Performance analysis of automatic assembly systems with in-line parallel stations

An automatic assembly system – a key tool for mass production – is generally composed of a number of workstations and a transport system. One common problem associated with automatic assembly systems is that some assembly operations may have relatively long cycle times. As a consequence, productivity, which is determined by the operations with the longest cycle time, can be reduced significantly. Therefore a special form of parallel workstation known as an in-line parallel (tandem-gated) station was developed to improve the performance of an automatic assembly system. In this design, stations working in parallel are installed in a serial structure and perform identical operations. Thus, more than one assembly may be processed simultaneously – a type of design especially beneficial when a stage requires a long operation cycle time. A typical example is a computer assembly system which performs long inspection operations to ensure that the quality level of each product is up to the acceptance level. In this paper, we describe a simulation study of the performance characteristics of this type of system, with a statistical analysis of each decision factor. Phenomena affecting the performance of in-line parallel stations, identified by the assistance of the computer graphical display, will then be discussed. An analytical model based on these phenomena identified is then developed. The results generated by the analytical model developed are validated by comparisons with the simulation results. Finally, guidelines for optimization of buffer size are presented.