Svetsaren 1/2008 - Esab

Figure 1. GMAW tack welding head, including PEH
Control on swivelling arm and laser tracking system.
without increasing the minimum pipe diameter to
be welded. It is, therefore, not easy to fulfil a
stable weld over a long distance.
ESAB`s solution is of a rigid, pre-stressed design
to be linearly accurate over long distances (Figure
2). The rear part of the boom is a steel frame that
is bolted to the concrete floor. The rear end of the
boom has a pivot point in the frame and can be
tilted by an hydraulic cylinder, to secure feeding-in
of the pipes without danger of collision. For height
positioning, the boom can be moved vertically to
adapt to different pipe diameters, having in mind
fixed carriages in height for the pipes.
Four steel wire brushes press on the inside surface
of the pipe for voltage pick-up and for stabilisation.
The voltage pick-up brushes are quite important to
get the right voltage signal back to the process
controller, to fulfil the demands of the given WPS.
This is believed to be a unique technique to correct
the voltage losses over the long distance to the
welding head. The stabilisation of the boom is a
further effect to keep the weld pool stable.
Due to the high torque of ESAB’s VEC wire feeding
motors, the decision was taken to position the wire
feeding equipments at the end of the boom, while
pushing the wire into the boom. This is different
from most solutions in the market, but advantageous
from a customers’ point of view. There is
more space at the welding head for the positioning
of the other components. and less weight at the
welding head side. Wire straightness devices and
wire feed motors are easily reachable and any
service or exchange of feeding or guiding rolls is
fast. There is also no temperature effect on the
wire feeders and the inbuilt tachometer controls.
Figure 2. Internal boom (18m) with welding head for longitudinal pipe welding.
Internal welding head
ESAB has developed internal welding heads
designed for up to 4 wires. As previously
mentioned, many different components had to be
integrated. The welding head itself is connected
with the internal boom via a small cross slide, to
always be guided in the middle of the weld
preparation. A laser sensor controls the welding
head via the cross slide. If a sideways movement
outside the limit of the cross slide is necessary, a
signal is transferred to the pipe carriage to turn
the pipe accordingly. The welding process is
supervised on an external monitor via a video
camera. Also, the laser signal is distributed on the
control panel. The wires are smoothly guided via
wire liners into the contact equipment of the
welding head (Figure 3). The contact equipment is
built up with spring-loaded contact jaws and fixed
spacers between the different wires. The spacers
have a fixed angle, so that the wires have a defined
fixed position for a given welding procedure. If a
different set up of the wires is needed when
changing pipe dimensions and accordingly the
WPS, the spacers can be exchanged for a
different set. This is normally not necessary.
Figure 3. Internal longitudinal welding head (4 wires) in test phase, with 4 voltage pick up brushes with pneumatic cylinders
in front and behind the welding head.
Return Current System
One of the most important safeguards for a stable
welding process is to secure the current flow from
28 - Svetsaren no. 1 - 2008