Experimental Investigation and Parametric Optimization of Regulated Metal Deposition Welding for Low Alloy Steel
Creators: name: Bandhu, Din
Publisher: name: figshare
Year: 2022
Subjects: subject: 10303 Optimisation
subject: FOS: Mathematics
subject: Mechanical Engineering
subject: FOS: Mechanical engineering
subject: 91099 Manufacturing Engineering not elsewhere classified
subject: FOS: Electrical engineering, electronic engineering, information engineering
subject: 90407 Process Control and Simulation
subject: FOS: Chemical engineering

description: Consumption of oil and gas has been tremendously increasing nowadays across the globe, and their discovery and accessibility will continue to grow in forthcoming years.<br>These sectors utilize low alloy steel in order to construct high-strength transmission pipelines. Conventional welding techniques such as gas metal arc (GMA) welding and<br>gas tungsten arc (GTA) welding are primarily used to construct the aforementioned pipelines. However, it is a challenging task to construct high-strength transmission<br>pipelines with high integrity and high weld quality at high welding speed. The conventional short-circuiting method of GMA welding leads to several problems such as weld puddle agitation, extreme penetration, inadequate fusion, outrageous spatter, burn through, porosity, and warping. Inadequacy of skilled welders is the primary cause for<br>the occurrence of such challenges. Though GTA welding is preferable for root pass in pipeline fabrication yielding excellent weld quality and corrosion-free products, it fails to<br>fulfill the growing demand for welded products due to its slow welding speed. The only way to overcome these problems is the adaptation of technologically advanced welding techniques that combine the goodness of cutting-edge power supply units with advanced software configuration. One such technique is Regulated Metal Deposition (RMD) welding. It improves welding quality and productivity on steel and its alloys. It is easy to learn and addresses the shortage of highly skilled and experienced welders by providing a smooth weld arc that accomplishes the work comparatively at a faster rate with high quality.<br>Therefore, this dissertation work systematically and experimentally examines the effects of RMD welding variables for low alloy steel with metal-cored filler wires. Welding current (A), welding voltage (V), and gas flow rate (GFR) have been considered as welding variables. The effects of these variables have been measured in terms of the welding output responses viz. heat-affected zone (HAZ), depth of penetration (DOP), bead width (BW), and bead height (BH). Taguchi’s L<sub>25</sub> orthogonal array has been utilized for the proper execution of experiments. Experimental trials, in the form of bead-on-plate, have been performed on low alloy steel plates using Miller’s ‘Continuum 500’ welding machine. ANOVA has been applied to investigate the effect of aforesaid welding variables on each welding output response. However, these output responses<br>are contradictory in nature as a lower value is preferable for the HAZ, BW, and BH whereas a higher value is preferable for DOP. Therefore, adequate knowledge and in-depth understanding of the process behavior is indeed necessary to identify the most favorable welding combination on which a manufacturer can rely. In this context, attempts have been made to determine the optimal welding combination using multiresponse optimization techniques viz. TOPSIS-Taguchi approach, PCA-Taguchi approach, and Rao algorithms. All these intended optimization techniques gave similar results as welding current = 100 A, welding voltage = 13 V, and gas flow rate = 21 LMP. Using this optimized welding combination, two 06 mm thick low alloy steel plates havebeen welded together. These welded plates have been subjected to heat treatment for residual stress removal and toughness enhancement. Thereafter, the weld coupons<br>have been prepared for characterizing their microstructural and mechanical attributes. The microstructural study has been done using optical microscopy. SEM-EDX analysis<br>has also been accomplished to examine the presence of carbide precipitates in the weldments. Mechanical attributes such as micro-hardness, tensile strength, and impact strength have been examined to check the viability of the RMD welding technique. A comparative study has also been carried out for the same material using the conventional GMA welding technique, in which the microstructure and mechanical attributes of RMD welded samples have been compared to those of GMA welded samples. The outcomes vindicate the viability of RMD welding and also articulate its<br>superiority over conventional GMA welding. <br>