Release policies for assembly systems

We consider a production system consisting of several fabrication lines feeding an assembly machine. The machines in the fabrication lines and at assembly are assumed to have general processing time distributions. Releases to the system are governed by the kanban release mechanism. We first derive a heuristic for the throughput of this system by replacing the assembly system under kanban release by an equivalent system under CONWIP release and by making use of an approximation for the throughput of a CONWIP assembly system (Duenyas, 1992). Comparisons with simulation show that this heuristic is robust over a wide range of conditions. We also address the issue of which release mechanism is more effective in obtaining a desired throughput level with the minimum possible work-in-process inventory level in the system. We present both analytical and simulation results to demonstrate that the CONWIP release policy seems to be a more effective release policy for assembly systems.