Mr. Fang asked: “Mr. Wu, this is an A3 smooth-surface panel, 0.8 mm thick, produced using a progressive die made of M2 high-speed steel. After polishing the die, we produced 1,000 units, and now there are scratches again. Would applying a PVD titanium coating solve the problem, or should we switch to a different type of die steel?”
To be honest, when using progressive dies to bend 0.8mm-thick A3 bright-finished sheet metal—which isn’t particularly hard or thick—we’re currently using M2 high-speed steel. After polishing the dies, scratches reappear after just 1,000 cycles. It’s so disappointing that such expensive die steel starts showing scratches after making only 1,000 products.
I remember a customer once told me that when they used Cr12MoV for bending and shaping iron pipes, the products kept getting scratched, and the operators were constantly complaining. But after switching to Yuhui’s custom-made DC53, the results improved significantly, and the operators stopped complaining. If it were Cr12MoV, I could understand it, but with a material as expensive as M2, I just can’t wrap my head around it getting scratched again after only 1,000 cycles.
Compared to the Yuhui DC53, this indicates that the smelting quality of their M2 high-speed steel is subpar—segregation is undoubtedly severe, and there are numerous microcracks. Otherwise, scratches wouldn’t appear after just 1,000 products. This is a smelting quality issue with the die steel, and there are only two solutions: either apply a coating or switch to a different type of die steel.
Coating is a form of chemical heat treatment that creates a dense film on the mold surface, which can cover the fine cracks caused by segregation in the base material. Moreover, this film is very hard and wear-resistant, with an excellent surface finish, reducing the coefficient of friction during molding and thereby solving the problem of scratches on the products.
If you want to switch materials, since you’re already using M2 high-speed steel—which costs several hundred per kilogram—it’s clear you have the budget. You could use tungsten steel or powdered high-speed steel; these mold materials, which are of high metallurgical quality and high hardness, won’t develop scratches so quickly.
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Wu Dejian’s tool steel, the chief of staff of the user, bought everything he had used.