The Certified Quality Process Handbook Chapter 18: Sampling Presented by Dr. Joan Burtner Certified Quality Engineer Associate Professor and Chair Dept. of Industrial Engineering and Industrial Management Mercer University

Introduction to Acceptance Sampling Acceptance Sampling Definition: the process of inspecting a portion of the product in a lot for the purpose of making a decision regarding classification of the entire lot as either conforming or nonconforming to quality specifications. Acceptance Sampling Advantages Lower inspection costs because fewer units are inspected Less time required (when compared to 100% inspection) Less risk of damage to the product due to reduced handling Increased emphasis on the supplier’s responsibility for quality IDM355 Fall 2015 Dr. Joan Burtner, Assoc. Prof. and Chair, Dept. of Industrial Engineering

Acceptance Sampling by Attributes Purpose Protection from accepting lots from a continuing process whose average quality deteriorates beyond an acceptable quality level Protection against isolated lots that may have levels of nonconformances greater than can be considered acceptable ANSI/ASQ Z1.4-2003 is the most widely used standard Acceptable Quality Level (AQL) – the maximum percent or fraction of nonconforming units in a lot or batch that, for the purposes of acceptance sampling, can be considered satisfactory as a process average Lot Tolerance Percent Defective (LTPD) – the poorest quality in an individual lot that should be accepted IDM355 Fall 2015 Dr. Joan Burtner, Assoc. Prof. and Chair, Dept. of Industrial Engineering

Producer’s and Consumer’s Risks Producer’s risk (alpha) The probability of rejecting a lot that is within the acceptable quality level The producer faces a possibility of having a lot rejected even though the lot has met the requirements set by the AQL Consumer’s risk (beta) The probability of acceptance for a designated numerical value of relatively poor submitted quality The probability of accepting a lot that has a quality level equal to the LTPD IDM355 Fall 2015 Dr. Joan Burtner, Assoc. Prof. and Chair, Dept. of Industrial Engineering

Single Sampling Plan Parameters A single sampling plan is described by the lot size, the sample size (n), and the acceptance number(c). Operating characteristic (OC) curves Graphical representation of the relationship of the probability of accepting a lot vs. the percent nonconforming Figure 18.3 – acceptance number c is held constant Figure 18.4 – sample size n is held constant IDM355 Fall 2015 Dr. Joan Burtner, Assoc. Prof. and Chair, Dept. of Industrial Engineering

Types of Sampling Plans Single The decision to accept or reject the lot is based on the results of the inspection of a single sample Reject the lot if the number of defective items in the sample is greater than the acceptance number (c) Double Take a sample of size n1. If the number of defective items is less than or equal to c1, accept the lot. If the number of defective items in the sample is greater than r1, reject the lot. Otherwise, take a second sample of size n2. If the number of combined defectives is less than or equal to c2, accept the lot. Otherwise reject the lot. Multiple (extension of double sampling for up to seven samples) IDM355 Fall 2015 Dr. Joan Burtner, Assoc. Prof. and Chair, Dept. of Industrial Engineering