When CNC machining metal parts like aluminum, stainless teel, brass, etc. we need heat treatment to help. Below are some common heat treatment methods for your reference.
Annealing
To reduce the hardness of the metal and increase its ductility, the annealing process involves heating and soaking the metal at a critical temperature before cooling. This helps relieve internal stress and makes the metal less likely to break when machined. You can use different annealing techniques such as full annealing, recrystallization annealing, partial annealing, or final annealing to achieve your desired final properties.
Normalizing is another annealing technique that involves heating the metal and then cooling it at room temperature much faster than typical annealing. Once the metal reaches a temperature of 40°C above its upper critical temperature, it soaks before cooling in the air. Normalizing relieves internal stresses caused by quenching, casting, or welding to prevent metal failure, thereby strengthening the metal and producing small, refined, and uniformly sized ferrite grains.
Surface Hardening
To harden the outside of a part without altering the inside, you can use a case hardening process. Case hardening, also known as case hardening or case hardening, produces parts that are less brittle and easier to machine than other methods of increasing overall metal hardness. One form of hardfacing involves heating the metal in a carbon-rich environment (carburizing), as this increases the strength and carbon content of the metal surface.
Precipitation Hardening
Precipitation hardening or aging produces strong and lightweight metals, making them a popular choice for heat-treating parts in the aerospace industry. If you have a malleable metal, you can heat it to a high temperature, quench it, then heat it to a lower temperature and heat it for a long time, so that the precipitates are uniformly dispersed throughout the grain structure of the metal, and increase its strength and hardness.
Relieve Pressure
CNC machining, forming, rolling, and straightening all cause stress inside the part that weakens it and reduces its overall quality. Stress relief will remove residual stress and improve the mechanical properties of the part without changing its structure or hardness. This process involves heating the metal to a temperature just below its lower critical boundary. The cooling process is always slow so that uniform parts with consistent mechanical properties can be produced.
Tempering
This two-part heat treatment increases the hardness, ductility, and resilience of iron-based alloys. During quenching, the metal is heated to high temperatures, changing its crystal structure from ferrite to austenite and allowing it to absorb more carbon. The metal will then be rapidly cooled to lock in the microstructural changes. Since quenching produces very hard parts, it is usually done after CNC machining.
To reduce brittleness, relieve internal stresses, and improve part life and mechanical properties, you can temper the metal by heating it to moderate temperatures below its critical point.
