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 even.

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.