Project scheduling for aggregate production scheduling in make-to-order environments

Production planning of highly customised and complex products is a difficult task and cannot be tackled efficiently by using well-known hierarchical approaches. The main reason is that aggregate production operations correspond to whole production phases, thus requiring planning, scheduling, and procurement activities to be considered at the same decision level. This makes project scheduling approaches particularly suitable for this context. However, the pervasive use of human resources (most operations are executed manually) poses other problems related to the definition of activity durations. In fact, the duration of an activity cannot be a priori defined because it is related to the amount of allotted resources, which in turn depends on the number of products processed at the same time in the shop floor and on the number of workers involved, which can also vary over time. This impacts also on the possibility of correctly modelling the precedence relations between aggregate activities. In this chapter we propose a way to tackle such problems, using a project scheduling approach with a variable intensity formulation and feeding precedence relations and show its application to a real industrial case.