What are the Methods for Mold Polishing?

With the widespread application of plastic products, such as daily chemical products and beverage packaging containers, the demand for mirror polishing of plastic mold cavities has increased. Particularly in the production of optical lenses and laser discs, the requirements for surface roughness and polishability are extremely high.

Polishing not only enhances the appearance of the workpiece but also improves the corrosion resistance and wear resistance of the material surface. Additionally, it provides other benefits such as easier demolding and reduced injection molding cycle times. Therefore, polishing is a crucial process in plastic mold manufacturing.

Common Polishing Methods

Mechanical Polishing

Mechanical polishing removes protrusions from the surface through cutting and plastic deformation of the material. Tools such as oilstones, wool wheels, and sandpaper are typically used, with manual operation being the primary method. For special parts like rotating surfaces, turntables and other auxiliary tools can be used. For high surface quality, ultra-fine polishing methods can be employed. This involves using special grinding tools and polishing fluids containing abrasives, achieving surface roughness as low as Ra0.008μm. This method is often used for optical lens molds.

Chemical Polishing

Chemical polishing involves dissolving micro-protrusions on the material surface in a chemical medium to obtain a smooth surface. The main advantage of this method is that it does not require complex equipment and can polish workpieces of complex shapes and multiple pieces simultaneously, making it highly efficient. The key to chemical polishing lies in the formulation of the polishing solution, typically achieving a surface roughness of several tens of micrometers.

Electrolytic Polishing

The principle of electrolytic polishing is similar to chemical polishing, where selective dissolution of tiny protrusions on the material surface smooths the surface. Compared to chemical polishing, it can eliminate the influence of cathode reactions and achieve better results. The electrochemical polishing process consists of two steps:

Macro-Leveling: Dissolution products diffuse into the electrolyte, reducing the surface roughness.

Micro-Leveling: Anodic polarization improves surface brightness, achieving Ra < 1μm.

Ultrasonic Polishing

Ultrasonic polishing involves placing the workpiece in a suspension of abrasives and applying ultrasonic oscillations, causing the abrasives to polish the surface. This method has minimal macroscopic force and does not deform the workpiece but is challenging to set up and operate. Combining ultrasonic processing with chemical or electrochemical methods can further enhance surface brightness.

Fluid Polishing

Fluid polishing relies on high-speed fluid carrying abrasives to scour the workpiece surface. Common methods include abrasive jet machining, liquid jet machining, and fluid dynamic polishing. Fluid dynamic polishing uses hydraulically driven liquid media with abrasives to rapidly flow over the workpiece surface. Special compounds with good flow properties at low pressure are often used as the media, mixed with abrasives like silicon carbide powder.

Magnetic Abrasive Polishing

Magnetic abrasive polishing uses magnetic abrasives under a magnetic field to form a brush that polishes the workpiece. This method offers high efficiency, good quality, easy control of processing conditions, and favorable working conditions. With suitable abrasives, surface roughness can reach Ra0.1μm.

Factors Affecting Polishing Quality

Several factors influence the quality of polishing:

Polishing Technique

Since mechanical polishing is primarily manual, the skill level of the technician significantly impacts the polishing quality. Additionally, the material of the mold, surface condition before polishing, and heat treatment process also play roles. High-quality steel is a prerequisite for achieving good polishing quality.

Material Hardness

Increased material hardness makes grinding more challenging but reduces surface roughness after polishing. Higher hardness materials require longer polishing times but have less risk of over-polishing.

Surface Condition of the products

The surface of steel can be damaged during machining due to heat, stress, or other factors, affecting the polishing outcome. Cutting parameters and the precision of EDM also impact the final polishing result.

By selecting appropriate polishing methods and controlling the influencing factors, the quality of mold polishing can be significantly improved to meet the production needs of various plastic products.

Grandshine is a professional factory specializing in mold production and OEM/ODM manufacturing of products. We welcome your inquiries.