Mr. Huang asked: “This punch is used to punch out these slotted gaskets (1.0 thick, 201 grade), with a slot width of 1.1. It frequently breaks off. What type of die steel should be used for this punch?”
After further discussion, we learned that the punch is made of LD die steel. Previously, it could punch 10,000 to 20,000 pieces, but now it breaks after only a few hundred.
The punch width is 1.1, the sheet thickness is 1.0, and the material is 201 stainless steel, which is relatively hard. Since the punch width is quite narrow—nearly equal to the sheet thickness—this type of narrow-edge, hard-material punching operation places extremely high demands on the die steel’s resistance to chipping; the punch is very prone to chipping.
LD is a 7Cr7Mo2V2Si cold-work die steel that can be heat-treated to a hardness of 60–62 HRC. It offers good wear resistance, but under the harsh operating conditions of small punches for narrow-edge, hard materials, its resistance to chipping is somewhat lacking, so it cannot withstand the stress. Additionally, the poor quality of current mold steel smelting and inadequate heat treatment processes result in inconsistent performance. The fact that it chipped after only a few hundred cycles further confirms this issue; a mold steel with better resistance to chipping must be selected.
For this type of narrow-edge, hard-material stamping, the punch should be made of 8566 anti-chipping steel. 8566 has four times the chipping resistance of high-speed steel SKH-9 and twice that of D2, with a hardness of HRC 58–60. It can resolve chipping issues that high-hardness die steels such as D2, DC53, and SKH-9 cannot address; In particular, under severe conditions—such as stainless steel stamping, thick-gauge sheet metal stamping, fine-blanking dies, sharp-corner stamping, narrow-flange stamping, and applications where the hole diameter is smaller than the sheet thickness or the stamping ratio is less than 1:1—cracking issues that standard die steels cannot resolve are all effectively addressed using 8566 anti-cracking steel.
Mr. Chen was using a progressive die to stamp 0.6 mm thick 1/2H stainless steel—a hard material—with a product narrow edge width of 1 mm. He was using an SKH-9 punch, which would crack after stamping just over 10,000 pieces. After switching to Yuhui 8566 die steel, the punch no longer cracked and could stamp 100,000 products in a single run—a very good result, equivalent to a 10-fold increase in punch life.
Of course, since the amount of material used for his punches is minimal, he could also choose a mold steel with even higher strength, such as PM23 powdered high-speed steel, which has a hardness of 64–66 HRC and better wear resistance than 8566 anti-chipping steel, resulting in an even longer punch life.
Although PM23 costs three times as much as 8566, the amount of material used for the punches is small, so the cost increase is minimal. With the same machining costs and the same mold change time, the longer the punch life, the more cost-effective it is.
From the perspective of punch life, given Mr. Huang’s punch material requirements, I would prioritize PM23 and recommend 8566 anti-chipping steel as a second choice. Once the issue of punch chipping is resolved, the better the wear resistance, the longer the service life, and the more cost-effective it is for the user.
Using 8566 die steel for punches prone to chipping makes for a world of difference between the old and new approaches.
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Wu Dejian’s tool steel, the chief of staff of the user, bought everything he had used.