Mirror polishing (primarily mechanical polishing, supplemented by chemical/electropolishing) follows the principle of "from coarse to fine, step by step," and is mainly divided into five core stages: pre-treatment, rough polishing, semi-fine polishing, fine polishing, and post-treatment. The specific process is as follows:
I. Pre-treatment (Preparation Stage)
1. Surface Cleaning: Use chemical (such as pickling, degreasing) or physical methods to thoroughly remove grease, dust, oxide scale, and machining residues from the workpiece surface, ensuring a clean surface to provide a good base for subsequent grinding.
II. Rough Polishing (Removal of Macroscopic Marks)
1. Purpose: Rapidly remove coarse machining marks (such as milling, EDM, grinding marks) and irregular contours from the workpiece surface and initially flatten the surface.
2.Operation: Use a high-speed (35,000–40,000 RPM) rotary polisher or ultrasonic grinding machine, combined with coarse-grit grinding discs (such as aluminum oxide grinding wheels, composite flap discs) for preliminary grinding.
III. Semi-Fine Polishing (Surface Refinement)
1. Purpose: Eliminate deeper grinding marks left by rough polishing, further flatten the surface, and lay a fine base for fine polishing.
2. Operation: Use sandpaper of different grit grades (such as 400#, 600#, 800#, 1000#, 1200#, 1500#) with kerosene or water for grinding, or use synthetic polishing discs for fine grinding. During grinding, pay attention to changing the grinding direction (45°–90°) to eliminate marks from the previous step.
IV. Fine Polishing (Mirror Formation)
1. Purpose: Remove fine grinding marks left by semi-fine polishing, eliminate surface micro-pits, and achieve a bright, mirror-like finish (Ra value can reach below 0.08 μm).
2. Operation: Use ultra-fine diamond polishing compound (such as 9 μm, 6 μm, 3 μm, 1 μm, 0.5 μm, etc.) with polishing cloth wheels, felt bobs, or adhesive felt for fine grinding. Fine polishing must be carried out in a dust-free environment, with light pressure to avoid "orange peel" or "pitting."
V. Post-treatment (Cleaning and Protection)
1. Thorough Cleaning: After each process step, thoroughly clean the workpiece surface to remove residual abrasives, oil stains, and moisture, preventing impurities from affecting the final mirror effect or causing corrosion.
2. Protective Treatment: After polishing is completed, perform anti-rust treatment on the workpiece surface (such as spraying anti-rust oil) and properly protect against dust.
Note: For complex-shaped, micro-sized or ultra-precision workpieces, chemical polishing, electropolishing or ultrasonic polishing may be combined for local treatment, but mechanical polishing remains the most mainstream process for achieving a mirror finish.
Author：Wangbo