An Efficient Computational Model for Magnetic Pulse Forming of Thin Structures

Electromagnetic forming (EMF) is one of the most popular high-speed forming processes for sheet metals. However, modeling this process in 3D often requires huge computational time since it deals with a strongly coupled multi-physics problem. The numerical tools that are capable of modeling this process rely either on shell elements-based approaches or on full 3D elements-based approaches. The former leads to reduced computational time at the expense of the accuracy, while the latter favors accuracy over computation time. Herein, a novel approach was developed to reduce CPU time while maintaining reasonable accuracy through building upon a 3D finite element analysis toolbox which was developed in CEMEF. This toolbox was used to solve magnetic pulse forming (MPF) of thin sheets. The problem was simulated under different conditions and the results were analyzed in-depth. Innovative techniques, such as developing a termination criterion and using adaptive re-meshing, were devised to overcome the encountered problems. Moreover, a solid shell element was implemented and tested for thin structure problems and its applicability was verified. The results of this element type were comparable to the results of the standard tetrahedral MINI element but with reduced simulation time.

Modeling of thin sheet forming processes by combining solid-shell finite element with isotropic elastoviscoplastic model. Application to magnetic pulse forming processes

Sheet metal alloys are used in many industries to save material, reduce weight and improve the overall performance of products. For the last decades, many types of elements have been developed to resolve the locking problems encountered in the simulation of thin structures. Among these approaches, a family of assumed-strain solid-shell elements has proved to be very efficient and attractive in simulating thin 3D structures with various constitutive models. Furthermore, these elements are able to account for anisotropic behavior of thin structures since isotropic yield functions cannot capture the real physics of some forming processes. In this work, von Mises isotropic yield criterion with Johnson-cook hardening model are combined with a linear prismatic solid-shell element to simulate sheet metal forming processes. A new element assembly technique has been developed to permit the assembly of prismatic elements in a tetrahedral element-based software. This technique splits the prism into multiple tetrahedral elements in such a way that all the cross-terms are accounted for. Furthermore, a tetrahedral based partitioning code has been modified to account for the new prismatic element shape without changing the core structure of the code. More accurate results were obtained using low number of solid-shell elements compared to its counterpart tetrahedral element (MINI element). This reduction in the number of elements accelerated the simulation, especially in the coupled magnetic-structure simulation used for magnetic pulse forming process. The proposed element and criteria are implemented into FORGE (in-house code developed at CEMEF) for simulating magnetic pulse forming process.

Springback Reduction of L-Shaped Part Using Magnetic Pulse Forming

This study proposes an electromagnetic-assisted stamping (EMAS) method with magnetic-force loading at the sheet end in order to control the springback phenomenon. The new method does not change the structure of the mold and does not generate a magnetic force at the sheet corner compared to traditional EMAS. Thus, the new approach could greatly extend the mold lifespan and could be readily adopted in commercial production environments. The effects of technological parameters, such as the distance between the blank holder and die, discharge voltage, and sheet thickness on the springback phenomenon were analyzed. Our results suggest that tangential stress and elastic strain energy both decrease with the increase of discharge voltage. The simulation method accurately predicted the deformation of the sheet during the quasi-static stamping and dynamic magnetic forming processes. The simulation and experimental results both show that as the discharge voltage increases, the bent angle after springback decreases.

On the induction heating contribution in magnetic pulse forming processes for tube forming application

Purpose The purpose of this paper is to study the influence of the induction heating phenomenon during magnetic pulse forming (MPF) of thin walled tube components. The approach is based on the advanced use of the multiphysics finite element software FORGE® coupling electromagnetism, heat transfer and solid mechanics. Although the global contribution of thermal effects is found to be almost negligible with respect to the volume forces, it can be observed that localized softening due to the heating process induces shock absorbing behavior. Design/methodology/approach Due to the strong multiphysics couplings between solid mechanics, electromagnetism and heat transfer, it is not always obvious to quantify the contributions of the various physical phenomena. It is thus intended here to take advantage of the numerical framework and tool that has developed to dissociate and quantify the influence of Joule heating phenomena due to eddy currents during MPF processes. Findings In this paper, the sensitivity of the MPF process has been analyzed to the induction heating source term for a specific tube forming case. An analysis of the electric output signal shows that inductance sensitivity to heating remains small when compared to the mechanical deformation. Regarding mechanical analysis of the process, induction heating contribution has a very slight impact at the global scale, but its effect is more noticeable at the small scale where it is likely that the localized heating induces shock absorption properties through softening. The extension of these results to other materials (for which the thermal dependency of mechanical behavior is different), as well as to a larger range of energy inputs, still needs to be carried out. Such phenomena should be considered for instance for high precision forming. Originality/value The analysis of the influence of heating due to eddy currents in magnetic pulse forming processes has not been extensively studied. The originality of this work is to try to quantify its effect on the process by using a numerical-based approach.