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.
Collison welding is a promising material-closed joining process that enables bonds with various advantages. It is already used as explosion welding to produce clad materials that cannot be joined otherwise. Other collision welding processes as electromagnetic pulse welding do not contain that amount of energy, but they can be used in mass production. In order to achieve a high process and product reliability, the process has to be designed accurately. But the process boundaries are not yet completely understood. In this paper, process windows for aluminium and copper joints, produced by a model test rig, are compared. Additionally, high speed observation and micro sections are used to enhance the knowledge about process boundaries and the influence of the jet. Keywords: Collision welding / process window / high speed observation / jet / electromagnetic pulse welding Das Kollisionsschweißen ist ein vielversprechendes stoffschlüssiges Fügeverfahren, das Verbindungen mit vielfältigen Vorteilen ermöglicht. Es wird bereits lange als Explosionsschweißverfahren eingesetzt, um plattierte Halbzeuge herzustellen, die sonst nicht gefügt werden können. Andere Kollisionsschweißverfahren wie das elektromagnetische Pulsschweißen verfügen nicht über diese Energiemenge, können aber in der Massenproduktion eingesetzt werden. Um eine hohe Prozess-und Produktzuverlässigkeit zu erreichen, muss allerdings der Prozess genau ausgelegt werden. Allerdings sind die Prozessgrenzen noch nicht vollständig verstanden. In diesem Beitrag werden Prozessfenster für Aluminium-und Kupferverbindungen verglichen, die auf einem Modellversuchsstand erzeugt werden. Darüber hinaus werden Hochgeschwindigkeitsbeobachtungen und Mikroschliffe genutzt, um das Wissen über die Prozessgrenzen und den Einfluss des Jets zu erweitern. Schlüsselwörter: Kollisionsschweißen / Prozessfenster / Hochgeschwindigkeitsbeobachtung / Jet / elektromagnetisches Pulsschweißen
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