deposition, while the 50 mm-mrad ap-
plications typically are brazing, heat
treating, and laser metal deposition.”
Wavelengths in the “9xx” nm wavelength range are slightly shorter than
those of traditional 1 µm lasers such as
disk, fiber, and Nd:YAG. These short-
er wavelengths allow better absorption in highly reflective materials such
as copper, brass, and aluminum, says
Ryba. Additionally, the lower-beam-quality versions are ideal for brazing
and surface treatments due to the large
divergence and the more distinct flattop mode profile, especially when compared to high-beam-quality disk and
fiber lasers where a relatively complex
beam delivery and large focal lengths
are needed to achieve the same desired
effects at the workpiece.
Replacing traditional processes
The attributes of high-power laser diodes
can lead to transformations in certain
areas of materials processing. “Major
‘direct-diode’ applications for these
products are transforming the surface
properties of large metal parts through
heat treating—historically called case
hardening—and cladding,” explains
Frank Gaebler, director of marketing at
Coherent (Santa Clara, CA).
Coherent manufactures laser diodes
and laser-diode arrays over a broad range
of output powers in configurations from
single emitters through linear bars (fi-
ber-coupled and free-space) up to 2D arrays of bars. The company’s most powerful system produces 10 k W of output
power at 975 nm; internally, it consists
of five bars, each derated to 2 k W to ensure tens of thousands of hours of maintenance-free operation at or above specified power, says Gaebler.
The free-space output of the laser system can be configured to deliver a variety of interchangeable beam shapes (with
widths from 1 to 12 mm and lengths from
6 to 36 mm) to enable rapid processing
of large areas with a high degree of control over process parameters.
The product is targeted at large-area
cladding applications to create a metal-
lurgically bonded layer on the surface of
a metal, usually some type of steel (see
Fig. 3). “This is typically done in order to
transform the surface properties—for im-
proved wear characteristics or high corro-
sion resistance—without modifying the
desirable bulk properties (such as tensile
strength and rigidity) of the part,” says
Gaebler. “Cladding is also often used to
refurbish worn parts.”
Traditionally, large parts were main-
ly clad by thermal spray (for example,
high-velocity oxygen-fuel spraying, or
HVOF) or plasma-transfer arc (PTA)
or, less commonly, electroplating, as
Gaebler explains. Thermal spraying is a
fast and relatively cheap process where
metal powder is melted and sprayed on
to the substrate, where it solidifies. The
