ESD/Mechanical Engineering Seminar

How Lean Can Lean Buffers Be?

By Jingshan Li, Staff Research Engineer, Manufacturing Systems Research Lab, General Motors Research and Development Center, Warren, Mi

Abstract:
The talk is intended to present a quantitative characterization of the smallest, i.e., lean, buffer capacity, which is necessary and sufficient to attain a desired throughput of a serial production line. The development is carried out based on parameterization of the buffer capacity in units of the average down time of the machines. In terms of this parameterization, the sought buffering is referred to as the Lean level of Buffering (LLB). 

For the case of machines with exponential reliability models, we derive closed formulas for calculating LLB in two- and three-machines lines. For longer lines, we develop an approximation technique and characterize its accuracy.

For the case of non-exponential machines, we derive an empirical law for calculating LLB as a function of machine efficiency, line efficiency, the number of machines in the system, and the coefficients of variation of up- and downtime. We verify this law using gamma, log-normal, and Weibull reliability models of the machines. Although this empirical law is just an upper bound of the true LLB, it still offers significant reduction of buffer capacity as compared with that based on the exponential assumption.

Along with their quantitative values, the results obtained provide a qualitative insight into the nature of lean buffering in serial production lines.

Contact Info:           
Jingshan Li, Staff Research Engineer
Manufacturing Systems Research Lab
General Motors Research and Development Center
Warren, MI
phone: 586.986.7071
email: jingshan.li@gm.com