Selecting machines and buffers in unreliable series-parallel production lines

This article formulates a new optimal design problem of a series-parallel manufacturing production line, where redundant machines and in-process buffers are included to achieve a greater production rate. The objective is to maximize production rate subject to a total cost constraint. Machines and buffers are chosen from a list of products available in the market. The buffers are characterized by their cost and size. The machines are characterized by their cost, failure rate, repair rate and processing time. To estimate series-parallel production line performance, an analytical decomposition-type approximation is proposed. Simulation results show that this approximate technique is very accurate. The optimal design problem is formulated as a combinatorial optimization one where the decision variables are buffers and types of machines, as well as the number of redundant machines. To solve this problem, the ant colony approach and the simulated annealing are illustrated and compared through several numerical examples