Magnesium alloy die-casting molds can form castings with high filling temperatures, complex internal cavities, long service life, easy high-temperature bonding between formed parts, and fast cooling rates. If traditional design methods are used, design workload will be large and mold design cycle will be long. At present, CAD/CAM/CAE/CAPP technology is core and key development direction of modern mold design. Using a dedicated CAD integrated system to quickly design magnesium alloy die-casting molds can not only shorten design cycle, but also improve rationality and processing accuracy of mold structure. This topic applies artificial intelligence to traditional magnesium alloy die-casting mold design, adopts development concept of big data + special magnesium alloy die-casting mold CAD system, uses VC++6.0 and Windows series windowed operating system integrated development environment to develop a magnesium alloy die-casting mold CAD integrated system based on big data analysis. System adopts Chinese interface, drop-down menu design, simple operation, and more accurate, fast and convenient die-casting mold design, which has good reference significance.
Taking magnesium alloy laptop back cover die-casting mold as an example, this paper introduces general process of rapidly designing magnesium alloy die-casting molds using a die-casting mold CAD integrated system based on big data analysis. This system can not only quickly and reasonably design side core pulling and complex cavity structure of die-casting mold, but also query relevant data of die-casting mold design. Practice has proven that this system can quickly complete design of cavity die-casting molds, and has reference value for rapid design of complex magnesium alloy die-casting molds.

AZ91D magnesium alloy laptop back cover replaces original engineering plastic. It has characteristics of low density (1.82g/cm3), high specific strength, good mechanical properties, good electromagnetic shielding, good electrical and thermal conductivity, good cutting performance, and good die-casting performance. It is one of ideal materials for back cover of laptop computers. However, it has disadvantages of large volume shrinkage (0.8%), difficulty in demoulding when opening mold, easy formation of concentrated shrinkage cavities and cracks. Geometric shape of magnesium alloy laptop back cover is shown in Figure 1. Its overall dimensions are 350mm*250mm*11mm, and average wall thickness is 0.6mm. There are holes and grooves for assembly around casting, especially if there are rectangular holes for assembly on the side, lateral core pulling mechanism needs to be considered. In order to simplify mold structure, demoulding mechanism adopts an inclined ejection method. According to design requirements, high-precision dimensions of fitting parts are selected as IT11, and the overall dimensions are selected as IT12. Minimum value of parallelism tolerance and coaxiality tolerance of die castings is 0.1mm.

 

Figure 1 3D view of laptop back cover

 

Figure 2 Specific design process of rapid die-casting mold

 

(a). Movable mold

 

(b) Fixed mold
Figure 3 Die-casting mold working parts
With guidance of rapid mold design system and visualization system, you only need to set shrinkage rate of magnesium alloy material (0.8%) to automatically generate die-casting mold working parts, including movable and fixed molds of die-casting mold, inclined slider and gating system. The entire process is automatically generated by software to avoid human errors and make mold cavity size more accurate. Mold core and cavity automatically generated by system are shown in Figure 3. In this link, big data analysis can be used. Because volume shrinkage of magnesium alloy die-casting parts is large, when castings are demoulded, castings will be difficult to demould due to large shrinkage. Forcible demoulding will cause large cracks and other defects. After construction of working parts of die-casting mold is completed, the overall mold cavity and gating system can be rounded through system software to minimize adhesion stress and avoid casting defects.

 

(a) CAD integrated system

 

 

(b) Standard mold base calling interface
Figure 4 Magnesium alloy die-casting mold CAD integrated system and standard mold base calling interface
 
 
Figure 5 Magnesium alloy die-casting mold CAD integrated system standard parts calling interface

 

Figure 6 Three-dimensional assembly diagram of die-casting mold

 

Figure 7 Two-dimensional assembly diagram of die-casting mold
1. Fixed mold base plate 2, 3, 11, 18, 19, 20, 24. Hexagon socket screws 4. Gate sleeve 5. Positioning screw 6. Fixed mold fixing plate 7. Guide pillar 8. Guide bush 9. Fixed mold Cavity 10. Moving mold core 12. Moving mold fixed plate 13. Support plate 14. Push rod 15. Push plate hexagon socket screw 16. Push rod fixed plate 17. Moving mold base plate 21. Return spring 22. Inclined top 23. Inclined Top fixed block 25.Reset lever

After the overall design of die-casting mold is completed and confirmed by mold motion interference inspection, the overall structure of die-casting mold is reviewed and verified based on big data analysis, details of die-casting mold are optimized and corrected, possible problems that may arise in later die-casting mold trial are predicted. Eliminate other design factors that cause defects in die-casting parts due to die-casting equipment and die-casting processes. When conditions permit, motion simulation and filling process simulation can be performed. After analyzing simulation results, the overall structure of die-casting mold can be optimized. After confirmation, digital manufacturing can be carried out to ensure one-time success in later die-casting mold trial. A single part can also directly generate a two-dimensional engineering drawing, which facilitates processing of a single part using traditional processing methods. The entire working process of magnesium alloy die-casting mold can be seen from two-dimensional assembly diagram. It can be seen that the overall side core-pulling mechanism of mold adopts an inclined top mechanism. Mold structure is simple, which reduces number of relatively moving parts in mold cavity and avoids damage to die-casting mold due to high cavity temperature and sintering of relatively moving parts in cavity.