top of page

6 Mould Polishing Techniques for Injection Moulding

What is Mould Polishing:


Mould polishing is the process of smoothing injection moulded surfaces. Using a range of techniques using tools such as wool wheels, whetstone strips and sandpaper, convex parts of the mould are cut, formed and smoothed. 


For greater precision in polishing, manufacturers will often use specialised tools and methods to help reduce surface toughness to around Ra 0.008. These specialised tools tightly press liquid containing various abrasives at high speeds to smooth the surface.

Importance of Plastic Injection Mould Polishing:

Mould polishing techniques are crucial for increasing the quality of the plastic mould and the quality of the final plastic component.


Overall there are two primary focuses during this process including:

Creating an easy and smooth injection moulding process:

With the mould having a smoother surface, those working with the part can easily remove the moulded plastic parts minimising injection moulding defects.

Improving the overall quality of the plastic injection part. 

As mentioned prior, smooth mould surfaces help enhance the appearance and quality of the final plastic component, enhancing both the wear and corrosion resistance of the part. Additionally, turnaround times for the parts can be significantly reduced when effective plastic mould polishing techniques are in place.

Mould Polishing Techniques

Mechanical Polishing:

Mechanical polishing involves using sandpaper, wool wheels, oil stones and other tools to help remove protruding parts of the mould. 


Operations with high surface requirements use polishing techniques that provide a higher level of precision. In these instances, special purpose moulding techniques using abrasives are pressed on the mould at high speeds to help produce a roughness of up to Ra 0.008μm.

Chemical Polishing:

The chemical polishing process involves soaking the material in a chemical medium to dissolve micro-projections on the object's surface.


This process is often used to help ease the smoothing process for parts with more complicated shapes. Using this technique, manufacturers can work on multiple parts simultaneously to achieve a higher efficiency level. Surface roughness obtained by chemical polishing averages around Ra 10μm.

Electrolytic Mould Polishing: 

Electropolishing works similarly to chemical polishing in the way that the surface is smoothed by selectively dissolving protrusions on the surface of the material. Electropolishing, however, eliminates the effect of cathode reaction to provide a smoother finish with an average smoothness of Ra <1μm.

Ultrasonic Mould Polishing:

Ultrasonic Mould Polishing uses abrasive suspension to polish brittle, hard materials. Ultrasonic polishers apply ultrasonic vibrations to tools to provide fast and effortless polishing with a good finish. The tool moves with a stroke length of 40μm up to 30,000 times per second. 

Ultrasonic polishing can be combined with chemical or electrochemical methods to provide a smoother, brighter finish.

Fluid Mould Polishing:

Fluid polishing involves using high speed flowing liquid and abrasive grains to wash the surface of the mould, therefore smoothing the surface. Standard fluid polishing techniques include abrasive jet processing, liquid jet processing and hydrodynamic grinding. 


  • Abrasive jet Machining: Process performed by mixing and spraying abrasives into a water stream.   

  • Liquid Jet Processing: Process of using highly pressurised water to cut, clean and smooth components.

  • Hydrodynamic Grinding: Hydraulic pressure carrying abrasive grains flow back and forth along the surface of the mould at high speed to smooth the surface of the part.

Magnetic Grinding and Polishing:

Magnetic polishing involves using a metal field to run tiny magnetic threads along the surface of a part to provide surface roughness of around Ra 0.1 μm. This method is highly efficient, provides high quality finished parts and is easily controllable. 


Mould polishing is an important manufacturing process to ensure high quality and a long lifespan for your injection moulded part/mould. With over 25 years in the manufacturing industry, our team has the skills and knowledge to recommend polishing methods to suit your designs needs. Contact our team today to see how we can help.

bottom of page