous.
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M IL-S TD -1235BComposed of 5 different continuous sampling plans.
CSP-1, CSP-2,CSP-F,CSP-T, CSP-VInspection by attributes, classified by severity: critical, major,and minor.Indexed by AOQL and AQL.
This standard has a special provision for criticalnonconformities (CSP-1 and CSP-F).The responsible authority (consumer) can require 100%inspection.Sampling plans are designed by code letter.Factors influencing selection of code letter:
Inspection time per unit of product, production rate, andproximity to other inspection station.
Table 10-15
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M IL-S TD -1235BCSP-1 and CSP-2
CSP-1 and 2 Dodges plans are included into the standard ina different form.
M IL-S TD -1235BCSP-F
It is a single-level continuous sampling procedure thatprovides for alternating sequences of 100% inspection andsampling inspection.The procedure is sama as CSP-1.Indexed by AOQL and by amount of product manufactured ina production interval.
Allow smaller clearance numbers to be used permits thisplan to be applied for short production-run situations or time-consuming inspection operation.
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There are 12 tables in this plans; each table represents adifferent AOQL value.
Example: AOQL=0.33%(Table10-16).
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M IL-S TD -1235BCSP- T
Multilevel continuous sampling procedure that provides for alternate sequences of 100% inspection and samplinginspection.The different between this plan and previous plans: Itprovides for a reduced sampling frequency upon
demonstration of superior product quality.Sampling procedure.
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Inspector inspects is released from 100% inspection.Sampling inspector inspects a fraction, f/4, of the units.
Sample units are selected in a random manner.
If Sampling Inspector finds 1 of
the nonconformities concerned
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Inspector inspects 100%of the units
When i consecutive units arefound free of nonconformities concerned
Inspector inspects is released from 100% inspection.Sampling inspector inspects a fraction, f, of the units.
Sample units are selected in a random manner.
If Sampling Inspector finds 1 of
the nonconformities
concerned
If Sampling Inspector finds i consecutive sample
Units are free of the
nonconformities concerned
Sampling inspector continues inspecting a fraction, f, of the units.Sample units are selected in a random manner.
If Sampling Inspector finds 1 of the nonconformities concerned
Inspector inspects 100% of the units
If Sampling Inspector finds 1 of
the nonconformitiesconcerned
If Sampling Inspector finds 1/3 i consecutive
sampleUnits are free of
the nonconformitiesconcerned
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E nd