Showing papers on "Arc welding published in 2006"

Evaluation of cold metal transfer (CMT) process for welding aluminium alloy

Abstract: Cold metal transfer (CMT) is an automated welding process based on dip transfer welding, characterised by controlled material deposition during the short circuit of the wire electrode to the workpiece. Preliminary results are presented examining the suitability of this process for welding aluminium alloy. Trials show that in comparison with pulsed metal inert gas (MIG) welding, CMT exhibits a higher electrode melting coefficient. By adjusting the short circuit duration penetration can be controlled with only a small change in electrode deposition. Furthermore, by mixing pulsed MIG welding with CMT welding the working envelope of the process is greatly extended allowing thicker material sections to be welded with improved weld bead aesthetics.

Experimental study on welding characteristics of CO2 laser TIG hybrid welding process

Abstract: The experiments of CO2 laser TIG paraxial hybrid welding with 4 mm thick AISI 321 stainless steel sheet have been performed. The arc images and welding characteristics have been investigated with different energy ratios between laser and arc. The experimental results indicate that the hybrid welding is similar to laser welding and has also two welding mechanisms: deep penetration welding and heat conduction welding. Because of the effect of keyhole induced by laser, the arc root can be stabilised and compressed, and the current density and the penetration depth are all increased significantly, which show the characteristics of deep penetration welding. However, when the current is increased to a critical value, the laser induced keyhole disappears and the arc expands obviously, which decreases the penetration depth, so that the welding mechanism has been changed from deep penetration welding to heat conduction welding. Furthermore, the effects of distance between laser beam and electrode, pulsed l...

Design, Construction, and Characterization of a Novel Robotic Welding Fume Generator and Inhalation Exposure System for Laboratory Animals

Abstract: Respiratory effects observed in welders have included lung function changes, metal fume fever, bronchitis, and a possible increase in the incidence of lung cancer. Many questions remain unanswered regarding the causality and possible underlying mechanisms associated with the potential toxic effects of welding fume inhalation. The objective of the present study was to construct a completely automated, computer-controlled welding fume generation and inhalation exposure system to simulate real workplace exposures. The system comprised a programmable six-axis robotic welding arm, a water-cooled arc welding torch, and a wire feeder that supplied the wire to the torch at a programmed rate. For the initial studies, gas metal arc welding was performed using a stainless steel electrode. A flexible trunk was attached to the robotic arm of the welder and was used to collect and transport fume from the vicinity of the arc to the animal exposure chamber. Undiluted fume concentrations consistently ranged from 90–150 mg...

Multimaterial car body design: challenge for welding and joining

Abstract: High safety and low weight are requested for modern automobiles. Both demands are met best by tailored application of different materials. Multimaterial car body design is a challenge for joining and welding.

Mechanism and possible solution for transverse solidification cracking in laser welding of high strength aluminium alloys

Abstract: In laser and hybrid laser/arc welding of high strength aluminium alloys, a large number of transverse cracks were found in the weld fusion zone. The cracking behaviour was evaluated experimentally and scanning electron microscopy images of crack surfaces confirmed that the cracks occurred when the weld fusion zone was in the semi-solid state. Thermal histories in the workpiece under representative welding conditions were measured and constitutive modelling of thermo-mechanical behaviour in the weld was performed. It was found that the cracking is related to the elongated temperature distribution in the welding direction, which induces a transverse tensile strain in the weld fusion zone during the cooling phase. One of the possible solutions to the cracking problem is to use an additional heat source to alter the temperature distribution and thus to reduce the cracking tendency. The effect of welding with an appropriately placed secondary heat source was verified by experimental tests.

New CMT arc welding process – welding of steel to aluminium dissimilar metals and welding of super-thin aluminium sheets

Abstract: (2006). New CMT arc welding process – welding of steel to aluminium dissimilar metals and welding of super-thin aluminium sheets. Welding International: Vol. 20, No. 6, pp. 440-445.

Simulation of weld pool dynamics in the stationary pulsed gas metal arc welding process and final weld shape

Abstract: The pulsed gas metal arc welding (GMAW-P) process was modeled numerically using a code based on the volume of fluid (VOF) technique, chosen primarily for its ability to accurately calculate the shape and motion of free fluid surfaces, which is needed for subsequent study of welding phenomena such as bead hump formation, incomplete fusion in narrow groove welds, and weld toe geometry. According to the mathematical models with parameters obtained from analysis of high-speed video images and data acquisition (DAQ) system, GMAW-P was simulated and then validated by comparison of measured and predicted weld deposit geometry, transient radius, and temperature history. Based on the weld simulation parameters, a parametric study of weld simulation was performed to demonstrate and understand the effectiveness of individual simulation parameters on heat and fluid flow in the molten weld pool and the final configuration of stationary welds. Constricted current density drastically increased the weld penetration and decreased the weld radius, primarily by reducing the convexity of the weld deposit and promoting heat transfer to the bottom of the weld pool. Conversely, decreased arc force and increased arc pressure radius both decreased the weld penetration for the same reason. Based on the understanding of weld pool spreading, GMAW-P was simulated with an additional heat source to demonstrate the utility of the simulation in predicting final weld shape in complex welding situations.

Study on Welder Training by Means of Haptic Guidance and Virtual Reality for Arc Welding

Abstract: Gaining and improving welding skill is important for welders. The advent of virtual reality (VR) technology provides a new kind of medium for skill training. In this paper, a haptic arc welding training method is proposed based on VR and haptic guidance. The training method is designed to emulate the presence of a human tutor which feedbacks forces to a welder to show the proper force/position relation within pre-defined trajectories for attaining hand-mind-eye coordination skills in a virtual environment. Three basic welding operation skills, namely maintaining the proper arc length, maintaining the proper electrode angle, and maintaining the proper traverse speed are selected for training. The Phantom haptic device is used as the haptic interface. The haptic guidance is realized with proportional-plus-derivative (PD) feedback control of the error between the current and ideal trajectory. The proposed method is cost-less, effective, and environment-friend for the training of both novice and skilled welders.

Real-time arc welding defect detection technique by means of plasma spectrum optical analysis

Abstract: An optimized technique for real-time spectral analysis of thermal plasmas, with application in the monitoring and defect detection of industrial welding processes, particularly arc-welding, is presented in this paper. The calculation of the plasma electronic temperature by means of a sub-pixel algorithm permits on-line quality assessment of the welds, allowing the detection of common defects to be found in the welding seam, such as oxidation due to insufficient shielding gas flux or lack of penetration caused by current fluctuations of the welding power source. The proposed technique has been successfully checked in a real-time arc-welding monitoring system, and experimental results of stainless-steel welds are also reported.

Artificial neural network modeling for evaluating of epitaxial growth of Ti6Al4V weldment

Abstract: The effect of epitaxial growth on microstructure of Ti–6Al–4V alloy weldment was examined by artificial neural networks (ANNs). The microplasma arc welding (MPAW) procedure was performed at different currents, welding speeds and flow rates of shielding and plasma gas. Microstructural characterizations were studied by optical and scanning electron microscopy (SEM). Finally, an artificial neural network was developed to predict grain size of fusion zone (FZ) at different currents and welding speeds. The results showed that a coarse primary β phase develops in the fusion zone as a result of epitaxial nucleation on coarsened β grains near the heat affected zone (NHAZ) which grow competitively into the molten weld pool. Based on ANNs analyses, a map of current and welding speed for α → β transformation in the HAZ can be constructed. For a lower energy input, grain growth of β phase in the HAZ could be restricted by α phase. The presence of small quantities of this phase at high peak temperatures in the weld cycle is sufficient to prevent the grain growth of β phase in HAZ and FZ.

Effects of current on droplet generation and arc plasma in gas metal arc welding

Abstract: In gas metal arc welding (GMAW), a technology using pulsed currents has been employed to achieve the one-droplet-per-pulse (ODPP) metal transfer mode with the advantages of low average currents, a stable and controllable droplet generation, and reduced spatter. In this paper, a comprehensive model was developed to study the effects of different current profiles on the droplet formation, plasma generation, metal transfer, and weld pool dynamics in GMAW. Five types of welding currents were studied, including two constant currents and three wave form currents. In each type, the transient temperature and velocity distributions of the arc plasma and the molten metal, and the shapes of the droplet and the weld pool were calculated. The results showed that a higher current generates smaller droplets, higher droplet frequency, and higher electromagnetic force that becomes the dominant factor detaching the droplet from the electrode tip. The model has demonstrated that a stable ODPP metal transfer mode can be achieved by choosing a current with proper wave form for given welding conditions.

An understanding of HSLA-65 plate steels

Abstract: HSLA-65 plate steels can be produced using one of five plate manufacturing techniques: normalizing, controlled rolling (CR), controlled rolling followed by accelerated cooling (CR-AC), direct quenching and tempering (DQT), or conventional quenching and tempering (QT (b) eliminate or substantially reduce the need for preheating during welding; (c) resist susceptibility to hydrogen-assisted cracking (HAC) in the weld heat affected zone (HAZ) when fusion (arc) welded using low heat-input conditions; and (d) depending on section thickness, facilitate high heat-input welding (about 2 kJ/mm) without significant loss of strength or toughness in the HAZ. However, application of this plate manufacturing process and of these controls produces significant differences in the metallurgical structure and range of mechanical properties of the HSLA-65 plate steels both among themselves and versus conventional higher strength steel (HSS) plates. For example, among the HSLA-65 plate steels, those produced by Q&T exhibit minimal variability in mechanical properties, especially in thicker plates. Besides variability in mechanical properties depending on plate thickness, the CR and CR-AC plate steels exhibit a relatively higher yield strength to ultimate tensile strength (YS/UTS) ratio than do DQT and Q&T steels. Such differences in processing and properties of HSLA-65 plate steels could potentially affect the selection and control of various secondary fabrication practices, including arc welding. Consequently, fabricators must exercise extreme caution when transferring allowable limits of certified secondary fabrication practices from one type of HSLA-65 plate steel to another, even for the same plate thickness.

Effect of shielding gas mixture on gas metal arc welding of HSLA steel using solid and flux-cored wires

Abstract: In this work, gas metal arc welding of high strength-low alloy (HSLA) steel with solid- and flux-cored arc welding wires using different shielding gas compositions was performed. The composition of filler wire and shielding gas in gas metal arc welds of HSLA steel determines the inclusion characteristics, microstructure and mechanical properties. Thus, acceptable weld metal properties in HSLA steel using gas metal arc welding (GMAW) process could be achieved with the proper combination of filler wire and shielding gas composition.

Autonomous Acquisition of Seam Coordinates for Arc Welding Robot Based on Visual Servoing

Abstract: Autonomous acquisition of seam coordinates is a key technology for developing advanced welding robot. This paper describes a position-based visual servo system for robotic seam tracking, which is able to autonomously acquire the seam coordinates of the planar butt joint in the robot base frame and plan the optimal camera angle before welding. A six-axis industrial robot is used in this system, which has an interface for communicating with the master computer. The developed visual sensor device is briefly presented that allows the charge-coupled device (CCD) cameras to rotate about the torch. A set of robust image processing algorithms are proposed so that no special requirements of light source are needed in this system. The feedback errors of this servo system are defined according to the characteristics of the seam image, and the robust tracking controller is developed. Both the image processing program and tracking control program run on the master computer. The experimental results on straight line seam and curve seam show that the accuracy of the seam coordinates acquired with this method is more adequate for high quality welding process.

Effects of welding parameters on melting energy of CO2 laser–GMA hybrid welding

Abstract: A series of CO2 laser–gas metal arc (GMA) hybrid welding experiments were carried out on the mild steel workpiece to investigate the effects of the welding parameters, such as laser power, arc current and the distance between laser and arc D LA, on the melting energy. A dimensionless parameter psi was introduced to indicate the change in the melting energy of hybrid welding. The results showed that with different welding parameters, the melting energy of hybrid welding was changed by the two heat sources (laser and arc) interaction. With an optimal combination welding parameters, psi can be increased up to 23%. Finally, the role of the two different mechanisms in the heat sources interaction was quantitatively discussed in terms of psi. It can be concluded that when D LA<4 mm, the interaction between the laser induced plasma and the arc plasma dominates the heat sources interaction, therefore the changes of melting energy, whereas the heat sources interaction is only dominated by the preheating me...

Incipient melting in partially melted zone during arc welding of AZ91D magnesium alloy

Abstract: Welding and simulation experiments were conducted to study the melting behaviour in the partially melted zone during welding of AZ91D magnesium alloy. A relatively sharp transition from partially melted zone to the zone of no melting was observed in the welded samples. This has been explained by the observations of a fast α + β eutectic melting rate and a low rate of dissolution of β-phase before melting using simulation experiments. Examination of the heating rates during welding and simulation experiments, together with the metallography observation, suggested that there is practically no “critical heating rate” and partial melting may always take place during welding.

The effect of friction stir processing on 5083-H321/5356 Al arc welds: Microstructural and mechanical analysis

Abstract: Friction stir processing (FSP) is used locally to modify the microstructure and thus mechanical properties of 5083-H321/5356 aluminum gas metal arc welds (GMAWs). Four specimen approaches were examined: as-arc welded, weld toe FSP (with arc weld on either the advancing or the retreating side of tool), and weld crown FSP. Microstructures within the fine-grained FSP region contained smaller constituent particles. Mg2Si and Al6(Fe,Mn), than those particles found in the arc weld nugget, heat-affected zone (HAZ), and base-metal (BM) locations. The FSP improved the monotonic tensile strength, yield strength, and elongation of 5083-H321/5356 Al arc welds by 6 to 9 pct, 7 to 13 pct, and 46 to 80 pct, respectively. The addition of FSP produced a 30 pct increase in the load necessary to reach 107 cycles during four-point bending fatigue. An analysis of strengthening mechanisms determined that solid-solution, grain-size, and precipitation strengthening made contributions to the calculated yield strength of the BM, are weld nugget, and FSP regions. In addition, the strength mechanism analysis demonstrated that FSP increased the amount of grain-size strengthening and precipitate strengthening by nearly 110 MPa, when compared to the arc weld nugget.

Simulative training device for manual arc welding operation

Abstract: The related training simulator for welding operation comprises: a simulating welding gun with a handle (8) connected to a step motor (9); a controller; and a simulated test piece. Wherein, arranging an active rolling wheel (4) on motor output shaft, a rolling base (6) with a driven rolling wheel on the motor base (7), and a welding rod (1) between (4) and (5). This invention can accelerate training with less consumption.

Magnetic stirring during laser welding of aluminum

Abstract: The use of magnetic fields to influence melt flow is a well-established method, e.g., in foundry technology. For arc welding processes (especially tungsten inert gas welding), a process called magnetic stirring was first proposed, patented, and investigated in the 1970s. The central aim was to improve (by the help of an alternating magnetic field coaxial with the arc axis) weld quality especially in aluminum by the combined effects of arc current and magnetic field. It was established that such fields are indeed capable of influencing weld bead appearance, of increasing the degree of dilution, of decreasing pore formation and of producing a finer grain structure. However, the process never gained wide industrial acceptance. In the late 1990s, some efforts have been taken to apply constant magnetic fields to laser welding processes, aiming at influencing weld geometry, reducing porosity, and potentially increasing welding speed. However, neither have any detailed statements been made on possibilities to in...

Reduction of nanoparticle exposure to welding aerosols by modification of the ventilation system in a workplace

Abstract: Nanometer particle size distributions were measured in booths with two different ventilation patterns in an occupational environment with welding operations underway. The measurements were used to illustrate the impact of change of ventilation methods (existing — with ventilation ducts located at the top, modified — with ventilation ducts located below the weld bench) on the aerosol size distributions at different locations: close to the weld, in the vicinity of the welder’s face, and in the exhaust duct. Particle number concentrations measured in the vicinity of the welder’s face (mask) during a horizontal standard arc welding process in a booth with ventilation at the top was in the range of 7.78×105 particles cm−3 with a geometric mean size of 181 nm and geometric standard deviation of 1.8. This reduced to 1.48×104 particles cm−3 in the vicinity of the welder’s face with the modified ventilation system. The clearance of the welding aerosol was also faster in the modified booth (6 min compared to 11 min in a conventional booth). Particles were collected in the booth for the various test conditions, and analyzed to determine their composition and morphology. The particles were composed of hazardous heavy metals such as manganese, chromium and nickel, and had varying morphologies.

A New Laser-Arc Hybrid Welding Technique Based on Energy Conservation

Abstract: Aiming at the problem of energy loss in the process of welding at present, a new hybrid welding technique that low powered laser (about 400 W) combined with arc was put forward. Taking magnesium alloys as objects, it was found that the new technique had many advantages such as high welding speed, deep penetration and high quality welded joint comparing with that welded by laser or arc alone. Besides, the mechanical properties of the welded joint were improved remarkably. Comparing with high powered laser (about 2000 W)-arc hybrid welding, the laser used in the new technique was about 400 W, which was about 1 /5 of that of the former, so the welding costs could be reduced markedly, while a great deal of energy was saved. In the research of arc behaviors, a new hybrid mechanism was proposed, in which the ability of arc to discharge was improved mainly because the laser pulse acted on the negative arc (electrode was positive and the specimen was negative) during the hybrid welding.

Overlap welding of magnesium AZ31B sheets using laser-arc hybrid process

Abstract: This paper presents the results of recent investigations on the overlap weldability of magnesium alloy AZ31B sheets by laser-arc hybrid welding process The effects of key welding parameters such as welding speed, defocusing distance, and laser-to-arc distance on overlap weldability of magnesium alloys sheets were analyzed, as well as the microstructure and properties of hybrid lap-welded joint The results showed that sound overlap-welded joints of magnesium alloy AZ31B sheets without defects can be obtained Among the welding parameters, defocusing distance and laser-to-arc distance were key factors to affect the penetration depth and bead shape It also found that the cross-section of hybrid overlap-welded joint appears a “thumb pin” shape due to the characteristics of laser-arc hybrid welding Hybrid overlap-welded joints can be divided into two parts: one was the zone of laser acting alone, while the other was the zone of laser and arc cooperation Besides, it was concluded that the tensile shear strength of AZ31B overlap-welded by laser-arc hybrid welding was 80% comparable to those of base metal, and the corrosion resistance of weld bead was equivalent to that of base metal in 5 mol% NaCl solution

Fast algorithm for spectral processing with application to on-line welding quality assurance

Abstract: A new technique is presented in this paper for the analysis of welding process emission spectra to accurately estimate in real-time the plasma electronic temperature. The estimation of the electronic temperature of the plasma, through the analysis of the emission lines from multiple atomic species, may be used to monitor possible perturbations during the welding process. Unlike traditional techniques, which usually involve peak fitting to Voigt functions using the Levenberg-Marquardt recursive method, sub-pixel algorithms are used to more accurately estimate the central wavelength of the peaks. Three different sub-pixel algorithms will be analysed and compared, and it will be shown that the LPO (linear phase operator) sub-pixel algorithm is a better solution within the proposed system. Experimental tests during TIG-welding using a fibre optic to capture the arc light, together with a low cost CCD-based spectrometer, show that some typical defects associated with perturbations in the electron temperature can be easily detected and identified with this technique. A typical processing time for multiple peak analysis is less than 20 ms running on a conventional PC.

Physical Phenomena and Porosity Prevention Mechanism in Laser-Arc Hybrid Welding

Abstract: Hybrid welding of stainless steels or aluminium alloys was performed with the heat sources of YAG laser and TIG, or YAG laser and MIG, respectively. The effects of welding conditions and melt flows on penetration depth, geometry and porosity formation were investigated with the X-ray transmission real-time observation method. Melt flows on penetration depth and geometry were consequently confirmed. Concerning porosity suppression, in TIG-YAG hybrid welding of stainless steel, no formation of bubbles was attributed to the absence of pores. On the other hand, disappearance of bubbles from the concave molten pool surface due to the arc pressure played an important role in reducing porosity in YAG-MIG hybrid welding of aluminium alloys at high arc currents.