Thermal modelling of alternating current square waveform arc welding

Abstract

The instantaneous change of polarity during the welding with square waveform alternative current (AC) creates two distinct but partially overlapping weld-pools. The conventional ellipsoidal heat source model lacks the versatility to embody the overlapping weld-pools in the numerical simulation. A new overlapping double ellipsoidal heat source model is proposed to simulate the thermal behaviour of the AC square waveform welding process. The dimensions of the overlapping heat source are determined first by solving the steady-state heat conduction equation. The heat source so developed is then used in finite element analysis for the computation of the transient temperature distribution. The numerical model is validated by comparison with the experimentally measured thermal cycle. The effect of process parameters, namely welding current, electrode negative ratio, current frequency, on the thermal behaviour and weld-pool geometry is analyzed. The interplay between the process parameters and the thermal cycle due to AC square waveform are the significant findings of the present work, e.g., increase in frequency stabilizes the arc on the cost of lowering the peak temperature. The computationally affordable welding heat transfer models, such as the present investigation, pave the way to resolve shop-floor significant issues such as residual stress and distortion.