Servo Hydraulic Innovation for Steel Forming

Forming technology specialist Hatebur is introducing a servo-hydraulic bar stop system for steel it designed to increase manufacturing productivity: by preventing shearing break-outs and scuffing on steel bars the new system optimizes bar surface quality and reduces the need for finish processing on formed parts.

“The servo-hydraulic bar stop optimizes the shear surface and boosts the quality of forged parts. That facilitates and speeds up the quality control and can make post processing obsolete. The technology enhances the productivity of manufacturers,” explained CEO Thomas Christoffel.

The new technology resulted from an in-depth research and development and will be offered for use on a variety of forming machine types, the developer noted. It is focused on "the first step" in metal forming: Before parts proceed through forming stations, the induction-heated steel bars need to be sheared off with very high precision.

The shearing process can induce a slight tilt and an oblique position for the sheared part. “Besides that, the shearing process changes into a tearing process towards the end, resulting in a so-called shearing break-out,” Christoffel added.

Sometimes scuffing is introduced at the sheared surface, which must be removed by sandblasting the finished forged parts.

The Hatebur servo hydraulic bar stop reduces tilting and oblique positioning, and the so the surfaces are virtually parallel. “Now, scuffing is rarely generated, and thus is practically never pressed into folds,” according to Hatebur’s Dr.-Ing. Mihai Vulcan.

Hatebur has been testing the technology since 2017 on a Hatebur HOTmatic HM75 XL hot forming machine, in partnership with a European automotive supplier. The scuffing on the shearing surface was minimized from 20% of the surface to just 1%.

The new bar stop technology also minimizes or eliminates the shearing break-out, resulting in a considerable quality improvement of the parts.

“If the quality control can be accelerated by only half a second per part,” Christoffel observed, “the technology already brings a real benefit to our customers.”

The shearing process is also quite fast: Depending on the bar diameter and the machine speed, it takes between 60 and 100 milliseconds. Only a servo hydraulic drive provides necessary dynamics and power density in a small space.

The Hatebur development team, led by Vulcan, applied an alternating position and force control. Should the bar stop deviate from its target position even by only a few hundredths of a millimeter, the position of the bar stop will be immediately adjusted via the servo valve. “This position control allows us to keep the actual distance between the blade and the bar stop constant during the whole shearing process,” Vulcan emphasized.

After the shearing process starts, the control shifts to a force control with position monitoring. Throughout the process, the integrated measuring technology records the process data.

When deviations are recognized, the automatic control adjusts imbalances immediately, ensuring an optimized surface quality.