Lead time management

In intermittent production systems, job shops, manufacturing lead times are often long and variable, yet only about 10% is due to the actual processing time. This is a major difficulty in planning production. Two alternative approaches exist for determining planning values for manufacturing lead times to use in production planning and control systems. The first is to treat them as independent uncontrollable variables. It is then a forecasting problem with the emphasis on minimising the impact of the forecasting errors. The second approach puts the emphasis on control and attempts to manage the average lead times to match pre-determined norms. This article reviews and compares these two approaches. It concludes that the second is the most appropriate but that it requires a close cooperation between the production and marketing functions of the firm. This is best achieved by regarding the firm as a hierarchical chain of backlogs connected by input/output relations.