Factors affecting surface roughness

Surface roughness is one of the important indicators to measure the quality of processed surfaces. It has a great influence on the wear resistance, corrosion resistance, fatigue strength and mating properties of the parts. However, there are many factors affecting the surface roughness during processing. In order to achieve good surface roughness, let's take a look at what these factors are.

First, the reason for the rough surface

1. Residual area : The residual area is the area of ​​the machined surface that has not been cut off after being cut by the main and auxiliary cutting edges.

2 , scales : when cutting high-speed steel cutters at low or medium speeds, such as low carbon steel, medium carbon steel, stainless steel, aluminum alloy, etc., often produce scaly burrs on the machined surface, called scales thorn. The appearance of scales significantly increases the surface roughness of the machined surface.

3 , built-up edge: in the cutting process, when the built-up edge, its protruding part can be cut into the workpiece instead of the cutting edge, draw a groove on the machined surface; when the built-up edge falls off, Part of the built-up edge fragments adhere to the machined surface, forming fine burrs, resulting in increased surface roughness.

4. Vibration : During the cutting process, due to the periodic vibration of the process system, streaks or ripple marks appear on the machined surface, and the surface roughness value is significantly increased.

Second, the factors affecting the surface roughness

All factors affecting the residual area, built-up edge, scale and vibration affect the surface roughness of the machined surface.

1. Cutting amount : The feed has the greatest influence on the residual area. The feed rate is reduced and the residual area is reduced.

When cutting plastic metal, when the cutting speed is very low or high, the surface roughness value is small. This is because the built-up edge is not easy to produce at low speeds; when the cutting speed is high, the plastic deformation is reduced, and the occurrence of scales can be eliminated. When cutting brittle materials, the influence of the cutting speed is small, because the material deformation is small, so the surface roughness value is also reduced.

2 , tool geometry parameters : tool nose radius, main declination and secondary declination have a greater impact on residual area and vibration. Generally, when the radius of the tool nose increases, the surface roughness value is small, but if the machine tool stiffness is low, the radius of the tool nose arc is too large or the lead angle is too small, due to the cutting force. The vibration is increased to increase the surface roughness value.

3 , tool material : different tool materials, the radius of the cutting edge arc and the time to maintain sharpness is different. High-speed steel tools can be sharpened sharply, but with a short hold time, so the surface roughness value is small at low speed cutting. After the carbide tool is sharpened, the cutting edge radius is large, and the cutting surface roughness value is small at high speed.

4. Workpiece material : When processing plastic material, the lower the plasticity of the workpiece material, the higher the hardness, the less the phenomenon of built-up edge, scale and chill, and the smaller the surface roughness value. Therefore, the surface roughness value of high carbon steel, medium carbon steel and quenched and tempered steel after processing is smaller than that of low carbon steel. When the cast iron is processed, the surface roughness value ratio of the cast iron is the same under the same processing conditions. Steel is big.

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