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IENG 486 - Lecture 19

IENG 486 - Lecture 19. Introduction to Mil Std 105E. 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

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IENG 486 - Lecture 19

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  1. IENG 486 - Lecture 19 Introduction to Mil Std 105E 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. 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 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 IENG 486 Statistical Quality & Process Control

  5. Switching Rules 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 IENG 486 Statistical Quality & Process Control

  7. Procedure for MIL STD 105E • 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 IENG 486 Statistical Quality & Process Control

  8. 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 IENG 486 Statistical Quality & Process Control

  9. 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: • Normal Inspection • Tightened Inspection • Reduced Inspection 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. IENG 486 Statistical Quality & Process Control

  11. Normal Insp. Level Lot Size = 2000 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. 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. 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. IENG 486 Statistical Quality & Process Control

  15. Questions & Issues IENG 486 Statistical Quality & Process Control

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