Comparison and application of surface roughness level
1. Surface roughness
Surface roughness refers to irregularities in the machined surface with small spacing and tiny peaks and valleys. The distance (wave pitch) between the two wave crests or troughs is very small (less than 1 mm), which constitutes a microscopic geometric shape error. The lower the surface roughness, the smoother the surface.
The formation of surface roughness is mainly determined by the processing method used and other factors, such as friction between the tool and the workpiece surface during the processing process, plastic deformation of the surface metal during chip separation and high frequency vibration in the process system. Due to different processing methods and workpiece materials, the depth, density, shape and texture of the marks left on the processed surface are different.
Surface roughness is generally divided into S points, which are specifically divided into: S<1 mm est la rugosité de la surface ; 1≤S≤10 mm est l'ondulation ; S>10mm is the shape; At the same time, the surface roughness evaluation parameters include the arithmetic average deviation of the profile (Ra) and the maximum height of the profile (Rz).
In addition, surface roughness is closely related to the adaptation properties, wear resistance, fatigue resistance, contact stiffness, vibration and noise of mechanical parts, and has an impact important on the lifespan and reliability of mechanical products. Controlling surface roughness is therefore crucial during machining.
2. Surface finish
Another term for surface roughness. Surface finish is based on human vision, while surface roughness is based on the actual microgeometric shape of the surface. After 1980s, China adopted surface roughness and abolished surface finishing in order to comply with international standards (ISO). After the promulgation of the national surface roughness standards GB3505-83 and GB1031-83, surface finishing was no longer used.
Comparative table of surface finish and surface roughness
Ra: value of the arithmetic mean deviation of the contour
*. The Ra in Scheme 1 is similar to the average value of each grade of the old national standard, which can guarantee the quality of the product and is recommended for large areas.
**. The Ra of option 2 is 25% higher than the upper limit of each grade of the old national standard. It is more economical and is recommended for smaller surfaces.
***. The Ra of Plan 3 conforms to the upper limit of each grade of the old national standard. It is used when it is difficult to improve the manufacturing accuracy of the product and the operation cannot be guaranteed by lowering it.
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