Heat flow to the workpiece from a TIG welding arc

Abstract

Less than half of the heat generated in a TIG welding arc (typically 1600 W at 16 V, 100 A) is transferred to the workpiece (anode). Convection, conduction and radiation from the gas occur over the whole of the arc region, but they represent relatively minor contributions to the total heat balance. The principal anode heating and cooling mechanisms involve electron and space-charge effects at the surface. These electron effects are evident in the workfunction (typically 4·5 V) which is dominant, the electron thermal energy transfer (1 V) and the anode fall (2 V), and they are concentrated in the restricted anode current spot so they may be considered as a localized heat source.Evaporation is most intense from the anode spot region and carries away some heat. However, most of the vapour condenses on the cooler, outer regions of the anode surface covered by the arc. In this way, heat is redistributed and diffused over a wider area. Vaporization effects explain the differences between previous measurements with cooled copper anodes (in which 80% of the arc power is transferred to the metal) and ones with practical, molten-steel welds (less than 50% heat transfer).

Usability of arc types in industrial welding

“…Later, this insight was extended by Quigley et al (1973) who noted that only 20% of the heat is carried by conduction from hot gases and 80% remains in the electric current. Depending on the precise nature of the plasma and the amount of current flowing through it, the welding arc temperature varies from 5,000 to 30,000 K (Naidu et al 2003;Robert and Messler 2004).…”

Arc power and efficiency in gas tungsten arc welding of aluminium

“…It is known that, with DCEN polarity, the majority of the heat transfer from the arc is by the electrons. 6,7 While heat losses to the cathode and surroundings are significant, much of the heat that is transferred to the tungsten electrode is subsequently recovered through thermionic emission of electrons. As a consequence, the majority of the arc power is delivered to the workpiece and relatively high arc efficiencies can be realised.…”

Heating and Electromagnetic Stirring in a Ladle Furnace. A Simulation Model.

“…In these calculations the net heat losses are used to predict radiative heat transfer to the anode. 19,21) …”

“…The contribution from the condensation heat flow created by the electrons passing the anode-fall and entering the liquid steel, Q A , can be expressed as follows 19) : (4) where V A is the anode fall voltage and q A is the work function (required anode fall to release an electron from the anode). In this investigation V A and q A were both assumed to be 4 V.…”