Applicability aspects of workload control in job shop production

The term Job Shop Production (JSP) describes a manufacturing environment that produces piece goods in small batches. It is a common manufacturing environment in small and medium-sized enterprises (SMEs). The incoming orders often differ in the number of ordered products, their design, process characteristics (for example, routeings, operation processing times, and set up times), or urgency. Because of this variation the control of the material flows in this type of companies is extremely complex. It can hardly be predicted how the production orders will be divided across the machines in future periods. A high demand on machines and varying production orders cause long waiting times of orders on the shop floor. The direct consequence is that lead times are long and unreliable, whereas nowadays short and reliable delivery times are required. Workload Control (WLC) methods are intended to realise a good logistical performance in JSP. These methods aim at controlling the workload on the shop floor (expressed in hours) for the different capacities (e.g. machines). In this context, a core decision is taken entailing the release of production orders to the shop floor. The orders are not sent to the shop floor immediately, but are collected in a so-called ‘order pool’. The collected orders are assessed periodically for release to the shop floor. A suitable order can be released as long as a maximum workload per capacity group is not exceeded. This order release method guarantees reliable throughput times and a stable and controllable situation at the shop floor. This thesis aims at adding to the existing workload control methods to be better able to cope with several specific aspects of JSP. The research is subdivided in three themes: the general applicability of WLC in JSP, the adjustment of WLC to the restricted availability of information, and the adaptation of WLC to semiinterchangeable machines.