Statistical Quality Control
Quality control deals with the subject matter of assurances and testing for failure of the products or services in the manufacturing processes. An important tool is control chart. Several types of control charts and their uses are explained. In each chart
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Statistical Quality Control
Abstract Quality control deals with the subject matter of assurances and testing for failure of the products or services in the manufacturing processes. An important tool is control chart. Several types of control charts and their uses are explained. In each chart, control lines showing Upper Control Limit (UCL), Centerline (CL), and Lower Control Limit (LCL) are developed and drawn. The sequence of construction of control charts and the limits is provided. The technique for development of “Control Zones” and the interpretations are provided. For examining the “Out of Control” Processes, WECO rules are used. The rules are summarized. Examples are provided in each case. Techniques for calculating tolerance limit, process capability, and sample size based on statistical process control are demonstrated with the help of examples.
Keywords Statistical quality control Manufacturing process Control limits Control zones Out of control WECO rules
18.1
Control charts
History
Manufacturers are having a tough time in the competitive market environment. Users are getting products of higher quality not only in any domestic market but also in the international market. This situation is creating a lot of pressure on the manufacturers not only in maintaining the quality but also improvement of the products over time. Quality control is a branch of engineering. It deals with the subject matter of assurance and testing for failure of the products or services in the design and production. The purpose is to see that the products meet or exceed users’ requirements or expectation. Quality is to be built into the process of production. Quality controls are tools that help the manufacturers identify the quality problems to the production process. Statistical Quality Control (SQC) is a tool that stems from the area of statistics. Our focus is on the quality control in the manufacturing process. Statistical Process Control (SPC) is an alternative term of SQC. © Springer Science+Business Media Singapore 2016 A.Q. Miah, Applied Statistics for Social and Management Sciences, DOI 10.1007/978-981-10-0401-8_18
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Statistical Quality Control
Walter A. Shewart did the pioneering works in the statistical process control in the early 1920s. Later during the World War II W. Edwards Deming applied SPC methods in the US. This led to the successfully improving quality in the manufacture of munitions and other strategically important products. Deming was also instrumental in introducing SPC methods to Japanese industry after war had ended (Wikipedia, free encyclopedia, website, 19 November 2009).
18.2
Areas of Statistical Quality Control
The quality professionals view the statistical quality control as divided into three parts (webiste: http://www.wiley.com/college/sc/reid/pdf 19 November 2009). These are discussed hereafter. (a) Descriptive Statistics: These are used to describe quality characteristics and relationships. These are mean, standard deviation, range, and a measure of the dist
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