The blankholding requirements for large panels, which comprimise the majority of exterior body panels, necessitates the use of double-action drawing to achieve proper control of metal movement. Many smaller, irregular shaped parts that present difficult problems in metal control are drawn by this method. In double-action drawing, punch is mounted on the inner slide of the press and the blankholder is mounted on anouter slide. The part is usually drawn open side up.
(Lascoe O.D., Handbook of Fabrication Processes, pg.193, Kayra Ermutlu)
Tooling for Drop-Hammers
Sheet metal is readily formed by the stamping action of heavy drop hammers. Most drop-hammer tooling today is cast metal (usually Kirksite or steel). Cast epoxy ceramic drop-hammers however, have shown that they can successfully form aluminum, titanium and steel with little or no tool wear. The tool-contruction cost for the epoxy-ceramic hammer die, exclusive of materials, is about onefourth that Kirksite. Data on tool life and repair costs for this tooling is currently incomplete.
(Lascoe O.D., Handbook of Fabrication Processes, pg.315, Kayra Ermutlu)
Double action drawing had been written before
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