Present situation and Prospect of the hottest die

2022-07-24
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The present situation and Prospect of die casting technology

Abstract: the development direction and key points of China's die casting industry are put forward from the higher and higher requirements of die casting Market for enterprises and die casting quality and the current status and development trend of die casting industry

key words: Die Casting Technology die casting equipment die casting alloy computer simulation

preface

since the advent of die casting in the 1940s, as a precision machining process for metal parts close to the final shape and size, its development is in the ascendant. New progress has been made in die-casting equipment and its control, die-casting process and die-casting alloy. At the same time, the market needs to produce a large number of complex thin-walled and beautiful metal parts to meet the increasingly high requirements for die castings in the automotive industry, electronic communication, household appliances, toys and other industries. However, some inherent problems of die castings have not been completely solved, and the potential of the alloy has not been brought into full play. Die casting industry is also faced with the task of further improving the technology and management level to ensure the high quality and low cost of castings

the current market is a dynamic market. In order to remain invincible in the competition, enterprises must be able to adjust their business strategies in time, which should be based on advanced technology and management. Technological innovation will become the focus of enterprise competition in the 21st century. Only by mastering the key technologies and adopting the advanced management system can we improve the response speed to the dynamic and changeable market and improve the competitiveness of enterprises

at present, the die casting industry in Guangdong Province and even the whole country still lags far behind the international advanced level. Since the reform and opening up, hundreds of die casting related enterprises have moved into Guangdong from Hong Kong. Therefore, the die casting industry in Guangdong has developed rapidly in the past ten years [1]. According to incomplete statistics, there are more than 600 die-casting manufacturers with a certain scale in the province. There are more than 8 manufacturers with an annual output of 3000 ~ 5000 tons of die-casting parts, more than 10 manufacturers with an annual output of 1000 ~ 3000 tons, and dozens of manufacturers with an annual output of 500 ~ 1000 tons. The annual output of zinc alloy die castings is nearly 100000 tons, and that of aluminum alloy die castings is about 40000 tons. The province has more than 2000 die-casting machines, the largest of which is the Italian die-casting machine with a clamping force of 21000 kn. There are 7 die-casting machine manufacturers and more than 10 die-casting peripheral equipment manufacturers in the province. The annual output of die casting machines is about 600, most of which are hot chamber machines. The main problems are as follows: the die-casting equipment is mainly small, and the control system is relatively backward; Die castings are mainly made of zinc alloy, most of which are non stressed parts such as household appliances and toys, and the proportion of parts such as automobiles and motorcycles is relatively small; Mold manufacturing is a weak link. There are many mold manufacturers, but most of them are small-scale, with backward equipment and long production cycle. Only a few mold factories have started to implement cad/CAM technology. There is still a long way to go to make China's die casting industry reach the world advanced level. Must carry out die casting technology innovation project; Develop new injection system and control system; Improve the internal quality of die castings; Develop new die casting technology; Research new die casting alloy materials; Implement modern management

The development of new die-casting equipment and its control system

pressure casting is a process of filling the mold cavity with liquid metal at a very high speed under high pressure. It is a complex dynamic thermodynamic process. On the one hand, die casting can produce metal castings with complex thin wall, beautiful surface and high precision. On the other hand, the general die-casting process is difficult to reach the laminar flow filling state, which involves gas and inclusions, and can not get a compact and heat treatable workpiece, which affects its mechanical properties. If we use the method of reducing the filling speed to improve the filling state of liquid metal, it is bound to sacrifice the advantages brought by the above die-casting production, and it is not necessarily effective for complex thin-walled parts. The production of high-quality, non porous thin-wall die castings is our goal, which is one of the chips to win in the competition of other die-casting processes

in order to improve competitiveness, the indicator of thin wall is also pushing up, which is a very flexible indicator. For example, in the 1950s, the thin-walled body of the automobile industry was 2 mm, and now it is 0 7 mm, which will be 0 5 mm。 The thin wall referred to by zinc die castings was 2 mm in the 1960s, 1 mm in the 1970s and 0.5 mm in the 1980s 7 mm, 0 3~0. 5 mm。 Aluminum die castings have a similar development, which was 0. 5% in the 1990s 5~1 mm。

dense thin-walled castings are filled with sufficient metal pressure and short filling time, that is, with high ingate flow rate and sufficient metal pressure in a very short time. This requires that the servo valve die-casting machine can produce both high injection speed and high metal pressure. That is, according to the casting process requirements, the die casting machine should be able to provide a certain injection energy, so as to achieve high-energy mold filling. To get 0 For dense castings with wall thickness below 75 mm, a die casting machine with injection energy above 550 kW · h is required

high energy filling can also adjust various process parameters to obtain high-quality die castings. High energy mold filling is the development direction of injection system of die casting machine. In order to achieve high mold filling energy, a die-casting machine must try to reduce the energy loss caused by various frictional resistance, local resistance and inertia force - pressure drop

in addition, the progressiveness of the die casting machine is mainly reflected in the stability and reproducibility in the production process, that is, each injection is as close as possible to the preset ideal injection curve. However, there are many variables that affect the stability of the die casting process [2]. Static factors such as the working state of die casting machine and die and the pressure of energy accumulator cannot be changed after the process equipment is selected

some variables caused by dynamic factors and human factors (such as the amount of metal and its temperature per injection, mold temperature, hydraulic oil viscosity, coating quality, artificially set parameters, etc.) must be corrected through injection control 1. Self locking: self locking 1 is generally inversely proportional to the transmission force. The average time for one shot is 20 ~ 80 ms. the filling time required for thin-walled aluminum alloy or magnesium alloy parts is shorter, which is 5 ~ 12 ms[3]. The shot control system must be able to control the shot curve with a response time of 2 ~ 8 ms, which is only about 10% of the time for one shot. This puts forward severe requirements for the electronic circuit system, that is, the electronic circuit control system must respond in a few microseconds. High reproducibility requires the installation of metal front sensor [4]. When the metal liquid seals the sensor, the front edge of the metal liquid is accurately identified, the information is fed back to the electronic control equipment, and the electronic instrument recalculates to obtain a stable and optimal injection curve. The development of advanced sensors promotes the development of die-casting machine and die-casting process. The structure and properties of die castings depend on the thermophysical conditions in the die casting cavity and its adjacent areas, so it is of great significance to develop thermal detectors and sensors close to the cavity

2 develop new die casting technology

2 1 semi solid alloy die casting

compared with all liquid and all solid alloys, the physical properties of semi-solid alloys have two characteristics. First, when the solid component of this semi-solid alloy exceeds 50%, its viscosity increases sharply with the increase of solid component. However, for non stirred alloys, when the solid component exceeds about 15%, the viscosity increases sharply with the increase of solid component. The other is that the alloy under intense stirring is miscible

it is precisely because the semi-solid alloy under intense stirring has this special physical property that its casting performance is excellent. In the case of high solid components, its fluidity is quite good, and it is not seriously reduced compared with the full liquid alloy. In addition, the feeding performance is also good. On the one hand, its shrinkage has been reduced. On the other hand, it can feed through the simultaneous flow of liquid and solid phases. Because the alloy is miscible, it is suitable for die-casting and extrusion processes which are subject to great shear during forming. Compared with all liquid alloys, semi-solid die casting is more unique

first, all liquid alloys are inconvenient to operate, which is an obstacle to improve working conditions and the degree of mechanization and automation. Semi solid alloys only show the same characteristics as fluids during forming, and can be handled like solids before forming, which is very beneficial to the organization of highly mechanized and automated production. Second, when semi-solid alloy die casting, the heating state of the mold has been greatly improved. One reason is that the temperature of the alloy itself has been reduced and the heat content has been reduced. The heat that semi-solid metal needs to dissipate from die casting to complete solidification is only about half of that of overheated metal. Another reason is that the semi-solid alloy has different modes of entering the mold cavity. It does not flow, and the degree of turbulence is low. It can basically achieve full wall thickness filling. The thermal impact on the mold is very low, and the service life of the mold is improved. Therefore, semi-solid die casting has great application prospects for high melting point alloys

semi-solid alloy also provides favorable conditions for manufacturing metal matrix composites by casting. It is a simple and convenient method to prepare composite materials by adding uncoated non-metallic particles into semi-solid alloy under intense stirring. Due to the existence of solid primary crystals in semi-solid alloys, non-metallic particles can be prevented from floating, sinking or agglomerating, and the distribution is relatively uniform. In addition, the surface of non-metallic particles is activated by intense stirring and friction, which makes them closely bound to the matrix alloy

although the concept of semi-solid alloy casting was put forward by M.C. Flemings et al in the early 1970s [5], so far, how to effectively prepare and shape semi-solid alloy slurry is still a problem [6, 7]. Application is limited, material selection is limited, and process specification requirements are very strict. In particular, the solid and liquid fractions shall be accurately controlled, and the deviation shall be within ± 3%. In order to meet the process requirements of semi-solid die casting, the design of process equipment is a key. H. Peng et al. [6] proposed the rheomolding process. The principle is that the liquid metal is sent into the specially designed injection molding machine barrel, which is sheared by the rotating screw device and cooled into semi-solid slurry. After meeting the process requirements, die-casting molding is carried out. One machine completes two processes (slurry production and die-casting). Temperature control is the key. N. Bradley et al. [8] proposed Thixomolding process, which is to feed solid magnesium metal particles or debris into the spiral injection molding machine. Under the condition of heating and shearing, the metal will be turned into slurry and die cast. This process has an additional shredding process

2. The spraying of release agent has a great relationship with the quality of die castings. When the release agent is sprayed from the spray device, if it is non atomized or non uniformly dispersed, the condensed liquid requires a longer time of vaporization. When this process is not completed, the mold is closed and the metal is forced into the hydraulic pressure, which will accelerate the vaporization of the lubricant and form a higher vapor pressure, which is often the root cause of casting porosity

water-based coatings have high requirements for process. There are strict requirements for mold temperature, and there is a "wetting temperature". If the mold temperature is lower than this limit, the coating can form a film. The "wetting temperature" varies with the composition. The thickness of the coating film should also be strictly controlled. If it is too thick, it will be cooled slowly, which is easy to form pores, and the casting surface is easy to wrinkle; It is easy to crack when it is too thin, and there are traces on the surface of the casting. The water-based coating emits smoke during spraying, which is not conducive to environmental protection

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