Yosuke Ogino

Numerical analysis of the heat source characteristics of a two-electrode TIG arc

Various kinds of multi-electrode welding processes are used to ensure high productivity in industrial fields such as shipbuilding, automotive manufacturing and pipe fabrication. However, it is difficult to obtain the optimum welding conditions for a specific product, because there are many operating parameters, and because welding phenomena are very complicated. In the present research, the heat source characteristics of a two-electrode TIG arc were numerically investigated using a 3D arc plasma model with a focus on the distance between the two electrodes. The arc plasma shape changed significantly, depending on the electrode spacing. The heat source characteristics, such as the heat input density and the arc pressure distribution, changed significantly when the electrode separation was varied. The maximum arc pressure of the two-electrode TIG arc was much lower than that of a single-electrode TIG. However, the total heat input of the two-electrode TIG arc was nearly constant and was independent of the electrode spacing. These heat source characteristics of the two-electrode TIG arc are useful for controlling the heat input distribution at a low arc pressure. Therefore, these results indicate the possibility of a heat source based on a two-electrode TIG arc that is capable of high heat input at low pressures.

Numerical simulation of metal transfer in argon gas-shielded GMAW

The gas metal arc welding (GMAW) process combines aspects of arc plasma, droplet transfer, and weld pool phenomena. In the GMAW process, an electrode wire is melted by heat from an arc plasma, and molten metal at the wire tip is deformed by various driving forces such as electromagnetic force, surface tension, and arc pressure. Subsequently, the molten droplet detaches from the tip of the wire and is transferred to the base metal. The arc plasma shape changes together with the metal transfer behavior, so the interaction between the arc plasma and the metal droplet changes from moment to moment. In this paper, we describe a unified arc model for GMAW, including metal transfer. In the model, we do not account for heat transfer in the metal, but the wire melting rate is determined by the arc current. The developed model can show transition from globular transfer at low currents to spray transfer at higher currents. It was found that electromagnetic force is the most important factor at high currents, but surface tension is more important than electromagnetic force at low currents in determining the transfer mode.

Numerical analysis of arc plasma and weld pool formation by a tandem TIG arc

Multi-electrode welding processes are used in various industrial fields for higher productivity. These processes can use many combinations of welding methods, current values and polarities, and electrode alignments. However, this complicates welding phenomena. In this research, we focused on the tandem tungsten inert gas (TIG) arc, which is a relatively simple multi-electrode welding process. We performed a numerical investigation into the tandem TIG arc plasma and weld pool formation to clarify the phenomena involved. The weld spot of a tandem TIG weld is ellipsoidal in appearance and is deeper than that of a single-electrode TIG weld. Reduction in the shear stress of the plasma flow in the tandem TIG weld leads to a deeper penetration. Furthermore, the influence of the electrode alignment is calculated, and it is determined that the weld spot appearance significantly changes. The appearance is strongly related to the arc plasma shape. These numerical results show good agreement with the experimental results, which proves that our model has relatively high reliability.

Numerical analysis of arc plasma behaviour in groove welding with 3D TIG arc model

Arc welding phenomena have been theoretically investigated by using various numerical models, which have been proposed and developed together with rapid progress of the computer technologies. However, most of the numerical models are two-dimensional axial symmetric models that are available only for stationary arc on the flat plate. Actual welding processes applied to the manufacturing field are carried out with various joint geometries and the welding arc moves on the base metal. Therefore, they should be non-axial symmetric phenomena and it is required to be discussed with a three-dimensional (3D) model. In this research, TIG arc characteristics in V-groove welding are numerically investigated by using our 3D numerical model. It is shown that both heat input and arc pressure on the groove surface are significantly different from the flat plate surface. In the groove heat input and arc pressure are varied sensitively with location and aiming of the TIG torch. Experimental results show the validity of calculation results of TIG arc heat input distribution on the groove surface.

Heat Input and Pressure Distribution of Tig Arc on Groove Surface

Arc welding phenomena have been theoretically investigated by using various numerical models, which have been proposed and developed together with rapid progress of the computer technologies. However, most of the numerical models are two-dimensional axial symmetric models that are available only for stationary arc on the plate. Actual welding processes applied to manufacturing field are performed with various joint geometries and the welding arc moves on the base metal. Therefore, they should be non-axial symmetric phenomena and it is required to be discussed with three-dimensional model. In this research, TIG arc characteristics in V-groove welding are numerically investigated by using a three-dimensional numerical model. It is shown that both heat input and arc pressure on the groove surface are significantly different from the flat plate surface. In the groove heat input and arc pressure vary sensitively with location and aiming of the TIG torch. Experimental results show the validity of calculation results of TIG arc heat input distribution on the groove surface.

Numerical study of the influence of gap between plates on weld pool formation in arc spot welding process

Arc spot welding is a low heat input process that it is suitable for lap joint welding of thin plates. In a typical arc spot welding process, a controlled short-circuit transfer process, such as cold metal transfer, is used to control the weld pool and/or the heat input to the base metal. In this study, the arc spot welding process is modeled in two dimensions to clarify the metal transfer and weld pool phenomena during the process. In this model, the arc plasma is not calculated and a pseudo arc is set as the conductor of current between the wire and the base metal; the heat input from the arc plasma is given by a simplified heat input model. Droplet formation, droplet transfer, and weld pool formation are included in the proposed model, and the influence of the welding conditions is investigated numerically. First, welding parameters, such as current and the wire feeding speed, are obtained from experimental observation as the input parameters of the model. The calculation result of the weld shape shows good agreement with the experimental result with adjustment of the heat input parameters. The influence of the gap between thin plates is investigated numerically. When a gap exists between the plates, the weld shape differs from that without a gap, and the numerical result is similar to the experimental result. This result shows that the heat conduction between the plates strongly affects the weld shape.

Numerical simulation of WAAM process by a GMAW weld pool model

Additive manufacturing (AM) is a high-productivity process which can make a near-net-shape structure. In this study, the focus is the wire-arc AM (WAAM) process. In the WAAM process, wire is the depositing material. The wire melts by an arc plasma and deposits layer by layer. To establish an advanced WAAM process, it is important to make a precise structure of the intended shape. In this study, a gas metal arc welding (GMAW) weld pool model is applied to WAAM process, and influence of the deposit condition on the shape of the deposition is numerically investigated. Firstly, influence of the interpass temperature is investigated. When cooling time is set appropriately, the deposition shape becomes higher and thinner. In addition, concerning influence of the welding direction, when the welding direction is reversed for each layer, the variance of the deposition height becomes small. These numerical results show that it is important to manage the temperature and torch motion for controlling the deposition shape. These numerical results have similar tendency with experimental results and show the GMAW weld pool model is a helpful tool to predict and control the WAAM process.