CLADDING TECHNOLOGY SHANXI CO., LTDExperimental Research on High-Power Fiber Laser and TIG Hybrid Welding
Literature Overview
This 2014 study, published in Laser & Optoelectronics Progress (中国激光), was conducted by the Beijing University of Technology Laser Engineering Research Institute under the National Natural Science Foundation of China (Grants 51275013 and 51175008) and the National Science and Technology Major Project (2013ZX04001-131). The research presents a comprehensive experimental investigation of high-power fiber laser–TIG hybrid welding, including process characterization, weld quality evaluation, and the influence of process parameters on weld geometry and mechanical properties.
Core Technical Points
Hybrid laser-arc welding combines the deep penetration and high efficiency of laser welding with the stable arc and good wetting characteristics of arc welding. The high-power fiber laser component provides the primary energy for deep penetration, while the TIG arc contributes additional heat input, improves arc stability, and reduces the sensitivity to beam positioning errors.
The hybrid process is particularly advantageous for welding medium to thick-section materials where pure laser welding may struggle with penetration depth or where pure arc welding lacks the productivity. The synergistic interaction between the laser and the arc creates a complex plasma environment that influences the weld pool dynamics, spatter formation, and weld geometry.
Process Configuration and Parameters
| Parameter | Range Investigated | Optimal Range |
|---|---|---|
| Fiber laser power | 2–6 kW | 3–5 kW |
| TIG current | 60–180 A | 100–150 A |
| Travel speed | 150–800 mm/min | 300–500 mm/min |
| Laser-arc distance | 0–3 mm | 0–1 mm |
| Arc lead angle | 0–15° | 5–10° |
| Shielding gas | Ar, Ar/CO2, Ar/He | Ar or Ar/He |
| Wire diameter | 1.0–1.6 mm | 1.2 mm |
Weld Geometry and Penetration
The hybrid process achieves significantly greater penetration depth than either process alone. At comparable power inputs, the penetration depth of the hybrid process can exceed that of pure laser welding by 20–50%, due to the additional heat input from the arc and the synergistic interaction between the laser plasma and the arc plasma.
The weld geometry exhibits a characteristic keyhole profile with a narrow top width and deep penetration, combined with good sidewall fusion and reduced undercut. The arc component fills the gap left by the laser keyhole, resulting in a smoother weld surface and reduced risk of incomplete fusion defects.
Penetration Comparison
| Process | Laser Power (kW) | Arc Current (A) | Penetration (mm) | Weld Width (mm) |
|---|---|---|---|---|
| Pure laser | 3 | 0 | 4.5 | 2.5 |
| Pure TIG | 0 | 150 | 2.0 | 8.0 |
| Hybrid | 3 | 150 | 6.5 | 4.0 |
| Hybrid | 5 | 150 | 8.0 | 4.5 |
Weld Quality and Defect Analysis
The hybrid process produces welds with reduced defect rates compared to pure laser welding, particularly in terms of porosity and incomplete fusion. The arc plasma acts as a stabilizing influence on the keyhole, reducing the tendency for keyhole collapse and porosity formation.
Common defects observed in hybrid laser-TIG welding include:
| Defect Type | Cause | Countermeasure |
|---|---|---|
| Porosity | Keyhole instability, gas entrapment | Optimize laser-arc distance, improve shielding |
| Incomplete fusion | Excessive travel speed, insufficient heat input | Reduce travel speed, increase power |
| Undercut | Excessive arc current, improper torch angle | Adjust arc lead angle, reduce current |
| Excessive spatter | High arc voltage, wire feed instability | Optimize wire feed parameters |
| Cracking | Residual stress, material composition | Post-weld stress relief, filler selection |
Mechanical Properties
The mechanical properties of hybrid welded joints are generally comparable to or better than those of pure laser welded joints. The weld metal tensile strength is influenced by the filler material composition and the dilution ratio, while the HAZ properties depend on the heat input and cooling rate.
The hybrid process produces a narrower HAZ compared to pure arc welding, due to the concentrated energy input of the laser component. This results in less microstructural degradation in the base metal and better retention of the base metal mechanical properties.
Plasma Interaction and Process Physics
The interaction between the laser beam and the TIG arc creates a complex plasma environment that influences the welding process dynamics. The laser-induced plasma plume can deflect the arc plasma, while the arc plasma can affect the laser beam propagation through the atmosphere. Understanding these interactions is essential for process optimization and stable operation.
The laser-arc distance is a critical parameter that determines the degree of interaction. At zero distance, the laser beam is focused directly onto the arc cathode, creating intense interaction but also increasing the risk of arc instability. At larger distances, the interaction is reduced, but the synergistic benefits are diminished.
Engineering Practice Implications
For pressure vessel fabrication, the high-power fiber laser–TIG hybrid process offers a viable alternative to conventional multi-pass arc welding for thick-section joints. The reduced number of passes required translates to shorter fabrication times, lower distortion, and reduced residual stress levels.
In the context of weld overlay cladding for bimetallic pressure vessels, the hybrid process can be adapted for single-pass or multi-pass overlay welding with high deposition rates. The laser component ensures deep penetration into the substrate for metallurgical bonding, while the arc component provides sufficient deposition rate for thick overlay layers.
The process qualification of hybrid laser-TIG welding under NB/T 47014 or ASME IX requires demonstration of weld quality through mechanical testing, non-destructive examination, and metallographic evaluation. The experimental data presented in this study provides a foundation for establishing qualified welding procedure specifications (WPS) for hybrid laser-TIG welding.
Study Insights and Reflections
This research contributes significantly to the understanding of the physical mechanisms governing hybrid laser-TIG welding and provides practical guidance for process parameter selection. The systematic investigation of process parameters and their effects on weld quality is essential for establishing reliable process windows for industrial application.
The study also highlights the importance of the laser-arc interaction in determining weld quality. The plasma morphology and dynamics, which are influenced by the relative positions and orientations of the laser beam and the TIG arc, play a crucial role in keyhole stability and defect formation. This insight is directly relevant to the design of hybrid welding systems for industrial applications.
For engineers involved in cladding and bimetallic product manufacturing, the hybrid laser-TIG process represents a versatile tool that can be adapted for various welding configurations, including butt joints, fillet joints, and overlay cladding. The ability to achieve deep penetration with good surface quality in a single pass makes it particularly attractive for fabrication of pressure vessel components where weld integrity is critical.