Thin-walled parts deform during processing? This shape-control strategy for 7075 aluminum alloy is incredibly reliable.

The causes of machining deformation in thin-walled weak-rigid aluminum alloy parts were analyzed, and a process plan was developed. By innovating clamping methods, creating split support fixtures, and optimizing machining toolpaths, the deformation problem during parts machining was effectively solved.

Introduction

As the company grows, its product range is expanding, and requirements for machining precision are becoming increasingly stringent. While dimensional and geometric tolerances for large structural components were previously generally set at ±0.05 mm, the baseline requirement for components undertaken in recent years is ±0.03 mm. Improvements addressing the machining of thin-walled aluminum alloy parts with low rigidity—specifically focusing on process planning, workholding methods, and toolpath strategies—can effectively control part deformation.

Machining challenges

Figure 1 illustrates a thin-walled aluminum alloy part with low rigidity. Made of 7075 aluminum alloy, the part measures 282 mm in length and 175.5 mm in width, with a main body thickness of 31 mm. Following machining, the minimum wall thickness is 2 mm, while the dimensional tolerances are ±0.03 mm for the spacing between the two supporting legs and ±0.03 mm for the mounting surface. Given that the material removal rate exceeds 95% and the space between the two supporting legs is open, the component is classified as a typical thin-walled part with low rigidity. The primary machining challenge lies in controlling the deformation of the two supporting legs; according to tolerance specifications, post-machining deformation must be kept within 0.05 mm. Any deformation would cause critical dimensions to fall outside the tolerance range, resulting in the part being scrapped.

Figure 1 Thin-walled aluminum alloy part with low rigidity

Process Analysis

The machining challenges are analyzed from the following aspects:

(1) Process requirements

Based on past machining experience, the part undergoes three stages of intermediate aging treatment. The first roughing pass leaves a 3 mm machining allowance for aging; the second leaves a 2 mm allowance; and the third leaves a 1 mm allowance.

(2) Clamping method

Based on the part's structural design, the following points must be observed: ① The part must not be subjected to external forces during clamping; if external force is used to secure it, the part will undergo springback deformation once the clamping force is released. ② The contact area for clamping must be sufficiently large, particularly at the two supporting legs. ③ Clamping must adhere to the principle of a unified datum. Since all surfaces of the part require machining and multiple clamping setups are necessary, a consistent datum must be established.

(3) Tool path planning

A well-designed tool path can significantly reduce the cutting forces exerted on the part during machining.

Process improvement measures

4.1 Relieving internal stress

Three aging treatments are performed during machining in accordance with specific process requirements to fully relieve internal stress within the material. Notably, during the second and third rough machining stages, the clamping force applied to the part must be strictly controlled; a torque wrench is used to ensure the clamping force remains below 15 N.

4.2 Innovative clamping method

For finish machining, the red surface shown in Figure 2 serves as the mounting and positioning surface, and the workpiece is secured to the fixture plate using 302 adhesive (see Figure 3). Based on the part's external profile angles, a V-shaped positioning block—matching the angle and featuring a height of 1 mm—is set on the fixture plate (see the yellow section in Figure 3); this effectively constrains five degrees of freedom, ensuring precise positioning. During clamping, the left and right inclined edges of the workpiece are aligned flush against the V-shaped positioning block on the fixture, and 302 adhesive is applied along the contact edges to secure the assembly. Once clamped, the part's external dimensions and square cavity are machined to meet design specifications.

Figure 2 Schematic of the mounting and locating surface

Figure 3 Workpiece secured to the fixture plate

The part is flipped and clamped in the same manner to machine the reverse side, ensuring the overall thickness dimension. With all six exterior faces now machined, only the internal cavity remains; a third clamping setup is required for this stage. To ensure sufficient clamping rigidity, specialized tooling must be designed to maximize the contact area.

4.3 Fabrication of Specialized Fixtures

Given the large dimensions of the part, fabricating the internal cavity machining fixture as a single, solid unit would result in significant material waste; therefore, a multi-piece design was adopted. As shown in Figure 4, the internal cavity machining fixture consists of three components: Fixture Part 1, Fixture Part 2, and Fixture Part 3. Since the part's external dimensions have already been machined to the final specifications, the fixture was fabricated with dimensions 0.06–0.10 mm larger than the part's profile on each side; this ensures the part fits smoothly and sits flush against the fixture's side and bottom surfaces. Once the part is placed in the fixture, it is first weighted down to ensure a tight fit before being bonded with 302 adhesive. Figure 5 illustrates the part's low-rigidity holes; Holes 1 and 2 are the areas most prone to deformation, necessitating reinforcement. After the 302 adhesive has cured, "diamond putty" (moldable epoxy putty) or fire-resistant putty can be packed into Holes 1 and 2. Alternatively, if these materials are unavailable, a tightly rolled, water-soaked towel can be inserted; this reinforces the part while simultaneously preventing resonance during machining.

Figure 4 Internal cavity machining fixture

Figure 5 Low-strength hole in the part

4.4 Optimization of Machining Toolpaths

The overall machining toolpath for the internal cavity is shown in Figure 6, while a magnified view of a section of the toolpath is shown in Figure 7. First, the toolpath follows a reciprocating motion along the length of the part, avoiding transverse movement to ensure the cutting force remains consistently oriented in a single direction. Second, minimizing sharp turns in the toolpath prevents spikes in instantaneous force during cutting, thereby ensuring a uniform cutting force throughout the process. Utilizing a five-axis machine tool and reducing the tool overhang length effectively enhances tool rigidity and machining efficiency, ensuring high machining quality.

Figure 6 Overall machining toolpath for the internal cavity

Figure 7 Close-up view of the internal cavity machining toolpath

After implementing the aforementioned improvements, the machining results for the parts are as shown in Figure 8. Full-dimensional inspection using a CMM confirmed that all dimensions met specifications, with part deformation controlled to within 0.03 mm.

Figure 8 Machining results of the part

Conclusion

As spacecraft evolve toward lightweight and highly integrated designs, the use of thin-walled and low-rigidity components has become increasingly common, making the control of machining-induced deformation a critical challenge. This paper presents a comprehensive analysis of the machining process for low-rigidity, thin-walled aluminum alloy parts. By optimizing process strategies, clamping methods, and toolpath planning—and by designing and fabricating a split-type support fixture—machining deformation was effectively controlled, resulting in improved product quality and manufacturing efficiency.