Positioning Cutting Aligning Notching Welding
www.industrial-lasers.com SEPTEMBER/OCTOBER 2017 Industrial Laser Solutions 17
convinced on its pickling line’s ability to weld
high-strength materials within a short cycle time.
Furthermore, its automatically controlled, reliable
process and easy maintenance concept are beneficial features.
The welding machine is not only a crucial technological piece of equipment in every strip processing line, but also an entry cycle time factor and one
key component for utilized and maximized pro-
duction. If coils are not joined properly, the whole
process will stop: every strip
break or machine stoppage has
the potential to affect upstream
and downstream operations,
resulting in significant financial
The weld seam is only utilized
for a few minutes—at the very
end of the line, it will often be
cut out, but weld seam require-
ments and a reliable welding
process are very high. The entire
process is fully automated and
the sequences to join both strip
ends successfully are always
the same. What changes is the
material to be welded regard-
ing steel quality, strip thickness,
strip width, and thickness jump
from one coil to the next.
The welding process takes place every 3 to 5
min. In a pickling line/tandem cold mill, the weld
seam is bent numerous times with high tension
(up to 65 tons), travels more than 1000m through
the line at high speed (up to 1200m/min), and
eventually gets rolled and significantly reduced in
thickness with high forces in five mill stands (up
to 1800 tons).
The rule, and not the exception, in a current steel
plant is the production of modern high-strength
grades with high contents of alloying elements.
These grades tend to create extreme hardness increases in the weld seam area.
Induction pre- and post-heat treatment, or even additional buffering wire during
laser beam welding, are mandatory for these high-tech steel grades to improve
the ductility of the weld to allow successful production without any weld seam
breakages during a line run.
Another major requirement of the machine is a low cycle time. Since the lines are
producing continuously, the needed stops for welding must be as short as possible.
The process starts with tail-out threading of exiting coil and head-in threading of
entering coil with two pinch roll units, which position both ends of the coils to be
laser beam-welded into the welding machine. Strip centering devices located at the
entry and exit side center-align
both strip ends. During strip
centering, the required welding
parameters are calculated in the
welder’s programmable logic
controller based on cast analysis and strip thickness coming
from level 2 data. The strip thickness is verified during clamping
of both strip ends.
A double cross-cut shear
is used to cut both strip ends
simultaneously to prepare the
strip ends for welding. The cut
scrap drops through the welder’s shear onto a scrap discharge system, which is com-
bined with the notcher scrap on
a conveying belt. Test welds or
notch samples can be conveyed
to the operator side for inspection. In conjunction with the cutting process, a hole
for the weld seam detection can be punched (FIGURE 2).
The prepared strip ends are aligned relative to each other in terms of width and
thickness to achieve the desired welding joint geometry. Before the strip ends are
welded together, the position and geometry of the welding joint are measured by a
camera. The position-controlled welding head guarantees the seam to be exactly
positioned on the joint. If there are any deviations in position or geometry because
of wear or wrong alignment of machine components, the welding traversing unit
adapts to the new conditions and automatically controls the welding head into the
correct position. In this way, the weld seam is always positioned exactly on the
joint, which prevents the weld seam from breaking. Furthermore, repairs can be
FIGURE 2. A metallographic cross-section of a laser-welded seam
(martensitic steel with tensile strength of 1200MPa) from a notch
sample after rolling; the weld seam was rolled full force with no
mill relief during weld seam transit through 6 mill stands.