Balancing mixed model assembly line with capacity adjustment to satisfy uncertain demands

In a mixed model assembly line, the demands for products are usually uncertain. When the actual demands are larger than expectation, capacity adjustments should be made. The difficulty and cost of these adjustments rely heavily on the initial balancing. To the best of knowledge, the convenience of future adjustment and corresponding cost have not been considered in literature. This paper investigates the line balancing problem in a mixed model assembly system which faces uncertain demand and makes use of overtime work to meet unexpected demands. The objective is to minimize the expected labor cost, including cost for normal operation and overtime work. A mathematical model is built and a method is proposed to estimate the cost lower bound, based on which a single pass heuristic is designed. The numerical experiment shows that the algorithm is effective and efficient.