method can weld
FIGURE 1. The YLR
LASER WELDS AT VERY HIGH SPEED
Fiber lasers have now become the first choice for most high- power laser process- ing applications, but it was in the <1k W average power category that continuous-wave (CW) single-mode fiber lasers were first introduced for cutting applications in the late 1990s. Although
these lasers may be modulated at up to ~50kHz, they cannot
easily address low-duty-cycle, high-peak-power, conduction-limited spot welding.
More recently, quasi-CW (QCW) fiber lasers have become a commercial success,
one of the main reasons being the ease with which this low-duty-cycle spot welding regime can be addressed when the laser is in high-peak-power pulsed mode.
Manipulating the beam over a large field of view at very high speed using a galvanometer scanner is now used in this way to weld consumer electronic devices.
This technique resembles a scaled-down version of the multi-kilowatt remote welding technique [ 1] now employed in the automotive industry for applications such
as welding car doors and seats.
The single-mode version of IPG Photonics’ YLR150/1500 AC laser QCW fiber laser
(FIGURE 1) is unique in two ways. First, the very high-brightness, single-mode version
can produce spot sizes <30µm with standard cutting optics, allowing additional uses
in cutting and drilling. Secondly, in CW mode, these lasers can operate at signifi-
cantly higher average power than in the pulsed mode—for example, the 150/1500
QCW, rated at 150W in pulsed mode with 1500W peak power, can operate at >230W
in CW mode. Here, we show that this high-brightness version can also weld a wide
variety of thin metals at very high speed in CW mode.
Much has been written on the topic of keyhole welding, almost all based on high-
power multi-kilowatt lasers. The earliest work on keyhole welding with very bright,
Miyamoto [ 2]. He showed that smaller
keyholes are more efficient in convert-
ing laser power into molten metal.
Using QCW single-mode fiber lasers
and small, focused spot sizes, we show
that the same highly efficient keyhole
mechanism can be accessed—we refer
to this as micro keyhole welding.
Welding high-reflectivity metals
Developments in lasers and beam
delivery components are expand-
ing the range of metals that may be