Selection of routes in a flexible manufacturing facility

Abstract

Routeing flexibility is defined as the ability to manufacture a product via several alternate routes in the same facility. A route is defined as the set of work centers or machines through which a product is processed, and the processing times at these work centers. Routeing flexibility permits the facility to adjust to changes in the production ratio. Typically, with every change in the production ratio, the FMS scheduler will assign routes to each product, so as to achieve a close to perfect load balance between work centers while minimizing the interference or setups between processing routes. The assigned routes will belong to the set of routes that have been implemented, and hence are available for scheduling. A route is described as implemented when the instructions, skills, tools, handling needs, and other auxiliaries associated with it have been positioned in the facility. The ability to change routes and optimize performance is therefore dependent on the routes which have been implemented. In this paper we assume that several good and feasible routes are generated by the process planner for each product. Since it is economically possible to implement only a few routes per product, the route selection problem is described as identifying the set of routes which should be implemented so as to optimize routeing flexibility related costs. The problem is formulated as a mixed integer program and rules for deriving tight initial solutions are proposed. Tests with sample problems were conducted, and model sensitivity to the scenario change factor and present worth factor were studied.