04/18/23 IENG 486 Statistical Quality & Process Control 1

IENG 486 - Lecture 19

Introduction to Mil Std 105E

04/18/23 IENG 486 Statistical Quality & Process Control 2

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.

04/18/23 IENG 486 Statistical Quality & Process Control 3

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

04/18/23 IENG 486 Statistical Quality & Process Control 4

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

04/18/23 IENG 486 Statistical Quality & Process Control 5

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

04/18/23 IENG 486 Statistical Quality & Process Control 6

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

04/18/23 IENG 486 Statistical Quality & Process Control 7

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

04/18/23 IENG 486 Statistical Quality & Process Control 8

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

04/18/23 IENG 486 Statistical Quality & Process Control 9

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

04/18/23 IENG 486 Statistical Quality & Process Control 10

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.

04/18/23 IENG 486 Statistical Quality & Process Control 11

Normal Insp. Level

Lot Size

= 2000

04/18/23 IENG 486 Statistical Quality & Process Control 12

AQL

Plan K

Sample 125 units.

Ac = 2, accept if defects ≤ 2.

Re = 3, reject entire lot if defects ≥ 3.

04/18/23 IENG 486 Statistical Quality & Process Control 13

AQL

Plan K

Sample 125 units

Ac = 1, accept if defects ≤ 1.

Re = 2, reject entire lot if defects ≥ 2.

04/18/23 IENG 486 Statistical Quality & Process Control 14

AQL

Plan K

Sample 50 units

Ac = 1, accept if defects ≤ 1.

Re = 3, reject entire lot if defects ≥ 3.

04/18/23 IENG 486 Statistical Quality & Process Control 15

Questions & Issues