With the continuous development of science and technology, the structure of parts is becoming more and more complicated. When using traditional casting technology to produce parts, the design and manufacture of molds will spend a lot of time, increasing the production cycle and research and development costs. The use of additive manufacturing technology can directly form complex-shaped sand molds through computer-aided design models, which has a huge impact on the casting industry. However, the current sand mold 3D printing is mainly to improve efficiency and reduce costs, but it does not have much impact on the performance of castings.
Recently, Santosh Reddy Sama of the School of Mechanical and Nuclear Engineering at Pennsylvania State University in the United States and others proposed a design rule for a complex gate system based on 3D printing technology to improve the casting performance of castings. The working principle of this technology is: for a given pouring condition, the data of the conical spiral and parabolic gate contour are calculated based on the Bernoulli equation, and the optimal parameter contour shape is finally obtained by using the constrained optimization algorithm with the parameters of the contour.
When designing the gate outline shape, it should be based on casting fluid dynamics, so that the gate outline shape meets three conditions to reduce casting defects. First, the velocity of the fluid at the bottom of the gate should be less than the minimum critical velocity (0.5m/s); second, the length of the gate should be minimized to reduce heat loss and allow sufficient time for the generated bubbles to escape the mold; finally, it should be avoided Sudden change in gate cross section or gate and runner junction.
The researchers used the Viridis 3D RAM printer to create different gates and molds, with a layered thickness of 0.4mm, and the raw materials were ViriCast powder and CSTRed adhesive produced by Viridis 3D. The 17-4 stainless steel alloy was cast at 2950°F to obtain parts.
(as shown in Figure 3 ). In the figure, AD is the microscopic morphology of the sample. The round black dots are oxide inclusions formed by the surface turbulence of the melt during the filling process. Observation shows that compared with straight gate castings, the inclusions of parabolic gate castings and conical spiral gate castings are reduced by 21% and 35%, respectively. The E-H is a computer tomography of the sample. From the figure, we can see that compared with the direct gate casting, the parabolic gate casting and the conical spiral gate casting reduce casting defects by 56% and 99.5%, respectively. Compare the ultimate bending strength of three samples.
(As shown in Figure 4) It can be seen that compared with straight gate castings, the strength of conical spiral gate castings has increased by 8.4%, while the strength of parabolic gate castings has increased by 4.1%.
Therefore, 3D printer technology can be used to manufacture special-shaped gates that are difficult to be manufactured by conventional methods, such as parabolic gates and conical spiral gates, which can not only greatly reduce casting defects such as inclusions, improve the yield of castings, but also greatly improve the mechanical and metallurgical properties of castings.
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