CLADDING TECHNOLOGY SHANXI CO., LTDEffect of TIG Welding Parameters on Holographic Interference Fringes
Literature Overview
This 2020 study by Fan Chenglei, Chen Chao, Lin Sanbao, Yang Chunli, and Di Zhongju from the State Key Laboratory of Advanced Welding and Joining at Harbin Institute of Technology investigates how TIG welding parameters influence the holographic interference fringe patterns observed during welding. The research was funded by the National Natural Science Foundation of China (Grant No. 51675130) and published in the Transactions of the China Welding Institution. Holographic interferometry is a full-field optical measurement technique that can detect sub-micron surface deformations, making it a powerful tool for studying welding-induced deformation and residual stress fields.
Core Technical Content
The study employed double-pulse holographic interferometry to record fringe patterns before and after welding, providing quantitative maps of surface displacement and strain fields. The TIG welding was performed on carbon steel plates with varying parameters including welding current (100–200 A), travel speed (50–150 mm/min), arc length (2–6 mm), and electrode stick-out (3–8 mm). The fringe patterns were analyzed to extract peak displacement values, displacement field symmetry, and deformation zone width.
The key finding is that welding current has the most significant influence on the deformation field. At 100 A, the peak displacement is approximately 0.05 mm with a narrow deformation zone width of 8 mm. At 200 A, the peak displacement increases to 0.18 mm with a deformation zone width of 22 mm. The deformation field exhibits a characteristic butterfly pattern symmetric about the weld centerline, with the maximum displacement occurring at a distance of approximately 1.5 times the weld width from the centerline.
Travel speed has a secondary but still significant effect. At 50 mm/min, the peak displacement is 0.12 mm, while at 150 mm/min it decreases to 0.06 mm. The deformation zone width also decreases with increasing travel speed, from 18 mm at 50 mm/min to 10 mm at 150 mm/min. Arc length and electrode stick-out have a more modest effect, primarily influencing the symmetry of the deformation field rather than the peak displacement magnitude.
Key Technical Parameters and Analysis
| Parameter | Low Value | High Value | Effect on Peak Displacement | Effect on Deformation Zone Width |
|---|---|---|---|---|
| Current (A) | 100 | 200 | Increases from 0.05 to 0.18 mm | Increases from 8 to 22 mm |
| Travel speed (mm/min) | 50 | 150 | Decreases from 0.12 to 0.06 mm | Decreases from 18 to 10 mm |
| Arc length (mm) | 2 | 6 | Increases from 0.07 to 0.11 mm | Increases from 12 to 18 mm |
| Electrode stick-out (mm) | 3 | 8 | Increases from 0.08 to 0.13 mm | Increases from 14 to 20 mm |
The deformation mechanism can be understood through the thermal cycle experienced by the plate. At high current and low travel speed, the large heat input causes extensive plastic deformation in a wide zone surrounding the weld. The material expands during heating and contracts during cooling, but the plastic flow during heating is not fully recovered during cooling, resulting in permanent deformation. At low current and high travel speed, the heat input is concentrated in a narrow zone, and the deformation is primarily elastic with limited plastic flow.
The holographic fringe patterns also reveal information about the residual stress field. The fringe density is highest in the region adjacent to the weld, indicating high strain gradients. The symmetry of the fringe pattern provides a qualitative measure of the balance between the compressive stress zone near the weld and the tensile stress zone further away. Asymmetric fringe patterns indicate uneven thermal input, which may be caused by arc instability, electrode misalignment, or joint geometry irregularities.
Engineering Practice Implications
The findings of this study have direct implications for welding procedure optimization in production environments. For applications where dimensional accuracy is critical, such as in aerospace structures, precision machinery, or thin-walled pressure vessels, the welding parameters should be selected to minimize deformation. A practical approach is to use lower current (100–140 A) with higher travel speed (100–150 mm/min) to reduce heat input and deformation. For thicker sections where higher heat input is necessary to achieve full penetration, deformation control strategies such as backstep welding, intermittent welding, or mechanical clamping should be employed.
The holographic interferometry technique itself offers a non-contact, full-field measurement capability that is valuable for process monitoring and quality control. In a production setting, simplified holographic or speckle interferometry systems could be used to monitor welding-induced deformation in real time, providing immediate feedback for process adjustment. The fringe pattern analysis can also be used to detect welding defects such as lack of fusion, undercut, or excessive burn-through, as these defects produce characteristic fringe anomalies.
Study Insights and Reflections
This research demonstrates the power of optical measurement techniques for understanding welding-induced deformation at a fundamental level. The quantitative relationship between welding parameters and deformation magnitude provides a basis for predictive modeling and process optimization. Engineers can use these findings to select welding parameters that minimize deformation while still achieving the required weld quality. The study also highlights the importance of understanding the deformation mechanism: by controlling the thermal cycle and plastic flow, it is possible to design welding sequences that minimize residual stress and distortion. For complex geometries, the deformation field can be predicted using finite element analysis calibrated with the experimental data from holographic measurements, enabling virtual process optimization before physical welding begins.