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Mechanical machining：Polishing&Mirror polishing
Polishing, as both a machining operation and a surface treatment method, focuses on improving the surface quality of workpieces by reducing roughness and enhancing glossiness.
In the field of machining, surface finish is a critical factor that directly affects the performance, appearance, and service life of mechanical parts. Among various surface treatment processes, polishing plays an indispensable role.
1. What is Polishing in Machining?
Polishing in machining refers to a precision surface finishing process that uses mechanical, chemical, or electrochemical methods to remove micro-scale unevenness from the workpiece surface.
Unlike rough machining processes such as turning, milling, or grinding, which primarily aim to shape the workpiece and control dimensional accuracy, polishing is a post-processing step focused on optimizing surface quality. Its core goal is to reduce the surface roughness (Ra) of the workpiece—typically from the range of 0.8–3.2 μm (after grinding) to below 0.8 μm, and even down to 0.01 μm for ultra-precision polishing. Additionally, polishing enhances the surface glossiness, making the workpiece surface smooth, bright, and free of visible defects such as burrs, tool marks, or scratches left by previous machining processes.
It should be emphasized that polishing is a "non-cutting" or "micro-cutting" process. During operation, the amount of material removed is extremely small (usually in the micron or sub-micron level), so it does not significantly affect the dimensional accuracy of the workpiece. This makes polishing particularly suitable for workpieces that have already achieved the required dimensions through prior machining but need further improvement in surface performance.
Polishing surface treatment is the application of polishing technology to achieve specific surface properties of workpieces, which is an important part of the overall machining process. Its core functions go beyond just improving appearance；
- Improving Corrosion Resistance
- Reducing Friction and Wear
- Enhancing Aesthetic and Decorative Value
- Facilitating Subsequent Processing
Chemical Polishing
Chemical polishing uses a chemical solution (usually a mixture of acids, bases, or salts) to selectively dissolve the micro-protrusions on the workpiece surface. The chemical reaction makes the surface smooth and bright without the need for mechanical friction. This method is particularly suitable for workpieces with complex shapes, as the chemical solution can evenly act on all surfaces, including internal cavities and narrow gaps.
Advantages: No mechanical stress on the workpiece surface; high efficiency, suitable for mass production; can polish complex-shaped workpieces.
Disadvantages: The chemical solution is corrosive and requires strict environmental protection measures; the surface roughness after polishing is not as low as that of mechanical or electrochemical polishing; the process parameters (temperature, time, solution concentration) are difficult to control.
Electrochemical Polishing
Electrochemical polishing (also known as electrolytic polishing) combines electrochemical reactions and chemical dissolution. The workpiece is used as the anode, and an inert material (such as lead or graphite) is used as the cathode. When an electric current is applied in a specific electrolytic solution, the micro-protrusions on the workpiece surface are preferentially dissolved, resulting in a smooth, bright, and corrosion-resistant surface.
Advantages: The polished surface has ultra-low roughness (up to mirror level); no residual stress, improving the fatigue resistance of the workpiece; high efficiency and good consistency, suitable for mass production; can polish workpieces with complex shapes.
Disadvantages: High equipment and operating costs; strict requirements on the electrolytic solution and process parameters; only applicable to conductive materials (mainly metals).