Targeted Weld Seam Formation and Energy Reduction at Magnetic Pulse Welding (MPW)

Abstract

Magnetic pulse welding is based on the high velocity impact of two joining partners and a promising technology especially for the joining of dissimilar metallic components. Under proper conditions, a solid-state bond forms at the overlapping interface that is typically at least as strong as the weaker base material. However, high thermal and mechanical loads act on the tool coil and provoke a limited lifetime. Furthermore, the prevalent magnetic fields obstruct a comprehensive process monitoring with conventional means. In this manuscript, approaches for reducing the load on the tool coil without compromising the joint quality are presented. This is obtained by an adaption of the coil geometry and the application of a boundary layer on one of the joining partners. Moreover, a new measuring system taking advantage of the naturally occurring impact flash is evaluated and successfully applied for the process development and detection of process disturbances.

Improving and monitoring the magnetic pulse welding process between dissimilar metals

“…A charging energy of 8 kJ was needed to achieve a circumferential weld seam. The application of a 5-μm nickel interlayer has enabled a reduction to 5.8 kJ while the weld seam length at the 180°p osition was even increased from 3.5 to 5.9 mm [25]. An additional experiment was performed, where the nickel interlayer has been mechanically removed prior to MPW along the first 5 mm behind the initial point of impact.…”

“…This leads to a change in the electromagnetic forming behavior and might affect the welding result. Furthermore, the process efficiency decreases in case the distance between the coil and the flyer increases [25]. It is therefore recommended to reduce the tool coil current as much as possible, following these two strategies for example:…”

“…The chemical reaction of some combinations of alloys is exothermic and can be utilized for example in reactive multilayer materials [27]. During MPW of aluminum and steel, an interlayer of nickel on the steel parent can lower the necessary impact velocity of the flyer and the tool coil current for a circumferential weld seam [25]. 2 Reduction of the necessary impact velocity by supporting the liquid state bonding mechanism.…”

Thermal Effects in Dissimilar Magnetic Pulse Welding

“…However, the influence of the slot is limited to approximately 10% of the circumference. Hence, the metallographic analysis of the welding interface was performed at the opposed position (180 • ), since it is representative for almost the complete circumference [27]. Selected welding trials were performed with anodized flyer tubes (layer thickness 5 µm), which enable the reconstruction of the material flow [28].…”

“…The initial wall thickness of 2 mm was reduced to 1.4 mm next to the initial impact zone of the free flyer edge and increased to 2.3 mm at the end of the close-fit zone. The indentation depth of the flyer into the parent was measured in analogy with [27] at different positions in the welding direction. The maximum value of 44 µm was found to be 0.5 mm behind the beginning of the welded zone and clearly below 10 µm at the end of the welded zone.…”