Material Formability and Coil Design in Electromagnetic Forming

Abstract

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.

Structuring by electromagnetic forming and by forming with an elastomer punch as a tool for component optimisation regarding mechanical stiffness and acoustic performance

“…This indicates that in case of structuring by EMF the forming limit of the material can be increased compared to alternative and more conventional techniques, an effect that is well known from previous publications as e.g. [9].…”

“…In addition to the mere substitution of conventional materials by typical lightweight ones such as aluminium and magnesium alloys, high-strength steels, and plastics, also the component design offers enormous weight saving potential [7][8][9]. A brief review of weight reduction via adapted part design starting from early and more theoretical approaches [10] up to current work [11] can be found in reference [12].…”

Experimental characterization of sheet metal deformation during electro-hydraulic forming

“…Seth et al (2005) experimentally measured the impact velocity of steel sheets on a steel punch (though strains were still measured by the etched-circle technique (Taylor, 1988) and attributed the enhanced formability to inertial stabilization and compressive stresses generated during impact. Other authors, such as Golovashchenko et al (2003), Golovashchenko and Mamutov (2005) and Golovashchenko (2007), determined only the post-mortem strain (via the circle-etching technique) in EMF and EHF experiments and attributed improved sheet formability to high strain-rates and high-rate impact with the tooling even though the strain and strain-rate history of the deforming sheet were unknown. Imbert et al (2005a) numerically modeled EMF of Al alloy sheet and concluded that high-strain rates (estimated to be on the order of 30,000-69,000/s in the locations where sheet impacts the die) and inertial stabilization alone could not be responsible for enhanced formability; instead, high through-thickness compressive and shear stresses and strains as well as non-linear strain-paths were the responsible factors.…”

Optimisation of component performance via structuring

“…Thus, EMF allows deeper structures compared to forming with elastomer tools, indicating an extended material formability for this high velocity forming process, an effect that is well known from previous publications as e.g. [9].…”