Stabilizing AHSS/UHSS forming via recommended tool grades
SSAB has over 40 years of experience in tool steel solutions for HSS. Our know-how is based on real-world production results from our customers, as well as attending different R&D projects studying long-run series. We encourage you to download our 40-page Tooling Solutions for Advanced High Strength Steels booklet for specific tool steel recommendations.
In forming operations, tooling failure mechanisms can include galling, wear, and plastic deformation, while blanking operations can also include chipping and cracking failures. With non-optimal tool steel methods, friction can build up over time, increasing the springback effect and putting your parts out of tolerance. Another problem can be chipping of the tool during blanking, resulting in poor cutting edges that lead to sudden risk of fractures in flanges.
SSAB provides very specific guidance for tool steel grades for the stamping of its Docol® AHSS/UHSS steel grades, with hardnesses ≥ 60 HRC to prevent plastification and typically recommending surface treatments (coatings). The initial higher costs for these high performance tool steels will be more than offset by a reduction in production stoppages and tooling refurbishments/maintenance costs.
Stamping higher strength AHSS/UHSS grades means higher pressures and an increased risk for galling. To ensure stable friction conditions, design a tool insert and use PVD/CVD or Duplex treated tooling steel. Before adding the coating, the polishing process is very essential. Polish the surface finish to at least Ra< 0.2 µm and, at very critical areas, down to Ra 0.05 µm to avoid cracking, galling, and increased friction.
For cold forming and blanking of AHSS/UHSS grades, consider SSAB's Toolox® tooling steel, with a surface-hardening capability for PVD, laser, induction, and nitriding. Toolox® steel has less friction due to its high level of micro cleanliness, a very high dampening ratio because of its vibration resistance, high fatigue strength, and high resistance to chipping and cracking.