| With the rapid development of the global railway transportation industry,people pay more and more attention to the problem of excessive energy consumption.The adoption of light and efficient structure and advanced welding technology has created a broad space for the energy conservation and emission reduction of China’s railway system.Friction stir welding(FSW)is a new solid-phase bonding technology,which has been widely used in the welding of aluminum alloy body.Needle less friction stir welding is a new welding technology developed on the basis of needle friction stir welding.Its weld shape is beautiful and avoids the keyhole defect at the end of the weld.This method improves the service life of the stirring head and can well avoid the defects of conventional FSW technology in welding aluminum alloy sheet,so as to obtain high-quality welded joints.With the development of computer numerical simulation technology,focusing on the state and fluidity of plastic materials during welding through simulation has splendid research significance for evaluating the welding effect of materials.The heat flow coupling model of friction stir welding process is established based on hydrodynamics.The welding solid model is established by using the three-dimensional modeling software,and the flow field is meshed by using the pre-processing module of the fluid simulation software.After setting the fluid boundary conditions by the finite element simulation software,the flow of plastic metal materials in the welding process is simulated.Comparing the simulated temperature field and flow field with the experimental results respectively,the maximum error between the simulated temperature and the experiment is 33.8k,and the maximum relative error is 4.5%.The weld morphology is consistent with the simulation results,which proves that the modeling is reasonable and reliable.By studying the effects of the shape of the shoulder of the stirring head and process parameters on the fluidity of the plastic metal in the process of FSW welding,the specific flow law of the material around the stirring head can be obtained.Six different shoulder shapes are designed and simulated,among which the concentric circular shape has the best fluidity.Combined with the law of minimum resistance in plastic forming,the correlation between shoulder groove and fluidity is preliminarily explained.Then six concentric shoulder shapes are designed,and it is found that the effects of different concentric shoulder shapes are still different.Further,the influence of shoulder shape on fluidity is explained from the perspective of flow channel change,and the results are in line with the continuity theorem of fluid.At the same time,the refinement research on the number of blades of fan-shaped shoulder and triangular shoulder is carried out.It is found that increasing the number of blades can stimulate the flow of plastic metal.According to the principle of "stirring extrusion suction",the reason for the circular flow of plastic metal in the closed space during welding is demonstrated.Finally,the simulation study of process parameters is carried out.In the same case,when the welding angle and welding speed are 2.5 ° and 1000 rpm respectively,the weld shape is beautiful and the welding effect is the best.The study of fluidity has important guiding significance for revealing the weld forming mechanism,predicting the formation of defects and optimizing the design of mixing head. |
