INFLUENCE OF SUPERIMPOSED MAGNETIC FIELD ON ARC STABILITY AND WELD CHARACTERISTICS IN CO2 WELDING

Abstract

Since its inception in 1948 MIG (Metal Inert Gas) weld-ing has grown with rapidity both in amount of 'application and in variety of techniques and equipment available for various types of work. However, owing to the high cost of inert gases (Argon and Helium) the interest was diverted to carbon-di-oxide for shielding. The ability of carbon-di-oxide to dissociate and recombine permits more heat energy to be absorbed in the gas. It also uses the free oxygen in the arc area to superheat the transferring metal from electrode. Inspite of above, the problems of arc blow, porosity and weld spatter are hurdles in its way. The application of magnetic field to the arc can lead to changes in its parameters, its position in space and also to the distortion of the arc. The interaction between the magnetic field of the arc itself and the magnetic field exter-nally superimposed on welding arc influences the transport of the heat from the electrode to the workpiece thus regulating the shape, size and appearance of welds by changing the nature of metal transfer and associated parameters. Definite influences of external magnetic fields on weld bead geometry, grain refinement and arc stability have been reported in literature in case of TIG, MIG and Submerged Arc Welding. However, similar investigations are not conducted in case of CO2 welding where arc characteristics are considerably different, The present work has been carried out to study the influence of external magnetic fields on CO2 weld characteris-tics and some other related parameters in cases of unsatis-factory welds without magnetic field. The following types of magnetic fields were super-imposed on CO2 welding arc :- (1) do transverse magnetic field with backward deflection. (2) do transverse magnetic field with forward deflection. (3) ac transverse magnetic field. (4) do longitudinal magnetic field. (5) ac longitudinal magnetic field. The influence of superimposed magnetic fields has been studied on the following :- (1) Arc stability/metal transfer. (2) Weld bead shape. (3) Weld bead cross-section. (4) Spatter. Definite modifications in the weld bead characteristics have been obtained in various ranges of particular type of mag-netic field. Although adverse results are also noticed with some types and ranges of field, but there is definite improve-ment in weld bead appearances, with selective field both in nature and range.