Coupler is the connecting device of rail vehicles. It needs to ensure that the connected carriages at both ends do not move horizontally and longitudinally. It is a key part to ensure the safe operation of trains. As the core bearing part of locomotive set connection, the stress state of coupler is complex and changeable, and it is affected by large impact, tension, compression and torque during operation. From the actual failure situation, fatigue failure is the main failure form of coupler. With the development of train design towards high speed, the train connecting device will bear greater random alternating load when it works. Zhu Tao of Southwest Jiaotong University and others have studied the quasi-static force analysis and longitudinal load distribution law of the coupler, pointing out that the root part of the traction flange under the coupler tongue is the most loaded part, the connecting part between the coupler head and the coupler tongue will bear the main alternating load, and the high stress parts of the coupler tongue, coupler lug, coupler body lock box, coupler yoke rear corner and so on are prone to fatigue, which plays a decisive role in the overall quality of the coupler. As a near net shape technology, investment casting is suitable for forming parts with complex cavity and structure. It has the characteristics of high dimensional accuracy and low surface roughness. However, investment casting of complex parts is easy to form shrinkage cavity, crack and other defects, resulting in high scrap rate. In actual production, the application of numerical simulation technology to simulate the forming process of investment castings and improve the quality of investment castings has become the most scientific and effective technical method. The optimal design of gating system and process parameters can ensure higher quality products. Many scholars at home and abroad have studied the investment casting process, which can accurately locate the location and shape of investment casting defects by means of CAE simulation and X-ray detection. By comparing the gating systems with different structural designs, analyzing the forming effects of different gating systems, determining the core process parameters such as pouring temperature, flow and heat transfer coefficient, and obtaining more reasonable riser design and sprue size parameters. It can be seen that the design of gating system and the selection of parameters have an important impact on the quality of investment casting products. In the actual production process of the coupler, the intersection of the coupler tongue and the coupler head will be prone to a certain degree of cracks, shrinkage and porosity defects. The micro cracks and small shrinkage porosity at the key parts of the coupler parts must be removed and welded for repair in the post-treatment process, while the investment castings with serious cracks, large shrinkage cavities and other casting defects will be directly scrapped, which not only increases the production cost and reduces the efficiency, but also makes the service performance of the parts uncontrollable. Therefore, this paper takes an investment casting coupler as the research object, uses ProCAST software to simulate the mold filling and solidification process of investment casting, and optimizes the gating system to eliminate the defects of key parts of investment casting and improve the yield.
1) Although the pouring scheme a of horizontal one-sided gate can ensure the complete filling of the mold cavity of investment casting, serious shrinkage casting defects will appear after solidification of important parts of investment casting, and the casting quality is not up to standard.
2) For the two-sided sprue scheme B of the investment casting, the mold filling in the mold cavity is stable and basically presents the sequential solidification mode, and the shrinkage cavity in the key parts of the investment casting disappears. During the solidification process, the stress in the abdomen of the coupler is the largest, and the stress in the thinner part of the edge is small, only about 200MPa. The overall investment casting stress is not high and the crack tendency is small.
3) The maximum tensile strength of the product trial produced under gating system scheme B is 675mpa, and the microstructure and properties meet the requirements. Through numerical analysis and gating system optimization, the problems of shrinkage cavity and crack defects in key parts of investment casting are solved, and the yield is improved.