Cold working is a metalworking technique that alters the structure of metal through mechanical stress, increasing strength and hardness while reducing ductility. It is cost-effective for high volume production but has a high initial capital cost and lower ductility. Cold rolling and cold forging are common methods used.
Cold working is a type of metalworking done by subjecting the metal to sufficient mechanical stress to cause plastic deformation, a permanent change in the crystalline structure of the metal. It gets its name because it is performed at temperatures below the recrystallization point of the metal and alters the structure of the metal through mechanical stress rather than heat. The technique increases the strength and hardness of a metal by reducing its ductility. A number of different processes are used in the modern metalworking industry and are applied to materials such as steel, aluminum and copper.
This type of metalworking strengthens the material through a process called work hardening or work hardening. When the mechanical stress on a metal becomes high enough, it causes permanent crystallographic defects, called dislocations, in the crystalline structure of the metal’s atoms. As the number of dislocations increases, it becomes more difficult for new ones to form or for existing defects to move through the crystal structure, making the metal more resistant to further deformation. This increases its yield strength and allows it to withstand greater stresses, but it also means that the metal becomes less ductile, and if the metal is overstressed, it will crack rather than bend.
Cold working is often more cost effective than working metal through heat treatment, especially for high volume production, because it produces comparable improvements in strength by using materials more efficiently and requiring fewer finishes. The high initial capital cost of this process, however, makes it less cost-effective than small-scale heat treatment. The lower ductility of cold worked metal also makes it inferior in some applications. Its greater resistance to deformation makes it less able to yield to forces that the metal isn’t strong enough to withstand, and so if the metal is put under too much stress, it can fracture rather than bend. Some metalsmiths use both methods at different points in the manufacturing process to impart the desired qualities to the metal.
There are several methods that can be used for cold working. The most common type is cold rolling, in which the metal being worked is squeezed through narrow spaces between rotating metal rolls. The movement of the rollers compresses the material, causing it to deform as it moves it through the gap. Another method is cold forging, where metal is shaped by forcing it into a mold with a press or hammer.
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