Showing papers on "Arc welding published in 2020"

A novel system for off-line 3D seam extraction and path planning based on point cloud segmentation for arc welding robot

Abstract: Due to ever increasing precision and automation demands in robotic welding, the automatic and robust 3D seam extraction has become a research hot-spot of the welding robots. At present, most of the research work about seam extraction is aimed at butt joints. Nevertheless,too little work has been devoted to fillet joints and lap joints. Consequently,to achieve robust 3D seam extraction of different weld seams, a novel seam extraction system is proposed according to the 3D structures of welding work pieces. Firstly, a fringe projection system based on Digital Light Processing(DLP) projector is designed to measure the appearance of welding work pieces. Secondly, fusion of the shape information of welding work piece, a 3D seam extraction algorithm is proposed based on point cloud segmentation. Finally, according to the space structure of weld seams, the 3D seam path model and pose estimation are solved based on the established mathematical model of weld seams. Experiments show that the proposed algorithm could well solve different weld seams, such as fillet joints, butt joints and lap joints. Meanwhile, it could well overcome the influence of the materials of welding work pieces, scratch and rust.

Reduction of Energy Input in Wire Arc Additive Manufacturing (WAAM) with Gas Metal Arc Welding (GMAW).

Abstract: Wire arc additive manufacturing (WAAM) by gas metal arc welding (GMAW) is a suitable option for the production of large volume metal parts. The main challenge is the high and periodic heat input of the arc on the generated layers, which directly affects geometrical features of the layers such as height and width as well as metallurgical properties such as grain size, solidification or material hardness. Therefore, processing with reduced energy input is necessary. This can be implemented with short arc welding regimes and respectively energy reduced welding processes. A highly efficient strategy for further energy reduction is the adjustment of contact tube to work piece distance (CTWD) during the welding process. Based on the current controlled GMAW process an increase of CTWD leads to a reduction of the welding current due to increased resistivity in the extended electrode and constant voltage of the power source. This study shows the results of systematically adjusted CTWD during WAAM of low-alloyed steel. Thereby, an energy reduction of up to 40% could be implemented leading to an adaptation of geometrical and microstructural features of additively manufactured work pieces.

Machine learning model to predict welding quality using air-coupled acoustic emission and weld inputs

Abstract: Weld evaluation processes are usually conducted in the post-weld stage. In this way, defects are found after the weld is completed, often resulting in disposal of expensive material or lengthy repair processes. Simultaneously, weld quality inspections tend to be performed manually by a human, even for an automated weld. Therefore, a proper real-time weld quality monitoring method associated with a decision-making strategy is needed to increase the productivity and automaticity in weld. In this study, acoustic emission (AE) as a real-time monitoring method is introduced for gas metal arc weld. The AE system is designed to cover a wide range of frequencies from 5 to 400 kHz. Additionally, the welding parameters (weld current, voltage, gas flow rate, and heat input) are recorded concurrently with AE. Different types of weld defects are artificially created to generate different signals. For the automated decision-making system, machine learning algorithms are used. Several features extracted from the AE and welding parameters feed into a machine learning algorithm. A new AE feature as the rate of AE energy accumulation extracted from time driven AE feature is defined. For decision-making, supervised learning models are trained and evaluated using testing data. General classification methods—such as Logistic Regression—predict each data-point separately. In this study, Adversarial Sequence Tagging method is applied to predict the presence of four weld states as good, excessive penetration, burn-through, porosity and porosity-excessive penetration. We explore the prediction task as a sequence tagging problem where the label of a data-point depends on its corresponding features as well as neighboring labels. When all the AE features as well as heat input are used in the feature set, the sequence tagging and logistic regression algorithms achieve a prediction accuracy of 91.18% and 82.35%, respectively, as compared to metallographic analysis.

Multi-response mathematical modelling, optimization and prediction of weld bead geometry in gas tungsten constricted arc welding (GTCAW) of Inconel 718 alloy sheets for aero-engine components

Abstract: The gas tungsten constricted arc welding (GTCAW) parameters namely Main Current, Delta Current, Delta Current Frequency and Welding Speed were optimized to obtain full penetration and optimum weld bead geometry using Response Surface Methodology (RSM) to join thin Inconel 718 alloy sheets (2 mm thick). Empirical relationships were formulated to predict the weld bead characteristics such as width of bead, depth of penetration, width of heat affected zone (HAZ) and area of fusion zone (FZ). The weld bead characteristics were predicted with good accuracy using developed empirical relationships. The direct and interaction effect of GTCAW parameters on weld bead geometry is discussed in this paper.

Effects of post-weld heat treatments on the microstructure, mechanical and corrosion properties of gas metal arc welded 304 stainless steel

Abstract: The purpose of this study is to determine the effects of post-annealing and post-tempering processes on the microstructure, mechanical properties and corrosion resistance of the AISI 304 stainless steel gas metal arc weldment.,Gas metal arc welding of AISI 304 stainless steel was carried out at an optimized processing condition. Thereafter, post-annealing and post-tempering processes were performed on the weldment. The microstructure, mechanical and electrochemical corrosion properties of the post-weld heat treated samples, as compared with the as-welded, were investigated.,The as-welded joint was characterized with sub-granular grain structure, martensite formation and Cr-rich carbides precipitates. This made it harder than the post-annealed and post-tempered joints. Because of slower cooling in the furnace, the post-annealed joint contained Cr-rich carbides precipitates. However, the microstructure of the post-tempered joint is more refined and significantly devoid of the carbide precipitates. Post-tempering process improved the elongation (∼23%), tensile (∼10%) and impact (∼31%) strengths of the gas metal arc AISI 304 stainless steel weldment, while post-annealing process improved the elongation (∼20%) and impact strength (∼72%). Owing to the refined grain structure and significant elimination of the Cr-rich carbide precipitates at the joint, the post-tempered joint exhibited better corrosion resistance in 3.5 Wt.% NaCl solution than the post-annealed and the as-welded joints.,The appropriate post-weld heat treatment that enhances microstructural homogeneity and quality of the AISI 304 gas metal arc welded joint was determined.

Effect of Heat Input on Evolution of Microstructure and Tensile Properties of Gas Tungsten Constricted Arc (GTCA) Welded Inconel 718 Alloy Sheets

Abstract: The significant effect of heat input on the microstructural characteristics and tensile properties of 2-mm-thick Inconel 718 alloy sheets joined by gas tungsten constricted arc welding process was investigated systematically. It involves the application of magnetic arc constriction technique to solve the heat input-related metallurgical problems in gas tungsten arc welding of Inconel 718 alloy such as segregation of Nb and laves phase evolution in weld metal region which drastically reduces the weld mechanical properties. Heat input range was used from 495 to 585 J/mm by varying Main Current from 60 to 80 A at distinct levels of 5 A. The average secondary dendrite arm spacing was increased from 6.31 to 8.92 μm, revealing the corresponding cooling rate between 2087 and 720 °C/s. Superior tensile properties were obtained at an optimum heat input of 518 J/mm. It exhibited 98.16 and 78% of base metal strength and ductility. It is attributed to the grain refinement in fusion zone microstructure and the evolution of lower amount of laves phase with finer and discrete morphology. The average size and volume fraction of laves phase for the current sample were 3.12 μm and 7.68%. The benefits of magnetic arc constriction and Delta Current pulsing were not achieved at higher heat input.

Plasma Arc Coatings Produced from Powder-Cored Wires with Steel Sheaths

Abstract: Plasma arc coatings produced from powder-cored wires developed at the Paton Electric Welding Institute that were deposited onto a low-carbon steel substrate were characterized. Interaction between the steel sheath (constituting at least 80 wt.% of the wire) and powder cores, such as B4C, B4C + ZrO2(nano), B4C + (Cr, Fe)7C3, and B4C + (Cr, Fe)7C3 + Al, in the arc plasma spraying process was analyzed. The resultant coatings were free of defects and had low porosity (to 2.5%) and lamellar structure. The core carbide components were found to dope the coating ferritic matrix and strengthen it with carbide, carboboride, and boride precipitates. An addition of 0.5% ZrO2 nanopowder refined the coating structure and participated in the formation of Fe2B and Fe3B precipitates. An aluminum addition within 10 wt.% did not led to iron aluminides but, being easily melted, activated the interaction between components, reduced porosity, and improved adhesion strength of the coatings. The coatings reached a microhardness of 6.25–8.59 GPa, being 4 to 5.5 times higher than the microhardness of the steel wire sheath. The development and use of such powder-cored wires expanded the application of plasma arc spraying, particularly for the protection of equipment against abrasive gas wear in chemical engineering, in the production of parts for pumps, compressors, and other components, and for the recovery of worn parts.

Effect of friction stir and activated-GTA welding processes on the 9Cr–1Mo steel to 316LN stainless steel dissimilar weld joints

Abstract: The consequence of friction stir welding (FSW) and activated-gas tungsten arc welding (A-GTAW) processes on the evolution of microstructure and mechanical properties of 9Cr–1Mo (P9) steel to 316LN ...

Path Planning with Automatic Seam Extraction over Point Cloud Models for Robotic Arc Welding

Abstract: This paper presents a point cloud based robotic system for arc welding. Using hand gesture controls, the system scans partial point cloud views of workpiece and reconstructs them into a complete 3D model by a linear iterative closest point algorithm. Then, a bilateral filter is extended to denoise the workpiece model and preserve important geometrical information. To extract the welding seam from the model, a novel intensity-based algorithm is proposed that detects edge points and generates a smooth 6-DOF welding path. The methods are tested on multiple workpieces with different joint types and poses. Experimental results prove the robustness and efficiency of this robotic system on automatic path planning for welding applications.

Effect of different welding parameters on residual stress and deformation of 20/0Cr18Ni9 dissimilar metal arc-welding joint

Abstract: Pipelines used for the petrochemical, energy, and other industries contain 20 steel and 0Cr18Ni9. This paper based on the finite element simulation software Simufact Welding, the residual stress fi...

Investigating the Advantages of Ultrasonic-assisted Welding Technique Applied in Underwater Wet Welding by in-situ X-ray Imaging Method.

Abstract: In this study, the effects of ultrasonic on melt pool dynamic, microstructure, and properties of underwater wet flux-cored arc welding (FCAW) joints were investigated. Ultrasonic vibration enhanced melt flow and weld pool oscillation. Grain fragmentation caused by cavitation changed microstructure morphology and decreased microstructure size. The proportion of polygonal ferrite (PF) reduced or even disappeared. The width of grain boundary ferrite (GBF) decreased from 34 to 10 μm, and the hardness increased from 204 to 276 HV. The tensile strength of the joint increased from 545 to 610 MPa, and the impact toughness increased from 65 to 71 J/mm2 due to the microstructure refinement at the optimum ultrasonic power.

Comparison of Properties of Hardfaced Layers Made by a Metal-Core-Covered Tubular Electrode with a Special Chemical Composition.

Abstract: In this article, the results of research on the metal-mineral-type abrasive wear of a wear-resistant plate made by a tubular electrode with a metallic core and an innovative chemical composition using the manual metal arc hardfacing process were presented. The properties of the new layer were compared to the results of eleven wear plates manufactured by global suppliers, including flux-cored arc welding gas-shielded (FCAW-GS, Deposition Process Reference Number: 138), flux-cored arc welding self-shielded (FCAW-SS, Deposition Process Reference Number: 114), automated hardfacing, and manual metal arc welding (MMAW, Deposition Process Reference Number: 111) hardfacing T Fe15 and T Fe16 alloys, according to EN 14700:2014. Characterization of the hardfaced layers was achieved by using hardness tests, optical microscopy, confocal microscopy, scanning electron microscopy, and EDS (Energy Dispersive Spectroscopy) and X-ray diffraction analyses. Based on wear resistance tests in laboratory conditions, in accordance with ASTM G65-00: Procedure A, and surface layer hardness tests, in accordance with PN-EN ISO 6508-1, the wear plates most suitable for use in metal-mineral conditions were chosen. The results demonstrated the high metal-mineral abrasive wear resistance of the deposit weld metal produced by the new covered tubular electrode. The tubular electrode demonstrated a high linear correlation between the surface wear resistance and the hardness of the metal matrix of the tested abrasive wear plates. In addition to hardness, size, shape, the dispersion of strengthening phases, and the base metal content, depending on hardfacing technology and technological parameters, impact wear resistance is represented by volumetric loss caused by effect-free or constrained dry abrasive medium contact. The presented results can be used in machine part material selection and wear planning for applications in inspection, conservation, and regeneration interval determination. The obtained results will be applied in a real-time wear rate prediction system based on the measurement of the working parameters.

Probe Pulse Conditions and Solidification Parameters for the Dissimilar Welding of Inconel 718 and AISI 316L Stainless Steel

Abstract: The present work addresses the weldability of dissimilar materials Inconel 718 and AISI 316L stainless steel through metallurgical and mechanical characterization of the joint. The 3D heat transfer model analyzes the solidification behavior for a pulsed arc energy source. However, intermetallic formation deteriorates the welded joint properties and promotes solidification cracking in the weld zone. We attempt to join these dissimilar materials without using any filler materials and allowing solidification with the use of a pulse current. The use of a pulse current during microplasma arc welding assists in the formation of a beneficial microstructure that produces strong welds. Since the solidification parameters (G·R and G/R) largely define the weld microstructure, their effect on the weld joint properties is investigated herein. With an increase in the pulse current, the (G/R) decreases and enables the formation of an equiaxed solidified structure in the weld zone. A reduction in the amount of various intermetallic phases is observed in the equiaxed regions compared to amount present in areas with a columnar structure. The tensile strength of the joint is superior to that of AISI 316L stainless steel, and failure is observed in the heat-affected zone of this material. The best joint efficiency herein of 108 pct and elongation of 35.3 pct is achieved for the welding condition having the lowest (G/R) value. An improvement in the elongation is achieved for the weld joint with a reduction in the (G/R) value.