Cold forging is a manufacturing process where a bar stock is inserted into a die and squeezed with a second closed die. The deformation starts at room temperature and changes the shape and size of the initial part until it has assumed the shape of the die.

Cold forging takes advantage of the plasticity of metals at room temperature to shape them. Before this processing method was applied, metals were mainly finished by cutting.

Cold forging increases tensile strength some and yield strength substantially while reducing ductility. Cold forging usually takes place near room temperature.

Cold forged parts require little or no finishing work which saves manufacturing costs. It is also less susceptible to contamination problems and the final component has a better overall surface finish.

Other benefits of cold forging include: Easier to impart directional properties, improved interchangeability, better reproducibility, greater dimensional control, handle high stresses and high loads and produce net shape or parts of net shape.

Process: 

Today, cold forging has risen in popularity. It offers a particularly effective way to work with aluminum. Metal parts manufacturers frequently rely upon specific “cold forming” processes.

During cold forging, a manufacturer pounds and compresses metal to produce dimensional changes at room temperature.

Currently, most cold forging occurs in highly automated mass production environments. This process offers an especially useful way to change the shape of aluminum and malleable metals, such as copper.

The process of “cold forming” (also known as “cold working”) refers to working with metal to shape it at room temperatures, sometimes by means of hammering or pounding mechanically.

During cold forging, a manufacturer will typically pound a workpiece in order to compress it into desired dimensions. For instance, companies often use hammers, power hammers, or dies to accomplish this objective.

Three popular metal forming processes have gained popularity worldwide: forward extrusion, backward extrusion, and heading (or “upsetting”). Automated machinery enables steel mills to utilize these technologies during mass production at high temperatures:

Forward Extrusion: Hot metal flows through a die formed in a desired cross-section. Widely popular in industrial settings, this process helps produce long solid extensions.

Method to reduce diameter, where, depending on % of reduction, the material flows open or trapped on the cavity of lesser diameter. 

Backward Extrusion: Ram force propels a solid die through stationary hot metal, permitting the generation of hollow components, such as metal pipes.

Method to make hollow shaped holes, where material flows backward around a penetrating punch.

Heading/Upsetting: A punch laterally compresses hot metal positioned horizontally within a strong metal die.

Method to form heads on fasteners, where material is upset at the face of dies and can be open or trapped to upset a particular shape.

Manufacturers have taken these three basic approaches and applied them to cold forming settings, also. While cold metal billets as a raw material won’t “flow”, of course, ram force may propel them in a desired direction vis-à-vis an extrusion die.

Used in conjunction with strong cold forging or warm forging dies, this powerful technology helps generate a variety of useful small metal components.

Advantages: 

No heating is required in cold forging processes.

This forging process offers a better interchangeability as well as reproducibility.

A better surface finish is achieved and contamination problems experienced are minimized.

Cold forging offers a superior dimensional control.

The capability to impart directional properties onto the metal being formed.

Disvantages: 

The production of an undesired residual stress.

Metals forged are less ductile and higher forces are required during cold forging processes.

Because of the higher forces required in this process, heavier and more powerful equipment is needed as well as stronger tooling.

Though capable of imparting directional properties onto the metal, these properties may be detrimental.

The surfaces of the metals used must be clean and scale free.

Because of the loss of ductility that accompanies strain hardening, intermediate anneals may be required.

Materials：

Materials that can be cold formed include, but are not limited to:

Carbon steels

Brass

Lead

Stainless steel

Copper

Aerospace Alloys

Alloy steels

Bronze

Precious metals

Aluminum

Nickel Alloys

Application Considerations

While cold forging may not be appropriate for every application, it can offer very significant advantages in the appropriate situations. Given that it requires specialized equipment as well as tooling and die investments, the use of cold forging should be balanced against overall production volumes, material costs, part strength requirements and Return on Investment (ROI) projections.

In some instances, where strength, shape and surface smoothness are of critical importance, cold forging is the only process that can efficiently produce parts that meet the required specifications. Consequently, some of these parts— such as complex pinion gears— are designed specifically to suit the cold forging process because they cannot be manufactured via machining or other processes.