1. Heat Input
In laser welding, energy is delivered in the form of a concentrated laser beam. This energy is absorbed by the surface of the metal and converted into heat. The amount of heat input depends on several factors:
Laser power
Welding speed
Beam focus
Material properties
Higher laser power or slower welding speed increases heat input, while better focus ensures more concentrated energy delivery. Different materials absorb laser energy differently depending on their reflectivity and thermal conductivity.
2. Molten Pool (Weld Pool) Formation
As the laser heats the metal surface, it reaches the melting point and forms a molten pool. The shape and size of the molten pool depend on:
Laser energy density
Exposure time
Heat conduction through the surrounding material
In deep penetration welding, the energy density is so high that the metal vaporizes, forming a narrow keyhole that allows the laser to penetrate deeper. In heat conduction welding, the energy is lower, and only the surface melts without forming a keyhole.
The molten metal flows within the pool due to surface tension, gravity, and the recoil pressure from metal vaporization. Proper control of this dynamic behavior is essential to avoid defects like porosity or uneven welds.
3. Solidification Process
After the laser beam moves away, the heat dissipates, and the molten pool begins to cool and solidify. The solidification process affects the final microstructure, strength, and appearance of the weld.
Key factors influencing solidification include:
Cooling rate: Faster cooling can lead to finer microstructures and stronger welds.
Alloy composition: Different elements solidify at different temperatures, which can influence grain structure.
Thermal gradients: Uneven cooling may cause stress, cracking, or distortion.
Controlling the heat input and cooling rate ensures that the weld solidifies smoothly without internal defects.
Conclusion
The energy transfer mechanism in laser welding involves three main stages: heat input, molten pool formation, and solidification. Each stage plays a vital role in determining weld quality. By understanding and controlling these processes, manufacturers can achieve stronger, cleaner, and more reliable welds.
--Rayther Laser Lyra Zhang