Surface treatment and aftertreatment of tools

The last step in the production of a tool part is often what determines how long the tool lasts: surface treatment and finishing. A correctly hardened punch with the right surface coating can last significantly longer than the same punch without — and on an injection mold's forming surfaces polishing directly determines what surface the finished plastic workpiece gets.

§Why post-process at all?

Even the best tool steel has a limit to how much wear and friction it can withstand in its raw form. Surface treatment adds an extra layer of protection or better surface quality on top of the machined and heat-treated steel without compromising the core's strength and ductility.

§PVD coatings: TiN, TiCN, and TiAlN

PVD (Physical Vapour Deposition) is a process where an extremely thin, hard ceramic layer is deposited on the tool's surface in a vacuum chamber. TiN (titanium nitride) gives a characteristic golden surface and good general wear resistance, TiCN adds carbon for even higher hardness, and TiAlN performs best at high temperatures — relevant for tools that get hot during use.

§Nitriding

Nitriding introduces nitrogen to the steel's surface at elevated temperature, which creates a hard, wear-resistant surface layer without the entire part needing to be heat-treated through. It is often used on form parts and stamps, where the core must remain tough while the surface must be able to resist wear from repeated contact.

§Polishing of mold surfaces

On an injection molding form, the form surface is equal to the workpiece surface — a rough form gives a rusty plastic workpiece, while a mirror-polished form gives a glossy workpiece. Polishing therefore often takes place in multiple steps with gradually finer abrasives, and on visible items, the requirement for surface quality can be so high that it takes significantly longer than the actual mechanical processing of the form.

§Quality control after treatment

After surface treatment, typically both hardness (with a hardness test) and layer thickness are checked to confirm that the treatment has actually had the desired effect before the tool is released for production or sent to the customer.