TIGアークにおけるビード形成におよぼす磁場の影響

Abstract

Experiments show that bead appearance becomes discontinuous (abnormal) when welding velocity increases over a certain high limit, other variables (welding current, arc voltage, etc.) being kept constant.Hicken and Jackson report that the bead appearance becomes continuous when arc is deflected to welding direction with use of transverse magnetic field.We have been interested in the above-mentioned experimental results.In order to find out their important factors, using transverse or longitudinal magnetic field, we have observed in detail the phenomena which have been brought about when all welds are being deposited on the mild steel with TIG arc.As the result, we have found out the following facts.(A) When magnetic field is not applied, molten metal is pushed down with plasma jet and molten layer in the bottom of pool becomes gradually thin in proportion to the increase of welding velocity. This thin molten layer tends to solidify instantly when the arc foot moves sometimes to another spot according to the arc character. This results in the formation of a naked solid surface in the bottom of the pool. This naked solid surface disturbs the free flow of the molten metal in the pool and the bead becomes discontinuous.(B) When arc is deflected to welding direction with use of transverse magnetic field, molten metal is pushed forward and the molten pool is always full of molten metal. (See Fig. 6 (a))(C) When magnetic direction is reversed, molten metal is positively blown away with plasma jet.This causes the formation of a naked solid surface in the pool more easily than (B) and consequently the bead becomes discontinuous. (See Fig. 6 (b))(D) When the longitudinal magnetic field is applied, molten metal rotates in the pool and so be naked solid surface is covered with molten metal.In the case of (A), bead appearance begins to become abnormal at the velocity of 200 mm/min.In the case of (B), bead appearance is always continuous for all the velocities in our experimental range.In the case of (C), bead appearance begins to become abnormal at the velocity of 120 mm/min.In the case of (D), bead appearance begins to become abnormal at the velocity of 280 mm/min.After all, it has become obvious that the naked solid surface causes the bead to be abnormal.