Investigation of Flux Activated Tungsten Inert Gas Welding & Hybrid Process

Abstract

The productivity of Gas Tungsten Arc Welding/Tungsten Inert Gas (GTAW/TIG) welding is low due to its less penetrating capability due to the less heat input of the process. A well-known process could enhance productivity, i.e., A – TIG (Activated – TIG) welding. This process could be accomplished by applying a thin layer of activated flux before welding. Presently, different grades of stainless steel are used in many industrial applications due to its excellent corrosion resistance and better mechanical properties over mild steel. The edge preparation cost and slow welding speed of the conventional GTAW/TIG welding make the process uneconomical. So, I accomplished different objectives to overcome the limitation of the conventional GTAW/TIG welding and explore the uses of A – TIG welding. The present dissertation work is an attempt to investigate the A – TIG welding process in the context of metallurgical changes and associated mechanisms. First, A – TIG welding was carried out at a fixed position (so-called stationary A – TIG welding) using different shielding environments to explore the mechanism behind deep penetration and growth of grains, dendrites, dendrite arm spacing and other metallurgical changes. Design of experiment with full factorial design approach has been adopted in the current investigations. The gas-metal and slag-metal reactions study were occurred in A – TIG welding and discussed in detail under Chapter – 4 (4.4.7). The objectives, as mentioned earlier, are accomplished using different stainless-steel grades (AISI 304, AISI 316 and Duplex 2205) and different oxide-based fluxes. A – TIG welding is further explored for a challenging position (i.e., Vertical uphill) and by developing a new hybrid process (Hybrid Arc Welding – HAW). The study of A – TIG welding for the challenging position was also accomplished using different shielding environments and using Taguchi experimental design methodology. Significant welding parameters were identified and discussed for the change in mechanical properties. The new hybrid arc welding process was developed to enhance the traditional submerged arc welding (SAW) and to enrich the A – TIG welding process by combining both the arc welding processes. Before proceeding to the HAW process, and to find out the optimise parameters, the Taguchi experimental design technique (L 9) was used for both the autogenous A – TIG welding and SAW on 16 mm thick AISI 304 stainless steel plates. After completing the Autogenous A – TIG (AA – TIG) welding and SAW on thick plates, HAW was conducted by combining both AA – TIG and SAW and using significant welding parameters for the qualitative research. Finally, a comparison has been made between the outcomes of the HAW and SAW processes. For further use in the hybrid process, the mechanical and metallurgical properties of the xxvi selected weld samples were analysed for both A – TIG and SAW. The study results show that the HAW process provides better weld quality and significant mechanical properties of the weldment than stand-alone A-TIG or SAW for thick plate welding. Furthermore, the experimental results/outcomes of the study indicated that the HAW could be the best process to achieve the desired mechanical properties of the weldment/weld metal. Finally, it concluded that the HAW process enhances productivity.