First of all, compared with ordinary lathes, CNC lathes have the function of constant linear speed cutting. Both the end face and the outer circle of different diameters can be processed at the same linear speed, which ensures that the surface roughness value is consistent and relatively small.
The ordinary lathe has a constant speed, and the cutting speed is different for different diameters. When the material of the workpiece and the tool, the finishing allowance and the tool angle are certain, the surface roughness depends on the cutting speed and feed rate.
When processing surfaces with different surface roughness, choose a small feed rate for a surface with a small roughness, and a larger feed rate for a surface with a large roughness. The variability is very good, which is difficult to achieve on ordinary lathes. Parts with complex contour shapes. Any plane curve can be approximated by a straight line or a circular arc. CNC precision machining has circular interpolation function, which can process a variety of complex contour parts. The use of cnc precision machining requires careful use of the operator.
CNC precision machining mainly includes fine turning, fine boring, fine milling, fine grinding and grinding processes:
(1) Fine turning and fine boring: Most of the precision light alloy (aluminum or magnesium alloy, etc.) parts of aircraft are processed by this method. Generally, natural single crystal diamond tools are used, and the radius of the blade arc is less than 0.1 microns. Machining on a high-precision lathe can obtain an accuracy of 1 micron and a surface unevenness with an average height difference of less than 0.2 microns, and the coordinate accuracy can reach ±2 microns.
(2) Fine milling: used to process aluminum or beryllium alloy structural parts with complex shapes. Rely on the precision of the machine tool’s guide rail and spindle to obtain high mutual position accuracy. High-speed milling using a carefully ground diamond head can obtain a precise mirror surface.
(3) Fine grinding: used for machining shaft or hole parts. Most of these parts are made of hardened steel, which has high hardness. Most high-precision grinding machine spindles use hydrostatic or dynamic pressure liquid bearings to ensure high stability. The ultimate accuracy of grinding is not only affected by the rigidity of the machine tool spindle and bed, but also related to the selection and balance of the grinding wheel, and the machining accuracy of the center hole of the workpiece. Fine grinding can obtain a dimensional accuracy of 1 micron and an out-of-roundness of 0.5 micron.
(4) Grinding: Use the principle of mutual research of mating parts to selectively process irregular convex parts on the processed surface. Abrasive particle diameter, cutting force and cutting heat can be precisely controlled, so it is the highest precision machining method in precision machining technology. The hydraulic or pneumatic matching parts of the precision servo components of the aircraft, and the bearing parts of the dynamic pressure gyro motor are processed in this way to achieve an accuracy of 0.1 or even 0.01 microns and a microscopic unevenness of 0.005 microns.