Quality Control

Related Terms: ISO 9000; Quality Circles; Total Quality Management (TQM)

Quality control is a methodology employed in manufacturing to prevent defects in manufactured products. Abbreviated as QC, the method has been implemented in a number of ways each of which has its own name and following. Quality control is typically associated with statistical approaches. Quality management has strong philosophical aspects based on the insight that quality is as much the result of management approaches as it is of specific activities. The modern quality movement is a fusion of American know-how originally developed at Bell Laboratories and Japanese enterprise and implementation. The several waves of quality control methods that have swept U.S. manufacturing since the 1950s are almost unthinkable except against the backdrop of Japanese industry achieving a world class reputation and thus producing stimulus. The movement is very closely associated with an American mathematician and physicist, W. Edwards Deming, although Deming was one of two prominent individuals who helped the Japanese forge their approaches to manufacturing; the other was Joseph M. Juran, a Rumanian immigrant to the United States. America's embrace of QC followed its successful application in Japan. Some type of statistical quality control is practiced in connection with most demanding manufacturing processes, but the more "qualitative" (no pun intended) aspects of QC have never been wholeheartedly embraced.

ORIGINS

Modern quality control originated with Walter A. Shewhart, then working at Bell Telephone Laboratories. Shewhart devised a control chart named after him in 1923 and in 1931 published his method in Economic Control of Quality of Manufactured Product. Shewhart's method saw its introduction at Western Electric Company's Hawthorn plant in 1926. Joseph Juran was one of the people trained in the technique. In 1928 he wrote a pamphlet entitled Statistical Methods Applied to Manufacturing Problems which was later incorporated into the AT&T Statistical Quality Control Handbook which is still in print. In 1951 Juran published his very influential Quality Control Handbook.

W. Edwards Deming went to Japan to assist in the preparation of the 1951 Japanese Census. Being an expert on statistical methods, the Japanese Union of Scientists and Engineers (JUSE), having heard of Shewhart's techniques, invited Deming to lecture on statistical quality control. Deming gave a series of lectures in 1950 aimed both at describing SQC and at motivating his audience of executives. He pointed out the linkage between quality, productivity, and potential gains in market share. He found an enthusiastic audience. JUSE also invited Juran to lecture in 1954 with similar success, but by that time Deming had achieved wide prominence in Japan. With the great success enjoyed by SQC in Japan, and through his own abilities as a teacher and promoter of quality control and related management approaches, Deming became the iconic figure in the field, the "father of quality control." JUSE established the, by now, prestigious Deming Prize for quality-related achievements by individuals and organizations.

Japanese improvements in industrial performance eventually aroused interest in the United States in the early 1970s, led by Lockheed Corporation. Quality control then took on a life of its own in this country.

QUALITY CONTROL FUNDAMENTALS

Before the advent of statistical quality control, control was exercised by inspecting the output of manufacturing processes and removing defective items. The modern technique established an upstream method for detecting deviations from specified quality—early detection—used to trigger analysis of causes and then changes to manufacturing procedures.

SQC requires that the producer first identify several characteristics of a product to be measured, typically its dimensions, fit with other parts, smoothness, reflectivity, etc. Carefully conducted test runs are made first; every part is measured and its measurements are recorded. Upper and lower boundaries are set for every measurement from one or repeated test runs, with the idea that any part that falls within these boundaries conforms to the product's quality standard. The center line between the boundaries is then used as a base-line for measurement. Once this quality standard is set, production can begin.

The quality control activity during production consists of taking samples from the run continuously, taking measurements on the samples immediately, and then plotting them rapidly on a Shewhart Chart. During production, measurements typically fall close to the center line, some above it, some below it, some on the center line. A certain amount of divergence is natural and cannot be avoided. So long as the plotted points are within the accepted boundaries, the product conforms to the quality standard. But SQC demands that if the plotted points begin to show a trend away from the center, rather than clustering randomly around it—or, worse yet, begin to fall outside the boundaries in either direction—then production must stop. The incoming raw material, the production machinery, and other inputs, such as lubricants, must next be examined to discover why results are trending in the wrong direction or fall outside the acceptable range.

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