Definition and expression of surface roughness
Surface roughness is generally formed by the processing method used and other factors, such as the friction between the tool and the part surface during processing, the plastic deformation of the surface layer metal when the chip is separated, and the high-frequency vibration in the process system. Due to the different processing methods and workpiece materials, the depth, density, shape and texture of the traces left on the processed surface are different.
Surface roughness is closely related to the matching properties, wear resistance, fatigue strength, contact stiffness, vibration and noise of mechanical parts, and has an important impact on the service life and reliability of mechanical products. Generally, Ra is used for labeling.
Contour arithmetic mean deviation Ra: the arithmetic mean of the absolute value of the contour deviation within the sampling length (lr). In actual measurement, the more the number of measurement points, the more accurate Ra is.
Maximum profile height Rz: the distance between the peak line and the bottom line of the profile.
Ra is preferred in the usual range of amplitude parameters.
Before 2006, there was another evaluation parameter in the national standard, which was expressed by Rz as "the ten-point height of micro-roughness".
The maximum height of the profile is represented by Ry. After 2006, the national standard canceled the ten-point height of microscopic roughness, and Rz was used to represent the maximum height of the profile.
Is surface roughness the same as surface finish?
Surface finish is another term for surface roughness. The surface finish is proposed according to the human visual point of view, while the surface roughness is proposed according to the actual microscopic geometry of the surface. Because it is in line with the international standard (ISO), China adopted surface roughness after the 1980s and abolished surface finish. After the promulgation of national standards for surface roughness GB3505-83 and GB1031-83, surface finish is no longer used.
