IntroductionMachining aims to generate the shape of work-piece form a solid body，or to improve the tolerances and surface finish of a previously formed work-piece，by removing excess materials in the form of Machining is capable of creating geometric configurations，tolerances， and surface finishes often unobtainable by any other However， machining removes materials， which has already been paid for， in the form of relatively small particles that are more difficult to recycle and are in greater danger of becoming Therefore，developments often aim at reducing or-if at all possible-eliminating machining， especially in mass For these reasons， machining has lost some important markets， yet， at the same time， it has also been developing and especially having captured new markets with the application of numerical Some feel for the important of machining may be gained from the observation that in 1983 there were about 2 million metal-cutting machine tools in the unite states ( of which some 5% were numerically controlled ) and that labor and overhead costs amounted to $125 billion， or 3% of the GNP
