•TIG–MAG hybrid arc welding can increase welding speed significantly.•High mechanical properties of hybrid arc weld were obtained.•The assistant TIG arc can stabilize the MAG welding current and arc ...voltage.•Stable hybridization is a key factor to stabilize the welding process.
A TIG–MAG hybrid arc welding process was proposed to achieve high speed welding. The influences of hybrid arc welding parameters on welding speed and weld appearance were studied through orthogonal experiment and the microstructures and mechanical properties of weld were tested and compared with that of the conventional MAG weld. The TIG–MAG hybrid arc welding speed could reach up to 3.5m/min for bead-on-plate welding of 2.5mm thick mild steel plate under the condition of high quality of weld appearance and 4.5m/min for butt welding of 2mm thick mild steel plate, respectively. The mechanical properties of hybrid arc weld were not lower than that of the conventional MAG weld. The assistant TIG arc could effectively stabilize the MAG welding current and MAG arc voltage in high speed TIG–MAG hybrid arc welding process. The stable hybridization obtained by balance between TIG and MAG welding current and proper wire-electrode distance was a key factor to stabilize the welding process.
As an effective welding method, rotating arc narrow gap MAG welding must ensure sidewall penetration, which is hard to realize when the groove is irregular in practical production. Therefore, it is ...significant to construct a weld form modeling for control weld penetration under the variable groove conditions. At first, the welding experiment system and the sensor system were set up. Arc sensing and visual sensing were applied to monitor the welding process, and effective algorithms were developed to extract the weld groove features. Three typical groove forms were considered and sufficient experiments were carried out to obtain enough experimental data. Furthermore, support vector machine is used to model the process. Welding current and the shortest distance between the arc center and the groove sidewall were used to predict the sidewall penetration. The verification results show that the model is effective under the condition that the height change of the groove is not more than 2 mm, the width change is not more than 2 mm, or the inclination angle of the bottom of the groove is not more than 10 degrees. The establishment of this model is very helpful to further control the formation of narrow gap welding.
The challenge to predict variations in penetration depth in one-sided fillet welds during robotized gas metal arc welding has been addressed by a pilot investigation of technical possibilities and ...limitations. The main cause for the variation in penetration depth is considered to be variation in joint gap size. Special attention has been paid in order to adopt the experimental conditions to conform to industrial welding conditions. The employed method uses in-process monitoring of joint gap size together with an empirical model relating penetration depth to gap size in order to predict this depth. The gap size estimates are based on image information from two cameras, one visual and one infrared. The results, that are evaluated off-line, confirm the development of a real-time method providing technical solutions that are industrially tractable. The results also pinpoint areas of further improvements towards increased robustness and reduced estimation uncertainties.
Lap welding is employed to join thin plate materials in car assemblies. The quality of welding depends on its conditions and seam tracking in the welding line. An arc sensor was employed by ...oscillating the welding torch in a thick weld. Since the welding torch was not oscillated in the welding of thin plate materials, the arc sensor could not be applied to lap welding. To trace the welding line, the weld pool in pulsed metal active gas (MAG) welding under the shielding gas of Ar 80% and CO2 20% was pictured using a CMOS camera. The weld pool was observed in the rear to the welding direction. The features of the weld pool were investigated to recognize the welding line. Since the arc affected the brightness of the weld pool, the timing of the shutter of the CMOS camera was synchronized with the current waveform to take clear weld pool images. The welding line was detected using an image processing method. In this paper, a banalization method and a pattern matching method was investigated. The pattern matching method is useful than the binarization method. A digital controller was designed to trace the welding line. The validity of the proposed method was verified by carrying out a tracking experiment.
Evaluating the welding joint quality in real time is difficult for chassis parts robotic gas-shielded welding. Series of metal active gas (MAG) joints were conducted in this paper to investigate the ...relationship between welding current, welding speed, energy input, and weld bead geometry. Bead width and bead reinforcement are obtained using a line-structured light measurement method, and the penetration depth of the bead is measured with the macroscopic metallurgical microscope. The ratio of penetration depth to the plate thickness and reinforcement is chosen as the evaluation criterion of the joint quality. Based on XGBoost algorithm, two data-driven models are proposed to recognize penetration status and predict the bead reinforcement. In the prediction results, the absolute error of the penetration coefficient is 0.079 at the maximum, and the average relative error is 11.06%. For the test result of reinforcement prediction model, the relative error is 20.5% on average. The test results show that the XGBoost-based models can be used for real-time prediction of welding quality.
A high-speed camera system has been used to observe the metal transfer with bead-on-plate welding. A stable pulsed streaming spray transfer was accompanied by arc jumping when the shielding gas of ...Ar+4%CO2+3%O2 was used, but the change of metal transfer mode had a tight relationship with the bell-shaped arc rather than critical current when a mixture of Ar+13%CO2+3%O2 was as shielding gas. With increasing CO2 concentration in the shielding gas, the bright arc area and arc length decreased due to the compression effect of carbon dioxide. Weld penetration and weld width increased slightly due to the higher arc force. The ferrite content in the weld metal increased slightly with increasing CO2 concentration in the shielding gas.
•Hybrid laser-MAG welding and laser welding were used to weld HG785D steel.•Different cooling rate led to difference of microstructure in both welded joints.•Grain size and microstructure types ...explain difference in mechanical properties.•Heat source melting efficiency of HLAW is larger compared to LBW.
Hybrid Laser-arc welding (HLAW) and laser beam welding (LBW) of HG785D steel were investigated by comparing microstructure, mechanical properties and heat source melting efficiency. Same microstructure of lath martensite (LM) was observed in fusion zone (FZ) of the two welded joints. However, coarser grain size and more random crystallographic orientations of FZ in HLAW joint were investigated via electron back-scatter diffraction (EBSD) analysis. M-A constituent and equiaxed ferrite (EF) were observed in finer-grain HAZ of HLAW joint, whereas fine martensite was obtained in LBW joint. More M-A constituent and granular bainite (GB) appeared in coarse-grain HAZ of HLAW joint. Higher heat input and lower cooling rate of HLAW compared to LBW resulted in presence of different microstructure. All the tensile specimen in both cases fractured at the base metal, while distinct difference in microhardness and low-temperature impact property was observed. Lower microhardness and higher impact energy of fusion zone were obtained in HLAW joint. Moreover, heat source melting efficiency of HLAW for 6-mm-thick HG785D steel plate could be improved by 26% compared to LBW.
•Microstructures of different weld areas were investigated using SEM.•Microhardness testing was performed throughout different weld regions.•Paris’s Law parameters were obtained for MAG S700MC welded ...joint.•Numerical simulations were validated through the experimental data.•Crack propagation in a rail example was evaluated by using cyclic loading.
Railway rails are subjected to complex dynamic loading, which promotes the fatigue crack propagation phenomenon. As newer demands arise for increasingly faster and more heavily burdened trains, the need for rails with improved mechanical properties increases as well. In this work, a high strength TMCP steel of S700MC grade aimed for rail production is evaluated regarding welding ability.
Steel joints were MAG welded and characterised regarding fatigue life. Fatigue tests were carried out using 0.1 stress ratio. Paris Law was assessed using Digital Image Correlation method. The weld seam and heat affected zone were characterised regarding microhardness variation throughout, and results were interpreted based on microstructural features.
The produced welds show different microstructure depending on the cooling rate from weld pass temperature. In the centre of the seam, weld root presents fine grain bainitic structure with HV0.1 around 336, while weld face shows coarse grain ferritic structure with HV0.1 around 307. Experimental data from fatigue tests were used to validate a numerical simulation; a difference below 7% was obtained. Experimental data were used to evaluate a case study regarding crack propagation in a railway rail. Numerical simulation showed that only 718,320 cycles are required to increase a crack with initial length 40 mm in 4 mm.
The results obtained from the joint experimental and numerical approach show that assessing the material properties and correlating them with the material microstructure is fundamental to develop applications for new materials, while simulation of the crack propagation phenomenon can be used to compare material performance.
Abstract MAG welding of 07MnMoVR steel was performed at the 2G and 3G positions, and weld formation, microstructure, residual stress, and tensile properties were compared. In this study, welds ...without defects were obtained at the 2G and 3G positions. The results showed that a larger distortion of the weld at the 3G position was present because of the higher heat input and that the perlage morphology was related to the introduction of the arc weaving process. In addition, the grain size of the filling pass was coarser than that of the cap pass because of the repeated heating process, and the grain sizes of the filling and cap passes increased by approximately 33% for the weld at the 3G position compared with that at the 2G position. In this case, the weld at the 3G position showed a larger residual stress and lower yield and tensile strengths, and the elongation rates and microhardness of the weld at the 3G position were lower than were those of the weld at the 2G position, regardless of the root pass, filling pass, or cap pass.
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