01 The concept of surface roughness

Surface roughness (surface roughness) refers to the processing of the surface has a small pitch and tiny peaks and valleys composed of micro-geometric error, can be understood as in the processing of products in the process of small pitch and tiny peaks and valleys of unevenness. The smaller the micro-geometric error of the machined surface, the higher the surface accuracy; conversely, the lower.

Surface geometry error:

Roughness: The term that responds to the microscopic geometric shape error of the machined surface of the part is called surface roughness, and the surface geometric shape error with a wave pitch of less than 1mm belongs to surface roughness.

Waviness: The geometric shape error with a wave distance of 1~10mm belongs to surface waviness.

Shape error: wave distance greater than 10mm of geometric shape error belongs to the shape error (macro-geometric error)

02 Factors of surface roughness formation

The formation of surface roughness is caused by the processing of the workpiece. Processing of materials due to plastic deformation, mechanical vibration, friction and other reasons, parts formed by cutting or other methods of surface, there is always a geometric shape error. Due to the different processing methods and workpiece materials, the processed surface leaves traces of the depth, sparseness, shape and texture are different.

03 Effect of surface roughness on workpiece

Surface roughness has an important impact on the service life and reliability of mechanical products, as follows:

1, surface roughness affects the wear resistance of parts. The rougher the surface, the smaller the effective contact area between the matching surfaces, the greater the pressure, the faster the wear.

2, surface roughness affects the stability of the nature of the fit. For clearance fit, the rougher the surface, the easier it is to wear, so that the gap gradually increased in the working process; for the interference fit, due to the assembly of the microscopic peaks will be squeezed flat, reducing the actual effective interference, reducing the strength of the joint.

3, surface roughness affects the fatigue strength of parts. Roughness of the surface of the part there are larger valleys, they are like sharp notches and cracks, very sensitive to stress concentration, thus affecting the fatigue strength of the part.

4, surface roughness affects the corrosion resistance of parts. Rough surface, easy to make corrosive gases or liquids through the surface of the microscopic valleys penetrate into the inner layer of the metal, resulting in surface corrosion.

5, surface roughness affects the sealing of parts. Rough surfaces can not be tightly fit between the gas or liquid leakage through the gaps between the contact surfaces.

6, surface roughness affects the contact stiffness of parts. Contact stiffness is the parts bonding surface under the action of external forces, the ability to resist contact deformation. The stiffness of the machine depends largely on the contact stiffness between the parts.

7, affecting the measurement accuracy of the parts. The surface roughness of the measured surface of the part and the measuring surface of the measuring tool will directly affect the accuracy of the measurement, especially in precision measurement.

In addition, the surface roughness of the parts of the coating, thermal conductivity and contact resistance, reflective ability and radiation properties, liquid and gas flow resistance, conductor surface current flow will have different degrees of influence.