Page 31 - MetalForming August 2013

quickly from a die button can create a vacuum and pull a slug. And, during operations where the part web is cut, it may take some time for gravity to clear the scrap away, so it does not interfere with part ejection.
With a servo press, the stamper can program the ram to slow down or dwell only for that brief portion of the stroke to allow the scrap to shed. The rest of the stroke can proceed at the optimum speed.
These and other operations repre- sent the curves in the track that would traditionally slow down the entire stroke of a conventional mechanical press. When taking on difficult-to-form materials such as stainless steels, tita- nium alloys and high-strength steels, the severity of the curves rises and the performance gains of a servo-drive press become even more evident.
Expected Results with Servo
With any given die, a stamper will experience some combination of the
operations described above. Each oper- ation has an optimum slide velocity that balances output (strokes/min.), tool life and part quality. In a standard press, the operation that requires the slowest slide velocity becomes the bot- tleneck, and forces the entire stroke to run at that speed. With a servo press, we can vary the slide speed during the stroke so that each operation runs at its optimum velocity. The result: higher throughput.
Each operation affects tool life—the impact of the tool steel against the mate- rial, the heat generated during forming or drawing, the vibration caused by the reverse load created during cutting. By optimizing the speed during these oper- ations, the stamper can increase tool life. This is especially noticeable during heavy blanking operations—here, reduc- ing impact velocity greatly reduces reverse tonnage.
Any given material will have a max- imum limit on slide velocity for impact, bending, coining and drawing opera-
tions. By setting the ideal speed for each of the forming operations, but only being restricted to the that specific speed during that forming operation’s travel, we can increase formability without restraining production rate. We also can begin drawing operations higher in the stroke without tearing the material, without sacrificing output and without stalling the press due to lack of energy. We produce less heat, reducing workhardening of the part and increasing tool life. This can allow the servo press to run less-expensive materials in certain operations, reduc- ing piece-part price.
In addition to reducing workpiece- material cost, tooling cost also can be reduced thanks to use of a servo press. Improved formability allows the tool- maker to perform more forming per station. This allows stampers to reduce the number of redraws required to achieve the net shape.
Restrike stations on bending opera- tions also can be eliminated, due to
Transforming Your Press into
a Servo Press
Hydraulic Press Drive PSH
Learn more voith.com / hydraulic-systems about PSH
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