What’s the best way to improve tooling life in metal stamping shop?

I receive many questions on how to improve high-speed progressive die hits per service, otherwise known as tooling life. How can I get more parts per service? How can I run tooling longer? Faster?

The most immediate answer is to add a coating to your tools. But first, you have to make sure your stamping process is predictable and repeatable with perfect part quality, and that starts with a robust tool design.

Fix Tool Design First

If your tool design is lacking, investing in coatings will be throwing good money after bad. Here are the most common design shortcomings I have seen:

• Die shoes that are too thin and sitting over a large opening in the bolster without proper support. They flex during stamping, which not only affects part quality by causing increased dimensional variation but also causes the cutting edges on the tooling to break down faster because of increased vibration.
• Guide pins and ball cages that are too small for the application. Again, they will flex, causing vibration during cutting and forming, which will lead to premature degradation.
• Poor, spotty, and inconsistent lubrication of the base material during stamping. I have seen felt pads with clothespins holding them in place and oil being dripped only on the top of the strip, leading to inconsistent lube spread. Your strip must be evenly coated top and bottom with just the right amount of lube. Too much can be as bad as too little.
• Designs that do not include proper slug retention, part ejection, and sensors to prevent tool damage. I would confidently state that more than half of stampers’ inefficiency and maintenance expenses are due to these issues.

Once you achieve a consistent and predictable stamping process—your tooling service life is repeatable to +/-10%—you can take service life to the next level with tooling coatings. If your tooling service life repeatability is a higher number historically, you need to figure out what is going on. If you get 100,000 hits per service today and only 50,000 hits per service tomorrow, tool coatings will not help you.

Focus on Coatings

At 1,000 SPM, we run simple flat blanks with minor forms and coins with great success using carbide tooling. With base materials of copper and thin-gauge stainless (0.005 to 0.012 in. thick), we achieve 10 to 20 million hits per service. We invested in the design and tool build, so these dies are very robust and can run for months on end. For us, going through the trouble of re-engineering the tooling to allow for the addition of coatings and then shipping it back and forth to the coater would bring us little benefit—we might gain another week of run time.

But for some extreme stamping applications, when we are forming and extruding material to its maximum capability, the stampings wouldn’t run at all without coatings.

Titanium aluminum nitride coating forms a thin oxide layer on the surface of the tooling, standing up to high temps and extreme pressure. It is very wear-resistant and works great on both steel and carbide.

Another option, vanadium carbide, is one of the hardest known metal carbides and offers excellent lubricity. Using VC on carbides of all grades has allowed us to exceed the engineering maximum allowable extrusion length and thickness. It also can be used on steel tooling.

We’ve also found VC to be the best choice when working with high-strength, low-alloy materials, which have extreme mechanical and corrosion resistance properties. The VC coating is diffused into the surface layer of the base material and offers a hardness of about 3,500 on the Vickers scale (compared to 1,800 for carbide).

Titanium nitride, with a 0.55 coefficient of friction, offers the consistent material flow, lubricity, and basic wear resistance that we need for coining applications. (At our first testing, however, we didn’t get the results we expected until our lubricant specialist pointed us in the right direction with an alternate lubricant, so always consult with your lubricant supplier.) It provides the wear properties of carbide but the toughness of hardened tool steel.

Remember, no two applications are exactly the same because of the tool build, materials, lubricants, and the presses they run in, so be sure to test several coating options under controlled conditions to find what works best.