In this paper, a technique fbr evaluating productivity in a flow shop based on the in-process inverrtories generated by an unbalance wotkload is proposed. Using this teehnique, an effieient imprQvement strategy can be obtained. There are two kinds of waiting in the production precess: the first one is "machining wait", which means the products in the previous process have to, wait because the following machining process is busy; and the other one is C'arrival wait" , which means the werkers

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... t the arrival ofthe product from the previous process. In-process inventory is generated by "machining wait". In most production systems, these two kinds of waiting phenornena have fuzzy characteristics since they are indefinitely or intentionally determined depending on the workers' situations. Considering that the employment of a push system determines these waiting phenomena uniquely, we propose an efficient production process improvement technique. A feature of our technique is that stagnation time in the in-process inventories is introduced as an index to evaluate the efficiency of the production precess. The proposed technique is achieved as fo11ows. FirstlM the proposed technique calculates the stagnation time at each process. Secondls the technique determines the processes that should be improved by priority. Once the improvement ofa process is achieved, the same technique is applied to fuid the next process to be improved. An efficieni production system can be designed by repeating these procedures. In order to apply this technique effectively, a prograrn that calculates the stagnation time of the fbcused production process was developed. This pregram was used at several medium and small companies in Nagasaki and the productivity was remarkably improved.