Page 55 - Welding Robots Technology, System Issues, and Applications

Welding Robots
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programmed in this unit. Memory for pre-programs and for set parameters is
frequently available in this unit.

When the torch cable is externally attached to the robot arm it is exposed to work-
piece interference and to premature wear. Modern robotic systems can include
special arms with internal cabling, in order to prevent interference, increasing cable
life.

2.2.2.3 Welding Torch

Main functions of the welding torch are to furnish the electrode with electrical
current and direct the electrode and gas flow to the work-piece. Main components
of the welding torch are the contact tube, where the current is transmitted to the
electrode, the nozzle, which provides a laminar gas flow to the weld pool, the torch
switch, which sends signals to the feed unit, and the handle. The handle supports
the gas and water (if necessary) tubes, the electrode guide tube and cables for
current and signals. MIG torches for low current and light duty cycle (up to 60%)
are gas cooled and torches for heavy duty cycle (up to 100%) and high current are
water cooled. Robotic torches are in general water cooled, but if gas cooled torches
are used they must be larger than manual torches. Alternatively air cooled torches,
which use shop compressed air, can be applied instead of water cooled torches
[16]. Robotic torches usually have emergency-stop capability to prevent damage to
the robot arm and the welding torch in the event of a collision. They are also
provided with automatic cleaning, that may include a pressurized air system for
blowing spatter out of the nozzle, a reamer for cleaning the internal nozzle
structure and an anti-spatter fluid delivery system.

Twin-wire GMA robotic welding torches can be used to reach higher deposition
rate and welding speed. In this case a side-by-side configuration is used, with both
wires being fed to close contact tips, in order to give a single weld pool.

2.2.3 Process Parameters

Welding parameters affect the way the electrode is transferred to the work-piece,
the arc stability, spatter generation, weld bead geometry and overall weld quality.
The main parameters of the process are current, voltage, travel speed, electrode
extension and electrode diameter, though others, such as electrode orientation,
electrode composition and shielding gas, also have direct influence on the metal
transfer mechanisms. These parameters are not independent. The current and
voltage, for example, are correlated by the arc characteristic curves shown in
Figure 2.10; voltage depends not only of the arc length but also on the electrode
extension and on the shielding gas.