Page 32 - MetalForming-Apr-2018-issue

Servo-Mechanical Presses
Rise to the Challenges of Hot Stamping
As hot stamping ramps up worldwide to take on advanced high-strength steels, metalformers look to servo-mechanical presses to boost efficiency, cycle time and line reliability.
Hot-forming (or press-harden- ing) technology continues to play a growing role in the stamping of structural automotive parts from advanced high-strength steels (AHSS). For example, automotive suppliers forming boron-alloyed steels heat blanks to 900 C prior to forming, to achieve a fully austenitic state. The heated blanks then remain in the press
Aitor Ormaetxea is managing director of the hot-forming division of Fagor Arrasate S. Coop., Gipuzkoa, Spain; www.fagorarrasate.com.
BY AITOR ORMAETXEA
with the die (water-cooled) closed until the steel temperature drops to 150 C. This process yields a fully martensitic steel with a tensile strength in the neighborhood of 1500 MPA or more.
The Role of Servo Presses
A critical success factor during hot stamping is the ability of the press to keep the die closed during the cooling process, requiring the slide to stop and stay at bottom dead center (BDC). Here’s where the unique capabilities of servo-mechanical presses shine— in particular the ability to provide force
control even while the ram remains stationary.
Much work has been done in recent years to evaluate the force stability of servo-mechanical presses at BDC, as well as motor-torque performance and the required restarting torque.
Having tested press performance over varying closing speed and press tonnage, researchers have found that presses are able to maintain position control to a dynamic accuracy of less than 0.01 mm; a peak motor torque of less than 3 percent of maximum ton- nage; and a starting torque similar at
A servo-mechanical press serves as the heart of a hot-stamping installation at Batz, a European automotive-parts supplier. The instal- lation has demonstrated significant energy savings and improvements in part quality, according to Batz officials.
30 MetalForming/April 2018 www.metalformingmagazine.com