First of all, compared with ordinary lathes, CNC lathes have constant linear speed cutting function, no matter for the end face or different diameters of the outer circle can be processed with the same linear speed, that is to ensure that the surface roughness value is consistent and relatively small. And ordinary lathe is a constant speed, different diameter cutting speed is different. The surface roughness depends on the cutting speed and feed speed when the workpiece and tool material, finishing allowance and tool Angle are given.
When processing surfaces with different surface roughness, small roughness surface with small feed speed, large roughness surface with larger feed speed, variability is very good, this is difficult to do in ordinary lathes. A part with a complex outline. Any plane curve can be approximated by a straight line or an arc. cnc precision machining has the function of arc interpolation, which can process all kinds of complex contour parts. The use of cnc precision machining needs the careful use of the operator.
CNC precision machining mainly includes fine turning, fine boring, fine milling, fine grinding and grinding technology:
(1) Fine turning and fine boring: most precision light alloy (aluminum or magnesium alloy, etc.) parts of aircraft are processed in this way. Generally use natural single crystal diamond tool, blade radius less than 0.1 micron. The precision of 1 micron and the average height difference of surface unevenness less than 0.2 micron can be obtained on high precision lathe, and the coordinate accuracy can be up to ±2 micron.
(2) Finishing milling: used for machining aluminum or beryllium alloy structural parts with complex shapes. Depending on the precision of the guide rail and spindle of the machine tool, the higher mutual position accuracy can be obtained. Precise mirror surfaces can be obtained by high speed milling with a carefully ground diamond head.
(3) Fine grinding: used for machining shaft or hole parts. Most of these parts are made of hardened steel, which has a high hardness. Most high precision grinding machine spindles use static or dynamic pressure liquid bearings to ensure high stability. The ultimate precision of grinding is not only affected by the stiffness of machine spindle and bed, but also related to the selection and balance of grinding wheel and machining accuracy of workpiece center hole. The dimensional accuracy of 1 micron and unroundness of 0.5 micron can be obtained by fine grinding.
(4) Grinding: select and process the irregular convex parts on the machined surface by using the principle of mutual grinding of mating parts. Abrasive diameter, cutting force and cutting heat can be controlled precisely, so it is a high precision machining method in precision machining technology. The hydraulic or pneumatic mating parts in the precision servo parts of aircraft and the bearing parts of the dynamic pressure gyromotor are processed by this method to achieve 0.1 or even 0.01 micron accuracy and 0.005 micron microscopic unevenness.