Group sequencing a printed circuit board assembly system via an expected sequence dependent set-up heuristic

In circuit board manufacturing, the production sequencing problem with sequence dependent set-ups is complicated by the fact that the amount of set-up required depends on not only the set-up directly before the current set-up, but can depend on all of the preceding set-ups. We present a case study that examines the use of a heuristic for estimating the expected number of set-ups from the sequence dependent set-ups. Our method is based on estimating the expected number of set-ups which may occur given a board-feeder set-up configuration. Once estimates for sequence dependent set-ups are established, they can be used to measure the similarity between boards in clustering algorithms and in nearest neighbour heuristics for group sequencing. The method is tested on an actual printed circuit board assembly system. Then, using a simulation of the assembly system, we compare the sequences generated using the expected number of set-ups distance measure and the Hamming distance measure to optimal sequences. Our results indicate that grouped sequences generated by using the expected number of set-ups had significantly better makespan performance when compared to sequences based on more traditional Hamming distance for the particular system under study. The significant gains in makespan resulted in only moderate increases in work in process and slight increases in manual station utilisation.