Many modern manufacturing management approaches present relationships between variables on the shop floor, aiming to increase the manager’s intuition about manufacturing dynamics. One of these is the relationship between lot size and average lead time, which is studied in this paper. Although this general relationship is widely recognized, only a selected number of authors address this relationship in a practical manner. This paper presenta and compares the effect of six continuous improvement programs (arrival variability, process variability, quality (defect rate), time to failure, repair time, and set up time) on lot size × lead time relationship in a multi-product, single-machine environment, by means of a combination of System Dynamics (FORRESTER, 1962) and Factory Physics (HOPP and SPEARMAN, 2008) approaches. Two sets of experiments are performed in this paper: a) A large (50%) improvement in each parameter separately, as might be obtained by a significant one-time investment; b) a small improvement in all parameters simultaneously. The results showed: (a) the positive effect of continuous improvement in shop floor variables on lead time ; (b) the importance of knowing the lot size × lead time curve and the effect of set up reduction programs before beginning with lot size reduction program; (c) that investing in small improvements in several variables is preferable regarding lead time than investing in a large improvement in just one variable; (d) some insights about modern manufacturing management paradigms such as: Lean Manufacturing and Quick Response Manufacturing.
Lot size; Lead time; System Dynamics; Factory Physics; Continuous improvement
