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Title: Analyses of Plasma Transferred Arc Welding Process
Authors: Mandal, S.
Keywords: Mechanical Engineering
Issue Date: 2017
Publisher: IIT Patna
Series/Report no.: TH-72;
Abstract: Metallic machine components frequently operate in extreme conditions and deteriorate due to wear, erosion, corrosion, impact loading etc. and finally get discarded for low performance. Plasma transferred arc welding (PTAW) process is being used for the repair and fabrication of engineering components that are used in chemical, fertilizer, nuclear power plants, food processing, petrochemical and their allied industries, also in agriculture and even in aircrafts and missiles. PTAWprocess is one of the fusion welding processes which is used for cladding. This welding process is being used to increase the service life of machine components of various industries by precise deposition of metal powders over the damaged components. This process is widely accepted by the industries due to its large deposition rate, low cost and low dilution. In the manufacturing industry, the deposited bead should be accurate in dimension, continuous and defect free. There are some difficulties in achieving low dilution, accuracy in dimensions and to maintain continuity and defects free depositions. The dilution and geometry of bead depend on heat input and proper control of other process parameters. Dilution influences the mechanical property of the deposited bead. To address this problem, a systematic investigation of the material deposited using PTAW process has been made through experiments as well as through analysis. An experimental study of material depositions by PTAW process has been done to understand the effects of four process parameters, i.e., scanning speed, powder feed rate, stand-off distance and current on bead geometry and dilution. For conducting the experiment, stainless steel powder SS304L and stainless steel plate SS316 have been used as deposited and substrate material respectively. From the analysis of the experimental data it has been found that the compound parameters energy deposition per unit length (power/scanning speed) and powder deposition per unit length (powder feed rate/scanning speed) are more appropriate parameters to explain certain trends of the results. From the measured bead geometry and dilution parameters, mathematical models have been developed using the Response Surface Methodology (RSM) to predict the effect of process parameters on bead geometry and dilution. The adequacy of the developed mathematical models have been tested using the Analysis of variance method (ANOVA). The confirmatory test run has been conducted to determine the accuracy of mathematical model. The response surfaces have been drawn at the end of regression analysis for understanding the interactive effect of process variables. Subsequently, the PTAW process parameters have been optimized using multi-objective optimization analysis to achieve maximum bead height, width and low dilution. The investigations on discontinuous bead formation by PTAWprocess have been conducted. Three types of depositions have been observed, namely continuous, partially continuous and discontinuous deposition. Based upon compound parameters, powder de position per unit length and energy deposition per unit length, a process map has been developed for different bead types. The discontinuities in the deposition can be overcome by increasing the energy deposition per unit length or by reducing the powder deposition per unit length. The Rosenthal equations, i.e., line heat source and point heat source have been used for the analysis of discontinuity in deposited layer. These equations have been solved to find out the power required for constant bead width or melt pool width. These results are compared graphically between the analytical values and experimental values for continuous, partially continuous and discontinuous beads on the basis of required energy deposition per unit length and powder deposition per unit length. The porosity inside the deposited beads and their sizes, location, shapes and quantity have been investigated through experiments. The effect of variation of scanning speed on porosity formation has been investigated. From this investigation, an optimum value of scanning speed has been observed for porosity free deposited layer.
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