Impellers are one of the important core components in aero-engines, chemical equipment, and power equipment. Their complex three-dimensional geometric shape and application of high-performance materials impose extremely high technical requirements on the manufacturing process. The traditional manufacturing routes always involve multiple equipment and multiple clamping operations, with problems of long cycle, error accumulation, and high resource tie-up. In recent years, with the gradual maturity of advanced processes like five-axis composite machining technology, linear friction welding, and electrochemical machining, the production models of structures like impellers and integral blisks are transforming with increasing speed.
Introduction
With the demands for continuously improving high thrust-to-weight ratio and high efficiency in aero-engines on the rise, the manufacturing accuracy, strength, and structural complexity of impellers as important parts are continuously enhanced. Especially with the background of large-scale application of integral blisk structures, the traditional process-divided machining mode could not meet the manufacturing demands of integration, high precision, and short cycle. To achieve one-stop completion from roughing to finishing, drilling, tapping, and even surface treatment, contemporary manufacturing is accelerating the application of multi-process composite machining equipment to enhance process chain efficiency and manufacturing stability with the “one machine, one clamp” idea. This trend is not only embodied in the manufacturing of high-end aero-engines but also promoted in high-end equipment in energy, chemical, and other fields.
Process Challenges in Impeller and Integral Blisk Manufacturing
High-Complexity Surfaces and Difficult Machinability of Materials
Impellers and integral blisk structures are typically manufactured from titanium alloys or nickel-based superalloys with high strength, high heat resistance, and corrosion resistance but very poor machinability. Blades are free-form surface components with complex machining paths, which place extremely strict demands on machine tool dynamic accuracy, tool rigidity, and machining strategy. Minor deviations will cause over-cutting or under-cutting, affecting aerodynamic performance and service life.
Process Dispersion and Clamping Error Accumulation
Traditional processes generally require process transfer operations between different machine tools, i.e., rough milling, finish milling, drilling, and thread machining, which leads to a number of clampings being increased. Each workstation change is at the risk of positioning errors. This is particularly true for integral blisk structures, for which the consistency requirement of each blade profile and disk dimensions is extremely high. Multi-clampings tremendously increase the chance of error accumulation.
Low Material Utilization and Resource Waste
Especially when number-controlled five-axis milling is used in integral blisks, cutting blades and disks from solid blanks generally leads to over 90% material removal rate, with serious material waste, long machining time, and high processing cost. Therefore, new forming technologies and combined machining need to be incorporated to improve material utilization efficiency and economy.
Key Paths of Multi-Process Composite Machining
Multi-process composite machining, being one of the primary ways to improve the integration and precision control level of impeller production, has been one of the key frameworks of high-end manufacturing equipment. It achieves process integration and digital simulation collaboration from roughing to finishing efficient closed-loop processing.
Process Integration and Path Fusion
Integrating various machining processes such as turning, milling, drilling, and tapping in a five-axis composite machining center, and integrating the complex geometric shape of the impeller and the necessary process requirements, an integrated machining route such as “rough milling—finish milling of blades—drilling of roots—end face tapping” can be devised. Relying on the high-end CAM software to automatically generate multi-axis tool paths can effectively reduce the process chain, save process conversion and handling time, and significantly improve the manufacturing efficiency and stability.
The model not only reduces the manufacturing process but also decreases the threshold of tool path planning and the skills of operators, so it is particularly suitable for high-consistency machining of mid-to-high-end batch impeller products.
Realization of Precision Unity with the “One Clamping” Concept
The composite machining equipment is equipped with high-rigidity precision fixtures and high-precision rotary worktables, enabling impellers to complete all operations with one clamping throughout the entire machining cycle. This kind of process significantly reduces the accumulation of datum errors caused by multi-clampings in a united coordinate system, significantly improving blade profile, disk coplanarity, and the geometric consistency of multiple blades.
To impeller structures with extremely high requirements for dynamic balance and axial precision in aerospace or high-speed power equipment, the one-clamping machining can significantly improve product precision and dynamic performance assurance.
Digital Simulation and Interference Elimination
Through the integration of CAD/CAM/CAE platforms, there is a overall simulation analysis of machining paths, tool orientations, and fixture interference, pre-filtering interference areas, tool jumping risks, and dead-angle machining blind areas. Additionally, intelligent machine tool control systems combined with real-time thermal error compensation mechanisms can be used to further enhance machining stability and size stability.
This strategy can significantly reduce trial cuts and tooling debug cycles, offering useful economic and quality assurance advantages in high-cost material or low-volume, high-value-added impeller production.
Support from New Composite Process Technologies
CNC High-Speed Milling (HSC)
Five-axis CNC high-speed milling (HSC) remains the main integral blisk machining technology. GE and Rolls-Royce utilize HSC technology in milling titanium alloy integral blisks, achieving one-time shaping of complex blade surfaces through high-speed spindles (>24,000 rpm) and multi-axis control. Teleflex Aerospace combines rough-finish paths and tool posture control, eliminating the manual polishing link and achieving double efficiency and quality improvement.
Linear Friction Welding (LFW) and Electrochemical Machining (ECM)
Linear friction welding, through solid-phase joining, can weld premanufactured disks and blades into one piece with perfection. Not only does it have better weld performance, but it also enables the design of dissimilar material combinations and novel structures (e.g., hollow blades), which has been applied widely by MTU, Rolls-Royce, and others for producing new engine integral blisks. Electrochemical machining, with no tool wear, favorable surface quality, and no heat-affected zone, can be used to machine high-hardness and heat-resistant alloy materials and is a necessary supplemental direction for future composite machining.
Key Elements for Promoting the Implementation of Composite Machining
- Reasonable equipment selection: Requires high-rigidity structure, five-axis capability, quick-change tool magazine, and thermal compensation system.
- Customized fixtures and paths: Design special fixtures according to impeller or integral blisk structures to avoid interference and achieve full-angle machining.
- Digital collaborative manufacturing: Combine machining simulation, quality inspection, and MES systems to achieve full-process visualization and optimized scheduling.
Conclusion
Multi-process composite machining technology is increasingly the primary process route of impeller manufacture and integral blisk production. With its process integration, integrated machining, and precision control, it not only improves manufacturing efficiency but also gives high-end equipment manufacturing sustainable development impetus. Based on artificial intelligence, digital twin, and intelligent tool technologies, future composite machining will be adaptive and intelligent, helping China reach new heights in the manufacturing of high-performance aviation power systems.
