Plasma Arc Welding Research Articles

Different path strategies for directed energy deposition of crossing intersections from stainless steel SS316L-Si

Additive manufacturing by directed energy deposition is of increasing interest within the scientific community. Over the past decade, this technology has gained ground with the production of parts from SS 316L-Si stainless steel, an industrial product in widespread use. Yet one of the main challenges when extending the use of this technology to the manufacture of medium complexity parts is how to achieve good intersections. This paper focuses on the use of Plasma Arc Welding (PAW) for the additive manufacturing of X-Cross intersections made of SS 316L-Si stainless steel alloy, defining its geometrical suitability and evaluating its productivity. Firstly, two strategies for the production of parts are presented: the energy control strategy on the curved path of a L-shaped wall and the variable amplitude waveform strategy (variable waving) for the continuous production of a X-cross intersection. A metallographic analysis of the samples extracted in the different tests was completed, focusing mainly on the transversal direction. Next, four deposition strategies based on discrete trajectories (cross-overlapping and cross-waving) and on continuous trajectories (waving and overlapping) are addressed in this paper for the production of cross intersections in a part of medium complexity and for the extension of its use in Near-Net-Shape (NNS) manufacturing. The mechanical properties and microstructure of samples manufactured with these deposition strategies are analysed by means of tensile tests and metallographic characterization. An analysis of the deposition energy and of the productivity is carried out for the four strategies. The productivity is analysed by means of different parameters such as the number of layers, the actual deposition rate and process times (deposition time, waiting time, standby time and idle time). The most advantageous strategies in terms of productivity were cross-waving and waving, achieving torch utilization rates relative to total time of 50 %. Methodologies and conditions for the manufacture of X-cross intersections are established. Finally, a study of the cross-intersection geometry obtained for each deposition strategy is performed. From the geometrical analysis of the crosses produced, it has been observed that the ratio of material used in the cross-overlapping sequence to produce a X-cross intersection in relation to the amount of material deposited is more than 10 % higher than in the other strategies.

Experimental studies on key-hole plasma arc welding process parameters of AISI 304 HCu stainless steel tube joints

AISI 304HCu is a super austenitic stainless steel with alloying elements adding its capacity to retain the ability to withstand mechanical and corrosion resistance at extreme service conditions. The investigation focuses on the feasibility studies on the effect of process parameters of Keyhole Plasma Arc Welding (KPAW). The stability of the keyhole on 9 mm thick tubes is by the action of welding current, gas flow rate and the standoff distance. The autogenous joint had a wine glass bead morphology with a minimum heat-affected zone. The influence of current is on the penetration, whereas the gas flow rate and standoff distance govern the geometric appearance. The fusion zone consists of vermicular δ ferrites within the austenitic matrix. The refined vermicular ferrite grains in the fusion zone of the KPAW joint record a maximum strength of 610 MPa and hardness of 230 HV. The failure region reflects the presence of coarse grains; because of the heat dissipation from the fusion zone. The cooling rate is high that it restricts the growth of the grains in the HAZ. The failure is by the ductile manner in KPAW joints.

Effect of Ultrasonic Power on Microstructural and Mechanical Properties of Al/Cu Plasma Arc Welding–Brazing Joints

Effect of Ultrasonic Power on Microstructural and Mechanical Properties of Al/Cu Plasma Arc Welding–Brazing Joints

Material properties of gradient copper‐nickel alloy fabricated by wire arc additive manufacturing based on bypass-current PAW

In this paper, the bypass-current plasma arc welding (BC-PAW) based on PAW was employed to fabricate copper-nickel (Cu-Ni) gradient thin-walled structures. The effect of forming accuracy and compositional homogeneity of the bypass current Cu-Ni structure was first verified by controlled experiments. The effect of Ni content on the microstructure and mechanical properties of Cu-Ni gradient structures fabricated using bypass current was then investigated, with a focus on grain orientation and texture analysis of the three intermediate Cu-Ni mixed gradient layers. The results showed that the use of bypass current in the additive manufacturing of Cu-Ni gradient structures can improve the forming accuracy and effectively eliminate lateral composition deviations within the gradient layers. In the Cu-Ni mixed gradient layers, the average grain size of the gradient layers decreased with increasing nickel content, and unusually large secondary grains appeared in different gradient layers. Due to the different Ni content, different degrees of amplitude modulation decomposition occurred in different gradient layers, resulting in changes of grain orientation and texture composition. Under the combined effects of solid solution strengthening, fine grain strengthening and amplitude modulation decomposition, the microhardness and tensile strength increased with increasing nickel content and then decreased, reaching a maximum near the side of the gradient composition biased toward nickel. The fracture analysis showed a transition from ductility to quasi-fracture.

Mechanical properties of plasma arc welded AISI304LN austenitic stainless steel at various temperatures

ABSTRACT AISI 304 grade austenitic stainless steels are widely used in a wide variety of fields such as chemical, automobile, food industries, etc. due to their good mechanical properties and corrosion resistivity. In this study, AISI 304LN austenitic stainless-steel couples were joined with plasma arc welding. The effect of temperature on the mechanical properties, formability and fracture morphologies of joints was evaluated. For this purpose, tensile testing of the joints was carried out in the temperature range of –50°C, and 25°C–850°C. Thus, the ultimate tensile strength, (UTS), yield strength, (YS) and elongation (EL%) amounts of welded joints were determined. The fracture morphologies of the tensile test samples were examined. It was observed that the rupture (except 850°C) occurred from the weld metal. The highest formability was obtained in the samples tested at 850°C. In addition, the existence range of dynamic strain aging (DSA) of the plasma arc welded samples was also investigated. The unsteady plastic flow between the yield and the ultimate tensile of the sample subjected to the tensile test at 250–550°C are evaluated as signs of DSA.

A Seam Tracking Method Based on an Image Segmentation Deep Convolutional Neural Network

Vision-based welding seam tracking is an important and unique branch of welding automation. Active vision seam tracking systems achieve accurate feature extraction by using an auxiliary light source, but this will introduce extra costs and the real-time performance will be affected. In contrast, passive vision systems achieve better real-time performance and their structure is relatively simple. This paper proposes a passive vision welding seam tracking system in Plasma Arc Welding (PAW) based on semantic segmentation. The BiseNetV2 network is adopted in this paper and online hard example mining (OHEM) is used to improve the segmentation effect. This network structure is a lightweight structure allowing effective image feature extraction. According to the segmentation results, the offset between the welding seam and the welding torch can be calculated. The results of the experiments show that the proposed method can achieve 57 FPS and the average error of the offset calculation is within 0.07 mm, meaning it can be used for real-time seam tracking.

EFFECTS OF RARE-EARTH METAL OXIDES ON THE TRIBOLOGICAL PROPERTIES OF PADDINGS FOR USE ON MINING MACHINE PARTS

The article presents the results of research on pad welds made using consumables in the process of metal active gas welding (MAG) combined with plasma arc welding (PAW). The pad weld consisted of a buffer layer and a wear-resistant working layer. Cerium, yttrium and lanthanum oxides were added to the powders to modify the working (active) layer. The HV10 hardness and friction coefficient testing was followed by measuring wear tracks and determining wear indicators (maximum wear track depth and area). Yttrium oxide was found to have a remarkably beneficial effect on nickel-based pad welds. In the case of iron-based welds, the most favourable outcome was observed for lanthanum oxide.

Keyhole status prediction based on voting ensemble convolutional neural networks and visualization by Grad-CAM in PAW

K-PAW (Keyhole Plasma Arc Welding) has a wide range of applications in welding medium-thick metal workpieces. However, the welding processes are vulnerable due to the fragile force balance on the liquid metal around the keyhole, and burn-through or lack of fusion might be caused. In order to optimize the welding quality, considerable work has been devoted to penetration/keyhole status prediction by visual sensing and deep learning algorithms. However, a single network model is challenging to extract comprehensive features of weak-discrimination weld pool images. This paper focused on the correspondence between the topside weld pool images and the prediction/keyhole status. A novel prediction method has been proposed based on eight classical CNNs trained, compared, and fused. For these single models, the prediction accuracy is higher than 95 %, with the speed of faster than 10 frames per second (FPS). The model visualization by the Grad-CAM method was performed to show the focused feature regions clearly. Although regarded as black boxes, these prediction models are considered robust when the extracted features are consistent with the prior knowledge. KeyholeVot, a voting ensemble decision model, was established based on the selected three robust models (i.e., InceptionNetV3, InceptionResNetV2, and XceptionNet) and achieved 96.62 % evaluation accuracy.

Thermal expansion behaviour of Invar 36 alloy parts fabricated by wire-arc additive manufacturing

Invar 36 alloy is of high interest in various industrial sectors, due to its reduced thermal expansion properties. This study aims to validate Wire-Arc Additive Manufacturing (WAAM) technology as a valid method for manufacturing aerospace tooling in Invar 36. The main novelty and the objective of this work is to study the properties of Invar deposited by WAAM technology and to provide guidelines for the manufacture of parts using this technology. To do so, the thermal expansion behaviour of Invar specimens manufactured using Gas Metal Arc Welding (GMAW)-based WAAM technology and Plasma Arc Welding (PAW)-based WAAM technology is analyzed for subsequent comparison with the values obtained from the laminated Invar sample used as the reference specimen. A wall is manufactured with each technology, for comparative purposes, from which specimens were extracted for the dilatometry test and metallographic analysis. The results of these analyses show the advantages of GMAW technology for the manufacture of Invar alloy parts, as it presents the same thermal expansion behaviour as the laminated reference material with less presence of precipitates and no macrostructural failures such as pores, cracks and lacks of fusion. Furthermore, to conclude, an aeronautical tooling that has been manufactured within this work demonstrated the potential of this technology to manufacture specialized aeronautical parts.

Fusion welding of refractory metals and ZrB2-SiC-ZrC ceramics

Molybdenum and a molybdenum alloy were fusion welded to ZrB2-based ceramics to determine if the electrical and thermal properties of the metals and ceramics affected their weldability. Commercial ceramic powders were hot pressed, machined into coupons, and preheated to 1600 °C before joining the ceramics to commercial metals using plasma arc welding. Weldability varied as indicated by the range of porosity observed within the fusion zones. Measured thermal and electrical properties appeared to have little to no effect on the weldability of metal-ceramic welds despite the large range of values measured across each property. Differences in melting temperatures between metal and ceramic coupons did affect weldability by changing the weld penetration depth into ceramic coupons. Future studies on metal-ceramic welds are suggested to investigate the effect that work function, melt viscosity, wetting, or other properties have on weldability.

Visual sensing and controlling of the keyhole in robotic plasma arc welding

With an advantage of “single-sided welding and double-sided forming,” plasma arc welding (PAW) has a great application potential in modern industrial production. The welding quality can be guaranteed by sensing and controlling of the keyhole. However, it is difficult to make an on-line observation on the back of base metal, and realize a dynamic registration of the visual sensor and welding torch. In this study, it has investigated the relationship between the welding condition and image feature of keyhole. Image processing is designed to obtain the weld pool image and conduct a template matching of the keyhole. The target feature of weld zone will be extracted and processed in real time. Besides, it has designed a digital controller for the welding robot and power source in this study and discussed control method to stabilize the keyhole and achieve good welding quality. Eventually, experiments are conducted to inspect the comprehensive performance of the welding control system with varying disturbance. This study is of important significance for the visual sensing and controlling of the keyhole in PAW. It will provide technical support for the weld quality control, and promote the development of welding technology based on machine vision in intelligent manufacturing field.

An easy-to-use multi-physical model to predict weld pool geometry in keyhole plasma arc welding

Plasma arc welding (PAW) can produce deep-penetration weld when a keyhole mode appears with high welding currents. The process involves complex thermal-hydrodynamical effect and electromagnetic effect, which requires fundamental research in multi-disciplinary fields to give full understanding. Therefore, an easy-to-use model, which includes an arc zone and a workpiece zone, was developed to calculate the keyhole PAW process with full consideration of multi-physical mechanisms. It calculates thermal plasma process and its heat transfer to workpiece. Meanwhile it predicts an accurate arc pressure and then treats it as a pressure source term in workpiece zone. In this way, the model can display a keyhole-like welding process with great convenience. Experimental results of arc pressure and weld pool geometry verify the model. Further research shows that the choice of different parameters in solid-liquid phase change model may cause a difference to calculated results. It's found that solid viscosity 20 N s/m2 and Mushy zone constant 108 are good choice. Welding characteristic concerning three different welding parameters is predicted to guide practical engineering application. It's found heat flux and arc pressure have a non-linear positive correlation with welding current and a significantly negative correlation with orifice diameter and distance from torch to workpiece. It also shows the noteworthy arc heating area is much larger than the noteworthy pressure striking area in PAW. Fusion depth is more sensitive than weld width to the variation of welding parameters.

Wire Arc Additive Manufacturing – A revolutionary method in additive manufacturing

Wire Arc Additive Manufacturing (WAAM) is a revolutionary process under the category of Direct Energy Deposition (DED) method in the field of Additive Manufacturing (AM). The research is being done exponentially since 2011 which is integrating into the advancement of production specifically for fourth Industrial Revolution (Industry 4.0). The deposition of filler metals in layers over the substrate is done mainly through Gas Metal Arc Welding (GMAW), Gas Tungsten Arc Welding (GTAW), and Plasma Arc Welding (PAW) which are leading heat input sources to fabricate the product with improved strength of material than from other DED's. Although defects are similar as of welding defects. In this paper, concepts and processes for WAAM have been studied thoroughly and a critical review is done on important and defining parameters of good quality WAAM manufactured products. It also focuses on the recent advancements in tuning the mechanical and microstructural properties of WAAM fabricated parts and the financial aspects of WAAM for the production of cost-effective fabricated materials.

Corrosion Behavior of 7A52 Aluminum Alloy Plasma Arc Welding Joint in Simulated Marine Atmosphere Environment

Corrosion behavior of 7A52 aluminum alloy plasma arc welding (PAW) joint was investigated in simulation of marine atmosphere environment with salt water spray test. The surface morphologies were observed by scanning electron microscopy (SEM), and the effect of corrosion time on corrosion behavior was discussed. The depth of spot corrosion, the corrosion dynamic characteristics, and the distribution of element of 7A52 aluminum alloy welding joint were analyzed by 3D and XRD Microscope. Results show that pitting corrosion is main morphology in heat effect zone at initial stage, pitting corrosion appears in matrix and welding joint with time. The main component compounds existing in the film include Al and O. The depth of pitting corrosion in the heat effect region is the maximum (3.008μm). The law of power function is followed in both phases of the corrosion weight increasing curve, and the corrosion rate decreases with time.

Effect of the Heat Input on Wire-Arc Additive Manufacturing of Invar 36 Alloy: Microstructure and Mechanical Properties

AbstractInvar, also known as FeNi36, is a material of great interest due to its unique properties, which makes it an excellent alternative for sectors such as tooling in aeronautics and aerospace. Its manufacture by means of wire arc additive manufacturing (WAAM) technology could extend its use. This paper aims to evaluate the comparison of two of the most widespread WAAM technologies: plasma arc welding (PAW) and gas metal arc welding (GMAW). This comparison is based on the analysis of wall geometry, metallography, and mechanical properties of the material produced by both technologies. The results show a slight increase in toughness and elongation before fracture and worse tensile strength data in the case of PAW, with average values of 485 MPa for ultimate tensile strength (UTS), 31% for elongation and 475 MPa, 40% in GMAW and PAW, respectively. All results gathered from the analysis show the possibility of successful manufacturing of Invar by means of WAAM technologies. The novelties presented in this paper allow us to establish relationships between the thermal input of the process itself and the mechanical and metallographic properties of the material produced.

Plasma arc welding of dissimilar ultrahigh-strength steel and aluminum alloy assisted by copper transition layer

Plasma arc welding of dissimilar DP1180 ultrahigh-strength steel and 5A06 aluminum alloy assisted by copper transition layer was applied and a hybrid joint was obtained consisting of two metallurgical bonding zones. The hybrid joint consisted of the weld formed by the fusion welding of steel and copper on steel side, unmelted Cu and the Cu-Al interface layer formed by liquid phase diffusion reaction. The unmelted Cu acted as a diffusion barrier between steel and Al-alloy, and no Fe-Al intermetallics were detected in the weld. The Cu-Al interface layer composed of Cu9Al4 + CuAl2 + CuAl2/α-Al eutectic and the formation mechanism of the Cu-Al interface layer was discussed. Mechanical testing of the hybrid joints revealed that the average tensile strength was 125 MPa and all the tensile samples fractured at Cu-Al interface layer containing Cu9Al4 and CuAl2.

Study on arc characteristics of different defects in pulsed micro-plasma arc welding

The shape of welding arc is closely related to the quality of welding. For micro plasma arc welding (MPAW), however, the change of arc shape is not obvious enough to evaluate the quality of welding, due to the small size of welding arc. Thus, it needs to extract the specific features of arc shape through image processing algorithm to judge its change quantitatively. Furthermore, for workpiece with bright surface, it is difficult to extract the arc shape directly from the arc images because of the strong arc reflection on the workpiece surface. In this paper, a new method based on vertical Sobel operator was proposed to overcome the above-mentioned challenges, and to extract the clear arc shapes from the arc images of pulse micro plasma arc welding (P-MPAW). The arc length, arc width and the height difference between two sides of arc were extracted as characteristic parameters to reveal the influence of different welding defects on the arc shape. The changes of arc characteristic parameters have been studied in depth, when there are different defects such as burn through, misalignment, undercut, concave deformation, excessive gap and overlap. The results show that, excessive welding gap and misalignment, caused by the assembly and machining accuracy, have obvious characteristics in the instantaneous arc shape. The defects caused by welding thermal process like burn through, concave deformation, overlap and undercut have their own distinctive characteristics in the changing process of the arc shape.

Influence of deposit and process parameters on microstructure and mechanical properties of Ti6Al4V obtained by DED-W (PAW)

Direct energy deposition with a wire feedstock (DED-W) of Ti6Al4V is a promising solution to produce large structures with a better buy-to-fly ratio than conventional manufacturing techniques. This study investigates the potential of a plasma arc welding (PAW) as a heat source for DED-W. In order to understand the influence of process parameters on material health, microstructure and mechanical properties, three types of specimens: (i) single deposits; (ii) stacked-deposits walls and (iii) three-dimensional block are built. Two sets of parameters have been determined via deposit energy versus wire feed speed's process windows in order to obtain either slender or wide elements. The adoption of an increased deposit energy for the first several layers radically decreases the necking at the connection with the base plate. Prior β grain's width increases with the time spent above the β transus, which is dictated by the height of the build. On the other hand, α plate's thickness might be governed by the delay between layers which changes the cooling rate. Strain localisation under tensile loading appear either on banding or in the vicinity of αgb layer. Mechanical properties anisotropy related to the columnar shape of prior β grains is more noticeable under Charpy notched impact tests than tensile tests.

Gravity effects on temperature distribution and material flow in the keyhole pool of VPPA Al welding

This study investigated heat and mass transfer as well as the effect of gravity on keyhole formation in the molten pool of keyhole plasma arc welding. The flow trajectory of the molten pool was obtained via high-speed camera images illuminated by a laser light system, and the temperature distribution was obtained using an infrared thermal camera. The experimental results showed that the molten metal flowed rearward and downward at the top surface of the weld pool and thereafter to the rear side of the keyhole. There are two types of reverse flow of molten metal on the rear side of the keyhole. The different welding positions had minimal effect on the flow pattern; however, the flow velocities were different. Further, for the temperature distribution, although the keyhole front side yielded a similar high-temperature area under different welding positions, the area of the high temperature on the keyhole rear side in the vertical position welding was much larger than that in the flat position. Consequently, the influence of the force on the keyhole molten pool was evaluated, and the flow pattern of the molten pool was found to be dominated by the sheer force. Moreover, the flow velocity and solidification morphology of the molten pool were affected by the gravity at different welding positions. In addition, the correlation mechanism of the temperature distribution, flow, and solidification morphology of the keyhole molten pool was analyzed using the combined action of shear force and gravity, which further revealed the mechanism of the influence of gravity on the keyhole welding process.

Effect of Nano-Y2O3 on the Microstructure and Properties of WC-Reinforced Ni-Based Composite Surfacing Layer.

In this study, a WC-reinforced Ni-based surfacing layer was prepared on Q235 steel plate by plasma arc welding. The effects of nano-Y2O3 with different contents (0 wt.%, 0.4 wt.%, 0.8 wt.%, 1.2 wt.%, and 1.6 wt.%) on the microstructure, phase composition, microhardness, and wear resistance of the surfacing layer were studied by scanning electron microscope (SEM), energy dispersive spectrometer (EDS), X-ray diffraction (XRD), microhardness test, and pin-on-disk test. The results show that the phase composition of the surfacing layer was γ-Ni, FeNi3 solid solution, WC, W2C, M23C6, M6C, Cr7C3, and other carbides. When the addition of nano-Y2O3 was 1.2 wt.%, it has a good improvement on microstructure grain refinement and carbide hard-phase increase. Compared with other contents, 1.2 wt.% nano-Y2O3 surfacing layer has the highest microhardness and the lowest friction coefficient and wear loss. At this time, the wear mechanism is abrasive wear accompanied by slight adhesive wear.