Mechanical polishing is a method that relies on cutting and plastic deformation of the material's surface to remove the protrusions after polishing, resulting in a smooth surface. It generally uses oil stones, wool wheels, sandpaper, etc., primarily operated by hand. For special parts like rotational surfaces, auxiliary tools such as turntables can be used. For high surface quality requirements, ultra precision polishing methods can be adopted.
Ultra precision polishing uses special tools pressed tightly against the workpiece's surface being processed in a high-speed rotating motion in a polishing liquid containing abrasives. This technology can achieve a surface roughness of Ra0.008μm, which is the highest among various polishing methods. Optical lens molds often use this method.
Chemical polishing allows the material's surface to microscopically dissolve preferentially in the elevated portions compared to the recessed parts in a chemical medium, resulting in a smooth surface. The main advantage of this method is that it does not require complex equipment, can polish workpieces of complex shapes, and can polish many workpieces simultaneously with high efficiency. The core issue of chemical polishing is the preparation of the polishing liquid. The surface roughness obtained by chemical polishing is generally tens of micrometers.
Electrolytic polishing is basically the same as chemical polishing, relying on the selective dissolution of the material's micro-protrusions to smooth the surface. Compared to chemical polishing, it can eliminate the effect of the cathode reaction, with better results. The electrochemical polishing process is divided into two steps:
1. Macroscopic leveling. The dissolution products diffuse into the electrolyte, and the surface geometric roughness decreases, Ra>1μm.
2. Microscopic smoothing. Anodic polarization increases surface brightness, Ra<1μm.
The workpiece is placed into an abrasive suspension and immersed in an ultrasonic field. The vibration effect of the ultrasound causes abrasives to polish the workpiece surface. Ultrasound processing has minimal macroscopic force, so it won't deform the workpiece, but tooling manufacturing and installation are relatively difficult.
Ultrasonic processing can be combined with chemical or electrochemical methods. Based on solution corrosion and electrolysis, ultrasonic vibration agitates the solution, causing dissolution products to leave the workpiece surface and uniformly distributing corrosion or electrolyte near the surface. The cavitation effect of ultrasound in the liquid can also inhibit the corrosion process, benefiting surface brightening.
Fluid polishing relies on the high-speed flow of liquid and the abrasive particles it carries to scour the workpiece surface for polishing purposes. Common methods include abrasive jet machining, liquid jet machining, and fluid power grinding.
Fluid power grinding is driven by hydraulics, where a liquid medium carrying abrasives flows rapidly back and forth over the workpiece surface. The medium primarily uses special compounds (polymer-like substances) that flow well under lower pressures mixed with abrasives. Silicon carbide powder can be used as an abrasive.
Magnetic abrasive polishing uses magnetic abrasives to form an abrasive brush under a magnetic field, which processes the workpiece by grinding. This method has high processing efficiency, good quality, easily controlled processing conditions, and favorable working conditions. With the right abrasives, surface roughness can reach Ra0.1μm.
