CNC Machining Deformation Control Technology of Aviation

Structural Parts

Modern commercial aircraft primarily use materials such as aluminum alloys, alloy steels, titanium alloys, and composites. Although the proportion of composites and titanium alloys used in aircraft bodies increases each year, aluminum alloys remain an indispensable primary material in large civilian aircraft due to their low density, high strength, and excellent corrosion resistance.

Integral structuring has a significant impact on the development cycle, production efficiency, and manufacturing costs. It can substantially reduce the workload of connection assembly, decrease the number of parts, reduce weight by 10% to 30%, and provide good sealing performance and structural integrity. Due to the high material removal rate, complex shapes, and relatively poor overall rigidity of large aerospace integral structural parts, CNC aluminum cutting requires higher standards.

This paper provides an in-depth analysis and study of deformation in the machining of aerospace aluminum alloys and proposes strategies for controlling deformation in the machining of integral structural parts.

Aluminum Alloy Structure Machining Deformation Status

The gravity and heat generated by the friction of the tool in the CNC machining of structural components will act on the workpiece, resulting in elastic deformation. If the cutting force exceeds the material’s elastic limit, the workpiece will experience compressive deformation under the cutting force and rebound deformation due to the influence of the cutting force.

First of all, the cutting heat generated during the cutting process will also lead to thermal expansion and deformation of the workpiece. The combined effect of these factors will increase the deformation of the workpiece, thus affecting the machining accuracy;

Secondly, during the machining process, the introduction of cutting heat creates a significant temperature difference between the surface and the substrate of the workpiece. This results in thermal expansion of the surface material, while the internal material remains relatively cooler, causing the surface to be under tension and the substrate under compression.

Lastly, the tool itself can also deform due to thermal and mechanical effects. The introduction of cutting heat can lead to residual stresses within the workpiece. The tensile stress induced by the stretched surface material and the compressive stress in the substrate disrupt the stress equilibrium within the workpiece.

Moreover, the presence of residual stress can cause warping and twisting of the workpiece post-machining, thereby affecting the precision and quality of the workpiece.

CNC Machining Deformation Control Techniques

Blank Residual Stress Regulation Technology

Residual stress in blanks can be eliminated through various methods. Heat treatment involves heating and cooling processes that can relieve the residual stress in blank materials. This method is often combined with mechanical stretching, where external stretching during heating and cooling reduces the residual stress in the blank. Vibration aging, which involves vibrating the blank material at certain frequencies and amplitudes, can also release internal stresses.

Optimization of Machining Parameters

Machining parameters significantly affect deformation. During the machining process, it is crucial to select cutting parameters, such as cutting speed, feed rate, and tool angle, based on the characteristics of the blank material and tools. This reduces the impact of cutting force and heat on the workpiece, thereby minimizing deformation. Additionally, optimizing cooling conditions through methods such as mist cooling or liquid immersion cooling can lower cutting temperatures and reduce workpiece deformation. Low-speed cutting techniques can also be employed to minimize machining deformation.

Optimization of Tool Path

Optimizing the tool path can help reduce machining deformation. Spiral tool paths can minimize the impact of cutting force and heat on the workpiece, thus reducing deformation. Layer-by-layer removal, controlling the machining depth and feed rate for each layer, ensures the precision and quality of the workpiece. Furthermore, five-axis machining can achieve comprehensive machining of the workpiece, thereby minimizing deformation.

Conclusion

Although aerospace aluminum alloys possess excellent machinability, the aerospace industry demands higher precision, quality, and machining efficiency. The requirements for machining accuracy and geometric tolerances of aerospace components are significantly more stringent than those in the automotive and other manufacturing industries.

Efficient machining, which combines high-speed machining technology and optimized cutting processes, is the key technology for machining large integral aerospace structural parts. The characteristics of efficient machining include a high material removal rate and short single-piece machining time, with optimized cutting parameters ensuring machining accuracy and surface quality.

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