4/24/2015ieng 486 statistical quality & process control 1 ieng 486 - lecture 19 introduction to...
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04/18/23 IENG 486 Statistical Quality & Process Control 1
IENG 486 - Lecture 19
Introduction to Mil Std 105E
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Assignment
Reading: Chapter 15
Sections 15.1 – 15.2.4: pp. 632 - 646 Sections 15.4 – 15.4.3: pp. 655 – 663
Homework: Download and complete Last Assign: Acceptance Sampling
Requires MS Word for Nomograph Requires MS Excel for AOQ pp.
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Military Standard 105E(MIL STD 105E)
(ANSI/ASQC Z1.4, ISO 2859)
Most widely used acceptance sampling system for attributes
MIL STD 105E is Acceptance Sampling System collection of sampling schemes
Can be used with single, double or multiple sampling plans We will consider single sampling plans for this course
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Inspection Types
Normal Inspection Used at start of inspection activity
Tightened Inspection Instituted when vendor’s recent quality history has deteriorated Acceptance requirements for lots are more stringent
Reduced Inspection Instituted when vendor’s recent quality history has been exceptionally
good Sample size is usually smaller than under normal inspection
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Switching Rules
- Production Steady- 10 consecutive lots accepted- Approved by responsible authority
NormalReduced Tightened
- Lot rejected- Irregular production- Lot meets neither accept nor reject criteria- Other conditions warrant return to normal inspection
2 out of 5 consecutive lotsrejected
5 consecutivelots accepted
10 consecutive lots remainon tightened inspection
Start
DiscontinueInspection
AND conditions
OR conditions
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Procedure for MIL STD 105E
STEP 1: Choose AQL MIL STD 105E designed around Acceptable Quality Level, AQL
Recall that the Acceptable Quality Level, AQL, is producer's largest acceptable fraction defective in process
Typical AQL range: 0.01% AQL 10% Specified by contract or authority responsible for sampling
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STEP 2: Choose inspection level Level II
Designated as normal
Level I Requires about one-half the amount of inspection as Level II Use when less discrimination needed
Level III Requires about twice as much inspection as Level II Use when more discrimination needed
S-1, S-2, S-3, S-4 Four special inspection levels used if very small samples necessary
Procedure for MIL STD 105E
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STEP 3–Determine lot size, N Lot size most likely dictated by vendor
STEP 4: Find sample size code letter From Table 15-4, p 657 Given lot size, N, and Inspection Level, use table to determine sample
size code letters
STEP 5: Determine appropriate type sampling plan Decide if Single, Double or Multiple sampling plan is to be used
Procedure for MIL STD 105E
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STEP 6: Find Sample Size, n, and Acceptance Level, c Given sample size letter code, use Master Tables: 15-5, 15-6,
and 15-7 on pp.658-660
Find n and c for all three inspection types: Normal Inspection Tightened Inspection Reduced Inspection
Procedure for MIL STD 105E
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Example
Suppose product comes from vendor in lots of size 2000 units. The acceptable quality level is 0.65%. Determine the MIL STD 105E acceptance-sampling system.
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AQL
Plan K
Sample 125 units.
Ac = 2, accept if defects ≤ 2.
Re = 3, reject entire lot if defects ≥ 3.
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AQL
Plan K
Sample 125 units
Ac = 1, accept if defects ≤ 1.
Re = 2, reject entire lot if defects ≥ 2.
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AQL
Plan K
Sample 50 units
Ac = 1, accept if defects ≤ 1.
Re = 3, reject entire lot if defects ≥ 3.