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Abstract
In numerical modelling of the resistance spot welding process, a significant input parameter is the value of the weld current and traditionally, the rms value corresponding to the actual, instantaneous current waveform is used. The rms value implies a constant weld current for the entire weld time instead of the real-time current waveforms. Although the rms value represents an effective approximation of the real-time current waveform, the influence of the peak current and of the current slopes in each half cycle on the welding process cannot be realised in modelling when the rms value is used. Mathematically, an alternating current waveform with higher peak value and lower current on-time in each half cycle may correspond to a rms value that is nearly similar corresponding to another waveform with lower peak value and larger current on-time in each half cycle. The resulting rate of heating and the subsequent size of the weld nugget may not be the same for both the current signals since the resistive heating in resistance spot welding is transient in nature. This is precisely observed in the present work through a detailed investigation using three different ac spot welding machines. A two-dimensional, axisymmetric model is used to analyse the spot welding process using both the actual current waveform and the corresponding rms value as inputs. The computed weld dimensions show better predictions with the instantaneous current waveform as input rather than the corresponding rms value.
