Ask the Stamping Expert: What are the best coatings to improve tooling life?

A: Coatings do work! Metal forming and stamping tools require surfaces that will withstand very aggressive environments for a very long time to yield high quality and consistent results. Although not every application gives you a big bang for your buck, some specific operations—such as extreme applications of metal extruding, drawing, coining, and forming—would be very difficult to do effectively without a tool coating.

Remember to consider the lubricant when choosing a coating. Coating trials often are done without addressing the lubricant, but the lubricant plays an important role: It creates the protective barrier between the tooling and the workpiece. When you coat tooling, you effectively change the tooling material that comes in contact with the workpiece, so you need to work with your lubrication supplier when executing a coating strategy.

Extruding

In extreme extruding applications, such as half- to full-hard stainless steels and INCONEL® alloys, coatings can greatly improve tooling life, especially when extruding material to lengths many times greater than the thickness of the base stock.

A titanium aluminum nitride (TiAlN) coating forms a thin oxide layer on the outer surface of the tooling. As it wears, the oxide layer re-forms in extreme and hot environments. The coating is very resistant to high temperatures and wear. It performs very well on steel and carbide tooling.

Drawing

For drawing, while the TiAlN coating will work, we prefer vanadium carbide (VC). This inorganic compound is an extremely hard ceramic material—one of the hardest metal carbides available.

In extreme drawing applications, VC can help you meet and even exceed the maximum draw application that can be achieved according to the raw material specifications. We commonly use this coating on carbide tooling, but it works well on steel as well.

Coining

Coining requires good material flow and wear resistance. The coating coefficient of friction and the lubrication become important factors, so be sure to consult your lubrication supplier.

For coining, titanium nitride coating works well. The coefficient of friction is relatively good at 0.55. This coating is hard and tough—harder than carbide and chrome—which makes it suitable for applications that require the wear resistance of carbide but the toughness of tool steel. It tends to stay on the tooling, which lengthens tooling life.

Forming

In extreme cases of forming tough metals, specifically the high-strength, low-alloy (HSLA) steels, the VC treatment is a good choice. HSLA steel is different from standard off-the-shelf steel. When you purchase 304 stainless steel, for example, it will meet a very specific chemical composition recipe. HSLA steels are designed to optimize specific mechanical and corrosion-resistance properties, which makes them desirable for some automotive industry applications.

VC is a diffusion layer on the material that offers extreme impact and wear resistance. While carbide is about 1,800 microhardness on the Vickers scale, VC coating is about 3,500 microhardness.