Laser beam welding (LBW) is a fusion welding technique used to fuse metal parts together through the use of a laser. At Carrs, we focus on the Nd:YAG (neodymium-doped yttrium aluminium garnet) solid-state lasers.
These lasers can be subclassified into pulsed lasers or continuous wave lasers (CW) depending on their operating mode.
Pulsed Nd:YAG lasers are usually operated in the Q-switching mode. In this mode, an optical switch located in the laser cavity waits for a maximum population inversion before dumping the power through the laser optics in the form of a pulse. The pulsed mode allows higher laser peak powers, but only for a short duration as the laser medium needs to recover before the next pulse.
Continuous Wave Lasers
For a continuous wave operation, the population inversion of the laser medium needs to be continually replenished by a steady pump source. This allows for a continuous laser operation, but only with a lower laser power (when compared to the pulsed lasers). The main reason for the lower power is the excessive heat produced by pumping the laser at higher power levels and the inability to effectively cool the laser medium down.
Why choose Pulsed or Continuous Wave?
Pulsed laser welding is achieved by short pulses which leads to a minimal amount of heat transferred onto the part being welded as this allows partial cooling to occur between each spot. Pulsed welding is then used on heat sensitive items which cannot be exposed to high temperatures. On the same hand, pulsed welding also allows for more control of the weld making it ideal for material cladding and repairs on smaller more intricate parts.
Continuous wave welding does not have the partial cooling effect seen on pulsed welding, which means the temperature will rise to higher values. However, this heat build up leads to deeper and wider welds allowing for the welding of thicker and bigger parts.
In terms of weld depths, pulsed welding shines between 0.1 to 1.5mm whilst continuous wave welding is used for depths between 1 to 6mm.
Benefits of Laser Welding
- Low thermal distortion – due to low heat input.
- Deep penetration without high heat input – high weld aspect ratio due to high power density.
- Minimal dilution when welding dissimilar metals – lower propensity for cracking.
- Smaller heat affected zones (HAZ) – when compared to other welding technologies.
- Ability to weld materials with variable thicknesses – welding of complicated joint geometries.
- Welding of heat sensitive applications – due to low heat input and a focused beam.
- High precision – exact placing of the energy spot via camera optics.
- Large working distance – no need for physical contact with parts to weld.