Please use this identifier to cite or link to this item: http://hdl.handle.net/10266/6227
Title: Studies on Joining and Deposition using Planar Movement Setup for GMAW
Authors: Kumar, Vinod
Supervisor: Bera, Tarun Kumar
Keywords: Automatic GMAW;Planar welding;Closed and Opened Profiles;Vertical Layer Deposition;Dissimilar Stainless-steel Joining;Activated Flux;Uniform Bead Geometry;Tensile Test;Bending Test;Micro-Hardness;SEM;Bond Graph Modelling
Issue Date: 10-Jun-2022
Abstract: Now-a-days, owing to the rapid advances in technology and immense human intervention, most of the industrial components are not fabricated by conventional manufacturing processes. Industrial automation plays a significant role in order to achieve high accuracy, reliability, precision and quality of industrial processes, but at higher expenses. Automation involved in controlling and operating the various equipment such as CNC machines, robotic welding arms, heat-treating ovens, boilers, stabilization of ships, aircraft, and vehicles mitigates human interventions. In recent years, 3D metal printing technique is tremendously used for building products by vertical layer depositions in various engineering applications. Various welding techniques such as gas metal arc welding (GMAW), laser arc welding, electron beam welding, gas tungsten arc welding (GTAW) and plasma arc welding (PAW) are used for additive manufacturing (AM), but GMAW based AM has gained tremendous popularity in the industry. GMAW based AM builds metallic parts by depositing layer over layer to achieve relatively higher deposition rates and denser structures. As fully automation is involved in GMAW based AM, constant contact tubes to work distance provides consistent bead geometry, low spatters, uniform heat input and deep penetration depth as compared to conventional manual welding. To address this challenge, a bi-directional automatic movement setup is indigenously designed and developed to obtain weld with uniform bead width along a desired path and having capability to perform vertical layer depositions for different open and closed profiles utilizing gas metal arc welding. A computer-aided design (CAD) model and a prototype of bi-directional movement setup for planar welding are first made for conceptualization and then, the setup is fabricated. It mainly consists of stepper motors, carriage, transmission system and guide ways. The welding torch is kept perpendicular to the substrate during deposition of all profiles. A trigger is provided under the torch holding device to manually switch on/off the welding torch whenever required. A dedicated electronic control unit is developed to independently control both stepper motors along two different axes for the desired positions of the welding torch during metal deposition. The control system is Arduino UNO based. The control system is responsible for starting of arc, controlling the speed of stepper motors, welding speed and precision of given trajectory during deposition. System modelling of the fabricated setup is carried out using a bond graph technique to predict different system behaviours as well as to predict the weld bead geometric path. The effectiveness of the automatic planar movement setup is validated to check the uniformity in bead width and path/profile of the deposited weld bead, to perform vertical layer deposition for different open profiles (e.g., spiral and S-shape) and closed profiles (e.g., circular, elliptical) and to build three-dimensional specimens through different paths strategies followed for deposition i.e., spiral-in (circular and square), raster (square, diagonal and circular) at different welding speeds. The dissimilar joining between three different grades of steels (austenitic (AISI 304, AISI 316) and duplex 2205 stainless steels) are welded in the presence of three activated fluxes (SiO2, TiO2 and CrO3) following Taguchi fractional factorial design of experiment (DOE) technique. The influences of welding parameters namely welding current, voltage, workpiece material, filler material and gas flow rate along with activated fluxes are investigated on the depth of penetration of dissimilar steels. Finally, the prepared welded specimens are tested under mechanical and metallurgical testing. Mechanical testing such as tensile strength, toughness, microhardness, flexural strength of the deposited specimens following ASTM (American Society for Testing and Materials) and IS (Indian Standards) are performed to investigate the influence of various process parameters. The microstructural characterization of the base metal, heat-affected zone and welded zone of the deposited parts is carried out using scanning electron microscopy (SEM). The experimental results reveal that the developed machine is suitable for effectively tracking the reference path and executing welding of any shape in two-dimension. The constant contact tube to work distance provided by the automated fabricated setup is required to achieve the significant consistency in weld bead width for all deposited profiles. The weld bead width increases due to lowest speed in case of spiral shaped weld profile and consequently, maximum heat is generated for this profile followed by S-shape, circular and elliptical profiles. The bead deposition is consistent i.e., deposited width and the layer heights all over the path of the deposition for different geometric shapes are almost uniform. Thus, the developed machine is also suitable for executing 3D metal deposition of any simple or complex shape. The fabricated setup is capable of building overhanging components with a maximum of 20˚ inclination. Maximum micro hardness value is observed in HAZ followed by weld metal and base metal in all the profiles. Comparatively better results are obtained from tensile, bending and microhardness testing and these results support that the deposited parts have dense structure. Amongst the five deposition strategies, raster linear (circular) exhibits highest tensile strength value followed by raster diagonal (square), raster (square), spiral-in (square) and spiral-in (circular). Among the activated fluxes, SiO2 significantly improves the bending strength and toughness as compared to tensile strength and microhardness.
URI: http://hdl.handle.net/10266/6227
Appears in Collections:Doctoral Theses@MED

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