Views:2 Author:Site Editor Publish Time: 2018-12-11 Origin:Site
Basically, Cold heading implies putting a material in a die and giving it shape by hammering. This is quite different from the hot forging where the metal is first heated before the forming process takes place. It is also different from casting where the metal is melted first then, solidified to give a certain shape.
Cold forming employs a special machine (the cold forming machine) to deform a metal at room temperature. After World War II, this process became practical.
It has been used in the production of headed parts especially fasteners where the typical one-die, two-punch is the common method applied. While the first blow combines partial head upset with shank extrusion, the second blow gets the head shape finished.
Cold forming involves some basic processes which include;
The one-die, two-blow header is a common type of the die and punch process used in making bolts or screws. Here, the material is struck with two different punches consecutively (i.e. one after the other)
With the single blow, there’s a limit to how much you can get the material deformed. So, to create the correct geometry of the head, there have to be two hits. The first blow makes a tulip-like shape. This is followed by a shifting mechanism which moves the first punch over while placing the second in position. Then a knockout pin pushes the piece out of the die immediately after the second blow.
On a multiple-die header, the transfer rack with fingers grabs and move the part from one die station to the next one. This transfer mechanism can actually turn the part around a 180 degree if needed. This ensures that the next punch hits precisely on the other end of the part.
In cold forming, the wire is the form of metal stock most often used. This wire may be half-inch in diameter or more than that. This metal stock comes in large coils which is convenient for feeding into the cold forming machines which produce many parts per minute.
It is important to introduce just the right amount of material into the die when metal is compressed within a die. Precision should be within plus or minus one percent though less than that is recommended. When the material is little, it won’t fill the die and will lead to bad part making.
On the other hand, if the material becomes too much, the parts can be malformed or the production of flash which would have to be removed as soon as possible. Again, if the material is in excess of the actual amount, the die may split when the punch hits. However, the design of the cold-forming machines is in such a way that it cuts the precise length of the wire. There should be precision in the diameter of the wire as well. Before cutting and forming the wire to get a nice and tight diameter tolerance, most shops will perform a final 3 to 10 % draw.
Originally, cold heading was used to create heads for fasteners. Today, the cold-forming machines are Not Just for Fasteners Anymore. In addition to fasteners, cold forming is applied in making many kinds of parts with complex shapes. Though the machines may be called “headers”, they do much more than heading.