In precision aviation parts processing, controlling surface residual stress is a core factor affecting the fatigue life, corrosion resistance, and dimensional stability of parts. Residual stress arises from the uneven plastic deformation between the material surface and the substrate during machining, the coupling effect of thermal stress, and volume changes caused by phase transformation. Precise control of process parameters can effectively suppress the generation of unfavorable residual stress or introduce a beneficial compressive stress layer, thereby improving the overall performance of the part.
Cutting speed is one of the key parameters affecting residual stress distribution. Under high-speed cutting conditions, the temperature in the cutting zone increases significantly, the material softening effect is enhanced, and plastic deformation tends to be more uniform, which helps reduce surface residual tensile stress. However, excessively high cutting speeds may lead to an expansion of the heat-affected zone, causing an imbalance of thermal stress between the substrate and the surface, which in turn exacerbates the fluctuation of residual stress. Therefore, it is necessary to select an appropriate cutting speed range based on material characteristics. For example, low-melting-point materials such as aluminum alloys are suitable for medium-to-high-speed cutting, while high-temperature materials such as titanium alloys require a combination of low-temperature cutting and high feed rates to balance the effects of thermal effects and mechanical loads.
The synergistic optimization of feed rate and depth of cut is crucial for residual stress control. Increasing the feed rate can shorten the contact time between the tool and the workpiece, reducing heat accumulation, but it exacerbates cutting force fluctuations, leading to an increase in the depth of the surface plastic deformation layer. The selection of the depth of cut must consider the balance between material removal rate and work hardening degree: shallow depths of cut easily induce a plowing effect, leading to concentration of residual compressive stress on the surface; large depths of cut may cause excessive cutting force, triggering elastic recovery of the matrix and forming residual tensile stress. In actual machining, a "shallow depth of cut, high feed" strategy is often adopted, using layered milling or helical interpolation paths to achieve gradient distribution control of residual stress.
The rational design of tool geometry parameters is a direct means of controlling residual stress. Increasing the tool rake angle can reduce friction in the cutting deformation zone, reduce cutting heat generation, and thus suppress residual tensile stress dominated by thermal stress; optimizing the clearance angle can improve the squeezing effect between the tool and the machined surface, avoiding residual stress rebound caused by elastic recovery. Furthermore, the application of the tool tip radius and finishing edge can smooth the cutting force distribution, reduce surface micro-defects, and thus reduce the risk of residual stress concentration. For example, in titanium alloy machining, using a tool combination with a large rake angle, small clearance angle, and negative inclination angle can significantly reduce the peak value of residual tensile stress on the surface.
The choice of cooling and lubrication method has a significant impact on the residual stress state. While traditional flood cooling effectively reduces cutting temperature, it may cause micro-cracks on the surface due to droplet impact, leading to worsening of residual stress. Minimum quantity lubrication (MQL) and cryogenic air cooling technology achieve gentle control of residual stress by reducing the thermo-mechanical coupling effect. For difficult-to-machine materials, such as nickel-based superalloys, nanofluid cooling can simultaneously improve lubrication performance and thermal conductivity, suppressing residual tensile stress while introducing residual compressive stress on the surface, significantly improving fatigue life.
Machining path planning and clamping optimization are indirect means of residual stress control. Sequential milling easily leads to stress accumulation and causes part deformation, while symmetrical milling or cross milling can achieve a uniform distribution of residual stress through the mutual cancellation of stress fields. The magnitude and direction of clamping force need to be dynamically adjusted according to the part stiffness to avoid residual stress gradients caused by local indentation or springback. For example, in the machining of thin-walled parts, flexible clamping techniques such as vacuum chucks or low-melting-point alloy filling can effectively reduce residual stress distortion caused by clamping.
The integrated application of post-processing is the ultimate guarantee for residual stress control. Vibration aging (VSR) induces microscopic plastic deformation of the material through low-frequency vibration, achieving the homogenization and release of residual stress; cryogenic treatment utilizes an ultra-low temperature environment to promote martensitic phase transformation, introducing a beneficial residual compressive stress layer. For high-precision parts, shot peening and laser shock peening (LSP) can further optimize the surface residual stress state. The former forms a compressive stress layer through shot impact, while the latter uses high-energy pulsed lasers to induce shock waves, achieving deep-level residual stress control.
Residual stress control in precision aviation parts processing needs to be integrated throughout the entire process, from process design and machining to post-processing. Through the synergistic optimization of cutting parameters, tool geometry, cooling methods, path planning, and post-processing technologies, precise control of residual stress can be achieved, providing key support for the high-performance, long-life manufacturing of aviation parts.
