Statistical Quality Control

Abstract

Statistical Quality Control is the application of statistical methods to manufacturing and industrial problems. These methods, which were first employed less than thirty years ago, are widely used today. The first assembly operation was performed many thousands of years ago when some stone age man fitted a stone to a wooden handle by means of some crude rope to make the first axe. Manufacturing in ancient times and up until less than two centuries ago was on a custom basis. One could not drive in at the corner service station to get a new wheel if he broke one on his wagon. A new one would have to be made and fitted in place. One of the biggest improvements in manufacturing practice was made just before 1800, when Eli Whitney made some parts for guns which were interchangeable. It was the comrrion thing during this period for one man to make his own tools, make the parts, inspect them, and then assemble them. Today, workmen usually performi very specialized functions. One of these specialized functions in a manufacturing plant is Quality Control. The first use of statistical methods to improve a manufacturing process was in the early 1920's. This was done by Dr. Walter Shewhart at the Bell Telephone Company. Since that time, the use of these techniques has spread to nearly all of the large manufacturing companies and many of the small ones. This growth was rather slow at first, but due primarily to the stimulus of the last war, these methods have become very widely used in recent years. Several companies report savings in the millions due to use of quality control techniques. Statistics is a field whichi presents many opportunities. Quality Control presents splendid opportunities for young men who lhave some knowledge of statistics and also some knowledge of engineering or manufacturing processes. There are also trenmendous possibilities for the application of these techniques to fields other than the manufacture of machine parts. Quality Control has been applied to chemical processes, packaging of food an]i other materials. fhere is an answer for a mathemratics teacher wh1o may be asked the question, What can I do with mathematics other than teach? The field of Quality Control can be divided into three branches: process control, acceptance sampling, and research and development. A brief description of some 6f the methods used will be given here. Process control concerns a manufacturer's inspection of his own product in order to determine: 1. what to do with the parts which have been made, (accept, rework, or reject) 2. what to do about the manufacturing process, (change it or not). This control is usually accomplished by statistical tools called control