Plastic Injection Mold Polishing Treatment

1. Introduction

With the increasingly widespread application of plastic products such as household items and beverage packaging containers, there is often a requirement for the surface of plastic mold cavities to achieve a mirror-like polishing level. Molds used for producing optical lenses, laser discs, and other products have extremely high surface roughness requirements, thus placing high demands on polishing.

Polishing not only enhances the appearance of the workpiece but also improves the surface's corrosion resistance, wear resistance, and other advantages. It can make the mold easier to demold and reduce the production cycle of injection molding. Therefore, polishing is an important process in plastic mold manufacturing.

2. Common Mold Polishing Methods

2.1 Mechanical Polishing

Mechanical polishing refers to the polishing method of cutting the surface of the material to remove the polished protrusions and obtain a smooth surface. It is generally done manually using oil stone bars, polishing wheels, sandpaper, etc. Special parts such as rotating surfaces can use auxiliary tools like turntables. For high surface quality requirements, ultra-precision grinding and polishing methods can be employed.

2.2 Chemical Polishing

Chemical polishing involves dissolving the microscopically raised portions of a material's surface in a chemical medium, resulting in a smooth surface. The main advantages of this method are that it does not require complex equipment, can polish complex-shaped workpieces, and allows for high efficiency when polishing multiple workpieces simultaneously. The key challenge of chemical polishing lies in the preparation of the polishing solution. The surface roughness achieved through chemical polishing is generally around 10μm.

2.3 Electrolytic Polishing

Electrolytic polishing utilizes electrolysis to selectively dissolve the micro-protrusions on the surface of metal workpieces, resulting in a smoother surface. Compared to chemical polishing, electrolytic polishing can eliminate the influence of cathodic reactions and achieve better results.

The electrolytic polishing process consists of two steps: (1) macro-level leveling, where the dissolved products diffuse into the electrolyte, leading to a reduction in the geometric roughness of the material surface (Ra > 1μm)

(2) micro-smoothing, where anodic polarization increases the surface brightness, resulting in a surface roughness of Ra < 1μm

2.4 Ultrasonic Polishing

The workpiece is immersed in a suspension containing abrasives, and then ultrasonic vibrations are applied through an ultrasonic generator, causing tiny grinding and polishing actions on the workpiece surface. Ultrasonic machining exerts minimal macroscopic force, preventing workpiece deformation, but it can be challenging regarding fixture fabrication and installation.

Ultrasonic processing can be combined with chemical or electrochemical methods. By applying ultrasonic vibration to the solution during the processes of corrosion or electrolysis, the dissolved products near the surface are removed more effectively, and the cavitation effect of ultrasound in the liquid can also inhibit the corrosion process, resulting in improved surface brightness.