Arc Temperature Research Articles

Thomson scattering diagnostics of steady state and pulsed welding processes without and with metal vapor

Thomson scattering is applied to measure temperature and density of electrons in the arc plasma of the direct current gas tungsten arc welding (GTAW) process and pulsed gas metal arc welding (GMAW) process. This diagnostic technique allows to determine these plasma parameters independent from the gas composition and heavy particles temperature. The experimental setup is adapted to perform measurements on stationary as well as transient processes. Spatial and temporal electron temperature and density profiles of a pure argon arc in the case of the GTAW process and argon arc with the presence of aluminum metal vapor in the case of the GMAW process were obtained. Additionally the data is used to estimate the concentration of the metal vapor in the GMAW plasma.

Interaction of a free burning arc with regenerative protective layers

The possible use of protective layers made of ceramic powders for walls in thermal plasma applications is studied. A stable free burning arc of currents up to 5 kA between copper- tungsten electrodes is used to analyse the arc interaction with samples coated by mixtures of CaCO3, MgCO3, and Mg(OH)2 with plaster. By means of optical emission spectroscopy the maximum arc temperature and the radiation impact on the surfaces are estimated to be around 15000 K and 20 MWm−2, respectively. Thermographic measurements confirm the efficient protection of substrates by all layer materials. Layers containing CaCO3 lead to the lowest heating of ceramic samples which may be caused by a strong evaporation of the layer material.

Experimental and theoretical study of internal fault arc in a closed container

The characteristics of an internal fault arc in an air closed cylindrical container have been investigated both experimentally and theoretically. Arc voltage, arc current as well as pressure variations at two different locations within the container are measured for electrode gap lengths of 10, 30 and 50 mm with peak current ranging from 1 to 20 kA of direct current (dc). The fraction of electric arc energy leading to pressure rise in the fault arc, which is known as the thermal transfer coefficient (kp), is also obtained according to the experimental data. The arc motion is recorded during the whole arcing by high-speed camera. The radiation intensities of the spectral lines at wavelengths of 510.64 and 515.39 nm of the Cu atom originated from the copper electrodes are detected by spectrometer, from which the arc temperature is obtained by means of the two-line method. A two-dimensional axisymmetric cylindrical coordinate model for fault arc is developed based on magneto-hydrodynamic (MHD) theory with coupled interactions among the flow, temperature, electromagnetic, turbulence and radiation fields taken into account, which simulates the distributions of temperature, pressure, arc voltage as well as kp. Particularly the internal pressure rise and propagation due to fault arc at different locations within the container are analysed. The results show that radiation and turbulence are two key energy transfer mechanisms in modelling the fault arc. Compared with the net emission coefficient radiation model, the P1 model is more suitable to calculate the pressure variation in fault arcs with the re-absorption effect contributing to the pressure rise considered. The computed pressure variation, arc temperature, arc voltage and kp agree with the experimental result within the error range.

Effect of high power CO2 and Yb:YAG laser radiation on the characteristics of TIG arc in atmospherical pressure argon and helium

Abstract The effects of laser radiation on the characteristics of the DC tungsten inert gas (TIG) arc were investigated by applying a high power slab CO 2 laser and a Yb:YAG disc laser. Experiment results reveal that the arc voltage–current curve shifts downwards, the arc column expands, and the arc temperature rises while the high power CO 2 laser beam vertically interacts with the TIG arc in argon. With the increase of the laser power, the voltage–current curve of the arc shifts downwards more significantly, and the closer the laser beam impingement on the arc to the cathode, the more the decrease in arc voltage. Moreover, the arc column expansion and the arc temperature rise occur mainly in the region between the laser beam incident position and the anode. However, the arc characteristics hardly change in the cases of the CO 2 laser–helium arc and YAG laser–arc interactions. The reason is that the inverse Bremsstrahlung absorption coefficients are greatly different due to the different electron densities of the argon and helium arcs and the different wave lengths of CO 2 and YAG lasers.

Effects of Transverse Magnetic Field with Different Alternating Currents on Heat Flux Density Distributions of Plasma Arc

An external transverse-alternating magnetic field with sinusoidal and triangular alternating currents was applied to a combined plasma arc to create a plasma arc for expanding the cross section of arc column and flatting the distributions of arc temperature. Two mathematical models were developed to describe the heat flux density distributions of the combined plasma arc driven by a transverse-alternating magnetic field with sinusoidal and triangular alternating currents. The behavior of plasma arc under the external transverse-alternating magnetic field imposed perpendicular to the plasma current was discussed theoretically and experimentally by changing various parameters such as working gas flux, arc current, magnetic flux density including its wave form and the standoff from the nozzle to the workpiece. The analytical results show that it is feasible to adjust the shape and heat flux density of the combined plasma arc by the transverse- alternating magnetic field, which expands the region of combined plasma arc thermal treatment and uniforms the heat flux density upon the workpiece. Changing the waveform of the alternating current can also control the heat flux density distribution. As well as, calculated heat flux density distributions of combined plasma arc driven by the external transverse-alternating magnetic field show a good agreement with experimental data. The magnetic field with triangular alternating current can flat the heat flux density distribution on the anode rather than sinusoidal one. This approach to flat the heat flux density distribution on the anode surface will give an effective controllability to the combined plasma arc application.

Investigation of molten pool oscillation during GMAW-P process based on a 3D model

In order to better reveal the oscillation mechanism of the pulsed gas metal arc welding (GMAW-P) process due to an alternately varied welding current, arc plasma and molten pool oscillation were simulated through a self-consistent three-dimensional model. Based on an experimental analysis of the dynamic variation of the arc plasma and molten pool captured by a high-speed camera, the model was validated by comparison of the measured and predicted results. The calculated results showed that arc pressure was the key factor causing the molten pool to oscillate. The variation in arc size and temperature from peak time to base time resulted in a great difference in the heat input and arc pressure acting on the molten pool. The surface deformation of the molten pool due to the varying degrees of arc pressure induced alternate displacement and backflow in the molten metal. The periodic iteration of deeper and shallower surface deformation, drain and backflow of molten metal caused the molten pool to oscillate at a certain frequency. In this condition, the arc pressure at the peak time is more than six times higher than that at the base time, and the maximum surface depression is 1.4 mm and 0.6 mm, respectively, for peak time and base time.

Effects of shielding gas composition on arc profile and molten pool dynamics in gas metal arc welding of steels

In gas metal arc welding, gases of different compositions are used to produce an arc plasma, which heats and melts the workpiece. They also protect the workpiece from the influence of the air during the welding process. This paper models gas metal arc welding (GMAW) processes using an in-house simulation code. It investigates the effects of the gas composition on the temperature distribution in the arc and on the molten pool dynamics in gas metal arc welding of steels. Pure argon, pure CO2 and different mixtures of argon and CO2 are considered in the study. The model is validated by comparing the calculated weld profiles with physical weld measurements. The numerical calculations reveal that gas composition greatly affects the arc temperature profile, heat transfer to the workpiece, and consequently the weld dimension. As the CO2 content in the shielding gas increases, a more constricted arc plasma with higher energy density is generated as a result of the increased current density in the arc centre and increased Lorentz force. The calculation also shows that the heat transferred from the arc to the workpiece increases with increasing CO2 content, resulting in a wider and deeper weld pool and decreased reinforcement height.

Modeling of Cold Metal Transfer Spot Welding of AA6061-T6 Aluminum Alloy and Galvanized Mild Steel

In this article, a three-dimensional (3D) transient unified model is developed to simulate the transport phenomena during the cold metal transfer (CMT) spot welding process of 1 mm thick aluminum AA6061-T6 and 1 mm thick galvanized mild steel (i.e., AISI 1009). The events of the CMT process are simulated, including arc generation and evolution; up-and-down movement of electrode, droplet formation and dipping into the weld pool; weld pool dynamics; zinc evaporation, and zinc vapor diffusion in the arc. The effects of the gap between the two workpieces and effects of zinc vapor evaporated from the steel surface on CMT process are studied. The results show that the arc temperature, velocity, and pressure keep changing during the CMT process, which is related to the variations of welding current, arc length, and zinc evaporation. It is found that the zinc evaporation leads to the extremely high arc pressure and the upward flow of zinc vapor near the steel surface, which would induce the arc instability and provide the drag force for the droplet impingement. The presence of the gap between the two workpieces can improve the expansion of the arc plasma, resulting in the smaller arc pressure and the more intensive upward flow of zinc vapor from the steel surface. The phenomena observed in the experiment are in agreement with the modeling results.

Effects of DC Component in Asymmetric Fault Current on the Thermal Recovery Characteristics of an SF<sub>6</sub> Autoexpansion Circuit Breaker

A 2-D magnetohydrodynamic arc model is used to study the thermal recovery processes with long and short arc durations in an autoexpansion circuit breaker where a significant dc component in the fault current exists. The influence of the dc component on the pressure built-up in the expansion volume was first investigated and the thermal recovery characteristics compared with cases where asymmetry of the fault current is negligible. Results show that, in comparison with the cases of symmetrical fault current, pressurization in the expansion volume is largely determined by the arc energy in the second half cycle of fault current, which is significantly influenced by the dc component. The dc component affects evidently the arc temperature at the current zero point and leads to a reduction in the critical rate of rise of recovery voltage.

Numerical analysis of Al vapour effects in gas metal arc welding of Al alloys

Using an in-house three-dimensional (GMAW) process simulation tool, the effects of Al vapour in the arc welding of aluminium alloys for various welding currents have been studied. The mathematical model, which takes into account the effects of metal vapour, is described. A bead-on-Al-plate problem is then modelled, with and without consideration of the Al vapour for various welding currents. The effects of the Al vapour on the energy flow of the system and the resulting weld profile are examined. The calculated plasma temperatures are compared with measured temperatures. The change of heat input to the workpiece due to the presence of Al vapour is examined. Finally, the calculated weld profiles with and without consideration of Al vapour are compared with actual weld profiles. It is found that the presence of Al vapour reduces the arc temperature and the weld depth significantly.

Measurement and Simulation of Low Carbon Steel Alloy Deposit Temperature in plasma Arc Welding Additive Manufacturing

Additive manufacturing has the potential to produce near-net shape parts directly from weld metal. Prior work has proved that it is possible to directly manufacture components with complex geometric features and with good productivity. However, under high productivity conditions, deposit temperature increases to a level that it is no longer possible to develop appropriate deposit microstructure and therefore mechanical properties. In this study, Plasma Arc welding was used to produce experimental deposits of 1018 low carbon steel under various conditions. An analytical heat flow model was developed to study the influence of interlayer wait time on deposit temperature and therefore grain size and hardness. The results of the model indicated that as wall height increased, the rate of deposit heat removal by conduction to the substrate decreased leading to a higher preheat temperature after a fixed interlayer wait time causing grain size to increase as wall height increased. However, the model results also show that as wall height increased, the deposit surface area from which heat energy is lost via convection and radiation increased. The model also demonstrated that the use of a means of forced convection to rapidly remove heat from the deposit could be an effective way to boost productivity and maintain smaller grain size and therefore higher hardness and strength in the deposit.

A modified Fowler–Milne method for monochromatic image analysis in multi-element arc plasma welding

The monochromatic images of 794.8nm Ar I and 487.98nm Ar II spectrums are obtained by high speed camera, and these images are normalized with respect to their relative maximum emission coefficient in a pure argon (single element) arc. The relative maximum emission coefficient of 487.98nm Ar II is calculated based on Olsen-Richter diagram. Unlike other spectroscopic methods, the presented method does not require spectra scan or the maximum emission coefficient of non-argon elements. This technique is applied to the measurement of radial profile of temperature and gas composition of argon–helium arc plasma in gas tungsten arc welding (GTAW), significant demixing occurs in the argon–helium arc plasma. Helium concentration in arc plasma is higher than that in original gas mixture, and it decreases as the point moves away from the axis along radial direction and increases as the point gets closer to the cathode. The calculated arc temperature and gas composition are compared with the data obtained using conventional method where a spectrometer is used for spectral line intensity measurement and two-line relative intensity method for calculation. Very good agreements have been observed. That means, the developed technique measures arc temperature and gas composition as accurate as the conventional spectroscopic methods. With the usage of a high speed camera, the developed technique enables measurement of arc temperature and gas composition distribution in a dynamic arc such as arc ignition, pulsing arc.

Practical methods for electrical and mechanical measurement of high speed elongated arc parameters

In this paper, we have presented measurement methods used to evaluate short circuit current interruption capability of a fast opening circuit breaker with opening velocities up to 36m/s. Such circuit breakers are the most critical components of future hybrid fault current limiting circuit breakers and therefore thorough understanding of fast elongating arcs is essential. The presented methods include measurement of cinematic parameters (displacement, speed and acceleration) and electrical parameters (arc voltage and current) as well as high speed optical measurement of arc appearance. Generated codes for sampling and wavelet de-noising of signals as well as developed image processing method for processing of digital arc images captured by high speed camera have been explained. Based on processed information gained by the measurements, arc starting time, arc ending time and arc temperature contours have also been calculated. Use of advanced simulation tools based on finite element method (FEM) equipped with moving mesh has been discussed to facilitate measurements and also to improve their accuracy. Practical measurements and simulation results prove each other and show good agreement with digital arc image processing output.

Physical characteristics of twin-wire indirect arc plasma

In this study, the behavior of arc in a twin-wire indirect arc welding is simulated for arc lengths of 5.2 mm, 6.2 mm and 7.2 mm. The plasma temperature is measured by spectrometric method. The results showed that increase in arc length increase the arc parameters (plasma temperature, current density, plasma velocity, heat flux and arc voltage) of twin-wire indirect arc (TWIA). The change in arc length was found to have little influence on the distribution and the variation in trend of arc parameters in the whole arc region. As the arc length increases, the arc parameters in cathode region increase at a slower rate than those of anode region. This probably is the reason for self-adjustment of TWIA and for the arc stability in a certain range of arc lengths. The temperature of anode region is slightly higher than that in the cathode region and other arc parameters have similar trends. The isotherms are displaced toward the anode side and the shape of TWIA is similar to an inclined and inverted bell. The displacement increases with increasing arc length. The experimental results of plasma temperatures are in good agreement with calculated results which verifies the accuracy of the calculated results.

Influence of DC Component of Short-Circuit Current on Arc Characteristics During the Arcing Period

The arcing processes of the short-circuit current with a significant dc component have been simulated under the long and short arcing time conditions, respectively, for an SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> auto-expansion circuit breaker based on an MHD arc model. The influences of the dc component are investigated compared with cases where the dc component is negligible. The results show that the arc temperature, pressure, and radius as well as the pressurization in the expansion volume are increased significantly under the second current peak gone up by the dc component and long arcing time condition. However, the arc temperature at the final current zero becomes high in the current peak and is reduced by the dc component and short arcing time cases. Thus, the dc component would not be ignored in the interrupting investigation and in the design of the interrupter.

S0420202 炭素繊維強化フェノール樹脂の昇温過程における劣化と変形([S042-02]セラミックスおよびセラミックス系複合材料(2),機械材料・材料加工部門)

The degradation and deformation of an ablator made of carbon fiber reinforced phenolic resin was observed after arc-plasma wind tunnel tests. The observation revealed the delamination was generated inside material and it caused the expansion in an out-of-plane direction. Under such a rapid heating condition, the thermal stress is induced inside material. In order to simulate the thermal stress inside material heated by the arc wind tunnel tests, temperature distributions and thermal stresses were calculated using simulation software: ABAQUAS. The thermal stress compressed in the in-plane direction by 10〜11 MPa which is close to the compressive strength of it. Consequently, the delamination observed after heating resulted from the rapid one-dimensional heating generating the thermal stress.

Arc Energy and Temperature During Its Propagation Over Ice-Covered Surfaces

The voltage and current waveforms during the propagation of an arc over an ice surface were measured and analyzed. The V-I characteristics of the discharge driven by ac power supply were studied. The instantaneous and per-cycle energy delivered to the arc column were calculated. The spectra of the emitted light during the arc propagation were collected and analyzed using a spectroscopic system. The rotational temperature was derived from the relative intensities of two groups of rotational lines corresponding to the peaks of the OH (A-X) (0, 0) vibrational band. The rotational temperatures of the experimental spectra for different current levels were derived. The relationship between the delivered energy to the arc column and the rotational temperature was studied and discussed.

Arc Behavior Numerical Analysis in GMAW Welding Deposition-Based Rapid Forming

Metal fluid flow in weld pool would influence final quality of forming part in GMAW welding deposition-based rapid forming process. To numerical study fluid flow in weld pool, heat and force effects on weld pool surface must been made clear firstly. A three-dimensional numerical model has been built to study arc behavior in GMAW welding deposition-based rapid forming process. Solving the model, heat flux and pressure distributions on the cathode were derived. Calculated results show that heat flux from the arc to the cathode is related to arc temperature nearly above the cathode, and is not monotonous about radial distance within 2 mm distance away from arc axis. A maximum pressure with a value of 800 Pa happens at 1mm away from arc axis.

Numerical analysis of arc characteristics in two-electrode GTAW

A two-dimensional numerical model is developed to describe the arc characteristics in two-electrode gas tungsten arc welding. The influence of different welding current, shielding gas, and shielding gas flow rate is investigated. The arc characteristics are analyzed by studying the distributions of physical quantities including arc temperature, electric potential, and total heat flux on the workpiece. The simulated results reveal that a higher arc temperature value is obtained in helium arc than in argon arc. For obtaining high arc temperature, there is an optimum range for shielding gas flow rate and too high or too low is not appropriate. In addition, the increase of welding current results in the increase of the maximum arc temperature, electric potential, and total heat flux. To validate the accuracy of simulated results, welding experiments are performed and the arc temperature is calculated by the spectral signal of arc plasma. The simulated results are compared with the experimental ones and there is a good agreement.

Determination of the plasma temperature in a pulsating arc

The distribution functions of arc pulsations depending on the current, gas mass flow rate, and the distance from the cathode in a plasmatron with a fixed arc length have been obtained. The distributions of the plasma emission intensity by the transverse image method have been measured. From these data, the temperature distribution over the arc radius has been determined and the influence of the pulsations on the measurement accuracy has been shown.