With the continuous improvement of the power-to-weight ratio in high-performance aeroengines, the role of the supercharged drum has become increasingly significant. These components typically feature complex structures and thin walls, making them highly susceptible to deformation during machining, which can negatively impact machining accuracy and overall processing quality, ultimately affecting engine performance. Titanium alloys are widely used in aerospace engines due to their exceptional strength, corrosion resistance, and high-temperature performance. In this paper, we focus on the supercharged drum of an aeroengine and explore how optimizing the manufacturing process can effectively control deformation in thin-walled parts, ensuring product quality and performance.
**1. Processing Characteristics of Titanium Alloys**
Titanium alloys are considered difficult-to-machine materials, primarily due to their inherent material properties and the structural complexity of the parts. The material characteristics that contribute to machining challenges include: low thermal conductivity, leading to poor heat dissipation and excessive cutting tool temperatures, which significantly reduce tool life and surface quality. Additionally, titanium has a low elastic modulus, making it prone to elastic deformation under cutting forces, increasing tool wear and causing cutting chatter. Its high chemical reactivity also leads to bonding and diffusion with the tool material, further reducing tool life. Lastly, titanium's low plasticity results in a small chip deformation coefficient and high chip flow speed, increasing the unit cutting force and accelerating tool wear.
The structural features of the part—such as its large diameter (over 800mm), height (around 400mm), and thin wall thickness (2.15mm)—add to the difficulty. Due to its poor rigidity, the part is prone to vibration during machining, which affects both cutting efficiency and surface quality. The dovetail groove in the pressurized stage is a closed profile with varying cavity sizes, making it hard for cutting fluid to reach the tool tip, leading to heat concentration. Moreover, the thin-wall structure makes it susceptible to tool deflection and residual stress release, resulting in significant deformation that impacts machining accuracy.
**2. Analysis of Deformation Causes**
Deformation in the supercharged drum is influenced by several factors within the manufacturing system, including clamping conditions, residual stresses, cutting forces, cutting heat, and vibrations. Improper clamping can introduce additional stress, especially in thin-walled parts, affecting dimensional and geometric accuracy. Residual stresses generated during machining can lead to plastic deformation when external forces are applied, altering the internal stress distribution and impacting the final part quality. Cutting forces and heat can cause vibrations and deformations, while the machine tool's rigidity, tool geometry, and cutting parameters also play a role. Among these, cutting forces, clamping forces, and residual stresses are the primary contributors to machining deformation.
**3. Process Design**
The supercharged drum is made from TC4 titanium alloy, supplied as a die-forged blank. Due to the limitations of ultrasonic flaw detection, the initial shape is relatively simple, while the final part requires a more complex profile, leading to uneven machining allowances. To address this, a rough machining step is performed to evenly distribute the machining allowance. After roughing, stress-relief heat treatment is carried out to eliminate residual stresses. A reference process is then arranged before finishing to improve positioning precision and prevent error accumulation. The main machining route includes: machining the ultrasonic surface, ultrasonic testing, rough internal and external profiles, stress relief heat treatment, benchmarking, fine internal and external profiling, milling blade installation grooves, and inspection.
**4. Deformation Control**
To manage deformation, the design of fixtures, selection of tools, optimization of cutting parameters, and path planning are all critical. Fixture design focuses on using rigid surfaces for positioning and applying axial clamping to avoid deformation. For thin-walled, high parts, auxiliary supports are added during roughing to increase rigidity and suppress vibration. Tool selection involves non-coated ultra-fine grain carbide tools with low affinity to titanium, improving tool life and reducing deformation. Cutting parameters are optimized to maintain stable cutting conditions, with speeds between 50–70 m/min, feeds of 0.1–0.2 mm/rev, and depths of cut between 0.3–1 mm. The cutting path is carefully planned to reduce stress concentration and ensure uniform material removal. NC programming also plays a key role in optimizing motion trajectories and improving surface finish. Finally, multiple stress-relief treatments are conducted to minimize deformation in high-precision parts.
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