In order tD enhance factory automation and unmanned productien, numerjcal controlled (NC) machine tools are widely used in many rnechanical processing factories, Whenever one machining part is changed to another, the operation of an NC machine tool has to be stopped in order to change some of the cutting teols on the turret too! holder. In this paper, a new concept of ttool module' is usect and the problem of reducing the number of tool changing operations for NC machine tools is diseussed, The problem is formulated as a O-1 integer pr(rgramming (O-1 ILP) problem on a bipartite graph and a branch and bound algorithm is proposed to select an optimal tool module. Since the LP relaxation problem obtained by dropping the integrality condition for the O-1 ILP problern has a special network structure like the well-known transportation problem, this LP is solved by certain network flow algorithm with utilizing its special structure Sorne numerical experiments are reported, and indicate that the algorithrn is reasonably efficient. FurtherTnore, possible extenslons of this method are discussed, which in turn ±ncreases the produc-t±vity. These bring an innovation in the aspect of factory management. However, the machine setup operations which tnclude the ehanging 205
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