Collision welding is a high-speed joining technology based on the plastic deformation of at least one of the joining partners. During the process, several phenomena like the formation of a so-called jet and a cloud of particles occur and enable bond formation. However, the interaction of these phenomena and how they are influenced by the amount of kinetic energy is still unclear. In this paper, the results of three series of experiments with two different setups to determine the influence of the process parameters on the fundamental phenomena and relevant mechanisms of bond formation are presented. The welding processes are monitored by different methods, like high-speed imaging, photonic Doppler velocimetry and light emission measurements. The weld interfaces are analyzed by ultrasonic investigations, metallographic analyses by optical and scanning electron microscopy, and characterized by tensile shear tests. The results provide detailed information on the influence of the different process parameters on the classical welding window and allow a prediction of the different bond mechanisms. They show that during a single magnetic pulse welding process aluminum both fusion-like and solid-state welding can occur. Furthermore, the findings allow predicting the formation of the weld interface with respect to location and shape as well as its mechanical strength.
Collision welding processes are accompanied by the ejection of a metal jet, a cloud of particles (CoP), or both phenomena, respectively. The purpose of this study is to investigate the formation, the characteristics as well as the influence of the CoP on weld formation. Impact welding experiments on three different setups in normal ambient atmosphere and under vacuum-like conditions are performed and monitored using a high-speed camera, accompanied by long-term exposures, recordings of the emission spectrum, and an evaluation of the CoP interaction with witness pins made of different materials. It was found that the CoP formed during the collision of the joining partners is compressed by the closing joining gap and particularly at small collision angles it can reach temperatures sufficient to melt the surfaces to be joined. This effect was proved using a tracer material that is detectable on the witness pins after welding. The formation of the CoP is reduced with increasing yield strength of the material and the escape of the CoP is hindered with increasing surface roughness. Both effects make welding with low-impact velocities difficult, whereas weld formation is facilitated using smooth surfaces and a reduced ambient pressure under vacuum-like conditions. Furthermore, the absence of surrounding air eases the process observation since exothermic oxidation reactions and shock compression of the gas are avoided. This also enables an estimation of the temperature in the joining gap, which was found to be more than 5600 K under normal ambient pressure.
The object of this investigation is to determine the influence of the jet velocity on the weld quality of sheet joints produced via magnetic pulse welding. The use of a suitable high-speed camera system enables to observe the jet in detail, to determine its velocity during the collision process and to compare them to the achieved qualities (tensile strength, weld seam characteristics) of the welded samples. The results show that the quality of the weld generally correlates with the jet velocity, however the mere consideration of its velocity proves not to be a promising approach for predicting a specific weld quality. It becomes evident that the jet thickness has to be considered, since quality-critical characteristics of the weld seam appears in greater extent when the jet thickness increases.Keywords: Magnetic pulse welding / asymmetric impact / jetting / high-speed imaging / weld quality Gegenstand der Untersuchung ist die Ermittlung des Einflusses der Jetgeschwindigkeit auf die Schweißnahtqualität magnetimpulsgeschweißter Blechverbindungen. Die Verwendung eines geeigneten Hochgeschwindigkeitskamerasystems ermöglicht es, den Jet im Detail zu beobachten sowie seine Geschwindigkeit während der Kollision zu erfassen und diese den erzielten Qualitäten (Zugfestigkeit, Schweißnahtcharakteristiken) der verschweißten Proben gegenüberzustellen. Die Ergebnisse verdeutlichen, dass die Qualität der Schweißverbindung im Allgemeinen mit der Jetgeschwindigkeit korreliert, jedoch erweist sich die alleinige Berücksichtigung seiner Geschwindigkeit als ein nicht vielversprechender Ansatz, um eine spezifische Schweißnahtqualität prognostizieren zu können. Es wird ersichtlich, dass die Jetdicke zu berücksichtigen ist, da qualitätskritische Schweißnahtcharakteristiken in größerem Ausmaß vorliegen, wenn die Jetdicke zunimmt.
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