WELDING PROCESS REDUCES SEAM
Diode laser brazing is a well-established method for joining galvanized steel sheets in series produc- tion of automotive bodies. Brazing optics, developed specifically for this application, are moved along the joint by means of robots. The
laser beam is transported by a fiber to the optics, and
copper silicon wire (CuSi3) is melted within the brazing process.
Key to the success of laser brazing technology, besides a
stability that is similar to a weld, is mainly with the high aes-
thetic quality of the joints. Laser-generated brazing seams
are known for their smooth, clean surfaces and junctions to
the joining parts. This is visually appealing and it almost completely spares post-processing, allowing immediate painting
after cleaning possible. Laser-based brazing enables such a
unique impression of the joint that, unlike conventional joining techniques, cover parts and their storage and assembly can be saved.
However, laser brazing technology has not been able to
meet—at least partially—the expectations placed on it.
Automobile manufacturers have increasingly moved towards
using hot-dip galvanized sheets in the body. Hot-dip galvanizing is more corrosion-resistant than the classical elec-
tro-galvanizing, so the changeover offers technical and economic advantages.
Laser brazing does not produce the usual results because
of the new surface features of the sheets. In areas close to the
joints, spatter increasingly occurs—especially micro-spat-
ters—that can hardly be recognized at the beginning, but
clearly appear after painting. The qual-
ity of the joint itself decreases, as it is
rougher and often shows the so-called
wavelets that, if excessive, can exceed
the required joint appearance. These
procedural difficulties have caused
automobile manufacturers to seek alternative solutions from
At that time, we had been testing brazing with a rectan-
gular spot instead of the traditional round single spot. To
produce a rectangular spot in a brazing optic, a homogeni-
zation module is put into a Scansonic ALO3 brazing optic
(FIGURE 1a). Such homogenizers have been used for years
by Laserline to create rectangular spots for hardening with
laser powers up to 10k W.
FIGURE 1. A
the Scansonic ALO3
brazing optic (a)
and the optimized
rectangle spot (OR