The investigation of mixed gases-welding bead forms relation in the shielding gas welding applications

Shielding gases which are used in the gas metal arc welding are divided into three parts which are inert gases, active gases and mixed gases. Shielding gases which are important welding parameter don't only protect the welding area but also affect welding bead form, chemical and mechanical properties of welding bead. In this thesis work, physical and chemical properties of shielding gases and the influence of shielding gases on the welding bead have been investigated. In the first chapter, the gas metal arc welding processes were explained. In the second chapter, the functions of shielding gases, the physical properties of shielding gases and the influence of mixed gases (the addition of oxygen and/or carbondioxide in the argon and helium shielding gases, argon-hydrogen mixed gases, argon-nitrogen mixed gases, argon-helium mixed gases) on the welding beads were explained. In the third chapter; the influence of shielding gases on the melting rate, in the fourth chapter the influence of shielding gases on the metal transfer forms, in the fifth chapter; the faults in the welding processes, in the sixth chapter; the cost of shielding gases were explained. Pure argon gas, 304 quality stainless steel and seven kinds of weldig current (140 A, 150 A, 160 A, 170 A, 180 A, 190 A, 200 A) were used in the experimental works and macro structures of the ensured seven welded test samples were investigated. The width, depth and surface radius of the welding bead were measured from the macro structure photos, the surface tension stress and penetration ratio of the weldind bead were calculated. The relationship between surface tension and shielding gases and the influence of surface tension on the welding bead form were established. The surface tension explains the Marangoni heat convection and it can be estimated with the weld bead size. When the weld bead forms which were ensured with pure argon gas and the different welding currents and the former investigations have been examined, the direction of the Marangoni heat convection is related to shielding gas and heat convection increases with the increasing welding current, which have been determined. When the influence of the welding current and argon gas on the Marangoni heat convection have been examined, direction of the Marangoni heat convection is from the welding bead center to the welding bead edges and therefore, the width of the welding bead increases, which have been observed. Key Words: Inert gases, active gases, mixed gases, welding bead form, surface tension, Marangoni heat convection.