Method to plasma arc weld and full-position pipe weld

摘要

This invention is to plasma arc weld using a keyhole mode to build a partially-penetrated keyhole and then a melt-in mode to finally reach the full penetration before switching to the base period. The full penetration is thus established during the peak period in two stages: keyhole stage and then melt-in stage. While the keyhole stage helps reduce the heat inputs and weld puddles, the melt-in stage finishes the full penetration at reduced impacts from the plasma jets producing the desired weld bead geometry and regularity. The duration of the melt-in stage is automatically determined using arc signals to assure the full penetration. In comparison with keyhole PAW, bead geometry and regularity are significantly improved with slightly increased net heat inputs. In comparison with melt-in PAW and GTAW, the net heat input is reduced approximately forty percent.