Introduction of Statistical Quality Control

From the moment we get up until the time we go to bed, we utilize a variety of products and services. For example, we use many things like as toothpaste, soap, detergent, clothing, food, gas stove, automobile, phone, computer, TV, electric bulb, and so on, as well as various services such as water supply, power, transportation, health care, education, and so on. Introduction of Statistical Quality Control

When we utilize these items and services, we all hope that they meet certain criteria. We say a product or service is of good quality if it meets the requirements required for proper usage. It is deemed to be of low quality if it does not meet the criteria.

In the face of ever-increasing market rivalry, the manufacturer’s or producer’s primary goal is to accomplish quality assurance in production and service organizations so that his/her product/service can compete in the market. To attain this goal, many statistical techniques for regulating product quality in relation to specified requirements or standards have been created. Introduction of Statistical Quality Control

Statistical Quality Control (SQC) is a strategy for regulating product quality versus specifications using statistical techniques.

You will learn about the ideas and numerous features of SQC in this unit. In Sec. 1.2, we define the term quality and discuss dimensions of quality, quality control and historical review of quality control. In Sec. 1.3, we describe various aspects of SQC, e.g., the elements and techniques of SQC, statistical process control and product control. We also discuss the causes of variation, which may be due to chance or could be assigned to some factors in the production process in Sec. 1.4. In Sec. 1.5, we introduce the control chart – a tool used in statistical quality control to indicate whether a process is under control or out-of-control. We explain the concept of 3σ limits, different patterns of the control chart and advantages and limitations of SQC in Secs. 1.5 to 1.8. In the next unit, you will study the control charts for variables.

1.1 Objectives

After studying this unit, you should be able to:

• explain the concepts of quality, quality control and statistical quality control (SQC);
• describe the need for statistical quality control;
• distinguish between causes of variation (chance causes and assignable causes) in the production process;
• describe the techniques of SQC;
• define process control and product control;
• explain the concept of control chart, the principle underlying 3σ limits and various control chart patterns; and

discuss advantages and limitations of SQC.