Page 48 - MetalForming April 2017

Precise
Hot Stamping
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A hydraulic press is specified for hot- forming operations due to precise control of stroke speed and increased dwell time. For in-die quenching, dies include chan- nels through which water flows to quickly cool parts. This action transforms the steel to a martensitic phase, a process that hardens the material. By routing the channels in certain ways, specified areas of the part can be bypassed for quench- ing. These areas become soft zones.
strictly via in-die technology,” he con- tinues. “But for local soft-zone require- ments, this is where we are starting to play with some of the front and rear rails where you want very localized bending moments—these applications fit very well for timely softening with lasers.”
Production Possibilities in the Future
Gestamp is progressing in R&D efforts related to what it calls Flex Laser Softzone technology. The company is continuing to industrialize the tech- nology and is working with its OEM customers on a variety of parts, ranging from pillars to rails, and on a variety of future vehicles with volumes ranging from niche-vehicle volumes to vehicles with high-volume production.
Belanger sees promise for the tech- nology not only in improving vehicle crash performance by controlling the kinematics during deformation, but also in improving deformation in resist- ance-spot-welded joints by increasing the ductility in the parent metal adja- cent to the spot weld. This increases the overall loading capability of the joint, Belanger explains.
The technology also offers another possibility: “Enable mechanical joining of alternative materials such as alu- minum or carbon-fiber-reinforced polymers into ultra-high-strength hot- stamped steel by selectively softening flanges to achieve robust clinching and/or riveting,” he says.
Until now, Belanger reports having used only a conventional hot-stamped- steel grade, 22MnB5, to prove out the technology, but says it can be applied to the new hot-stamped steels emerg- ing in the marketplace. MF

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Combines with Laser Cutting
“Hot stamping occurs in its con- ventional form, with a laser used as a follow-up process,” Belanger says. “The laser technology can target certain areas, reheating and tempering in very specific locations to reduce the strength and increase elongation.”
There are a few ways to configure a hot-stamping/laser operation, offers Belanger, noting that laser softening can work with a laser cutter because, for the most part, hot-stamped parts undergo post-forming laser trimming.
One option: a cell configuration with a two-way table, where a post-formed part rotates into a laser-cutting oper- ation for softening and cutting. Anoth- er: a three-way table, with the loaded part rotated into separate laser-based cutting and softening operations.
“We feel that hot stamping plus laser softening is limited to low-volume pro- duction, but eventually it will handle typical automotive volumes,” says Belanger. “That will require capital investment, such as changing a laser- cutting cell to a three-station footprint. The key to productivity is to make sure that the cycle times for laser softening are not significantly greater than the cycle times for cutting.
“As for part size, B-pillars, with large soft zones, may have to be produced

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MetalForming/April 2017
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