Research On Electromagnetic Forming Of Thin-walled Sheet Based On The Inner-field Uniform Pressure Actuator

Thin-walled and hollow lightweight alloy sheets can greatly improve the carrying capacity and performance of the equipment and have a wide application prospect in new energy vehicles,hydrogen energy fuel cells,and other fields.However,the traditional quasi-static forming process used to process such components tends to result in wrinkle,rupture,and other defects,leading to poor forming quality,high manufacturing cost,and other problems.As a non-contact high-speed forming process,electromagnetic forming technology has unique advantages in improving the material forming limit and reducing the wrinkling and spring-back of workpieces,which provides an important technical way to solve the shortcomings of the existing thin-walled light-alloy sheet metal forming process.However,as a typical structure actuator,the traditional uniform pressure actuator(UPA)has the problems of coil strength and contact arcing,and the uniform pressure electromagnetic forming process also lacks systematic analysis,which restricts its wide application.Aiming at the above problems,the electromagnetic forming technology based on the inner-field UPA and its application in thin-walled sheet forming have been systematically studied and the relevant results have important theoretical guiding significance and practical application value for the in-depth understanding of the process of uniform pressure electromagnetic forming and promoting the development of electromagnetic forming technology.In terms of structure design,a new type of inner-field UPA is invented,which solves the contact arc and coil strength problems of the traditional UPA.The new structure puts the forming coil externally and the conductive channel and the workpiece internally,which can generate mutual squeezing electromagnetic force between the workpiece and the conductive channel,effectively solving the contact arc problem of the traditional UPA.At the same time,this structure provides an open and reinforced space for the inner-field UPA to ensure that it has higher coil strength and service life.Simulations and experiments show that under the same discharge energy and coil size,the workpiece magnetic field,workpiece induced current and workpiece forming depth of the inner-field UPA are increased by 25%,22% and 60%respectively compared with the outer-field UPA.In terms of theoretical analysis,the full analytical modeling and analysis of the electromagnetic process based on UPA are realized.Among them,the functional relationship between circuit parameters and coil current,workpiece current,workpiece electromagnetic force,and the corresponding peak value is established based on the equivalent circuit method,which provides a theoretical basis for the regulation of circuit parameters of the forming system.Based on the mirror image method,the analytical expressions of the magnetic pressure on the workpiece surface and the electromagnetic force of the coil wire with the geometric size and coil current as variables are obtained.The fundamental reason for the high forming efficiency of the inner-field UPA and the effect of the coil turn spacing on the magnetic pressure distribution on the workpiece is described.Based on the method separation of variables,the analytical expressions of induced current,magnetic field intensity,and electromagnetic force at any point inside the workpiece are given with geometric size,coil current,and material electrical parameters as variables.The effects of parameters such as conductivity and thickness of workpiece on the time-space characteristics of the workpiece electromagnetic force are revealed.In terms of forming process and application research,the uniform-velocity method(UVM)for thin-walled sheet metal and the corresponding experimental device are proposed,and research on 100 μm thick titanium bipolar plate forming and titanium plate blanking is carried out.Firstly,a three-dimensional finite element model of circuit-magnetic field-structure dynamic coupling of the UPA is established.Experiments and simulations show that there is a uniform velocity range in the forming process,which can realize the uniform pressure forming of thin-walled plates.and the proportion of this interval to the length of the workpiece is negatively correlated with the forming height.On this basis,the structural mechanical stability and influence analysis of the traditional and new UPAs are compared.The research shows that there is an optimal coil height to maximize the electromagnetic force of the workpiece.the failure mechanism of the traditional UPA lies in the fracture of the end of the workpiece or the opening of the contact area,and the Zylon composite fiber can effectively share the stress of the coil wire of the inner-field UPA.Finally,based on this device,the machining of titanium bipolar plate with a maximum channel depth of 0.32 mm and a minimum channel fluctuation of 3.75% titanium bipolar plate and the punching of titanium plate with a 3 mm radius hole are realized under discharge energy 7.5 k J,which proves the feasibility of the inner-field UPA and the UVM method.Finally,the work of this dissertation is summarized and the future work is prospected.