Polishing Methods For Plastic Molds

Mechanical polishing
Mechanical polishing is a polishing method that obtains a smooth surface by removing the convex parts after polishing through cutting and plastic deformation of the material surface. It generally uses oilstone strips, wool wheels, sandpaper, etc., and is mainly manually operated. Special parts such as the surface of the rotating body can use auxiliary tools such as a turntable. For high surface quality requirements, ultra precision polishing can be used. Ultra precision polishing is the use of specially designed grinding tools, which are tightly pressed onto the machined surface of the workpiece in a polishing fluid containing abrasives and perform high-speed rotational motion. By utilizing this technology, Ra0.008 can be achieved μ The surface roughness of m is the highest among various polishing methods. This method is often used in optical lens molds.
chemical polishing
Chemical polishing is the process of allowing materials to preferentially dissolve the micro protruding parts of the surface in a chemical medium, resulting in a smooth surface. The main advantage of this method is that it does not require complex equipment and can polish workpieces with complex shapes. It can simultaneously polish many workpieces with high efficiency. The core issue of chemical polishing is the preparation of polishing solution. The surface roughness obtained by chemical polishing is generally in the order of 10 μ M.
Electropolishing
The basic principle of Electropolishing is the same as that of chemical polishing, that is, by selectively dissolving the small protruding parts on the surface of the material, the surface is smooth. Compared with chemical polishing, it can eliminate the influence of cathodic reaction and achieve better results. The electrochemical polishing process is divided into two steps: ⑴ Macroscopic leveling and diffusion of dissolved products into the electrolyte, resulting in a decrease in the geometric roughness of the material surface, with Ra>1 μ m. ⑵ Low light level flat anodic polarization, increased surface brightness, Ra<1 μ M.
Ultrasonic polishing
Place the workpiece in an abrasive suspension and place it together in an ultrasonic field, relying on the oscillation effect of the ultrasonic wave to grind and polish the abrasive on the surface of the workpiece. Ultrasonic machining has low macroscopic force and will not cause deformation of the workpiece, but it is difficult to make and install tooling. Ultrasonic machining can be combined with chemical or electrochemical methods. On the basis of solution corrosion and electrolysis, ultrasonic vibration is applied to stir the solution to separate the dissolved products on the surface of the workpiece, and the corrosion or electrolyte near the surface is uniform; The cavitation effect of ultrasound in liquids can also suppress the corrosion process, which is conducive to surface brightening.
Fluid polishing
Fluid polishing relies on the high-speed flow of liquid and its carried abrasive particles to wash the surface of the workpiece to achieve the purpose of polishing. Common methods include abrasive jet machining, liquid jet machining, Fluid power grinding, etc. Fluid power grinding is driven by hydraulic pressure, which makes the liquid medium carrying abrasive particles flow back and forth across the workpiece surface at a high speed. The medium is mainly made of special compounds (polymer like substances) with good flowability under low pressure and mixed with abrasives, which can be silicon carbide powder.
Magnetic abrasive polishing
Magnetic abrasive polishing is the use of magnetic abrasives to form abrasive brushes under the action of a magnetic field, which grind and process workpieces. This method has high processing efficiency, good quality, easy control of processing conditions, and good working conditions. Using suitable abrasives, the surface roughness can reach Ra0.1 μ M. The mechanical polishing method used in plastic mold processing differs greatly from the surface polishing required in other industries. Strictly speaking, mold polishing should be referred to as mirror processing. It not only has high requirements for polishing itself, but also has high standards for surface flatness, smoothness, and geometric accuracy. Surface polishing generally only requires obtaining a bright surface. The standard for mirror processing is divided into four levels: AO=Ra0.008 μ m. A1=Ra0.016 μ m. A3=Ra0.032 μ m. A4=Ra0.063 μ m. Since Electropolishing, fluid polishing and other methods are difficult to accurately control the geometric accuracy of parts, and the surface quality of chemical polishing, ultrasonic polishing, magnetic abrasive polishing and other methods cannot meet the requirements, the mirror surface processing of precision molds is mainly mechanical polishing.
Basic program
To achieve high-quality polishing results, the most important thing is to have high-quality polishing tools and accessories such as oilstones, sandpaper, and diamond grinding paste. The selection of polishing program depends on the surface condition after the initial processing, such as machining, Electrical discharge machining, grinding, etc.