The so-called internal stress in the field of precision parts machining is the stress that remains inside the workpiece when the external load is removed. Internal stresses are produced by uneven volume changes in the internal macroscopic or microscopic organization of the workpiece during the machining process.
A part with internal stress is in a state of unstable relative equilibrium and can maintain a temporary stability of shape accuracy. However, its internal organization has a strong tendency to return to a stable state without internal stress, once the external conditions have changed, such as changes in ambient temperature, continued cutting, impact, etc., the temporary balance of internal stress will be broken and redistributed, the part will produce the corresponding deformation, thereby destroying the original accuracy.
Precision parts processing in order to reduce or eliminate the impact of internal stress on the accuracy of parts processing, in the design of the parts structure, should try to simplify the structure, consider the wall thickness uniformity, in order to reduce the internal stress generated in the casting, forging blank manufacturing, cutting processing, roughing, finishing should be separated in different processes, is a certain interval after roughing to allow the redistribution of internal stress, in order to reduce the impact on the finishing process.