A STUDY OF ARC FORCE, POOL DEPRESSION, AND WELD PENETRATION DURING GAS TUNGSTEN ARC-WELDING

Weld pool depression, arc force, weld penetration, and their interrela tions have been studied as a function of welding current. Pool depress ion and welding arc force have been measured simultaneously using a re cently developed technique. We found quadratic dependence of arc force on current, confirming similar findings in previous studies. Pool dep ression is essentially zero below a threshold level of current (200 A in this experiment) and then increases quadratically with current. A p erfectly linear relation between arc force and pool depression was fou nd in the Current range from 200 to 350 A, with pool depression onset at about 0.35 g force (0.34 . 10(-2)N). The total surface tension and gravitational forces were calculated, from the measured surface topogr aphy, and found to be about five times that required to balance the ar c force at 300 A. Thus electromagnetic and hydrodynamic forces must be taken into account to explain the measured levels of pool depression. The relation between weld penetration and pool depression for differe nt welding currents has been established. Three distinct regimes of we ld penetration on weld current were found. First, for small currents t he weld penetration increases rapidly with current. In the second regi me, the weld penetration dependence on current saturates because of th e thermal isolation of the base metal from the arc plasma heat source caused by the welding pool. At the onset of weld pool depression (at a bout 200 A), a transition occurs in the third regime, in which weld pe netration increases more rapidly with current due to pool depression. Weld penetration and pool depression in this regime are closely relate d, and thus, the weld pool depression value is potentially useful for controlling weld penetration.