We know that precision machining requires high precision. Precision machining has good rigidity, high manufacturing precision, and accurate tool setting, so it can process parts with high precision requirements. So which parts are suitable for precision machining?
First of all, compared with ordinary lathes, CNC lathes have the function of constant line speed cutting, which can be processed with the same line speed regardless of the end face of the car or the outer circle of different diameters, which ensures that the surface roughness value is consistent and relatively small. . The ordinary lathe is a constant speed, and the cutting speed is different for different diameters. In the case of constant workpiece and tool material, finishing allowance and tool angle, the surface roughness depends on the cutting speed and feed rate.
When machining surfaces with different surface roughness, a small feed rate is used for the surface with small roughness, and a larger feed rate is used for the surface with large roughness, and the variability is very good, which is difficult to achieve in 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 the function of circular interpolation, which can process parts with various complex contours. The use of CNC precision machining requires careful use by 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 the aircraft are processed by this method. Generally, a natural single-crystal diamond tool is 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 fewer than 0.2 microns, and the coordinate accuracy can reach ±2 microns.
(2) Fine milling: It is used to process aluminum or beryllium alloy structural parts with complex shapes. Relying on the accuracy of the guide rail and spindle of the machine tool to obtain high mutual position accuracy. High-speed milling with carefully ground diamond tips results in a precise mirror finish.
(3) Fine grinding: used for machining shaft or hole parts. Most of these parts are made of hardened steel with high hardness. Most high-precision grinder spindles use hydrostatic or hydrodynamic fluid 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, the machining accuracy of the center hole of the workpiece, and other factors. Fine grinding achieves 1-micron dimensional accuracy and 0.5-micron out-of-roundness.
(4) Grinding: Use the principle of mutual grinding of mating parts to selectively process the irregular raised parts on the machined surface. Abrasive particle diameter, cutting force, and cutting heat can be precisely controlled, so it is a high-precision machining method in precision machining technology. The hydraulic or pneumatic fittings in the precision servo parts of the aircraft and the bearing parts of the dynamic pressure gyro motor are all processed by this method to achieve an accuracy of 0.1 or even 0.01 microns and a microscopic unevenness of 0.005 microns.