How to control the surface roughness of precision metal processing

With the progress of science and technology and the development of society, people have put forward higher and higher requirements for the performance and quality of precision processed products. The performance and quality of the product are determined by the product design, and are guaranteed by the quality of precision metal processing, manufacturing and assembly. Its quality includes two aspects: processing accuracy and surface quality. The surface quality of precision mechanical parts is one of the most important indicators, especially for the reliability of parts under high speed, high temperature and high pressure conditions.
The machined surface is to change the size, shape and performance of the rough surface by precision machining or other methods to make it meet the requirements of the design pattern. However, the outer surface formed by turning precision mechanical parts is not a completely ideal surface. After processing, a very thin surface layer is formed on the surface of the part, and its characteristics are very different from those of the internal matrix. In precision hardware processing, the surface is under the complex stress state of wedging, squeezing, breaking and friction during the entire cutting process, undergoing elastic and plastic deformation, and changing under the combined action of cutting force, cutting heat and surrounding media The original geometric features and physical and mechanical properties of the surface of the workpiece are improved. Therefore, using 'surface quality' to evaluate the degree of conformity between the geometric, physical, chemical or other engineering properties of the surface layer of the processed part and the technical requirements of the part, the main content expressed is divided into the following aspects.
Surface roughness: the micro-geometric features composed of small pitch peaks and valleys on the surface of precision metal processing. It is mainly formed by the motion trajectory of the cutting tool in precision machining, and the ratio of the wave height to the wavelength Generally greater than 1:50.
Surface waviness: the intermediate geometric shape error between the macroscopic geometric shape error and the surface roughness. It is mainly caused by the offset and vibration of the cutting tool. The ratio of the wave height to the wavelength is generally 1:50 to 1 :1000.
Surface processing texture: The main direction of the surface microstructure, which depends on the precision machining method used for surface formation, that is, the relationship between the main motion and the feed motion.
Scars: Defects in some individual positions on the surface of precision metal processing. Most of them are randomly distributed. Such as burrs, cracks and scratches.
The physical and mechanical properties of the surface layer: During the processing of precision mechanical parts, various complex physical and chemical changes occur on the surface of the parts, causing changes in the physical and mechanical properties of the surface layer. It mainly includes the following three aspects: the work hardening of the surface layer, the change of the metallographic structure of the surface layer, and the residual stress of the surface layer.
The effect of surface quality on the performance of parts: The surface quality reflects some geometric characteristics and the physical and mechanical properties of the surface layer. It has a great influence on the wear resistance, matching quality, fatigue strength, corrosion resistance and contact stiffness of precision hardware processing. The service life of precision hardware depends to a large extent on the wear resistance of the parts. The wear resistance of the parts is related to factors such as the material of the friction pair, the lubrication conditions of the working environment and the surface quality of the parts. Under other conditions, The surface quality of the parts plays an important role.