How to Draw Metal in Dies
The successful drawing of metal in dies depends on the firm, even
pressure which does not allow the strain to be greater on one part
than on another, and the perfect fitting of the sections of the
die so as to prevent the metal from wrinkling or buckling. These
conditions are secured by delicately adjusted springs and many automatic
attachments to control the action of the machine.
The metal must also be of the right degree of ductility for the
drawing process. Cast iron is too hard and must be made into wrought
iron, which is soft and fibrous. Steel must be annealed. The metal
is coated with a thin film of oil or grease while it is being worked.
The drawing of a deep shell is not accomplished by one stroke of
the punch. There are sometimes five or six operations, the shell
being drawn first on dies having outside blank holders and then
on those having inside blank holders, each one having a smaller
diameter than the one before.
Figure 4 shows how many steps are necessary in drawing a tube,
and the frontispiece shows several of the large number of operations
performed in making such a simple article as a funnel. Eighteen
additional operations are required after the twelfth stamping operation
to finish the funnel.
Figure 4. Operations in Drawing a Tube.
The shells for the larger articles are made on drawing dies with
as few seams as possible, so that the surface may be smooth and
Ears, handles, sprouts, etc., are electrically welded, so that
the metal in the body of the article and that in the attachment
unite as one.