Machining method with accuracy of 1 μ m. Precision machining is realized by using precision machine tools, precision measuring tools and meters under strictly controlled environmental conditions. The machining accuracy reaches or exceeds 0.1 μ m, which is called ultra precision machining. In the aerospace industry, precision machining is mainly used to process precision mechanical parts in aircraft control equipment, such as precision mating parts in hydraulic and pneumatic servo mechanisms, frames and shells of gyroscopes, air floating, liquid floating bearing components and floats. The precision parts of aircraft have complex structure, small stiffness, high precision requirements, and the proportion of difficult to machine materials is large.
The process effect of precision machining is:
① The geometric shape and mutual position accuracy of parts shall reach micron or angular second level;
② The limit or feature dimension tolerance of the part is less than micrometer;
③ The micro unevenness of part surface (average height difference of surface unevenness) is less than 0.1 μ m;
④ Mutual accessories can meet the requirements of combining force;
⑤ Some parts can also meet the requirements of precise mechanical or other physical characteristics, such as the torsional stiffness of the torsion bar of the float gyroscope, the stiffness coefficient of the flexible element, etc.
Precision machining mainly includes precision turning, precision boring, precision milling, precision grinding and grinding.
① Fine turning and fine boring: Most of the precision light alloy (aluminum or magnesium alloy, etc.) parts of aircraft are processed in this way. The natural single crystal diamond cutter is generally used, and the arc radius of the blade is less than 0.1 μ m. The precision of 1 μ m and the surface roughness with an average height difference of less than 0.2 μ m can be obtained by machining on a high-precision lathe, and the coordinate accuracy can reach ± 2 μ m.
② Finish milling: used for processing aluminum or beryllium alloy structural parts with complex shapes. Rely on the accuracy of the guideway and spindle of the machine tool to obtain higher mutual position accuracy. Precise mirror surface can be obtained by high-speed milling with carefully ground diamond cutter head. 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 grinding machine spindles use hydrostatic or hydrodynamic liquid bearings to ensure high stability. The limit precision of grinding is not only affected by the rigidity of machine tool spindle and machine bed, but also related to the selection and balance of grinding wheel, the machining precision of workpiece center hole and other factors. The precision of 1 μ m and out of roundness of 0.5 μ m can be obtained by fine grinding.
④ Grinding: use the principle of mutual grinding of mating parts to select and process the irregular convex parts on the machined surface. Abrasive grain diameter, cutting force and cutting heat can be precisely controlled, so it is the highest precision processing method in precision machining technology. The hydraulic or pneumatic mating parts in the precision servo components of the aircraft and the bearing parts of the dynamic pressure gyro motor are all processed in this way to achieve the accuracy of 0.1 or even 0.01 μ m and the micro unevenness of 0.005 μ m.
