0.12–0.2 thick tin-plated red copper, using SKH-9 high-speed steel. Currently, after 20,000 production cycles, the punch and cutting edge show wear at the R-corner, causing burrs. What type of die steel would be better? Question from a viewer during Live Stream #297
There are two types of wear: one is friction wear caused by insufficient wear resistance, which typically occurs only after a certain number of products have been produced. This is easy to resolve; simply selecting a mold steel with better wear resistance will extend the mold’s service life.
The other type is adhesive wear caused by material adhesion, which occurs shortly after the mold is put into use. It generally happens during the stamping of soft materials; even though the material you’re using appears hard, it may still lack sufficient wear resistance. This is typically caused by segregation defects in the mold steel, resulting from microscopic cracks in the microstructure that are invisible to the naked eye. This issue can be resolved by selecting mold steel with high-quality smelting.
This user is stamping 0.12–0.2 mm-thick red copper. This material is very soft and thin, so in theory, it shouldn’t be difficult to stamp. Furthermore, SKH-9 is a high-speed steel with a hardness of HRC 62–64, which already offers excellent wear resistance. However, after stamping only 20,000 parts, the cutting edge has worn down and developed burrs—this is a classic case of adhesive wear caused by material sticking.
Since copper is not a hard material, the die does not need to be overly hard; the key is its non-stick properties. Given the current situation—where the SKH-9 die developed burrs after only 20,000 stampings—there are three solutions:
First, apply a surface coating to the existing SKH-9 die to improve surface finish and cover any microcracks. This is a cost-effective measure that can significantly extend the die’s service life.
If you wish to change the die steel, you can switch to 8566 die steel. There are already successful case studies of 8566 being used for stamping copper, and since its price is comparable to SKH-9, your material costs will not increase.
Mr. Wu was stamping 0.3-mm copper inserts on a high-speed press. The Cr12MoV punch was not wear-resistant and developed burrs after only a few stamping cycles. Due to the high stamping speed and frequent die changes, the customer was very dissatisfied. However, after switching to 8566, the punch was able to withstand over 1 million stamping cycles, producing more than 100,000 units per day, and lasted for about 10 days. The customer reported that the results were very good.
Third option: If you’re concerned that 8566 isn’t wear-resistant enough, you can choose PM23 powdered high-speed steel, with a hardness of HRC 64–66. It utilizes an advanced powder metallurgy process that avoids the segregation issues commonly found in high-speed steel. Therefore, when punching copper with PM23, copper powder won’t stick to the punch. Moreover, its hardness is higher than SKH-9, and its wear resistance is better than SKH-9, making it very effective. However, it costs twice as much as SKH-9, so you’ll need to consider the cost implications.
Based on the user’s mold operating conditions, I provide three solutions for them to choose from to help resolve their pressing steel selection issues—that’s my daily work.
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Wu Dejian’s tool steel, the chief of staff of the user, bought everything he had used.