The New Steels: If You Cant Form em Cold, Form em Hot
Seminar attendees learned to what extent the hot-stamping process has been developed and commercialized, not only from presentations by representatives from AP&T, which manufactures the presses and the material-handling equipment needed to move steel through a hot-stamping line, but also from AP&T’s supplier partners:
• Thyssen Krupp Steel AG, supplier of hot-stamped ultra-high-strength manganese-boron steels;
• Stamping-simulation-software provider ESI Group, which, attendees were told, is focusing much of its efforts on better understanding the temperature dependence of friction during forming, and more accurately simulating cooling rates and heat transfer at varying pressures;
• Schwartz GmbH, manufacturer of the heattreat equipment used to warm steel blanks prior to stamping;
• Bohler-Uddeholm, which has developed tool steels specifically to handle the punishment that dies experience when working with these new steel alloys; and
• Fiat, which in September 2008 will christen a new facility solely to support its burgeoning hot-stamping operations.
Hot stamping of ultra-high-strength steels, including boron steels (such as Usibor 1500 stamped by Fiat and its suppliers including Gestamp, Benteler and Magna, and MBW 1500 manganese-boron steel from ThyssenKrupp) has become an accepted practice for automotive parts such as B- and A-pillar reinforcements, cross-member and roof reinforcements, and rear and front bumpers.
Alloy MBW 1500, attendees were told, has numerous applications on the VW Passat—sill-plate inner, B-pillar inner, side impact beam, etc.
To develop tooling that can function reliably at the high temperature of hot stamping (approximately 1700 F), Bohler-Uddeholm has developed a series of tool-steel grades with excellent temper resistance and hot yield strength, and good toughness at elevated temperatures.
And, AP&T engineers discussed issues such as handling heated blanks as they transfer from furnace to hydraulic press to trimming operations. The hot blanks move to the press over a roller table; engineers explained a roller design that limits contact between the workpiece and the rollers to minimize cooling of the steel. Grippers that carry the blank from the table into the die include shields for heat protection. Press technology designed for hot stamping includes temperature monitoring in the die with controls that ensure that the process stays within a prescribed temperature window.
In 2006, Fiat decided that, based on the success that some of its suppliers were having with hot forming, it would investigate hot-stamping some parts itself. Hot forming accounts for 14 percent (by weight) of the parts on its newest car model, and yields an average weight reduction of 22 percent compared to cold forming. To develop its own hot-stamping capabilities, it started working on a new building at its facility in November 2007 in Cassino, Italy, to house hot-stamping lines. Startup is slated for completion in September 2008. Two lines will feature robotic loading and stacking, with anticipated cycle times of 10 to 20 sec. to produce B-pillars, roof rails and reinforcement stampings.
AP&T North America, Inc.: 704/292-2900; apt-usa.com
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