Operator Scheduling Under the Lean Manufacturing Principles in Over-Size Product Manufacturing Facilities

Abstract

This paper discusses the scheduling of operators on work elements in manufacturing environments where lean principles are adopted. Our experience with the industry revealed that the practice of lean manufacturing in organizations that manufacture oversized products, such as buses, aircrafts and locomotives differs from other organizations. The most obvious two differences are: the longer Takt times (average time between demands); and the fact that the work-stations are mainly placed in various locations inside/around the product and the operators can carryout activities in parallel in these work stations. Since the demand for the large products is considerably low, Takt time (average time between demands) is usually in the orders of hours. As a result, a product undergoes several modifications during a Takt time. The assembly process of the oversized products involves coordinated work of a number of tasks. While some of the tasks have strict precedence relationship with other activities, the others can be performed simultaneously. In this context, our problem is to assign N different operators to M different tasks with two alternative objectives; minimizing the discrepancies between the operators’ workloads and minimizing the number of operators used. The main constraint is to complete all the tasks within a given Takt time. We modeled the problem under both identical operator and non-identical operator assumptions. Various sensitivity analyses are discussed and the several examples are provided.