Complexity index as a base for decision making whether to introduce NC or conventional machines

Numerical control (NC) systems are widely used in industry today, especially in the metal working industry. In developing countries, many industries are introducing NC machines and the economics of the change assumed great significance. In some cases, even conventional machines (automatic mass production or transfer line machines) are good enough. Hence the decision of machining a component through an NC machine is in the hands of management. This warrants a direct and simple approach to decision making for selecting the more economical of the two machining methods. This paper attempts to arrive at a yardstick, termed the complexity index, used for deciding whether the component should be routed through the conventional machine or the NC machine. A rigorous and quantitative approach of discriminant analysis is adopted for various manufacturing components to obtain the discriminant function. The complexity index for a manufacturing component is taken to be its discriminant score which is used for assigning the components either to the conventional or to the NC machines. Statistical tests of significance of such a classification procedure are performed. An acceptance level for each group (conventional and NC groups) is calculated (based on the mean score of each group) to determine the minimum complexity index for arriving at the decision rule. In this paper, the approach is presented with the aid of a case study.