Shop Note. Machinability of Metals

摘要

The Watertown Arsenal is a jobbing shop devoted to the manufacture of proto-types of artillery carriages and cannon. The design requirements of ordnance are mandatory in demanding high strength and great emphasis is placed on the saving of weight. Maintenance features such as resistance to corrosion and wear must be given careful consideration. Extreme precision in the fabrication and fitting of parts is essential for accuracy in operation. The severe requirements of design do not generally permit the selection of those metals known to the trade as 'free machining'. The metal prescribed, with the physical requirements clearly specified, must be used by the shop. The problem of how to work this metal to the best advantage with the machine tools available is one that must be solved by the production department. Under the conditions cited machinability may be defined as 'that quality of a metal which permits it to be formed by selected cutting tools into a shape suitable for the purpose intended'. In all probability Watertown Arsenal has a greater variety of problems in 'Machinability' than any commercial plant would ever be called upon to solve. Experience at the arsenal has shown that selections of combinations of speeds, feeds, depth of cut, tool material, tool shape, clearance and rake angle of tools, position of tools in respect to work, method of supporting work, rigidity of tool mounting and machines, kind of coolant and lubricant used, method of applying coolant, type of chip and amount of furnishing all have a definite bearing on machining presentation paper delivered before joint meeting of Army ordnance association and American Socity of metals at Watertown Arsenal, December 3, 1937.