Investigation of droplet formation and transfer in GMA welding
Zabirov, Alexander; Reisgen, Uwe (Thesis advisor); Schein, Jochen (Thesis advisor)
Aachen / Shaker Verlag (2016) [Dissertation / PhD Thesis]
Page(s): 1 Online-Ressource (XXIV, 152, A-52 Seiten) : Illustrationen
Gas Metal Arc (GMA) welding is one of the most common methods in welding technology. It was invented at the beginning of the XXth century and is applied in many fields of industry until now. For almost every alloy used in industry, the GMA welding can be applied thanks to its variations (MIG/MAG including cored wire electrode welding, electrogas welding, plasma gas metal arc welding), inexpensive consumables and equipment. Despite the long-standing and widely spread application of this process, it still has not been completely understood due to the complex physical phenomena involved and their interaction with each other. As a consequence of this, its potential is not completely revealed and the research topic “physical phenomena in GMA welding” is still relevant.The goal of this work is the attainment of new knowledge about the GMA welding process in relation to the physical phenomena of the droplet formation, detachment and its transfer. For this, the effect of different welding process parameters on these physical phenomena is studied. Finally, it is studied how the droplet detachment and droplet transfer can be controlled by these process parameters. These studies are performed with the help of modern theoretical and experimental methods. The obtained results can be used not only for a better understanding of the welding process, but also for helping to apply in the industry, for example, low-spatter, more stable and energy-saving welding processes.One of the most important physical phenomena in GMA welding include the droplet formation and its transfer to the weld pool. The process stability, the weld seam geometry, the chemical composition and mechanical properties of weld seam, as well as the safety of welding construction depend on these processes. Therefore, the mentioned phenomena are very important for the quality and profitability of the welding process. The droplet transfer serves the GMA welding as an energy and mass transporter between the welding power source and electrode and the weld pool. With it, the GMA welding process can be purposefully controlled, even though the physical phenomena are in a complex interaction with each another.Both methodical approaches, the theoretical and the experimental, are applied for different, partially overlapping parameter ranges. The theoretical approach is applied mainly for non-measurable properties, like properties of the anode boundary layer, arc plasma and evaporation processes. The experimental approach makes it possible to observe the general process pattern and is used for measurable properties like droplet diameter, droplet velocity and arc length. The theoretical approach incorporates both, the physical-mathematical modelling and the numerical simulation of the metal transfer in GMA welding. The knowledge acquired with the help of numerical studies can be used to optimize the chemical composition for welding materials or to calculate and optimize the chemical composition of the weld seam. For the numerical analysis, different approaches are applied whereby the models implemented in ANSYS CFX software were validated by the simplified numerical experiments and were afterwards complemented with models based on the current process knowledge. In the experimental approach, modern measuring techniques are used in order to observe and analyse the welding process. For this, visual recordings of the welding process were made with a high-speed camera, synchronized with recordings of the welding current and voltage. Finally, the dependencies of the welding process parameters in relation to the droplet formation and droplet transfer are determined. For this, the process parameters are widely varied. In this work, new knowledge in the topic concerning the droplet formation and droplet transfer was obtained which leads to a better understanding of GMA welding process and makes it possible to benefit more from its potential which finally saves resources and costs. The models used in this work for the droplet formation and droplet transfer consider physical phenomena that for the first time, have been formulated, presented and summarized in the form of such models. The experimental approach has both complemented the theoretical approach and extended the understanding of the process.