A Douyin user messaged me asking: “I’ve used DC53, CALDIE, and SKH55 for the mandrel in round tube punching. After producing about 5,000 pieces, it broke. What tool steel should I use?”
This type of mandrel is used for punching tubular parts. It extends into the tube but is used as a cutting edge, with one end suspended in the air. Since the mandrel is small and involves drilling, there is very little material to support the edge. This leads to insufficient strength: low-hardness steel will suffer from corner collapse and dull cutting edges, while high-hardness steel is prone to breaking. For this application, you should select a die steel with high hardness and good toughness.
The user is currently using DC53, CALDIE, and SKH55, all of which are prone to breaking. They break after just 5,000 pieces. This is because the mold steel used is too brittle, and the material selection is incorrect.
Of these three materials, SKH55 is likely the one that breaks most easily. It is a high-speed steel containing 5.5% cobalt with a hardness of 63–64HRC. While it offers excellent wear resistance, it is very brittle, so it’s normal for it to break easily. The next most prone to breaking is DC53, a high-carbon steel with a carbon content of 1.0%. A common drawback of high-carbon steel is its poor toughness. The same applies to CALDIE: although it performs better than DC53, it is still too brittle. The fact that it breaks after just 5,000 stamping cycles further confirms this.
For this type of single-sided cantilevered bridge-type mandrel fracture, I recommend the high-toughness LG die steel.
LG is a proprietary high-toughness die steel developed by Yuhui Company. LG’s toughness is 8 to 9 times that of DC53, with a hardness of 54–58HRC. It is so tough that it will not break even if bent by hand.
Mr. Chen, who manufactures stamped pipe fittings, had been using single-arm cantilever mandrels made of Cr12MoV, SKD11, and DC53. However, all of them broke after just a few hundred to a thousand pieces, making production unfeasible due to excessive mandrel wear, high costs, and low efficiency.
But after switching to Yuhui’s high-toughness LG die steel, the mandrels remained intact even after stamping over 30,000 pieces. The mandrel lifespan has increased from a few hundred to a thousand cycles to 30,000 cycles—a 30-fold improvement.
This user has used DC53, CALDIE, and SKH55 for round tube punching mandrels, but they all broke after producing around 5,000 pieces. I recommend you use high-toughness LG tool steel.
Using LG tool steel for mold cracking is like stepping into a liberated zone.
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Wu Dejian’s tool steel, the chief of staff of the user, bought everything he had used.