Complete Machine | Northwestern Polytechnical University: Key Technologies, Hot Technologies and Basic Technologies for Advanced Aero-engine Manufacturing – Two-Engine Power First

 

Thrust-to-weight ratio and power-to-weight ratio are the most important technical indicators for measuring and evaluating the advancement of aero-engines. In order to pursue an engine thrust-to-weight ratio of more than 10, aero-engines have been using new materials and introducing new structures to reduce the weight of aero-engine parts while significantly increasing the temperature before the engine turbine.

 

This has put forward higher technical requirements for engine manufacturing and promoted the emergence and development of new technologies for aero-engine manufacturing. A series of key manufacturing technologies developed for the development of high-performance aero-engines will become or have become the direction of advanced manufacturing technology development.

 

This article introduces key manufacturing technologies for aero-engines from three levels: key technologies, hot technologies and basic technologies. Manufacturing key technologies are technologies that must be possessed in the development of advanced aero-engines; manufacturing hot technologies are technologies that must be studied to improve engine manufacturing efficiency and manufacturing quality; manufacturing basic technologies are technologies that should be gradually accumulated and developed for engine development and mass production, representing the soft power of engine manufacturing technology level and production capacity.

 

Key Technologies For Aircraft Engine Manufacturing

 

 1 Single Crystal Turbine Blade Manufacturing Technology

 

The temperature before the turbine of modern aircraft engines has been greatly improved. The temperature before the turbine of the F119 engine is as high as 1900~2050K. The turbine blades cast by traditional processes cannot withstand such high temperatures at all, and may even be melted and unable to work effectively.

 

Single crystal turbine blades have successfully solved the problem of high temperature resistance of turbine blades of a first-stage engine with a thrust-to-weight ratio of 10. The excellent high temperature resistance of single crystal turbine blades mainly depends on the fact that there is only one crystal in the entire blade, thereby eliminating the defects in high temperature performance between grain boundaries caused by the polycrystalline structure of equiaxed crystals and directional crystallization blades.

 

Single crystal turbine blades are the engine parts with the most manufacturing processes, the longest cycle, the lowest pass rate, and the most stringent foreign blockade and monopoly among all parts of aircraft engines.

 

The manufacturing process of single crystal turbine blades includes core pressing, core repair, core sintering, core inspection, matching of core and outer mold, wax mold injection, wax mold X-ray inspection, wax mold wall thickness detection, wax mold trimming, wax mold assembly, seeding system and pouring and riser assembly, paint sand removal, shell mold drying, shell mold dewaxing, shell mold baking, blade pouring, single crystal solidification, shell cleaning and sand blowing, initial inspection, fluorescent inspection, core removal, grinding, chord width measurement, blade X-ray inspection, X-ray film inspection, surface inspection, blade finishing, blade wall thickness detection, final inspection and other manufacturing links. In addition, the design and manufacturing of turbine blade precision casting molds must also be completed.

 

 

Single crystal turbine blades are currently only manufactured in a few countries in the world, such as the United States, Russia, the United Kingdom, France, and China. In recent years, China has also made great progress in the manufacture of single crystal turbine blades. It has developed a single crystal turbine blade for a first-stage engine with a thrust-to-weight ratio of 10 and mass-produced single crystal turbine blades for a turboshaft engine with a high power-to-weight ratio.

 

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2.High-Efficiency, High-Precision, And Low-Cost Processing Technology For Integral Blades

 

The application of integral blade technology has promoted the innovation of aero-engine structural design and the leap of manufacturing technology, achieved the goal of engine weight reduction and efficiency increase, and improved the reliability of engine operation.

 

At the same time, the thin thickness of the blades, the high-efficiency aerodynamic design of large bending and torsion, and the problem of poor blade rigidity, easy deformation and difficult control during processing; the narrow and deep airflow channel between the blades makes the blade processing process difficult to realize; high-strength materials such as titanium alloys and high-temperature alloys are difficult to cut and process, and the efficiency is low. The new engines of the United States and Britain in the 1980s began to apply integral blade technology, and my country’s integral blade technology started around 1996.

 

The application of integral blade disk technology has promoted the development of the integrated technology of engine parts structure. The tandem integral blade disk structure with drum blade disk, shaft blade disk, disk-drum-shaft combined blade disk, hoop closed blade disk, rectifier stator ring blade disk and two-stage or multi-stage blade disk combination has been applied in the development of new aircraft engines; the functional structure of the integral blade disk has developed large and small blade structure blade disks and oblique flow rotor blade disks on the basis of axial flow blade disks and centrifugal impellers.

 

Since the integral blade disk was applied to high-performance aircraft engines, the integral blade disk manufacturing technology has been developing and improving. At present, there are mainly 5 process methods for integral blade disk processing: lost wax precision casting integral blade disk, electron beam welding integral blade disk, electrochemical machining integral blade disk, linear friction welding integral blade disk and five-axis CNC machine tool processing integral blade disk and other process methods.

 

The five-axis CNC machine tool processing integral blade disk process method is the earliest technical research and development, the widest engineering application, and the most mature technology in the manufacturing of integral blade disks of domestic aircraft engines.

 

Among them, the slotting process, symmetrical spiral milling blade profile finishing process, blade leading and trailing edge processing error compensation technology and integral blade disc blade profile adaptive processing technology are the key to the development and application of this technology [1].

 

The integral blade discs of foreign T700 engines, BR715 engine supercharger stages, and EJ200 engines are manufactured using this processing method. The integral blade discs of my country’s CJ1000A, WS500 and other aircraft engines are also manufactured using five-axis CNC machining technology. Figure 1 shows the first-stage integral blade disc of the high-pressure compressor of a commercial aircraft engine manufactured in my country.

 

 

Hollow Blade Manufacturing Technology

 

The fan of a turbofan engine is far away from the combustion chamber and has a low heat load, but the requirements of advanced aircraft engines for its aerodynamic efficiency and the ability to prevent damage from foreign objects are constantly increasing. High-performance aircraft engine fans all use wide-chord, shoulder-free, hollow fan blades.

 

The hollow fan blades with a triangular truss structure developed by Rolls-Royce are an improvement on the original honeycomb sandwich blades. Rolls-Royce calls it the second-generation hollow fan blade. Its process is to use a superplastic forming/diffusion bonding (SPF/DB) combined process method to make three layers of titanium alloy plates into wide-chord hollow fan blades. The hollow part of the blade has a triangular truss structure. This structural blade has been used on the “Trent” engine of Boeing 777 and A330 aircraft. my country’s manufacturing technology for hollow fan blades with a triangular truss structure has also made breakthroughs (Figure 2 shows the hollow fan blades and the internal triangular structure), but a lot of strength, vibration, fatigue tests and process optimization research are still needed to meet engineering applications.

 

The manufacturing process of hollow blades is as follows: first, three titanium alloy plates are prepared and placed in three layers: upper, middle and lower. The middle layer is the core plate, and the upper and lower layers are the blade basin and blade back plates respectively. Then, the three titanium alloy plates are degreased and pickled, the middle layer is sprayed with solder paste, the titanium plates are welded, molded and heated, argon gas purified, diffusion bonded, superplastic formed, furnace cooled, surface chemical washed, blade root and intake and exhaust edge processed, and blade inspected. [2] Superplastic forming/diffusion bonding (SPF/DB) is used to form a fan hollow blade.

 

4 High-end Bearing Manufacturing Technology

 

Bearings are one of the key components of aircraft engines. While operating at a high speed of tens of thousands of revolutions per minute for a long time, bearings must also withstand the huge centrifugal force and various forms of extrusion stress, friction and ultra-high temperature generated by the high-speed rotation of the engine rotor. The quality and performance of bearings directly affect engine performance, life, reliability and flight safety.

 

The development and production of high-end bearings are closely related to the intersection of contact mechanics, lubrication theory, tribology and other disciplines, as well as basic research on fatigue and damage, heat treatment and material organization. At the same time, a large number of technical problems in design, materials, manufacturing, manufacturing equipment, detection and testing, grease and lubrication must be solved.

 

At present, the research and development, manufacturing and sales of high-end bearings are basically monopolized by bearing manufacturers in Western countries such as Timken, NSK, SKF, FAG, etc. my country’s aviation engine manufacturing technology is backward, and the production capacity and research level of domestic bearing manufacturers are simply unable to provide high-end bearings suitable for advanced aviation engines in the short term.

 

Bearings have become the “Mount Everest” that is difficult to climb in the research and development of my country’s aviation engines, greatly restricting the development of my country’s high-performance aviation engines.

 

5 Powder Turbine Disc Manufacturing Technology

 

The turbine disc of an aviation engine is subjected to the superposition of high temperature and high stress, with harsh working conditions, complex preparation process and high technical difficulty, which has become one of the difficulties in the development of my country’s engines.

 

Based on the advantages of powder high-temperature alloys such as excellent comprehensive mechanical properties and good hot and cold process performance, powder turbine discs are widely used in foreign high-performance aviation engines.

 

The manufacturing of powder turbine discs includes a series of key manufacturing technologies such as material research, master alloy smelting, powder preparation and processing, hot isostatic pressing, isothermal forging, heat treatment, and high-precision detection and evaluation. It carries a series of key manufacturing technologies that are indispensable for advanced aircraft engine manufacturing.

 

The trend of foreign powder turbine disc research is to develop from high-strength turbine discs to damage-resistant turbine discs in terms of turbine disc performance, and the powder making process is developed towards ultra-pure fine powder. While adopting hot isostatic pressing molding process, the molding process also develops extrusion molding process and isothermal forging molding process.

 

In China, the Beijing Institute of Aeronautical Materials has developed a variety of aircraft engine powder turbine discs, solving the key manufacturing technology problems of advanced aircraft engine powder turbine discs, but the engineering manufacturing problem of powder turbine discs has not been completely solved.

 

6 Composite Material Manufacturing Technology

 

Composite material technology has been widely used in high-performance aircraft engines. In order to meet the needs of developing LEAP engines, Snecma used three-dimensional resin transfer molding (RTM) technology to process and manufacture composite fan cases and composite fan blades. The LEAP engine parts manufactured by RTM technology are not only high in strength, but also have a mass of only half that of titanium alloy parts with the same structure.

 

In the process of developing the F119 engine, Pratt & Whitney developed continuous SiC fiber reinforced titanium-based composite wide-chord fan blades. This type of composite blade has high stiffness, light weight, and impact resistance, and is called the third-generation wide-chord fan blade.

 

The third-stage fan rotor of the F119 turbofan engine is all made of this material. In China, composite material manufacturing technology is also used in the manufacturing of aircraft engine parts. Melt-generated TiB2 particle-reinforced aluminum-based composite fan blades have made great progress, but the high-efficiency processing, surface strengthening, fatigue resistance and foreign object damage prevention technology of TiB2 particle-reinforced aluminum-based composite fan blades are the key and difficulty in realizing the engineering application research of fan blades of this material.

 

 

Aero Engine Manufacturing Hot Technologies

1Recrystallization Suppression Technology

 

The excellent properties of single crystal superalloys mainly come from the elimination of grain boundaries by single crystal blades, while the occurrence of recrystallization will significantly reduce the high temperature resistance of the original single crystal alloys. After single crystal blades are cast and formed, subsequent processing such as air film hole processing, tenon grinding, edge plate side milling, blade tip casting process hole welding, heat treatment, and assembly must be performed. During engine operation, the blades are subjected to high-speed rotation. The impact of hot and cold airflow, high temperature, huge load, severe vibration, etc. may cause recrystallization, and many turbine blade failures have occurred.

 

Therefore, in recent years, domestic and foreign research has used related methods such as pre-recovery heat treatment, carburizing, coating, and removal of surface deformation layers to inhibit recrystallization and add boundary strengthening elements to repair recrystallization.

 

2  3D Printing Technology

 

3D printing, also known as additive manufacturing, integrates multiple technologies such as CAD, CAM, powder metallurgy, and laser processing. Using 3D printing technology, we can turn the “brain” thinking into a three-dimensional entity and print the part image on the computer into a “real” part. 3D printing technology has brought about “revolutionary” changes in manufacturing technology and processing concepts.

 

Monash University in Australia has successfully manufactured the world’s first 3D printed jet engine. At the same time, it also cooperates with Boeing, Airbus Group and Safran Group to provide Boeing and others with 3D printed engine prototypes for flight testing. Using 3D printing technology, the manufacturing time of engine parts can be shortened from 3 months to 6 days.

 

 

In China, 3D printing technology is used to repair and reuse the worn parts of the blade tips of the high-pressure compressor rotor blades of turbofan engines. Non-load-bearing parts and stator parts on the engine are manufactured using 3D printing technology, but the mechanical properties of the parts are being actively evaluated. At the same time, extensive research has been carried out on the use of 3D printing technology to manufacture engine rotor parts and load-bearing parts.

 

3 Blade Inlet and Outlet Edge (Front and Rear Edge) Processing Technology

 

The processing quality of the inlet and outlet edges of aircraft engine blades is one of the key factors affecting the aerodynamic performance of aircraft engines. The inlet and outlet edges are also prone to blade defects and sensitive areas for titanium alloy defects. A large number of engine failure events are caused by processing defects in the inlet and outlet edges of blades.

 

Because the inlet and outlet edges of blades are the thinnest parts of the blades and the edge parts of the blades, they have poor rigidity and large processing deformation. The processed blade inlet and outlet edges often have square heads and pointed heads. In the mass production of engine blades, the key process issues of efficient and high-quality blade inlet and outlet edge processing have not been completely solved.

 

4 Adaptive Processing Technology

 

Adaptive processing technology is divided into three forms, namely, adaptive planning of tool path, adaptive control of CNC system and adaptive processing combined with digital detection.

 

Domestic adaptive processing technology has been successfully applied in the processing of precision forging/rolling blades of aircraft engines, repair of damaged blades and linear friction welding of integral blade disks. Although adaptive processing technology has made breakthroughs and developments in theory and practice, the engineering application of adaptive processing technology is still a hot technology in the research of aircraft engine manufacturing.

 

5 Anti-Fatigue Manufacturing Technology

 

Part material fatigue and surface processing defects have become the main causes of failure of aircraft engine parts, and failure failures have become an increasing trend, so “anti-fatigue manufacturing” has become a hot technology in aircraft engine manufacturing. Anti-fatigue manufacturing technology refers to the manufacturing process that improves the fatigue life of parts by changing the organization and stress distribution state of the material during the manufacturing process of the parts without changing the material and cross-sectional size of the parts.

 

Fatigue life is mainly affected by factors such as heat treatment, environmental corrosion, surface quality, stress concentration, and surface stress. The main method of anti-fatigue manufacturing is to reduce stress concentration and improve the surface strength of parts.

 

Reducing stress concentration is to ensure the integrity of the machined surface, and the best way to improve the surface strength of parts is shot peening. In the anti-fatigue manufacturing of aircraft engines, a variety of new shot peening media have been developed in the traditional shot peening process, and new processes such as laser shot peening, ultrasonic shot peening and high-pressure water shot peening have also been widely used.

 

6 Bird Strike Prevention Technology

 

Bird strikes occur frequently, and the resulting damage has become an unavoidable problem in the development of aircraft engines. Extensive research has been carried out both at home and abroad. In July 2015, the US FAA issued a notice on “Requirements for Bird Strike on Transport Aircraft”. The release of this requirement not only puts forward specific requirements and regulations for the future of aircraft engines to prevent bird strikes and foreign objects, but also points out another new research direction for the development of new materials and new structure manufacturing technologies for engines.

 

 

1 Precision Blank Making Technology

 

Precision blank making technology includes precision forging blank making, precision casting blank making and 3D printing technology blank making. It is a technology that provides “food” for modern aircraft engine manufacturing. The blanks of traditional engine parts are “black, large and rough”, and most of the materials in the blanks are removed and consumed in subsequent processing.

 

In the past 30 years, the blade precision forging production line, isothermal forging manufacturing process of blade disk parts blank manufacturing and casing blank die forging manufacturing process have been developed in the blank making of blades, blade disks and casings of aircraft engine fan compressors; the lost wax precision casting method is used in the blank making of turbine blades, integral turbine disks and integral turbine guides; the integral precision casting blank making technology in the blank making of accessory casings and complex shells.

 

With the continuous development and maturity of 3D printing technology, more and more complex aircraft engine structural parts with complex structures, small quantities and urgent supply in the development of aircraft engines are manufactured and processed by 3D printing technology. Figure 4 is a 3D printed integral blade disk blank test piece.

 

 

2 High-Efficiency And High-Quality Welding Technology

 

Component integration is the trend of the development and change of new aircraft engine parts structure, and high-efficiency welding technology is one of the most effective ways to achieve component integration. Welding processes such as diffusion welding, linear friction welding, and electron beam welding are the three key technologies for realizing the integrated manufacturing of aircraft engine components.

 

Diffusion connection welding is also called SPF/DB technology. This technology is a combined process technology of forming and welding, that is, diffusion welding is performed during the superplastic forming process, and superplastic forming is achieved during the diffusion welding. Wide-chord hollow fan blades are manufactured using SPF/DB technology. With the development of wide-chord hollow fan blade technology, the process difficulty and molding time of wide-chord hollow fan blades have greatly increased. The qualification rate and mechanics of hollow fan blades have also increased. Performance, molding efficiency and cost have also improved significantly, and the criteria for qualifying wide-chord hollow fan blades continue to evolve.

 

Linear friction welding is developed based on inertial friction welding technology. It uses the mutual motion between two contacting workpieces to generate heat, and plastic deformation occurs in the area near the contact surface. When the temperature of the friction heating zone reaches a certain requirement, the vibration and relative friction movement stop, and the two workpieces are connected together in a solid state. Linear friction welding technology welds the hollow blades and the disc together, which makes the aeroengine hollow blade integral blisk.

 

Electron beam welding uses the energy of high-power-density electron beams to weld parts of various materials. The welding process is controlled by computers to ensure the controllable range of welding thickness and welding accuracy [4].

 

Electron beam welding combines two or more stages of aeroengine blisks into a tandem blisk, which not only reduces the weight of components by replacing bolt connections, but also improves the rigidity and strength of the rotor assembly. Rolls-Royce used electron beam welding to achieve the welding of medium-pressure compressor and high-pressure compressor rotor components; Pratt & Whitney used electron beam welding to achieve the PW400 booster stage drum, high-pressure compressor stage 2~8 rotor components, 9 ~Welding of the 11th stage rotor assembly, welding of the low pressure turbine stage 2, stage 4 turbine disk and grate ring.

 

Domestically, in the manufacturing of advanced aerospace engines, electron beam welding is used to achieve the welding of grade 5 to 7 high-temperature alloy blisk components for high-pressure compressors.

 

3Tool, Machine Tool And Component Integration Technology

 

Almost all parts on aeroengines require machining, and machining is inseparable from cutting tools and machine tools. Modern aero-engine manufacturing technology has led to rapid development of tool technology and machine tool functions.

 

In recent years, in order to achieve efficient and low-cost manufacturing of aero-engine parts, manufacturing technology research has been carried out at home and abroad to treat workpieces, tools and machine tools as an integral system from the perspectives of kinematics, vibration and mechanics, that is, tool-machine tool-component integration. Comprehensive manufacturing technology has made great progress.

 

As the most direct and main tool for cutting, cutting tools play a vital role in cutting aerospace engine titanium alloys, high-temperature alloys, stainless steel and other processing materials. However, traditional cutting tools can no longer meet the requirements of efficient machining of modern aerospace engines. Cutting tools are developing and continuously improving in the direction of “high precision, high efficiency, high reliability and specialization”. At the same time, special tools for composite material processing and smart tools equipped with tool life prediction are also beginning to be applied.

 

The development of CNC machine tools originated from solving the processing problems of aviation parts. Almost all parts on aerospace engines are manufactured by CNC machine tools. High precision, high speed, composite, intelligence and environmental protection are the inevitable directions for the development of machine tools in the future. Follow the public account: The power of the two machines comes first, free access to massive data on the two machines, and focus on the key technologies of the two machines!

 

4 Development And Application Of Basic Database

 

Simulation technology is widely used in the design, testing and manufacturing of foreign aerospace engines to simulate the characteristics of related parts, components or the entire engine, simulating the deformation of forgings, solidification of castings, connection of welding parts, and the cutting process of materials in parts processing.

 

In order to develop high-performance aero engines, engine research institutes and universities have introduced a large amount of simulation software from abroad. However, the process databases that match them are not sold in our country. Even if some databases are sold, they are sold at a high price, and some are sold at high prices. The price exceeds several times the price of simulation software.

 

my country’s engine design and manufacturing basically rely on experience. Due to the shortage of engine manufacturing talents, the performance of the aero engines developed cannot be compared with that of American and British engines, and the manufacturing price remains high.

 

Therefore, a database of commonly used and special materials cutting, welding, casting, and forging processes for aerospace engines that are closely related to engine manufacturing is developed. Especially in cutting processing, it promotes the combination of tool manufacturing technology research and material cutting technology research, and the development of general tools and special tool development. It is imperative to research on basic manufacturing technologies such as combination.

 

5 Engineering Application Technology For Navigation Marks, National Standards And National Military Standards

 

In recent years, in conjunction with the development of new aircraft, although aviation manufacturing experts and material experts have developed a large number of navigation marks, national standards, and national military standards, making important contributions to the development of new aeroengines, due to the conditions at the time, There are limitations, relevant standards are not coordinated with each other, and some imperfect problems have been found in engineering applications.

 

For example, parts of the same brand of material (imitation materials) that are forged according to current standards have large processing deformations and low manufacturing efficiency, while parts that are forged according to American standards have almost no processing deformation problems in subsequent processing; the hardness index of some stainless steel heat treatments The range is very wide and even exceeds the upper limit of mechanical cutting. Moreover, these are not isolated phenomena. Therefore, standard engineering research closely related to aero-engine manufacturing must be carried out as soon as possible.

 

6 Processing Waste Recycling And ReuseTechnology

 

High-performance aero engines require the use of high-strength, high-temperature-resistant materials. The compressor and turbine components near the combustion chamber use a large number of nickel-based and cobalt-based super heat-resistant alloys. Fans and compressor blades, casings, and disks use a large number of titanium alloys and high-temperature alloys. alloy material.

 

These materials are all precious metals. On the one hand, these metals themselves are very valuable; on the other hand, national reserves and mineral deposits are limited. As time goes by, the sharp contradiction between the demand and inventory of titanium alloys and super heat-resistant alloys in aero-engine manufacturing will become increasingly prominent. Follow the public account: The power of the two machines comes first, free access to massive data on the two machines, and focus on the key technologies of the two machines!

 

During the manufacturing process of engine parts, almost 60% to 90% of the chips are removed from the sprue risers of castings, the “fat heads and big ears” of forging blanks, blisks and integral components, etc. The recovery rate is very low and cannot be reused. The rate is even lower and the waste caused is extremely serious.

 

In foreign countries, the recycling and reuse of processed materials are carried out at the national level, while in China most of these materials are sent to waste recycling stations. According to statistics and analysis, 50% of the cost of aero-engine parts comes from the materials themselves.

 

How to system recycle. How to remove H, O and other impurity elements in recycled materials is a difficult technical and hot issue in reusing recycled materials.

 

 

Conclusion

 

In recent years, in order to meet the needs of national security and national economic development, various types of early warning aircraft, fighter jets, helicopters, large passenger and transport aircraft have been flying in the blue sky, but most of them still lack a strong “Chinese heart”. The ARJ21 passenger aircraft made in China is equipped with the CF34-10A engine of the United States, and the C919 large passenger aircraft made in China is equipped with the LEAP-X1C engine developed by the United States and France. We must turn this page as soon as possible.

 

It is believed that with the comprehensive layout of Made in China 2025 and the development of major aviation engine projects, through the unremitting efforts of aviation engine people, the key technologies, basic technologies and hot technologies of aviation engine manufacturing will be gradually solved, and the goal of installing a healthy and strong “Chinese heart” on Chinese aircraft will be realized soon.