2. 2 new spraying technology
The spraying of the release agent has a great relationship with the quality of the die casting. If the release agent is non-atomized or non-uniformly dispersed when ejected from the spraying device, the condensed liquid requires a longer time of vaporization. When the process is not completed, the mold is clamped and the metal is hydraulically forced to accelerate the lubricant. Vaporization and the formation of higher vapor pressures are often the source of loose casting.
Water-based coatings are highly demanding on the process. There is a strict requirement for mold temperature and a "wetting temperature". If the mold temperature is below this limit, the coating can form a film. The "wetting temperature" is different depending on the composition. The thickness of the coating film should also be strictly controlled. When it is too thick, the cooling is slow, and the pores are easily formed. The surface of the casting is also easy to wrinkle; when it is too thin, it is easy to crack, and the surface of the casting is marked. Water-based paints emit smoke when sprayed, which is not conducive to environmental protection.
When the molten metal is poured into the pressure chamber, local solidification phenomenon often occurs, and the dispersed chilled structure is formed. After the cavity is punched into the cavity, the mechanical properties of the casting are obviously reduced. Spraying liquid paint into the pressure chamber does not completely solve the problem.
To this end, many researchers are committed to the development of solid lubricants or semi-permanent coatings. The goal is to improve mold life, prevent welding, improve casting quality and improve environmental conditions.
3 Development of new die-cast alloy materials
3. 1 metal matrix composites MMCs)
Lightweight, reduced fuel consumption and emissions, and improved performance to ensure quality and safety are the main directions in the development of today's automotive industry. Among the new materials, metal matrix composites are expected to have an important position in the development of the automotive industry in the future due to their high specific strength, specific modulus, wear resistance and friction reduction performance, thermal strength and low thermal expansion coefficient. In particular, the use of casting processes to manufacture metal matrix composite parts has certain advantages. The process is relatively simple, the cost is low, and the application has limited limitations. A lot of development research work has been done. According to David Weiss et al. [9], SiC particle reinforced aluminum matrix composites have been successfully die-cast, and the filling properties are sometimes better than those of ordinary aluminum alloys, and the surface quality is satisfactory. The tool used is the same as that of general aluminum die casting.
Zinc-aluminum matrix composites have good prospects for wear-resistant antifriction materials [10]. The ZA227 alloy is used as a matrix, and is combined with graphite in a molten state to form a uniform slurry, which is formed by extrusion casting. The microstructure shows that the metal 2 graphite interface is well bonded and the graphite distribution is uniform. This material has a higher load carrying capacity than the bronze ZQSn62623 when the graphite mass fraction is less than 5%. The coefficient of linear expansion drops by more than 10%. Friction reduction, wear resistance and relative seizure resistance are much better than the base alloy ZA227.
3. 2 die-cast magnesium alloy
Magnesium alloys are known as metals since the 1990s [11,12] and have developed rapidly in recent years. North American production is expected to increase by a factor of three by 2006. The automotive industry is the largest user of magnesium die castings with a market share of around 80%.
The goal is to further reduce the weight of the car. General Motors uses die casting to produce magnesium alloy automotive wheels. Japanese light metal strain) Magnesium alloy wheels produced by oxygen-filled die-casting are 15% lighter than aluminum wheels. It is estimated that by the year 2000, cylinders, hoods, roof panels, door frames, rear hatches, wheels, etc. will be die casted with magnesium alloy. In terms of electronic equipment, new designs must be designed to withstand unwanted signal interference and should be shielded. Magnesium alloys have this property. For example, the radar positioner housing replaces the plastic with magnesium alloy, and the weight is equivalent, and the strength and impact resistance are improved.
The reason why magnesium alloy has a wide application prospect is because it also has the following advantages.
1) Low density 1. 8 g / cm3), similar to many engineering plastics 1. 43g / cm3). It has higher specific strength than aluminum alloy.
2) Good casting properties.
3) The cost is competitive, because the magnesium is light, the magnesium price is 1.5 times the aluminum price is competitive.
Magnesium is rich in reserves and contains 6 million tons of magnesium per cubic mile of seawater. The magnesite in Dashiqiao City, Liaoning Province, China accounts for more than 60% of the world's reserves, and the grade is 40% higher. It can be profited from the use of hot chamber die casting. The anti-corrosion problem that previously affected the total cost has been solved. Studies have shown that low corrosion resistance is caused by trace heavy metal elements. When it reaches a certain purity, its anti-corrosion ability is equivalent to that of aluminum alloy.
3. 3 high aluminum zinc base alloy ZA
Since 1979, high-aluminum zinc-based alloy die-casting has become one of the most dynamic aspects of ZA alloy technology. ZA alloy die casting offers the only opportunity to design high-strength, wear-resistant and lightweight castings to replace heavier materials and costly manufacturing methods.
The most outstanding features of ZA alloys are high strength and excellent tribological properties.
The tensile strength of high-aluminum zinc-based alloy is about 20% to 35% higher than that of aluminum alloy 380, and 50% to 70% higher than that of magnesium alloy AZ91. The tensile strength of die-cast ZA28 is about 394 MPa, ZA212 is 422 MPa, and ZA227 is 450 MPa. Recent studies have shown that the strength of thin-walled die-casting parts is higher than the above. Therefore, the specific strength of ZA227 die castings is close to 380 alloy. It is very competitive in the automotive industry.
ZA alloys, especially ZA227, have high wear resistance and are superior to traditional wear-resistant alloy materials such as tin bronze and aluminum bronze. Its die casting can be used for the transmission and other parts of the off-road winch.
Another great advantage of ZA alloy is its low melting temperature and low energy consumption, which is about 1/3 of that of aluminum alloy.
5 至1. 0毫米。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。. Can meet the requirements of lightweight castings. The processing performance is also very good, the cutting speed can be 3 to 5 times that of cast iron, and the tool life is extended.
4 Improve the ability to respond quickly to the market, promote parallel engineering CE) and rapid prototyping technology (RPM)
4. 1 Concurrent Engineering
The rapid advances in technology in the past decade have been enough to revolutionize the die-casting industry. These latest technologies include: improved sensors and control systems, faster and more reliable computers and software, wide-area 3D 3D) CAD and analysis capabilities, improved electronic data exchange and interface technology, and rapid prototyping technology . The biggest advantage of using these technologies is that the amount of information is expanded and used in parallel. Process design at the same time in the product design phase, taking into account all the factors of the product's entire production cycle, greatly reducing the time to market.
4. 2 Rapid Prototyping Technology
The so-called rapid prototyping technology, simply means that the 3D CAD data of the part to be produced is horizontally cut on the computer, and the laser is used to scan and solidify the model material such as photocurable resin. After the scan is completed, the final product stacked is the required model.
Rapid prototyping methods such as Stereolitho graphy and Laminated Object Manufacturing have been used in many products. In the past, most of it was used to design and manufacture inspection tools. The current development is to pave the way for manufacturing molds. This makes developing new products faster.
At present, the die-casting industry mainly uses rapid prototyping technology to manufacture molds for gravity casting such as sand casting or gypsum casting, and then casts the mold castings to be developed. Die casting dies can also be fabricated directly using rapid prototyping techniques. But the problem to consider is the tolerance accuracy problem. CNC can produce high-precision die-casting molds with long cycle times and high costs. Perhaps the casting mold can reach the final shape and then machined to the final tolerance. The development of new die-casting molds with rapid prototyping technology is promising.
5 Carry out research and development of CAD/CAE/CAM system
In the 1990s, the third generation of hydraulically driven die casting machines appeared, with greater power and speed, with higher precision and reliability. However, it is still very difficult to produce high quality non-porous thin wall die castings. The reason is that there is still a lack of accurate prediction of the behavior of molten metal in the cavity.
As the depth and breadth of applications of computers in the die casting process continue to increase, problems in die casting should be gradually solved.
The application of computers in the die casting process has not been long, but it is progressing rapidly. At first, only the choice of die casting process parameters, the design of the gating system. Later, the solidification simulation of the die casting can be performed, showing the temperature distribution of the mold, predicting the position of the shrinkage cavity and the stress distribution. Shortly afterwards, the filling simulation was developed to predict the failure of pouring, cold separation and other filling-related defects. Filling and solidification simulations are more accurate and faster due to improvements in computer models and improved computer hardware performance. Not only can the die-casting mold be designed, but also the graphics and instructions can be formed, output to the CNC machine tool for mold processing, and the CAD/CAE/CAM system is initially established.
In order to make the simulation result closer to the actual situation of the die-casting process, the processed die-casting mold can be successfully tested at one time. Still need to do a lot of work. On the one hand, through the gradual deepening of the understanding of the die-casting process, more physical quantities related to it are brought into the computer model. As recently considered [16], during the injection process, the shear stress during the flow of the melt irreversibly converts the mechanical energy into heat energy, which causes the viscosity to decrease, which is advantageous for the feeding. Filling simulations are also more accurate due to the effect of back pressure on the filling pattern. To provide more accurate physical boundary conditions for the filling simulation, the injection curve is predicted according to the mechanical parameters and characteristics of the die casting machine to avoid the injection punch speed exceeding the critical speed and the ingate flow rate exceeding the maximum value during filling.
On the other hand, since the die casting process is carried out under high pressure and high speed, there are many influencing factors of static and dynamic. Therefore, a large amount of basic theoretical work is required, and an accurate mathematical model is established to describe the complicated die casting process system.
6 Promote computer integrated manufacturing system CIMS)
The implementation of CIMS project is to use the data generated by various departments of computer network and database integration, and comprehensively apply modern management technology, manufacturing technology, information technology and system engineering technology to integrate the four elements of people, technology, equipment, operation and management in the whole process of enterprise production. It integrates information flow and material flow organically, and realizes the overall optimization of the enterprise, and solves a series of problems faced by enterprises in participating in competition, so as to achieve high efficiency, high quality, low consumption and fast listing, so that the enterprise can remain undefeated in the competition. place. CIMS is a means of winning competition.
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