Current status and development trend of precision thermal processing technology
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In the past decade, the United States has placed great emphasis on the development of precision thermal processing and performance-enhancing integration technologies. For example, precision thermoforming of aluminum-lithium alloy powder parts can increase the specific stiffness of parts by 30%; silicon carbide/aluminum composite materials can increase the specific stiffness of parts by 30%-75%; single-crystal blade casting can increase turbine temperature by 55°C. 10% fuel saving; rapid solidification powder laminated turbine blades can increase engine turbine temperature by 220 ° C, fuel consumption by 8.4%, aircraft takeoff quality by 7.4%, and engine thrust-to-weight ratio by 30% to 50%. The development of precision thermal processing technology, and the integration of research on improving the performance of parts and components, in line with the requirements of China's national defense science and technology development on the key basic processing technology research institute.
First, precision casting
The precision casting forming process not only shortens the development cycle of new weapons, reduces costs, but also improves the flexibility and reliability of weapons. For example, after the cabin of the cruise missile produced by Boeing Company of the United States adopts the aluminum alloy precision casting process, the cost of the projectile is reduced by 30%, the man-hour required for each missile is reduced from 8,000 hours to 5,500 hours, and the reliability is improved and the weight is reduced.
The United States Oak Ridge National Laboratory, the American Precision Casting Company and the NASA Lewis Research Center have conducted extensive research on precision casting of A1 intermetallic compounds and special alloys such as Ti and Ni. They use a one-shot forming process to process turbojets and turbofan guides, reducing machining time by 40% and cost by 30%. The precision casting process of China's military industrial system is quite different from that of foreign countries. For example, the missile cabin is mainly made of low and differential pressure casting. Ordinary clay sand casting production section, low dimensional accuracy, poor surface quality, internal defects, secondary oxidation of alloy liquid, mechanical properties are not high, the scrap rate is as high as 20% to 30%, currently only can be cast in China. A section below 4m. In addition, mechanical processing methods such as missile tails and some parts of aircraft are still used, which not only has a long production cycle, high cost, but also poor reliability. In the special alloy precision casting process, there is also a big gap, such as the single-piece hollow no-blade blade precision casting process, which has been applied to military production in foreign countries, and the country is still in the research stage. The research on the precision casting process of the A1 intermetallic compound has not yet begun.
In summary, compared with foreign countries, China is about 10-15 years behind in precision casting technology. In order to shorten the development and production cycle of new weapons, reduce costs and improve reliability, it is necessary to strengthen the research of precision casting technology.
Second, precision plastic forming
Precision plastic processing technology is highly valued in industrialized countries, and a large amount of funds are invested to give priority to development. In the 1970s, the US Air Force hosted the "Forging Process Modernization Program", which aims to modernize the important process of forging and use CAD/CAM more to reduce the manufacturing cycle of new forgings by 75%. In 1992, the US Department of Defense proposed the "Military Key Technology List", which includes isostatic forming technology, numerical control computer controlled spinning, plastic deformation and shear forming machinery, superplastic forming/diffusion joining process, hydraulic extension forming process, etc. Precision plastic forming process. In addition, in recent years, foreign countries have also developed "forging and blade precision forging processes for large die forgings", "rapid solidification powder lamination process" and "strong spinning forming process for large and complex structural parts" for aerospace products. “Superplastic forming process for difficult-to-deform materialsâ€, “Forming process for advanced materials (such as metal matrix composites, ceramic matrix composites, etc.)â€. Recently, with the penetration of computer and automation technology into the hot forming process, sheet forming flexible manufacturing systems have also begun to emerge.
(1) Superplastic forming American Hughes Company and BAE Company rank among the top in the world in superplastic forming technology. At present, the alloy superplastic forming process has been widely used in the manufacture of missile casings, propellant tanks, fairings, spherical cylinders, corrugated plates and engine components. Superplastic forming processes for aluminum alloys, magnesium alloys, nickel-based superalloys, and metal matrix composites are also being studied. China's superplastic forming technology has been applied in the aerospace and machinery industries, such as satellite components, missiles and rocket gas cylinders in the aerospace industry, and the superplastic forming method is used to manufacture the Qin alloy recovery tank of reconnaissance satellites. At the same time, the superplastic forming process of zinc, copper, aluminum and alloy is basically mastered, and the minimum forming thickness is up to 0.3 mm, and the shape is also complicated. However, the problem of uniformity of wall thickness has yet to be resolved.
(2) Strong spinning in the United States using powerful spinning technology. Has been able to produce a diameter of 3.9m, radial dimensional accuracy of 0.05mm, surface roughness RaO. Missile housing with 16-0.32 μm and wall thickness difference <0.03 mm. Almost all kinds of metals can be spin-formed, and the process is stable, and the equipment has been enlarged, versatile and automated. Advanced spinning processes and equipment such as offset spinning and CNC have also been widely used.
There are hundreds of kinds in China, and millions of parts are made by spinning process, including body, tail pipe, head, combustion chamber, casing, nozzle and so on. Various external spinning processes have been developed, including low temperature and high temperature spinning technology and equipment, which can rotate the head piece with a maximum diameter of 5m, and the maximum rotary table is 60 tons. The aerospace system has produced a large solid-state high-strength steel head and aluminum alloy head with a strong spinning process, with a diameter of 2.5 m; liquid rocket silver alloy tube. The diameter of the outlet is 0.28m; the aluminum alloy shell of the tactical missile has a diameter of 0.46m; the alloy hemisphere of the spherical container of the engine has a diameter of 0.53m and a reduction ratio of 50% to 75%. The gap between China and abroad is mainly manifested in the fact that China can only spin cylindrical parts, cones and simple curved shapes. Most of the large-sized shells still use the coil welding process, and there are often residual stresses in the components. The heat affected zone is also prone to delayed cracking; the large-scale spinning parts have poor dimensional accuracy, which is very difficult for subsequent assembly welding; although the internal rotation process with shallow ribs and cylindrical parts has achieved some results, the diameter of the rotating cylinder Small, the ribs are very shallow; the spinning equipment is mostly old, the wrong pitch spinning, CNC spinning and recording spinning are just starting.
(III) New technology and new technology for precision forming of thin-plate precision-formed thin-plate complex components have been widely used in Russia, the United States and other countries. The discharge forming equipment of Russia, the United States and other countries has been serialized, and the maximum energy of the equipment is 500KJ. Russia has been able to produce dozens of missile parts including A1-Li alloy hard-to-deform materials, with a maximum size of 1200mm × 1000mm × 6mm (diameter × height × thickness). At present, polyurethane soft mold forming technology has become an important forming method in the aerospace industry. The Russian TY-154 aircraft factory has used this technology to produce more than 10,000 parts. In the United States, France and other countries, CNC pull-shaped skins and siding have been widely used. The rolling process of special-shaped cross-section frame parts has been widely used. Large-scale launch vehicles generally use integral aluminum alloy ring forgings.
In China, traditional methods are also used in the formation of complex members of thin plates. Electromagnetic forming has just been used in production, and equipment energy is low, coil technology has not yet passed; electro-hydraulic forming is still blank, polyurethane soft-mold forming technology has only a few simple applications, the technology is still immature; CNC skin-drawing and engine are strict The application of space-oriented catheters is still blank.
(4) Precision Molding and Forming Foreign countries have widely used precision molding technology to manufacture weapons. Alcoa Corporation uses isothermal forming to manufacture F-14 fighter frame alloy alloy reinforcing plate and support base. The former has a projected area of ​​10320mm2, the forging weight is 0.32Kg, and the minimum wall thickness of the rib is 3.17mm. The latter has a projected area of ​​13545 mm2, a forging weight of O.82 kg and a minimum thickness of 2.67 mm. The US Pratt & Whitney Company used the isothermal forging process to produce the turbine disk of the F100 engine, which was reduced from 112.5kg to 56.7kg. Commonly used precision molding techniques, such as closed forging, precision forming using splitting principle, and isothermal forming, have been used in military production abroad. In China, the first two technologies have just started, and isothermal forming has been applied. At present, the precision molding technology is still less applied in China, and the precision is also poor. The foreign precision is ±0.05-0.10mm, and the country is ±0.1-0.25mm.
Third, special heat treatment
The special heat treatment process is one of the key manufacturing technologies of the defense industry system. In order to accelerate the development of its space shuttle, the United States has formed a consortium of five companies to jointly develop and heat-treat five new materials, namely high-temperature Ti-Al compounds, C/C and ceramic matrix composites, and high creep strength materials. And high thermal conductivity materials. The United States has a special craft. The treated 8089 alloy can be used at temperatures up to 400 ° C. The toughening treatment of intermetallic compounds can significantly improve toughness, and is more suitable for use at high temperatures. Ti3A1 can be used at 816 ° C and TiAl can be used at 1083 ° C; it is an ideal material for space shuttles and aerospace engines. The United States has used shape memory alloys for satellite self-expanding antennas and pipe joints, and has made great progress in the study of missile self-propelled tails. The PSII surface thermal modification technology, led by the University of Wisconsin, has been used in aerospace engines and satellite shaft parts and bearings, and significant progress has been made. President Clinton has personally inspected the process technology.
Vacuum and atmosphere heat treatment are widely used in aerospace structural parts treatment, such as special carburizing beam, no oxidation, small deformation of workpiece and wide application range, such as carburizing or nitriding on the surface of gear structural parts, missiles and spacecraft. De-stressing, strengthening or toughening treatment of alloys or steels. Typical structures such as instrument parts, transmission structures, fuel tanks, engine casings, etc.; more than 50% of US heat treatment furnaces are vacuum heat treatment furnaces. Complete specifications, Jackie Chan supporting. The fourth generation of the latest gas quenching furnace - double chamber high pressure vacuum gas quenching furnace has also begun to apply. In addition, computerized control has been widely adopted in vacuum heat treatment furnaces. At present, vacuum chemical heat treatment and vacuum gas quenching heat treatment have been developed, including high pressure vacuum gas quenching, high flow rate vacuum gas quenching and high pressure high flow rate vacuum gas quenching technology.
Laser heat treatment technology has been widely used in aerospace, aerospace, electronics, instrumentation and other fields, such as various complex surface parts, micro-components, parts requiring localized processing components, microelectronic devices, large-scale integrated circuit production and repair, precision optics. Components, precision measuring components, etc. Among them, laser quenching is the earliest and most widely used laser processing technology, which can process materials such as alloy, aluminum alloy, alloy steel and carbon steel. For example, the blocking cam of the ignition zone of the MKlO guided rocket launching system uses AISl4340 steel and replaces the original nitriding treatment with 1.2KW laser surface treatment. The highest hardness is increased from 55Rc to 62Rc, and the hardened layer depth is increased from 0.01-0.02in. 0.015—0.030in, and the processing guide of each group of 4 cams is shortened from the original 60 days to 1 hour. The hardness of the surface of the alloy parts can be increased by 75% to 125% after laser quenching. At present, the research level has reached 5% to 20% higher than ordinary quenching by laser surface treatment. The laser coating is firmly combined, the melting layer is only 0.05-0.13mm, laser alloying and amorphous treatment, and the melting layer is only 1-10μm. At present, the main research units in the world include IBM in the United States, Battle Research Institute, Naval Research Laboratory, Laser Application Company, etc.; Rawls-Royce Company of the United Kingdom, Imperial University of the United Kingdom, etc.; Center, Murata Company, etc. Domestic research has also been carried out in this field and significant results have been achieved. However, due to the late start and insufficient investment, there is still a certain gap compared with foreign countries. Therefore, during the "Ninth Five-Year Plan" period, efforts should be made to carry out research to further narrow the gap with foreign countries.
4. Special welding technology <br> Due to the special working environment and requirements of aerospace products, it is necessary to continuously adopt some new structural materials, special structural forms and connection technologies, which requires new welding processes and equipment to meet the requirements of weapon systems. . The facts show that it is impossible to make any spacecraft without welding technology. Therefore, the welding technology level of the countries in the aerospace industry is the highest in the world, and the speed of the stock is also the fastest.
Each of the two aerospace industry developed countries in the United States and Russia is always accompanied by the development of a series of special welding technologies to ensure the manufacturing needs of new models. For example, in the United States, the Saturn V carrier rocket was developed. When Russia developed the energy carrier rocket, the diameter of the aluminum alloy tank reached 10m and 8m respectively, and the wall thickness reached 25mm and 42mm. Conventional welding technology could not adapt to the manufacture of this new model. Need, the United States and Russia have developed a special welding technology suitable for vertical assembly and welding. The United States has developed VPPA (Variable Polar Plasma Arc) welding processes and equipment to complete the manufacture of large aluminum alloy tanks. Russia has developed a partial vacuum electric beam welding process and equipment, and completed the manufacture of the energy-sized large aluminum alloy tank. The research scope of special welding technology is very broad. The following is a brief introduction to the development status of domestic and foreign countries in several directional research fields:
(I) Automated Intelligent Welding Technology Modern aerospace products have extremely high requirements in terms of manufacturing precision and quality assurance (quality stability and reliability). It is urgent to adopt an automated intelligent welding technology that can completely replace manual operation. For example, the US Marshall Space Flight Center is organizing some of NASA's universities and industrial departments to develop automated intelligent welding systems that meet the needs of manufacturing large aluminum alloy tanks. At the end of 1993, the system was nearing completion. It is said to consist of a variety of quality sensors, mathematical models of the welding process and computer-controlled welding devices, which are estimated to be operational. Although China has made some achievements in the welding automation of medium-sized aluminum alloy tanks and has already used them for production, there is still a big gap in terms of intelligence. I hope that some hardware and software will be introduced from abroad during the "Ninth Five-Year Plan" period. Some key technologies and software will be developed by our own research and development guidelines to overcome this "automated intelligent welding technology" to meet the needs of China's new model aerospace product manufacturing technology. During the "Ninth Five-Year Plan" period, it approached or caught up with the level of advanced countries.
(II) Welding of new materials and dissimilar materials Many components of aerospace products require almost no quality and performance as much as possible, so many new structural materials (ceramics, composites, intermetallic compounds, amorphous) are used. Materials, oriented crystalline materials, refractory metal materials, functional materials, etc.), which brings difficulties to the connection of new materials or dissimilar materials. The developed countries of the aerospace industry have carried out a lot of research work on the requirements of the connection of these new materials and different materials. According to different material combinations, the required joints are obtained by solid-state connection or fusion connection to meet the working requirements of the components. For example, Russia has successfully manufactured a high-pressure combustion-supported sandwich structure liquid engine thrust chamber welded by a combination of copper, stainless steel and different metal materials. The process is novel, advanced and reasonable, and meets the requirements of structural design. The US and Russian space departments used special pre-treatment, followed by brazing or diffusion welding, and successfully welded B/A1 composite pipe and aluminum alloy pipe or titanium alloy pipe, successfully manufacturing the bearing truss in the spacecraft. Moreover, the welding technology of metal and ceramics has been successfully solved. There are many methods for welding, but the ideal method is to use Ag-Cu-Ti alloy as the active solder and braze with the strain relief transition material.
China's 703, Harbin Institute of Technology, 621 and other units have carried out research on the welding technology of new materials and dissimilar materials, and have achieved some results, but there is still a big gap compared with advanced countries. The main reason is that our basic research and applied basic research in this area are too weak, the means are too backward, and the manpower and material resources invested are too small.
(III) Micro-connection technology The control circuit of the spacecraft and the high reliability, high density and miniaturization of the payload are the long-term goals of the aerospace industry. Solving these problems can not only greatly reduce the spacecraft launch cost, but also greatly improve the reliability and operating frequency of the control system, which has an important impact on extending the life of the satellite. Advanced countries such as the United States and Russia have adopted a large number of advanced electronic device assembly technologies such as surface assembly technology, micro-assembly technology and multi-chip assembly in the spacecraft control system, so that the control system and satellite have achieved the goal of miniaturization and light weight. Due to the backwardness of micro-connection technology in China, the control system of spacecraft still mainly adopts jack assembly, which is difficult to achieve sufficient miniaturization and light weight. The State Key Laboratory of Welding of Harbin Institute of Technology has the earliest established micro-connection research laboratory in China. It has carried out many years of research work on surface-assembled micro-connection technology. Now it is related to the Ministry of Industry, 504 Department of Aerospace and Shanghai Space Agency. Cooperation, combined with the needs of spacecraft to carry out research on micro-joining technology.
(IV) Advanced Melt Welding Process The manufacture of aluminum alloy large fuel tanks for large thrust launch vehicles and spacecraft or aluminum alloy pressure shells for space shuttles and spacecrafts is mainly based on fusion welding technology. A need is made for the manufacture of large fuel tanks or pressure shells of different constructions and sizes. Different welding processes and equipment have been developed abroad, and the manufacturing tasks of aerospace products have been successfully completed.
The advanced fusion welding technology developed by the United States and Russia mainly includes: narrow gap helium gas protection melting electrode welding process, multi-layer welding, welding thickness is not limited, Russia has successfully welded aluminum alloy tanks with thickness of 40mm and 80mm; DC is connected to helium gas shielded tungsten argon arc welding. Russia successfully completed the production task of 3-8mm thick workpiece by single pass welding process; partial vacuum electron beam welding technology, Russia has been successfully used for aluminum alloy tank with thickness of 42mm Welding; flash butt welding technology. Russia has been successfully used to produce large cross-section (50-80 × 103mm2) aluminum alloy ring frame or longitudinal joint welding; variable polarity plasma arc perforation welding. The United States has successfully developed and used to weld large aluminum alloy containers with a thickness of 16mm, which is an ideal aluminum alloy welding process without internal defects. In the domestic research on the new welding process, almost all of them are in a blank or just starting stage, and research work needs to be carried out as soon as possible.
In addition, advanced automatic welding processes have been developed for the welding of various stainless steel, titanium alloy and aluminum alloy conduits in spacecraft, and a leak-proof joint inspection method has been developed to ensure the safe operation of the conduit system. China is still in the situation of manual welding in the field of duct welding. The quality inspection methods after welding are also relatively backward.
Research work is urgently needed to change this seriously backward situation. Both the United States and Russia have successfully applied the CO2 laser welding technology to the welding of the alloy skin and the casting skeleton in the missile air rudder. The weld quality and the deformation reduction have achieved ideal results. My country is basically in a blank or just starting stage in this regard. The State Key Laboratory of Welding of Harbin Institute of Technology has introduced a CO2 laser processing system with a power of 2KW, and is carrying out research work required in conjunction with the aerospace industry.