REHM TIGER 180 AC/DC ULTRA, Operating Instructions Manual

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Operation
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With AC welding the negative pole is usually on the electrode. The negative pole
is the cooler pole, this means that the current capacity and the service life of the
tungsten electrodes is significantly longer than with positive pole welding.
With DC welding the capacity of the electrode is strongly affected by the balance
setting. The balance setting is used to distribute the positive and negative share
of the welding current between the electrode and the workpiece. During the
positive half-wave the aluminium oxide skin is destroyed and a high temperature
occurs on the electrode. During the negative half-wave the electrode cools down
and the aluminium is heated. As only a short plus pulse is required to break the
aluminium oxide skin, the REHM TIG system can be worked with a high negative
share.
This has many advantages:
1. The temperature load on the electrode is reduced
2. The electrode can be subject to a stronger current
3. The electrode current range increases
4. Welding can take place with a pointed electrode
5. The arc is narrower
6. The penetration is deeper
7. The thermal influence zone of the weld seam is lower
8. The weld speed is higher
9. The thermal input into the workpiece is reduced
A high-voltage ignition device is installed in the REHM TIGER systems as
standard for contactless ignition of the welding arc. The high-voltage causes the
path between the tungsten electrode and the workpiece to become so electrically
ionised that the welding arc can jump the gap. A higher oxide content in the
electrode and a closer distance to the workpiece positively influence the ignition
response.
With DC and AC welding the arc can be ignited by the installed program control
both with and without high-voltage. Proceed as follows:
The HF setting is positioned at “Off”, the tungsten electrode is brought into
contact with the workpiece, then the torch trigger is actuated and the electrode is
lifted from the workpiece by tipping the torch over the gas nozzle. The ignition of
the arc without high-voltage is an advantage if, for example, welding is necessary
in a crankcase or repair welding is to be performed on an electronically controlled
machine, on which the high-voltage ignition equipment could cause a fault to the
control sequence.
REHM TIG systems are particularly suitable as welding current sources for
electrode welding due to their fast and precise control dynamics. The current
strength setting and polarity depends on the electrode manufacture. Positive pole
welding is used when welding with basic electrodes.
More information can be found in the book series from
DVS-Verlag GmbH
Aachener Str. 172
40223 Düsseldorf
www.dvs-verlag.de
AC welding
DC welding
Ignition
with and without
high-voltage (HF)
Welding with rod
electrodes