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 are characterized by 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 excellent strength, corrosion resistance, and ability to maintain structural integrity at high temperatures. 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 titanium alloy components, ensuring high-quality output.
**1. Processing Characteristics of Titanium Alloys**
Titanium alloys are considered difficult-to-machine materials, primarily due to their inherent material properties and the complexity of part geometry. First, titanium has low thermal conductivity, leading to poor heat dissipation during cutting. This results in elevated cutting tool temperatures, which significantly reduce tool life and compromise surface finish. Second, titanium has a low modulus of elasticity, making it prone to elastic deformation under cutting forces. This leads to increased tool wear and potential cutting chatter. Third, titanium exhibits high chemical reactivity, causing it to bond with the tool material, resulting in adhesion and diffusion that further shorten tool life. Finally, titanium’s low plasticity and small chip deformation coefficient lead to high cutting forces, accelerating tool wear and increasing the risk of deformation.
The structural characteristics of the supercharged drum also contribute to processing challenges. The drum is typically over 800 mm in diameter and about 400 mm in height, with a wall thickness of only 2.15 mm. Its thin-wall design makes it highly flexible, leading to cutting vibrations that affect both efficiency and surface quality. Additionally, the closed-profile dovetail grooves in the pressurized stage make it difficult for cutting fluid to reach the tool tip, leading to localized heat buildup and reduced cooling effectiveness. Furthermore, the thin walls are prone to tool deflection and residual stress release, which can cause significant deformation during machining.
**2. Analysis of Deformation Causes**
Several factors contribute to deformation in the supercharged drum. Key among them are clamping conditions, residual stresses, cutting forces, heat generation, and vibration. Improper clamping can introduce additional stresses, especially in thin-walled parts, leading to dimensional inaccuracies and surface deformation. Residual stresses generated during machining can cause plastic deformation when external forces are applied, altering the part's shape. Cutting forces and heat can induce vibration and deformation, while machine tool rigidity, tool geometry, and cutting parameters also play a role. Among these, cutting force, clamping force, and residual stress are the primary causes of machining deformation.
**3. Process Design**
The supercharged drum is made from Ti-6Al-4V (TC4) titanium alloy, supplied as a forged blank. Due to the limitations of ultrasonic testing, the initial blank has a relatively simple profile, while the final part requires a much more complex shape. This results in uneven machining allowances across different surfaces. To address this, a roughing operation is performed first to remove excess material and balance the allowance. After roughing, a stress-relief heat treatment is conducted to eliminate residual stresses. A reference process is then implemented before finishing to ensure accurate positioning and prevent error accumulation. The main machining route includes: machining the ultrasonic surface → ultrasonic inspection → rough internal and external profiling → stress relief heat treatment → benchmarking → fine internal and external profiling → milling blade and locking grooves → final inspection.
**4. Deformation Control**
To manage deformation in titanium alloy parts, a comprehensive approach is taken, considering clamping, tools, cutting parameters, and tool paths.
(1) **Fixture Design**: The fixture is designed to use rigid surfaces for positioning, employing axial clamping to avoid deformation under clamping force. For parts with high aspect ratios and thin walls, specific positioning strategies are used to lower the center of gravity and improve rigidity. Auxiliary supports are added to enhance stability and suppress vibration during roughing.
(2) **Tool Selection and Geometry**: Tool materials with low affinity to titanium are chosen, such as non-coated ultra-fine tungsten-cobalt carbide. Larger back angles (αo = 15–18°) and front angles (γo = 10°) help reduce friction and cutting forces. A smaller nose radius (rε = 1–2 mm) improves heat dissipation and tool strength.
(3) **Cutting Parameters**: A lower cutting speed (v = 50–70 m/min), moderate feed rate (f = 0.1–0.2 mm/rev), and shallow depth of cut (ap = 0.3–1 mm) are recommended to minimize heat generation and tool wear. Coolant is used extensively to maintain optimal cutting conditions and reduce deformation.
(4) **Tool Path Strategy**: Tool paths are optimized to start with larger surfaces and progress to smaller ones, ensuring even material removal. Roughing uses layered cutting to improve efficiency and reduce deformation, while finishing employs contour-based methods to achieve high surface quality.
(5) **NC Programming**: The NC program is tailored to the part’s geometry, using cycle programming during roughing to control stress and improve chip evacuation. During finishing, tangential arc cutting is used to avoid visible tool marks and ensure smooth surface finish.
(6) **Heat Treatment**: Stress-relieving heat treatments are incorporated after roughing and semi-finishing to eliminate residual stresses and reduce deformation risks in high-precision parts.
By integrating these strategies, the machining of titanium alloy supercharged drums can be optimized to achieve high precision, minimal deformation, and improved overall quality.
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