The Heading Machine Process
Cold heading machines transform a metal blank into intricately shaped fasteners without the use of any heat. The process utilizes high speed automated “cold-headers” that can transform a metal wire into an intricately shaped part with a tooling progression at speeds up to 400 pieces per minute. This equipment is capable of forming parts from hard metals, such as quenched and tempered alloy steels, low-carbon tempered high-strength steels, and ferritic stainless steels.
The first step in the heading machine process involves cutting the long, continuous metal coil into a shorter section, which is then fed into the machine. The slug, which is the portion of the coil that has been cut off, then travels through a series of dies and punches, where it is upset into various desired shapes. Typical shapes produced by cold heading include hexagonal, round, or square heads, with or without radial slots, and pierced or pin-type drive recesses.
Upsetting is the most common method of forming in a cold header. Using a reciprocating hammer, the slug is forced into a preformed die, which in turn forms the desired head of the fastener. This process is accomplished by varying the force of the hammer, and in some cases, multiple blows are used. Upsetting is usually done with open tooling, although in some cases it may be performed between closed dies. The slug may also be extruded, either forward or backward, by varying the speed of the ram or by modifying the design of the die.
Other cold forming techniques, such as sizing, piercing, and trimming, can be used to produce complex fasteners that cannot be made with upsetting alone. However, sizing, piercing, or trimming cannot be performed on very thick materials such as high-grade stainless steels and can only be done with a limited number of blows. This is why these types of fasteners are typically manufactured through secondary operations.
Other processes that can be used in conjunction with cold heading include swaging and thread rolling, both of which are done on the finished fasteners after they have been formed. This allows them to achieve additional features that would be impossible in a machining operation, such as the ability to attach different types of threading to the fasteners or to make holes in the heads. These secondary operations are often done on a separate machine from the cold heading machine and are referred to as auxiliary forming processes. As a result of these auxiliary forming methods, cold headed parts have less offal or scrap than do machinable fasteners. This reduces the amount of material that is wasted in the production of a single fastener and helps to save on material costs and processing time. As a result of these benefits, the cold heading process is becoming increasingly popular for making components and fasteners that are both durable and cost-effective. This has been fueled by increased metallurgical knowledge and advances in cold forming technology that have enabled the use of tougher grades of material in cold headed parts.