In welded structures using robotized metal active gas (MAG) welding, unwanted variation in penetration depth is typically observed. This is due to uncertainties in the process parameters which cannot ...be fully controlled. In this work, an analytical probabilistic model is developed to predict the probability of satisfying a target penetration, in the presence of these uncertainties. The proposed probabilistic model incorporates both aleatory process parameter uncertainties and epistemic measurement uncertainties. The latter is evaluated using a novel digital tool for weld penetration measurement. The applicability of the model is demonstrated on fillet welds based on an experimental investigation. The studied input process parameters are voltage, current, travel speed, and torch travel angle. The uncertainties in these parameters are modelled using adequate probability distributions and a statistical correlation based on the volt-ampere characteristic of the power source. Using the proposed probabilistic model, it is shown that a traditional deterministic approach in setting the input process parameters typically results in only a 50
%
probability of satisfying a target penetration level. It is also shown that, using the proposed expressions, process parameter set-ups satisfying a desired probability level can be simply identified. Furthermore, the contribution of the input uncertainties to the variation of weld penetration is quantified. This work paves the way to make effective use of the robotic welding, by targeting a specified probability of satisfying a desired weld penetration depth as well as predicting its variation.
Weld deviation detection is a precondition for welding automation. Capturing high-quality welding images and extracting deviation information using image processing methods are two steps for weld ...deviation detection. In this paper, based on the analysis of the imaging characteristics during metal active gas (MAG) welding process, real-time welding images are acquired clearly and steadily using a wide dynamic range vision sensor. According to the connection relationship between the top of the arc and the end of the wire during MAG welding process, a method for determining the wire centreline is proposed. After extracting the precise arc region, the region of interest (ROI) is segmented along the welding direction. To detect the two edges of the V-groove, an improved Canny algorithm is developed. Furthermore, both the Hough Transform and a screening method based on prior knowledge are used to connect V-groove edges. The V-groove centreline is then determined. As a result, the weld deviation between the wire centreline and the V-groove centreline is calculated. Further experiments showed that the precision range of deviation detection can be controlled within ±0.25 mm, which can meet the requirement of real-time welding. This deviation can be used as the input variable for a welding robot, thus laying the foundation for MAG welding automation.
Weldment inspection is a critical process in the metal industry. It is first conducted visually, then manually and finally using instrumental techniques such as ultrasound. We made one hundred metal ...inert/active gas (MIG/MAG) weldments on plates of naval steel S275JR+N with no defects, and inducing pores, slag intrusion and cracks. With the objective of the three-dimensional reconstruction of the welding defects, phased array ultrasound inspections were carried out. Error-free weldment probes were used to provide the noise level. The results can be summarized as follows. (i) The top view obtained from the phased array provided no conclusive information about the welding defects. The values of the echo amplitudes were about 70 mV for pores and cracks, and greater than 150 mV for slag intrusion, all of which showed great variability. (ii) The sectional data did not lie at the same depths and they needed to be interpolated. (iii) The interpolated sectional views, or C-scans, allowed the computation of top views at any depth, as well as the three-dimensional reconstruction of the defects. (iv) The use of the simplest tool, consisting of the frequency histogram and its statistical moments, was sufficient to classify the defects. The mean echo amplitudes were 33 mV for pores, 72.16 mV for slag intrusion and 43.19 mV for cracks, with standard deviations of 8.84 mV, 24.64 mV and 12.39 mV, respectively. These findings represent the first step in the automatic classification of welding defects.
The presence of Cr(VI) in welding fumes classifies them as carcinogens, posing a health risk to welders. Therefore, it is crucial to minimize welders’ exposure to Cr(VI) by understanding the role of ...shielding gases in the generation of Cr(VI) during welding. This article offers valuable insights into the impact of shielding gases’ oxygen index on Cr(VI) production in welding fumes and highlights key variables that influence the Cr(VI) generation during welding. The study reveals that the behavior of shielding gases in Cr(VI) production varies between flux-cored arc welding (FCAW) and solid stainless-steel wires, with the oxidation index of the shielding gas playing a significant role in solid stainless-steel wires. Furthermore, the study indicates that the arc stability and ionization potential of shielding gases also affect the amount of Cr(VI) produced. Interestingly, the use of a CO
2
and O
2
mixture with Ar resulted in the lowest formation of Cr(VI). In FCAW, the highest levels of Cr(VI) were observed when argon was used as the shielding gas, primarily due to the presence of Na and K in the wires, which promote the oxidation of Cr(III) to Cr(VI). Conversely, the utilization of oxidizing shielding gases reduces the formation of Cr(VI) as Na and K react with oxygen to form their oxides, thereby reducing the availability of these elements to form chromates and dichromates.
The sustainable and resource-efficient production of wind energy plants requires the use of modern high-strength fine-grain structural steels. This applies to both foundation and erection structures, ...like mobile or ship cranes. During the assembly of steel structures, unacceptable defects can occasionally be found in the weld area. In most cases, the economical solution would be local thermal gouging of the affected areas and re-welding. Due to the high shrinkage restraint of the joint groove in the overall structure, the superposition of global and local welding-induced stresses may lead to crack formation and component failure, particularly in interaction with the degradation of the microstructure and mechanical properties of high-strength steels during the repair process. However, manufacturers hardly have any information about these issues and there is a lack of recommendations and guidelines to take these safety-relevant aspects into account in adequate repair concepts. The aim of this research is to derive recommendations for repair concepts appropriate to the stresses and materials involved providing a basis for standards and guidelines to avoid cold cracking, damage and expensive reworking especially for high-strength steels. Part 1 of this study involves systematic investigations of influences of shrinkage restraint during repair welding of two high-strength steels S500MLO for offshore application and S960QL for mobile crane structures. The quantification of the shrinkage restraint of repair weld joints was achieved by means of experimental and numerical restraint intensity analysis. In welding experiments with self-restrained slot specimens, restraint intensity and introduction of hydrogen via the welding arc using anti spatter spray were varied systematically to analyse the effect on welding result, residual stresses and cold cracking. It could be shown that increasing restraint intensities result in significantly higher transverse residual stress levels. In the case of hydrogen introduction S500MLO showed no cold cracking independent of the restraint conditions. However, S960QL was found to be considerably cold cracking sensitive if hydrogen is introduced. With increasing restraint intensity length and number of cold cracks increases significantly. Part 2
1
of this study is focussed on microstructure and residual stresses due to gouging and stress optimization via adequate heat control parameters in repair welding.
In this study, we performed a numerical simulation and experimental measurements on a steel circular patch welded structure to investigate the temperature and residual stress field distributions ...caused by the application of buried-arc welding technology. The temperature histories during the welding and subsequent cooling process were recorded for two locations, with the thermocouples mounted inside the plate close to the weld bead. On the upper surface of the welded model, the temperature-time changes during the cooling process were monitored using an infrared camera. The numerically calculated temperature values correlated well with the experimentally measured ones, while the maximum deviation of the measured and calculated temperatures was within 9%. Based on the numerical result analysis regarding circumferential and radial stresses after the completion of the welding process, it is concluded that both stresses are primarily tensile within the circular disk. Outside the disk, the circumferential stresses turn from tensile to compressive, while on the other hand the radial stresses disappear towards the ends of the plate.
The thick plate narrow gap welding of 25Cr2NiMo1V rotor steel is achieved by metal active gas arc welding, in which the weld gap was 18.04–19.9 mm. After welding, the weldment was heat treated at 580 ...°C (20 h). The impact and tensile properties in the as-welded and heat-treated were studied. The results show that after heat treatment, the coarse carbides in the center of the weld were transformed into fine granular carbides distributed along the grain boundaries, and the quantity of carbide precipitates in the weld near the fusion line was reduced. The tensile fracture mode changed from a ductile fracture to a combination of brittle and ductile fractures, and the tensile strength of the weld metal changed from 605 MPa to 543 MPa. After heat-treated, the radiation zone of the weld center changed from a brittle fracture to a combination of brittle and ductile fractures, and the impact energy changed from 141 J to 183 J; the characteristics of the brittle fracture in the radial zone of the fusion line were more obvious, and the impact energy changed from 113 J to 95 J. Therefore, after heat treatment, the toughness of the welded metal was improved, without reducing the strength and hardness of the welded metal to a large extent.
The paper presents the results of quality assessment of welded joints. The scope of the work was to investigate the non-destructive testing: visual testing (VT), penetration testing (PT) and ...radiological testing (RT). The study included also the survey breaking the macro- and microstructural test on the welded joint section. The research has shown that the use of the welding consumables in form of a wire 4Si1 to joint HARDOX 450® with Strenx 700MC® ensures the required ,,B” quality of welded joints in accordance with regulatory requirements. The analyzed joint was characterized by typical microstructure for native materials used.
The article is the result of research evaluating the quality of fillet welds used in the production of rear seat backrests for passenger cars and manufactured robotically by Cold Metal Transfer (CMT) ...robotic Metal Active Gas (MAG) welding. When robotizing the process, parameters such as the speed of the process itself, accuracy and quality of the welded joints are important. Dual-phase ferritic-martensitic steel HCX 590X was used for the experiment and four weld nodes were evaluated. The quality of welded joints was evaluated by visual and capillary methods. Based on the metallographic analysis, the weld depth of the weld root was evaluated. The measured values were subsequently processed by statistical method ANalysis Of Variance (ANOVA). The research confirmed that the final quality of the welds depends on the depth of the weld root weld into the Base Material (BM). This parameter has the greatest effect on the welds made and results in the entire product being taken out of service.
Abstract In this study, the parameters of Metal Inert Gas (MIG) and Metal Active Gas (MAG) were investigated of AISI 316L/ER 316L. A quaternary shielding gas mixture consisting of Argon (Ar), Helium ...(He), Carbon Dioxide (CO 2 ), and Nitrogen (N 2 ) was chosen. The Taguchi orthogonal array (OA-L9) methodology was employed to explore optimal welding settings, including arc current (120A, 160A, 200A), wire feed rate (3, 3.5, 4 m min −1 ), and shielding gas combination (G1, G2, G3). The findings highlighted the importance of shielding gas in influencing the ultimate tensile strength (UTS), elongation percentage (EL%), and material toughness of welding joints. Notably, the highest UTS (515.77 MPa), EL% (20.85%), and material toughness (133J) were achieved by the specific group gas combination shown as G1. It is recommended to configure welding parameters to an arc current of 160A, a wire feed rate of 4 m min −1 , and the G1 gas combination. Welded specimens using a G1 gas mixture showcased the best UTS and EL%. Additionally, it was found that the fusion zone (FZ) and heat-affected zone (HAZ) hardness are most profoundly influenced by the choice of gas combination (G2), resulting in the best hardness values of 253.79 HV and 239.68 HV, respectively. The optimal parameters for achieving the desired material hardness were precisely identified as (120A, 3 m min −1 , G2). These insights offer a pathway to enhance welding performance and, in turn, elevate the quality and efficiency of industrial applications.
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