Six Sigma Based Control Chart for Fraction Defectives

Abstract A control chart is a statistical device used for the study and control of a repetitive process. W. A. Shewart (1931) of Bell Telephone Laboratories suggested control charts based on three sigma limits. Now the companies in developed and developing countries started applying Six Sigma initiatives in their manufacturing process, which results in a lesser number of defects. The companies practicing Six Sigma initiatives are expected to produce 3.4 or less number of defects per million opportunities, a concept suggested by Motorola (1980). If the companies practicing Six Sigma initiatives use the control limits suggested by Shewhart, then no point falls outside the control limits because of the improvement in the quality of the process. In this paper, an attempt is made to construct a Six Sigma based control chart for fraction defectives specially designed for the companies applying Six Sigma initiatives in their organization. Suitable tables are also constructed and presented for engineers to take quick decisions.