1. Low pressure casting process
With the development of science and technology, the disadvantages of using gravity casting to produce aluminum alloy wheel hub are also highlighted. The cost of gravity casting is low, but the product quality is not high, and there are many defects such as shrinkage porosity, slag inclusion, shrinkage cavity, etc., resulting in poor mechanical properties. Therefore, more and more enterprises have improved the production process, Aluminum alloy wheel hub is produced by low-pressure casting. At present, aluminum alloy wheel hub produced by low-pressure casting accounts for more than 80% of the total output in China.
The structure of aluminum alloy wheel hub made by low-pressure casting is compact and its mechanical properties are good. This is mainly due to the application of compressed air to the alloy melt in the furnace, which makes the alloy melt squeeze into the mold cavity from the riser connected with the furnace and into the mold cavity. After the alloy melt fills the mold cavity and solidifies under a certain pressure, the air in the furnace cavity is released, Allow the non solidified molten liquid to return to the furnace. Generally, the filling pressure is not more than 0.95 kg / cm2.
Although the performance of low-pressure casting wheel hub is better than that of gravity casting wheel hub, there are still some common defects in casting. In order to further improve the product performance, many scholars have carried out research on the internal structure of low-pressure casting wheel hub. Jia Xiaofei et al. [7] of Hebei University of technology have carried out research on the internal structure of low-pressure casting aluminum alloy wheel hub, It is found that the distance between the secondary dendrite arm of α – Al at the spoke and the wheel center is 48 μ m and 55 μ m, which is easy to produce casting defects such as shrinkage cavity, shrinkage porosity, porosity, etc.; segregation is easy to appear near the outer bead seat of the wheel hub, resulting in uneven performance; the grain at the rim is small, and the Si phase change quality is good. In addition, a series of detailed optimization solutions are put forward based on the analysis of the defects found.
2. Application of simulation software in low pressure casting
One of the advantages of aluminum alloy wheel hub compared with steel wheel hub is its fashionable appearance, which also means the diversity of structure and shape of aluminum alloy wheel hub products. The traditional design, trial production, process and design optimization, mass production process route lack of flexibility, it is difficult to succeed at one time, and the product renewal cycle is long, which seriously affects the product renewal cycle. With the development of computer technology, The simulation of the casting process is more and more accurate, and now it has been widely used in the low-pressure casting production of aluminum alloy hub.
The common casting simulation software includes ProCAST, ANSYS, z-cast and many simulation software independently developed in China. At the same time, the common modeling software includes UG, Pro / E, CAD and so on. Researchers use this kind of simulation software to analyze and study the low-pressure casting aluminum alloy wheel hub from the aspects of shape design, filling, solidification process and mold. Shape design optimization, Some scholars use ANSYS to study the spokes of low-pressure casting aluminum alloy wheel hub. It is found that if the back groove is added to the spokes, the mechanical strength of the wheel hub will not be reduced, and the material consumption can be saved. The weight of the wheel hub will be reduced from 11.62 kg to 7.86 kg, a decrease of 41%, greatly reducing the material cost of a single wheel hub; Feng Xudong et al. Used z-cast to analyze the filling and solidification process of aluminum alloy wheel hub. When the filling temperature was set at 713 ℃ for the first time, when the filling temperature was 40%, the molten alloy was trapped by the flange arm above the bottom flange to produce air entrainment, resulting in turbulence, which could not realize the sequential solidification. Later, the simulated casting temperature was raised to 730 ℃ and the casting speed was reduced, and the previous defects were found to be controlled, Low pressure casting mould has a great influence on the forming of aluminum alloy. Ma Ying et al. Based on the mould material, through ProCAST simulation analysis and comparison of the diffluent cones made of 93 w-5ni-2cu alloy and H13 alloy, found that the production cycle of aluminum alloy hub can be shortened by using tungsten diffluent cones, as shown in Table 2. It can reduce the shrinkage cavity and porosity defects in the center of hub, and the structure is compact, The mechanical properties were improved. Zhao Lihong et al. Simulated the thermal field of different wall thickness mold and wall thickness casting in low-pressure casting with ANSYS, judged the rationality of mold wall thickness and casting wall thickness by biwo number Bi, and adjusted the temperature field which can provide a sequential solidification.