How to control the surface roughness of precision hardware processing

How to control the surface roughness of precision hardware 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 precision hardware processing, manufacturing and assembly quality, whose quality includes both machining accuracy and surface quality. The surface quality of precision mechanical parts is one of the most important indicators, especially for the reliability of the parts at high speed, high temperature and high pressure conditions.

Processing surface is to change the size, shape and performance of the blank surface through precision machining or other methods, so that it can meet the requirements of the design pattern. But the outer circular surface formed by the machining of precision mechanical parts is not a completely ideal surface. After processing, a very thin surface layer is formed on the surface of the parts, and its characteristics are very different from the characteristics of the internal matrix. During precision hardware processing, the surface is in the complex stress state of wedge, extrusion, fracture and friction during the whole cutting process, and conducts elastic and plastic deformation. Under the joint action of the cutting force, cutting heat and the surrounding medium, the original geometric characteristics and physical and mechanical properties of the workpiece surface are changed. Therefore, the "surface quality" is used to evaluate the processed surface layer geometry, physical, chemical or other engineering performance of the parts and the technical requirements of the parts, the main content is divided into the following aspects.

Surface roughness: the microscopic geometric shape characteristic composed of small spacing of peaks and valleys on the surface of precision hardware processing is mainly formed by the movement trajectory of the cutting tool in precision machining, and the ratio of wave height and wavelength is generally greater than 1:50.

Surface wavewave: the intermediate geometry error between the macroscopic geometry error and the surface roughness, it is mainly caused by the offset and vibration of the cutting tool, the ratio of wave height and 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 in the surface formation, that is, the relationship between the main movement and the feed movement.

Scar: precision hardware processing surface of some individual positions of the defects, they are mostly randomly distributed. For example, burrs, cracks and scratches.

The physical and mechanical properties of the surface layer: in the processing process of precision mechanical parts, various complex physical and chemical changes occur on the surface of the parts, which causes the change of the physical and mechanical properties of the surface layer. It mainly includes the following three aspects: the hardening of the surface layer processing, the change of the metallographic organization of the surface layer, and the residual stress of the surface layer.

Effect of surface quality on the performance of parts:

The surface quality reflects some geometrical characteristics and the physical and mechanical properties of the surface layer. It has a great impact on the precision hardware processing wear resistance, matching quality, fatigue resistance strength, corrosion resistance and contact stiffness and other aspects of the use of performance. The service life of precision hardware depends to a large extent on the wear resistance of the parts, the wear resistance of the parts and the friction auxiliary materials, the lubrication conditions of the working environment and the surface quality of the parts, in other conditions, the surface quality of the parts plays a very important role.

pressure casting