Showing papers on "Gas metal arc welding published in 2018"

Wire arc additive manufacturing of Al-6Mg alloy using variable polarity cold metal transfer arc as power source

Abstract: A variable polarity cold metal transfer (VP-CMT) arc power source with different arc modes was employed in additive manufacturing Al-6Mg alloy parts. The microstructures were characterized using scanning electron microscopy with electron back-scattered diffraction. Even equiaxed grains in size of 20.6–28.5 µm with random orientation were obtained under VP-CMT mode, while a large number of columnar grains in bigger size exist in samples under other arc modes. Tensile strength of the VP-CMT sample with a maximum of 333 MPa is higher than that of the Al-6Mg wrought alloys due to fine-grain strengthening. However, the tensile strength of the VP-CMT sample in different tensile direction was anisotropic, with a percentage of 8–27%. The comprehensive analysis of defects and grain orientation showed that the micro pores in interlayer pore region lead to the anisotropy.

Numerical simulation of WAAM process by a GMAW weld pool model

Abstract: Additive manufacturing (AM) is a high-productivity process which can make a near-net-shape structure. In this study, the focus is the wire-arc AM (WAAM) process. In the WAAM process, wire is the depositing material. The wire melts by an arc plasma and deposits layer by layer. To establish an advanced WAAM process, it is important to make a precise structure of the intended shape. In this study, a gas metal arc welding (GMAW) weld pool model is applied to WAAM process, and influence of the deposit condition on the shape of the deposition is numerically investigated. Firstly, influence of the interpass temperature is investigated. When cooling time is set appropriately, the deposition shape becomes higher and thinner. In addition, concerning influence of the welding direction, when the welding direction is reversed for each layer, the variance of the deposition height becomes small. These numerical results show that it is important to manage the temperature and torch motion for controlling the deposition shape. These numerical results have similar tendency with experimental results and show the GMAW weld pool model is a helpful tool to predict and control the WAAM process.

Abrasive wear of high chromium Fe-Cr-C hardfacing alloys

Abstract: Weld deposits are one of the most used economical ways of the wear resistance increase. The study compares the characteristics of the overlay material welded-on and the abrasive wear resistance. The research has been carried out using hardfacing alloys reinforced with primary chromium carbides and complex carbides. The overlay material was deposited on the low-carbon steel S235JR using the gas metal arc welding (GMAW) method. Four different commercial overlay materials were studied in terms of the microstructure effect. The abrasion wear testing was carried out using the abrasive cloth of grit 120 according to CSN 01 5084. The microstructure characterisation and surface analysis were made using optical and scanning electron microscopy. The results illustrate a significant effect of primary carbides on the abrasive wear resistance of weld deposits.

Understanding and overcoming of abnormity at start and end of the weld bead in additive manufacturing with GMAW

Abstract: Weld bead geometry at start and end of the bead is often abnormal compared with the middle region, which will greatly affect the forming in gas metal arc welding (GMAW) additive manufacturing. The study’s aim is to investigate the causes and the optimization strategy of the weld bead abnormity at the unstable region. The weld pool dynamics, convection, and the extension process were analyzed through a three-dimensional transient fluid model and the finite element analysis of thermal behavior. The results showed that the abnormal bead geometry can be attributed to the backward fluid flow and the metal swelling in the weld pool, and the length of the initial bulky region is positively correlated with the inclined shape at the end, as well as the length of the weld pool. Some strategies to control the bead abnormity through adjusting the welding parameters, the crater filling options, and the path planning patterns were proposed. These methods contributed to the continuous and smooth deposition surface and laid the foundation of GMAW-based additive manufacturing process.

Hot wire-assisted gas metal arc welding of hypereutectic FeCrC hardfacing alloys: Microstructure and wear properties

Abstract: The deposition welding of hypereutectic FeCrC hardfacing alloys requires low dilution rates in order to ensure the specified chemical composition and thus the precipitation of primary M7C3 (M = Fe, Cr) carbides, which affect the abrasive wear resistance of the hardfacing. Because dilution is critical in determining the above mentioned criteria during surfacing, the development of deposition welding processes with reduced thermal impact and hence reduced dilution of the base material is a main focus of current research. For the purpose of improving the processing properties of gas metal arc welding (GMAW) in hardfacing applications, the potential of an additional hot wire (HW-GMAW) was investigated. The application of a hot wire enabled the independent adjustment of the deposition and dilution rates. Furthermore, the dilution and microstructural properties could be adjusted independently of the deposition rate. HW-GMAW enabled hypereutectic solidification in the first layer, even at very high deposition rates of 9 kg/h. In this manner, a primary M7C3 carbide content reaching 17% by area (A%) was achieved in the first layer. In comparison to single-layer GMAW overlays the wear properties were improved.

Analysis of Favorable Process Conditions for the Manufacturing of Thin-Wall Pieces of Mild Steel Obtained by Wire and Arc Additive Manufacturing (WAAM).

Abstract: One of the challenges in additive manufacturing (AM) of metallic materials is to obtain workpieces free of defects with excellent physical, mechanical, and metallurgical properties. In wire and arc additive manufacturing (WAAM) the influences of process conditions on thermal history, microstructure and resultant mechanical and surface properties of parts must be analyzed. In this work, 3D metallic parts of mild steel wire (American Welding Society-AWS ER70S-6) are built with a WAAM process by depositing layers of material on a substrate of a S235 JR steel sheet of 3 mm thickness under different process conditions, using as welding process the gas metal arc welding (GMAW) with cold metal transfer (CMT) technology, combined with a positioning system such as a computer numerical controlled (CNC) milling machine. Considering the hardness profiles, the estimated ultimate tensile strengths (UTS) derived from the hardness measurements and the microstructure findings, it can be concluded that the most favorable process conditions are the ones provided by CMT, with homogeneous hardness profiles, good mechanical strengths in accordance to conditions defined by standard, and without formation of a decohesionated external layer; CMT Continuous is the optimal option as the mechanical properties are better than single CMT.

Using Genetic Algorithms with Multi-Objective Optimization to Adjust Finite Element Models of Welded Joints

Abstract: To ensure realistic results when modeling welded joints using the finite element method (FEM), it is essential to appropriately characterize the thermo-mechanical behavior of the elastic-plastic Finite Element (FE) models. This task is complex. Any small differences between the actual welded joints and the welded joints based on FEM can be amplified enormously in the presence of nonlinearities. Due to the intense concentration of heat on a small area to create such joints, the regions near the weld line undergo severe thermal cycles. These generate significant angular distortion due mainly to the residual stresses. This paper proposes a method to determine the parameters that are most appropriate for modeling the Butt joint single V-groove welded joint FE models’ thermo-mechanical behavior that were created by the one-pass Gas Metal Arc Welding (GMAW). The method is based on experimental data, as well as genetic algorithms (GA) with multi-objective functions. As a practical example, the proposed methodology is validated with three different welded joints specimens that are manufactured by different voltages and currents (26 volts and 140 amps, 28 volts and 210 amps, and 35 volts and 260 amps). The electrode orientation, shielding gas flow rate, distance between nozzle and plate, and welding speed were considered to be constant for all of the specimens that were studied, and their values were 80°, 20.0 L/min, 4.0 mm, and 6 mm/s, respectively. The base material was EN 235JR low carbon steel, whereas the weld bead was ER70S-6 for the three specimens that were welded. An agreement between the temperature field and the angular distortion that was obtained by the adjusted FE models and those that were obtained experimentally demonstrates that the proposed methodology may be valid for automatically determining the most appropriate parameters.

Arc-based additive manufacturing of steel components—comparison of wire- and powder-based variants

Abstract: Additive manufacturing of components, layer-by-layer, offers several advantages compared to conventional production technologies such as higher material utilization efficiency and increased geometric possibilities. Arc-based additive manufacturing processes have the additional advantage of an almost unlimited assembly space, higher deposition rates, and an improved utilization factor of raw materials. Up to now, the gas metal arc welding variant, cold metal transfer (CMT), and other wire-based process combinations have been used predominantly in this field. Disadvantages of wire-based methods are the restricted availability of different types of wire consumables, the wire feed rate directly coupled to the heat input, and the lack of possibility to create multi-material structures with one heat source in-situ. Within this work, the 3D plasma-metal deposition (3DPMD) method, based on a plasma powder deposition process is introduced. 3DPMD has some advantages compared to the established plasma powder process and wire-based CMT process. Basis for this evaluation is the production of geometrically complex structures by the different methods (CMT & 3DPMD) and their subsequent characterization. Structures are fabricated using welding robots with the path control directly generated from the CAD files. In summary, 3DPMD offers increased flexibility in terms of material selection as well as the possibility to build graded structures. By using subroutines realized from a special postprocessor, it is possible to generate metal structures with standard welding robots directly from the CAD drawings. Microstructures and properties are directly related to the process and therefore material-process-property relationships are discussed within this work.

Welding of S960MC with undermatching filler material

Abstract: High strength structural steels are in high demand thanks to their favorable mechanical properties. They offer high strength with sufficient toughness and good forming capabilities. Applications range from shipbuilding, to offshore constructions, cranes, and pipelines. A lot of current research focuses on weldability of high strength low alloy (HSLA) steels, especially improving the toughness in the weld zone, i.e., weld metal (WM) and heat affected zone (HAZ). In the present work, four different fusion welding processes using undermatching filler metal are compared on 8-mm thick sheets of S960MC structural steel. The welding processes include electron beam, laser hybrid, plasma, and gas metal arc welding. The welded joints are characterized by means of mechanical testing, tensile, impact, and hardness testing, and microstructural investigaton, light optical, and scanning electron microscopy. Furthermore, microprobe analysis of the weld metal was used to investigate the chemical composition of the weld metal.

Feature based three axes computer aided manufacturing software for wire arc additive manufacturing dedicated to thin walled components

Abstract: WAAM (Wire-Arc-Additive-Manufacturing) is a metal additive manufacturing process using arc welding to create large components with high deposition rate. The workpiece quality and the process productivity are strongly dependent both on the process parameters (wire feed speed, voltage and current) and on the selected deposition path. Currently, the CAM (Computer-Aided-Manufacturing) software dedicated to WAAM rely on a multi-pass strategy to create the component layers, i.e. each layer is built overlapping multiple welding passes. However, since WAAM can create wide layers, a single pass strategy can improve the process efficiency when dealing with thin walled components. This paper proposes CAM software dedicated to WAAM, using a single pass strategy. The proposed solution uses a midsurface representation of the workpiece as input, to generate the deposition toolpath. A feature recognition module is proposed, to identify the critical features of the part, such as free end walls, t-crossings, direct-crossings and isolated tubulars. A specific strategy is developed and proposed for each one of the selected features, with the aim of minimizing the geometrical errors and to ensure the required machining allowances for the subsequent finishing operations. The effectiveness of the proposed strategy is verified manufacturing a test case.

Review of current waveform control effects on weld geometry in gas metal arc welding process

Abstract: Control of welding parameters is an important factor in gas metal arc welding (GMAW) because these parameters determine the heat input, cooling conditions, and time during which the microstructure and the geometry of the weld are formed. It is therefore essential that sufficient heat is transferred to highly conductive metals like aluminum and appropriate heat input used with very sensitive metals such as stainless steel and high-strength steels or when welding dissimilar metals. The objective of this study is to identify parameters of current, voltage waveforms, and electrode feeding motion that directly contribute to improvement in metal and heat transfer conditions from the electrode to the base metals. The effects of these parameters on welded joint geometry are determined. The work critically reviews research on the effect on welded joints of control of current waveform, voltage, and the alternating electrode and analyzes the different parameters that promote forces acting during metal transfer. Experiments and case studies based on controlled waveforms are discussed. The analysis shows that in controlled short-circuit gas metal arc welding (CS-GMAW), all identified parameters contribute to control of heat input and reduction in the amount of spatter and fumes generated. Variable polarity gas metal arc welding (VP-GMAW) is found to be particularly effective for aluminum welding because of its good control of mass metal transfer and weld penetration. Mixed waveform approaches (i.e., 20 pulses/controlled short circuit) improve weldability in difficult welding positions.

An investigation on plasma-MIG hybrid welding of 5083 aluminum alloy

Abstract: Plasma-MIG (metal inert-gas) hybrid welding is an advanced welding technology of aluminum alloys, which integrates the advantages of deep penetration in plasma arc welding and excellent filling ability in MIG welding. In this paper, the 5083 aluminum alloy plates with 6-mm thickness were welded using paraxial plasma-MIG hybrid welding. The influence of processing parameters such as the welding speed, plasma current, MIG current, and plasma gas flow rate on the weld forming was investigated, and the microstructure and mechanical behavior of welded joint under the typical parameters were studied. Both the penetration depth and weld width decreased with the increase of welding speed, increased with the increase of MIG current. While plasma arc current and plasma gas flow rate mainly affected penetration depth. The welding joint underwent the different thermal cycles in the different regions, which resulted in the different microstructure. Compared with the lower part of welding joint, the secondary phases in the upper part were bulkier and the dendrite arm spacing was wider, and the width in the partially melted zone (PMZ) was smaller. The tensile strength and the elongation of the welding joint were 274 MPa and 12.42%, which is approximately 85.63 and 95% of that of base metal, respectively.