Development of group setup strategies for makespan minimisation in PCB assembly

Balancing setup effort and actual production time is an important issue in medium-variety, medium-volume printed circuit board (PCB) assembly. By grouping batches of similar PCB types to be processed with a common machine setup, the total time required for setting up the component feeders in the magazine of the placement machine can be reduced. On the other hand, the assembly times per PCB increase, since it is no longer possible to optimise the feeder locations in the magazine for each PCB type individually. In order to balance the savings in setup time and the increase in assembly time and to minimise the global makespan, we propose efficient grouping procedures which include machine-specific algorithms for fine-tuning the machine operations for a group of PCBs. Hence, the actual placement times are reflected much more accurately, compared with conventional grouping procedures which merely analyse the component similarity between pairs of PCBs. Two different agglomerative clustering techniques are proposed. One is based on average linkage clustering, the other on a novel hierarchical clustering approach using an inclusion tree representation of the PCB types. Both take the limited capacity of the component magazine into account. We demonstrate the effectiveness of our approach in an extensive numerical investigation of a single-gantry collect-and-place machine equipped with a rotary placement head and an interchangeable feeder trolley. Compared to conventional methodologies, the proposed group setup strategies reduce the global makespan for a given number of batches significantly.