Surface hardening is a critical process in CNC machining that improves the wear resistance, fatigue strength, and durability of metal components by increasing the hardness of their outer layer while retaining a tough core. Several advanced processes are employed to achieve this, each with unique advantages and applications.

　　Induction hardening is a widely used technique in CNC machining. It involves using an induction coil to generate a high-frequency electromagnetic field, which heats the surface of the metal component to austenitizing temperature (above 900°C for steel) followed by rapid quenching (using water or oil). This process creates a hard martensitic layer on the surface, typically 0.5 to 5 mm thick, while the core remains relatively soft and ductile. Induction hardening is highly efficient, allowing for precise control over the hardened area, making it ideal for components like gears, shafts, and camshafts where specific surfaces need hardening.

　　Laser surface hardening is another innovative process. A high-power laser beam is focused on the surface of the CNC-machined part, heating it to the austenitizing temperature, and the heat is rapidly conducted away by the cold base material, resulting in self-quenching. This process offers exceptional precision, enabling hardening of complex geometries and small areas with minimal distortion. The hardened layer is typically thinner (0.1 to 1 mm) than that achieved with induction hardening, making it suitable for high-precision components such as tooling, molds, and aerospace parts. Laser hardening also produces a fine-grained microstructure, enhancing surface hardness and wear resistance.

　　Carburizing and nitriding are chemical surface hardening processes. Carburizing involves heating the component in a carbon-rich atmosphere (often using gases like methane or propane) at around 850-950°C, allowing carbon to diffuse into the surface. After quenching, the surface becomes hard due to the formation of martensite, while the core remains tough. This process is suitable for low-carbon steels and is used in components requiring high surface hardness and impact resistance, such as gears and bearings. Nitriding, on the other hand, diffuses nitrogen into the surface of the metal (usually at 500-570°C) to form nitride compounds, creating a hard, wear-resistant layer without the need for quenching. This results in minimal distortion, making it ideal for precision CNC-machined parts like valve stems and hydraulic components.

　　Each surface hardening process offers distinct benefits, and the choice depends on factors such as the material of the component, desired hardness depth, dimensional accuracy requirements, and production volume. These processes play a crucial role in enhancing the performance and longevity of CNC-machined parts across various industries.