Method to monitor and control weld penetration in gas tungsten welding and full-position pipe welding
The invention discloses a method to determine the weld joint penetration from arc voltage measurements in gas tungsten arc welding (GTAW). It is based on an observation on the dynamic weld pool surface in GTAW—the surface tends to first expand toward the electrode and then be pushed away from the electrode after full penetration is established. For the pool surface in GTAW, localized partial keyholes around the arc axis as in plasma arc welding are not significant. The pool surface is relatively smooth. The arc voltage that reflects changes in the arc length thus first tends to reduce and then increases after full penetration is established. This invention thus tracks the arc voltage until the decrease slope becomes insignificant. Once full penetration is established, the current is reduced to decrease the weld penetration or first decrease the penetration growth for a certain period and then decrease the weld penetration.
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YuMing Xiangrong Zeng
Zhang Li Shao