Showing papers on "Arc welding published in 2005"

Fatigue strength of steel and aluminium welded joints based on generalised stress intensity factors and local strain energy values

Abstract: Weld bead geometry cannot, by its nature, be precisely defined. Parameters such as bead shape and toe radius vary from joint to joint even in well-controlled manufacturing operations. In the present paper the weld toe region is modelled as a sharp, zero radius, V-shaped notch and the intensity of asymptotic stress distributions obeying Williams’ solution are quantified by means of the Notch Stress Intensity Factors (NSIFs). When the constancy of the angle included between weld flanks and main plates is assured and the angle is large enough to make mode II contribution non-singular, mode I NSIF can be directly used to summarise the fatigue strength of welded joints having very different geometry. By using a large amount of experimental data taken from the literature and related to a V-notch angle of 135°, two NSIF-based bands are reported for steel and aluminium welded joints under a nominal load ratio about equal to zero. A third band is reported for steel welded joints with failures originated from the weld roots, where the lack of penetration zone is treated as a crack-like notch and units for NSIFs are the same as conventional SIF used in LEFM. Afterwards, in order to overcome the problem related to the variability of the V-notch opening angle, the synthesis is made by simply using a scalar quantity, i.e. the mean value of the strain energy averaged in the structural volume surrounding the notch tips. This energy is given in closed form on the basis of the relevant NSIFs for modes I and II and the radius RC of the averaging zone is carefully identified with reference to conventional arc welding processes. RC for welded joints made of steel and aluminium considered here is 0.28 mm and 0.12 mm, respectively. Different values of RC might characterise welded joints obtained from high-power processes, in particular from automated laser beam welding. The local-energy based criterion is applied to steel welded joints under prevailing mode I (with failures both at the weld root and toe) and to aluminium welded joints under mode I and mixed load modes (with mode II contribution prevailing on that ascribable to mode I). Surprising, the mean value of ΔW related to the two groups of welded materials was found practically coincident at 2 million cycles. More than 750 fatigue data have been considered in the analyses reported herein.

Review of laser hybrid welding

Abstract: In this article, an overview of the hybrid welding process is given. After a short historic overview, a review of the fundamental phenomenon taking place when a laser (CO2 or Nd:YAG) interacts in the same molten pool as a more conventional source of energy, e.g. tungsten in-active gas, plasma, or metal inactive gas/metal active gas. This is followed by reports of how the many process parameters governing the hybrid welding process can be set and how the choice of secondary energy source, shielding gas, etc. can affect the overall welding process. An overview of the benefits and drawbacks of hybrid welding is presented, including reports on gap bridging ability, changes in welding speed and weld penetration, overall weld quality, and changes in heat input to the material being welded. This overview is followed by a few examples of industrial applications of hybrid welding. Finally, a section is devoted to explain about further work required in order to understand and tackle the hybrid welding process more efficiently in the future.In this article, an overview of the hybrid welding process is given. After a short historic overview, a review of the fundamental phenomenon taking place when a laser (CO2 or Nd:YAG) interacts in the same molten pool as a more conventional source of energy, e.g. tungsten in-active gas, plasma, or metal inactive gas/metal active gas. This is followed by reports of how the many process parameters governing the hybrid welding process can be set and how the choice of secondary energy source, shielding gas, etc. can affect the overall welding process. An overview of the benefits and drawbacks of hybrid welding is presented, including reports on gap bridging ability, changes in welding speed and weld penetration, overall weld quality, and changes in heat input to the material being welded. This overview is followed by a few examples of industrial applications of hybrid welding. Finally, a section is devoted to explain about further work required in order to understand and tackle the hybrid welding process more ...

Three stage power source for electric ARC welding

Abstract: A three stage power source for an electric arc welding process comprising an input stage having an AC input and a first DC output signal; a second stage in the form of an unregulated DC to DC converter having an input connected to the first DC output signal, a network of switches switched at a high frequency with a given duty cycle to convert the input into a first internal AC signal, an isolation transformer with a primary winding driven by the first internal high frequency AC signal and a secondary winding for creating a second internal high frequency AC signal and a rectifier to convert the second internal AC signal into a second DC output signal of the second stage, with a magnitude related to the duty cycle of the switches; and, a third stage to convert the second DC output signal to a welding output for welding wherein the input stage has a regulated DC to DC converter with a boost power switch having an active soft switching circuit.

Effects of torch configuration and welding current on weld bead formation in high speed tandem pulsed gas metal arc welding of steel sheets

Abstract: Undercut and humping bead are the common defects that limit the maximum welding speed of tandem pulsed gas metal arc (GMA) welding. In order to increase the maximum welding speed, effects of the inclination angle, interwire distance and welding current ratio between the leading wire and trailing wire on bead formation in high speed welding are investigated. The undercut and humping bead is attributed to the irregular flow of molten metal towards the rear part of the weld pool. This irregular flow can be prevented by the trailing wire with a push angle from 5° to 13° , which provides an appropriate component of arc force in the welding direction. The irregular flow is also related to the distance between the leading wire and the trailing wire, and the flow becomes regular when the distance is in the range 9–12 mm. Moreover, the stabilisation of the bulge of the weld pool between the two wires, the presence of enough molten metal below the trailing arc, and the reduced velocity of molten metal flow ...

Torch for electric arc welding system

Abstract: A torch for connection to an electric arc welding system having a wire feeder, a power source and a weld process controller for the power source. The torch being connected to the front end of a welding gun, which gun has a rear end with a first unique component of a connector. The welding system has a second component of the connector matching the first component. The gun has a communication channel extending from the torch to the first component for transmitting data to the welding system through the connector. The torch has a memory with an identification code outputted on the communication channel to the first component and the system has a decoder circuit connected to the second component and responsive to a selected identification code.

Application of Magnetic Pulse Welding for Aluminum Alloys and SPCC Steel Sheets Joint

Abstract: The magnetic pulse welding (MPW) is a cold weld process of conductive metals to the similar or dissimilar material. MPW uses magnetic pressure to drive the primary metal against the target metal sweeping away surface contaminants while forcing intimate metal-tometal contact, thereby producing a solid-state weld. In this paper the MPW method and its application for several aluminium alloy (A1050, A2017, A3004, A5182, A5052, A6016, and A7075) and steel (SPCC) sheets joint were investigated and the process parameters and welding characteristics are reported.

Pore formation during hybrid laser-tungsten inert gas arc welding of magnesium alloy AZ31B—mechanism and remedy

Abstract: One of the major concerns during high speed welding of magnesium alloys is the presence of porosity in the weld metal that can deteriorate mechanical properties. This study seeks to analyze the presence method and quantity of pore during hybrid laser-tungsten inert gas arc (TIG) welding of magnesium alloy AZ31B by radiography, optical microscopy and electron probe microanalysis (EMPA). At the same time, it identifies both the mechanism of pore formation and a remedy for this problem. The experimental results indicate that lacking of shielding gas for laser beam is the dominant cause of macroporosity formation during the hybrid of laser-TIG welding of magnesium Alloys AZ31B plate, and hydrogen is not main cause to form large pores. A favorable weld without porosity can be obtained by appending lateral shielding gas for laser beam.

Laser induced stabilisation of the welding arc

Abstract: This paper deals with the influence of laser radiation on the stability of the welding arc. Experiments were conducted using a low power (500 W) Nd:YAG laser in combination with a gas tungsten welding arc. The laser induced arc stabilising effect was measured under various experimental conditions. It was found that the stabilising effect can be explained in terms of two phenomena: the absorption of laser energy by the arc plasma and the change of the arc plasma composition caused by strong evaporation of workpiece material. Both phenomena lead to a reduction of the effective ionisation potential of the plasma and thus provide a more conductive, stable plasma channel for arc root and column that overcomes disturbance by external forces. The proposed stabilisation mechanism was validated by measuring the absorption of laser energy by the arc plasma using a laser energy meter and the changes of arc plasma composition caused by the laser radiation by means of emission spectroscopy.

A heat-transfer and fluid-flow-based model to obtain a specific weld geometry using various combinations of welding variables

Abstract: Numerical heat transfer and fluid flow models have provided significant insight into welding processes and welded materials that could not have been achieved otherwise. However, the use of these models has been limited by two major problems. First, the model predictions do not always agree with the experimental results because some input parameters such as the arc efficiency cannot be accurately prescribed. Second, and more important, these models cannot determine multiple pathways or sets of welding variables that can lead to a particular weld attribute such as the weld pool geometry, which is defined by an equilibrium temperature surface. Here we show that the computational heat transfer and fluid flow models of fusion welding can overcome the aforementioned difficulties by combining with a genetic algorithm. The reliability of the convective heat transfer model can be significantly improved by optimizing the values of the uncertain input parameters from a limited volume of the experimental data. Furthermore, the procedure can calculate multiple sets of welding variables, each leading to the same weld geometry. These multiple paths were obtained via a global search using a genetic algorithm within the phenomenological framework of the equations of conservation of mass, momentum, and energy. This computational procedure was applied to the gas tungsten arc welding of Ti–6Al–4V alloy to calculate various sets of welding variables to achieve a specified weld geometry. The calculated sets of welding parameters showed wide variations of values. However, each set of welding parameters resulted in a specified geometry showing the effectiveness of the computational procedure.

Evaluation of TIG flux welding on the characteristics of stainless steel

Abstract: The aim of the present study was to investigate the effect of specific oxide fluxes on the surface appearance, weld morphology, retained δ ferrite content, hot cracking susceptibility, angular distortion and mechanical properties obtained with the tungsten inert gas (TIG) process applied to the welding of 5 mm thick austenitic stainless steel plates. An autogenous gas tungsten arc welding process was applied to stainless steels through a thin layer of activating flux to produce a bead on plate welded joint. The MnO2 and ZnO fluxes used were packed in powdered form. The experimental results indicated that the 80% MnO2–20% ZnO mixture can give full penetration and also a satisfactory surface appearance for type 304 stainless steel TIG flux welds. TIG welding with MnO2 and/or ZnO can increase the measured ferrite number in welds, and tends to reduce hot cracking susceptibility in as welded structures. It was also found that TIG flux welding can significantly reduce the angular distortion of stainless...

Acquisition of Weld Seam Dimensional Position Information for Arc Welding Robot Based on Vision Computing

Abstract: Recognition and identification of weld environment and seam dimensional position by computer vision is a key technology for developing advanced autonomous welding robot. Aiming at requirements for recognition of weld seam image characteristics, this paper first presents an improved algorithm of subpixel edge detection based on Zernike moments. Comparing with the Ghosal’s original algorithm, the improved algorithm deals with mask effect and first derivative model on edge gradient direction so that it has the strong robust to noise, self-thinning ability and higher locating precision. An algorithm based on ZMs to extract line is also proposed, the comparative results with SHT and RHT show the method has the highest calculation speed and accuracy. The stereovision technology is developed to identify dimensional position of weld seam by computing dimensional coordinates of the weld seam. According to characteristics of weld seam, view field scope model and stereovision model based on baseline are studied and a stereo matching method is presented. In order to evaluate the algorithms and models presented in this paper, a welding robot systems with single camera fixed on the weld torch end-effector has been established for the robot to identify the dimensional position of typical weld seam by one-item and two-position method. The experiment results on S-shape and saddle-shape weld seams show that the vision computing method developed in this paper can be used for acquiring weld seam dimensional position information in welding robot system. Thus the welding path is mapped before the welding operation is executed.

Synergetic effects of hybrid laser/arc welding

Abstract: The present study reports the results of a study examining the synergetic effects of hybrid laser/arc welding. Experiments were carried out with a 500 W Nd:YAG laser in combination with standard gas tungsten arc welding equipment and attention was focused on two aspects: the heat transfer efficiency and the melting efficiency. The heat transfer efficiency was determined by calorimetric measurements, whereas the melting efficiency was obtained from the transverse cross-sections of welds produced under various conditions. In addition, analytic calculations of the melting efficiency were performed on the basis of a modified form of the Rosenthal equation. The results show that the interaction of the laser and the arc does not lead to a noticeable change in the heat transfer efficiency, but results in a significant increase in the melting efficiency. The observed synergic melting effect is caused by addition of the two heat sources (laser and arc) and the contraction of the arc by the laser beam.

Grain refinement through arc manipulation techniques in Al–Cu alloy GTA welds

Abstract: Effect of three arc manipulation processes pulsed current welding, magnetic arc oscillation and the simultaneous application of pulsed current and arc oscillation, on the weld metal grain structure and tensile properties of the welds were investigated. Initial studies were conducted on autogenous welds made on 3.5 mm thick 2219-T6 plates, to identify and optimize, welding parameters resulting in fine equiaxed grains in the weld metal. Welds were made on 8.5 mm thick 2219-T87 plates using the optimized parameters and tested for tensile properties. All three techniques resulted in fine equiaxed grains in weld metals and optimum parameters were suggested based on the extent of refinement. Fine-grained weld metals exhibited better yield and ultimate tensile strengths and significant improvement in percent elongation. The reasons for the same were explained with the help of TEM and EPMA studies.

A fuzzy-logic based optical sensor for online weld defect-detection

Abstract: This paper describes an intelligent optical sensor for real time defect detection in gas metal arc welding processes. The sensor measures the radiations emitted by the plasma surrounding the welding arc, and analyzes the information in real time to determine an index of local quality of the weld. The data processing algorithm encompasses a Kalman filter to reduce the heavy amount of noise affecting the measured signals, and an intelligent fuzzy system to assess the degree of acceptability of the weld. The fuzzy system is also able to detect the risk of specific problems (e.g., anomalies in the current, voltage or speed of the arc, contamination with other materials, holes) and the position of defects along the welding line. In an extensive experimental comparison, the fuzzy system outperforms a former version of the detection algorithm based on a statistical approach.

Welding robots

Abstract: Using robots in industrial welding operations is common but far from being a streamlined technological process. The problems are with the robots, still in their early design stages and difficult to use and program by regular operators; the welding process, which is complex and not really well known and the human-machine interfaces, which are unnatural and not really working. In this article, these problems are discussed, and a system designed with the double objective of serving R&D efforts on welding applications and to assist industrial partners working with welding setups is presented. The use of object-oriented and distributed software to assist industrial robotic welding applications is discussed. The system is explained in some detail and demonstrated using two test cases that reproduce two situations common in industry: multilayer butt welding and multipoint fillet welding.

Method and device for combined laser-arc welding with control of laser unit according to welding torch

Abstract: The invention relates to a method for combined laser-arc welding and to a device (1) for combined laser-arc welding, comprising a laser unit (2) for producing a laser beam (3), a welding torch (4) for producing an arc (5), a supply unit (6) for the laser unit (2) and a supply unit (7) for the welding torch (4). In order to optimize the energy balance and to adapt the combined laser-arc welding process to the respective conditions, a device (14) is provided for controlling the laser unit (2) according to the welding torch (4). The laser output (PLaser) is adapted to the arc output (PArc) and is controlled by means of a closed control circuit.

Laser visual sensing for seam tracking in robotic arc welding of titanium alloys

Abstract: Sensor errors arose from detecting the weld-seam profile of titanium alloys with laser-based vision sensors because the surface of such a material is highly reflective to a laser light. In this study, the correct weld-seam profile was established from the distorted raw data by signal processing. Furthermore, a fully automatic seam-tracking system was developed. This system featured training and saving of the template, autofinding of the starting welding point, auto–calibration, detection of seam position and groove dimensions and tracking control. The system was capable of tracking V-groove, fillet, lap and butt joints of titanium alloys with high accuracy of less than 0.4 mm.

Laser stabilisation of arc cathode spots in titanium welding

Abstract: Cathode spot formation is very pronounced during arc welding of titanium and titanium alloys. The dynamic behaviour of these spots was observed to interfere with metal transfer during welding, this interference being a fundamental cause of poor weld quality in these alloys. In the present work, stabilisation of the arc cathode spot with a focused Nd–YAG laser beam during pulsed gas metal arc welding of titanium was investigated. The laser beam was focused near the leading edge of the weld pool and the laser power and focus spot size were varied to determine the values required to confine the cathode spot to the laser focus position. The results showed that, for fixed welding conditions, the laser power required to prevent cathode spot motion varied as a function of focus spot size. The required laser power was minimised at 200 W for a spot size of 0.6 mm. The laser stabilised arcs had lower voltage but approximately the same current density as stabilised arcs. Increased welding speeds required mar...

Method for operation of a welding unit welding unit and welding torch for such a welding unit

Abstract: The invention relates to a method for operation of a welding unit (1), for the execution of welding processes with a welding device (2) and a welding torch (10), whereby operational states for the welding processes are recorded and, depending on the operational state, vibrations which may be felt are generated and a welding unit (1) and a welding torch (10), for carrying out said method. According to the invention, the possibility of providing feedback about particular operational states to people involved in the welding process, in particular, the welder, without the same having to look away from the welding spot or the arc (15) may be achieved, whereby, in particular, the welding current (I) or the welding voltage (V) are modulated, depending on the operational state, to generate acoustic vibrations in the arc occurring during welding, or, depending on the operational state, mechanical vibrations are generated. The vibrations can also be felt by the welder without looking away from welding spot or the arc (15).

Influence of welding processes on microstructure and mechanical properties of dissimilar austenitic-ferritic stainless steel welds

Abstract: Dissimilar metal welding of austenitic (AISI 304)-ferritic (AISI 430) stainless steel has been taken up to understand the influence of the welding process on microstructure and mechanical properties. Fusion welding processes, namely, gas tungsten arc welding (GTAW), electron beam welding (EBW), and friction welding, have been employed. The GTAW and EBW processes were selected to understand the heat input effects, while friction welding was included to compare fusion and solid-state welding processes. The material used for fusion welding studies is 20-mm-thick, hot-rolled, and annealed plate. Rods of 18 mm diameter machined from the same plate material were used for friction welding studies. In GTAW, ER 430 filler material was employed for dissimilar metal combination, while other welds are autogenous. Gas tungsten arc welds consisted of coarse columnar grains. In electron beam welds, the microstructure consisted of predominantely equiaxed grains on the austenitic stainless steel side, while colum...

Power source for electric arc welding

Abstract: A power source for an electric arc welding process, wherein the power source comprises an input stage having an AC input and a first DC output signal; a second stage in the form of an unregulated DC to DC converter having an input connected to the first DC output signal and an output in the form of a second DC output signal electrically isolated from the first DC output signal and with a magnitude of a given ratio to the first DC output signal; and, a third stage to convert the second DC output signal to a welding output for the welding process.

Weld decay-resistant austenitic stainless steel by grain boundary engineering

Abstract: This paper presents an example of grain boundary engineering (GBE) for improving intergranular-corrosion and weld-decay resistance of austenitic stainless steel. Transmission and scanning electron microscope (TEM and SEM) observations demonstrated that coincidence site lattice (CSL) boundaries possess strong resistance to intergranular precipitation and corrosion in weld decay region of a type 304 austenitic stainless steel weldment. A thermomechanical treatment for GBE was tried for improvement of intergranular corrosion resistance of the 304 austenitic stainless steel. The grain boundary character distribution (GBCD) was examined by orientation imaging microscopy (OIM). The sensitivity to intergranular corrosion was reduced by the thermomechanical treatment and indicated a minimum at a small roll-reduction. The frequency of CSL boundaries indicated a maximum at the small roll-reduction. The corrosion rate was much smaller in the thermomechanical-treated specimen than in the base material for long time sensitization. The optimum thermomechanical treatment introduced a high frequency of CSL boundaries and the clear discontinuity of corrosive random boundary network in the material, and resulted in the high intergranular corrosion resistance arresting the propagation of intergranular corrosion from the surface. The optimized 304 stainless steel showed an excellent resistance to weld decay during arc welding.

Arc welding torch

Abstract: [PROBLEMS] To perform adjustment operations such as inching, retracting, and gas checking of a welding wire by an operator using a button provided on an arc welding torch without using a button provided on a welding power source or a remote control. Provide a welding torch that can be performed. In an arc welding torch, one of a plurality of adjustment modes including an inching mode for feeding a welding wire in a forward direction, a retract mode for feeding a welding wire in a reverse direction, and a gas check mode for discharging a shielding gas. The adjustment mode selection means 23 for selecting one, the display means 22 for displaying the adjustment mode selected by the adjustment mode selection means in an identifiable manner, and the adjustment mode selected by the adjustment mode selection means An execution button 24 for outputting an adjustment mode command MC and data sending means for sending the adjustment mode command to the welding power source are provided. [Selection] Figure 2

EFFECT OF MICROPLASMA ARC WELDING PROCESS PARAMETERS ON GRAIN GROWTH AND POROSITY DISTRIBUTION OF THIN SHEET Ti6AL4V ALLOY WELDMENT

Abstract: In the present investigation, the effect of microplasma arc welding (MPAW) process parameters on grain growth and porosity distribution of thin sheet Ti6Al4V alloy weldment has been examined. The MPAW procedure was performed at different current, welding speed, and flow rates of shielding and plasma gas. Metallographic characterization was carried out by light microscopy and scanning electron microscopy (SEM). The results have shown that beyond a threshold energy, burn of the metal in Ti6Al4V thin sheet alloy can occur. This case should be considered for any selection of welding process parameters. Furthermore, in MPAW there are a number of threshold parameters that can control weldment size. Metallographic characterization has shown that coarse primary beta grains exist in the fusion zone. This is due to the fact that these grains have nucleated epitaxially upon coarsened beta grains in the near heat affected zone (NHAZ) and grown competitively into the molten weld pool. Evaluation of grain size...

Chopper output stage for arc welder power source

Abstract: Power sources are disclosed for electric arc welding or cutting processes, in which an interleaved multiphase switching converter is provided with a plurality of converter power circuits to convert a DC signal to a regulated signal suitable for welding.