Showing papers on "Arc welding published in 2003"

Pulmonary effects of welding fumes: Review of worker and experimental animal studies†

Abstract: Background Approximately one million workers worldwide perform welding as part of their work duties. Electric arc welding processes produce metal fumes and gases which may be harmful to exposed workers. Methods This review summarizes human and animals studies which have examined the effect of welding fume exposure on respiratory health. An extensive search of the scientific and occupational health literature was performed, acquiring published articles which examined the effects of welding on all aspects of worker and laboratory animal health. The databases accessed included PubMed, Ovid, NIOSHTIC, and TOXNET. Results Pulmonary effects observed in full-time welders have included metal fume fever, airway irritation, lung function changes, susceptibility to pulmonary infection, and a possible increase in the incidence of lung cancer. Although limited in most cases, animal studies have tended to support the findings from epidemiologic studies. Conclusions Despite the numerous studies on welding fumes, incomplete information still exists regarding the causality and possible underlying mechanisms associated with welding fume inhalation and pulmonary disease. The use of animal models and the ability to control the welding fume exposure in toxicology studies could be utilized in an attempt to develop a better understanding of how welding fumes affect pulmonary health. Am. J. Ind. Med. 43:350–360, 2003. Published 2003 Wiley-Liss, Inc.

Modeling of heat transfer and fluid flow during gas tungsten arc spot welding of low carbon steel

Abstract: The evolution of temperature and velocity fields during gas tungsten arc spot welding of AISI 1005 steel was studied using a transient numerical model. The calculated geometry of the weld fusion zone and heat affected zone and the weld thermal cycles were in good agreement with the corresponding experimental results. Dimensional analysis was used to understand the importance of heat transfer by conduction and convection at various stages of the evolution of the weld pool and the role of various driving forces for convection in the liquid pool. The calculated cooling rates are found to be almost independent of position between the 1073 and 773 K (800 and 500 °C) temperature range, but vary significantly at the onset of solidification at different portions of the weld pool. During solidification, the mushy zone grew significantly with time until the pure liquid region vanished. The solidification rate of the mushy zone/solid interface was shown to increase while the temperature gradient in the mushy zone at...

Modeling of temperature field and solidified surface profile during gas–metal arc fillet welding

Abstract: The temperature profiles, weld pool shape and size, and the nature of the solidified weld pool reinforcement surface during gas–metal arc (GMA) welding of fillet joints were studied using a three-dimensional numerical heat transfer model. The model solves the energy conservation equation using a boundary fitted coordinate system. The weld pool surface profile was calculated by minimizing the total surface energy. Apart from the direct transport of heat from the welding arc, additional heat from the metal droplets was modeled considering a volumetric heat source. The calculated shape and size of the fusion zone, finger penetration characteristic of the GMA welds, and the solidified free surface profile were in fair agreement with the experimental results for various welding conditions. In particular, the computed values of important geometric parameters of fillet welds, i.e., the leg length, the penetration depth, and the actual throat, agreed well with those measured experimentally for various heat inputs...

Penetration and Defect Formation in High-Current Arc Welding At high currents, the weld pool turns into a thin liquid film, causing humping, undercutting, and fingerlike penetration

Abstract: An explanation for penetra- tion and defect generation in the weld pool at high currents is proposed. In this regime, the arc pressure pushes the molten metal to the rear of the weld pool, creating a thin layer of liquid metal under the arc. Premature solidification of this thin layer initiates humping, split bead, parallel humping, tunnel porosity, and un- dercutting. The thin nature of the liquid layer is the cause of increased penetration at high currents. We propose a simple model to predict the onset and type of humping defect.

Penetration and defect formation in high-current arc welding

Abstract: The work performed during the three previous years can be roughly divided into two main categories: (1) development of advanced modeling techniques; and (2) modeling of arc welding process. The work in the first category comprised the development of the Order of Magnitude Scaling (OMS) technique, which is complementary to numerical modeling techniques such as finite elements, but it provides approximate formulas instead of just numerical results. Borrowing concepts from OMS, another modeling technique based on empirical data was also developed. During this stage special software was also developed. The second category comprised the application of OMS to the three main subsystems of arc welding: the weld pool, the arc, and the electrode. For each of these subsystems they found scaling laws and regimes. With this knowledge, they analyzed the generation of weld pool defects during high current arc welding, proposed a mechanistic description of the process, and possible solutions.

Coded welding consumable

Abstract: Information pertaining to characteristics of consumables such as metal welding electrode wire and shielding gas and which characteristics are useful in connection with adjusting welding parameters in an arc welding process and/or selecting between operating modes in a welding system are encoded on welding wire and/or on other memory components such as bar code labels and tags, RFID cards and tags, IC cards, and Touch Memory buttons, and the memory device is scanned prior to and/or at the point of use of the welding wire or shielding gas for enabling tracking of product distribution, manual and/or automatic selection of an operating mode for the welding system, manual and/or automatic adjustment of welding parameters in a given operating mode, consumables inventory, and the like.

Electric arc welding system

Abstract: An electric arc welding system for creating a first AC welding arc with a first current waveform between a first electrode and a workpiece by a first power supply and a second AC welding arc with a second current waveform between a second electrode and a workpiece by a second power supply as the first and second electrodes are moved in unison along a welding path, where the first and second power supply each comprising a high speed switching inverter creating its waveform by a number of current pulses occurring at a frequency of at least 18 kHz with the magnitude of each current pulse controlled by a wave shaper and the polarity of the waveforms is controlled by a signal The first AC waveform has a positive portion substantially different in energy than its negative portion and/or has either a different shape and/or a synthesized sinusoidal portion

Calculation of three-dimensional electromagnetic force field during arc welding

Abstract: Electromagnetic force is an important driving force for convection in the weld pool during arc welding. Accurate calculation of the electromagnetic force field requires complex numerical calculations of three-dimensional current density and magnetic flux fields. Several simplifying assumptions have been suggested to avoid the complex calculations. The resulting analytical expressions for the electromagnetic force field have been widely used without any critical evaluation of their intrinsic merit, since accurate numerical calculations were difficult in the past because of lack of fast computers. A numerical model has been developed to accurately calculate the current density and magnetic flux fields and the resulting electromagnetic force field in three dimensions in the entire weldment. The model can take into account any current distribution on the work piece surface and evaluate the effects of different arc locations and work piece geometry on the electromagnetic force field. Contributions of the electrode current, arc plasma, and current distribution inside the three-dimensional work piece to the magnetic field and the electromagnetic force field are determined. The electromagnetic force field computed from the model is compared with those obtained from the commonly used simplified expressions of electromagnetic force to examine the accuracy of the commonly used simplifying assumptions. The accuracy of the computed electromagnetic force field can be significantly improved by using the proposed numerical model.

Flaws in friction stir welds

Abstract: One of the major drivers for using friction stir welding for aluminium fabrication is the low incidence of weld flaws compared to that produced by conventional arc welding. However, the process does have its own characteristic flaws. A number of different process variables affect the quality of a joint produced by friction stir welding: tool design, tool rotation and travel speeds, tool heel plunge depth and tilt angle, welding gap, thickness mismatch and plate thickness variation. Successful, reproducible welds may be produced by operating within process “windows”. However, problems may arise when the welding conditions deviate from the standard operating window. In such circumstances, flaws may be generated. In the current work, a number of flaws encountered in friction stir welds, in particular voids, joint line remnants and root flaws were generated in an Al-Cu-Mn-Si-Mg alloy by using welding parameters outside of the established tolerance box for producing flaw-free welds. The welds were characterised using X-ray and ultrasonic non-destructive testing techniques and by metallographic sectioning. The causes of such features are described and recommendations are made to prevent their occurrence.

Control method and system for metal arc welding

Abstract: A method of controlling an arc welding system during a welding process is disclosed. The welding process has a plurality of welding cycles in which a consumable electrode (14) is advanced towards a workpiece (16). The method includes dynamically regulating a rate of advancement and instantaneous melt rate of the electrode during each welding cycle in response to predetermined events occurring during the welding process. The melt rate may be coordinated with the rate of advancement of the electrode to provide a wide range of stable deposition rates with a shielding gas such as CO2. An arc welding system for carrying out the method is also disclosed.

Luminescence sensing system for welding

Abstract: A method and apparatus can adaptively control a pulsed power arc welding process. A trainable system can recognize an empirical transfer mode from a signal emitted during an arc welding pulse and determine a pulsed power parameter set to produce a modified transfer mode in a subsequent pulse, by controlling a power source the parameter set.

Robotic Welding Systems with Vision-Sensing and Self-learning Neuron Control of Arc Welding Dynamic Process

Abstract: This paper addresses the vision sensing and neuron control techniques for real-time sensing and control of weld pool dynamics during robotic arc welding. Current teaching playback welding robots are not provided with this real-time function for sensing and control of the welding process. In our research, using composite filtering technology, a computer vision sensing system was established and clear weld pool images were captured during robotic-pulsed Gas Tungsten Arc Welding (GTAW). A corresponding image processing algorithm has been developed to pick up characteristic parameters of the weld pool in real-time. Furthermore, an ANN model of the weld pool dynamic process of robotic-pulsed GTAW was developed. Based on neuron self-learning PSD controller design, the real-time control of weld pool dynamics during the pulsed GTAW process has been realized in robotic systems.

Workplace Exposure to Submicron Particle Mass and Number Concentrations From Manual Arc Welding of Carbon Steel

Abstract: Particle emissions from manual shielded metal arc welding of carbon steel were sampled in a typical industrial maintenance and metal fabrication workplace environment. Particle number measurements over the size range from 14 nm to 10 µm using a scanning mobility particle sizer and an optical particle counter showed that welding produced an approximately lognormal particle mode with a 120 nm count median and a geometric standard deviation of 2.07. This study produced welding particle number concentrations on the order of 2×105/cm3 in the building air 8.5 m away from the welding. Workplace exposure samples were below the current 8-hour American Conference of Governmental Industrial Hygienists mass concentration threshold limit value of 5 mg/m3. Submicron particles comprised 80% of the total aerosol mass collected by a cascade impactor during welding. The concentration of larger particles was indistinguishable from indoor background. Microscopy showed that the welding emissions are dominated by clusters form...

Interaction of both plasmas in CO 2 laser-MAG hybrid welding of carbon steel

Abstract: Researches and developments of laser and arc hybrid welding has been curried out since in 1978. Especially, CO 2 laser and TIG hybrid welding has been studied for increasing the penetration depth and welding speed. Recently laser and MIG/MAG/Plasma hybrid welding processes have been developed and applied to industries. It was recognized as a new welding process that promote the flexibility of the process for increasing the penetration depth, welding speed and allowable joint gap and improving the quality of the welds. In the present work, CO 2 Laser-MAG hybrid welding of carbon steel (SM490) was investigated to make clear the phenomenon and characteristics of hybrid welding process comparing with laser welding and MAG process. The effects of many process parameters such as welding current, arc voltage, welding speed, defocusing distance, laser-to-arc distance on penetration depth, bead shape, spatter, arc stability and plasma formation were investigated in the present work. Especially, the interaction of laser plasma and MAG arc plasma was considered by changing the laser to arc distance (=D LA ).

Near real time arc welding monitor

Abstract: An arc welding monitor designed to aid in the instruction of electric arc welding, provide data that can be used for inspection and quality assurance of individual welds, and provide an archive record of the arc welding process for future reference and analysis. A sensor is used to unobtrusively measure the welding arc parameters. The measurements are transmitted in real-time from the welding station to an instructor/supervisor workstation via a radio frequency data link. The received data is graphically displayed in near-real-time on the instructor/supervisor workstation computer screen. The data can be analyzed by standard statistical analysis tools to qualitatively grade the weld, be stored on computer disk storage media for later retrieval and analysis, or printed in a graphic display. Interpretation of the graphical display and statistical analysis is used to critique and instruct welder operator technique or to indicate process flaws that warrant further inspection of suspected welds.

Prediction and Optimisation of Weld Bead Geometry of Plasma Transferred Arc Hardfaced Valve Seat Rings

Abstract: Automatic weld hardfacing is being employed increasingly in process and power industries. Plasma transferred arc welding (PTAW) has become a natural choice for automatic hardfacing due to its reliability, better process control, ease of use, low dilution and high volume production. Increasing the use of PTAW in its automatic mode, will increase dependence on the use of equations to predict the dimensions of the weld bead. The development of such mathematical equations using a five factor, five level factorial technique to predict the geometry of the weld in the deposition of Stellite 6 (Co-Cr-A) alloy onto carbon steel valve seat rings (ASTM A105) is presented. The developed models have been checked for their adequacy and significance by the F test and t test respectively. Main and interaction effects of the control factors on dilution and bead geometry are presented in a graphical form that aids rapid selection of the process parameters to achieve the desired quality of overlay. The results obtai...

Method of repairing a stationary shroud of a gas turbine engine using plasma transferred arc welding

Abstract: A stationary shroud of a gas turbine engine made of a base metal is repaired by removing any damaged material from a flow-path region of the stationary shroud to leave an initially exposed base-metal flow-path surface; and applying a base-metal restoration overlying the initially exposed flow-path surface. The base-metal restoration is applied by furnishing a source of a structural material that is compatible with the base metal, and depositing the source of the structural material overlying the initially exposed base-metal flow-path surface of the stationary shroud by plasma transferred arc welding to form a repaired base-metal flow-path surface. An environmentally resistant rub coating may be applied overlying the base-metal restoration.

Steel wire for carbon dioxide shielded arc welding and welding process using the same

Abstract: A steel wire for use in the straight polarity carbon dioxide shielded arc welding, which comprises 0.003 to 0.20 mass % of C, 0.05 to 2.5 mass % of Si, 0.25 to 3.5 mass % of Mn, 0.015 to 0.100 mass % of REM (rare earth metals), 0.001 to 0.05 mass % of P, 0.001 to 0.05 mass % of S, and the balanced amount of Fe and inevitable impurities; the steel wire which further comprises 0.0100 mass % or less of O; the steel wire which still further comprises one or more of 0.02 to 0.50 mass % of Ti, 0.02 to 0.50 mass % of Zr and 0.02 to 3.00 mass % of Al; the steel wire which still further comprises 0.0001 to 0.0150 mass % of K; the steel wire which still further comprises 3.0 mass % or less of Cr, 3.0 mass % or less of Ni, 1.5 mass % or lass of Mo, 3.0 mass % or less of Cu, 0.015 mass % or less of B, 0.20 mass % or less of Mg, 0.5 mass % or less of Nb, 0.5 mass % or less of V, 0.020 mass % or less of N; and a welding process which uses one of the above steel wires. The welding process allows the spray transfer of a molten droplet and thus allows the reduction of sputtering and also the formation of a weld bead of an excellent shape, in the carbon dioxide shielded arc welding using a shield gas containing CO2 gas as its main component.

Improved Ferrite Number prediction model that accounts for cooling rate effects: Part 2: Model results

Abstract: A new Ferrite Number prediction model, ORFN (Oak Ridge Ferrite Number), was developed in Part 1 of this study (Welding Journal, January 2003) and, in this contribution, the model predictions are evaluated and compared with predictions of other models. The ORFN quantitatively takes account of cooling rate effects on the Ferrite Number for the first time. It is shown the new ORFN model presents very good agreement with experimental data and is significantly more accurate than existing constitution diagrams or recently developed composition-only neural network models. The model is equally valid for austenitic stainless steels and duplex stainless steels. Furthermore, the model is applicable to both conventional arc welding conditions as well as high cooling rate conditions prevalent during high energy beam welding, such as laser beam welding, and high-speed arc welding.

Yag laser induced arc filler wire composite welding method and welding equipment

Abstract: A combined welding method with a filler wire using both a YAG laser and an electric arc, and a combined welding device with a filler wire using both a YAG laser and an electric arc. The welding is performed by directing a laser focus of a YAG laser on base materials and for welding in the vicinity of the focus by a filler wire, connecting a power source for applying a voltage to the filler wire between the filler wire and the base materials for welding, irradiating a YAG laser on the base materials for welding in the connecting condition, whereby an arc is induced to the filler wire by a plume (plasma-activated gas and the metal vapor), and holding the plume generated by YAG laser inside and outside of a keyhole.

Latest MIG, TIG arc-YAG laser hybrid welding systems for various welding products

Abstract: Laser welding is capable of high-efficiency low-strain welding, and so its applications are started to various products. We have also put the high-power YAG laser of up to 10 kW to practical welding use for various products. On the other hand the weakest point of this laser welding is considered to be strict in the welding gap aiming allowance. In order to solve this problem, we have developed hybrid welding of TIG, MIG arc and YAG laser, taking the most advantages of both the laser and arc welding. Since the electrode is coaxial to the optical axis of the YAG laser in this process, it can be applied to welding of various objects. In the coaxial MIG, TIG-YAG welding, in order to make irradiation positions of the YAG laser beams having been guided in a wire or an electrode focused to the same position, the beam transmitted in fibers is separated to form a space between the separated beams, in which the laser is guided. With this method the beam-irradiating area can be brought near or to the arc-generating point. This enables welding of all directions even for the member of a three-dimensional shape. This time we carried out welding for various materials and have made their welding of up to 1 mm or more in welding groove gap possible. We have realized high-speed 1-pass butt welding of 4m/min in welding speed with the laser power of 3 kW for an aluminum alloy plate of approximately 4 mm thick. For a mild steel plate also we have realized butt welding of 1m/min with 5 kW for 6 mm thick. Further, in welding of stainless steel we have shown its welding possibility, by stabilizing the arc with the YAG laser in the welding atmosphere of pure argon, and shown that this welding is effective in high-efficiency welding of various materials. Here we will report the fundamental welding performances and applications to various objects for the coaxial MIG, TIG-YAG welding we have developed.

Effect of dual torch technique on duplex stainless steel welds

Abstract: Duplex stainless steels are characterized by balanced ferrite/austenite microstructures and are well known for their superior corrosion resistance and higher strength compared with the common austenitic stainless steels. One major concern, however, is that welding might degrade the corrosion resistance by producing unbalanced phase content, detrimental precipitates, and possible embrittlement of the weldment. In this paper, a dual-torch arc welding technique (plasma torch followed by a gas tungsten arc (GTA) torch) was proposed. Effects of the dual-torch technique on the microstructural changes and corrosion properties were investigated. The preliminary study indicated that a correlation between the welding parameters and the microstructural changes and corrosion resistance existed. It was found that the corrosion rate increases with increasing torch pitch and/or decreasing GTA welding current. By adjusting the distance between the torches, modification of weld microstructure may be realized. Although further studies are required to fine-tune the technique, the present study demonstrated the potential of using dual torch technique to improve weldability of duplex stainless steels.