Page 38 - MetalForming May 2014

Tackle Challenging Materials with
Servo Presses
Leverage the numerous advantages of servo-press technology to stamp high-strength steels and aluminum alloys.
BY UWE KRETH
Metal stampers face the chal- lenges of forming advanced and varied materials while maintaining high levels of quality and throughput. At times it can be difficult to achieve both, especially when faced with challenging materials such as alu- minum alloys and high-strength steels (HSS) that require slower forming speeds to achieve the desired quality, and a stable process. This contradiction of expectations can be resolved by using servo-direct press technology.
The advantages of programming a servo-driven press to form advanced materials can be compared to racing a bicycle through a curvy, hilly course. The rider gains speed down the hills,
Uwe Kreth is head of project planning– automotive press technology, at Schuler; e-mail info@schulerinc.com; www.schu- lergroup.com.
slows down to navigate the curves and then accelerates out of the curves to achieve maximum speed without los- ing control. This is how a servo press can accommodate the needs of the forming cycle when stamping advanced materials, by adapting to the require- ments of the cycle. Just as a cyclist that races the entire course at the slow cor- nering speed will lose the race, so will a traditional mechanical press with an eccentric drive, forced to operate at the slowest forming speed throughout the entire cycle.
When forming special materials such as aluminum or HSS, several fac- tors in the die influence the optimum forming speed. These include speed requirements of the blankholder as it opens or closes; special forming oper- ations from cams within the die; and vibrations due to breakthrough as the material cuts. Programming the servo
drive to accommodate these factors can greatly improve quality, die-com- ponent life and process stability while also delivering improved throughput.
Blankholders’ Impact on Slide Speed
When trimming materials such as aluminum or HSS, a blankholder inside the die fixes the part in place before the slide moves the die to begin the trimming operation. In the case of HSS, the blankholder must hold the part in place to ensure the blank does not move during the high-tonnage cut- ting operation. The stamper must take great care to control the process and ensure there is no excess energy emit- ted and that the process remains sta- ble. Note: a similar reduction in speed is required when the slide touches the blankholder for drawing processes, as well.
36 MetalForming/May 2014
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