The Output Process of Serial Production Lines of General Machines with Finite Buffers

Little is known about the interaction among manufacturing subsystems in a factory. The output of one manufacturing subsystem is usually the input to one or more others in the plant. For example, a production line may provide input to another manufacturing stage, a shipping system, or an automated parts conveyor. In all of these examples, the characteristics of the output from the production line can affect the subsequent process. This paper examines the output process of a serial production line of N machines with general processing time distributions and finite buffer capacities. Simulation is used to examine the effects of line length, buffer capacity, and buffer placement on the inter-departure distribution and correlation structure (autocorrelation function) of the output process of the production line. Results from this analysis are useful in setting production line design parameters and in determining the extent to which buffer placement can be used to control the variability of the output process, and thereby the amount of work-in-process present in downstream subsystems. Additional insights are provided to help explain why small buffers in production lines are normally adequate and to help us better understand the effects of buffers on tightly coupled production systems. By using a variety of processing time distributions, previously unknown effects attributed to skew of processing time are revealed. Since skew can often be reduced or eliminated by operator training, these effects are of particular interest since they can help to quantify some of the benefits of training.