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An environment of intensified competition has resulted from the advancement of foreign competitors in the past twenty years. In response to increased competitive pressures, some American firms have turned to different manufacturing systems to improve their competitive postures. Two notable manufacturing systems of recent years are Just-in-Time (JIT) and the theory of constraints (TOC). Due, in part, to the obvious successes of the Japanese use of it, JIT has become the better publicized and researched of the two manufacturing systems.
If a firm can learn how to maximize its throughput, it can potentially compete more effectively in the marketplace. However, when a firm makes a commitment to a production technology or philosophy, it must realize that no one system is best in all situations. In this study, a computer simulation was used to compare TOC, JIT, and traditional manufacturing systems.
JUST-IN-TIME AND THEORY OF CONSTRAINTS COMPARED
There are two major areas in which the JIT and TOC approaches differ. First, JIT advocates a balanced plant. That is, each resource has the same output capability in relation to the plant's needs. On the other hand, TOC indicates that it is acceptable to have an unbalanced plant. Here, one resource may have less output capability than other resources. This is the constraint resource. Dependency is broken by placing a buffer only in front of the constraint. Additional inventory is considered to be wasteful since it will increase lead time and work-in-process (WIP) inventory. JIT eliminates dependence between workstations by working to eliminate random problems and processing time variations at each workstation. TOC only seeks to reduce variation at the constraining resource, since it is considered wasteful to expend energy reducing variation at other workstations.
A second major difference is that TOC uses different-sized transfer and process batches. In contrast, JIT uses transfer and process batches that are equal. This makes TOC more suitable for batch environments than JIT and means that TOC has a wider range of applicability than does JIT [4].
While the TOC and JIT philosophies differ in certain details, they are similar in a number of other aspects. For example, each system shares a common interest in the process of continuous improvement. Furthermore, each system emphasizes quality and reduced WIP inventories.
Both JIT...