Precision Machine Tool
Precision Machine Tool
a metalcutting tool for precision machining of parts. There are precision-type lathes, drilling and boring machines, grinders, gear cutters, and milling machines. Precision machine tools are classified as machine tools of increased precision (precision class P), high precision (class H), superhigh precision (class A), and highest precision (class S). Precision machine tools make it possible to produce articles of grade of fit 11, with geometrically regular surfaces, precisely aligned axes, and low surface roughness. As a rule, articles so produced meet the standards of surface roughness class 2 (V 2); V 1 standards can be met under certain conditions. High-precision machining (within tolerances of several microns) requires the use of critical parts and components of increased precision and of precision and superhigh precision rolling-contact bearings, as well as the use of hydrodynamic, hydrostatic, and aerostatic bearings. Deformation caused by thermal stress and vibration must be reduced, and the rigidity of subassemblies must be increased. High-precision instrumentation for active monitoring must be used. The machine tools must be equipped wth chip-removal systems and with systems for the fine filtration of the lubricating and cooling fluids. A high degree of automation of the machine tools and of the processes of loading and removal of articles is required. Accuracy in the motions performed by the moving parts of machine tools is especially important. This accuracy is achieved by such means as the use of special high-precision parts for the base, guides, and basic elements of transport and feed mechanisms and by reduction of friction in transport mechanisms of mobile subassemblies.
Thermal deformations of the blanks, frame, devices, and other parts and subassemblies in precision machine tools may be caused by heat evolution owing to friction and the working of hydraulic drives and electrical devices and by the heat transferred by the lubricating and cooling fluids from the cutting zone. Such deformation may be reduced by placing heat sources at a distance from the machine tool and by the use of temperature-stabilized lubrication systems and of cooling devices in the lubrication and cooling system. For machining of especially precise parts, the precision tools are installed in rooms with constant temperature. In order to eliminate vibrations—particularly those that occur at high spindle-rotation frequencies—the rotating parts of precision machine tools are subjected to careful dynamic balancing. Electric motors and pumps are mounted either away from the frame or on special flexible supports on the frame. The foundations of precision machine tools are insulated against vibration.
New trends in precision machine-tool design are directed at developing more varieties and sizes and precision machine tools with numerical control. Other trends include the development of machine tools with longer operating life and increased reliability. The most advanced machines are equipped with precision counting and measuring devices and with self-adjusting control systems.
REFERENCESKucher, I. M. Metallorezhushchie stanki, 2nd ed. Leningrad, 1969.
Tekhnologicheskaia nadezhnost’ stankov, Moscow, 1971.
Metallorezhushchie stanki. Moscow, 1973.
B. V. PROTOPOPOV