Spectroscopic investigation of the high-current phase of a pulsed GMAW process

International audienceWhile metal vapours have an important impact on the efficiency of the pulsed gas metal arc welding process, only a few papers are focused on this effect. In this paper, methods based on emission spectroscopy are performed to improve the understanding of the physical phenomena occurring during the high-current pulse. Boltzmann plots applied to iron lines, the Stark broadening of the 696.5 nm argon line and composition calculations assuming local thermodynamic equilibrium are used to determine characteristic parameters of the plasma. It is observed that the central part of the arc is mainly composed of iron. The percentage of iron increases quickly at the beginning of the high-current pulse, and slowly decreases, when the central part broadens. During the high-current phase the temperature profile has a minimum value of around 8000 K at the axis of the arc while the argon envelope of the central part reaches temperatures of approximately 13.000 K. High percentage of iron and high radiation of the plasma at the centre can explain the measured shape of the temperature profile

3D static and time-dependent modelling of a dc transferred arc twin torch system

International audienceThe transferred arc plasma torch device consists of two electrodes generating a plasma arc sustained by means of an electric current flowing through the body of the discharge. Modeling works investigating of transferred electric arc discharges generated between two suspended metallic electrodes, in the so called twin torch configuration, are scarce. The discharge generated by this particular plasma source configuration is characterized by a complex shape and fluid dynamics and needs a 3D description in order to be realistically predicted. The extended discharge length that goes from the tungsten pencil cathode to the flat copper anode without any particular confinement wall and the fluid dynamics and magnetic forces acting on the arc may induce an unsteady behavior. In order to capture the dynamic behavior of a twin torch discharge, a 3D time dependent plasma arc model has been developed using a customized commercial code FLUENT form in both Local Thermodynamic Equilibrium (LTE) and non-LTE. A two temperature (2T) model has been developed taking into account only the thermal non-equilibrium effects in argon plasma. The main differences between LTE and 2T models results concern the increased extension of the horizontal section of the discharge and the predicted reduced (of about 60-80V) voltage drop between the electrodes when using a 2T model

Control of Rheology, Strength and Fibre Bond of UHPC with Additions - Effect of Packing Density and Addition Type.

This contribution illustrates the effect of additions different in type and fineness and maximum packing density on the macroscopic properties, rheology and bond of steel fibres of UHPC. The results show that the properties of the UHPC investigated were decisively affected by the particle size distribution of the additions rather than the type of material. A new packing density test for fine materials (< 125 μm) was developed to provide calibrated input parameters for the calculation of the maximum packing density of UHPC with different additions. The rheological properties, and therefore fresh concrete workability, were affected by the maximum packing density of the UHPC bulk matrix. The bond strength of steel fibres in a straight pull-out test was affected by addition exchange too. Again, this is explained by packing density effects. Based on packing density calculations as well as SEM and EDX investigations, higher fibre bond strength is explained by a larger proportion of very fine particles in the matrix adjacent to the fibre ITZ which leads to a decrease in the maximum packing density of the fibre ITZ