Page 46 - MetalForming April 2017

Hot Stamping: Local Soft
Local Soft
Zones Via
Zones Via
Laser
Laser
As steels get stronger, hot stamping with localized softening—now very localized via lasers—is a game changer in automotive applications.
Steel blanks enter a furnace in the first stage of the hot-stamping process. Heat- ing the blanks to above 900 C makes them more malleable while shifting the steel to a full austenitic phase.
ing processes—the former shifting the steel to a full austenitic phase followed by the latter for transformation to a full martensitic phase—create the hardened material while not overly stressing the tooling, thus the material can be formed more easily prior to reaching its final hardened state.
Via this process, ultra-hard steel is formed into complex shapes, resulting in lightweight yet strong parts that, otherwise, typically would require thicker, heavier cold-stamped parts welded together.
By using improved validation meas- ures such as advanced forming and crash simulation data and software, Honda and Gestamp were able to bet- ter localize soft zones in the die during hot stamping, resulting in production of rear rails in the 2015 Honda Civic with soft-zone features that enable improved impact-energy absorption in the event of a crash. The develop- ment earned Honda and Gestamp the
BY LOUIS A. KREN, SENIOR EDITOR
Developed in the early-1970s and first used to provide wear resistance for knives, lawn- mower blades and shovels, press hard- ening—or hot stamping—was con- ceived as a means to replace cold stamping and secondary batch hard- ening with a forming/quenching process within a single tool. Today, hot stamping finds itself in the midst of a renaissance, owing to automotive light- weighting and safety trends.
Thanks to decades of R&D, hot stamping has undergone generational technology changes that now enable it to serve as a viable process for pro- duction of front and rear crash-zone parts, well past its early automotive applications for impact beams and pil- lars. Key is the ability to create ever more specific soft zones in the parts, according to Paul Belanger, director of
Gestamp R&D North America. “Migration of high-strength steels into the crash zones is probably due to control of soft zones,” Belanger says, “and the ability to design for them and know the kinematics of the parts during the crash event. This knowledge allows
for significant weight savings.”
Hot stamping enables higher- strength steels to be formed into com- plex shapes more efficiently than via traditional cold stamping. Basically, steel blanks are fed into tunnel or stacked furnaces and heated to a tem- perature (above 900 C) that makes the blanks malleable. Blanks move into the press, typically a hydraulic model due to the need to control stroke rate and enable dwell time, for forming, followed immediately by in-die quenching for 3 to 10 sec.; in-die water channels serve this purpose. The heating and quench-
44 MetalForming/April 2017
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