TWI Industrial Member Report Summary 134/1981
By W Lucas and M Butler
In the investigation into the effect of variations in material composition and welding equipment performance in metal inert gas (MIG) and manual metal arc (MMA) welding a study was made of the influence of the temporal behaviour of welding parameters on arc stability. To facilitate monitoring and statistical analysis of the welding current and arc voltage waveform, a minicomputer was successfully interfaced with the appropriate welding systems for real-time collection of data and subsequent off-line analysis; special software was written not only for the acquisition of data on the short term fluctuations in the welding current waveform, which are associated with the transfer of metal from the electrode, but also for conducting statistical analysis of the fluctuations or peaks recorded.
The preliminary study of the statistical behaviour of the welding parameters in MIG welding has shown that there is a definitive relationship between the stability of the arc and metal transfer and the regularity of the parameter fluctuation. In particular, the most stable arc exhibited a smaller variation in the peak current levels and the time period of the fluctuations, as shown by the standard deviation of the distribution of the values. Of equal importance, the welding parameters producing the most stable welding arc were also shown to be less likely to generate weld defects such as undercutting and excessive reinforcement.