Load-based order review release strategies for shop floor control

Abstract

The basic aim of this thesis is to grasp the notion of order release in terms of system performance and develop a load-based hierarchical order release policy. Basically, order review/ release (ORR) is a decoupling mechanism to manage transitions of orders from planning system to the shop floor and it is a decision point for determining the release time of a job. ORR mechanism used has a two level, load-oriented structure for release of jobs into shop floor. Incidentally, two fundamental manipulation methods are applied in order release phase. In the first level, machine routes of jobs are sorted regarding workload balancing of machines and in the second level, workload bounding method is applied. Besides the classical shop environments used in the literature, releases of orders are achieved in a flexible manufacturing environment as a novel approach. Flexible process plans of jobs are fixed at the release phase, and part routing execution is avoided on the floor. On comparing the results of proposed methods, the results showed that ORR methods do improve performance measures and is an effective tool when used with an appropriate parameter set. Threshold level and period parameters are the critical ones in this set. A proper threshold level is tried to be estimated by inducement of some desired mean queue sizes and predetermined layout and job mix definitions. On the other hand, periodic structure of ORR mechanism is tried to be eliminated by implementing a pull-type and self-triggered structure. Studying the ORR policies under different job flow patterns has been an important aspect of the study that reinforces the conclusions drawn, especially on the effect of introducing process plan flexibility..