Industry News
Why Do Aircraft Engines Use Integral Blades?
2024-08-19
Aircraft engines are the "heart" of aircraft and are also known as the "crown jewel of industry". Their manufacturing integrates many cutting-edge technologies in modern industry, involving materials, machining, thermodynamics and other fields. As countries have higher and higher requirements for engine performance, new structures, new technologies, and new processes in research and development and application are still constantly challenging the peak of modern industry. One of the important factors in improving the thrust-to-weight ratio of aircraft engines is the integral blade.
Advantages of integral blades
Before the appearance of integral blades, the rotor blades of the engine needed to be connected to the wheel disc through tenons, tenons and locking devices, but this structure gradually failed to meet the needs of high-performance aircraft engines. The integral blade that integrates the engine rotor blades and the wheel disc was designed. It has become a must-have structure for high thrust-to-weight ratio engines and has been widely used in military and civil aircraft engines. It has the following advantages.
1. Weight reduction
Since the rim of the wheel disc does not need to be machined with tenons for installing blades, the radial size of the rim can be greatly reduced, thereby significantly reducing the mass of the rotor.
2. Reduce the number of parts
In addition to the fact that the wheel disc and the blades are integrated, the reduction of locking devices is also an important reason. The reliability requirements of aircraft engines are extremely strict, and the simplified rotor structure plays a great role in improving reliability.
3. Reduce airflow loss
The escape loss caused by the gap in the traditional connection method is eliminated, the engine working efficiency is improved, and the thrust is increased.
The integral blade disk, which not only reduces weight but also increases thrust, is conducive to improving the thrust-to-weight ratio. Naturally, it is not an easy "pearl" to pick. On the one hand, the integral blade disk mostly uses difficult-to-process materials such as titanium alloy and high-temperature alloy; on the other hand, its blades are thin and the blade shape is complex, which puts extremely high demands on manufacturing technology. In addition, when the rotor blades are damaged, they cannot be replaced separately, which may cause the integral blade disk to be scrapped, and the repair technology is another problem.
Manufacturing of integral blade disks
At present, there are three main technologies for manufacturing integral blade disks.
1. Five-axis linkage CNC milling
Five-axis linkage CNC milling is widely used in the field of integral blade disc manufacturing due to its advantages such as rapid response, high reliability, good processing flexibility and short production preparation cycle. The main milling methods include side milling, plunge milling and cycloidal milling. The key factors to ensure the success of integral blade disc processing include:
1) Five-axis linkage machine tools with good dynamic characteristics
2) Optimized professional CAM software
3) Tools and application knowledge dedicated to titanium alloy/high-temperature alloy processing
2. Electrochemical machining
Electrochemical machining is an excellent method for machining the integral blade disc channel of an aircraft engine. There are several processing technologies in electrochemical machining, such as electrolytic sleeve material, contour electrolytic machining and CNC electrolytic machining.
Since electrochemical machining mainly uses the characteristics of metal anode dissolution in electrolyte, when applying electrochemical machining technology, the cathode part will not be lost, and the workpiece will not be affected by cutting force, machining heat, etc. during machining, which reduces the residual stress of the integral blade disc channel of the aircraft engine after machining.
In addition, compared with five-axis milling, electrochemical machining significantly reduces the working hours, and can be used in the rough machining, semi-finishing and finishing stages. No manual polishing is required after machining. Therefore, it is one of the important development directions of aero-engine integral blade channel machining.
3. Welding
The blades are processed separately, and the pre-processed blades are welded to the blade disk by electron beam welding, linear friction welding or vacuum solid-state diffusion bonding in the later stage. Its advantage is that it can be used for the manufacture of integral blades with inconsistent blade and wheel materials.
When welding is used, the quality of blade welding is required to be high, which directly affects the performance and reliability of the integral blade disk of the aero-engine. Moreover, since the actual shapes of the blades used in the welded blade disk are not consistent, the positions of the blades after welding are not consistent due to the limitation of welding accuracy. It is necessary to use adaptive processing technology to perform personalized precision CNC milling for each blade.
In addition, welding is a very important technology in the repair of the integral blade disk. Among them, linear friction welding is a solid phase welding technology with high welding joint quality and good reproducibility. It is one of the more reliable and trustworthy welding technologies for welding high thrust-to-weight ratio aircraft engine rotor components.
Application of integral blade disk
1. EJ200 aircraft engine
The EJ200 aircraft engine has a total of 3-stage fans and 5-stage high-pressure compressors. Single blades are welded to the wheel disk by electron beam to form an integral blade disk, which is used in the 3rd stage fan and the 1st stage high-pressure compressor. The integral blade disk is not welded together with the rotor of other stages to form a multi-stage integral rotor, but is connected with short bolts. Generally speaking, it is in the early stage of the application of integral blade disk.
2. F414 turbofan engine
In the F414 turbofan engine, the 2nd and 3rd stages of the 3-stage fan and the first 3 stages of the 7th stage high-pressure compressor use integral blade disks, which are processed by electrochemical methods. GE has also developed a feasible repair method. On this basis, the integral blades of the second and third stages of the fan are welded together to form an integral rotor, and the first and second stages of the compressor are also welded together, which further reduces the weight of the rotor and improves the durability of the engine.
Compared with EJ200, F414 has taken another big step forward in the application of integral blades.
3. F119-PW-100 engine
The three-stage fan and the six-stage high-pressure compressor all use integral blades, and the first-stage fan blades are hollow. The hollow blades are welded to the wheel disc through linear friction welding to form an integral blade, which reduces the weight of the rotor of this stage by 32kg.
4. BR715 engine
Integral blades have also been used in large civilian engines. The BR715 engine uses five-axis linkage CNC milling technology to process integral blades, which are used on the second-stage boost compressor after the fan, and the front and rear integral blades are welded together to form an integral rotor. It is used on the Boeing 717.
