Electromagnetic Tube Bulging Research Articles

Electromagnetic tube bulging due to axial pressure produced with a rigid drive block

Electromagnetic tube bulging due to axial pressure produced with a rigid drive block

Electromagnetic Force Distribution and Wall Thickness Reduction of Three-Coil Electromagnetic Tube Bulging With Axial Compression

In the conventional electromagnetic tube expansion, tube wall thickness tends to decrease significantly while the workpiece is expanded. This paper is aimed at introducing a new technique using three-coil electromagnetic tube bulging with axial compression as an innovative solution for this issue. To validate the feasibility of the proposed technique and investigate the electromagnetic force distribution along the workpiece, COMSOL software is used to construct a detailed finite element analysis model for the proposed electromagnetic coupling model. Results show that the ratio of the axial and the radial electromagnetic forces increases linearly with the increase of the height and the outer diameter of the top and bottom coils. Furthermore, the tube deformation profile and the wall thickness are compared with two different coil structures. Comparison analysis reveals that for the same axial to radial electromagnetic forces ratio, the effect of prohibiting the wall thickness reduction using different coil structures is quite similar. The new method is expected to have a good potential in enhancing the tube-forming performance.

Investigation of the electromagnetic attractive forming utilizing a dual-coil system for tube bulging

The electromagnetic force between the tube and the coil is generally dominated by repulsive Lorentz force in the existing electromagnetic tube forming systems. In these cases, the coil has to be placed inside the tube for tube bulging, which makes it difficult to achieve when the inner space of the tube is not large enough to accommodate the coil. To solve this problem, a new electromagnetic tube bulging process with an external dual-coil system was developed in this work. According to both numerical and experimental studies, it has been demonstrated that the AA6061-O aluminum alloy tube with a diameter of 33 mm and a thickness of 1 mm can be attracted toward the coil, and the maximum deformation is more than 4 mm after a single discharge. Meanwhile, the tube deformation can be significantly increased by multiple discharges using the attractive forming process. Furthermore, a series of simulations and experiments were carried out to systematically investigate the attractive forming behavior of the tube under different discharge conditions, showing that the discharge voltages of the two coils and the current waveform controlled by a crowbar circuit have a great impact on the tube forming.

Cladding of aluminum alloy 6061-T6 to mild steel by an electromagnetic tube bulging process: finite element modeling

Bimetal tubes have useful applications in various industries where service conditions demand more different requirements in the tube core than its outside surface. The recent use of electromagnetic forces to deform or join metallic workpieces at high speeds has undergone rapid growth for materials processing. However, to date, no sufficient systematic understanding of the underlying principles of a subsequent high-speed electromagnetic tube bulging process to manufacture bimetal tubes has been gained. In this work, magnetic pulse cladding of Al/Fe clad bimetal tubes was analyzed by finite element modeling (FEM) using ANSYS software. The validity of FEM analyses was first confirmed by experiments in terms of the deformed shape. Second, the effect of cladding parameters (such as axial feeding being the dominant factor in the multi-step process) on the bulging and thinning behavior of the Al clad tube was presented in detail. Both the numerical simulation and experimental results show that no more than 70% of the bulging-coil length is an appropriate amount for the feeding length to prevent defects from being introduced by non-uniform deformation in the transition zone of the Al clad tube. The distributions of the magnetic flux line, magnetic force, and plastic strain in different cladding steps were then analyzed. It was concluded that during the multi-step cladding process, there was an uneven distribution of the magnetic field force along the transition zone. Consequently, inharmonious plastic deformation behavior occurs, which results in a limited acceleration of the transition zone to a certain impact velocity.

Effect of coil length and relative position on electromagnetic tube bulging

A loose coupling method is adopted to study electromagnetic tube bulging, and effect of processing parameters on electromagnetic tube bulging is analyzed. The results show that critical relative length increases with the increasing of coil length, when coil approaches infinite length, critical length approximates 1. With the rise of relative position, radial magnetic pressure acting on the top end of tube increases, when relative position is equal or greater than 30 mm, radial magnetic pressure of tube top end remains unvaried. Relative position of 30–50 mm is optimal position for electromagnetic tube flanging.

Tube bulging process using multidirectional magnetic pressure

The ANSYS software was used to establish an electromagnetic-structural coupling model and simulate the electromagnetic tube bulging process. Compared to the experimental results, the maximum simulation error was approximately 4 % at the longitudinal center of the tube. Then, the simulation method was used to analyze the effects of multidirectional magnetic force on the tube bulging process. The results indicate that an axial magnetic force can be generated at the tube end by setting the coil at the end of the tube. The values of material flow, stress, plastic strain, and thickness in different forming processes were compared. Compared to traditional forming processes, electromagnetic tube bulging with multidirectional magnetic pressure can significantly increase the axial feeding, decrease the tensile stress, and reduce the thickness at the easily broken position. Therefore, a higher bulging height can be obtained by the new method.

Electromagnetic forming process: estimation of magnetic pressure in tube expansion and numerical simulation

Electromagnetic forming (EMF) is a non conventional metal working process that relies on the use of electromagnetic forces to deform metallic workpieces at high speeds. This study is divided out into three parts. The first part presents a method for calculating the process parameters; namely the electromagnetic problem. An in-house code written in FORTRAN is developed for the electromagnetic tube expansion. In the second part, the results obtained from the in-house code are compared with those obtained from the free finite element magnetic software FEMM. In addition to this verification, the results of the in-house code are compared with the experimental ones available in the literature. The in-house code is then introduced in the finite element commercial code ABAQUS/ Explicit. The third part presents the simulation of the electromagnetic tube bulging forming process for metal tubes using ABAQUS/Explicit with an axi-symmetric model. The simulations have been carried out for Al 1050 aluminium tubes of 1.0mm thickness. This part also provides the comparison between the numerical simulations and the available experimental studies in the literature. Finite element simulations of the tube expansion predicted the experimental trends.

Effect of tube size on electromagnetic tube bulging

The commercial finite code ANSYS was employed for the simulation of the electromagnetic tube bulging process. The finite element model and boundary conditions were thoroughly discussed. ANSYS/EMAG was used to model the time varying electromagnetic field in order to obtain the radial and axial magnetic pressure acting on the tube. The magnetic pressure was then used as boundary conditions to model the high velocity deformation of various length tube with ANSYS/LSDYNA. The time space distribution of magnetic pressure on various length tubes was presented. Effect of tube size on the distribution of radial magnetic pressure and axial magnetic pressure and high velocity deformation were discussed. According to the radial magnetic pressure ratio of tube end to tube center and corresponding dimensionless length ratio of tube to coil, the free electromagnetic tube bulging was studied in classification. The calculated results show good agreements with practice.

Simulation of electromagnetic tube bulging based on loose coupling method

A loose coupling method is used to solve the electromagnetic tube bulging. ANSYS/ EMAG is used to model the time varying electromagnetic field with the discharge current used as excitation, in order to obtain the radial and axial magnetic pressure acting on the tube, the magnetic pressure is then used as boundary conditions to model the high velocity deformation of tube with DYNAFORM. The radial magnetic pressure on the tube decreases from the center to the tube end, axial magnetic pressure is greater near the location equal to the coil height and slight in the other region. The radial displacement of deformed workpieces is distributed uniformly near the tube center and decreases from the center to the end; Deformation from the location equal to coil height to the tube end is little. This distribution is consistent with the distribution of radial pressure; Effect of the axial magnetic pressure on deformation can be ignored. The calculated results show well agreements with the experimental results.

Effects of Various Working Conditions on Tube Bulging by Electrode Contact Method.

Optimum forming conditions of electromagnetic tube bulging using direct electrode contact methods are analytically and experimentally investigated. In this paper, the effects of changing the forming conditions such as the length of electrode, the capacitance of capacitor bank and charged energy are simulated by FEM for deformation and forming efficiency, and these results are in good agreement with the experimental ones. The forming mechanism is clarified. As the capacitance of capacitor bank and the length of electrode increase, the amplitude of current waves decrease and the period of current increase. The bulge height is reduced when the electrode length increase, but the forming efficiency increase with the electrode length increasing. The larger the capacitance of capacitor bank, the longer the electrode length, the higher the forming efficiency.

Electromagnetic Tube Bulging by Direct Electrode Contact.

A method of electromagnetic tube bulging by direct electrode contact is studied. The magnetic pressure is produced by a huge impactive electric current which passes through the electrode contact and the tube. The current is generated by the transient phenomenon of discharge on the condenser bank. An analysis of tube bulging is made using the finite-element method, and a formulation of the finite-element method based on the axisymmetrical membrane shell theory is developed. Impulsive magnetic pressure is assumed as an internal pressure load. The acceleration, velocity and displacement, and the (final profile and strain distribution are given. These agree approximately with experimental values.

The effect of a field shaper in electromagnetic tube bulging

The results of experiments into the use of a field shaper for the bulging of a tube are presented and the major factors determining the final profile of the tube and the capability of the control of forming to achieve the desired profile are discussed. It is shown that an approximate prediction of the bulged shape can be given by the combination of the geometry of the field shaper and the charged energy in the condensor bank. The field shaper is usually applied to localized deformation, so that the efficiency of the process drops: however, it has great advantage in the prevention of mechanical failure of the forming coil, and is a useful and practical tool for the process.