Current Situation and Development of Aluminum Alloy Forging Technology

On the basis of expounding the important position of aluminum alloy forging production in the national economy, this paper introduces in detail the development, current situation and level of aluminum alloy forging technology in China. The aluminum alloy forging production and technology in China have developed by leaps and bounds, and a complete aluminum alloy forging production system has been formed, which can basically meet the needs of national economy and national defense construction. At the same time, the article also compares with the aluminum alloy forging technology of foreign advanced countries, and finds out our gap. With the implementation of China's large aircraft project and other large key projects, the 800MN vertical die forging hydraulic press is being built, which will promote China to become a big and powerful aluminum alloy forging country in the world. Finally, the specific direction and measures for the future development of aluminum alloy forging production in China are proposed.
key word
aluminium alloy; Forging; forging and pressing; Forging technology; Non ferrous metals
Forging production is one of the main ways to provide machine parts blanks to various industries in the national economy. The advantage of forging production is that it can not only obtain the shape of mechanical parts, but also improve the internal structure of materials and provide excellent mechanical properties. For the important mechanical parts with large force and high mechanical property requirements, most of them are manufactured by forging. Aluminum alloy has a series of advantages, such as low density, high specific strength and stiffness, and has been widely used in various industrial sectors. Aluminum alloy forging parts have become an indispensable material for mechanical parts in various industrial sectors. Especially in the past decade, with the progress of science and technology and the development of national economy, higher and higher requirements for materials have been put forward, forcing aluminum alloy forgings to develop in the direction of large-scale integration, high strength and high toughness, complex and accurate, and greatly promoting the development of large and medium-sized hydraulic presses and forging ring machines
one ▶
Development Status and Level of Aluminum Alloy Forging Production in China
Forging production has a long history in China. More than 3300 years ago, in the early period of Yin Ruins culture, forging has been used in weapons production. However, before the founding of New China, China's forging production was still very backward. After the founding of the People's Republic of China, forging production has developed rapidly. Free forging hydraulic presses below 125MN, 300MN die forging hydraulic presses, die forging hammers below 160kN, friction presses below 16000kN, and hot die forging presses below 8000 kN have been equipped in a series of forging plants. However, up to now, China's aluminum processing enterprises have only 9 large and medium-sized aluminum forging (hydraulic) presses of 300MN, 100MN, 60MN, 50MN and 30MN, 1 100MN multi-directional die pressing hydraulic press and 2 F5m ring rolling machines. The annual production capacity of aluminum forgings is only about 15kt. The maximum projected area of aluminum alloy die forgings is 2.5m2, the maximum length is 7m, the maximum width is 3.5m, the maximum diameter of the forging ring is 5m, and the diameter of the disc is Φ 534mm~ Φ 730mm aluminum alloy strand reel and Φ Automobile wheel rim of about 600mm. The product variety is relatively small, and the proportion of die forgings is relatively low. For example, die forgings in industrial developed countries account for about 80% of all forgings, while in China they only account for about 30%. CAD/CAM/CAE and die forging process simulation have entered the practical stage, while many forging plants in China have just started in this regard. The automation level and process technology level of process equipment are also relatively backward. At present, China's aluminum alloy forging industry has made great progress in terms of technical equipment, mold design and manufacturing, product output and scale, production efficiency and batch production, product quality and efficiency, and has established an aluminum alloy forging system with Chinese characteristics, which can basically meet the needs of China's national economic development. However, there is a certain gap with the advanced level abroad, which cannot meet the growing demand for aluminum alloy forgings in domestic and foreign markets and the pace of lightweight requirements for transportation (such as aircraft, automobiles, high-speed trains, ships, etc.) (replacing steel forgings with aluminum forgings). For this reason, China should concentrate its manpower, material resources and financial resources to improve the level of technological equipment and production process of aluminum alloy forging and pressing production in China as soon as possible, and build several large and medium-sized modern aluminum alloy forging and pressing production lines as soon as possible, so as to narrow the gap with foreign advanced level as soon as possible, and meet the needs of domestic and foreign markets to the greatest extent. Fortunately, with the implementation of China's large aircraft project and other large key projects, 200MN heavy horizontal extruders and 450MN, 800MN vertical die forging hydraulic presses (see the figure below) are being built, which will greatly improve China's forging equipment level and promote China's progress towards a world leading aluminum alloy forging country and power.

two ▶
The main gap between China and the international advanced level
At present, the largest aluminum alloy forging and pressing enterprise with the most advanced equipment and the most complete varieties in China should be the Southwest Aluminum Processing Factory, which has a world-class 300MN die forging hydraulic press, 100MN multi-directional die forging hydraulic press, 60MN forging hydraulic press and complete supporting auxiliary equipment, as well as trimming, straightening, sawing machine processing, die making and testing equipment. It is a factory specializing in providing high-quality aluminum alloy forgings and die forgings for aerospace and other departments. The United States is one of the most developed countries in aluminum alloy forging production and technology in the world at present. The Cleveland Forging Plant under Alcoa is its most representative aluminum alloy forging enterprise, with 30, 40, 8015030500MN and other forging hydraulic presses; 7~10, 13, 16, 20, 25~30, 40~60MN mechanical presses and 6, 8, 18, 36, 110, 150 MN forging hammers, as well as complete auxiliary equipment and public facilities. The following is a comparative analysis between China's aluminum forging technology and the international advanced level, taking these two plants as representatives.
Gap 1
Scale, capacity, variety and quality
On the whole, Cleveland Forging Factory is much larger than SWA, with more varieties, larger specifications, wider uses, higher production efficiency and product quality. Therefore, the economic benefits will be better.
Gap 2
Production technology
Forging blank
The blank required for die forging is prepared by free forging. The main factors affecting the free forging technology are the installation level of the forging machine and the operation technology of the forging workers. Alcoa's forging and blank making are mainly completed on the 30MN forging hydraulic press. This equipment is small and flexible. There is a main die seat and a number of auxiliary die seats on the workbench, which are suitable for forging, rotating and rolling blanks; There is a forging operator. Because the shape of forging billet is often complex, which requires repeated upsetting, flattening, and stretching, and the billet moves and rolls frequently on the workbench, this forging equipment is very suitable, and has the advantages of convenient operation, safety, labor saving, high labor efficiency, and good forging billet quality. The forging and blank making of SWA processing plant is completed on the 60MN forging hydraulic press. The equipment has large capacity (in fact, the forging pressure of each pass is very small) and is inflexible. Although there is a rail forging car, since there is only one main die seat on the working table of the hydraulic press, it is still inconvenient to move and roll the blank, which requires the cooperation of several forging workers. This is not only laborious and time-consuming, but also unsafe, with low labor efficiency and rough forging quality.
Die forging
Compared with Alcoa, the main gap in die forging process is the mechanization and lubrication technology of loading and unloading materials. Aluminum Corporation of America adopts trackless operation vehicle (i.e. loading and unloading manipulator) for billet discharging, mold loading and mold discharging, and crown block is only used for mold loading and unloading. However, the Southwest Aluminum Processing Plant uses the crane to load and unload materials. Every time a material is molded by the hydraulic press, the hydraulic press needs to be started to move the workbench once, and the production efficiency of the shift is low. For example, if 300MN die forging hydraulic press is used to produce aluminum die forgings with a projection area of 0.5mm2, Alcoa can forge an average of 12 pieces per hour, while Southwest Aluminum can forge an average of 6 pieces, with an efficiency difference of 50%. Another fatal weakness is that the frequent operation of the workbench accelerates the wear and tear of the workbench and control valve, resulting in frequent equipment failures, greatly reducing the effective working time of the equipment, and significantly increasing the cost.
In order to improve the flow performance of metal in the forging die chamber and prevent metal from sticking to the die, aluminum die forging must be lubricated. Because the lubrication technology directly affects the internal quality, external quality and production efficiency of die forgings, countries around the world attach great importance to the research of lubrication technology (including lubricants and lubrication methods). Compared with Alcoa, except that the type of lubricant is relatively monotonous (the mixture of graphite and mineral oil is used for aluminum die forging), the lubrication method is very backward. At present, the Southwest Aluminum Processing Factory still adopts the traditional painting method, while the spraying method has been adopted abroad. The biggest disadvantage of the brushing method is that the lubrication of the die chamber is uneven, especially for the narrow and deep die chamber, either there is no lubricant or there is too much lubricant, resulting in serious die sticking and poor material forming. Alcoa forging plant has established a centralized lubrication station to provide high-pressure lubricant for several die forging hydraulic press sets. The lubricator can use the spray gun as long as it is connected with the lubricant pipe on the machine table. This not only ensures the quality of lubrication, but also facilitates operation and management, so that the work site is free from oil pollution.
Mold design and production
The design, manufacture and use level of moulds directly affect the development speed of new products, product quality, energy saving and consumption reduction, and labor productivity. Therefore, the developed industrial countries attach great importance to it. One of the important reasons for the slow development of aluminum die forging varieties in China is that the die design and manufacturing technology is backward and the production cycle is long.
Alcoa attaches great importance to the design and manufacture of forging dies. The company's technology center (located in Pittsbugh) has a department and professional personnel engaged in computer aided design and manufacturing (CAD/CAM). However, the domestic forging die design (CAD) has not been popularized, and it is only applied to the axisymmetric rotary forging die. As for CAM, there are fewer users, and it is still in the initial stage, as is the case with the Southwest Aluminum Processing Factory. Mold design requires continuous accumulation of production experience, so even college graduates need years of efforts to have the ability to independently design more complex molds. The expert system of CAD has accumulated rich practical experience of many design experts, and mold designers can use them to carry out high-quality and efficient design work. The mold designed has high accuracy and short time, which greatly speeds up the pace of product development.
In addition, 5CrNiMo and 5CrMnMo are mainly used as forging die materials in China, which have poor heat resistance and low service life. However, H13 (4Cr5MoSiV1) is widely used in the United States. This steel has good red hardness at 500C, high impact toughness, no cracking when water-cooled, and long service life.
Testing technology and equipment
Aviation die forgings are mostly stressed structural parts with high internal quality requirements, which often need to be tested by immersion ultrasonic testing. Alcoa is equipped with large-scale immersion ultrasonic testing equipment, which is highly automated. The large water tank is equipped with an automatic lifting stage and an automatic scanner. The inspector will clamp the workpiece to be tested on the stage, adjust the scanner, lower the stage below the water surface, and then the automatic detection can be carried out. Although the Southwest Aluminum Processing Plant has water immersion flaw detection devices, they are all manually operated with low efficiency.
Fluorescent penetrant testing is also an important and effective testing method in the processing of aluminum alloy die forgings, which can detect defects such as folds and cracks easily formed on the surface of forgings. Generally, the surface defects of aluminum die forgings form diffuse reflection of light after polishing, and the inspector cannot judge whether the defects have been removed with the naked eye or magnifying glass, which requires fluorescent penetrant testing. Alcoa is equipped with such equipment, while the Southwest Aluminum Processing Plant does not have such equipment at present. During the inspection of finished products, the factory adopts the method of repeated etching, that is, the cleaned forgings are framed and hoisted into the alkali tank, acid tank and water tank for etching, so as to eliminate the diffuse reflection effect of the defective parts, and then checked again. In this way, the labor intensity of workers is high, the efficiency is low, and the forging surface is easy to be damaged.
From the above analysis, not only on the whole, but also on the technical level, China's aluminum alloy forging production and technology level still lags behind the international advanced level. At present, China has become a big country in aluminum alloy forging, but it is not yet a powerful country. We still have a lot of work to do in order to surpass the world's advanced level as soon as possible and become a real large and powerful aluminum alloy forging country.

three ▶
Development Direction of Aluminum Alloy Forging Production and Technology
After decades of efforts, China's aluminum alloy forging production and technology have made rapid progress. A complete aluminum alloy forging production system has been formed, which can basically meet the needs of national economy and national defense construction. However, aluminum alloy forging, rolling and extrusion production is still small, accounting for a very low proportion of aluminum (2%~3%). With the progress of social economic civilization and safety, especially the requirements of energy-saving and environmental protection for lightweight, aluminum alloy forging production and high-quality forgings are far from meeting the needs of social development. In order to adapt to this development trend, it is urgent to vigorously develop aluminum alloy forging production and technology.
Development direction 1
Expand scale, increase production capacity, increase varieties and expand application fields of aluminum alloy forgings
Development direction 2
Design and manufacture more large-scale, high-speed multi-function forging equipment, and set up several large-scale, advanced and multi-purpose aluminum alloy forging production lines
Development Direction 3
Improve the quality of forged parts to meet the needs of further development of national economy and national defense and military industry
Development Direction 4
R&D and application of new technologies, new processes, new materials and new equipment, and constantly improve the technical content of aluminum alloy forging production, so as to achieve the purposes of high efficiency, high yield, high quality, low cost, high efficiency, energy conservation, environmental protection and safety.
Improve the internal quality of forgings, improve the cost performance ratio, and improve the competitiveness of aluminum alloy forgings, that is, improve the mechanical properties (strength, plasticity, toughness, fatigue strength) and reliability of aluminum alloy forgings. This requires better application of the theory of metal plastic deformation; Apply materials with better internal quality, such as developing new alloys and casting high-quality billets; Precise heating, forging and heat treatment before forging; NDT shall be carried out more strictly and widely for forged parts.
Research and development of advanced labor-saving forging process, energy saving and consumption reduction, and improvement of environmental protection conditions. The research and development of efficient forging process has always been a research field that researchers are keen on. At present, the main ways to save labor are to reduce the restraint coefficient, and to reduce the deformation resistance by shunting in practical production; The superplastic forming and liquid die forging in actual production belong to the method of reducing rheological stress; Reduce the contact area; Research and development of new forging methods; Reduce friction resistance and use new lubricants.
Development and application of precision forging process. Forgings can meet the tolerance requirements without further machining. At present, the precision of forgings can be controlled within 0.01-0.05mm. Net forming and near net final forging belong to these methods. Less or no cutting is the most important measure and direction for the mechanical industry to improve material utilization, improve labor productivity and reduce energy consumption.
Information, automation and management modernization of forging engineering. The integration technology of CAD, CAE, CAM and CAD/CAE/CAM is promoted and applied in the forging process to realize the virtual production of the whole forging process, the automation of the design and manufacturing of tools and dies, the prediction of the organizational properties and defects of forgings after forging, and the online quality inspection and online control of the forging process are realized by artificial intelligence, neural network and expert system. The information management of forging process and production process will effectively improve the efficiency of production process.
Development and application of micro forming technology. Generally, it refers to the deformation of parts less than 0.5mm, and the lattice size of materials used for such deformation has not changed much. At present, with the rapid development of microelectronics industry, the demand for micro forming technology is growing. But one of the difficulties of micro forming technology is its size effect.
Research, development and application of environment-friendly forming technology. The green and harmless forging process reduces environmental hazards. At the same time, the forging process saves energy, promotes energy conservation and emission reduction, and promotes environment-friendly forming processes.