Simulation analysis of assembly systems with multiple highlift stations

One common problem associated with automatic assembly systems is that some assembly operations may have relatively long cycle times. As a consequence, the productivity, as determined by the operations with the longest cycle time, can be reduced significantly. Therefore, a special form of parallel workstation known as a highlift station was developed to improve the performance of an automatic assembly system. We will first discuss phenomena affecting the performance of highlift stations. Then, simulation is used to study the performance characteristics of the system under different manufacturing environments. The factors under investigation include: (i) time to clear the defective assemblies, (ii) percent of defective assemblies, (iii) total number of highlift stations installed and (iv) downstream buffer size installed. In general, the productivity of serial assembly systems increases as buffer units increase and the marginal effect diminishes. However, the productivity of highlift systems can be maximized when the total buffer units in front of the highlift stations is set equal to the number of highlift stations installed. This result will be discussed in detail in this paper.