As detailed in Fastradius’ article “The Benefits of Heat Treating Metal,” CNC machining is a subtractive manufacturing process, wherein cutting tools sculpt solid blocks into the desired part shape. To ensure a smooth machining process and achieve superior final part quality, the workability of the metals used is of paramount importance. Moreover, the properties of the metal part can be significantly enhanced after the machining process through a crucial step: heat treatments.
The Heat Treatment Process Heat treatment processes encompass heating the metal until its microstructure undergoes a transformation, followed by holding the metal in that state (soaking) before a controlled cooling process hardens the material. The duration of soaking varies depending on the specific heat treatment process, the type of metal, and the size of the part. Longer soak times induce greater microstructure changes, subsequently affecting the mechanical properties of the metal.
Adjusting the rate of cooling and employing different surrounding conditions can also modify the metal’s structure and properties. While brine serves as the fastest cooling medium, alternative options include oil, water, forced air, or furnaces.
Heat treatments can be strategically integrated into the manufacturing process, impacting parts at different stages to attain their initial, intermediate, or final properties. During CNC machining, a heat treatment may precede the machining process, reducing lead times and enhancing the metal’s workability. Alternatively, heat treatments might be applied post-machining to bolster hardness and durability.
Common CNC Heat Treatments Annealing: One prevalent heat treatment, annealing, is employed to reduce the metal’s hardness and increase its ductility. This process involves heating the metal to a critical temperature, followed by a controlled cooling phase. Annealing helps alleviate internal stresses, rendering the metal less prone to fractures during machining. Different annealing techniques, such as full annealing, recrystallization annealing, partial annealing, and final annealing, offer versatility in achieving desired properties.
Normalizing: Normalizing is another annealing technique characterized by rapid cooling at room temperature, contrasting with traditional annealing. This process involves heating the metal, soaking it 40°C above its upper critical temperature, and then cooling it in the air. Normalizing effectively relieves internal stress resulting from quenching, casting, or welding, reinforcing the metal and producing small, refined, and uniformly sized ferritic grains.
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