Pulsed Current Gas Metal Arc Welding under Different Shielding and Pulse Parameters; Part 2: Behaviour of Metal Transfer

Abstract

The behaviour of metal transfer and arc stiffness understood in terms of arc pressure (P a ) of pulsed current gas metal arc welding (P-GMAW) using mild steel filler wire have been studied with respect to change in pulse parameters under different gas shieldings of Arϩ2%CO 2 and Arϩ18%CO 2 . The arc environment revealing the droplet transfer from electrode to weld pool in bead on plate weld deposition has been studied by high speed video graphy. Effect of pulse parameters has been considered by their hypothetically proposed summarized influence defined by a dimensionless factor f, mean current (I m ) and arc voltage. The droplet diameter and velocity of droplet at the time of detachment are found to vary significantly with the variation of f. At a given f the experimentally measured behaviour of metal transfer is found well in agreement to their corresponding theoretical estimates. The average droplet diameter transferred per pulse predominantly reduces but, the velocity of metal transfer at the time of detachment enhances with the increase of f under both the shielding gases. In general a higher values of f, I m and arc voltage enhances the P a depending upon type of gas shielding. The use of Arϩ2%CO 2 shielding gas reduces the droplet diameter and enhances the arc pressure than that observed under Arϩ18%CO 2 gas shielding.

Pulsed Current Gas Metal Arc Welding under Different Shielding and Pulse Parameters; Part 1: Arc Characteristics

“…It is found that a low arc voltage of about 24 V creates instability in shielding jacket due to relatively low arc pressure. 21) However, during pulse off period (Fig. 13) the disturbance in arc profile has been found comparatively more than that of the pulse on time.…”

“…The interruption of arc profile and shielding in P-GMAW process at an appropriate gas flow rate largely depends upon degree of fluctuation in arc pressure at different arc stiffness and arc length. The arc length and stiffness primarily varies as a function of f, I m and arc voltage [11][12][13]21) whereas the degree of fluctuation of arc pressure significantly depends upon the ratio of (I b /I p ) as observed earlier. 11,12) The fluctuation in arcing due to large variation of I b and I p causing low I b /I p ratio may create instability in shielding gas jacket resulting into formation of vortex at the boundary of arc profile.…”

“…5(g)-5(i)). In this context here it may further be noted ( Table 1) that the increase of f enhances the ratio of (I b /I p ) but increases the arc stiffness as a function of its pressure, 12,21) when both of them favours the adverse influence of fluctuation of arc pressure on stability in arc environment under the pulsed current. Thus, it can be inferred that at any level of I m the variation in f, (I b /I p ) and arc voltage significantly influences the stability of arc environment when their high values are beneficial to maintain a stable arc environment in P-GMAW process.…”

“…This aspect in terms of arc stiffness has been discussed further in part-2 of presentation of this work. 21) …”

“…[4][5][6][7][8][9][10] But it is often pointed out that the quality of P-GMA weld very much depends upon arc characteristics [11][12][13][14][15] affecting the energy distribution in welding dictated by the pulse parameters and shielding environment. However, the thermal behaviour of weld depending upon arc characteristics significantly influences the chemistry, microstructure and stresses of the weld.…”