1.2 What material is best for thinning and drawing 1.2-thick cold-rolled steel sheets without damaging the die? We’re currently using DC53 with a titanium coating, but it starts to show wire marks after fewer than 1,000 pieces. Question from a viewer during Live Stream #297
Strain lines on drawing dies are the bane of every drawing operator’s existence. As soon as strain lines appear, the product is defective, which means the die needs to be repaired. Having to repair the die after just 1,000 parts is extremely frustrating.
Applying a coating to a die is labor-intensive, time-consuming, and expensive, yet if it only lasts for 1,000 parts before it’s done for, it’s a real headache.
Wire drawing in drawing dies is generally caused by adhesive wear resulting from material adhesion. Adhesive wear is caused by microscopic cracks in the die steel’s microstructure that are invisible to the naked eye; this is due to poor smelting quality and segregation in the microstructure.
To prevent wire drawing in drawing dies, it is essential to select die steel with high smelting quality, uniform microstructure, and no microscopic cracks.
Normally, using DC53 with a titanium coating for drawing dies is a reasonable choice of material and a sound approach; such dies should not develop wire drawing issues so quickly.
However, the fact that stringing occurs after only 1,000 products—even when working with relatively soft cold-rolled sheet that is only 1.2 mm thick—is highly unreasonable. This indicates that the DC53 currently in use suffers from severe microstructural segregation and numerous microscopic cracks, which the titanium coating cannot fully mask, resulting in stringing after just 1,000 products.
If you do not wish to use DC53, you can switch to wear-resistant steel 6077 or the higher-performance 8503 die steel.
Wear-resistant steel 6077 is produced via an electroslag process with high purity and undergoes six-sided forging, resulting in a uniform microstructure with few microcracks. With a hardness of HRC 60–63, its resistance to chipping is three times that of chromium steel.
Mr. Tan said that the 6077 wear-resistant steel he bought last time worked quite well. I use it to deep-draw 0.7mm galvanized sheet metal into motor housings with a draw height of 30mm. We’ve already produced 3 million units, and we’ve never had a customer complaint. Previously, when we used DC53, the parts would start showing wire marks after only a few products, and we’d get scolded by customers. Now that we’re using 6077 wear-resistant steel, although wire marks do appear after a certain period of use, a quick polish is all it takes to make the die reusable. Since the production frequency isn’t very high, customers don’t complain. Plus, 6077 wear-resistant steel isn’t expensive. Now that a single die can produce 3 million units, I’m completely satisfied. I run a die manufacturing plant—as long as customers don’t complain, I’m happy.
When using 6077 wear-resistant steel to deep-draw 1.2 cold-rolled sheet, it won’t develop wire marks after just 1,000 units. If you’re willing to apply a coating, the results will be even better.
Of course, when making drawing dies, you can also use 8503 die steel, which has better non-stick properties. 8503 has twice the toughness of DC53 and a hardness of 55–61 HRC. Compared to DC53, its performance is doubled without a corresponding increase in price, and it offers the added benefit of non-stick properties.
Customers in the automotive wheel hub industry have already verified that non-stick 8503 steel performs better than Cr12MoV with a coating when used for wheel hub drawing dies, and the dies do not exhibit stringing.
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Wu Dejian’s tool steel, the chief of staff of the user, bought everything he had used.