Explore the vast range of titles available.

In this study, the microstructural features of 7A52 heat-treatable aluminum alloys welded by variable polarity plasma arc (VPPA) combined with gas metal arc welding (GMAW) (VPPA–GMAW) were investigated and compared with those of 7A52 aluminum alloys welded by GMAW. The grain structures and modification of the precipitates were analyzed by optical microscopy and transmission electron microscopy. Complementary to modification of the precipitates, the precipitation evolution in the heat-affected zone and magnesium loss in the fusion zone were measured by differential scanning calorimetry and inductively coupled plasma spectroscopy. In VPPA–GMAW, the weld only needs one pass by depositing on one side of the 10-mm-thick aluminum alloy plates because of the large penetration capability of VPPA and good fluidity of the molten metal in the weld pool. Accordingly, the effect of excessive heat input on the microstructure can be minimized. The results show that the grain growth is not obvious and the magnesium loss is small in the fusion zone of VPPA–GMAW compared with that of GMAW under the condition of equal heat input to the workpiece. Small precipitates inside the grains remain homogeneously distributed, and a large volume fraction of the η′ phase exists. The VPPA–GMAW weld exhibits less tendency to soften; thus, VPPA–GMAW is appropriate for welding thick-plate aluminum alloys with a high production rate.

15CDV6 is one of the widely used high strength low alloy steels in the applications of aerospace, automotive, and defense components. Welding plays a key role in all these joining applications. In this research, an attempt is made to join 15CDV6 high strength low alloy (HSLA) steel using a spin arc gas metal arc welding process (SA-GMAW) with 3.7 mm thick 15CDV6 plates and joined in butt joint configuration at three different spin rotation speed (SRS), viz., 1200, 1500, and 1800 rpm. The effect of SRS on the weld quality was studied by measuring the depth of penetration, bead width, tensile strength, and microhardness. The results indicate that increasing the SRS increases the side wall fusion. A spin rotation of 1200 rpm with 230 A, and 24 V makes a good quality weld with comparatively better strength weldment (WM) than base metal (BM). The slower spin rotational speed maintains a moderate temperature in the weld pool, causing the creation of vanadium carbide precipitates that have an impact on the mechanical properties.

The behavior of the welding arc in the pulsed DC and AC gas metal arc welding processes was studied using real-time recorded current, voltage waveforms, and synchronized high-speed video at different electrode negative (EN) ratios for a constant wire feed rate. The regression equations were developed to predict the arc root dimensions as a function of welding current, voltage, time, and the EN ratio. A methodology was proposed to estimate the available energy rate distribution to the electrode and the base plate during the positive and negative cycles in pulsed AC gas metal arc welding (pulsed AC-GMAW) process. For an approximately equal peak positive current, the increase in the pulse time enhanced the molten electrode droplet diameter, arc plasma distribution, and the arc root dimensions. The fraction of the available arc energy rate supplied to the base plate was higher in positive pulse when compared to the negative pulse. A three-dimensional finite element modeling of pulsed DC-GMAW and pulsed AC-GMAW processes was performed to estimate the weld pool profile and temperature distribution in the weldment. The computed weld width, penetration, and the thermal cycles were in reasonable agreement with the corresponding experimental results. The peak temperature of the region in the weld pool near to the Gaussian distributed heat source experience fluctuations which were in synchronization with the current waveform. Increase in the EN ratio decreased the peak temperature while increased the cooling rate in the weldment. This reduced the bainite phase and enhanced the martensite phase in the weldment.

Purpose Wire + arc additive manufacturing (WAAM) uses existing welding technology to make a part from metal deposited in an almost net shape. WAAM is flexible in that it can use multiple materials successively or simultaneously during the manufacturing of a single component. Design/methodology/approach In this work, a gas metal arc welding (GMAW) based wire + arc additive manufacturing (WAAM) system has been developed to use two material successively and fabricate bimetallic additively manufactured structure (BAMS) of low carbon steel and AISI 316L stainless steel (SS). Findings The interface shows two distinctive zones of LCS and SS deposits without any weld defects. The hardness profile shows a sudden increase of hardness at the interface, which is attributed to the migration of chromium from the SS. The tensile test results show that the bimetallic specimens failed at the LCS side, as LCS has lower strength of the materials used. Originality/value The microstructural features and mechanical properties are studied in-depth with special emphasis on the bimetallic interface.

Variable polarity plasma arc-gas metal arc welding (VPPA-GMAW) is a superior technology for welding thick plates of high-strength aluminum alloys. It integrates the advantages of energy focusing and high penetration depth in VPPA welding, and those of high welding efficiency and wide range of technological parameters in GMAW process. In this work, we investigated the droplet momentum in paraxial VPPA-GMAW hybrid welding of 7A52 aluminum alloys, and the technological parameters of welding process was also optimized. The images of droplet transfer were captured by high-speed camera, while the droplet speeds and sizes were statistically analyzed by t tests of independent samples. The results showed that the speeds of droplet arriving at the weld pool were significantly between GMAW and VPPA-GMAW processes, and the droplet speed increases with increasing plasma currents within a certain range. Meanwhile, the droplet momentum in VPPA-GMAW process is larger than that in conventional GMAW process. We also found that as the droplet momentum increased, the depression of weld pool grew more obvious and greatly facilitated the deep-penetration welding. In VPPA-GMAW process, it became more and more easier for the droplet to fall off the wire when the electromagnetic force gradually increased during pulse period. Droplet movement through the arc zone was further accelerated since the central pressure of arc column increased during base period. This research can provide some theoretical support for thick plate welding of high-strength aluminum alloys and help for deeper understanding of the hybrid arc coupling mechanism.

In the present study, an attempt is made to investigate and optimize the bead geometries of bead width (BW) and bead height (BH) of SS-309L using an SS316L substrate by employing a gas metal arc welding (GMAW)-based wire-arc additive manufacturing (WAAM) process. The Box–Behnken design approach was used to conduct the trials of single-layer depositions with input variables of travel speed (TS), voltage (V), and gas mixture ratio (GMR). The developed multi-variable regression models were tested for feasibility using ANOVA and residual plots. The data obtained indicated that V had the most significant impact on BW, followed by TS and GMR. For BH, TS had the most significant impact, followed by GMR and V. The results of single-response optimization using a passing vehicle search (PVS) algorithm showed a maximum BH of 9.48 mm and a minimum BW of 5.90 mm. To tackle the contradictory situation, a multi-objective PVS algorithm was employed, which produced non-dominated solutions. A multi-layered structure was successfully fabricated at the optimal parametric settings of TS at 20 mm/s, of voltage at 22 V, and of GMR at 3. For multi-layer structures, fusion among the layers was observed to be good, and they were found to be free from the disbonding of layers. This revealed the suitability of the PVS algorithm for generating suitable optimal WAAM variables. We consider the current work highly beneficial for users fabricating multi-layer structures.

Wire-and-arc-additive manufacturing (WAAM) is an additive manufacturing technology with a high deposition rate. WAAM usually employs a layer wise build-up strategy. This makes it necessary to know the height of each deposited layer to determine the height the z-axis has to travel after each layer. Current bead geometry models (BGM) lead to variations, which can gradually accumulate over the layers. The present study focuses on the development of a closed-loop control system capable of keeping the contact tube working distance (CTWD) constant during short-circuit gas metal arc welding (GMAW) based WAAM. The algorithm calculates the CTWD based on the resistance during the short circuit. The closed-loop strategy is compared to an open-loop control strategy, which moves along a predefined height step after each layer. Using the proposed control strategy, WAAM becomes a fully automated process without the need for preliminary experiments to determine the height step. Only a short calibration slope is necessary for a complete closed-loop additive build-up. To study the influence of the control strategy on the workpiece the energy input, mechanical strength, microhardness, porosity, and microstructure were analyzed. It is shown that the CTWD of the open-loop deposited component increases slowly. Due to the novel control approach, this is prevented by the closed-loop control, while the mechanical strength and microhardness remain.

It is essential to understand the power-arc model and the relationship of various parameters in pulsed gas metal arc welding (P-GMAW) process, in order to obtain stable arc length and droplet transfer. In this study, we analyzed the linear model of the GMAW process with some reasonable assumptions. A mathematical power-arc model of P-GMAW was established through an experimental statistical method by using a commercial welding power supply. Then, the mathematical model was applied combined with the adaptive arc length control strategy in the P-GMAW process of Al–Mg alloy by using the self-developed welding power supply. The experimental results indicated that the arc length of P-GMAW process for Al–Mg alloy kept uniform when using the experimental mathematical model and adaptive arc length control strategy. One drop per pulse (ODPP) droplet transfer mode was observed without spatters and cracks by carefully designing the preset parameters. The adaptive arc length control strategy showed good feasibility in Al–Mg alloy welding.

Appropriate selection of wire–arc additive manufacturing (WAAM) variables imparts bead geometries with characteristics of multi-layer structures. Thus, the present study aimed to optimize the gas metal arc welding (GMAW)-based WAAM variables of travel speed (TS), wire feed speed (WFS), and voltage (V) for the bead geometries of bead width (BW) and bead height (BH) on an SS 316L substrate. Single-layer depositions were made through a metallic wire of SS 316L by following an experimental matrix of the Box–Behnken design (BBD) technique. Multivariable regression equations were generated for design variables and responses, and ANOVA was used to investigate the feasibility of the obtained regression equations. WFS was the highest contributor affecting the BW, followed by V and TS, while WFS was again the highest contributor affecting the BH, followed by TS and V. Heat transfer search (HTS) optimization was used to attain optimal combinations. The single-objective optimization result showed a maximum bead height and minimum bead width of 6.72 mm and 3.72 mm, respectively. A multi-layer structure was then fabricated by considering an optimization case study, and it showed optimized parameters at a WFS of 5.50 m/min, TS of 141 mm/min, and voltage of 19 V with the bead height and bead width of 5.01 mm and 7.81 mm, respectively. The multi-layered structure obtained at the optimized parameter was found to be free from disbonding, and seamless fusion was detected between the obtained layers of the structure. The authors believe that the present study will be beneficial for industrial applications for the fabrication of multi-layer structures.

The experiments of wire arc additive manufacturing (WAAM) with general pulsed gas metal arc welding (GMAW) machine were performed to optimize process parameters. As optimized conditions, 140A welding current, 34 V welding voltage, 40 cm/min welding speed, and 15 mm contact tip to work distance (CTWD), were selected. Welding current and voltage affected heat input. Lower deposition, short circuit mode, and spatters were obtained by insufficient heat input. The melting of previous layer and lower height were obtained by excessive heat input. Welding speed and CTWD affected surface state and arc stability. Unsound surface and bead shape due to short circuit mode and spatters were observed in slow welding speed and short CTWD conditions. Arc instability were also observed in fast welding speed and long CTWD conditions. With the optimized process parameter, curved propeller shape blade was manufactured by the change of robot arm teaching point. It can be considered that the desired sufficient quality was obtained due to curved shape.