Influence of axial workpiece position in the coil for the electromagnetic pulse joining

Magnetic Pulse Welding (MPW) enables the fabrication of joints via the harnessing of Lorentz forces, which result from discharging a current pulse through a coil. In the process an outer piece (flyer) is accelerated onto an inner piece (parent), and welding is achieved using propagating impact fronts. The working length of the experimental setup allows for various shapes of the deformation front, and each configuration has its own advantages and drawbacks. The objective of this work is to show how the working length of tubular MPW specimens affects the front propagation as well as to indicate ways to optimize the front propagations, which are vital to the welding result. It is shown that for steel-aluminum joints, three different front regimes exist, which are related to geometrical factors. These results may be used to avoid seemingly favorable but nevertheless suboptimal conditions for flyer movement, which reduce the weld quality and the energy efficiency of the process. Additionally, the methodology presented here may allow for faster process optimization without the need for time-consuming metallographic analyses

Effects of Reactive Interlayers in Magnetic Pulse Welding

Surface coatings affect the joint formation in magnetic pulse welding processes (MPW). Two types of coatings were identified in former studies. Anodized layers, for instance, are detrimental for the weld formation if they are not removed before or during welding. Contrastingly, a nickel layer on a steel parent part was found to be advantageous since it increased the weld seam length when it was impacted by an aluminum flyer. This paper gives insights into the welding mechanism with nickel coatings during MPW and explains one reason for the improved weld formation. Metallographic analyses showed that the coating is evidently not fractured, but an interlayer between aluminum and nickel is formed. Scanning electron microscopy and energy dispersive X-ray spectroscopy revealed that nickel and aluminum have interacted. The energy release rate of the exothermic reaction is higher than the reaction of aluminum with steel in direct contact. Since all other parameters were kept constant, it is assumed that the additional heat of the nickel-aluminum reaction promotes the welding effect, especially at positions with lower impact pressures. This effect, for instance, enables a significant reduction of the required impact energy for MPW. The formation of the interaction zone was studied for different well defined collision conditions. A newly developed process measurement system was utilized, which records the characteristic process light emission and enables insights into the prevalent collision conditions

Metal forming beyond shaping: Predicting and setting product properties

Metal forming is not only shaping the form of a product, it is also influencing its mechanical and physical properties over its entire volume. Advanced analysis methods recently enable accurate prediction of these properties and allow for setting these properties deterministically during the forming process. Effective measurement methods ensure the setting of these predicted properties. Several real examples demonstrate the impressive achievements and indicate the necessity of a paradigm change in designing products by including manufacturing-induced effects in the initial dimensioning. This paradigm change will lead to lightweight components and serve environmentally benign designs