13 sampling tech 5

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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MIL-STD-1235 (ORD) superseded MIL-STD-1235A(MU) (1974) MIL-STD-1235B (1981).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.


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


the nonconformitiesconcerned

If Sampling Inspector finds 1/3 i consecutive

sampleUnits are free of

the nonconformitiesconcerned


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E nd

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