IENG 486 - Lecture 19 Introduction to Mil Std 105E 4/13/2015 IENG 486 Statistical Quality & Process Control 1 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 4/13/2015 Requires MS Word for Nomograph Requires MS Excel for AOQ pp. IENG 486 Statistical Quality & Process Control 2 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 4/13/2015 IENG 486 Statistical Quality & Process Control 3 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 4/13/2015 IENG 486 Statistical Quality & Process Control 4 Switching Rules Start AND conditions - Production Steady - 10 consecutive lots accepted - Approved by responsible authority Reduced 2 out of 5 consecutive lots rejected Normal Tightened OR conditions - Lot rejected - Irregular production - Lot meets neither accept nor reject criteria - Other conditions warrant return to normal inspection 5 consecutive lots accepted 10 consecutive lots remain on tightened inspection Discontinue Inspection 4/13/2015 IENG 486 Statistical Quality & Process Control 5 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: 4/13/2015 0.01% AQL 10% Specified by contract or authority responsible for sampling IENG 486 Statistical Quality & Process Control 6 Procedure for MIL STD 105E STEP 2: Choose inspection level Level II Level I Requires about one-half the amount of inspection as Level II Use when less discrimination needed Level III Designated as normal Requires about twice as much inspection as Level II Use when more discrimination needed S-1, S-2, S-3, S-4 4/13/2015 Four special inspection levels used if very small samples necessary IENG 486 Statistical Quality & Process Control 7 Procedure for MIL STD 105E 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 4/13/2015 IENG 486 Statistical Quality & Process Control 8 Procedure for MIL STD 105E 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: 4/13/2015 Normal Inspection Tightened Inspection Reduced Inspection IENG 486 Statistical Quality & Process Control 9 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. 4/13/2015 IENG 486 Statistical Quality & Process Control 10 Normal Insp. Level Lot Size = 2000 4/13/2015 IENG 486 Statistical Quality & Process Control 11 AQL Plan K Sample 125 units. Ac = 2, accept if defects ≤ 2. Re = 3, reject entire lot if defects ≥ 3. 4/13/2015 IENG 486 Statistical Quality & Process Control 12 AQL Plan K Sample 125 units Ac = 1, accept if defects ≤ 1. Re = 2, reject entire lot if defects ≥ 2. 4/13/2015 IENG 486 Statistical Quality & Process Control 13 AQL Plan K Sample 50 units Ac = 1, accept if defects ≤ 1. Re = 3, reject entire lot if defects ≥ 3. 4/13/2015 IENG 486 Statistical Quality & Process Control 14 Questions & Issues 4/13/2015 IENG 486 Statistical Quality & Process Control 15