Cold heading is a process that uses die forms and punches to create variably shaped parts from metal wire. The process is able to reproduce exact specifications reliably. Cold heading, as indicated by the name, does not use heat to reshape raw material; it uses force driven by a punch to push material through a die into a new shape.
The cold forming process, another name for cold heading, begins with metal wire. Depending on the end use of the product, the wire can be various grades of steel, copper, brass, or other alloys. The wire feeds into the process and is sheared off by a cutter at a length that yields a volume of wire exactly equivalent to the amount of material needed for the finished product.
The process continues with the formation of the head of the finished piece. The cold heading process is predominantly used in the production of bolts, screws, and other fasteners, which must have a specifically shaped head. The head shape can be produced with a die, a punch, or the combination of the two. If the end of the punch is shaped rather than flat, this forms part of the head shape of the finished piece.
Designs used for cold heading are often referred to by the number of steps in the process. A two die/three blow process means the feed wire is forced into two different die shapes and is struck by three different punch blows. The number of blows required relates to the degree of size reduction required from the feed wire to the die. Generally one blow cannot effectively reduce the size by more than 30%.
If required, the cold headed part can be threaded or machined after the cold heading process has been completed. Completed parts are often heat-treated to harden and anneal the metal. To finish the parts, the surface can be cleaned to remove residual lubricants or coated or plated for certain applications.
Cold heading is a form of extrusion, but it has an advantage over other extrusion methods — it can be used on materials that are not heat tolerant. It can be more cost effective than milling, machining, or etching because it wastes none of the feed stock. It also costs less than hot heading because it requires no heat. The process is quick and can be set up to produce a huge number of designs. There are, however, some shapes that cannot be produced without heat and some materials that are insufficiently elastic to be formed without heat, and are therefore unsuitable for cold forming.