Surface roughness (machining term)

Surface roughness refers to the unevenness of the processed surface with small spacing and tiny peaks and valleys. The distance (wave distance) between two wave crests or two wave troughs is very small (less than 1mm), which is a microscopic geometric error. The smaller the surface roughness, the smoother the surface. Usually, morphological characteristics with a wave distance less than 1 mm are attributed to surface roughness, morphological characteristics with a size of 1 to 10 mm are defined as surface waviness, and morphological characteristics with a size greater than 10 mm are defined as surface topography.
Surface roughness is generally caused by the processing method used and other factors, such as the friction between the tool and the part surface during the processing process, the plastic deformation of the surface metal when chips are separated, high-frequency vibration in the process system, etc. 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 closely related to the matching performance, 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.
Evaluation parameters
height characteristic parameters
Contour arithmetic mean deviation Ra: the arithmetic mean of the absolute value of the contour offset within the sampling length lr. In actual measurement, the more measurement points, the more accurate Ra is.
Maximum profile height Rz: the distance between the peak line and the bottom line of the valley.
Assessment basis
Sampling length
The sampling length lr is the length of the reference line specified for evaluating surface roughness. The sampling length should be selected based on the actual surface formation and texture characteristics of the part, and the length should be selected to reflect the surface roughness characteristics. The sampling length should be measured in the general direction of the actual surface profile. The sampling length is specified and selected to limit and reduce the effects of surface waviness and form errors on surface roughness measurements.
In the field of mechanical processing, drawings including metal stamping parts, sheet metal parts, machined parts, etc. are widely marked with product surface roughness requirements. Therefore, in various industries such as auto parts, engineering machinery, medical equipment, aerospace, and shipbuilding machinery, etc. All can be seen.

Post time: Nov-29-2023