By Brett Thompson
Alaser beam is a remarkable thing. A continuous-wattage laser beam has energy densities more than 4 trillion
times higher than the sun’s focused energy, and
manufacturers have determined ways to utilize
this extraordinarily high power density to do
everything from cutting and welding sheet
metal to drilling holes in PCB boards.
Lasers can cut, join, and subtract material.
They can even add material via laser metal deposition or 3D printing. We can vary power levels,
pulse frequencies,;and;energy densities via beam
diameter manipulation,;among other;ways, all so
that the laser beam can induce the right;material
reactions;for;various processes. Truly, the laser’s
use to industry is vast and varied.
Wavelength Absorption in Cutting
Di;erent materials interact di;erently with
various wavelengths of light, making some laser sources more e;cient at processing certain
materials than others. For example, one of the
known benefits of cutting metal for industrial
applications with 1-µm-wavelength lasers is the
increase in speed when compared to cutting
with CO2 lasers. Much of this comes from the
high absorbency of that wavelength of light into,
for example, carbon steel (see Figure 1). A small
beam of light e;ectively absorbed into the steel
being cut translates directly into higher speeds
when fusion cutting (that is, cutting with a nonreactive gas such as nitrogen) in carbon steel.
During cutting with a solid-state laser such
as a disk or fiber, the focused beam diameter,
combined with the high absorption percentage
of the laser’s emission, allows for very fast cut
speeds. This performance bump over CO2 is
seen primarily in thin to medium-thick materials,
with the advantage shrinking as material thickness grows. The diameter of the beam can be
controlled to an extent via such things as light
collimation or by shifting the position of the focusing lens (see Figure 2), but there’s a limit to
how large or small a beam can be produced.
Beam diameter range is determined by the
size of the beam delivery fiber (see Figure 3).
A 100-µm beam delivery fiber is common for
lasers used for cutting sheet metal. This core
diameter delivers high beam quality and high
cut speeds. As material thicknesses become
greater, the very small spot size becomes a liability, limiting performance, cut quality, and
To mitigate this, it is possible to choose a
larger core diameter. The downside to this, of
course, is that the minimal beam diameter becomes much larger than what the smaller core
can provide. Although quality and process reliability improve substantially, speed in thinner
materials is compromised.
This is where the dual-core fiber can help.
One core of a small diameter is installed coaxially to a core of a large diameter. A programmable shutter changes which core is active. Such a
fiber is designed to make a laser cutting system
achieve high speeds in thin materials and high
quality and reliability in thicker materials.
Beam Diameter and Focus in Welding
Beam diameter serves another function when
welding. While not new by any means, laser
welding has a lot of appeal, both at job shops
and OEMs, because of its potential cost savings from less rework; greater engineering flexibility; and the elimination of expensive, time-consuming downstream processes like grinding
In sheet metal, laser welding occurs in two primary ways: heat conduction welding and deep-penetration welding. Heat conduction welding
uses a strongly defocused beam situated above
the workpiece. The beam’s focus position typically ranges from 6 to 12 mm above the workpiece surface, but it can be as high as 25 mm.
» Figure 1
Energy from the 1-micron wavelength of the disk and fiber laser helps increase cutting speeds during fusion cutting.
From cutting to welding to ablating,
the laser’s potential continues to grow