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1. Aeroengine materials and technical characteristics
Aeroengines work under extreme conditions of high temperature, high pressure, and high rotational speed. They also require low weight, low fuel consumption, high reliability, long life, and reusability. They are high-end products that are interdisciplinary. It is characterized by the accumulation of core technologies. Without core technology, there is no modern advanced engine. Modern advanced aero-engines have higher performance requirements for unit thrust, thrust-to-weight ratio, supersonic cruise, thrust vectoring, stealth performance, high reliability, long life, and good maintainability, and are more demanding on materials and manufacturing technology. Bring from: the application of common alloys to new high-temperature, light-weight, high-strength alloys; applications from metallic materials to a large number of non-metallic materials, composite materials; transformations from machining to special machining; from material manufacturing to precision forming and increasing Material manufacturing; mainly from the assurance of geometric shape to surface integrity control; from test verification to simulation verification; from single process research to multi-process coupling law research; from digitization, automation, information to intelligent manufacturing Wait.
Advanced engine new materials and complex structures make parts processing more difficult, and some even traditional mechanical machining can not be realized at all. Special processing technology has become an irreplaceable technology in some fields, and it has become more and more widely used, making up for traditional machinery. Insufficient processing. At present, the traditional EDM, electrochemical machining, laser processing, electron beam and ion beam processing and other special processing technologies have been used in a large number of aeroengine manufacturing applications. However, with the advent of advanced engine new materials and new structures, special processing technologies New developments and applications have also been obtained. Multi-axis electric discharge machining technology for closed-type integral blades, precision electrolytic machining technology for integral blades, ultra-fast laser processing technology for ceramic-based composite materials, laser shock-strengthening technology, and high-pressure water jet hardening technology, etc. The development of new structural components, as well as the improvement of surface integrity and reliability requirements, have played an increasingly important role.
2. Application of special processing technology on advanced engines
(1) EDM technology is the most widely used special processing technology. It is widely used in aero-engine manufacturing, such as WEDM, EDM, EDM, EDM and EDM surfaces. Strengthening and so on.
In recent years, with the advancement of advanced engine performance, the application of traditional EDM technology has been limited. For example, new engine turbine blades use single-crystal blades, and EDM drilling technology has remelted layers, micro cracks, and heat. Affected areas and other defects, but was forbidden for the single crystal blade film hole processing. Fig. 1 shows the metallographic photographs of the EDM of the turbine blade film holes. The thickness of the remelted layer is generally 0.01 to 0.04mm.
At the same time, however, the emergence of new structural components such as the advanced engine's overall blade disk has also promoted the development and application of EDM technology. For example, the overall bladed disk structure has developed a high-efficiency CNC discharge mill because of its high processing cost and long cycle time. The technology, such as the crown-closed integral blade disk, is difficult to achieve due to its structure, and the development of five-axis linkage EDM machining technology to solve this problem, the process method is five-axis linkage EDM, and then With the aid of abrasive flow processing to remove the remelted layer of its processing surface, it meets the requirements for use. Figure 2 shows the electrodes and test pieces of the crowned integral blade disk machined using a five-axis EDM machine. Figure 3 shows an integrated crowned blade disk machined with abrasive grains.
(2) Electrolytic machining has its advantages in the processing of special processing objects (such as difficult-to-machine materials or parts with complex shapes, small dimensions, and extremely low rigidity), especially in aero engine blades, machine borings and other complex surface parts The manufacturing field has been widely used to greatly increase production efficiency and reduce manufacturing costs.
Due to the performance design requirements of advanced aero-engines, compressor blades are generally made of advanced nickel-based superalloys or titanium alloys, titanium-aluminum alloys, and other new materials. The three-dimensional design of the special leaf shapes such as swaying is used to make the compressors difficult and difficult to process. Cutting force influences deformation and requires high precision. Traditional machining and electrolytic machining are difficult to meet the processing requirements of this high-precision and complex blade type. Precision Electrochemical Machining Technology (PECM) is produced to meet this special processing requirement. It has its unique advantages in thin profile and small radius blade shape processing. The processing precision reaches 0.03mm and it meets advanced aero engines. Demand.
Precision electrolytic machining is also one of the preferred methods in a variety of manufacturing methods of the overall blade disk, which can realize a complete process from the entire blade blank to the final blade profile forming. Generally adopts two steps of initial forming and final forming. The initial forming adopts nesting processing method to remove most of the materials, and the final forming adopts profiling processing method. The final reachable blade profile accuracy is ≤ 0.06mm, and the surface roughness of high-temperature alloy materials. The value of Ra≤0.2μm achieves precision manufacturing of the entire leaf disc without allowance, thereby replacing the numerically controlled milling and manual polishing, which can increase the production efficiency several times and reduce the manufacturing cost by more than 50%.
(3) Electro-hydraulic beam processing hole depth ratio of 150/1, hole diameter range of 0.13 to 1.5 mm, hole machining accuracy of ± 0.025mm, surface roughness value of Ra = 1.6μm, the hole entrance naturally forms a small R round No sharp edges. Electro-hydraulic beam processing hole shown in Figure 4.
Electro-hydraulic beam processing turbine blade surface has good surface integrity, no remelting layer, micro-cracks and heat affected zone, processing of single crystal alloys does not have the risk of recrystallization, so it has become the advanced engine single crystal blade film cooling hole processing The preferred process.
(4) The laser processing technology was first applied to the engine combustion chamber, the cutting of the external casing of the afterburner, and the manufacture of holes in the turbine blades. However, due to the limitations of machining accuracy and repeatability due to traditional laser processing, the application of the laser is limited. not much. However, for some special parts, the use of laser drilling, can achieve better results, such as the use of YAG laser rotary cutting processing, for the turbo-turbine turbine blade film hole processing, and then gradually replaced by EDM high-speed drilling. In addition, it is also very advantageous for processing high-hardness, non-conductor material micro-holes and a large number of group-hole parts, such as the engine diffuser heat shield, the inner and outer wall of the flame tube, and other structural parts, and it is currently applied to the engine. More extensive.
With the development of laser technology, new technologies such as laser welding, laser additive manufacturing, laser shock reinforcement, water-guided laser processing, and laser cleaning have been continuously developed and applied, providing more technological options for advanced engine manufacturing. Such as laser shock-strengthening technology, with deep metal surface strengthening layer, surface residual compressive stress, good accessibility and high efficiency, significantly improve the material's resistance to fatigue, wear and stress corrosion, resulting in a residual compressive stress depth of up to 1 ～2mm is 3～5 times of ultrasonic peening and 5～10 times of conventional peening. It has the advantages of improving fatigue resistance, prolonging fatigue life, inhibiting the formation and expansion of cracks, etc., thus becoming the overall blade of advanced aero engine. Key technology of blade ring surface strengthening.
(5) High pressure water jet processing technology has been widely used in engine parts cutting, drilling and cleaning. In addition, exploratory studies have also been carried out on the cutting of new composite materials and on the processing of special structural parts of the leaf disk, and a water stripping technique for removing engine blade coatings has been developed.
The water jet enhancement technology is the use of high-pressure water jets to impact the workpiece impact force to achieve the strengthening of the metal material surface. On the basis of improving the fatigue properties of the material, a good surface quality of the material can be obtained. Water jet enhancement requirements have been explicitly proposed on components such as advanced engine turbine disks.
3. Outlook of special processing technology
Special processing technology plays an irreplaceable role in the manufacture of advanced aero engines. It can be said that “no advanced engines can be manufactured without special processingâ€. 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 at universities and research institutes and enterprises at home and abroad. With the continuous emergence of advanced engine new materials and new structures, the original special processing technology has also expanded new applications. For example, nickel-aluminum-based new materials have very poor machinability, and electrolytic machining is very suitable for machining and can meet the accuracy requirements. Another example is the use of traditional photographic electrolytic processing methods for new porous laminate structures, and the emergence of ultra-fast laser cold processing technology has brought new solutions to the single crystal blade air film hole processing.
Special processing technology has been widely used in the development of various difficult-to-machine materials and special structural parts such as advanced engine casings, integral blade disks, 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 placed on the development of special processing and manufacturing technologies. Special processing technologies are also being developed in the direction of precision, automation, and intelligence.
The high performance of advanced aero-engines requires the design of a large number of new materials such as integrated structures, lightweight structures, advanced cooling structures, and composite materials, powder metallurgy, and intermetallic compounds that require special machining. This paper studies the characteristics of special processing technologies such as EDM, electrolysis, laser, ultrasonic, and water jets, and their new applications in advanced engines. It explains the advantages of special processing technologies and the special role that has been highlighted in the development of advanced engines.