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Job shops are the most numerous manufacturing firms as compared to continuous flow (production∕assembly line) manufacturing. Roughly 75% of all manufacturing occurs in batch sizes of less than 10,000 pieces, and probably two-thirds of that population have batch (lot) sizes of less than 1,000. The basic premise of quality control including statistical quality control applies to all types of factories. However, as lot sizes decrease it becomes ever more difficult to use statistical process control. In many factories, since every item in extremis may be distinctly different from the one before or the one following it, typical quality control statistical techniques often fail to achieve the goal of ensuring that the products meet the design objectives. Therefore, individualized process control is essential for success. In job shop process control, analytical evaluations are made for adequacy of design, producibility, shop performance, minimization of costs, and so forth. A fully implemented process control system affects almost all phases of engineering and manufacturing operations and is a vital link in the design engineering∕manufacturing interface.
This chapter explains how a successful job shop process control system works. Since job shop process control includes most continuous process quality control procedures, those will also be included. We will consider the dynamic nature of the system, how manufacturing losses are controlled, how goals are measured, how statistical concepts can be utilized, how Total Quality Management (TQM) and continuous improvement concepts such as six sigma are utilized, and, most important, why it works.