The Chapter Nine of Operation Management

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Quality Control and Improvement
Chapter outline
9.1 9.2 9.3 9.4 9.5 9.6 9.7 9.8 9.9 Design 'Of quality control systems Process quality control Attribute control Variables control Using control charts Continuous improvement Six Sigma Lean and Six Sigma Quality control and improvement in industry Student Internet exercises Solved problems Discussion questions Problems Selected bibliography

9.10 Key points

I

In the last chapter, we reviewed the long history of quality management. In the early 1900s, inspection shifted from the workers to a formal quality control department. This created tension between the workers and the inspectors, which is still evident in some companies today. But those who use the modern ideas of quality control are able to avoid these tensions and create a positive environment for quality improvement. In 1924, Walter A. Shewhart of the Bell Telephone Labs developed a statisti­ cal quality control chart. Two others from the Bell Labs, H. F. Dodge and H. G. Romig, further developed the theory of statistical quality control in the 1930s. But little was done in industry until World War II in the early 1940s. The war created the demand for huge quantities of military goods from industry. The mil­ itary required that industry adopt the new methods of statistical quality control to help ensure that the goods they ordered would meet government standards. As a result, statistical methods for control of quality were widely adopted by 169

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Part Three

Quality

industry during the early 1940s. In later years, however, these methods were abandoned, only to be rediscovered in the 1980s as a valid way to ensure qual­ ity products and services. The service industries have been reluctant to adopt the methods of statistical quality control. While some service companies have made impressive gains in use of these methods, many others have lagged behind. As a result, there is a tremendous opportunity to use the methods of statistical quality control and improvement in service companies. After World War II, in 1946, the American Society for Quality (ASQ)l was formed. While the initial emphasis was on statistical quality control methods, the focus has now broadened to include customer needs, total quality management, and continuous improvement. The ASQ has also been focusing on spreading the ideas of quality management to service industries. Our emphasis in this chapter will be on process definition, statistical quality control, and continuous improvement. We advance the idea that quality control is the stabilization and maintenance of a process to produce consistent output. This means the process does not vary significantly in its important quality char­ acteristics that are being controlled. Continuous improvement can only occur once the process has been brought under control and stabilized. We also advance the idea- that the organization consists of many interrelated processes that need to be controlled in order to produce quality products and services. It follows that quality control and continuous improvement are highly cross-functional in nature and require the participation and support of the entire organization. The Operations Leader box about implementing statistical process control (SPC) at Milliken & Co. explains how these ideas are being applied in industry.

9.1

DESIGN OF QUALITY CONTROL SYSTEMS
All quality control must start with the process itself. Actually, a process of pro­ duction is composed of many subprocesses, each having its own intermediate product or service. A process can be an individual machine, a group of machines, or any of the many clerical and administrative processes that exist in the organization. Each of these processes has its own internal customers and its own products or services that are produced. The customer is the next process (or processes) that receives the work output. For example, the customer of the design department is the machine shop that makes...
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