Page 45 - MetalForming April 2020

The Science of Forming
steels to estimate the maximum amount of sheet metal motion available for different combinations of major and minor sur- face strains. However, most other grades do not follow these classical equations, discovered by Dr. Stuart Keeler (the found- ing author of this Science of Forming column); detailed exper- iments are needed to create FLCs for these grades.
Springback is one of the most significant challenges stam- pers face when working with higher-strength steels. The AHSS Guidelines describe the causes of springback, and present different ways that users can correct for the associated dimen- sional problems.
Applications using press hardenable steels continue to expand. After hot forming and quenching, strengths can reach, or exceed, 2000 MPa. Complex shapes can be achieved owing to forming at high temperatures, and in-die quenching will minimize springback. The guidelines document offers process-design details describing the challenges associated with these products.
The proper use of simulation tools impacts AHSS stamping success, requiring inputs appropriate for each grade. The AHSS Application Guidelines provides generic stress-strain curves useful for early feasibility analysis before selecting a production supplier. Other key inputs are described, with useful data shown.
Lastly, the AHSS Application Guidelines addresses tech- niques for joining AHSS grades, which must be modified from those used for mild and conventional high-strength steels. Among the topics covered: challenges and solutions associated with resistance spot welding of variable thickness stack-ups; arc, laser, and hybrid welding; weld bonding; mechanical joining; paint baking effects related to joining; and liquid-metal and hydrogen embrittlement, and corrective actions for each.
Learn and Follow Along
Experience with advanced steel grades has dramatically increased since the AHSS Guidelines was last published. This leads to one of the major additions coming with the next release: an increased number of case studies, which aim to take users through the thought process of creating successful, robust stampings made from AHSS grades.
While we’ve always referred to the lower arc of the figure as the “banana curve,” a better description, considering the options now available, might be the “football graph.” AHSS applications will continue to proliferate at automotive OEM and supplier plants; follow developments by signing up to receive updates at www.ahssinsights.org. MF
Danny Schaeffler is the technical editor for metallurgy and forming for the upcoming release of the AHSS Guidelines. Contact him at ds@EQSgroup.com to contribute a case study to the Advanced High Strength Steels Application Guidelines. We’re looking for lessons-learned, where things may not have gone smoothly at first. We will be giving full attribution where requested, including links to your company.
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