Polishing is a finishing process that creates a smooth surface through different methods. Metal polishing has not only decorative value, but also serves a practical purpose. In different polishing processes, their working principle, advantages, disadvantages and uses vary a lot. Here we’ll get into the different types of polishing process and their basics.
Polishing is a surface finishing process that uses physical machinery or chemicals to reduce the surface roughness of objects. Polishing technology is mainly used in precision machinery and optical industries. The surface of the polished CNC component or workpiece is smooth and has a good reflection effect. After polishing, the thickness of the workpiece will be reduced and easily scratched. So the surface must be cleaned with fine velvet cloth, suede, swan feather and special cleaner.
1. Mechanical polishing – How does mechanical polishing work?
Mechanical polishing is a polishing method relies on cutting and plastic deformation of the material surface, and obtain a smooth surface by removing the polished convexities. Generally, abrasive stick, felt wheels, sandpaper are used for mechanical polishing, and mainly are manual operations. Special parts like the rotating body can use auxiliary tools such as turntables, ultra-precision polishing can be used for those who need high surface quality. Ultra-precision polishing is the use of special abrasive tools, which are pressed against the processed surface of the work piece in a polishing fluid containing abrasives for high-speed rotation. The surface roughness of 0.008μm can be achieved by using this technology, which is the best among various polishing methods. Optical lens molds often use this method.
Advantages of mechanical polishing
– High brightness
– Improved surface finish
– Reduced product adhesion
– Better surface cleanability
– Higher aesthetic appeal
Disadvantages of mechanical polishing
– High labor intensity
– Polished parts may be harmful
– Complicated parts can’t be treated
– Gloss can’t be consistent and can’t last a long time
– Could be vulnerable to corrosion
– The mechanical strength of the surface is weakened
2. Chemical polishing – How does chemical polishing work?
In chemical polishing, the microscopically protruding part of the material surface is preferentially dissolved than the concave part in the chemical medium, so a smooth surface could be obtained. During the chemical polishing, the effect of the solution and galvanic couples on the metal surface causes the formation of a passivation layer. The direct result of chemical polishing is the smoothing and polishing of micro roughness and the parallel dissolution of the upper layer. Chemical polishing is usually applied as a quick method of obtaining a desired result, rather than a solution for achieving perfect surface.
Advantages of chemical polishing
– Workpieces with complex shapes can be polished
– High efficiency
– Several parts can be polished at the same time
– Less equipment investment
– Good corrosion resistance
Disadvantages of chemical polishing
– Brightness inhomogeneous
– Difficult to heat
– Gas easy to overflow
– Harmful gas may be released
– Adjustment and regeneration of polishing solutions are difficult
3. Electrolytic polishing (Electropolishing) – How does Electrolytic polishing work?
Electrolytic polishing, also known as Electrolytic polishing, electrochemical polishing, or anodic polishing. The basic principle of electrolytic polishing is the same as that of chemical polishing, namely by using the dissolving solutions to dissolve the small protrusions on the surface and get a smooth surface. But compared with chemical polishing, the effect of cathode reaction can be eliminated, and the polishing effect is better. Electropolishing removes material from a metallic workpiece, reducing the surface roughness by levelling micro-peaks and valleys, improving the surface finish.
Advantages of Electrolytic Polishing
– Luster lasts ling
– Internal and external color are consistent
– An extensive range of materials can be handled
– Low cost, short cycle
– Little pollution
– High corrosion resistance
Disadvantages of Electrolytic Polishing
– High investment in equipment
– Complex pre-polishing process
– Poor universality of electrolyte
– Tooling and auxiliary electrodes are required for complex parts
– Mass production requires cooling facilities