Cold heading, also known as cold forming, is a continuous manufacturing process used to modify metal wire at or below room temperature to develop fittings and fasteners.
High-speed forging allows coiled wire or rod, made of stainless steel, copper, brass, aluminum, and more, to be fed into cold heading equipment and cut at a precise length. The material is then sent through die cavities and tool cavities to distort and shape it into the correct fitting or fastener.
The cold forming process can be utilized to remove small amounts of metal and to reduce and expand the length and diameter of coiled wire.
Oil lubrication is used to prevent die wearing in cold heading processes. When the lubricant is applied, heat vaporizes resulting in oil smoke and oil mist, based on the type of lubrication being used, oil smoke and mist may be sticky.
The volume of smoke and mist produced by cold forming machines will vary based on the diameter of the stock, the speed, what metal is being used, and what process is being performed. Cold heading machines are known to operate quickly and remove more material when larger stock is being processed creating heavier oil smoke and mist.
There are a number of techniques that can be utilized in the cold heading process. The type of technique an operator uses is based on the metal being altered and the shape that needs to be produced.
One or more techniques may be utilized depending on the purpose of the finished fastener or fitting.
The most widely used cold heading techniques are forward extrusion, backward extrusion, and upset.
Forward Extrusion - a technique used to reduce the diameter of a metal.
The forward extrusion process forces a material to flow or become captured in a cavity with a smaller diameter (depending on the percentage of reduction).
When metal is being driven through the cavity, substantial weight is utilized to condense the metal down onto itself.
Because aluminum, gold, and tin are softer metals they offer an advantageous yield when compressing, while iron and steel are denser and not able to achieve fittings and fasteners that are as thin.
Backward Extrusion - a process designed to create hollow shaped holes where material flows backward around a workpiece and then develops a penetrating punch that forces pieces of material through the holes without truly cutting the metal out.
Upset - a final method that forms heads on fasteners.
A material is upset at the face of dies where it can be opened or trapped to develop a specific shape. Upset offers a great deal of diversity and helps control the concentricity (a complex tolerance that is used for high-precision parts to create a tolerance zone for the median points) of a completed part.
Upset allows cold heading manufacturers to produce precise shapes and designs such as square, offset, eccentric, or elliptic with lugs, necks, fins, and collars.
With CNC programming, cold forming can produce virtually any design or part. Some of the most common cold headed parts and head styles are listed below.