Heat Treatment Process for CNC Machined Metal Parts

November 26, 2020

Computer numerical control (CNC) machining is a type of manufacturing process that utilises pre-programmed software in determining the movement of tools and pieces of equipment. With this type of manufacturing process, stock material such as metal, plastic, and wood can boast a wide variety of shapes and designs that are needed for different industries.

To date, numerous end products maximise CNC machined metal parts. Some of these products are fittings, housings, brackets, rollers, and suspension arms. But before these products can be fabricated, most of the CNC machined metal parts still have to undergo various heat treatment processes. Heat treatment processes are intended to make metals more workable once they will be fabricated and manufactured into different products. They also help improve the properties of metal parts.

Heat treatment processes that can be used for CNC machined metal parts are as follows:


Annealing is a heat treatment process that can change the physical or chemical properties of a metal part. Some of the changes that can be obtained out of annealing include reduced hardness and increased ductility. This process is done by heating a CNC machined part to a critical temperature, maintaining the temperature for a specific amount of time, and air cooling the metal part slowly.

Case Hardening

Case hardening is another heat treatment process that involves the hardening of a part’s surface without altering its underneath metal layer. A thin exterior layer of harder metal is known to develop to CNC machined metal parts that undergo case hardening. Metal parts that are made from iron and steel have low carbon content. And with the application of heat and carbon-rich substance to their surfaces, they can easily obtain a durable, wear-resistant outer layer that can be useful for different applications.

Quenching and Tempering

Quenching and tampering are two-part heat treatment process that can increase the hardness of CNC machined steel parts. During the quenching process, a specific part is subjected to a high temperature, causing the crystalline structure of the part to change from being ferrite to austenite. Afterwards, the quenched part is cooled rapidly to effectively secure the phase change.

Tempering, alternatively, is done to heat quenched metal parts to high temperatures. The heat out of the tempering process is intended to reduce the brittleness of the material and improve its strength.

Stress Relieving

CNC machined metal parts are often subjected to stress, which can compromise their quality as they are further processed. Fortunately, stress-relieving can easily preserve the overall quality of these metal parts. Stress-relieving involves the heating of these metal parts to high temperatures and consequently cooling them slowly. This process, however, is only applied to remove residual stresses, helping the parts obtain huge improvements over their mechanical properties.

Precipitation Hardening

Precipitation hardening is somehow similar to quenching and tempering with some additional steps. Under precipitation hardening, the metal part is heated to a high temperature, quenched, and then heated again to a much lower temperature. As the part is heated to a low temperature, the precipitates in the alloy are dispersed. Additionally, the irregular movement within the microstructure is reduced, helping the part obtain increased strength and hardness.

To know more about heat treatment processes, you can contact us at Gunna Engineering.


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