Tool management in flexible manufacturing systems with tool movement policy

Abstract

In a flexible manufacturing system (FMS) where a large number of tool types are required, tool management is vital for maintaining high productivity. The purpose of this thesis is to study several tool-related problems in FMSs operating with the tool movement policy, i.e., the policy to move tools to the machines where they are needed. In the first part of the thesis, we consider a tool loading problem in FMSs in which each part visits only one of the machines for its entire processing. If a machine does not have on its tool magazine tools needed for processing a part, it can borrow the tools from other machines or a tool crib, or use alternative tools instead. The problem is to assign parts and tools to machines to maximize the system throughput. Since the objective is difficult to deal with directly, we use an intermediate objective of minimizing the number of tool transfers among the machines and between the machines and the tool crib. Since it is computationally intractable to find optimal solutions for practical problems, a heuristic procedure is developed. The heuristic is compared with an existing heuristic through example problems. The second part addresses the tool switching problem of a flexible machine. It is assumed that a set of parts to be produced on the machine is known and the number of tools required to produce all the parts is larger than the capacity of the tool magazine. Switching tools in the tool magazine requires a tool transporter which has a limited carrying capacity to travel between the tool crib and the machine. The problem is to determine an optimal production sequence of the parts and its corresponding tool replacement schedule such that the travel frequency of the tool transporter is minimized. The problem is formulated into a mathematical programming. For the problem with a given production sequence, an optimal tool replacement schedule is found. Also, several heuristics are suggested for the part sequencing problem and their ...