N. Mbonde and G.J. Oliver (South Africa)
Welding process parameters; shielding gas composition; Transfer modes; Heat Input; Bead shape, and Ionization Potential.
The study on improvement of process parameters and development of different shielding gas compositions in GMAW has been of increasing interest for the purpose of improving welding productivity, esthetics of the resulting bead as well as minimizing the total process costs while maintaining a desired quality. In this study the effects of various process parameters and shielding gas composition on droplet formation, transfer modes and weld bead dimensions for a common structural metal EN8 (mild steel) welded using semi-automatic gas metal arc welding plant were investigated. The bead-on-plate welding were performed using a range of welding currents, arc voltages, welding speeds and feeds as well as various shielding gas compositions to determine an optimum process parameters that would result in high productivity and high quality weld bead. As a result of this study it has been observed that, the best weld results i.e. droplet size, transfer modes, and weld bead shapes are always achieved if both suitable and optimum process parameters (welding current, arc voltage, welding speed and shielding gas composition) are chosen. Physical gas properties found to affect metal transfer, wetting behaviour, depth of penetration, shape of penetration, travel speed and arc starting. Compared with gases with high ionisation energy (e.g. helium), gases with low ionisation energy (e.g. argon) facilitate arc starting and arc stabilization. Proper doping of inert gases with reasonable amounts of active components such as CO2, NO or O2 results in arc stabilisation which can improve the weld result. The dissociation energy of polyatomic components in gas mixtures enhances the heat input to the base material due to the energy released by recombination.
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