TWI Industrial Member Report Summary 168/1981
By W Lucas and J A Eardley
Background
Literature concerning the problem of cast to cast material variation in TIG welding is reviewed. In discussing the mechanisms by which differences in material composition could affect weld bead penetration, the factors which are considered to be the most likely cause of variations in weld bead penetration are those modifying the arc characteristics (arc plasma energy, anode root size) and the weld pool behaviour (weld pool motion and chemistry, surface tension). The review emphasises the point that there is no common agreement as to the dominant mechanism, i.e. whether slight variations in the anc characteristics or weld pool behaviour will influence weld bead penetration, or indeed as to which elements need to be more closely controlled. Whilst low ionisation, low boiling point elements such as Al, Ca and Mn were reported as affecting the arc characteristics, elements such as S, O, Te and Se, which are in turn influenced by the low boiling point elements were suggested to influence the weld pool behaviour through their effect on surface tension.
Finally, information is presented on the welding techniques which have been demonstrated to offer potential for overcoming, or at least minimising the effects of material variations on TIG welding.