During heating and cooling, the internal crystal structure and stress of metal redistribute, causing volume to expand or contract. Thin parts, long parts, and asymmetrical workpieces are especially prone to deformation. Residual stress after quenching often causes warping, while tempering may slightly stabilize dimensions. Different materials and heat treatment methods produce significantly different deformation directions and magnitudes, so actual process measurements are required rather than relying solely on theoretical values.

Provide material grade, heat treatment type, and process sequence (e.g., rough machining first, then carburizing and quenching, then finish grinding), and indicate which dimensions are the final references after heat treatment. This information allows the CNC shop to incorporate compensation strategies during quoting and trial production. For features with tolerances tighter than ±0.02 mm, it is recommended to note this in the inquiry so the shop can assess whether secondary positioning or dedicated fixtures are needed.