Surface Treatment Technology – Mold Polishing

Last Updated on September 18, 2023 by assistant

As the manufacturing industry develops toward diversification and high-end development, how to improve the surface effect of industrial products is an important task for mold manufacturing. To polish parts to achieve a refined finish, engineers employ a variety of industrial finishing techniques. Polishing is an important process to improve the quality of molds. Mastering reasonable polishing methods can improve the quality and service life of the mold, thereby improving product quality. This article mainly explains common polishing methods. Here are the details.

#1. Mechanical Polishing

Mechanical polishing is a polishing method that obtains a smooth surface by removing the convex parts caused by cutting and plastic deformation on the material surface. Usually, manual operation mainly uses grinding tools such as oilstone strips, wool wheels, and sandpaper. When encountering special parts, such as the surface of a rotating body, auxiliary tools such as turntables will be used for matching polishing. Mechanical polishing is the main method of mold polishing. If parts with relatively high surface requirements are needed, super-fine polishing is generally used.

Ultra-precision polishing uses a special mold to press the workpiece on the surface to be processed in a polishing fluid containing abrasives and rotated at high speed. This method is often used for surface treatment of optical lens molds. In addition, the surface roughness of the workpiece processed by this technology can reach Ra0.008μm, which is the best surface roughness among various polishing methods. This is also one of the reasons why mechanical polishing can become the main method among many mold polishing methods.

#2. Chemical Polishing

Chemical polishing uses a prepared polishing solution and puts the workpiece material into it so that the microscopic convex parts on the surface are dissolved preferentially than the concave parts, thereby obtaining a smooth surface. The surface roughness obtained by chemical polishing is generally Ra10μm. The advantage of chemical polishing is that it can polish workpieces with complex shapes without the need for complex equipment. Chemical polishing is an efficient polishing process that supports polishing multiple workpieces at the same time.

#3. Electropolishing

Electrolytic polishing is also called electrochemical polishing. The basic principle is the same as chemical polishing. Since the liquid film layer on the tiny protrusions is thinner, the resistance is smaller. Therefore, tiny protruding parts of the workpiece are dissolved preferentially, resulting in a smooth surface effect. Different from chemical polishing, electrolytic polishing eliminates the influence of cathode reaction, and the polishing effect will be more significant.

The electrochemical polishing process can be roughly divided into two steps:
(1) Macroleveling dissolution products diffuse into the electrolyte, and the geometric roughness of the material surface is reduced, Ra>1μm;
(2) Low-light plane anodic polarization improves surface brightness, Ra<1μm.

#4. Ultrasonic polishing

Ultrasonic polishing is based on solution corrosion and electrolysis. It uses the oscillation of ultrasonic waves to stir the solution to separate the dissolved products from the surface of the workpiece placed in the abrasive suspension, thereby achieving the effect of surface grinding and polishing. Not only that, ultrasonic machining is less powerful. Will not cause deformation of the workpiece. In addition, the cavitation effect of ultrasonic waves in liquids can also inhibit the corrosion process and facilitate surface brightness. It is worth noting that the production and installation of this kind of technical tooling is relatively difficult, which greatly tests the production level of the manufacturer.

#5. Fluid polishing

Fluid polishing refers to the use of abrasive particles carried by high-speed flowing liquid to scour the surface of the workpiece under the drive of the hydraulic system to achieve the purpose of polishing. The media for this process is usually made of silicon carbide powder, a special compound (also known as a polymer-like substance) that has good flow properties at lower pressures.

#6. Magnetic grinding and polishing

Magnetic grinding and polishing refers to the use of magnetic abrasives to form an abrasive brush under the action of a magnetic field, and then grind the workpiece. The processing method has good quality, high efficiency, and easy control of processing conditions. Using appropriate abrasives, the surface roughness of the workpiece can reach Ra0.1μm.

#7. EDM ultrasonic composite polishing

EDM ultrasonic composite polishing refers to the use of ultrasonic waves and a dedicated high-frequency narrow pulse high peak current pulse power supply for composite polishing. This technology can simultaneously act on the corrosion of the workpiece surface by ultrasonic vibration and electric pulse, and quickly reduce its surface roughness. This is very effective for polishing rough surfaces of molds processed by turning, milling, EDM, wire cutting, and other processes. It can effectively increase the polishing speed of workpieces with a surface roughness Ra above 1.6μm.

#8. Plasma nano polishing

This is a brand-new metal surface treatment process. Its polished surface roughness is within 1mm. Plasma nano polishing is an electromagnetic gas discharge phenomenon that uses positively charged ion nuclei to rub against the workpiece to be polished. The surface of the workpiece instantly shines.

Final thoughts

Mold polishing is an excellent means of improving the aesthetics of molded parts and ensuring high product quality. Current polishing technology mainly relies on manual work. If not handled properly during the polishing process, uneven surface hardness or differences in properties will result. In the process of plastic mold processing, the polishing of the mold is called mirror processing. It not only has high requirements for polishing itself but also has high standards for surface flatness, smoothness, and geometric accuracy. Ruitai Mold Polishing has more than ten years of rich processing experience. Therefore, if you need polishing services, you can contact us and we will provide you with the best processing services.

Warm reminder: Since it is difficult to accurately control the geometric accuracy of parts by electrolytic polishing, fluid polishing, and other methods, and the surface quality of chemical polishing, ultrasonic polishing, magnetic grinding and polishing, and other methods cannot meet the requirements, the mirror processing of precision molds is still based on mechanical polishing.