Summary:
Extrusion die casting and die forging is a kind of continuous casting and continuous forging technology. This paper introduces the technology and equipment of multi-directional extrusion die casting die forging and the technical realization principle of the invention of die, points out the shortcomings of unidirectional extrusion die casting die forging technology and the problems existing in the die locking resistance mechanism of traditional casting device, and puts forward a recommended scheme for the development of equipment with high forging pressure and high die locking force. The development trend of multi-directional extrusion die casting die forging technology is introduced. It is considered that the continuous casting and continuous forging technology and equipment technology represented by extrusion die casting die forging is the synthesis of die casting, low-pressure (differential pressure, gravity) casting and semi-solid processing technology, and an effective form of “mechanical foundation ultimate forming technology”. Extrusion die casting and die forging technology can not only produce all kinds of meltable metals, but also make semi-solid processing from laboratory technology to the forefront of industrial application. In particular, the characteristics of semi-solid extrusion die casting and forging process of flame retardant magnesium alloy are introduced, its industrial economic advantages are analyzed, and its prospect of promoting the great development of magnesium alloy casting and forging industry in China is predicted.
Key words: die casting die forging liquid die forging * * multidirectional die forging die forging continuous casting continuous forging semi-solid processing magnesium alloy
Because the tensile strength of ordinary hard aluminum alloy is between 380-450mpa, which is almost twice that of ordinary cast aluminum alloy, while the strength of super hard aluminum alloy can reach 600MPa. Although the unit price of deformed aluminum alloy is higher than that of cast aluminum alloy, and its forming cost is also higher than that of casting process, the cost performance of the latter is significantly higher than that of the former because it can significantly reduce the product structure size, coupled with further heat treatment strengthening, welding and surface anodizing. Therefore, in more and more occasions, it is hoped to use or use deformed aluminum alloy to produce parts. For the use occasions of sports parts, such as aircraft, ships, cars, motorcycles, sports bicycles, etc., the energy-saving and speed benefits brought by reducing weight, deformed aluminum alloy has irreplaceable advantages.
Due to the remarkable progress of continuous casting and continuous forging technology, deformed aluminum alloy blanks with the same complex structure as die castings can also be produced easily and smoothly at similar workshop cost. Therefore, using deformed aluminum alloy to replace traditional cast aluminum alloy to produce blanks not only has economic advantages, but also has become a trend and trend.
1. Basic situation and performance comparison of cast aluminum alloy and deformed aluminum alloy
1.1 industrial aluminum ingots are divided into two categories: cast aluminum alloy and deformed aluminum alloy. Generally speaking, cast aluminum alloy is suitable for producing aluminum castings by casting method, while deformed aluminum alloy is suitable for producing aluminum products by pressure machining (extrusion and forging).
1.2 wrought aluminum alloys include: antirust aluminum (LF), hard aluminum (ly), super hard aluminum (LC), forged aluminum (LD) and special aluminum (LT). Because the average comprehensive mechanical properties of wrought aluminum alloys are higher than those of cast aluminum alloys (the forging properties of cast aluminum alloys are also several percent higher than their as cast properties on average), many brands of wrought aluminum alloys can also improve their mechanical properties through heat treatment means such as quenching and aging. Therefore, it is hoped that wrought aluminum alloys can be more applied in industrial design to meet the requirements of use.
1.3. Two factors limit the application scope of forged aluminum alloy or weaken its industrial economy:
First, the casting performance of deformed aluminum alloy is very poor, and its liquid fluidity is generally only one-third of that of cast aluminum alloy. It is difficult to produce blanks with complex structure by traditional casting methods.
Second, even if the deformed aluminum alloy blank is produced by casting method, if the shrinkage, porosity and pore pinhole defects commonly existing in the casting process can not be solved, the subsequent heat treatment and surface anodizing process can not be continued.
The most fundamental reason is that even if the internal defects of the as cast deformed aluminum alloy blank are eliminated, the performance after heat treatment is greatly reduced due to the coarse metallographic grains and dendrites, or it is only similar to the performance of ordinary cast aluminum alloy. Using this relatively expensive material variety will lose its due economic significance. However, the emergence of continuous casting and continuous forging technology has effectively changed this situation.
2. Brief introduction of continuous casting and Forging Technology
Continuous casting and forging technology refers to the continuous completion of blank filling and forging production with the same set of molds in the same equipment. Its essence is a process technology realized by relying on the function of equipment. Therefore, different continuous casting and forging equipment have different subdivision processes of continuous casting and forging.
2.1 continuous casting and continuous forging equipment can be divided into horizontal and vertical according to the equipment placement mode, and can be divided into cold chamber type and hot chamber type according to the casting soup feeding mode. Continuous casting and continuous forging process can be divided into unidirectional continuous casting and continuous forging and multidirectional continuous casting and continuous forging according to the number of forging power cylinders installed in the equipment.
2.2 two typical continuous casting and forging processes and equipment: one is the “liquid metal die forging” (or “melt forging”) invented by the Soviet Union and completed by hydraulic press, while the other is the “pressure casting die forging” (or “extrusion die casting die forging” – referred to as “die casting die forging”) realized by using the patented technology of China’s invention.
2.2.1 “liquid metal die forging” process and equipment technology
For the “liquid metal die forging” process, although we can not clearly see the obvious separation process of “casting” and “forging”, the essence of this process completed by hydraulic press can still be classified as a kind of continuous casting and continuous forging process. It is also a kind of unidirectional continuous casting and continuous forging process.
The “liquid metal die forging” process completed by hydraulic press can produce some blanks with less complex structure and low requirements for axial dimensional accuracy of blanks.
Because the hydraulic press is a universal universal equipment, even if the double movable beam hydraulic press is used, it still has only three power heads. Therefore, it is difficult to complete the continuous casting and continuous forging process that requires multiple power heads and continuous compound movement. In addition, it has no filling mechanism, so the complex blank can not be produced at all.
In production practice, the process completed with this equipment has low production efficiency and poor industrial economy. Due to the lack of technological means, workers have to operate and contact high-temperature molds and blanks by hand at close distance, which not only has high labor intensity, but also does not meet the requirements of safe and civilized production of modern industry. The lack of process means also causes this production process to rely too much on the skills of operators, resulting in low repeatability and reliability of the process. It can no longer meet the requirements of the progress of industrial production.
2.2.2 advanced “die casting and forging” process and equipment technology
The technology and equipment of “die casting and forging” is referred to as “die casting and forging” technology for short. The “die casting” in this is not the “high-pressure die casting” we understand in a narrow sense, but a broad concept, that is, it includes all the process concepts of casting filling, such as high-pressure die casting, low-pressure casting, gravity casting, vacuum suction casting and so on.
Therefore, “die casting and die forging” technology is a continuous casting and continuous forging process that takes “die forging” as the ultimate feature, no matter what kind of casting and filling method is used. Continuous casting and forging process is also known as a “principle process”.
At present, the most commonly used equipment is the horizontal cold chamber (hot chamber) die casting die forging machine. Its shape is similar to that of the traditional die casting machine, and can be matched with the traditional ironing, spray cooling and parts taking manipulator. It has been able to produce “die casting die forging” equipment with a maximum forging pressure of more than 30000 kn, and can produce blank parts including forging hub of large truck and forging cylinder block of automobile engine. It can also produce continuous casting and forging blanks of magnesium alloy and ferrous metal. Because its production rhythm is basically the same as that of ordinary die-casting machine, the process cost of workshop production is almost the same as that of die-casting process.
Continuous casting and continuous forging production of deformed aluminum alloy
3.1 similarities and differences between deformed aluminum alloy and ordinary cast aluminum alloy continuous casting and continuous forging production
In terms of form, the continuous casting and forging production of deformed aluminum alloy is not very different from that of ordinary cast aluminum alloy: the production equipment is the same, and the overall structure and size of the die are the same, but there are many differences in the internal structure and production process parameters of the die.
3.2. The filling process parameters are different. Because the casting fluidity of deformed aluminum alloy is much lower than that of cast aluminum alloy, its filling speed and filling pressure are different from that of ordinary cast aluminum alloy, and the filling pressure is generally required to be improved; As the mold filling speed is relatively small, the temperature control requirements of the mold need to be more strict. During normal production, the requirements for the heat balance of the die will be higher. In addition, the slow down of mold filling speed generally requires the appropriate increase of the initial casting temperature of the soup.
3.3 differences in the internal structure of the mold. Because the fluidity of deformed aluminum alloy is lower than that of cast aluminum alloy, it also requires that the inner sprue of the mold be relatively wider and thicker. However, the differences between different wrought aluminum alloys and blanks with different structures still exist, which requires us to solve it from a practical point of view. It needs to explore the process of optimal die structure parameters.
3.4. Comprehensively consider and solve the problem of insufficient fluidity of deformed aluminum alloy. We can’t look at the fluidity of deformed aluminum alloy independently, but aim at the final blank forming quality.
The current “die casting die forging machine”, whose filling speed, filling pressure and die forging force are designed to be stepless and adjustable, provides the broadest means for us to comprehensively weigh the forming process characteristics of different aluminum alloys. In addition, the control of initial casting temperature and final forging temperature, on the one hand, due to the “substitution effect” of various parameters on other parameters, It requires our technicians to be quite proficient in the whole set of equipment and process. On the other hand, it also provides us with a broad space for the flexible use of this set of process technology, which greatly reduces the difficulty of production technology, including difficult to form and deform aluminum alloy.
3.5. Pay attention to the structural and technological analysis of blanks. The analysis of the structure and manufacturability of the blank is the basis for formulating the process implementation plan. It is the key to the process effect and even the success or failure of the process. It requires the internal grasp of die casting and die forging technology by process technicians.
Among them, the most important is the classification scheme. We can’t follow the parting idea of die-casting die, but should follow the parting idea of forging die. But the biggest challenge lies in the extent to which we can pull the core to form. If all the blanks are designed according to the forging process and all the core pulling are not produced, the characteristics, economic advantages and practical significance of continuous casting and continuous forging process will be lost!
3.6. Residual material removal. The strength and toughness of deformed aluminum alloy are higher than that of cast aluminum alloy, and the coarser and thicker inner sprue will make the removal of residual material a new problem. The general suggestion is: consider the details of the design of the inner sprue, cooperate with the stamping structure of the die, and use the action of the forging step to form a folding structure. If manual breaking cannot be achieved, the convenience of mechanical cutting shall be considered.
4. Conclusion
Continuous casting and continuous forging of wrought aluminum alloy is a new thing. It meets the development requirements of modern industrial products towards lightweight and high strength, and has a good application prospect. The difference between the continuous casting and continuous forging production of deformed aluminum alloy and that of ordinary cast aluminum alloy is not large, and the technical difficulty lies in the operable control. Mastering the continuous casting and continuous forging process of ordinary cast aluminum alloy is the basis for producing continuous casting and continuous forging of deformed aluminum alloy blank with complex structure. The “extrusion die casting die forging machine” is the most industrial and economical process and equipment for continuous casting and forging of deformed aluminum alloy.