Parts without chips

“Cold heading is basically putting material in a die and hammering on it” according to one industry expert. Unlike hot forging, where the metal is heated before forming, or casting, where the metal is melted and solidified, cold heading and other methods of cold forming cause the metal to deform at room temperature. Though there was a U.S. patent issued in 1794 for a “cold header” (really a rivet machine), cold forming became a practical fabrication technology after World War II.

Die and Punch

Modern cold-forming machines, also called headers or parts formers, provide from one to seven die stations, opposite a number of punches mounted on a slide, which usually moves horizontally. A common type used for making bolts or screws is the one-die, two-blow header, similar to the example shown. This has one die, which is the diameter of the shank of the bolt or screw being formed. The material in the die is struck with two different punches, one after the other.

There is a limit to how much you can deform the material with a single blow, so two hits are often necessary to create the correct geometry of the head, said Steve Copeland, vice president of sales and marketing, Reed Machinery, Inc., Worcester, Mass. The first blow makes a shape like a tulip. Then a shifting mechanism moves the first punch over and places the second one in position. The second punch comes in to produce the finished shape of the head. After the second blow, a knockout pin pushes the piece out of the die. On a multiple-die header, there is a transfer rack with fingers that grab the part and move it from one die station to the next. If needed, the transfer mechanism can turn the part around 180 degrees so the next punch hits the other end of the part.