Thomas Vacca Thomas Vacca
Director of Engineering

Best Tool Steel for High-Speed Stamping?

April 29, 2024
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Q: What’s the best tool steel for my high-speed stamping applications?

This is a very important question. The right tool steel can double—or halve—the number of hits you get from tooling before it requires service. Obviously, this has a serious impact on the tooling bottom line. You need a thorough understanding of the tool steel’s mechanical properties and apply them as needed to suit your specific application. How will the steel flex when mechanical forces are applied? Proper heat treatment also is crucial to success.

Hardness and toughness are the two most critical properties I look for when choosing a tool steel for my cutting and coining processes. 

Hardness. Hardness is the ability of a tool steel to withstand indentation after proper heat treatment. If you are stamping relatively light-gauge material (less than 0.015 in. thick), opt for the hardest possible cutting tooling … most of the time that is carbide. That is, of course, if the cutting geometry is not so fine that the geometry lacks the strength to hold up. If that is the case, back down on the hardness and look for increased toughness. I cannot stress enough that you must pay close attention to proper heat treatment, annealing and tempering. You might even double- or triple-temper for maximum toughness.

Toughness. This is the ability of the material to absorb energy and shock without degradation. One job I worked on required a forming arbor with a nonsymmetrical load applied. We tried several materials, based on hardness, to no success. Then we tried materials that were not as hard but were tougher—Crucible 3V. We sacrificed tool life but achieved results that allowed us to run consistently. A high-toughness material, such as the CPM grade of tool steel, will provide maximum break resistance. Proper heat treatment, stress relieving and triple tempering were required. In addition, we added cryogenic freezing between the last two tempers. The cryogenic freezing process, while underutilized, makes all of the difference in achieving success.

Tensile strength. Most designers place a lot of weight on the importance of tensile strength when choosing tool steel for their stamping dies. But I submit that shear strength and compression strength are just as valuable. Typically, I do not consider tensile strength as a primary requirement when choosing tool steels. I value other properties more. But, in part or product design, it’s the opposite, because tensile strength is a measure of how much tension force can be applied before the product deforms.

Fatigue strength. This is another property I generally do not consider unless it is for an extreme forming application. If I manufactured springs, it would be at the top of my list because fatigue strength dictates to how many times the material can be cycled through load and no load before failure.

Elasticity. This is a very important property when excessive load is applied in coining and forming. Anytime that the material must flex and return to its original shape without any permanent deformation, elasticity is key.

Coefficient of expansion. Thermal expansion is the tendency for matter to change in shape, area and volume in response to a change in temperature. Steel grows when it is warmed up. I once had a stamping project in which the progression of the stamped strip was critical (±0.0020 in.). The die was 2.5 ft. long. The die chase was made from A6 steel, our standard for die chases. We learned the hard way that when the die chase was heated by 20 F in our high-speed stamping press, the progression on the final stamped strip grew by 0.0020 in. We were forced to air-condition the inside of the cabinet that enclosed the press to keep it precisely at 75 F.   

Consider several other material properties such as malleability, ductility, abrasion resistance and brittleness. But again, hardness, toughness and fatigue are the main die-steel considerations for a typical high-speed-stamping application.   

In conclusion, 25% of stamping problems are material-related; 75% design-related. Eliminating vibration absolutely is critical to stamping success. Build very robust dies: Thick die shoe; large, accurate pins; and thick ball-cage guides. Stagger the punches to minimize the snapthrough shock. Minimize the press stroke. These approaches can quadruple the number of parts yielded per tooling service. Remember, carbide does not wear as does conventional steel. The edges disintegrate. Steel deforms. With carbide: no vibration, no wear.

Good luck and happy stamping! MF

Send your questions for Tom Vacca to kbachman@pma.org.

Industry-Related Terms: Abrasion Resistance, Case, Coining, Die, Ductility, Forming, Run, Stroke, Tempering, Tensile Strength
View Glossary of Metalforming Terms

Technologies: Stamping Presses, Tooling

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