Laser-Arc Welding Explained: The Hybrid Approach

The use of laser deep penetration welding technology (i.e., keyhole welding) allows for welding metal thicknesses of over 20mm in a single pass with high welding speeds and a relatively small heat-affected zone. Due to the fine nature of the laser beam, the joint gap requirements during welding are high (<0.1mm), and the bridging ability of the molten pool is relatively poor.

Additionally, the intense reflection from the workpiece surface affects the transfer of beam energy to the workpiece, causing the evaporation, gasification, and ionization of the molten metal, forming photo-induced plasma, which significantly affects the stability of the welding process. As a result, the actual energy utilization of the laser during welding is extremely low.

Taking a CO2 laser as an example, its quantum efficiency is 38%, and its electro-optical efficiency is 15% to 20%, resulting in a total efficiency of less than 20% during laser operation, leading to significant energy wastage.

On the other hand, arc welding, as a mature metal joining technology, has been widely used in the industry. However, due to the limitation of beam energy density, the welding thickness and speed of arc welding are relatively small compared to high-energy beam welding. The heat-affected zone of the weld seam is relatively large, and the weld seam has a smaller depth-to-width ratio.

Due to the strong bridging ability of the electric arc, the joint gap requirements for the welding workpiece are not strict, allowing for up to 10% of the workpiece thickness, and the arc energy utilization rate exceeds 60% of the output power.

Laser-arc hybrid heat source welding technology is an emerging special manufacturing technology that combines two heat sources with drastically different physical properties and energy transfer mechanisms, simultaneously acting on the same processing position.

This approach fully leverages the advantages of both heat sources while compensating for their respective shortcomings, resulting in a completely new and efficient heat source. The schematic diagram of the laser-arc hybrid welding principle is shown in Figure 3-88.

Compared to single heat source welding, using hybrid heat source welding can double the welding speed under the same process parameters. Compared to using the laser beam alone, the penetration depth of the joint increases by 20%. Furthermore, the requirements for the quality of the laser beam, joint gap, and weld tracking accuracy are significantly relaxed.

Even with a joint root gap of 1mm, good joint formation can be achieved using laser-arc hybrid heat source welding, surpassing the capabilities of laser welding with filler wire. This approach effectively utilizes the advantages of both methods: the arc softens the workpiece surface initially, followed by the high-energy laser beam piercing the workpiece to create a small hole for high-speed keyhole welding.

The involvement of the arc not only reduces the reflectivity of the metal surface to the laser beam but also allows the arc plasma to absorb the photo-induced plasma, effectively improving the energy transfer efficiency of the laser beam.

Therefore, the laser-arc hybrid heat source is an ideal welding heat source for aluminum alloys. After adopting laser-arc hybrid heat source welding technology, the welding speed has doubled, welding distortion has significantly decreased, welding capability is on par with laser welding, and the bridging transition capability is stronger than that of laser welding. Additionally, the hardness in the weld seam area noticeably decreases.

Figure 3-88: Schematic diagram of laser-arc hybrid welding principle
Figure 3-88: Schematic diagram of laser-arc hybrid welding principle

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