A time-varying lot size method for the economic lot scheduling problem with shelf life considerations

Most studies on the economic lot scheduling problem with shelf life considerations adopt the common cycle approach which usually gives a result with high cost. Basic period method has been applied to this problem recently resulting in a lower cost. This paper takes a time-varying lot size approach. Two models are formulated to optimise the production schedule for any given production sequence, one assuming that production of each product starts only when the inventory of this product becomes zero, and the other relaxing this restriction. To generate production sequences, we use an existing heuristic and also develop a new heuristic. Numerical experiments on a benchmark problem show that at all the utilisation levels tested the new method outperforms previous methods. Further experiments show that the production frequencies for the products, production sequence and a less restricted scheduling model all contribute to the low production cost. [Received: 22 August 2006; Revised: 28 October 2007; Accepted: 12 December 2007]