Design and Optimization of Die Casting Process for Magnesium Alloy Radar Shell Based on Numerical Simulation

Transcription

1 01 International Conference on Mechanical and Mechatronics Engineering (ICMME 01) ISBN: Design and Optimization of Die Casting Process for Magnesium Alloy Radar Shell Based on Numerical Simulation Dan WANG, Yong SU *, Meng BAI, He-fa CHENG, Jin YU and Lan-jun LIU School of Materials Science and Engineering, Hefei University of Technology, Hefei 30009, China *Corresponding author Keywords: Magnesium alloy, Radar shell, Gating system, Orthogonal experiment. Abstract. According to the material requirements and structure characteristics of the radar shell, the different die-casting process schemes were designed preliminarily. Then, the finite element analysis software Procast was used to simulate schemes. At the same time, the best process scheme was selected by analyzing simulation results. On the basis of the selected scheme, the overflow system was added, which reduced the volume content of shrinkage porosity of the casting. Secondly, the design of the orthogonal experiment was used to optimize the scheme, and the optimal process parameters were obtained. As a result, through the actual production and application, obtaining magnesium alloy die castings of shell with excellent quality. Introduction Magnesium alloy is a kind of industrial light alloy material which has developed rapidly in recent years, its density is the smallest in all kinds of die-casting alloy, only one forth of steel and two thirds of aluminum, in addition, there is a high specific strength and stiffness [1]; magnesium alloy liquid viscosity is low, good liquidity, easy to fill the thin-walled complex cavity; the melting point and latent heat of crystallization of magnesium alloy is low, solidification speed faster after filling cavity, higher production efficiency, longer mold life; shrinkage of the casting is uniform and predictable, good composition and size stability, production of die castings with high dimensional accuracy, better processing performance []. As a series of excellent characteristics of die casting magnesium alloy, the production efficiency and quality are guaranteed, and it has been widely used in the aerospace, automotive electronics, medical equipment and other fields [3]. The finite element analysis software Procast is used to simulate the radar shell model, and predict the location of the defect may occur and optimize process scheme [,5]. Furthermore, it can provide guidance for practical production, making the volume of shrinkage porosity of castings get lower and the comprehensive performance become better. Analysis of Parts Structure and Material Performance The die casting of magnesium alloy shell, is the octagonal thin-walled pieces, the side length of 330 mm, convex round table maximum outer diameter of 0 mm. The wall thickness of complicated shell is uneven, the maximum wall thickness of 5 mm, the minimum wall thickness of mm. The surface of shell has a great deal of convex platforms and stiffeners. Figure 1 shows the Shell model. Figure 1. Radar shell: upper surface, lower surface.

2 Radar shell material for the AM60, it not only has good plasticity, toughness and corrosion resistance, but also a high tensile strength. It can be used in structural parts that can withstand shock loads and require high safety performance [6,]. Table 1 is the chemical composition of AM60. Table 1. Chemical composition of the AM60 alloy in wt.%. Al Mn Zn Cu Si Other Mg max 0.05max 0.01max Bal. Process Scheme Gating System According to the structural characteristics of the radar shell, three kinds of different schemes were developed, and the simulation was carried out. The mold material was H13, the setting parameters were as follows: pouring temperature, 660 C; injection velocity, 3.5 m/s; preheated temperature of the mold, 00 C. Figures -, respectively for the simulation results of three kinds of gating system scheme that molten metal fill mold cavity at different times. Figure (a, b and c) is the filling process of scheme 1. The molten metal is divided into two strands after through the sprue, and then enters the cavity from gate. Until s, molten metal begin to join the junctions, filling unsteadily and converging slowly. Scheme adds a horizontal runner based on the scheme 1. Figure 3 (a, b and c) is the filling process of the scheme. It can be seen that molten metal of the middle runner fill the cavity first, on both sides of molten metal enter the mold cavity until s. This leads to situation of convection and air entrainment potentially. Figure (a, b and c) is the filling process of scheme 3. It shows that molten metal is divided into four strands, and they fill the mold cavity in the meantime. The molten metal pushes forward after converging, smoothly and steadily, no obvious phenomenon of convection and air entrainment. The cavity has been filled with the molten metal at 0.091s. From the above three schemes, the filling time of these schemes is 0.09 s, s and s respectively. It can be known that scheme the time required is the longest, and compared with the former two, molten metal of the scheme 3 filling more uniform, flowing smoother. (c) Figure. Scheme 1 filling process: s, s, (c) 0.09 s (c) Figure 3. Scheme filling process: s, 0.08 s, (c) s. 3

3 Overflow System (c) Figure. Scheme 3 filling process: s, s, (c) s. Based on the filling process of scheme 3, the overflow system is added. The overflow groove is set on both sides of cavity where molten metal begin to fill, which is aimed to exclude the gas in the front of molten metal and cold molten metal, reduce the eddy current and remove gas back to either side of the runner. And the overflow tank is set at the final filling place of the molten metal, which is aimed to improve the mold heat balance state and the conditions of filling, exhaust [8,9]. Figure 5 shows the filling process after adding overflow system. It can be seen that the whole filling process is smooth, and there is no obvious phenomenon of convection and air entrainment. Figure 6 shows that the shrinkage porosity distribution of scheme before and after improvement. That is, the purple parts of the circle mark in the picture. It can be count by Procast that the volume of shrinkage porosity are 0.35 cm 3, cm 3, respectively. It manifest that the latter volume decrease a lot compared with the former. It can be known that the set of the overflow tank is reasonable, the slag inclusion is collected effectively and the content of internal defects in castings gets to reduce. (c) Figure 5. Filling process of adding overflow system: 0.06 s, s, (c) s. Figure 6. Distribution of shrinkage porosity: Before improvement, After improvement. Figure is the X-ray inspection of the die castings produced by the above scheme. The defect is concentrated in the four cylinders of the largest diameter and the middle of non-uniform thickness convex platform, consistent with the simulation results. In order to obtain a more reasonable scheme, the need for further optimization.

4 Figure. X-ray inspection of the casting: cylinders, convex platform. Optimization of Process Parameters For the sake of obtaining the best solution and process parameters, an orthogonal experiment scheme is designed. Three factors are selected, as follows: pouring temperature, mold temperature and injection velocity. At the same time, every scheme is simulated and analyzed. Table is the factors and levels. Table. Orthogonal experiment. Factors Levels Pouring temperature [ C] Mold temperature [ C] Injection velocity [m/s] A B C The volume sum of shrinkage porosity is taken as an index, the lower the index, the more reasonable the scheme, the better the quality of the casting. Moreover, the range analysis of the simulation results is conducted. Table 3 shows the results of orthogonal experiment and range analysis. Table 3. Results of orthogonal experiment and range analysis. Levels Factors A B C Vacant column The volume sum of shrinkage porosity [cm 3 ] L L L L L L L L L K1 K K3 K 1 / Index summation The average of

5 K/3 K3/3 Range the sum of indexes By analyzing the simulation results of orthogonal experiment, the volume sum of shrinkage porosity of scheme 3 is the least. Namely, when pouring temperature is 660 C, preheated temperature of the mold is 0 C, injection velocity is.0 m/s, the quality of die casting is optimal. Meanwhile, by range analysis of the simulation results, it can be concluded that injection velocity have the greatest influence on the test results, the smallest is preheated temperature of the mold. The use of the best parameters for production, the die castings isn t appear cold shut, misrun, cracks and other defects. Figure 8 shows the X-ray inspection, the volume of shrinkage porosity of the cylinders and convex platform is lower. Through the prediction of defect position that casting may occur, playing a guiding role in the actual production and improve quality of the casting. Figure 9 is the die-casting. Figure 8. X-ray inspection of the optimized casting: cylinders, convex platform. Figure 9. Die castings: with gating system, without gating system. Conclusion In this paper, through the simulation and optimization of pouring scheme, the die castings of excellent quality were finally obtained.the three conclusions were drawn in the following: (1) According to the structural characteristics of the shell, the ProCAST is used to simulate different scheme designed. Based on the comparison of filling process for each scheme, the most reasonable solution is obtained. () On the basis of the pouring scheme, the overflow system was added. The result of simulation shows that the volume sum of shrinkage porosity gets to decrease, indicating that the placement of the overflow tank is reasonable. 6

6 (3) The process parameters were optimized by orthogonal experiment. When pouring temperature, preheated temperature of the mold and injection velocity is 660 C, 0 C and.0m/s respectively, the volume of shrinkage porosity of the casting reach to the lowest level and the quality is the best. From the range analysis, it can be seen that injection velocity have the greatest influence on the test results, the smallest is preheated temperature of the mold. Acknowledgments This research was supported by granted from The National Key Research and Development Program of China (No YFB ). References [1] Y. Lu, F. Taheri, M.A. Gharghouri, H.P. Han. Experimental and numerical study of the effects of porosity on fatigue crack initiation of HPDC magnesium AM60B alloy, J. Journal of Alloys and Compounds. 0 (009) [] Cato Døruma, Odd Sture Hopperstad, Odd-Geir Lademo, Magnus Langseth. Numerical modelling of the structural behaviour of thin-walled cast magnesium components using a through-process approach, J. Materials and Design. 8 (00) [3] B.D. Lee, U.H. Baek, and J.W. Han. Optimization of Gating System Design for Die Casting of Thin Magnesium Alloy-Based Multi-Cavity LCD Housings, J. Journal of Materials Engineering and Performance. 1 (01) [] J.P. Weiler, J.T. Wood. Modeling fracture properties in a die-cast AM60B magnesium alloy II-The effects of the size and location of porosity determined using finite element simulations, J. Materials Science and Engineering A. 5 (009) 3-3. [5] B.H. Hu, K.K. Tong, X.P. Niu, I. Pinwill. Design and optimisation of runner and gating systems for the die casting of thin-walled magnesium telecommunication parts through numerical simulation, J. Journal of Materials Processing Technology. 105 (000) [6] You Lu, Farid Taheri, Michael Gharghouri. Study of fatigue crack incubation and propagation mechanisms in a HPDC AM60B magnesium alloy, J. Journal of Alloys and Compounds. 66 (008) 1-. [] C. Dørum, O.S. Hopperstad, O.-G. Lademo, M. Langseth. Numerical modelling of the structural behavior of thin-walled cast magnesium components, J. International Journal of Solids and Structures. (005) [8] Hong Yan, Wenwei Zhuang, Yong Hu, Qiansheng Zhang, Hong Jin. Numerical simulation of AZ91D alloy automobile plug in pressure die casting process, J. Journal of Materials Processing Technology (009) [9] C. Dørum, O.S. Hopperstad, T. Berstad, D. Dispinar. Numerical modelling of magnesium die-castings using stochastic fracture parameters, J. Engineering Fracture Mechanics. 6 (009) 3-8.