Numerical Simulation of Arc Characteristics for Hollow Tungsten Electrode TIG Welding

Literature Overview

Published in The International Journal of Advanced Manufacturing Technology (2021) by researchers from Southwest Jiaotong University, this paper presents a numerical simulation of the arc characteristics for gas tungsten arc (GTAW / TIG) welding using a hollow tungsten electrode. The study was supported by the National Key R&D Program of China (Grant 2016YFB1102103-3) and the Sichuan Provincial Key R&D Program (Grant 2020YFG0096). The hollow tungsten electrode is a modified electrode design that introduces a gas flow through the interior of the electrode, which can enhance the arc stability, improve the heat input, and increase the welding speed. This research is particularly relevant to the fabrication of clad plates and bimetal components, where the control of the welding process is critical to achieving the desired weld quality.

Core Technical Content

The authors developed a numerical model to simulate the arc characteristics for hollow tungsten electrode TIG welding. The model incorporates the effects of the gas flow through the electrode, the electromagnetic forces, the heat transfer, and the fluid dynamics in the welding zone. The numerical results were validated against experimental measurements, and the agreement between the simulated and measured values was found to be satisfactory.

The numerical simulation revealed that the hollow tungsten electrode significantly alters the arc behavior compared to a conventional solid tungsten electrode. The gas flow through the electrode enhances the arc stability by providing a continuous supply of shielding gas directly to the arc root. The gas flow also increases the heat input by enhancing the convective heat transfer from the arc to the workpiece. The increased heat input results in a deeper weld penetration and a higher welding speed, which are beneficial for the fabrication of clad plates and bimetal components.

Numerical Model and Simulation Approach

The numerical model developed by the authors is based on the magnetohydrodynamic (MHD) equations, which describe the coupled behavior of the electromagnetic field, the fluid flow, and the heat transfer in the welding zone. The model incorporates the effects of the gas flow through the hollow electrode, which is modeled as a source term in the momentum equation. The electromagnetic forces are calculated from the current density and the magnetic field, and the heat transfer is modeled using the energy equation with appropriate boundary conditions.

The numerical model was solved using a finite element method (FEM) with a mesh that was refined near the electrode and the workpiece to capture the steep gradients in the electromagnetic field and the heat flux. The time step was chosen to be small enough to ensure the convergence of the solution and to capture the transient behavior of the welding process. The model was validated against experimental measurements of the arc voltage, the weld penetration, and the bead geometry, and the agreement was found to be satisfactory.

The simulation results showed that the gas flow through the hollow electrode has a significant effect on the arc characteristics. The gas flow enhances the arc stability by providing a continuous supply of shielding gas to the arc root, which reduces the arc oscillation and the spatter. The gas flow also increases the heat input by enhancing the convective heat transfer from the arc to the workpiece, which results in a deeper weld penetration and a higher welding speed.

Engineering Implications for Cladding and Bimetal Fabrication

The findings of this study have direct implications for the fabrication of clad plates and bimetal components. The hollow tungsten electrode offers several advantages for the welding of clad plates, including enhanced arc stability, increased heat input, deeper weld penetration, and higher welding speed. These advantages can be exploited to improve the productivity and the quality of the clad plate fabrication process.

In the fabrication of stainless steel / carbon steel clad plates, the hollow tungsten electrode can be used to increase the welding speed while maintaining the desired weld penetration and bead geometry. The enhanced arc stability provided by the gas flow through the electrode can reduce the arc oscillation and the spatter, which can improve the weld quality and reduce the need for rework. The increased heat input can also be used to reduce the number of weld passes required, which can further improve the productivity.

In the fabrication of nickel-based alloy clad plates, the hollow tungsten electrode can be used to control the dilution ratio between the clad metal and the backing metal. The deeper weld penetration provided by the hollow electrode can increase the dilution ratio, which may be acceptable for nickel-based alloys. However, the dilution ratio must be carefully controlled to ensure that the functional properties of the clad layer are not compromised.

Key Technical Points and Implementation Considerations

The implementation of the hollow tungsten electrode in the welding process requires careful consideration of several factors. The gas flow through the electrode must be controlled to ensure that it does not disrupt the shielding gas flow and cause porosity in the weld. The gas flow rate must be optimized to provide the desired enhancement of the arc stability and the heat input without causing excessive spatter or other defects.

The hollow tungsten electrode also requires a special power supply that can accommodate the gas flow through the electrode. The power supply must be able to provide a stable current and voltage to the electrode, and the gas flow must be controlled independently to ensure that the arc characteristics are maintained within the desired range.

The study also highlights the importance of numerical simulation in the optimization of the welding process. The numerical model developed by the authors provides a powerful tool for predicting the arc characteristics and the weld quality for different welding parameters and electrode designs. The model can be used to optimize the welding parameters and the electrode design before the welding process is carried out, which can reduce the need for trial-and-error experimentation and improve the efficiency of the process development.

Study Insights and Implications

This study provides valuable insights into the arc characteristics for hollow tungsten electrode TIG welding and demonstrates the potential of this electrode design for improving the welding process. The numerical simulation results show that the hollow tungsten electrode can enhance the arc stability, increase the heat input, and improve the weld penetration and welding speed. These advantages can be exploited to improve the productivity and the quality of the clad plate fabrication process.

For engineers involved in the fabrication of clad plates and bimetal components, the study underscores the importance of numerical simulation in the optimization of the welding process. The numerical model developed by the authors provides a powerful tool for predicting the arc characteristics and the weld quality for different welding parameters and electrode designs. The model can be used to optimize the welding parameters and the electrode design before the welding process is carried out, which can reduce the need for trial-and-error experimentation and improve the efficiency of the process development.

In summary, this study provides a valuable contribution to the understanding of the arc characteristics for hollow tungsten electrode TIG welding and demonstrates the potential of this electrode design for improving the welding process. The findings have direct implications for the fabrication of clad plates and bimetal components, where the control of the welding process is critical to achieving the desired weld quality. The study also highlights the importance of numerical simulation in the optimization of the welding process and the development of new electrode designs.