CLADDING TECHNOLOGY SHANXI CO., LTDNumerical Simulation of Weld Pool Temperature Field in Copper TIG Welding Without Preheating
Literature Overview
This study, published in the Chinese Journal of Welding in 2006 by Lei Yucheng and colleagues from the School of Materials Science and Engineering at Jiangsu University, investigates the weld pool temperature field during gas tungsten arc welding (GTAW) of copper without preheating. The research was funded under the National 863 High-Tech Research and Development Program (Project No. 2003AA305970). The work addresses a critical practical challenge in copper welding: the extremely high thermal conductivity of copper (approximately 398 W/m·K for pure copper) causes rapid heat dissipation from the weld zone, making it notoriously difficult to achieve complete melting and penetration without significant preheating. The authors employed numerical simulation techniques to model the transient temperature distribution within the weld pool, providing insights that can guide process parameter optimization for field applications where preheating is impractical.
Core Technical Content and Methodology
The fundamental challenge in copper TIG welding lies in the material's exceptional thermal conductivity, which is roughly four times that of carbon steel and nearly twice that of austenitic stainless steel. This property causes the arc heat input to dissipate rapidly into the base metal, resulting in shallow weld pools and incomplete fusion. The authors developed a three-dimensional transient thermal model to simulate the weld pool behavior, accounting for the moving heat source (typically modeled as a double-ellipsoidal or Gaussian distribution), convective and radiative heat losses at the surface, and the temperature-dependent thermal properties of copper.
Key Simulation Parameters
| Parameter | Typical Range | Notes |
|---|---|---|
| Arc current | 200–350 A | Higher currents compensate for heat loss |
| Arc voltage | 12–18 V | Depends on electrode extension and shielding |
| Travel speed | 50–150 mm/min | Slower speeds increase heat input per unit length |
| Electrode diameter | 3.2–4.0 mm | Tungsten, typically AC or DCEN |
| Shielding gas | Argon or Argon-Helium mix | Helium improves arc temperature |
| Base metal thickness | 6–25 mm | Simulation validated against this range |
| Preheating temperature | 0 °C (ambient) | No preheat condition studied |
The numerical model solved the heat conduction equation with a moving heat source term, incorporating the latent heat of fusion and solidification effects. The authors compared simulation results with experimental measurements obtained through thermocouple readings and macrograph examination of cross-sections. The weld pool dimensions (width, depth, and shape) predicted by the model showed reasonable agreement with experimental observations, validating the approach.
Key Technical Insights and Engineering Implications
Temperature Distribution Characteristics
The simulation results reveal that without preheating, the peak temperature at the weld pool surface reaches approximately 1600–1800 °C, while the temperature drops sharply within a few millimeters from the weld centerline. The liquid region is elongated in the direction of travel, and the solidification front moves rapidly due to the high thermal conductivity. The solidification rate is significantly higher than in steel welding, which promotes columnar grain growth and increases susceptibility to hot cracking.
Process Optimization Recommendations
Based on the simulation results, the authors proposed several strategies for achieving sound welds in copper TIG welding without preheating:
- Increased current density: Using smaller diameter tungsten electrodes to concentrate the heat input into a smaller area, thereby raising the local temperature above the melting point more effectively.
- Helium-containing shielding gas: Argon-helium mixtures (e.g., 75% Ar + 25% He) produce higher arc temperatures and deeper penetration due to the higher ionization energy of helium.
- Reduced travel speed: Slower welding speeds allow more time for heat to accumulate in the weld zone, increasing penetration depth.
- Electrode work angle control: Tilting the electrode forward (in the direction of travel) focuses the arc heat onto the leading edge of the weld pool, promoting deeper penetration.
Connection to Bimetal and Cladding Applications
While this study focuses on copper homogeneous welding, the findings have direct relevance to bimetal manufacturing involving copper-steel clad plates and copper/steel weld-overlay pressure vessels. In copper-steel bimetallic joints, the thermal mismatch between the two metals creates additional challenges: the copper side dissipates heat rapidly while the steel side retains heat, leading to asymmetric weld pool shapes and potential interface cracking. The simulation methodology developed in this study can be extended to model dissimilar metal weld pools, providing engineers with predictive tools for optimizing cladding process parameters.
Critical Reflection and Practical Considerations
The study's primary limitation is that it models the thermal field only, without coupling the thermal analysis to fluid flow, solidification, or residual stress calculations. In practice, the weld pool dynamics in copper are strongly influenced by thermocapillary convection and buoyancy-driven flow, which affect the actual weld shape and defect formation. Furthermore, copper welding is highly susceptible to hydrogen porosity due to copper's ability to dissolve hydrogen at high temperatures and release it during solidification. The simulation does not address this critical defect mechanism.
From an engineering practice perspective, the findings underscore the importance of process simulation as a complementary tool to empirical trial-and-error approaches. In the fabrication of copper-clad pressure vessels or copper-steel heat exchangers, where preheating may be restricted by design constraints or production schedules, understanding the weld pool thermal behavior enables engineers to select appropriate parameters that ensure full penetration and sound welds without resorting to extensive preheating that may be impractical for large-scale components.
Summary and Study Insights
This study provides a valuable foundation for understanding the thermal behavior of copper during TIG welding without preheating, demonstrating that numerical simulation can effectively predict weld pool geometry and guide process parameter selection. The key takeaway for practicing engineers is that copper's high thermal conductivity demands higher energy density inputs, and that the absence of preheating can be compensated through strategic adjustments to current, travel speed, shielding gas composition, and electrode geometry. For those involved in bimetal product manufacturing involving copper-steel interfaces, this work highlights the need for coupled multiphysics simulation approaches that account for both thermal and mechanical effects, as well as the critical role of hydrogen control in preventing porosity defects.