No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
A Novel Tool Design Strategy for Electromagnetic Forming
Abstract
To make the advantages of electromagnetic forming applicable for industrial manufacturing, a three step tool design strategy is suggested. At first, simplified decoupled electromagnetic and structural mechanical simulations are used for creating a preliminary design via a systematic iterative optimization process. The selected design is verified in more accurate coupled simulations. A prototypic realization serves for further optimization, if necessary. The applicability of the approach is proved on the basis of an inductor system for magnetic pulse welding of tubes.
... Despite these advantages, there are still restraints using this technology in industrial environments (Golovashchenko, 2006). According toNeugebauer et al. (2014), insufficient knowledge about the design of durable and likewise efficient working coils is one of the main reasons for this. The efficiency of the electromagnetic forming process Á is defined by the ratio of plastic strain energy E F to the initial charging energy of the pulse generator E C (Daube and Mattke, 1968). ...
Coils in electromagnetic forming operations are exposed to mechanical as well as thermal loads. Especially in case of high volume production the thermal loading due to Joule heat losses needs to be considered in the coil and process design to prevent thermal overstressing. For this purpose an analytical approach to calculate the Joule heat losses in a one-turn coil with rectangular cross section is presented. It takes the geometrical and physical properties of coil and workpiece as well as the amplitude, frequency, and damping behavior of the discharge current into account. While a simplified approach assumes a constant electrical conductivity of the coil, the enhanced approach considers the temperature-dependent course of the electrical conductivity. Verification of the analytical model is realized using a combination of experimental and numerical investigations. Fiber-optical measurements of the coil temperature are used to verify the simulation. The Joule heat loss per unit length determined with the verified numerical model is then used to evaluate the prediction quality of the analytical approach. Different conductor materials (CuCr1Zr, Cu-ETP, and EN AW-1050A), conductor geometries, and discharge energies are analyzed in this verification procedure. Compared to the numerical Joule heat prediction an average deviation of 13.1% and 9.0% is determined for the simplified and the enhanced analytical model, respectively. Especially in case of higher discharge energies the enhanced model shows an improved accuracy and should be preferred over the simplified approach. Considering complexity and accuracy, the analytical approach is a proper instrument for the thermal coil and process design in electromagnetic forming operations.
... A numerical simulation of the hydroforming process has shown that the joint has to withstand a maximum shear force of approximately 42 kN [5] In the next step an appropriate inductor system consisting of a suitable tool coil and a fieldshaper was designed for the magnetic pulse welding process (see Fig. 1a). For dimensioning this tool a methodology efficiently combining simplified decoupled and more accurate coupled electromagnetic and structural mechanical simulations was used [6,7]. The inductor system was realised by Poynting GmbH (Germany) and applied at IWU for producing hybrid tubes depicted in Fig. 1 ...
To reduce weight of a component and improve its performance, the part properties have to be adapted to the requirements, the load profile, and the function of the product. This leads to a continuously increasing complexity of the components necessitating innovative manufacturing strategies for producing the desired shapes from materials that are difficult to handle. Hydroforming offers high potential for fulfilling this demand, especially, if it is applied in deliberate process integrations, combinations, and chains that allow exploiting complementary advantages of all technologies involved. The paper presents four examples of such manufacturing strategies: magnetic pulse welding followed by tube hydroforming, deep drawing combined with injection moulding and hydroforming using the molten plastic, free bending or roll forming followed by hydroforming, and deep drawing with integrated media forming.
Joining of functionally adapted and weight-optimized semi-finished parts by electromagnetic compression is investigated taking into account that the resulting component is further processed by hydroforming. For this purpose both ends of an aluminum tube are connected to steel tubes. During the subsequent hydroforming of the hybrid tube the joints are exposed to extreme loading. Finite-Element-Simulation is applied for characterizing and quantifying these loads. The electromagnetic joining process is analyzed, the joints are characterized by microstructural analysis and the resulting properties of the joint are evaluated by model experiments.
The magnetic pulse welding (MPW) is a cold weld process of conductive metals to the similar or dissimilar material. MPW uses magnetic pressure to drive the primary metal against the target metal sweeping away surface contaminants while forcing intimate metal-to-metal contact, thereby producing a solid-state weld. In this paper the MPW method and its application for several aluminium alloy (A1050, A2017, A3004, A5182, A5052, A6016, and A7075) and steel (SPCC) sheets joint were investigated and the process parameters and welding characteristics are reported.
The magnetic pulse welding (MPW) is a cold weld process of conductive metals to the similar or dissimilar material. MPW uses magnetic pressure to drive the primary metal against the target metal sweeping away surface contaminants while forcing intimate metal-to- metal contact, thereby producing a solid-state weld. In this paper the MPW method and its application for several aluminium alloy (A1050, A2017, A3004, A5182, A5052, A6016, and A7075) and steel (SPCC) sheets joint were investigated and the process parameters and welding characteristics are reported.
Coil design influences the distribution of electromagnetic forces applied to both the blank and the coil. The required energy of the process is usually defined by deformation of the blank. However, the discharge also results in a significant amount of heat being generated and accumulating in the coil. Therefore, EMF process design involves working with three different problems: 1) propagation of an electromagnetic field through the coil-blank system and generation of pulsed electromagnetic pressure in specified areas, 2) high-rate deformation of the blank, and 3) heat accumulation and transfer through the coil with the cooling system. In the current work, propagation of an electromagnetic field in the coil, blank, die and surrounding air was defined using a consistent set of quasi stationary Maxwell equations applying a corresponding set of parameters for each media. Furthermore, a deformation of the blank driven by electromagnetic forces distributed through the volume of the blank was modeled using a solid mechanics equation of motion and the elastic plastic flow theory. During the discharge of capacitors the process was considered to be adiabatic due to the short duration of the pulse, so a heat transfer during the discharge time was neglected. The distribution of electric current density integrated during the discharge process defines the increase of temperature at every element of the coil. The distribution of temperature was calculated as a function of time using the energy conservation law.
Kurzfassung
Mit dem Ziel, die Verfahrensvorteile der elektromagnetischen Umformung nutzbar für die Industrie zu machen, wurde folgende Werkzeugauslegungsstrategie vorgeschlagen: mit einfachen mechanischen und elektromagnetischen Simulationen wird eine Vorauslegung vorgenommen, die durch gekoppelte Simulation und prototypische Umsetzung überprüft wird. Diese Auslegungsstrategie wurde bei der Gestaltung eines Werkzeuges zum Fügen durch elektromagnetische Kompression erprobt und verifiziert.
In a previous report it was demonstrated that the forming limits of BCC interstitial free iron could be significantly increased by forming at high strain rates which were induced using a technique known as electrohydraulic forming. In that report two possible reasons for the increased formability were discussed: (1) a change in the material constitutive law at high rate, making it more formable, and (2) inertial forces slowing the growth of imperfections. Because the material's hardness was similar at the same strains at low and high rates, and inertial forces were demonstrably large, it was suggested that inertial effects were likely to be responsible for the increased forming limits. Here, more evidence is presented that inertial forces are responsible for the formability increase and it is suggested that this effect is both large and general. Specifically the authors have used similar procedures to examine two FCC materials (annealed and quenched 6061 aluminum and annealed oxygen-free high-conductivity (OFHC) copper). Both these materials show very similar increases in formability at high workpiece velocities. A simple model is presented that shows that high workpiece velocities are expected to increase forming limits. The required velocities are accessible with existing technology.
Electromagnetic forming is an impulse or high-speed forming technology using pulsed magnetic field to apply Lorentz’ forces to workpieces preferably made of a highly electrically conductive material without mechanical contact and without a working medium. Thus hollow profiles can be compressed or expanded and flat or three-dimensionally preformed sheet metal can be shaped and joined as well as cutting operations can be performed. Due to extremely high velocities and strain rates in comparison to conventional quasistatic processes, forming limits can be extended for several materials. In this article, the state of the art of electromagnetic forming is reviewed considering:•basic research work regarding the process principle, significant parameters on the acting loads, the resulting workpiece deformation, and their interactions, and the energy transfer during the process;•application-oriented research work and applications in the field of forming, joining, cutting, and process combinations including electromagnetic forming incorporated into conventional forming technologies.Moreover, research on the material behavior at the process specific high strain rates and on the equipment applied for electromagnetic forming is regarded. On the basis of this survey it is described why electromagnetic forming has not been widely initiated in industrial manufacturing processes up to now. Fields and topics where further research is required are identified and prospects for future industrial implementation of the process are given.
Pulsed electromagnetic forming is based on high-voltage discharge of capacitors through a coil. An intense transient magnetic
field is generated in the coil and through interaction with the metal work-piece; pressure in the form of a magnetic pulse
is built up to do the work. Data on formability of two aluminum alloys employed for exterior (6111-T4) and interior (5754)
automotive body panels will be shown. Comparison of traditional Forming Limit Diagrams obtained by stretching of aluminum
sheet with hemispherical punch to the results on formability, where hemispherical punch is replaced by a coil will be provided.
It will be shown that material formability in high-rate forming conditions can significantly depend upon interaction with
the forming die: electromagnetic forming into an open round window provides only slight improvement in formability, while
forming in a V-shape die or into a conical die indicates a significant improvement. An important part of the electromagnetic
forming technology is the design of the coil. The coil failure modes and measures preventing them are discussed.
The aim of this approach is to determine material characteristics of aluminium alloys at very high strain rates, in the form of a relationship between yield stress, plastic strain and strain rate. To achieve high strain rates up to 10$^4$ s$^{-1}$ the electromagnetic forming process (EMF) is applied, where a pulsed magnetic field is used to form materials with a high electrical conductivity in process times between 20$\mu$s - 50$\mu$s. The forces resulting from the magnetic field and acting on the specimen, which in the considered setup is a tube, can be approximated as a time and location dependent pressure distribution. To compute the associated flow curve array, where the strain rate represents the third dimension, a new method will be proposed that combines an on-line measurement technique with iterative finite element simulations. During the electromagnetic compression of the specimen, the radial displacement of one significant point at the inner tube surface is measured on-line. These measured data are compared to the numerical results during the whole forming process and the deviations will be computed. Based on these differences an automate modification of material data is realised until the experimental data and the numerical solutions fit well. The advantage that EMF is a contactless forming process can be used to determine material characteristics without any influence of friction. Additionally, in contrast to other testing methods the assumption of a mean strain rate over the process time is not needed, because the evaluation is carried out by means of finite element simulations.