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Holddown is a desired die cushion feature for both mechanical
and hydraulic presses. In hydraulic presses, it prevents from backdriving
the ram. Without the holddown, die cushion follows the ram during the
return part of the stroke and can basically push the ram up. Holddown
delays the return of the die cushion until ram is out of the way. In case
of mechanical presses, such function can be particularly useful in drawing
operations where additional time is needed to remove the work piece or
on long draws where a rapid return might distort the part.
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