Techniques for Eliminating Residual Stress in CNC Machining

　　Residual stress in CNC - machined workpieces can cause long - term dimensional instability and affect the mechanical properties of the parts. Several techniques are available to eliminate or reduce residual stress.

　　One of the most common methods is heat treatment. Stress - relieving annealing is widely used, where the workpiece is heated to a specific temperature below the critical point and then slowly cooled. This process allows the internal stress to be released as the atoms in the material have more mobility at elevated temperatures. For example, for steel workpieces, stress - relieving annealing at around 550 - 650°C can effectively reduce residual stress.

　　Vibratory stress relief (VSR) is another effective technique. In VSR, the workpiece is excited by a vibrator at a specific frequency for a certain period. The mechanical vibrations cause the internal stress to redistribute and gradually decrease. This method is non - thermal, making it suitable for materials that are sensitive to heat treatment. It is also more cost - effective and environmentally friendly compared to heat treatment, as it does not require large - scale heating equipment.

　　Shot peening can also be used to modify residual stress. High - velocity shots are propelled onto the surface of the workpiece, creating a compressive stress layer on the surface. This compressive stress counteracts the tensile residual stress inside the workpiece, improving its fatigue resistance and dimensional stability. The size, shape, and velocity of the shots, as well as the coverage area, need to be carefully controlled to achieve the desired stress - reducing effect.