Heat Treatment Process in Machining Technology

With the advancement of aerospace, industrial, microelectronics, and modern and bioengineering technologies, the demand for highly precise mechanical components—whose feature sizes range from the micrometer to the millimeter scale—is becoming increasingly urgent. The distinctive complexity of their geometries, the diversification of materials, and the ever‑tighter tolerances in dimensions and surface quality have become defining characteristics of such high‑precision mechanical parts, as well as of miniature devices and systems. Consequently, the requirements regarding functional performance, material properties, structural design, and other attributes are steadily rising.

With the rapid advancement of modern precision machining, a wide array of precision machining techniques has emerged, including micro‑precision machining, rapid prototyping, and ultra‑precision machining.

Inserting heat treatment at the appropriate stage of precision machining ensures effective coordination between cold and hot processes, thereby preventing distortion caused by heat treatment. The scheduling of heat treatment, depending on its intended purpose, is generally categorized as follows:

1. The purpose of preliminary heat treatment is to eliminate internal stresses generated during blank manufacturing, improve the machinability of the metal material, and prepare for subsequent heat treatments. Preliminary heat treatments include tempering, annealing, and normalizing, and are typically scheduled before or after rough machining. When performed prior to rough machining, it enhances the material’s machinability; when carried out after rough machining, it helps relieve residual internal stresses.

2. Heat treatment is generally scheduled after rough machining and semi‑finishing, and before and after finishing. For heat treatments that cause significant distortion, such as carburizing and quenching or tempering, they should be performed prior to finishing to allow for correction of thermal‑induced deformation during the finishing operations. In contrast, heat treatments that result in minimal distortion, such as nitriding, may be carried out after finishing.