How cold forging works — from a wire slug to a finished part

Cold forging (also called cold heading or cold forming) shapes steel wire in a series of dies at room temperature. Each blow moves the metal a little further towards the finished shape. Because the steel is not heated, the part comes out with a clean surface and close tolerances, and very little material is wasted.

Step by step

• Wire in — the process starts with a coil of cold heading quality (CHQ) wire, drawn to size and usually spheroidise annealed so it can take heavy deformation without cracking.
• Cut-off — the machine feeds the wire and shears a slug of exactly the right volume.
• Upset — the first station shortens and thickens the slug where the head will be.
• Pre-form and form — the next stations build the head, flange, collar or shank step by step; some parts are also extruded to reduce a diameter.
• Trim and pierce — a hex head can be trimmed through a hex die, and nuts are pierced to open the hole.
• Secondary operations — threads are rolled (not cut), and holes, slots or patches are added where the part needs them.

Why parts are stronger

Machining cuts through the grain of the steel. Cold forging bends the grain to follow the shape of the part, especially under the head and at the flange. Rolled threads keep that unbroken grain flow as well, which helps fatigue life. The steel also work-hardens as it is formed.

What the machines look like

Multi-station formers carry the part from one die to the next with transfer fingers. REL runs three- to seven-station machines, with load sensors on the die blocks that stop the press if the forming force goes out of range, and forges extra-long parts up to 330 mm, including splined and drive shafts.

Standards and values are summarised for general guidance — always work to your drawing and the current edition of the standard. Related REL page.