Numerical Simulation of Temperature Field in Non-Preheated TIG Welding of Copper

Literature Overview

This paper by Lei Yucheng, Yu Wenxia, and Li Caihui from Jiangsu University investigates the numerical simulation of the temperature field during non-preheated TIG welding of copper, published in the Journal of Jiangsu University in 2005. The work was supported by the National "863" Program (Project 2003AA305970), reflecting the significant industrial interest in copper welding technology at that time. The authors address a well-known challenge in the welding community: copper's exceptionally high thermal conductivity and diffusivity, which traditionally necessitates preheating to achieve adequate penetration and fusion.

Core Technical Approach

The authors established a three-dimensional non-steady-state numerical model for the TIG welding molten pool geometry under a moving arc, grounded in the fundamental principle of energy conservation. A key methodological contribution is the introduction of the concept of thermal enthalpy and the adoption of a surface double-elliptical heat source distribution model. This dual-ellipse approach better captures the asymmetric heat input characteristic of the TIG arc, where the leading edge of the weld pool receives more intense heating than the trailing edge.

The experimental program focused on thick-walled copper specimens welded without preheating, using an Ar+N2 mixed shielding gas to enhance the thermal effect of the arc. The inclusion of nitrogen in the shielding gas mixture is a deliberate process choice aimed at increasing the ionization potential and arc temperature, thereby compensating for the extreme heat loss inherent to copper.

Key Technical Parameters and Findings

The experimental results confirmed that the thermal effect of the arc was significantly enhanced through the Ar+N2 shielding gas combination, making non-preheated TIG welding of copper technically feasible. The authors further investigated the temperature field under different process parameters and established relationships between welding parameters and weld penetration depth and weld width. Comparison between calculated and experimentally measured values showed reasonable agreement, validating the reliability and correctness of the numerical model.

Engineering Practice Implications

From a practical standpoint, this research carries important implications for copper welding operations in electrical equipment manufacturing, heat exchanger fabrication, and conductor assembly. The traditional practice of preheating copper to temperatures as high as 200-400°C is energy-intensive, time-consuming, and can introduce unwanted microstructural changes in the base material. The demonstrated feasibility of non-preheated welding, enabled by the Ar+N2 gas mixture and optimized process parameters, offers a pathway to reduced production costs and improved efficiency.

However, engineers should note that the absence of preheating does not eliminate the need for careful process control. The heat dissipation rate in copper remains extremely high, and even with enhanced arc thermal input, achieving full penetration in thick sections may still require multiple passes with strict interpass temperature management. The numerical model developed in this study provides a valuable tool for pre-planning weld sequences and predicting thermal cycles without relying exclusively on trial-and-error approaches.

Study Insights and Reflections

The most valuable aspect of this work is the systematic correlation between numerical predictions and experimental measurements. The use of a double-elliptical heat source model represents a meaningful improvement over the simpler Gaussian or Rosenthal models that were more common in early welding simulation studies. The enthalpy-based formulation is particularly important for materials undergoing phase changes, as it avoids the need for explicit tracking of the solid-liquid interface during the simulation.

One area where further development would be beneficial is the incorporation of convection heat transfer at the pool surface and the effects of gas dynamics on the arc-heat transfer interaction. Future work could also explore the metallurgical consequences of the Ar+N2 gas mixture, specifically whether nitrogen pickup in the weld metal could lead to porosity or embrittlement in copper alloys. The study provides a solid foundation for advancing copper welding technology through computational modeling and rational process design.