Potentials of Pulse Magnetic Forming and Joining

Abstract

Magnetic pulse production methods such as forming, joining or separating demonstrate innovative high-speed processes. Such processes can be realized using a capacitor and an appropriate tool coil for forming and welding processes. The process strain rates, which can amount to 20,000 s-1, increase the formability of metallic materials significantly. Magnesium and aluminium alloys find a wider application in the automotive industry due to their light weight potential. Through the low density of these materials, the vehicle weight can be reduced considerably. Due to the hexagonal lattice of magnesium alloys industry-relevant deformation in metal forming processes can only be achieved in hot forming processes. The high-speed forming allows a significant increase of deformability of this alloy. The use of dissimilar metals in an assembly requires the development of innovative joining methods. Apart from being used form and force closure the magnetic pulse welding and adhesive bonding material with different partners is possible. Currently at the Institute for Machine Tools and Factory Management (IWF), TU Berlin, various research topics in the field of pulsed magnetic are investigated. The magnetic pulse sheet metal forming of magnesium alloys at room temperature is investigated in a basic research project. A defined demarcation of high-speed forming with respect to the quasi-static deformation is done by means of hardness measurements in the deformation zone. For this purpose a suitable experimental setup with different matrices is constructed. The experimental results of the pulse magnetic deformation are iteratively compared with simulation results. The aim is to develop a new material model which gives a precise prediction about the high-speed process. In the field of magnetic pulse welding, both basic research and industry-related research projects conducted at the IWF. The process requires an adapted tool coil geometry that meets the requirements of the weld geometry. Different coil geometries and weld geometries and possible applications are presented by way of example, the welding quality is quantified by means of different analytical methods. The material microstructure in the weld zone, characterized by light and scanning electron microscopy shows the typical features of a shock welded joint, as also observed in explosive welding.

Probing Magnetic Pulse Welding of Thin-Walled Tubes

“…A capacitor bank is charged by a power supply to store the required amount of energy, which is released instantaneously into a coil by using a high-current switch. The resulting discharge current of high magnitude and high frequency induces an intense transient EM field inside the coil, which induces eddy current in the outer tube [2]. The induced eddy current causes a differential EM field on both sides of the outer tube, resulting in an EM pressure that, in turn, causes the outer tube to impact onto the internal tube with high velocity [3].…”

“…The induced eddy current causes a differential EM field on both sides of the outer tube, resulting in an EM pressure that, in turn, causes the outer tube to impact onto the internal tube with high velocity [3]. As a result of the collision between the outer and the inner tubes at a certain angle, the tubes experience intense localized plastic deformation and a jet is generated along the surfaces of the materials before they make contact, which is able to remove the surface impurities and promote consolidation between the clean mating surfaces under EM pressure [2,3].…”

Analytical Estimation of Electromagnetic Pressure, Flyer Impact Velocity, and Welded Joint Length in Magnetic Pulse Welding

“…For MPW of similar and dissimilar metallic sheets, the reported values of the EM field and pressure were in the range of 25 to 27 T, and 248 to 290 Mpa, respectively [12,13]. The thickness of these sheets varied in the range of 0.8 to 1.0 mm [12,13]. These investigations have provided a practical knowledge base of the EM field, and pressure to obtain a qualitative joint during MPW of metallic tubes and sheets.…”

“…The flyer impact velocity (v i ) is influenced primarily by the EM pressure (p), the stand-off distance (s), the wall thickness of flyer (e f ), and density (ρ f ) of the flyer material [12,14,15,48,54]. A numerical solution of Equation ( 5) can compute the flyer impact velocity but will require huge computational resources and time.…”

“…Often, internal supports were used inside the target tubes to enhance the stiffness and avoid plastic collapse of the tubular assembly due to the high velocity impact of the flyer onto the target [11]. For MPW of similar and dissimilar metallic sheets, the reported values of the EM field and pressure were in the range of 25 to 27 T, and 248 to 290 Mpa, respectively [12,13]. The thickness of these sheets varied in the range of 0.8 to 1.0 mm [12,13].…”