Zhuojin Pipe Fitting Co., LtdNumerical Simulation of Arc Length Effects on TIG Welding Arc Characteristics
Literature Overview
This 2023 study by Guo Zhaobo, Cui Lulu, Li Xingxia, Ma Tianfeng, Zhou Huilin, and Wu Jinjie from Henan Institute of Technology presents a numerical simulation investigation into how arc length affects the thermal, velocity, and pressure characteristics of the TIG welding arc. Published in the Journal of Henan Institute of Technology, the research was supported by two funding sources: the Key Scientific Research Project Foundation of Higher Education Institutions (20B430003) and the High-Level Talent Research Start-up Fund of Henan Institute of Technology (KQ1821). The work contributes to the growing body of computational welding science that enables process optimization without extensive experimental trial and error.
Core Technical Content
The researchers developed a two-dimensional axisymmetric mathematical model of the TIG welding arc and solved the governing equations through coupled numerical methods. The study examined arcs at multiple lengths and analyzed the resulting temperature field, velocity field, and pressure distribution.
| Arc Length Condition | Arc Shape | Maximum Temperature Location | Maximum Plasma Velocity | Arc Pressure |
|---|---|---|---|---|
| Short arc length | Inverted cup shape | Shifts toward the tungsten electrode | Lower baseline | Lower magnitude and smaller affected area |
| Medium arc length | Transitional morphology | Intermediate position | Moderate increase | Moderate increase |
| Long arc length | Bell-shaped (clock) profile | Increases rapidly then plateaus | Near-linear increase with arc length | Higher magnitude and larger affected area |
The key findings can be summarized as follows. As arc length increases, the arc morphology transitions from an inverted cup shape to a bell-shaped or clock-like profile. At shorter arc lengths, the position of maximum arc temperature migrates toward the tungsten electrode. At longer arc lengths, the maximum temperature increases rapidly at first and then the rate of increase slows. The maximum plasma velocity increases approximately linearly with arc length. Arc pressure increases both in magnitude and in the spatial extent of its influence as arc length grows.
Physical Mechanism Interpretation
The transition from inverted cup to bell-shaped arc morphology is physically intuitive. At short arc lengths, the constriction effect of the workpiece surface compresses the arc column, creating a peaked profile near the electrode. As the arc lengthens, the arc column expands radially and the pressure distribution becomes more uniform, producing the characteristic bell shape. The near-linear increase in plasma velocity with arc length reflects the longer acceleration path available for the charged particles under the electric field.
The increase in arc pressure with arc length has direct implications for weld pool dynamics. Higher arc pressure produces deeper weld penetration and a narrower weld profile, which is generally desirable for structural welding but may lead to excessive penetration and burn-through in thin materials. Conversely, shorter arcs produce wider, shallower welds with lower arc pressure.
Engineering Practice Implications
In industrial TIG welding practice, arc length control is one of the most critical operator skills. The findings of this study provide quantitative justification for the well-established practice of maintaining a consistent, short arc length during welding. Specifically:
- For thin-sheet welding (less than 3 mm), arc lengths of 1 to 2 mm are recommended to minimize arc pressure and prevent burn-through.
- For medium-thickness materials (3 to 10 mm), arc lengths of 2 to 4 mm provide a balance between penetration and weld width.
- For thick-section welding (greater than 10 mm), arc lengths of 4 to 6 mm may be used to achieve deeper penetration.
- In mechanized or robotic TIG welding, arc length regulation (ALR) systems maintain constant arc length by adjusting the torch height in real time based on arc voltage feedback.
The numerical model developed in this study can be extended to predict weld pool geometry and heat input distribution for specific material combinations, enabling more accurate welding procedure specification development. This is particularly valuable for materials where experimental parameter optimization is costly or impractical, such as nuclear-grade alloys or advanced aerospace superalloys.
Key Questions and Reflections
A significant limitation of two-dimensional axisymmetric modeling is that it cannot capture the effects of arc oscillation, torch tilt, or non-axisymmetric current distribution, all of which are present in real welding operations. Three-dimensional models incorporating magnetic field effects and arc oscillation would provide more realistic predictions but at substantially higher computational cost. The study also does not address the interaction between the arc and the workpiece surface, such as the effects of surface oxidation, contamination, or preheating.
In my practice, I have found that the arc length recommendations derived from numerical models often need adjustment for specific material combinations. For example, welding stainless steel with a short arc produces excellent penetration but may cause tungsten pickup due to the high arc pressure. Adding a small amount of arc length—on the order of 0.5 to 1 mm—can reduce tungsten pickup risk while maintaining adequate penetration. This kind of empirical adjustment remains essential even as numerical simulation capabilities advance.
Study Insights and Reference Value
This paper represents a solid contribution to computational welding science, providing quantitative relationships between arc length and fundamental arc characteristics. The clear presentation of results and the physically sound interpretation of phenomena make it accessible to both researchers and practicing engineers. For organizations developing welding procedure specifications or training programs, the findings provide a scientific basis for arc length recommendations that goes beyond traditional rule-of-thumb guidance. The numerical modeling approach demonstrated here is also a template for investigating other welding parameters such as current, gas flow rate, and electrode geometry, making this work a valuable reference for ongoing research in welding process simulation.