| Electromagnetic riveting is a new type of connection technology developed on the basis of electromagnetic forming,it is widely used in the fields of aviation and automobile.Compared with the conventional riveting,the electromagnetic riveting has the advantages of fast forming,stable quality,small noise and so on.Because of the high impact energy,the large-diameter rivet can be riveted by electromagnetic riveting.In this paper,from the point of theory analysis,the induction current and riveting impact force in the electromagnetic riveting process are mainly studied,and the deformation and stress state of the rivet are solved by the deformation boundary condition of rivet,so that the interference quantity of the riveted test piece is distributed along the axial direction.Finally,the feasibility of double-head riveting is explored.Firstly,according to the principle of electromagnetic riveting,the electromagnetic riveting coil is simplified into a double-coils model.In order to reduce the calculation error,the driving piece is considered as five independent ring coils,and the inductance and mutual inductance of the coil are calculated by introducing the inductance calculation formula.And substituting it into the voltage balance equation to obtain the induced current on the driving plate,the riveting impact force can be obtained according to the ampere law.The calculation results show that the current distribution in the driving piece is not uniform,the induced current of the half area of the radius is the smallest,the current law of the current induced by the current in the region adjacent to the driving piece is consistent with the current law of the discharge equipment,and the obtained riveting impact force is approximately sinusoidal.The law and the theory of the measurement of impact force are basically consistent with the theory.In order to obtain the interference quantity of the electromagnetic riveting specimen,in this paper,the propagation of the stress wave in one-dimensional model and the space-symmetric model are analyzed from the angle of the stress wave,and the electromagnetic impact force is substituted into the boundary condition of the rivet in combination with the basic theory of the stress wave.According to the theory of thick-wall cylinder under dynamic load,the radial displacement rule of rivet particles is calculated,and the radial displacement and stress expression of rivet are obtained according to the principle of volume invariant and the upper boundary method,and finally,the law of the interference quantity along the axial distribution is obtained and verified by experiments.The calculation and experimental results show that the interference quantity is unevenly distributed along the axial direction,and the near-interference quantity from the impact end is larger.According to the defect that the interference quantity is uneven in rivet distribution,the electromagnetic riveting process is improved,and the quasi-static and electromagnetic device of electromagnetic double-head riveting is designed.Three riveting specimens are analyzed from the tensile,shear and fatigue properties of the riveted joint,and three riveting modes of rivet interference are compared in the axial distribution.The microstructure of two studs is observed through metallographic experiment.The experimental results show that the quasi-static double-head riveting has obvious buckling phenomenon during the experiment,not obviously promoted in the performance,while the performance of the electromagnetic double-head riveted joint is riveted by the electromagnetic single-head and is relatively uniform in the interference quantity distribution,which is of great significance to the application of electromagnetic double-head riveting. |
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