Current situation and development trend of the hot

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Current situation and development trend of precision hot working technology

Abstract: precision hot working technology is one of the key manufacturing technologies of weapon system, mainly including precision casting, precision plastic forming, special heat treatment and special welding technology. Precision thermal processing technology has the advantages of short production cycle, low cost, good parts performance, high product reliability, and nearly no allowance for blank making. Countries all over the world attach great importance to it because there are considerable bubbles in the samples

key words: precision thermal processing, technology, current situation, development trend

in the past decade, the United States has paid great attention to the development of precision thermal processing and integrated technology to improve performance. For example, precision hot forming of aluminum lithium alloy powder parts can increase the specific stiffness of parts by 30%; Silicon carbide/aluminum composites can increase the specific stiffness of parts by 30% - 75%; Precision casting of single crystal blades can increase turbine temperature by 55 ℃ and save fuel by 10%; The rapidly solidified powder laminated turbine blade can increase the turbine temperature of the engine by 220 ℃, reduce the fuel consumption by 8.4%, reduce the takeoff quality of the aircraft by 7.4%, and increase the thrust weight ratio of the engine by 30% - 50%. The development of precision thermal processing technology and its integration with the research on improving the performance of parts meet the requirements of the development of national defense science and technology for the research of key basic processing technology

I. precision casting

precision casting forming technology can not only shorten the development cycle of new weapons and reduce costs, but also improve the flexibility and reliability of weapons. For example, after the aluminum alloy precision casting process is adopted for the cabin of the cruise missile produced by Boeing, the cost of the missile body is reduced by 30%, and the man hour required for each missile is reduced from 8000 hours to 5500 hours, with improved reliability and reduced weight

American Oak Ridge National Laboratory, American precision casting company and NASA Lewis Research Center have conducted a lot of research on the precision casting of A1 series intermetallic compounds and Ti, Ni based and other special alloys. They use the one-time forming and precision casting process to process the turbojet and turbofan guides, which reduces the machining time by 40% and the cost by 30%. Compared with foreign countries, the precision casting technology of China's military industry system is far behind. For example, the missile cabin mainly adopts low and differential pressure casting method. Ordinary clay sand mold production cabin has low dimensional accuracy, poor surface quality, many internal defects, serious secondary oxidation of alloy liquid, low mechanical properties, and the scrap rate is as high as 20% - 30%. At present, only cabin sections below 1.4m can be cast in China. In addition, some components of missile tail and aircraft are still machined, which not only has long production cycle, high cost, but also poor reliability. There is also a big gap in the precision casting process of special alloys, such as the precision casting process of single product hollow leaves without allowance, which has been applied to military production abroad, but it is still in the research stage in China. As for the precision casting process of A1 intermetallic compounds, the research has not yet started

To sum up, compared with foreign countries, China lags behind about 10-15 years 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

II. Precision plastic forming

precision plastic processing technology is highly valued in industrial developed countries, and a large amount of funds are invested to give priority to development. In the 1970s, the U.S. Air Force presided over the formulation of the "forging process modernization plan", which aims to modernize the important process of forging, use more CAD/CAM, and reduce the manufacturing cycle of new forgings by 75%. In 1992, the U.S. Department of defense put forward the "list of military key technologies", which includes precision plastic forming processes such as isobaric forming process, CNC computer-controlled spinning, plastic deformation and shear forming machinery, superplastic forming/diffusion bonding process, hydraulic extension forming process, etc. In addition, in recent years, foreign countries have also developed "forging of large die forgings and precision forging of blades", "rapid solidification powder lamination process", "powerful spinning process of large complex structural parts", "superplastic forming process of difficult to deform materials", "forming process of advanced materials (such as metal matrix composites, ceramic matrix composites, etc.) with aerospace products as the application objects". Recently, with the penetration of computer and automation technology into hot forming process, sheet metal forming flexible manufacturing system has also begun to emerge

(I) superplastic forming

Hughes, BAE and others in the United States rank in the forefront of the world in superplastic forming technology. At present, Qin alloy superplastic forming process has been widely used to manufacture missile shell, propellant storage tank, fairing, spherical gas cylinder, corrugated plate and engine parts. Superplastic forming processes of aluminum alloys, magnesium alloys, nickel base superalloys, metal matrix composites, etc. 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 cylinders in the aerospace industry, and the superplastic forming method is used to manufacture the Qin alloy recovery capsule of reconnaissance satellite. At the same time, we have basically mastered the superplastic forming process of zinc, copper, aluminum and Qin alloys. The minimum forming thickness can reach 0.3mm, and the shape is also complex. However, the problem of wall thickness uniformity remains to be solved

(II) strong spinning

the United States uses strong spinning technology. It has been able to produce diameter of 3.9m, radial dimension accuracy of 0.05mm, and surface roughness rao.16-0.32 μ m. Missile shell with wall thickness difference less than 0.03mm. Almost all kinds of metals can be formed by spinning, and the process is stable, and the equipment has been large-scale, multipurpose and automation. Staggered spinning, CNC and other advanced spinning processes and equipment have also been widely used

there are hundreds of kinds in China, and millions of parts adopt spinning technology, including shell body, tailpipe, head, combustion chamber, shell, nozzle, etc. Various external spinning processes have been developed, including low-temperature and high-temperature spinning technology and equipment, which can spin head pieces with a maximum diameter of 5m, and the maximum spinning machine is 60 tons. The aerospace system has adopted the powerful spinning process to produce the high-strength steel head and aluminum alloy head of large solid motor, with a diameter of 2.5m; Liquid rocket silver alloy tube. Outlet diameter 0.28M; Tactical missile aluminum alloy shell, diameter 0.46M; The Qin alloy hemispherical body of the engine spherical container has a diameter of 0.53M and a thinning rate of 50% - 75%. The gap between China and foreign countries is mainly manifested in that China can only spin cylindrical parts, conical parts and parts with simple curved surface shape. Most large-size shells still use the coil butt welding process. There are often residual stresses in the components, and it is also easy to produce delayed cracks in the heat affected zone of the weld; The dimensional accuracy of large spinning parts is poor, which causes great difficulties for subsequent assembly and welding; Although some achievements have been made in the internal spinning process with shallow ribs and cylindrical parts, the diameter of the rotatable cylinder is small and the ribs are very shallow; Most spinning equipment are relatively old, and stagger spinning, numerical control spinning and record back spinning are just starting

(III) sheet metal precision forming

the new process and technology of precision forming of sheet metal complex components have been widely used in Russia, the United States and other countries. The discharge forming equipment in 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 deformation materials, with the maximum size of 1200mm × 1000mm × 6mm (diameter × height × Thickness). At present, polyurethane soft die forming technology has become an important forming means in aerospace industry. Russian ty-154 aircraft factory has used this technology to produce more than 10000 parts. In the United States, France and other countries, CNC stretch skin and wall panels have been widely used, and the rolling process of special-shaped cross-section frame parts has been widely used. Integral aluminum alloy ring forgings are widely used in large launch vehicles

traditional processes are still used in the forming of complex components of thin plates in China. Electromagnetic forming is just used in production, and the equipment energy is low, and the coil technology has not passed the test; Electrohydraulic forming is still a blank, polyurethane soft die forming technology has only a few simple applications, and the technology is not mature; The application of NC skin stretching and engine with strict requirements for space direction conduit is still blank

(IV) precision molding

precision molding technology has been widely used abroad to manufacture weapons. Alcoa adopts isothermal forming to manufacture the Qin alloy reinforcing plate and supporting base parts of F-14 fighter frame. The former has a projected area of 10320mm2, the forging weight is 0.32kg, and the minimum wall thickness of the reinforcing rib is 3.17mm. The latter has a projected area of 13545mm2, a forging weight of 0.82kg and a minimum thickness of 2.67mm. Pratt Whitney company of the United States uses isothermal forging process to produce F100 engine turbine disk, and the weight is reduced from 112.5kg of the original ordinary die forgings to 56.7kg. The commonly used precision die forming technologies, such as block forging, precision forming using shunt 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 to a certain extent. At present, precision molding technology is less applied in China, and the accuracy is poor. The accuracy abroad is ± 0.05-0.10mm, and that in China is ± 0.1-0.25mm

III. special heat treatment

special heat treatment process is one of the key manufacturing technologies of the national defense industrial system. In order to accelerate the development of its space shuttle, the United States has formed a consortium of five companies to jointly develop the forming and heat treatment processes for five new materials, namely, high-temperature Ti Al compounds, C/C and ceramic matrix composites, high creep strength materials and high thermal conductivity materials. The service temperature of 8089 alloy treated by special process in the United States can reach 400 ℃. The toughness of intermetallics can be significantly improved after toughening treatment, which is more suitable for use at high temperature. Ti3A1 can be used at 816 ℃ and TiAl can be used at 1083 ℃; It is an ideal material for space shuttle and aeroengine. The United States has used shape memory alloys in satellite self expanding antennas and pipe joints, and great progress has been made in the research of missile self expanding tail. PSII surface thermal modification technology led by the University of Wisconsin in the United States has been used in aero-engine and satellite shaft parts and bearings, and significant progress has been made. President Clinton has personally inspected this process technology

vacuum and atmosphere heat treatment is widely used in the treatment of aerospace structural parts, such as the surface carburization or nitriding of gear structural parts, stress relief, reinforcement or toughening of various alloys or steel parts of missiles and spacecraft, because of its unique advantages of no pollution beam, no oxidation, small workpiece deformation and wide application range. Typical structures such as instrument parts, transmission structure, fuel storage tank, engine shell, etc; More than 50% of heat treatment furnaces in the United States are vacuum heat treatment furnaces. Complete specifications, Chenglong matching. The fourth generation of the latest gas quenching furnace - double chamber high-pressure vacuum gas quenching furnace has also been applied. In addition, computer control has been widely used in vacuum heat treatment furnaces. At present, it has developed into vacuum chemical heat treatment and vacuum gas quenching heat treatment, 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 aviation, aerospace, electronics, instruments and other fields abroad, such as various complex surface parts, micro components, components requiring local strengthening treatment, micro electronic devices, production and repair of large-scale integrated circuits, precision optical components, precision measurement components, etc. Among them, laser quenching is the earliest and most widely used laser processing technology, which can process Qin alloy, aluminum alloy, alloy steel, carbon steel and other materials. For example, the blocking cam in the ignition area of mklo guided rocket launch system adopts aisl4340 steel, and uses 1.2kW laser surface treatment to replace the original nitriding treatment. The maximum hardness is increased from 55rc to 62rc, and the depth of hardened layer is increased from 0.01-0.02in to

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