As industrial products evolve towards diversification and higher quality, improving the quality of molds, which directly impacts product quality, is an important task. In the manufacturing process of titanium alloy screw molds, the smoothing and polishing of the mold surface after initial machining, known as surface grinding and polishing, is a crucial process for enhancing mold quality. Mastering appropriate polishing methods can improve the quality and lifespan of titanium alloy screw molds, ultimately leading to higher product quality.
Common Polishing Methods and Their Working Principles
1. Mechanical Polishing
Mechanical polishing removes protrusions on the workpiece surface by cutting or causing plastic deformation, resulting in a smooth surface. It typically uses materials such as oilstones, felt polishing wheels, and sandpaper, and is primarily a manual process. For higher surface quality requirements, superfinishing can be used. Superfinishing employs a specially designed grinding tool that rotates at high speed while being pressed against the workpiece surface in a polishing solution containing abrasive particles. This technique can achieve a surface roughness of Ra 0.008 μm, which is the best surface finish among various polishing methods. Optical lens molds often utilize this method. Mechanical polishing is the primary method for polishing molds.
2. Chemical polishing
Chemical polishing involves dissolving the micro-protrusions on the surface of a material in a chemical solution, preferentially removing the raised areas more quickly than the recessed areas, thus achieving a smooth surface. This method can polish workpieces of complex shapes, and multiple workpieces can be polished simultaneously, resulting in high efficiency. The surface roughness obtained through chemical polishing is generally around Ra 10 μm.
3. Electrolytic Polishing
The basic principle of electrolytic polishing is similar to chemical polishing: it involves selectively dissolving minute protrusions on the surface of the material to achieve a smooth surface. Compared with chemical polishing, it eliminates the effects of cathodic reactions and yields better results.
4. Ultrasonic Polishing
Ultrasonic polishing is a processing method that utilizes ultrasonic vibrations of the tool tip to polish brittle and hard materials using an abrasive slurry. The workpiece is placed in the abrasive slurry and subjected to ultrasonic vibrations. The oscillating motion of the ultrasonic waves causes the abrasive particles to grind and polish the workpiece surface. Ultrasonic polishing exerts minimal macroscopic force, preventing workpiece deformation, but the tooling design and installation are relatively complex.
5. Fluid Polishing
Fluid polishing utilizes a flowing liquid, carrying abrasive particles, to polish the surface of the workpiece. This method is driven by hydraulic pressure. The polishing medium is typically a special compound (a polymer-like substance) with good flowability at low pressure, to which abrasives, such as silicon carbide powder, are added.
6. Magnetic Abrasive Polishing
Magnetic abrasive polishing uses magnetic abrasive particles, which form an abrasive brush under the influence of a magnetic field, to polish the workpiece. This method offers high efficiency, good quality, and easy control of processing parameters. With suitable abrasives, surface roughness can be reduced to Ra 0.1 μm.
7. Ultrasonic-Electrical Discharge Composite Polishing
To improve the polishing speed of workpieces with surface roughness above Ra 1.6 μm, ultrasonic waves and a high-frequency, narrow-pulse, high-peak current power supply are used in a composite polishing process. The combined effect of ultrasonic vibration and electrical discharge erosion rapidly reduces surface roughness. This method is particularly effective for polishing rough surfaces of molds processed by machining, milling, EDM, or wire cutting.
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