Plastic injection mold makers face a very daunting task when it comes to picking the correct coating for carbide inserts. Just consider the number of quality companies offering carbide inserts, plus the geometries and coatings available from each company!

Add the choices for carbide insert substrates, coolants, high speed machining and the many types of tool steels used in mold making and the selection process becomes even more complicated.

This article is one of a series dealing with carbide inserts, specifically the coatings used. There are quite a few coatings in use for the machining of injection mold cores and cavities. Our discussion will focus on the milling of cores and cavities rather than mold bases.

Carbide inserts are comprised of three main features:

  • Substrate material
  • Type of coating
  • Insert geometry

What are substrates?The substrate is the base material used in the carbide insert. Most thinly coated carbide inserts use tungsten carbide, grade C-2. This is commonly used for a wide range of coated inserts, and it is increasingly less important what type of carbide substrate is used because the coatings are so efficient. However, there are many grades of substrates that can be used depending on the application.

How are coatings applied to the substrate?

The various coatings used on carbide inserts, such as diamond coatings, are applied by chemical vapor deposition, or CVD. The diamond must stick to the substrate with very strong adhesion in order to function well in a machining application.