Warm Forming: characteristics and benefits

What is forming? 
Forming is a procedure that allows mainly primary machining processes starting from an appropriately sized metal wire section, ultimately obtaining a rough-finished piece with a well-defined shape.
In cold forming, for example, the wire section is progressively deformed by a progressive press using a series of specially shaped dies [for more details, click on this link and read our article].

A question of temperature
Deformation processes are categorised according to the operation (primary or secondary) and operating temperature.
If we define the recrystallisation temperature as the temperature at which new, undeformed grains are fully formed in about one hour, cold working can be defined as processes conducted below this temperature, and hot working as processes conducted above it. As the name suggests, warm machining entails processes conducted at intermediate temperatures and thus represents a compromise between cold and hot machining processes.

Warm Forming
Warm Forming processes belong to a category of warm machining operations. Specifically, within a broad range approximately 0.4 times higher than the melting temperature of the metal alloy (expressed in Kelvin, typically around 500°C for stainless steels), a phenomenon known as dynamic recovery occurs, which involves the annihilation and reorganisation of internal crystal defects (dislocations) into lower-energy configurations. As a result, the material experiences reduced work-hardening and mechanical strength, accompanied by increased ductility and formability.
The process is characterised by high productivity (suitable for medium to large production batches) and is used to manufacture small to medium-sized components with high-quality mechanical and surface properties. This process is particularly valued in the production of mechanical components for the automotive industry, given the demand for parts with complex shapes and geometries.

For certain types of components, warm forming can be exploited to retain the inherent advantages of cold forming while offering additional benefits over both cold and hot forming.

Advantages over cold forming:

• greater ductility and formability in processing;
• possibility to form materials that do not lend themselves to cold forming (e.g. stainless steel, titanium);
• possibility to create more geometrically complex shapes and achieve greater deformation in steels that can be cold-formed;
• less work-hardening of the material and reduced residual stresses (especially beneficial for subsequent processing);
• virtually no need for annealing;
• lower forces and power requirements during the production process.

Advantages over hot forming:

• improved mechanical properties;
• greater dimensional accuracy and improved surface finish;
• no significant porosity, which is typical of hot forming;
• lower operating costs.

Why use warm forming?
The choice of one technique over the other depends on both the material and type of product being made. For example, using Warm Forming, certain stainless steel alloys (typically not suitable for cold forming) can be formed while meeting stringent client specifications, particularly in the automotive industry. This process also produces components with excellent mechanical properties and offers greater cost optimisation compared to traditional production methods.