Page 108 - Welding Robots Technology, System Issues, and Applications

Welding Robots
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resulting in an automatic adjustment of the arc length towards its stable operating
point. Decreasing the arc length has the opposite effect. This indicates that a
change in contact-tube to work-piece distance is reflected almost entirely in the
change of the electrode extension.

The metal transfer mode is not the only property of the welding process that is
influenced by the weld current. Penetration width, depth, burn-off rate, arc stability
and arc rooting are all also influenced by the weld current. It is thus desirable that
the mean current is constant and stable. The current is not so easy to control since
small variations in arc voltage results in a large current swing. From the discussion
on the physics of the GMAW process it follows that the mean amplitude of the
weld current is likely to be a suitable feature for detection of changes in weld
quality.

3.7 Fault Detection Using Monitoring

The strength and appearance of the weld joint are important properties when
welding two metal pieces together. In GMAW the strength of the weld joint is
mainly determined by the bead width and weld penetration. Parameters in GMAW
which affect the weld penetration and bead geometry are for example:

x Welding current
x Arc voltage
x Welding speed
x Wire feed rate
x Electrode extension
x Electrode composition and diameter
x Shielded gas composition and flow rate

Considerable skill and experience are needed to select the optimal welding
parameters for each weld application. Deviation from the optimal settings of the
parameters may change the weld joint geometry and cause deterioration in the weld
joint strength. Furthermore, deviation from the optimal settings will also increase
the probability of such weld defects as cracks, porosity, undercuts, microfissures,
etc., which will further decrease the strength of the weld joint.