Mirror Finishing

Mirror finishing is the highest level of metal cutting and is the most effective means to improve the service life of mechanical components.

Mirror Finishing

The mirror surface is a traditional synonym for very good roughness after machining, and it can clearly reflect the metal surface of the image.


No matter what kind of metal processing method is used, there will always be fine unevenness on the surface of the part, and there will be staggered peaks and valleys.

The roughened surface can be seen with the naked eye, and the finished surface can still be observed with a magnifying glass or microscope.

This is the surface roughness of the part after processing, which used to be called surface finish.

The parameters for surface roughness are composed of height parameters, spacing parameters and comprehensive parameters.

Mirror surface processing is generally refer to a surface with a roughness of <0.8um, and it’s been called: mirror finishing.

Processing methods

The mechanical methods for obtaining mirrors are: material removal, no cutting (rolling).

Ways to remove materials are: grinding, polishing, and electric sparking.

No cutting methods are: rolling (using mirror tools), extrusion.

The following prerequisites must be met for material removal:

  • Large amount of equipment investment (some grinders are worth more than 1 million);
  • Skilled and experienced technical workers;
  • Spacious working environment;
  • A large number of cooling and lubricating media (oil or liquid);
  • Environmentally polluted waste disposal;
  • Expensive grinding wheel.

Non-cutting rolling (with mirror tools) must have the following prerequisites:

  • No need for large equipment investment (a mirror tool value of about 1,300 yuan);
  • Skilled workers who are not skilled and experienced;
  • Spacious working environment;
  • No need for a large amount of cooling and lubricating medium (oil or liquid);
  • No disposal of waste that pollutes the environment.

The mirror surface is generally removed between Ra0.8-0.08um; the non-cutting method (with mirror tool) is generally between Ra0.4-0.05um.

There is basically no limit to the hardness of the material to be processed. The non-cutting method (with mirror tool) is required to process the mirror to a material hardness of HRC<40°, and the diamond mirror tool HRC<70°.

The hardness of the surface of the mirror workpiece is not changed by the material removal method, and the abrasion resistance does not increase.

Advantages and disadvantages of non-cutting rolling process


  • Improve the surface roughness, and the roughness can reach Ra≤0.08um.
  • Correct the roundness, the ellipticity can be ≤0.01mm.
  • Improve the surface hardness, so that the force deformation is eliminated, the hardness is increased by HV ≥ 40 °
  • There is residual stress layer after processing to increase fatigue strength by 30%.
  • Improve the quality of the coordination, reduce wear and extend the life of the parts, but the processing costs of the parts are reduced.


  • Rolling will produce a hardened layer on the surface of the workpiece. This layer has obvious delamination with the internal material, which is likely to cause the surface layer to fall off.
  • The rolling process is difficult to master, improper handling make it easy to cause waste.
  • Rigid force, 1000N-3000N, the damage to the guide rail of the machine tool transmission mechanism is serious, and seriously damage the accuracy and life of the machine.
  • The tool has a short service life, easy to damage, and in high comprehensive cost.
  • It is impossible to process the parts with poor rigidity such as slender rods and thin-walled pipe fittings.


Mirror processing has a wide range of applications, in particular: hydraulic cylinders, hydraulic valves, and piston rods require not only good surface finishing but also wear resistance, while not wearing seal rings or seals.

Most hydraulic cylinders leak over the sealing cap after a period of time because of wear on the seal ring or seal during movement.

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