Application of computer simulation technology in casting field

1.Three dimensional simulation of physical field in mold filling process

Numerical simulation of physical field in mold filling process, including numerical simulation of flow field in mold filling process, temperature field and stress field in solidification process, as well as numerical simulation of microstructure and grain growth and morphology. The numerical simulation of single or coupled integrated field in the casting process can intuitively analyze the defects in the casting forming process and find out the internal causes, which is helpful to optimize the casting process and obtain high-quality castings.

1.1 Flow field

The flow of molten metal in the mold cavity directly determines the quality of the casting. If the mold filling is unfavorable, there will be defects such as cold shut and insufficient pouring. Therefore, it is of great significance to study the mold filling process of molten metal to obtain high-quality casting blanks. Sun Xun and others creatively combined the three-dimensional heat transfer simulation platform of casting process based on Patanka’s power function method and point heat flow method of heat transfer boundary conditions and considering heat convection and heat diffusion with the filling process simulation analysis software established by SOLA-VOF algorithm [9], The flow and heat transfer of molten iron in the shell of nodular iron reducer during mold filling and solidification are successfully predicted, the solidification time of riser neck is accurately calculated, and the casting process is optimized according to this, and satisfactory results are obtained. Liu Jingfeng et al. Established a three-dimensional flow field simulation platform for molten metal filling process by using SOLA-VOF algorithm [10], and simulated and analyzed the three-dimensional flow field of ZG25 filling process. The results are similar to the classical calculation example of three-dimensional flow field in the filling process of standard experimental castings. The flow field algorithm is successful and the calculation accuracy is high.

1.2 Temperature field

In the process of mold filling, the distribution law of temperature field will directly affect whether there will be shrinkage cavity, segregation and other defects in the casting. Jia ruijiao et al. Numerically simulated the temperature field of aluminum alloy wheel hub of electric vehicle in the solidification process of sand mold gravity casting with the help of finite element simulation software ProCAST. The results show that the three-dimensional temperature field numerical simulation can accurately reflect the distribution law and dynamic change of temperature field during solidification, and provide a reference for optimizing the process. Hu Wenyi et al. Calculated and simulated the influence of pouring speed on the temperature field of AZ31 magnesium alloy large-size slab during continuous casting. The calculation results show that with the increase of pouring speed, the position of initial solidification shell decreases and the depth of liquid cavity increases. It is calculated that the optimal pouring speed of AZ31 magnesium alloy large-size slab continuous casting process is 30 ~ 35 mm / min, During solidification, the maximum temperature gradient appeared at the contact between the slab at the bottom of the mold and the cooling water.

Ma Zhaomin developed the temperature field analysis software based on ANSYS, and obtained the temperature field change law of diesel engine cylinder head casting from pouring to room temperature under different process parameters. With full consideration of material, structure and other comprehensive factors, three sand falling temperature process schemes were compared, and the optimal process scheme was obtained. In order to solve the quality problems such as shrinkage cavity and porosity in the casting production of an aluminum alloy hub, Zhang Yafei and others simulated the transient nonlinear temperature field analysis of the casting process of the product with the help of ANSYS simulation platform. Combined with the calculation results, four factors that have a great impact on the forming process of the product were separated by orthogonal experiment, and the mold was optimized, The service life of the die is effectively improved. Chen Shijun and others used ANSYS to simulate the three-dimensional temperature field of copper mold casting, and predicted the solidification defects and cracks of copper mold in the cooling process of die casting. After optimization, the calculation results are consistent with the actual production.

1.3 Stress field

By simulating the distribution law of stress field in the solidification process of castings, the defects such as hot crack and deformation of castings can be effectively predicted. At present, the simulation of stress field in casting process is mainly focused on cast iron, steel castings and aluminum and magnesium alloy castings. Zou Shuliang and others analyzed the stress field of the new Fe-W alloy stress frame under three different pouring temperatures, pouring speeds and sand mold preheating temperatures by using ProCAST. The study found that the sand mold preheating temperature had a great influence on the residual stress and deformation, and the sand mold preheating temperature was inversely proportional to the casting residual stress and deformation; Pouring temperature has the least effect on casting deformation, and pouring temperature is directly proportional to residual stress and deformation; The pouring speed has the least effect on the residual stress, and the pouring speed is inversely proportional to the residual stress and strain.

At the same time, the optimum pouring speed, pouring temperature and sand mold preheating temperature are calculated, which can guide the actual production. Based on the analysis of the temperature field in the solidification process of aluminum alloy cylinder head, Zhao Yongmei used the indirect method, applied the calculation results of the temperature field as the body load to the structural analysis, analyzed the casting stress in the solidification process, and effectively prevented the occurrence of casting cracks by combining the optimized cooling process and appropriately delaying the sand falling time. In order to verify the rationality of the investment casting process improvement scheme of the guide impeller, Zhang Jie simulated and analyzed the relationship between the mechanical properties and the temperature change in the casting process. It was found that increasing the shell preheating temperature can significantly reduce the effective stress at both ends of the blade at the end of cooling. The results were applied to production and achieved good results.

1.4 Multi field coupling

At present, the application research of casting simulation has developed from single field such as stress field, temperature field and flow field to multi field coupling integration, focusing on the analysis of the impact of multi field coupling on the whole casting process, so that the whole casting simulation process can be effectively combined macroscopically and microscopically, so as to provide positive guidance for the development and optimization of casting process scheme. According to the existing process parameters, Bai Qingling et al. Studied the influence of the coupling of temperature field, stress field and flow field on the melting and casting process of large-size 7050 aluminum alloy round ingot. The results show that the biggest factor affecting the stress field is the pouring speed, which far exceeds the influence of temperature and water flow on the stress field, and optimized the casting process accordingly, The hot crack problem of 800 mm ingot in the production process was solved. Feng Yuchen and others studied the stress distribution law of diesel engine fuselage at different temperatures during casting solidification. Liu Zhilong loaded the temperature field results in the mold obtained in fluent into ANSYS for thermal coupling simulation, analyzed the flow, heat transfer and stress coupling in the extra thick slab continuous casting mold, and successfully predicted the location of crack according to the law of shell stress distribution. Xu Yan used the thermal mechanical two-way coupling model to simulate the casting. The results show that the temperature distribution of the casting is closer to the experimental results by using the two-way coupling method, which provides a guiding basis for preventing hot cracking.

2.Casting microstructure simulation

With the help of three-dimensional numerical simulation technology, the nucleation and evolution mechanism of solidification structure of castings can be analyzed intuitively. The main methods include deterministic method, probability theory method and phase field method. In recent years, solidification microstructure simulation technology has made rapid development, but it is still far from industrial application. Li Bin et al. Made statistical analysis on a large number of experimental data, established a dendrite growth model, numerically simulated the macro solidification and microstructure evolution process of ZL114A aluminum alloy during low pressure casting by using the finite difference method, and successfully predicted the grain size, secondary dendrite arm spacing and eutectic structure content in different parts of the casting, The simulation results are highly consistent with the experimental results. Zhou Zhimin and others proposed a semi-solid alloy design method based on microstructure evolution simulation, and studied the effects of element composition and content, pouring temperature and pouring speed on solidification structure and composition distribution of Al Cu alloy in semi continuous casting process. It is found that when the Cu alloy content is 8.00%, the effects of pouring speed and pouring temperature on the microstructure can be ignored, and the semi-solid alloy structure with uniform size and distribution can be obtained. Zhang Yanhua et al. Established the temperature field and phase transformation field model of 5% Al Cu alloy semi continuous casting process, determined the nucleation of each cell in the semi continuous casting process by using the average undercooling of the primary cell in the liquid-solid phase transformation zone, and described the grain growth by using the solute diffusion model. It was found that uniform and fine semi-solid structure was obtained when the pouring speed was 2.0 mm / s, which was consistent with the experimental results. Chen Rui et al. Established a nucleation model suitable for equiaxed solidification of aluminum alloy, simulated the microstructure evolution of Al-7Si mg aluminum alloy during solidification, and found that the secondary dendrite arm spacing decreased with the increase of cooling rate. It was verified that the results were consistent with the experimental results.

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