Cold heading is a metal forming process that uses powerful hammers and dies to shape raw materials into net shaped or near-net shaped fasteners without any heat. It is a cost-effective alternative to machining and is capable of producing a larger quantity of parts with closer tolerances. Its versatility also allows it to produce more complex and intricate fasteners that would not be possible with a cutting machine. It is used to manufacture a wide variety of different fasteners such as screws, rivets, nuts, and bolts. These include standard fasteners and specialty pieces such as those used in bridges, automotive manufacturing, and electronics.
During the Cold Heading process, starting from a slug that is cut from a continuous coil of wire material; the machine utilizes a series of powerful punches and dies to form the part in progressive steps. This enables the part to be formed without losing any of its original volume and thus creating stronger parts with better grain flow and finish. It is the most popular method for producing fasteners and can be applied to a wide range of metals.
There are a number of different types of cold heading machine The type of machine needed will depend on the size and complexity of the part that is required. Some machines are able to perform multiple operations in a single pass such as extruding, upsetting, and thread rolling. Others are more limited in their capabilities and can only be used for a single operation such as piercing or trimming.
Upsetting is a common cold heading technique. This is done by reducing the height of the slug and increasing the diameter. This is accomplished using open or closed tooling depending on the location and size of the upset. This is a form of metal forging and can be used to create the heads on fasteners as well as internal drive recesses.
After the upsetting has been completed, a punch or die is then used to compress the material. This forces the slug into an impression or cavity in the die. This is the head of the fastener. This is the most important step in cold heading and can be done with open, between, or enclosed tooling – again depending on the location and size of the head.
The last two processes in a heading progression are piercing and trimming. This is when a pin or other device is thrust inside the head and shears the web, allowing for a hole to be inserted into the part. The piercing is then finished with a reamer which opens the hole to the proper diameter. The trimming is the final step in the cold heading process and is performed after all of the piercing and forming has been completed.
Unlike machining, which generates up to 60% waste, the cold heading process produces minimal scrap. There are a few exceptions to this rule, however. Depending on the size and type of the part, a trimmed edge or an un-formed pierced surface may be necessary. In these cases, a small amount of offal can be produced. Otherwise, a very high percentage of the starting slug is utilized in the final fastener.