In the process of industrial product diversification, improving the quality of molds, which directly affects product quality, has become a key task. In the manufacturing process of titanium alloy screw molds, the smoothing and mirror-finishing processes after shape processing—namely, the grinding and polishing of part surfaces—are crucial steps in improving mold quality. Mastering appropriate polishing methods can not only improve the quality and service life of titanium alloy screw molds but also further ensure product quality. Recently, Titanium Home has also focused on this key industry technology and reported on it. Below, we will introduce several commonly used mold polishing methods and their working principles in detail.
I. Mechanical Polishing
Mechanical polishing removes protruding parts from the workpiece surface by cutting or causing plastic deformation, thereby obtaining a smooth surface. Tools such as oilstones, wool wheels, and sandpaper are typically used, and the process is mainly manual. For workpieces with high surface quality requirements, ultra-precision polishing can be used. Ultra-precision polishing uses specially made abrasive tools, which are pressed tightly against the workpiece surface in a polishing fluid containing abrasives and subjected to high-speed rotation. Using this technology, the surface roughness of the workpiece can reach Ra 0.008 μm, which is the lowest among many polishing methods. This method is commonly used for optical lens molds. Mechanical polishing occupies a dominant position in the field of mold polishing.
II. Chemical Polishing
Chemical polishing involves placing the material in a chemical medium, causing the microscopic protrusions on the surface to dissolve preferentially compared to the concave parts, thus obtaining a smooth surface. This method can polish workpieces with complex shapes and can polish multiple workpieces simultaneously, resulting in high efficiency. However, the surface roughness obtained by chemical polishing is generally Ra 10 μm.
III. Electrolytic Polishing
The basic principle of electrolytic polishing is similar to that of chemical polishing, relying on the selective dissolution of the tiny protrusions on the material surface to make the surface smooth. Compared with chemical polishing, electrolytic polishing can eliminate the influence of the cathode reaction, resulting in better polishing effects.
IV. Ultrasonic Polishing
Ultrasonic polishing utilizes the ultrasonic vibration of the tool's cross-section to process brittle and hard materials with the aid of an abrasive suspension. Specifically, the workpiece is placed in the abrasive suspension and simultaneously placed within the ultrasonic field. The oscillation of the ultrasound causes the abrasive to grind and polish the workpiece surface. Ultrasonic machining involves relatively small macroscopic forces, preventing workpiece deformation, but tooling fabrication and installation are relatively difficult.
V. Fluid Polishing
Fluid polishing relies on flowing liquid and the abrasive particles it carries to scour the workpiece surface, achieving polishing. Hydrodynamic grinding is hydraulically driven, using a special compound (polymer-like substance) with good fluidity at low pressure, mixed with abrasives, such as silicon carbide powder.
VI. Magnetic Abrasive Polishing
Magnetic abrasive polishing utilizes magnetic abrasives, forming an abrasive brush under the influence of a magnetic field to grind the workpiece. This method offers high efficiency, good quality, and easily controllable processing conditions. With suitable abrasives, a surface roughness of Ra 0.1 μm can be achieved.
VII. Electrical Discharge and Ultrasonic Composite Polishing
To improve the polishing speed of workpieces with a surface roughness Ra of 1.6 μm or higher, ultrasonic polishing combined with a dedicated high-frequency, narrow-pulse, high-peak-current pulse power supply can be used. This composite polishing method combines the advantages of ultrasonic and electrical discharge polishing, effectively improving polishing efficiency and quality.
Different polishing methods have their own characteristics and applicable scopes. In the actual polishing process of titanium alloy screw molds, it is necessary to select the appropriate polishing method or combine multiple methods according to the specific requirements of the mold, the complexity of its shape, the surface roughness requirements, etc., to achieve the ideal polishing effect, improve the quality of the mold, and lay the foundation for the production of high-quality titanium alloy screw products.
