CLADDING TECHNOLOGY SHANXI CO., LTDRotary Dual-Focus Laser-TIG Hybrid Welding of 304 Stainless Steel
Literature Overview
This paper, published in the Journal of Beihang University in 2008 by Li Xiaohui, Wang Su, and Xia Caiyun from Beihang University, investigates the rotary dual-focus laser-TIG hybrid welding process for 304 stainless steel. The study explores the synergistic effects of combining a rotating dual-focus laser beam with a TIG arc to achieve deep penetration and high welding speed while maintaining good weld quality.
Core Technical Content
The rotary dual-focus laser-TIG hybrid welding process combines a laser beam with a TIG arc in a coaxial configuration. The laser beam is focused into two focal spots that are rotated around the weld axis, creating a helical heat input pattern. The TIG arc provides additional heat input and a stable arc force that helps to stabilize the keyhole and reduce porosity. The dual-focus configuration allows for a wider heat input area compared to a single-focus laser, which reduces the tendency for excessive penetration and burn-through.
The authors used a fiber laser with a power of 4 kW and a TIG arc with a current of 100 to 150 A. The laser beam was focused into two focal spots with a separation distance of 2 to 4 mm, and the focal spots were rotated at a speed of 500 to 2000 rpm. The welding speed was 2 to 5 m/min, which is significantly higher than conventional TIG welding speeds of 0.5 to 1.5 m/min.
Key Welding Parameters
| Parameter | Conventional TIG | Rotary Dual-Focus Laser-TIG Hybrid |
|---|---|---|
| Heat source | TIG arc only | Laser + TIG arc |
| Laser power | N/A | 4 kW |
| TIG current | 100 - 150 A | 100 - 150 A |
| Welding speed | 0.5 - 1.5 m/min | 2 - 5 m/min |
| Penetration depth | 1 - 3 mm | 5 - 15 mm |
| Weld width | 4 - 8 mm | 3 - 6 mm |
| Rotation speed | N/A | 500 - 2000 rpm |
The authors conducted microstructural analysis, mechanical property testing, and non-destructive testing of the weld joints. The results show that the rotary dual-focus laser-TIG hybrid welding process produces weld joints with excellent mechanical properties and low defect rates. The weld metal exhibits a fine, equiaxed grain structure with a grain size of 20 to 50 micrometers, which is finer than the grain structure produced by conventional TIG welding.
Interpretation of Technical Points
The rotary dual-focus configuration is a key innovation in this paper. By rotating the two focal spots around the weld axis, the heat input is distributed more uniformly along the weld length, which reduces the tendency for excessive penetration and burn-through. The dual-focus configuration also creates a wider heat input area, which promotes the formation of a more equiaxed grain structure in the weld metal.
The combination of the laser beam and the TIG arc provides several synergistic benefits. The laser beam creates a deep, narrow keyhole that achieves high penetration, while the TIG arc provides additional heat input and a stable arc force that helps to stabilize the keyhole and reduce porosity. The TIG arc also provides a shielding gas flow that protects the weld pool from atmospheric contamination, which is particularly important for stainless steel welding.
Microstructural and Mechanical Properties
| Property | Base Metal (304 SS) | Conventional TIG Weld | Rotary Dual-Focus Laser-TIG Hybrid Weld |
|---|---|---|---|
| Grain size | 50 - 100 μm | 50 - 80 μm | 20 - 50 μm |
| Tensile strength | 520 - 620 MPa | 480 - 550 MPa | 500 - 580 MPa |
| Elongation | 40 - 50% | 35 - 45% | 38 - 48% |
| Hardness | 150 - 180 HV | 140 - 170 HV | 150 - 180 HV |
| Defect rate | N/A | 2 - 5% | < 1% |
The mechanical properties of the rotary dual-focus laser-TIG hybrid weld joints are comparable to or better than those of conventional TIG weld joints. The tensile strength is slightly lower than the base metal, which is typical for stainless steel welds, but the elongation and hardness are maintained at levels that are comparable to the base metal. The defect rate is significantly lower than that of conventional TIG welding, which is attributed to the stable keyhole and the improved shielding gas coverage provided by the TIG arc.
Integration with Engineering Practice
The rotary dual-focus laser-TIG hybrid welding process is particularly suitable for welding thick-walled 304 stainless steel components where high welding speed and deep penetration are required. For example, in the fabrication of stainless steel pressure vessels and heat exchangers, this process can be used to achieve single-pass welding of thick plates with excellent mechanical properties and low defect rates.
The process is also applicable to weld overlay cladding of 304 stainless steel on carbon steel substrates. The deep penetration and high welding speed of the laser-TIG hybrid process allow for the deposition of thick overlay layers in a single pass, which reduces the number of passes required and improves the dilution control. However, the implementation of this process requires specialized equipment, including a high-power fiber laser, a rotary dual-focus lens, and a TIG welding power source, which may be costly for small-scale production.
Key Questions and Reflections
One question that arises from this paper is the effect of the rotary dual-focus configuration on the weld geometry and the dilution ratio. The authors primarily studied the welding of 304 stainless steel to 304 stainless steel, but in practice, the process may be used to weld dissimilar materials, such as 304 stainless steel to carbon steel. In such cases, the dilution ratio must be carefully controlled to prevent the formation of brittle intermetallic compounds at the weld interface.
Another consideration is the effect of the rotation speed on the weld quality. At low rotation speeds, the heat input may be concentrated in a narrow area, leading to excessive penetration and burn-through. At high rotation speeds, the heat input may be too diffuse, leading to incomplete fusion and lack of penetration. The authors found that an optimal rotation speed of 1000 to 1500 rpm provides the best weld quality, but this may vary depending on the material thickness and the welding parameters.
Study Insights and Implications
This paper demonstrates the potential of the rotary dual-focus laser-TIG hybrid welding process for achieving high-quality weld joints in 304 stainless steel. The combination of a rotating dual-focus laser beam and a TIG arc provides synergistic benefits that result in deep penetration, high welding speed, and low defect rates. For engineers involved in stainless steel welding and cladding, this process offers a promising alternative to conventional TIG welding, particularly for thick-walled components where single-pass welding is desired. The key takeaway is that the rotary dual-focus laser-TIG hybrid welding process is a versatile and efficient technology for stainless steel welding, but its successful implementation requires careful optimization of the welding parameters and the use of appropriate equipment.