Electromagnetic Metal Forming Research Articles

Evaluation of efficiency of air channel cooling of a multiple-turn coil for electromagnetic metal forming

s An efficient and safe method of air channel cooling for multiple-turn coils is proposed. Minimal discharge cycle duration for electromagnetic unit is defined for performing large number of similar electromagnetic metal forming technological operations. Keywords: electromagnetic metal forming, multiple-turn coil, cooling, vortex tube, ejector. amokhvalov.vn@ssau.ru, chernikov.dg@ssau.ru, vvz@ssau.ru

ВОЗДУШНОЕ КАНАЛЬНОЕ ОХЛАЖДЕНИЕ ОДНОВИТКОВОГО ИНДУКТОРА ДЛЯ МАГНИТНО-ИМПУЛЬСНОЙ ОБРАБОТКИ МЕТАЛЛОВ

This paper evaluates the efficiency of cooling a coil, fitted with an internal channel, for a one-turn inductor for electromagnetic metal forming, using a low-temperature air from a vortex tube, with and without an ejector. The experiment data shows that at constant pressure on the vortex tube entrance the highest cooling efficiency and intensity are reached at values β>1, where β is an ejector diaphragm to nozzle section area relation. The results show that air channel cooling of a coil for a one-turn inductor using air from vortex tube has considerably high efficiency and high safety parameters.

Inverse Identification of a Constitutive Model for High-Speed Forming Simulation: An Application to Electromagnetic Metal Forming

Forming simulation requires a constitutive model whose parameters are typically determined with tensile tests assumed static. However, this conventional approach is impractical for high-speed forming simulation characterized by high strain rates inducing transient effects. To identify constitutive parameters in relation to high-speed forming simulation, we formulated the problem of constitutive modeling as inverse parameter estimation addressed by regularized nonlinear least squares. Regarding the proposed inverse constitutive modeling, we adopted the L-curve method for proper regularization and model order reduction for rapid simulation. For demonstration, we corroborated the proposed strategy by identifying the modified Johnson–Cook model in the context of a free bulge test with electromagnetic metal forming simulation. The L-curve method allowed us to systematically choose a regularization parameter, and model order reduction brought enormous computational savings. After identifying constitutive parameters, we successfully verified and validated the reduced and original simulation models, respectively, with a manufactured workpiece. In addition, we validated the numerically identified constitutive model with a dynamic material test using a split Hopkinson pressure bar. Overall, we showed that inverse constitutive modeling for high-speed forming simulation can be effectively tackled by regularized nonlinear least squares with the help of an L-curve and a reduced-order model.

Hand-Held Magnetic Field Meter Based on Colossal Magnetoresistance-B-Scalar Sensor

This paper describes a newly developed hand-held magnetic field meter, which enables the measurement of the magnitude of pulsed, alternating, or permanent magnetic flux density in a range from 0.06 up to 10 T. The device measures the magnitude of magnetic flux density independent of the field direction (B-scalar) and its measurement frequency ranges from dc to 100 kHz. This magnetometer consists of a hand-held magnetic field measurement meter and a pluggable probe whose main element is a spintronic sensor based on the colossal magnetoresistance (CMR) phenomenon. The new design of a probe containing a temperature sensor and a CMR-B-scalar sensor made from two manganite films with different resistivity versus temperature dependences ensures a reduced response signal dependence on temperature and thus increased the accuracy of the measurements. The hand-held meter has a graphical color touch screen for the display of the waveforms and provides measurements without the use of external oscilloscopes or other analog graphing devices. This magnetometer can be used for various industrial and scientific applications such as for the investigation of high-power electrical motors, fast high electrical current transients appearing in cases of the commutation of pulsed power circuits, for the measurement of pulsed magnetic fields in magnetic coils, or for measuring the dynamics of magnetic fields during electromagnetic metal forming and welding.

Two-stage Finite Element Simulation to Predict Deformation and Stresses in Electromagnetic Formed Component

Magnesium and Aluminium alloys are desirable for the automotive and electronic appliances industries due to their high strength-to-weight ratio, corrosion resistance and weldability. However applications of the Magnesium and Aluminium alloys were very difficult due to their very low formability at room temperature, despite their advantages. One of the high speed forming technologies like Electromagnetic Metal Forming (EMF), can be a useful forming method for low formability light-weight materials such as aluminium and magnesium alloys in overcoming the limitations of conventional forming methods. EMF process refers to the high velocity and high strain rate deformation of low-formability materials driven by electromagnetic forces that are generated by the rapid discharge current through forming coil. This technology depends on the properties of the sheet metal, as well as the process parameters such as electromagnetic force in a practical forming operation which in turn depends on selection of proper shape of forming coil to get uniform and high magnitude electromagnetic force for achieving the desired deformation of the sheet. Therefore, the purpose of this research effort is to analyse the dynamic behaviour of work piece under various forming coil shapes with Magnesium alloys or composite. To achieve these objectives, Finite Element Method in two steps is used. In stage one the Electromagnetic force on the component will be estimated using ANSYS Emag/EM module of LS DYNA/ABAQUS for different combinations of the process parameters like current density, gap between coil and sheet, coil shape and the coil thickness etc. followed by application of an Optimization technique to find the best combination. The obtained force will then be applied on the component and the corresponding deformation and other performance parameters will be obtained using ANSYS Structural in second stage. The stage one numerical results are compared with analytical results to check the correctness of the developed simulated environment.

Analysis of electromagnetic sheet metal forming process: Experimental and FE study of mutual inductance and current pulse

Electromagnetic metal forming (EMF) is a high velocity forming process which uses electromagnetic body force to deform metal work piece. The challenging aspect of simulation of this process is complexity of magnetic pressure distribution and high speed deformation. Furthermore, coupling these two a spects is so important in order to analyze EMF. In this study, a simple approach has been proposed for simulation of EMF using two strong finite element commercial codes separately for modeling of electromagnetic and mechanical phenomena of this process. Another challenging aspect of this process is determination of the current pulse which is discharged into the electromagnetic actuator. So, the effect of mutual inductance on discharged current and deformation were also investigated by experiments. Validation of this numerical approach was done by comparing the measured and simulated final deflection and strain distribution.

A frequency domain approach for computing the Lorentz force in electromagnetic metal forming

In this paper we present a finite element model in frequency domain which computes the Lorentz force that drives an electromagnetic forming (EMF) process. The only input data required are the electrical parameters of the capacitor bank, the coil and the work piece. The main advantage of this approach is that it provides an explicit relation between the parameters of the EMF process and the frequency of the discharge, which is a key parameter in the design of an optimum EMF system. The method is computationally efficient because it only requires to solve time-harmonic Maxwell’s equations for a few frequencies and it can be very useful for coil design and for testing modeling conditions on complex three-dimensional geometries.

A numerical model for the search of the optimum frequency in electromagnetic metal forming

Electromagnetic forming (EMF) is a high velocity forming technique that reshapes electrically conductive materials by abruptly discharging a bank of capacitors through a coil. The oscillation frequency of the discharge is a key parameter in the design of an EMF system. For a given initial stored energy, there exist a frequency that produces the maximum workpiece deformation. Once we know it, we can set the electrical parameters of the EMF system to make the current intensity oscillate with this optimum frequency. This saves energy and money, preventing also the premature wearing of the coil. The objective of the present paper is to find the optimum frequency of an EMF system. Using the results provided by a finite element model in frequency domain, we are able to obtain the current flowing trough the coil, the Lorentz force acting on the workpiece, a function relating the electrical parameters of the EMF system with frequency and the optimum frequency of the discharge. Our approach can be very useful for coil design and for modeling complex three-dimensional geometries. To validate the method presented here, we apply it to tube compression and tube expansion processes and compare our results with those provided by other authors.

Introduction of an Electromagnetism Module in LS-DYNA for Coupled Mechanical-Thermal-Electromagnetic Simulations

A new electromagnetism module is being developed in LS-DYNA for coupled mechanical/thermal/electromagnetic simulations. One of the main applications of this module is Electromagnetic Metal Forming. The electromagnetic fields are solved using a Finite Element Method for the conductors coupled with a Boundary Element Method for the surrounding air/insulators. Both methods use elements based on discrete differential forms for improved accuracy. The physics, numerical methods and capabilities of this new module are presented in detail as well as its coupling with the mechanical and thermal solvers of LS-DYNA. This module is then illustrated on two Electromagnetic Metal Forming cases, the forming of an aluminum sheet on a conical die using a spiral coil, and the forming of an aluminum sheet on a v-shaped die using a “double pancake” coil. The experimental setups are presented as well as comparisons between experimental and numerical results.

Coupling Experiment and Simulation in Electromagnetic Forming Using Photon Doppler Velocimetry

Modeling electromagnetic forming processes is in many ways simpler than modeling traditional metal forming processes. In electromagnetic forming the problem is often dominated by inertial acceleration by a magnetic field. This is a much better posed problem than the more traditional ones that are often dominated by complex three dimensional constitutive behavior and frictional effects. However, important aspects of the problem are dominated by the constitutive properties of the material, and often electromagnetic forming is performed in a regime where there is little reliable material strength data. Strain rates are often high (10 2 to 10 4 s -1 is the typical range for electromagnetic forming). Also, heat is generated both by ohmic heating as well as by plastic deformation, and peak temperatures can be quite high. Also, while hightemperature, high-strain-rate data is scarce, there is little or no data in cases where temperature rises significantly over very short times (tens of micro-seconds) as happens in electromagnetic metal forming. This rapid temperature rise is very important to the material response because the short time scales largely preclude the material from recovery and recrystallization processes and precipitates cannot dissolve as they normally would in an age-hardening alloy in these time scales. This presentation will show how advanced instrumentation, particularly the Photon Doppler Velocimeter (PDV) can be coupled with electromagnetic forming and provide both avenues to characterize material as well as to provide very critical tests of numerical models of the process.

An arbitrary Lagrangian Eulerian approach to the three-dimensional simulation of electromagnetic forming

Electromagnetic metal forming is a contact-free high-speed forming process in which strain rates of more than 103s−1 are achieved. The deformation of the workpiece is driven by the Lorentz force, a material body force, that results from the interaction of a pulsed magnetic field with eddy currents induced in the workpiece by the magnetic field itself. In this work, a coupled 3D simulation of this process is presented. For the mechanical structure a thermoelastic, viscoplastic, electromagnetic material model is relevant, which is incorporated in a large-deformation dynamic formulation. The evolution of the electromagnetic fields is governed by Maxwell’s equations under quasi-static conditions. Their numerical solution in 3D requires particular arrangements due to problems connected with an adequate gauging of the fields. Hence, Nédélec elements are employed. Coupling between the thermomechanical and electromagnetic subsystems takes the form of the Lorentz force, the electromotive intensity, and the current geometry of the workpiece. A staggered scheme based on a Lagrangian mesh for the workpiece and an ALE formulation for the electromagnetic field is utilized to solve the coupled system, guaranteeing the efficiency and accuracy of the data transfer between the two meshes.

Inverse error propagation and model identification for coupled dynamic problems with application to electromagnetic metal forming

The purpose of this work is the development and application of strategies to identify material model parameters for metals at high strain-rates using data obtained from high-speed electromagnetic metal forming. To this end, a staggered algorithm for the finite-element-based numerical solution of the coupled electromagnetic-mechanical boundary-value problem has been developed based on mixed Eulerian–Lagrangian multigrid methods. On this basis, the parameter determination together with a sensitivity analysis and error estimation are carried out. After verifying the validity of this approach using synthetic data sets, it is applied to the identification of material parameters using experimental results from electromagnetic tube forming.

Algorithmic formulation and numerical implementation of coupled electromagnetic‐inelastic continuum models for electromagnetic metal forming

AbstractThe purpose of this work is the algorithmic formulation and implementation of a recent coupled electromagnetic‐inelastic continuum field model (Continuum Mech. Thermodyn. 2005; 17:1–16) for a class of engineering materials, which can be dynamically formed using strong magnetic fields. Although in general relevant, temperature effects are for the applications of interest here minimal and are neglected for simplicity. In this case, the coupling is due, on the one hand, to the Lorentz force acting as an additional body force in the material. On the other hand, the spatio‐temporal development of the magnetic field is very sensitive to changes in the shape of the workpiece, resulting in additional coupling. The algorithmic formulation and numerical implementation of this coupled model is based on mixed‐element discretization of the deformation and electromagnetic fields combined with an implicit, staggered numerical solution scheme on two meshes. In particular, the mechanical degrees of freedom are solved on a Lagrangian mesh and the electromagnetic ones on an Eulerian one. The issues of the convergence behaviour of the staggered algorithm and the influence of data transfer between the meshes on the solution is discussed in detail. Finally, the numerical implementation of the model is applied to the modelling and simulation of electromagnetic sheet forming. Copyright © 2006 John Wiley & Sons, Ltd.

Error estimates for discretizations of coupled electromagnetic‐mechanical problems

AbstractIn this note, a method is outlined to obtain a priori error estimates for the finite element discretization of coupled electromagnetic mechanical problems as arise, e.g., in electromagnetic metal forming. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Continuum thermodynamic formulation of models for electromagnetic thermoinelastic solids with application in electromagnetic metal forming

The purpose of this work is the formulation and application of a continuum thermodynamic approach to the phenomenological modeling of a class of engineering materials which can be dynamically formed using strong magnetic fields. This is carried out in the framework of a thermodynamic, internal-variable-based formulation in which the deformation, temperature and magnetic fields are in general coupled. This coupling takes the form of the Lorentz force as an additional supply of momentum, and the electromotive power as an additional supply of energy, in the material. In the current approach, the basic thermomechanical field relations for mass, momentum and moment of momentum are obtained from the total energy balance via invariance, and completed by Maxwell’s field equations. The constitutive formulation is based on the exploitation of the Muller-Liu entropy principle, here for the case of isotropic thermoelastic, viscoplastic material behaviour. The resulting reduced constitutive and field relations and restrictions are then applied to the modeling and simulation of high-speed electromagnetic forming of metal tubes and sheet metal. In this context, scaling arguments show that, over the relevant length- and timescales of engineering interest, the evolution of the magnetic field is diffusive in nature, and thermal conduction is negligible. Comparison of the simulation and experimental results for the final sheet metal form shows very good agreement.

Summary of theoretical and experiment development of a novel electromagnetic technique for remote repositioning of coolant tube spaces in CANDU nuclear reactors

The authors describe the experimental and theoretical development of a novel electromagnetic method to reposition the spacers used between the pressure and calandria tubes in a CANDU nuclear reactor without dismantling the fuel channels. The method was successfully developed and implemented to reposition the dislocation spacers in five CANDU reactors in Ontario,. The savings in reactor repair costs, interest charges, and replacement energy costs were on the order of hundreds of millions of dollars. There are a number of other applications of the electromagnetic technique which may also benefit from the analysis and experimental development, especially for pulse power, electromagnetic metal forming, and fusion technologies. >

Novel electromagnetic technique for repositioning of coolant tube spacers in CANDU nuclear reactors

A novel electromagnetic technique to reposition the coolant tube spacers in the fuel channels of CANDU nuclear reactors was successfully developed in the fall of 1983 at Ontario Hydro Research Division. The need to reposition dislocated spacers in noncommissioned reactors was discovered subsequent to the rupture of a pressure tube in one reactor at the Pickering Nuclear Generator Station in Ontario. A contributing factor to the failure of the tube was the fact that the annular spacers (garter springs), used to maintain the coaxial configuration between the pressure tube and its surrounding calandria tube, had been displaced longitudinally for a number of years. Subsequent to this finding, it was discovered that a number of garter springs in noncommissioned nuclear reactors were displaced due to vibration induced by various sources during the construction stage. Since the garter springs are not directly accessible by mechanical means, extensive dismantling of the fuel channels would have been necessary to reposition the springs in their designated locations. This paper describes a novel method to reposition the garter springs without dismantling the fuel channels. The method consists of exerting a force on the springs in the direction of the required displacement by applying a large electromagnetic impulse (generated by a 200-kJ capacitor bank) to a drive coil inserted into the pressure tube opposite the spacer. The repositioning of displaced garter springs in five new reactors in Ontario has been carried out successfully in 1984. The saving in reactor repair cost, interest charges, and replacement energy cost was on the order of hundreds of millions of dollars. Equally large benefits and savings will be realized if the need to use this technique in commissioned reactors arises. Also, the related development of strong compact coils and low-resistance pulse power cable have significant implications and advantages in various other applications related to the pulse power industry, in general, and to electromagnetic metal forming and fusion technologies, specifically.