Component replacement policies for reworkable assemblies

In an assembly process, test operations are often introduced to ensure product quality. After having been rejected by a test operation due to a bad component, a product may be sent to a rework station for component replacement. Some products, however, may have two or more identical components for better reliability or higher capacity. For example, a rack holds a number of identical magnetic storage devices or a computer has multiple processors. Under this situation, different replacement policies may be considered. Bad components can be replaced by either untested ones or known good ones. In the latter case, the assembly line must keep an inventory of good components. Contingent on the condition of replacement components and the method of inventory replenishment, three different policies are identified. Under the first policy, all bad components will be replaced by untested ones, and therefore, the product must be retested. The second policy will replace all bad components with good ones if available. In this case, no additional test is required. However, if the number of bad components is greater than the inventory level, all components (both good and bad) will be replaced by untested ones. Then the product is sent for retest and good components are placed in inventory. Policy III always replaces the bad ones with good ones. It is assumed that all (good) replacement components come from an independent source. If there are not enough good components for replacement, the product must wait. This paper investigates all three policies, using stochastic models. The performance of a policy is dependent on yield, test time, product configuration, and production demand. A good choice should consider the tradeoff between production lead time and inventory cycle. Numerical results, derived from a real-life case, are presented.