Advanced Processing Techniques for Complex-Shaped High-Precision Aluminum Alloy Thin-Walled Parts

Aluminum alloy thin-walled structural components, known for their lightweight, compressive strength, and corrosion resistance, are widely used in aerospace spare parts to reduce overall aircraft weight and enhance flight performance. However, due to their large size and high surface quality requirements, conventional machining methods often induce residual stresses, resulting in dimensional changes and difficulties in meeting product specifications. This article focuses on a complex-shaped high-precision aluminum alloy thin-walled part used in aerospace applications. By optimizing the machining process and strategically arranging heat treatment, cold working, and electrical discharge machining (EDM) operations, a controllable process route with improved machining quality and efficiency is established.

Processing Challenges

The material of the thin-walled part is 2D14 high-strength hard alloy with relatively large overall volume and thin walls, demanding high dimensional accuracy and geometric tolerances. Machining involves milling cavities and profiles, where clamping-induced stresses during machining lead to dimensional deviations. These deviations prevent meeting the high-precision requirements of aerospace components.

Process Arrangement

1. Overall Process Route

Based on the part's features and processing challenges, a rational sequence of operations is devised, incorporating cold working, EDM, and heat treatment. The overall process arrangement is illustrated in Figure 1, with the part's external structure depicted in Figure 2.

2. Heat Treatment

Implementation of stabilization heat treatment is crucial. The first stabilization involves placing the roughed workpiece in an artificial aging furnace, heating it to 250–290°C, holding it for 2–4 hours, and then air-cooling it. The second stabilization entails placing the semi-finished workpiece in the aging furnace, heating it to 250–290°C, holding it for 1–2 hours, and subjecting it to thermal cycling. Aluminum alloy undergoes thermal cycling by placing the component in a low-temperature container at -70 to -50°C for 1–2 hours. For enhanced effects, cryogenic treatment in liquid nitrogen can be applied, with cooling rate insignificantly affecting thermal cycling outcomes.

3. Cold Working

To avoid deformation during CNC milling, the process is divided into roughing, semi-finishing, and finishing stages. During roughing, a tool speed of 6000–7000 rpm efficiently removes material and forms the part's overall contour, leaving 3–5 mm allowance for semi-finishing. Semi-finishing at a tool speed of 2000–2500 rpm ensures surface roughness and brightness, leaving 0.5–1 mm allowance for finishing. Finishing with reduced tool speed of 1500–1800 rpm eliminates allowances and ensures surface quality.

4. Electrical Discharge Machining (EDM)

After completing cavity and profile machining, the workpiece retains process clamping at both ends. To avoid stress-induced deformation during clamping removal, EDM is employed. This non-contact discharge machining eliminates mechanical deformations and errors. Utilizing positive polarity (workpiece as anode, electrode wire as cathode) and selecting current of 3–5 A, pulse width of 30–50 μs, and duty cycle of 1:7 to 1:5 ensures efficient EDM.

Conclusion

This article optimizes the processing of complex-shaped high-precision thin-walled parts made of aluminum alloy, addressing their challenging machining characteristics. By rationalizing the sequence of cold working, heat treatment, and EDM operations and selecting appropriate tools and methods for roughing, semi-finishing, and finishing, the quality and efficiency of part production are effectively ensured, breaking away from reliance on high-end machine tools. Practical validation demonstrates the rational layout of the process route, scientific and compact arrangement of operations, avoidance of dimensional changes during mechanical machining, reduced turnaround time, and enhanced production efficiency.