| High-performance light-weight sheet and tube parts as well as their manufacturing technology occupies a pivotal position in the field of advanced manufacturing,which is an important safeguard of achieving light-weight equipment for enhanced performance,energy conservation and environmental protection.Light-weight materials,represented by Aluminum Alloy,have a poor forming performance using the traditional quasi-static stamping process,such as easy fracture,large springback and poor surface quality.Electromagnetic forming with high-speed,non-contact and single-die features is considered to be one of the most promising methods to solve these problems.However,the existing electromagnetic forming has not formed a perfect system for both theories and of technologies.Therefore,the expected effects have not been obtained in the field of sheet and tube forming,and the performance of the device and the process level still need deeper study.On this basis,a systematic study of electromagnetic tube bulging-drawing forming is carried out through investigating numerical method,forming setup and deformation behavior of 6063 aluminum alloy tube,in order to promote the development of electromagnetic forming technology.First of all,constructing an effective numerical simulation method of electromagnetic forming is important to promote the application and development of electromagnetic forming.Therefore,the mathematical models and finite-element models of equivalent circuit,electromagnetic field and structure field are expounded in this paper,and the shortages of loose coupling method and sequential coupling method based on pure finite-element analysis in accuracy and convergence are analyzed.On this basis,a novel mathematical model based on the current filament method and finite-element method is proposed and is implemented through scientific calculation software MATLAB and finite-element software ANSYS.On the one hand,the numerical method considers the coupling between excitation current,electromagnetic force and tube deformation behavior,which improves the calculation precision.On the other hand,because the calculation of electromagnetic field is realized through current filament method based on the principle of equivalent circuit,instead of finite-element method,the problem of air mesh distortionunder the condition of large deformation is avoided in coupling solution of electromagnetic field and structure field.It provides an effective simulation method for the numerical simulation of the electromagnetic tube bulging in the following chapters,and a new method for electromagnetic simulation of other tube and sheet parts.Secondly,the development of high-performance electromagnetic forming device is the premise of experimental researches and process exploration for electromagnetic forming.Therefore,in view of the problems of low forming ability and poor controllability of the existing electromagnetic forming device,the idea of designation in pulsed high magnetic field device is adopted for developing electromagnetic tube expansion device,which can effectively improve the performance level of the device.For example,the thermal performance of coil and working life of pulsed capacitor bank can be improved through the optimization of circuit topology by introducing crowbar circuit;Based on the high power switching semiconductor device(thyristor)and time-control system,the connection of the multi-coil and multi-power supply is realized,which provides an important technical approach for the generation and regulation of specific forming magnetic fields;Based on the strengthening technology and winding process of high-field pulsed magnet,the mechanical strength of the forming coil is effectively improved.On this basis,an experimental system with multi-coils and multi-power supply is set up,which can realize the generation and control of two or multi-direction forming magnetic fields,and provide the device platform for experimental studies in the following chapters.Meanwhile,it could be useful as guidance for the development of similar electromagnetic forming machines.Finally,the study of the forming behavior of workpiece under different conditions could play an important role in improving and optimizing the forming device and process.Therefore,(1)the paper carried out the numerical and experimental studies of electromagnetic tube bulging-drawing forming under single coil and single power system.It is found that the distribution of electromagnetic force on tube is related to the height ratio of the coil and the tube,which directly determines the forming behavior of the tube.In the electromagnetic bulging system with a single coil,the electromagnetic force acting on tube has a single distribution and poor controllability,resulting in the tube can not meet the requirements of deformation depth and material flow at the end of tube.With theincrease of initial discharge voltage,when the coil length is less than or equal to the length of the tube,the tube will break up;while the bottom "fit" phenomenon will appear when coil length is greater than the tube,which makes it difficult to further increase the deformation depth of tube.In addition,the friction force will also affect the deformation depth and the material flow at the end of tube,and the influence of the friction force on the electromagnetic bulging depends on the distribution of the radial electromagnetic force on tube.(2)the paper carried out the numerical and experimental studies of electromagnetic tube bulging-drawing forming under multi-coils and multi-power systems.In order to improve the forming ability and controllability of forming system using single coil and single power system,the triple-coil electromagnetic tube forming technique and the background field assisted forming technique are proposed and carried out.It is found that for the triple-coil forming system,the axial force and radial electromagnetic force acting on the tube can be independently controlled by the up-down coil group and the central coil with the aid of two sets of independent pulse capacitor power supply,in which the up-down coil group consists of two coils on the lower and upper ends of the tube.Thus this can improve the bulging behavior.For the background field assisted electromagnetic bulging system,to obtain the same bulging depth of tube,the discharge voltage,current and force level in the forming coil can be effectively reduced,and then can improve the working life of the capacitor,coil and thyristor switches. |
PDF Full Text Request