Showing papers on "Gas metal arc welding published in 1994"

Interactive laser welding at elevated temperatures of superalloy articles

Abstract: A process is provided for laser welding a superalloy article (20) by pre-heating the entire weld area and region adjacent to the weld area of the article to a ductile temperature within the range of 1400-2100 degrees F with an induction heat coil (14) and maintaining such tem-perature during welding and solidification of the weld; and welding the preheated ar-ticle using a laser (11) with a powder al-loy feed (12), with a control system which controls the laser powder feed (12) and a motion system on which the article is fix-tured, wherein the control system includes a vision system which digitizes the weld area of the article (20) providing a path for the laser to follow.

Control of Microstructures and Properties in Steel Arc Welds

Abstract: Control of Microstructures and Properties in Steel Arc Welds provides an overview of the most recent developments in welding metallurgy. Topics discussed include common welding processes, the thermal cycle during welding, defects that may occur during the welding process, the metallurgy of the material, metallurgical processes in the heat-affected zone and the fused metal, and the relationship between microstructures and mechanical properties. The book's final chapter presents examples of welded joints, illustrating how modern theories are capable of predicting the microstructure and properties of these joints. This book is an excellent resource for welding engineers, metallurgists, materials scientists, and others interested in the subject.

Three-dimensional finite element modeling of gas metal-arc welding

Abstract: The modeling of the gas metal-arc (GMA) welding process in three dimensions for moving heat sources has been attempted using the finite element method. The occurrence of finger penetration in the weldment resulting from a streaming type of metal transfer at high contents is explained by assuming that the heat content of transferring droplets is distributed in a certain volume of the workpiece below the arc. Volumetric distribution of the heat content of transferring droplets has been considered as an internal heat-generation term, and the differences between penetration characteristics in two cases of globular and streaming conditions of metal transfer have been analyzed. It is shown that weld penetration depends on the depth at which the droplets distribute their energy inside the workpieces. Temperature dependence of thermophysical properties,i.e., thermal conductivity and specific heat, has been included. Latent heat is incorporated by a direct iteration method. Heat losses from the plate caused by convection and radiation are also considered. The model is validated by predicting the weld-bead dimensions and comparing them with experimental data.

A Study on the Three-Dimensional Analysis of Heat and Fluid Flow in Gas Metal Arc Welding Using Boundary-Fitted Coordinates

Abstract: Computer simulation of three-dimensional heat transfer and fluid flow in gas metal arc (GMA) welding has been studied by considering the three driving forces for weld pool convection, that is the electromagnetic force, the buoyancy force, and the surface tension force at the weld pool surface. Molten surface deformation, particularly in the case of GMA welding, plays a significant part in the actual weld size and should be considered in order to accurately evaluate the weld pool convection. The size and profile of the weld pool are strongly influenced by the volume of molten electrode wire, impinging force of the arc plasma, and surface tension of molten metal. In the numerical simulation, difficulties associated with the irregular shape of the weld bead have been successfully overcome by adopting a boundary-fitted coordinate system that eliminates the analytical complexity at the weld pool and bead surface boundary. The method used in this paper has the capacity to determine the weld bead and penetration profile by solving the surface equation and convection equations simultaneously.

Dynamic Modeling and Adaptive Control of the Gas Metal Arc Welding Process

Abstract: Control of the welding process is a very important step in welding automation. Since the welding process is complex and highly nonlinear, it is very difficult to accurately model the process for real-time control. In this research, a discretetime transfer function matrix model for gas metal arc welding process is proposed. This empirical model takes the common dynamics for each output and inherent process and measurement delays into account. Although this linearized model is valid only around the operating point of interest, the adaptation mechanism employed in the control system render this model useful over a wide operating range. Since welding is inherently a nonlinear and multi-input, multi-output process, a multivariable adaptive control system is used for high performance

An electrode extension model for gas metal arc welding

Abstract: The electrode extension during gas metal arc welding is predicted using a one-dimensional model of the melting electrode. Joule heating in the electrode, heat directly applied to the end of the electrode from the condensing electrons, and heat transferred from the droplet, together with conduction along the electrode are considered. The thermal conductivity, the thermal diffusivity, and the electrical resistivity of the electrode material are allowed to vary with temperature. The steady-state electrode extension is predicted to an accuracy of 1.9 mm. The onset of short-circuiting as the current is decreased for a given electrode feed speed is predicted within 9%. Dynamic analysis shows that the gas metal arc welding process acts as a low-pass filter for electrode extension with respect to the square of the current and with respect to electrode feed speed. As the mean welding current is increased, the electrode extension (or arc length is the contact-tube-to-work distance is constant) has a smaller response to perturbations in the current or electrode feed speed. The quasi-linear transfer functions between electrode extension and current squared and between electrode extension and electrode feed speed can be described by one zero, two pole parametric fits. The transfer functions are linear inmore » the amplitude of the excitation up to 10% of the mean excitation. The model transfer functions were verified with experiments.« less

Mathematical models of transport phenomena associated with arc-welding processes: A survey

Abstract: A comprehensive survey is presented of research on transport phenomena, that is, heat flow, fluid flow, mass transfer, and electrodynamics, associated with arc welding. Both gas-metal arc-welding (GMAW) and gas-tungsten arc welding (GTAW) systems are considered, and appropriate emphasis is placed on the intrinsic differences between these systems. The topics discussed include the behaviour of the arc, and its interaction with both the electrode and the surrounding medium, on the one hand, and the behaviour of the weld pool on the other. The limited work done on the coupling between arcs, electrodes, and weld pools is also discussed, as are some process-control issues, but the problems of thermal stress evolution and stress-induced deformation in the solid state are not treated. A critical discussion of the comparison between model predictions and experimental measurements is a key feature of the presentation, which concludes with a discussion of the critical problems that still need to be addressed.

Effect of welding variables and solidification substructure on weld metal porosity

Abstract: Porosity is defined as cavity-type discontinuities formed by gas entrapment during solidification. Causes of porosity in fusion welds are the dissolved gases in weld metal and welding process variables that control the solidification rate. To study the mechanisms of porosity formation in weld metal, single-pass gas tungsten-arc weld metal was produced using the bead-on-plate technique on three nickel-copper alloys (80 wt pct Ni-20 wt pct Cu, 65 wt pct Ni-35 wt pct Cu, 35 wt pct Ni-65 wt pct Cu). Four different welding speeds were used under various amounts of nitrogen content in argon-shielding atmosphere. A qualitative model was proposed to characterize the effect of welding variables and solidification substructure on bulk and interdendritic porosity formation. Increasing amounts of nitrogen gas (from 0.2 pct to 6.0 pct in volume) introduced in argon-shielding atmosphere increased the amount of porosity in weld metal. The amount of bulk and total porosity increased as the solubility of nitrogen in the weld metal alloy decreased. The solidification rate of the weld pool is the most important factor controlling the mechanism of porosity formation. The observed amount of bulk pores in this study increased with the increase of welding speed; that is, if the time is insufficient for dissolved and evolved gases to escape during solidification, porosity will result. However, a decrease in the amount of interdendritic pores was observed with increasing welding speed in the 80Ni-20Cu and 35Ni-65Cu alloys. This decrease can be related to the effect of solidification rate on the balance between the disjoining pressure, resistance of the liquid film to be disrupted, repulsion of the bubble from the solidification front, and the hydrodynamic force resisting the movement of the bubble. This balance determines the ability of the cellular solidification front to “equilibrium” capture the pores. Furthermore, the observed decrease of interdendritic porosity with increasing welding speed (80Ni-20Cu and 35Ni-65Cu alloys) can also be related to the time for nucleation and growth of pores in the molten weld metal and their entrapment in the interdendritic channels of a dendritic solidification front. This phenomenon is considered a “nonequilibrium capture” of pores. On the other hand, the 65Ni-35Cu alloy that exhibited a structural transition in solidification substructure with the variation of welding speed showed a slight increase in the amount of interdendritic pores. This increase was correlated to the change of pore-capture mechanism from an equilibrium to a nonequilibrium mode as the solidification substructure changed from cellular to cellular dendritic. To substantiate that the controlling mechanism of interdendritic porosity formation is the nonequilibrium capture, a good correlation between the measured mean pore radius and the interdendritic arm spacing was found.

Process and apparatus for welding sheet metal edges

Abstract: Sheet metal edges to be welded are preheated prior to welding. At a given welding speed, this results in a smaller temperature gradient in the material to be welded. Consequently the welding speed can be increased, or material which would otherwise provide poor weld quality can be welded at a high temperature gradient. The preheating is carried out for example by high-frequency excitation of the material to be welded.

CO2 shielding gas effects in laser welding mild steel

Abstract: The most widely used shielding gases for laser welding of steels are helium and argon. Helium produces significantly more penetration than argon in penetration‐mode laser beam welding. Another gas that has been proposed as an alternative to these inert gases is carbon dioxide. The benefits of using carbon dioxide as a shielding gas for laser welding are that it costs less than helium and argon and that it provides nearly the same penetration as helium. The major drawback to its use as a shielding gas for mild steel is that it can cause porosity and other weld discontinuities. In this investigation helium and carbon dioxide were investigated as shielding gases in the laser welding of a fully killed 1018 steel, a semikilled 1018 steel, and an unkilled 1018 steel. Helium was generally found to produce discontinuity‐free welds, although small quantities of very fine centerline porosity were observed in the fully killed and semikilled steels. Carbon dioxide was found to provide an average of 70% of the penetration obtained with helium. The surface appearance and formation of porosity in welds made using carbon dioxide shielding was found to be dependent on the amount of deoxidizing element in the weld pool. While porosity‐free welds were formed in the semikilled steel (0.22% Si), low silicon or other deoxidizer content resulted in poor surface appearance and entrapped porosity in both the fully killed and unkilled steels in this investigation, presumably due to the formation of carbon monoxide in the weld pool. The addition of ferrosilicon powder to the weld pool effectively controlled the formation of carbon monoxide in these welds and resulted in porosity‐free welds with carbon dioxide shielding. The results of this investigation indicate that carbon dioxide can be used as a cost‐effective shielding gas for penetration‐mode welding of carbon steels. It was found that sufficient levels of deoxidizing elements must, however, be available in the molten pool to control porosity.

Physics of welding (III) ‐ Melting rate and temperature distribution of electrode wire

Abstract: (1995). Physics of welding (III) ‐ Melting rate and temperature distribution of electrode wire. Welding International: Vol. 9, No. 5, pp. 348-351.

Shielding gas arc welding method for non-ferrous metals, especially aluminium materials

Abstract: The invention relates to a shielding gas arc welding method for non-ferrous materials, in particular aluminium materials and aluminium alloys, for example AlSi, which method comprises the continuous supply, during welding operation, of a shielding gas containing argon and/or helium to the weld spot (welding point) adjacent to the electrode. According to the invention, a shielding gas is proposed which in addition to argon and/or helium comprises a carbon dioxide fraction or an oxygen fraction or a fraction of a mixture of these gases of from 0.01 to 0.7 % by volume, preferably from 0.01 to 0.1 % by volume (from 100 to 7000 or 1000 ppm, respectively).

Mapping the droplet transfer modes for an ER100S-1 GMAW electrode

Abstract: Welds were made with a 1.2- mm-diameter AWS ER100S-1 electrode using Ar-2% 02 shielding gas to map the effects of contact-tube- to-work distance (13,19 and 25 mm), current, voltage, and wire feed rate on metal transfer. The droplet transfer modes were identified for each map by both the sound of the arc and images from a laser back-lit high­ speed video system. The modes were cor­ related to digital records of the voltage and current fluctuations. The maps con­ tain detailed information on the spray transfer mode, including the boundaries of drop spray, streaming spray and rotat­ ing spray modes. The metal transfer mode boundaries shifted with an increase in contact-tube-to-work distance. Increas­ ing the contact-tube-to-work distance from 13 to 19 mm resulted in a 1 5 mm/s increase in the wire feed rate for the glob- ular-to-drop-spray transition. isting robotic actuators can duplicate the precision of human arm movements in manipulating the electrode along the joint, but substantial improvements are needed in sensor and control system technology. Monitoring of the electrical signals (through-the-arc sensing) is one sensing strategy for an intelligent welding control system. Electrical perturbations related to metal droplet transfer in gas metal arc welding (GMAW) can be used to sense changes in the welding conditions. The control loop would contain rules based on the expertise of a human welder and allow the controller to make the proper responses to the conditions detected by the sensors. A through-the-ar c sensing strategy does not intrude into the arc re­ gion and eliminates sensor-workpiece in­ terference and sensor blinding problems. Although the electrical signals were correlated to arc characteristics as early as 1955 (Ref. 1), recent advances in dig­ ital signal capture and processing tech-

The influence of power source dynamics on wire melting rate in pulsed GMA welding

Abstract: The welding wire melting rate during conventional direct current (DC) gas metal arc (GMA) welding may be modeled empirically by a simple expression relating material constants, current and electrode extension. The resultant equation is found to be in good agreement when welding at moderate or high currents. In the case of pulsed GMA welding, it has already been shown that a good approximation to the observed melting behavior may be obtained by assuming that the DC equation is instantaneously valid and integrating over one pulse cycle. This article extends earlier work to consider the influence of power source dynamics on the integrated expression. Calculations have been made for two cases: an idealized trapezoidal waveform and a more representative exponential form. Predictions indicate that under certain circumstances response rate can have a significant influence over the wire melting rate at a given mean current. The validity of this prediction has been tested experimentally for the idealized trapezoidal waveform and results are presented for comparison. The significance of power source dynamics is discussed with reference to static output characteristics and the resultant influence on metal droplet detachment.

Method for arc welding fault detection

Abstract: A method for sensing and controlling the weld quality of gas metal arc welding employs sampling of the welding current and voltage signals and making determinations of the weld quality state based on information embedded in those signals. The signals are processed such that the quality of the weld can be determined and the appropriate steps are taken to respond to the detected quality level. If the quality level is deemed unacceptable the process is terminated and the operator is alerted. The method includes determinations based on the standard deviation of the electrical signal, the summed power spectrum of the electrical signal, and/or the average absolute value of the time derivative of the electrical signal.

Adaptive control of temperature in arc welding

Abstract: We have outlined our approach for developing an integrated system for controlling centerline bead temperature in arc welding. An optical thermography system, based on an inexpensive and readily available video camera, was presented. Temperature measurements obtained with this system are within 10% of those measured by a calibrated two-color optical pyrometer. A low-order model describing the centerline temperature dynamics was developed. Two strategies for tuning a simple PI temperature controller were given. We first used off-line sensitivity-based tuning to optimize the controller gains. This method is adequate for systems whose dynamics are time invariant. For GMAW, however, the plant parameters can vary widely due to changes in plate thickness as well as other operating parameters. For this reason we applied a sensitivity-based pseudogradient adaptive algorithm for self-tuning the PI controller. The self-tuning controller is robust to changes in the operating conditions and is therefore more useful than a PI controller with fixed gains. It is also insensitive to the noise present in the GMAW system. The control design presented in this paper makes no attempt to counter the delay between the arc current command and centerline temperature output. Instead, the sample time was deliberately increased so that this delay could be ignored. To increase the bandwidth of the closed-loop system it is necessary to incorporate a Smith predictor or similar mechanism to increase the response time of the closed-loop system. We are currently investigating the design of a predictive controller. >

Plasma parameters near a small anode in a high-pressure arc (gas metal arc welding)

Abstract: The size of the arc attachment at the anode of gas metal are welding (GMAW) is small compared to the arc column. The small anode attachment results in a high current density and high Joule heating near the anode. It is believed that this is the reason why the voltage in such an arc rises with current which is in contrast to an almost current-independent V-I characteristic in the case of a large anode. The equation to describe the distribution of plasma parameters near a small are anode is presented. Calculations have been performed for an atmospheric pressure arc in argon in the 50 A to 500 A current range and for the anode sizes of 0.5 mm to 2 mm. Calculations showed that: (1) the voltage drop across the anode layer rises with the current, and (2) there is an electron temperature maximum close to the anode. The calculated volt-ampere characteristic of the anode layer is in agreement with experimental data. The calculated heat flux to the anode is slightly higher than that measured. It is believed that this difference is due to anode vaporization. The thermal balance of the anode is discussed.

Sensors and control systems in arc welding

Abstract: Part 1: General review. Introduction to sensing systems and their application in arc welding processes. State-of-the-art review of sensors and their application in welding processes. Control system. Basis for welding process control. Sensor techniques and welding robots. Analysis of questionnaire results on sensor application to welding processes. Future aspects and subject. Part 2: Collected papers on applications of sensors to welding processes. Groove tracking control by laser sensing method. Development of automatic multi-layer welding system applying laser sensing technique. Online visual sensor system for arc-welding robot. Welding robot with visual seam tracking sensor. An arc-welding robot with a compact visual sensor. Development of robot for three-dimensional multi-layer welding with vision sensor. Visual arc sensor (ARC-EYE). Fuzzy control of CO2 short-arc welding. Application of fuzzy neural network to welding line tracking. Magnetic control of arc in high speed TIG welding. Adaptive control of welding condition using visual sensing. Automatic welding system with laser optical sensor for heavy-wall structures. Group-control system of narrow-gap MIG welding. Automatic control technique for narrow gap GMA welding. A study on automatic control system of one-side submerged arc welding by flux copper backing. Touch sensor and arc sensor for arc welding robots. Application of arc sensor to robotic seam tracking. Dynamic analysis of arc-length and its application to arc-sensing. Robot welding with arc sensing. Arc sensing method by fuzzy control. Development and application of arc sensor control with high speed rotating arc process. Groove tracking control by arc welding current. Automatic seam tracking and bead height control by arc sensor. Through-the-arc sensing control of welding speed for one-sided welding. Some kinds of wire ground sensors. Application of touch sensor to arc welding robot. Automatic welding for LNG corrugated membrane. Welding process monitoring by arc sound. Vibrating reed sensor for tracing the centre of narrow groove. Development of ultra heat-resistant electro-magnetic sensing system for automatic tracking of welding joint. Motion generation of an off-line programming system of an arc-welding robot. Application of an off-line teaching system for arc welding robots. Development and availability of IC-card welding system for automatic welding. Development of remote-controlled circumferential TIG welding system. In-process control system in one side SAW. Application of arc sensor and visual sensor on arc welding robots. Intelligent arc welding robot and simultaneous control of penetration depth and bead height. NC welding robot for large structures. Development of fully automatic pipe welding system.

Plasma arc augmented laser welding

Abstract: The authors describe a technique of arc augmentation to increase the capability of the laser during laser welding. The novel process, Plasma Arc augmented Laser Welding, is still under development.

Plasma welding process

Abstract: In a plasma welding process, a voltage is applied between an electrode and an object to be welded so as to generate a plasma arc with a plasma gas directed through a torch to surround the electrode, and welding is performed using the plasma arc as a heat source. The process cyclically varies energy contained in the plasma arc by cyclically varying a plasma gas flow rate.

Workpiece cleaning during variable polarity plasma arc welding of aluminum

Abstract: Variable Polarity Plasma Arc welding has proved to be extremely successful in welding aluminum alloys despite their adherent refractory oxide. This success has been attributed to removal of the oxide during the reverse polarity cycle. In situ optical spectroscopy is used to measure the amount of hydrogen and oxygen in the plasma arc with a minimum detectable limit of less than 100 ppm. It was found that the amount of contamination is independent of surface preparation and torch speed. Using this information, it is proposed that the predominant mechanism for reverse polarity cleaning in aluminum is dielectric breakdown of the surface oxide ahead of the torch rather than by ion sputtering.

Automatic simultaneous control of bead height and back bead shape using an arc sensor in one‐sided welding with a backing plate

Abstract: Summary This paper describes an automatic welding system that can simultaneously control the bead height and back bead shape during one‐sided MAG welding with a backing plate. The system uses a high‐speed rotating arc welding process together with an arc sensing technique for seam tracking and torch height control. The arc sensing technique is also used to detect variations in the groove shape. The detection mechanism is described in detail in this paper. The system further uses a newly developed welding parameter control method in which only the wire feedrate and welding voltage are adaptively controlled, the other welding conditions being kept constant. This method is able to keep the bead height constant and retain the back bead shape even if the groove shape changes. Initial welding experimental results have shown the system to be effective and satisfactory for controlling the weld bead shape in one‐sided GMAW (MIG/MAG) with a backing plate.

Laser welding of polymers

Abstract: Deep penetration welding and cutting of metals can be carried out at high speed with relatively low laser power. The efficient coupling of the laser radiation to the metal is due to the formation of a “keyhole.” Over the years, an attempt has been made to transfer the results on metals to plastics. It will be shown here that keyhole welding of plastics is limited to the very restricted set of plastics that have a boiling point. Volume heating, a mechanism that is not applicable to metals, is restricted to plastics with a good transparency for the incident radiation and with a high optical quality. Finally, surface heating is shown to be the most common mechanism for heating plastics.

Device for cleansing welding torches

Abstract: The present invention relates to a device for automatically cleaning and cutting off the wire in the nozzles of MIG/MAG welding equipment. It is characterized in that the device, which is portable, comprises a centering member (2) for insertion of a nozzle (1), and milling means (4, 5) to millcoated parts (6) of the nozzle, as well as possibly a cutting member (10) for the foremost part of the welding bead (7) of material applied, the milling means and cutting member if any (4, 5 and 10, respectively) being rotated by a drive means (3), designed to start automatically upon insertion of the nozzle (1).

High speed gas shield arc welding equipment and method therefor

Abstract: PURPOSE: To highly speedily execute fillet welding by installing a twin-wire welding torch which feeds two welding wires into a power feeding chip inside the same welding torch on one pole, at least, among two or three poles as the welding electrode. CONSTITUTION: Twin wire torches 1A, 1B, 2A, 2B of a pair of two fed with wire feeding rollers are introduced into wire guides 9, 10 through wire conduits 5, 6 connected to a preceding wire welding torch 3 and a succeeding twin wire welding torch 4. Then, power feeding chips 7, 8A, 8B are attached so that the interval L between the rear end of the welding wire 1B of the preceding twin wire welding torch 3 and the top end of the welding wire 2A of the succeeding twin wire wedding torch 4 is kept in a prescribed value. While feeding the shield gas onto the welding arc part through tubes 11, 12 arranged on before and behind sides of the welding torch 3, 4, two electrodes MAG welding is executed with four wires. Therefore, the welding current is divided onto four wires, the arc force is dispersed, and the highly speedy welding can be realized. COPYRIGHT: (C)1995,JPO