Jörg Zschetzsche

Visualization and Optimization of Shielding Gas Flows in Arc Welding

GMA welding is one of the most frequently applied welding techniques in industry. Particularly the joining of aluminium, high alloyed steels or titanium requires a cover of shielding gas in order to provide a low PPM concentration of oxygen. The result of the welding process depends essentially on the chemical and thermophysical properties of the process gas used. Consequently, it is necessary to be able to describe and to analyse its flow with respect to various influencing variables. However, it is very difficult to realize this during arc welding processes; a poor access is predominant due to the covered areas inside the welding torch and temperatures of up to 20 000 K cause the strong radiation of the arc and electromagnetic fields. This paper deals with experimental and numerical methods for visualization and quantification of process gas flows in arc welding and gives examples for their technical applications. Unlike previous work, the described methods consider the arc as a dynamic element which determinates the gas flow. Advanced Particle Image Velocimetry (PIV) and Schlieren measurement were used for characterization of the flow field in the direct vicinity of the arc in GTA and GMA welding. Furthermore, a numerical model including magneto-hydrodynamics and turbulence models was used for a detailed visualization of the flow in the free jet and in the hidden interior of the torch. It is based on a commercial CFD code which allows to model complex 3-D geometries of torch and workpiece design. Mixing effects and turbulence model were validated by oxygen measurements in the gas shield.

Numerical simulation strategies and test setup for resistance spot welding process with motion overlay

The continuing trend of lightweight construction within the industry requires joining methods for lightweight materials, such as aluminium alloys, that provide a safe and reliable result. One of these processes is resistance spot welding. Its high level of automation and efficiency lead to being one of the most widely used joining methods. The current problem in resistance spot welding of aluminium alloys is the high wear of the electrodes. One reason is the insulating effect of the aluminium oxide layer. The high electrical resistance of the oxide results in local temperature rise and an increased wear on the electrodes. In the extreme, after less than 100 spot welds, the process reliability is no longer guaranteed. A way to reduce the wear is the mechanical destruction of the oxide layer. One possibility is to rotate the welding gun and thus the electrodes around the z-axis, as KUKA’s RoboSpin realizes it.Another approach is currently investigated at Technische Universität Dresden. The focus is on frictionless and frictional movement of the electrode in the form of rotations around the y-axis and movement in the x-direction. For this purpose, a new experimental setup has been developed, which provides all the required degrees of freedom. To gain a better insight into the processes and the contexts of action, simulation models are created based on the finite element method with ANSYS multi-physics and implemented as a network model in MATLAB/Simulink. This paper introduces the new process kinematics, describes the experimental setup and shows first simulation results to perform proof of concept and model verification.