What is polishing?
Polishing refers to the use of mechanical, chemical or electrochemical action to reduce the surface roughness of the workpiece in order to obtain a bright, flat surface processing method.
The polishing process is divided into six types
Mechanical polishing
Mechanical batch is only by cutting, plastic deformation of the material surface to remove the polished convex and smooth surface polishing method, generally use the whitetstone strip, wool wheel, sandpaper, etc., to manual operation as the host of special parts such as the surface of the rotary body, can use the rotary table and other auxiliary tools
Turn the motion. The surface roughness of the workpiece by mechanical polishing can reach Ra=0.3-3.0u.
Cavitation polishing
Chemical polishing is to make the material in the chemical medium, the surface of the micro-convex part is preferentially dissolved than the concave part, so as to obtain a smooth surface; The surface roughness of the workpiece obtained by chemical polishing can reach Ra=0.5-10umno.
Electrolytic pumping
The basic principle of electrolytic polishing is the same as that of chemical polishing, that is, selectively dissolve small protruding parts on the surface of the material to make the surface smooth. Compared with chemical polishing, the effect of eliminating.the cathode reaction ag is better. The electrochemical polishing process is divided into two steps:
- The macro leveling dissolved product diffused into the electrolyte, the surface roughness of the material decreased, Ra>lum.
- Microscopic flat anode polarization, surface roughness improved, Ra<lum.
Ultrasonic polishing
The workpiece is put into the abrasive suspension and placed together in the ultrasonic field, and the abrasive is ground and polished on the workpiece surface by relying on the oscillation of the ultrasonic wave. The commonly used ultrasonic frequency is 16-30kHz, and the abrasives used are emery, boron carbide, silicon carbide, alumina and so on. Ultrasonic processing can be combined with chemical or electrochemical methods.On the basis of solution corrosion and electrolysis, ultrasonic vibration is applied to stir the solution, so that the dissolved products on the surface of the workpiece are separated, and the corrosion or electrolyte near the surface is uniform.
Fluid polishing
Fluid polishing relies on high-speed flowing liquid and the abrasive particles it carries to brush the workpiece surface to achieve the purpose of polishing. Common methods include abrasive jet machining, liquid jet machining, hydrodynamic grinding and so on.
Hydrodynamic grinding is driven by hydraulic pressure to make liquid medium with abrasive particles flow through the workpiece surface at high speed. The medium is mainly made of special compounds (polymer-like substances) with good fluidity under low pressure and mixed with abrasives, which can be silicon carbide powder.
Magnetic grinding and polishing
Magnetic grinding and polishing is the use of magnetic abrasive under the action of magnetic field to form an abrasive brush, grinding the workpiece. This method has high processing efficiency and good quality, the grinding workpiece does not affect its original shape and dimensional accuracy, the finished product does not deform after processing, does not damage the surface, the surface roughness can reach Ra0.1um, and the surface form shows bright metallic luster.
Advantages and disadvantages of six polishing processes
Advantages of mechanical polishing
The structure of mechanical polishing equipment is relatively simple, the price is generally low, and the brightness of the processed parts is high.
Disadvantages of mechanical polishing
- Mechanical polishing is difficult to polish the workpiece with complex shape or special pattern and pattern on the surface;
- Easy to produce metal dust, affecting the health of polishing workers:
- The technical level of workers is high, the consistency and stability of workpiece quality is difficult to control:
Disadvantages of chemical polishing
Advantages of Chemical Polishing
- Simple equipment and uniform surface roughness of parts after processing.
- Easy operation, energy saving, and the ability to polish many workpieces simultaneously.
- High efficiency and the ability to polish complex-shaped workpieces.
- Machining inevitably leaves micro-cracks and residual stresses that are difficult to see by the naked eye on the surface of the workpiece, which may affect the quality and service life of the workpiece and have safety risks.
Electropolishing
Advantages:
- The internal and external color is consistent, the luster is durable, can process hard materials, soft materials and thin wall, complex shape, small parts and coins;
- The polishing amount is very small, the dimensional accuracy and shape accuracy after polishing can be controlled within 0.01mm
- High polishing rate, polishing speed is not affected by the hardness of the material
- Simple process, easy operation, simple equipment, small investment.
Disadvantages:
- The treatment before polishing is more complex and the versatility of the electrolyte is poor, the service life is short, and the corrosion is strong and difficult to deal with.
- It can not eliminate the original surface of the “rough ripple”, the workpiece surface of the matrix roughness requirements, generally should be Ra1.6 below.
Magnetic grinding polishing advantages
- It can achieve very low roughness, generally used for polishing precision optical lenses.
- Because the whole workpiece is in the liquid, the polishing heat is easy to disperse, will not cause overheating in the local position of the workpiece, which is conducive to avoid polishing orange peel.
- All parts of the workpiece are in uniform contact with the fluid, to ensure that the polishing effect is uniform, and is not limited by the shape of the workpiece.
Ultrasonic polishing
Advantages:
Ultrasonic cavitation in the liquid can inhibit the corrosion process, which is conducive to surface brightness
Dsadvantage:
Ultrasonic processing macroscopic force is small, will not cause workpiece deformation, but tooling production and installation is more difficult.
