Semi solid die casting has the characteristics of low forming temperature, long mold life, small solidification shrinkage of castings, and excellent performance. However, due to issues in the design of the semi-solid rheological die-casting process, the product is prone to defects such as gas entrapment, shrinkage, and porosity. The filling and solidification process of A356 aluminum alloy block semi-solid die casting was numerically simulated using casting simulation software. The flow field and velocity field during the filling process were analyzed, and three sets of semi-solid die casting process parameters were designed. The optimal process parameters for block semi-solid die casting were determined through experiments, and qualified block castings were produced.

Graphic and textual results

The pressure block is a relatively simple component with uneven wall thickness. The three-dimensional diagram of the pressure block is shown in Figure 1. The component has a symmetrical surface structure; There is a blind hole with a diameter of 9mm on the side, which needs to be formed by side core pulling; At the connection between the two side walls and the curved wall, there is a significant difference in wall thickness, which can easily lead to stress concentration and defects such as shrinkage, porosity, and thermal cracking during the cooling process. When designing the cross-sectional area of the sprue, it should be larger than that of liquid die casting, and its thickness is generally about 50% of the wall thickness of the die casting. Side gates are used in the design of block die-casting parts. According to the calculation, the cross-sectional area of the sprue is 52.5 square meters, with a thickness of 1.5 millimeters and a width of 0.7 times the side length of the casting, which is 35 millimeters.

Based on the structure and simulation analysis results of the block casting, a semi-solid die-casting mold for the block casting was designed, as shown in Figure 8. Semi solid die-casting molds are structurally similar to general die-casting molds. Before production, the mold needs to be fully preheated. Due to the lower temperature and shorter solidification time of semi-solid molds, the preheating of the mold is higher than that of liquid die-casting molds, generally at 280-300 ℃. Heating elements and temperature measurement holes need to be designed on the moving and fixed mold sleeve plates, and thermocouples need to be installed for temperature measurement to control the mold temperature. At the same time, it is required that the temperature of each part of the mold is uniform and stable.

1. Moving mold seat plate 2. Cushion block 3. Push plate 4, 20, 23. Push rod 5. Limit nail 6. Push rod fixing plate 7, 11, 16. Screw 8. Push plate guide column 9. Push plate guide sleeve 10, 18. Pin 12. Support plate 13. Moving mold insert block 14. Moving mold sleeve plate 15. Fixed mold sleeve plate 17. Fixed mold seat plate 19. Reset rod 21, 22. Core 24. Fixed mold insert block 25. Pouring mouth sleeve 26. Moving mold gate insert block 27. Fixed mold gate insert block 28. Fixed mold guide sleeve 29. Fixed mold guide column 30. Heating system

(1) According to the structure of the block casting, a pouring system for semi-solid die casting of the block was designed. Through numerical simulation, the pouring system was filled smoothly and defects were reduced.
(2) The cross-sectional area of the sprue in the semi-solid die-casting mold is larger than that of the sprue in the liquid die-casting metal, and the thickness of the sprue in the block is 50% of the casting wall thickness.
(3) The process parameters for preparing semi-solid slurry are as follows: stirring temperature of 580 ℃, stirring current of 450A, stirring frequency of 6Hz, and stirring time of 25min. The quality of the pressed block produced by die-casting is good.

Author of this article:
Xiao Shilong
School of Art and Design, Shenyang University of Technology
Huang Yong'an, Chen Zhen, Du Xiaoming, Meng Zhaoxin
School of Materials Science and Engineering, Shenyang University of Technology
This article is from the magazine "Special Casting and Nonferrous Alloys",
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