Showing papers on "Arc welding published in 2011"

Fibre laser welding of dissimilar alloys of Ti-6Al-4V and Inconel 718 for aerospace applications

Abstract: Challenges in dissimilar materials welding are the differences of physical and chemical properties between welding materials and the formation of intermetallic brittle phases resulting in the degradation of mechanical properties of welds. However, dissimilar materials welding is increasingly demanded from the industry as it can effectively reduce material costs and improve the design. In aerospace applications, Ti-6Al-4V titanium alloy and Inconel 718 nickel alloy have been widely used because of their superior corrosion resistance and mechanical properties. In this study, a single-mode continuous-wave fibre laser was used in butt welding of Ti-6Al-4V to Inconel 718. Investigations including metallurgical and mechanical examinations were carried out by means of varying processing parameters, such as laser power, welding speed and the laser beam offset position from the interface of the metals. Simple analytical modelling analysis was undertaken to explain the phenomena that occurred in this process. Results showed that the formation of intermetallic brittle phases and welding defects could be effectively restricted at welding conditions produced by the combination of higher laser power, higher welding speed and shifting the laser beam from the interface to the Inconel 718 alloy side. The amount of heat input and position of laser beam to improve the Ti-6Al-4V/Inconel 718 weld quality are suggested.

Virtual testing and inspection of a virtual weldment

Abstract: Arc welding simulations that provide simulation of virtual destructive and non destructive testing and inspection of virtual weldments for training purposes. The virtual testing simulations may be performed on virtual weldments created using a virtual reality welding simulator system (e.g., a virtual reality arc welding (VRAW) system). The virtual inspection simulations may be performed on "pre-canned" (i.e. pre-defined) virtual weldments or using virtual weldments created using a virtual reality welding simulator system. In general, virtual testing may be performed using a virtual reality welding simulator system (e.g., a virtual reality arc welding (VRAW) system), and virtual inspection may be performed using a standalone virtual weldment inspection (VWI) system or using a virtual reality welding simulator system (e.g., a virtual reality arc welding (VRAW) system). However, in accordance with certain enhanced embodiments of the present invention, virtual testing may also be performed on a standalone VWI system.

A self-consistent three-dimensional model of the arc, electrode and weld pool in gas–metal arc welding

Abstract: The development of a three-dimensional computational model of gas–metal arc welding is described. The wire electrode, arc plasma and weld pool are included in the computational domain self-consistently. The model takes into account the motion of the electrode, flow in the weld pool, deformation of the weld-pool surface and the influence of metal droplet transfer. Results are presented for welding of an aluminium alloy. The current density distribution at the interface between the arc and the weld pool is strongly dependent on the surface profile of the weld pool. This in turn affects the temperature distribution in the weld pool. The momentum transferred by the droplet affects the direction of flow in the weld pool, and together with the energy transfer, increases the weld-pool depth. The results demonstrate the importance of including the arc plasma in the computational domain. Fair agreement is found between a measured weld profile and the predictions of the model. Inclusion of the influence of metal vapour in the model is expected to improve the agreement.

Welding of thick stainless steel plates up to 50 mm with high brightness lasers

Abstract: Thick-section stainless steels are widely used in the components and structures for nuclear power plants. Laser welding is being considered as a high-efficiency method instead of arc welding for some components, so as to improve the production efficiency and reduce the residual stresses of the heat-affected zone. In this paper, multipasses narrow-gap welding of 50 mm thick Type 316L plates with an 8 kW disk laser was first investigated. The effect of welding conditions on the weld bead geometry and welding defects was studied. It shows that lack of fusion could be prevented by optimizing the relationship between laser power intensity and the deposited metal volume. Butt joint of 50 mm thick plates with narrow gap could be performed with eight-layers welding at laser power of 6 kW and welding speed of 0.4 m/min. In order to reduce the weld passes further, gas jet assisted laser welding was tried to weld thick Type 316L plates with a 10 kW fiber laser. The result shows that butt-joint welding of 40 mm plates without filler wire could be carried out at 0.3 m/min welding speed with no porosity or other welding defects. As for 50 mm thick plate, a good weld bead could be obtained with bead-on-plate welding from both sides at 0.2 m/min welding speed.

Analysis of hybrid Nd:Yag laser-MAG arc welding processes.

Abstract: In the hybrid laser-arc welding process, a laser beam and an electric arc are coupled in order to combine the advantages of both processes: high welding speed, low thermal load and high depth penetration thanks to the laser; less demanding on joint preparation/fit-up, typical of arc welding. Thus the hybrid laser-MIG/MAG (Metal Inert or Active Gas) arc welding has very interesting properties: the improvement of productivity results in higher welding speeds, thicker welded materials, joint fit-up allowance, better stability of molten pool and improvement of joint metallurgical quality. The understanding of the main relevant involved physical processes are therefore necessary if one wants for example elaborate adequate simulations of this process. Also, for an efficient use of this process, it is necessary to precisely understand the complex physical phenomena that govern this welding technique. This paper investigates the analysis of the effect of the main operating parameters for the laser alone, MAG alone and hybrid Laser/MAG welding processes. The use of a high speed video camera allows us to precisely characterize the melt pool 3D geometry such as the measurements of its depression and its length and the phenomena occurring inside the melt pool through keyhole-melt pool-droplet interaction. These experimental results will form a database that is used for the validation of a three-dimensional thermal model of the hybrid welding process for a rather wide range of operating parameters where the 3-D geometry of the melt pool is taken into account.

Optimization of parameters of submerged arc weld using non conventional techniques

Abstract: In submerged arc welding (SAW), weld quality is greatly affected by the weld parameters such as welding current, welding speed; arc voltage and electrode stickout since they are closely related to the geometry of weld bead, a relationship which is thought to be complicated because of the non-linear characteristics. However, trial-and-error methods to determine optimal conditions incur considerable time and cost. In order to overcome these problems, non-traditional methods have been suggested. Bead-on-plate welds were carried out on mild steel plates using semi automatic SAW machine. Data were collected as per Taguchi's Design of Experiments and regression analysis was carried to establish input-output relationships of the process. By this relationship, an attempt was made to minimize weld bead width, a good indicator of bead geometry, using optimization procedures based on the genetic algorithm (GA) and particle swarm optimization (PSO) algorithm to determine optimal weld parameters. The optimized values obtained from these techniques were compared with experimental results and presented.

Arc welding control method

Abstract: In a method for controlling pulse arc welding where an arc is created between a wire and a base material, a pulse waveform different from the pulse waveform for steady-state welding is outputted when a predetermined time has passed since short-circuit welding control was started at arc start, and after a sufficiently large melt pool is formed, the pulse waveform for the steady-state welding is outputted This reduces the generation of spatters after an arc is created and until the arc is stabilized

An Arc Welding Robot Control for a Shaped Metal Deposition Plant: Modular Software Interface and Sensors

Abstract: This paper is focused on the study and the control of a process of robotic arc welding. The system developed has been used to study the whole process and to develop an automatic controller for the arc process of deposition. The process consists of a shaped metal deposition (SMD) system that is an innovative method for the manufacturing of metal objects, which uses a layer-by-layer deposition technique. A useful software interface has been implemented in a Labview environment to study the system and to develop and tune the parameters of an automatic controller.

Seeing aid or other sensory aid or interface for activities such as electric arc welding

Abstract: A method, means, apparatus, and system is disclosed, for use with an electrically controllable light-producing activity, or possibly an electrically-controlled sound producing activity. In one embodiment, the light is modulated to affect an imaging function, as a secondary effect, without substantially affecting a primary or main purpose of the light-producing activity. In another embodiment, the light is modulated to affect an imaging function, as a secondary effect, in conjunction with effects on the primary or main purpose of the light-producing activity. The invention is useful, for example, in TIG (Tungsten Inert Gas) welding where the light-producing arc, and possibly some light-producing utility lights, are modulated to improve a computer vision system (such as an auto darkening welding helmet or a headup display for a welding helmet) that helps a person see better. Cybernetic and physiological sensing is disclosed such as EEG, ECG, and the like, in conjunction with wearable computing.

Welding and Joining of Magnesium Alloys

Abstract: Welding and joining of magnesium alloys exert a profound effect on magnesium application expansion, especially in ground and air transportations where large-size, complex components are required. This applies to joints between different grades of cast and wrought magnesium alloys and to dissimilar joints with other materials, most frequently with aluminum and steel. Due to specific physical properties of magnesium, its welding requires low and well controlled power input. Moreover, very high affinity of magnesium alloys to oxygen requires shielding gases which protect the liquid weld from an environment. To magnify complexity, also solid state reaction with oxygen, which forms a thermodynamically stable natural oxide layer on magnesium surface, is an inherent deficiency of joining (Czerwinski, 2008). Both the conventional and novel welding techniques were adapted to satisfy these requirements, including arc welding, resistance spot welding, electromagnetic welding, friction stir welding, electron beam and laser welding. Since fusion welding has a tendency to generate porosities and part distortion, many alternative joining practices were implemented. These include soldering, brazing, adhesive bonding and mechanical fastening. However, also the latter techniques have disadvantages associated, for example, with stress induced by drilling holes during mechanical fastening, preheating during clinching or extensive surface preparation in adhesive bonding. Hence, experiments are in progress with completely novel ideas of magnesium joining. An application of magnesium is often in multi-material structures, requiring dissimilar joints, involving magnesium alloys as one side where on another end there are alloys with drastically different properties. How to weld dissimilar materials is one of the most difficult problems in welding. A difference in physicochemical properties of dissimilar joint components creates challenges for mechanically bolted assemblies as well. Due to its very low electronegative potential, magnesium is susceptible to galvanic corrosion thus affecting performance of mechanical joints in conductive environments. This chapter covers key aspects of magnesium welding and joining along with engineering applications, challenges and still existing limitations. For each technique, the typical joint characteristics and possible defects are outlined with particular attention paid to weld metallurgy and its relationship with weld strength, ductility and corrosion resistance. Although fundamentals for each technique are provided, the primary focus is on recent global activities.

Effects of Zn-Based Alloys Coating on Mechanical Properties and Interfacial Microstructures of Steel/Aluminum Alloy Dissimilar Metals Joints Using Resistance Spot Welding

Abstract: The effects of Zn-based alloys coating (Zn, Al-Zn and Al-Mg-Zn) on the bondability of steel/aluminum alloy dissimilar metals joints were evaluated, in order to achieve strength in lower welding current. In the joint with Zn-based alloys insert, the oxide film on the aluminum alloy was sufficiently removed through eutectic reaction of Zn-based alloys and aluminum. In the joint with Zn-coated steel (GI), higher welding current is necessary to discharge the zinc coating and the oxide film from the bonding interface sufficiently. The thinner aluminum plate after welding and the thick reaction layer cause the decrease of cross tensile strength in the joints with no coating steel (SPCC) and Al-Zn-coated steel. Using Al-Mg-Zn-coated steel, higher strength was achieved in a lower welding current. This is because Al-Mg-Zn-coating melted at lower temperature than Zn and Al-Zn-coating, and the removal of the coating material and the oxide film on the aluminum alloy were sufficiently performed in the lower welding current.

Three-dimensional modelling of arc behaviour and gas shield quality in tandem gas–metal arc welding using anti-phase pulse synchronization

Abstract: The paper presents a transient three-dimensional model of an anti-phase-synchronized pulsed tandem gas–metal arc welding process, which is used to analyse arc interactions and their influence on the gas shield flow. The shielding gases considered are pure argon and a mixture of argon with 18% CO2. Comparison of the temperature fields predicted by the model with high-speed images indicates that the essential features of the interactions between the arcs are captured. The paper demonstrates strong arc deflection and kinking, especially during the low-current phase of the pulse, in agreement with experimental observations. These effects are more distinct for the argon mixture with 18% CO2. The second part of the paper demonstrates the effects of arc deflection and instabilities on the shielding gas flow and the occurrence of air contamination in the process region. The results allow an improved understanding of the causes of periodic instabilities and weld seam imperfections such as porosity, spatter, heat-tint oxidation and fume deposits.