Every solution creates its own problems. When automakers demanded lighter body structures to boost fuel economy, the steel industry responded with significantly tougher alloys and heat-treatment technologies, allowing designers to increase load ratings, reduce the amount of metal used, and cut weight.
To deal with those tougher steels, engineers at automotive supplier GNS America developed a hot-stamping technology in which metal blanks get heated in furnaces and enter stamping presses red hot. The process makes the tough steel more formable and less likely to spring back to its pre-stamped shape, supporting the thin, complex body structures that automakers need. But there was a problem.
“We developed our own hot-stamping process to be cost competitive,” says Elie Mordovanaki, general manager of operations and engineering for Merit Technologies Worldwide, GNS America’s hot-stamping division. “However, mechanical trimming is not optimal after the heat treating process takes place.”
The hot-stamped A-pillars and roof pillars need holes and other fine features cut into them so they can be welded to other structural automotive components. However, between the tougher alloys and the heat treatment from hot-stamping, the finished parts are so hard that drills and other tools can damage them before cutting.
“High tensile strengths are always good and bad. The more strength, the higher the load capacity of the part, and that’s what our customers want,” says Moon-Gyu Kong, chairman of GNS America. “But the more strength, the harder it is to process the parts. That leads to more time and cost.”
After exploring several options, GNS turned to high-powered laser cutters from Trumpf Inc. to create fine features on high-strength steel parts. GNS uses laser cutters to support seven hot-stamping lines in Canton, Michigan, and another four lines in Holland, Michigan. The company also has stamping operations in Poland, China, and Korea and plans to open a plant in Mexico this year. Trumpf recently produced its 1,000th TruLaser Cell, which it then delivered to GNS to support operations in Canton.
Kong says the Trumpf equipment was initially more expensive than some competing products, “but long term, Trumpf wins on cost. Higher speeds, higher machine availability, and faster maintenance all lower production costs.”
Hot-stamping process
Like most stamping companies, GNS gets blanks from outside suppliers that it forms into automotive parts. Kong says ideally, he would like to create holes and features for finished parts in the blanks. Before hot-stamping, those metal parts are more pliable, so drilling and traditional cutting wouldn’t harm the part.
Unfortunately, adding holes can weaken the blanks in the stamping process. Thousands of pounds of force hit the blank, and that force needs to be distributed around the part as it conforms to shaping dies. Holes and other features could create weak points, lowering structural stiffness, so the blanks remain whole until after stamping.
At GNS’ Canton plant, gas-fired furnaces flank each of the company’s massive stamping presses. Robots pull red-hot blanks from the furnaces and feed them into the presses. The parts are still hot after forming, but Mordovanaki says they cool quickly, allowing workers to handle them and bring them to the cutting room. Kong says only extra-tough, hot-stamped parts get sent to the Trumpf laser cutters. Less-alloyed or non-heat-treated parts get cut on other equipment.
Workers load parts onto the rotary table that feeds the TruLaser Cell. With large pillars, such as roof structures that can span several feet, two parts get loaded onto the table. With smaller parts, there’s room for more components. The table rotates, bringing the uncut parts into the machine, where the 5-axis system moves the laser head over the parts to allow 3kW lasers to follow their program and cut small features into the steel. While the lasers cut, GNS employees remove finished parts from the table and load new components.
Frank Geyer, product manager for laser systems at Trumpf, says the need for lightweighting in the auto industry has made hot stamping necessary for several components, and laser cutting is growing in popularity as it supports efficiently and productively cutting the high-strength metals while still getting the fine features needed in finished parts.
“We’re seeing a lot of examples where mechanical systems aren’t up to the cutting challenge. Fire departments are increasing the force on the jaws-of-life systems they use to cut people out of cars in accidents. And we’re even seeing interest from repair shops that have to work on damaged car bodies,” Kong says.
Mordovanaki says GNS has been very happy with its Trumpf equipment because other than scheduled downtime for maintenance, it’s always been ready for use.
“We have a strong partnership with Trumpf. The relationship has worked out nicely for both of us,” Mordovanaki concludes.
GNS America
Trumpf Inc.
About the author: Robert Schoenberger is the editor of TMV and can be reached at 216.393.0271 or rschoenberger@gie.net.
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