PLASMA-ARC WELDING - A MATHEMATICAL-MODEL OF THE ARC

A number of models of plasma arc welding have been constructed, includ ing some that describe the arc itself. Relatively few rely solely on t he physics of a plasma arc and the associated fluid dynamics for const ruction of mathematical models; for the most part they use a mixture o f empirical results and basic physical principles. Models that depend on physical principles only have the advantage that they produce the k ind of insight that makes them flexible enough to be applicable to sit uations for which they were not originally envisaged. Such an approach reduces the development time for revised models and increases confide nce in modelling procedures. An example of this approach is considered here in more detail, with particular attention to the plasma arc. Inf ormation is obtained about the relative importance of radiation in the determination of plasma temperatures, and the transport of energy in the plasma jet itself. The mean temperature distribution along the len gth of the arc is considered using the ideas of classical thermodynami cs. The fluid dynamical momentum balance of the arc is considered in s ome detail and it is found that these considerations play a substantia l role in the determination of its shape. Two different kinds of solut ion are found, corresponding to the transferred arc and the non-transf erred arc; the first type tend to broaden overall towards the work pie ce whereas the latter more closely resemble conventional flames.