Special processing technology indispensable in aero engine manufacturing

Abstract: The high performance of advanced aero-engines requires the design to adopt a large number of overall structures, lightweight structures, advanced cooling structures, and new materials such as composite materials, powder metallurgy, and intermetallic compounds, and these components need to be formed by special processing. This paper studies the characteristics of special processing technologies such as electric spark, electrolysis, laser, ultrasonic and water jet and their new applications in advanced engines, and explains the advantages of special processing technologies and their special effects in the development of advanced engines.

1. Aeroengine materials and technical characteristics

　　The aero engine works under extreme conditions of high temperature, high pressure and high speed. At the same time, it requires light weight, low fuel consumption, high reliability, long life, and reusability. It is a high-end product that blends multiple disciplines. Its characteristic is the accumulation of core technologies. Without core technologies, there would be no modern advanced engines. Modern advanced aero-engines have higher performance requirements for unit thrust, thrust-to-weight ratio, supersonic cruise, thrust vectoring function, stealth performance, high reliability, long life, and good maintainability. The requirements for materials and manufacturing technology are more stringent. Brings: from ordinary alloys to the application of new high-temperature resistant, lightweight and high-strength alloys; from metal materials to the application of a large number of non-metallic materials and composite materials; from mechanical processing to special processing; from reduced material manufacturing to precision forming and augmentation Material manufacturing; from ensuring geometric form to surface integrity control; from experimental verification to simulation verification; from single-process research to multi-process coupling law research; from digitization, automation, informatization to intelligent manufacturing Wait.

Advanced engine new materials and complex structures make parts processing more and more difficult, and some even traditional mechanical processing can’t be achieved at all. Special processing technologies have become irreplaceable technologies in some fields, and their applications have become more and more extensive, making up for traditional machinery. Insufficient processing. At present, traditional special processing technologies such as EDM, electrochemical processing, laser processing, electron beam and ion beam processing have been widely used in aviation engine manufacturing. However, with the emergence of advanced engine new materials and new structures, special processing technologies Also got new development and application. The multi-axis EDM technology of the closed blisk, the precision electrochemical machining technology of the blisk, the ultra-fast laser processing technology of ceramic matrix composite materials, the laser shock strengthening technology and the high-pressure water jet strengthening technology, etc., are the new materials for advanced engines. , The development of new structural parts, and the improvement of surface integrity and reliability requirements have played an increasingly important role.

2. Application of special processing technology to advanced engines

(1) EDM technology is the most widely used special processing technology. It is widely used in aviation engine manufacturing, such as wire EDM, EDM forming, EDM grinding, EDM drilling and EDM surface Strengthen and so on.

In recent years, with the improvement of advanced engine performance, the application of traditional EDM technology has been restricted. For example, new engine turbine blades use single crystal blades, while EDM drilling technology has remelted layers, microcracks, and heat. Defects such as the affected zone are prohibited from being used for the processing of air film holes in single crystal blades. Figure 1 shows the metallographic photo of the gas film hole EDM of the turbine blade. The thickness of the remelted layer is generally 0.01～0.04mm.

But at the same time, the emergence of new structural parts such as advanced engine blisks has promoted the development and application of EDM technology. For example, the blisk structure has developed CNC high-efficiency electric discharge milling due to its high processing cost and long cycle. For example, it is difficult to realize the mechanical milling of closed blisks with a crown due to its structure, and the development of five-axis linkage EDM processing technology to solve this problem, the process method is five-axis linkage EDM processing, and then It is supplemented by abrasive flow processing to remove the remelted layer on the processed surface, thereby meeting the requirements of use. Figure 2 shows the electrode and test piece with a crowned blisk processed by a five-axis EDM, and Figure 3 shows the crowned blisk processed by abrasive particle flow.

(2) Electrochemical machining has advantages in the processing of special machining objects (such as difficult-to-machine materials or parts with complex shapes, small dimensions, and extremely low rigidity), especially in complex profile parts such as aero engine blades and casings The manufacturing field is widely used, greatly improving production efficiency and reducing manufacturing costs.

Due to the performance design requirements of advanced aero-engines, the compressor blade materials generally use advanced nickel-based superalloys or titanium alloys and titanium aluminum alloys and other new materials, and use special blade shapes with three-dimensional designs such as bends and sweeps, which are difficult and easy to process. It is deformed due to the influence of cutting force and requires high precision. Traditional mechanical processing and electrochemical processing are difficult to meet the processing requirements of this high-precision and complex airfoil. Precision Electrochemical Machining Technology (PECM) is produced to meet this special processing requirement. It exerts its unique advantages in the processing of thin-shaped and small-radius blades. The processing accuracy reaches 0.03mm, which meets the needs of advanced aero-engines. Demand.

　　Precision electrochemical machining is also one of the preferred methods among the many manufacturing methods of the blisk. It can realize the complete process from the rough blisk to the shape of the final blade profile. Generally, two steps of initial forming and final forming are adopted. The initial forming adopts nesting processing method to remove most of the material, and the final forming adopts profiling processing method, and finally the blade profile contour accuracy is ≤0.06mm, and the surface roughness of the high-temperature alloy material The value of Ra≤0.2μm can realize the precision manufacturing of the whole blisk without margin, thereby replacing the numerical control milling and manual polishing, which can increase the production efficiency by several times and reduce the manufacturing cost by more than 50%.

(3) The depth-to-diameter ratio of the holes processed by the electro-hydraulic beam is 150/1, the hole diameter ranges from 0.13 to 1.5 mm, the hole processing accuracy is ±0.025mm, the surface roughness value is Ra=1.6μm, and the entrance and exit of the hole naturally form a small R rounded corner , No sharp edges. The small holes processed by the electro-hydraulic beam are shown in Figure 4.

Electro-hydraulic beam machining of turbine blades has good surface integrity, no remelting layer, microcracks and heat-affected zones, and there is no risk of recrystallization in processing single crystal alloys. Therefore, it has become the advanced engine single crystal blade gas film cooling hole processing The preferred process.

(4) Laser processing technology was first applied to the cutting of engine combustion chambers, afterburner outer shells, and turbine blade hole making. However, traditional laser processing is limited by processing precision and low repeatability, so it is used in engines. not much. However, for some special parts, laser drilling can achieve better benefits. For example, YAG laser rotary cutting is used for gas film hole processing of turbojet engine turbine blades, which is gradually replaced by high-speed electric spark drilling. In addition, it is also very advantageous to process small holes of high hardness and non-conducting materials and a large number of group hole parts, such as perforation processing of structural parts such as engine diffuser heat shield, inner and outer walls of flame cylinders, which are currently used in engines Wider.

　　 With the development of laser technology, new technologies such as laser welding, laser additive manufacturing, laser shock strengthening, water-guided laser processing and laser cleaning have been continuously developed and applied, providing more technical options for advanced engine manufacturing. For example, laser shock strengthening technology has the advantages of deep metal surface strengthening layer, surface residual compressive stress, good accessibility and high efficiency. It significantly improves the material's fatigue resistance, wear and stress corrosion resistance, and the residual compressive stress depth can reach 1 ～2mm, which is 3 to 5 times that of ultrasonic shot peening and 5 to 10 times that of conventional shot peening. It has the advantages of improving fatigue strength, prolonging fatigue life, inhibiting the formation and expansion of cracks, and so on. Therefore, it has become an advanced aero-engine blisk, The key technology of blade ring blade surface strengthening.

　　 (5) High-pressure water jet processing technology has been widely used in engine parts cutting, drilling and cleaning. In addition, exploratory research has been carried out in the cutting of new composite materials and the processing of special structural parts of the integral blisk, and the development of water stripping technology for removing engine blade coatings.

The 　　 water jet strengthening technology uses the impact force generated by the high-pressure water jet to hit the workpiece to strengthen the surface of the metal material. On the basis of improving the fatigue performance of the material, a good surface quality of the material can be obtained. In advanced engine turbine disks and other parts, the demand for water jet enhancement has been clearly put forward.

3. Prospects of Special Processing Technology

　　Special processing technology has played an irreplaceable role in the manufacture of advanced aero-engines. It can be said that "advanced engines cannot be manufactured without special processing." In addition, there are new special processing technologies such as electrolytic grinding, abrasive flow, ion beam and electron beam, which have been continuously developed and applied in some universities, research institutes and enterprises at home and abroad. With the continuous emergence of new materials and new structures for advanced engines, the original special processing technology has also expanded into new uses. For example, the machinability of nickel-aluminum-based new material blades is very poor, while electrolytic machining is very suitable for processing and can meet the accuracy requirements Another example is the use of traditional photographic electrochemical machining methods for the new porous laminate structure, and the emergence of ultra-fast laser cold machining technology has brought new solutions for the air film hole machining of single crystal blades.

　　Special processing technology has been widely used in the development of various difficult-to-process materials and special structural parts such as advanced engine casings, integral blisks, single crystal blades and composite materials, and has solved the development problems. With the rapid development of advanced engine technology, the requirements for manufacturing technology are endless, and higher requirements are put forward for the development of special processing and manufacturing technology. Special processing technology is also developing in the direction of precision, automation and intelligence.