Strengthening Metals through Cold Working
Usually, metals are cast or forged into the desired shape after being made malleable through heat application. But, metals can also by changing their shape without using heat. This process is called cold working or plastic deformation. In this metalworking technique, a metal is subjected to mechanical stress to cause a permanent change to its crystalline structure.
How the Process Works
Cold working is performed at temperatures below the re-crystallization point and mechanical stress instead of heat. This process is used for initiate a change. This is usually the technique applied to steel, copper, and aluminum, like when making angle iron. After cold working these metals, their permanent defects will alter their crystalline makeup. With such defects, the ability of their crystals to move within the metal structure is reduced. Also, the metals will have more resistance to further deformation.
Common Methods of Work Hardening
Despite the many options for work hardening available, it is important for manufacturers to decide to which to use. This depends on the use to which the metal will be put. Below are the common kinds of work hardening:
- Sheet metal bending. This cold working process involves deforming metal over a work axis, thus, making a change in the geometry of the metal. The shape changes in this method while the metal’s volume remains constant.
- Cold rolling. This includes having the metal passing through pairs of rollers to minimize its thickness or ensure thickness uniformity. While it moves through the rollers where it is compressed, its grains are deformed.
- Sizing. This involves squeezing areas of ductile castings or forgings to the desired thickness. This method is used mainly on flats and basses.
- Drawing. This involves pulling the metal through a small hole or die. This is aimed at minimizing the diameter of a metal wire or rod while increasing the length of the product. In this method, the raw material is pushed into the die through compression force to make sure the re-crystallization takes place while the shape of the metal changes.
- Extrusion. This process involves placing a billet in a chamber and forcing it through a die. To produce a cylindrical product, the die opening can be round but it can also have a variety of shapes.
- Squeezing. The majority of cold-working squeezing processes have identical hot-working counterparts. Deforming cold is meant to get better dimensional accuracy and surface finish.