We present results obtained by two non-equilibrium modelling approaches and experiments on low-intensity short-length arcs in argon at atmospheric pressure. The first one considers a quasi-neutral arc column combined with boundary conditions on the electrodes based on the energy balance in the space-charge sheaths. The second approach applies a unified description over the entire gap and solves the Poisson equation for the self-consistent electric field. The experiments provide the arc voltage.

Electrical measurements and numerical modelling of dc tungsten-inert gas arcs are carried out in order to determine the electric field and the voltage, and to study their importance to the plasma-electrode interaction. The configuration under consideration is very typical for tungsten-inert gas welding processes and includes a conically shaped cathode made of doped tungsten and atmospheric pressure argon as a shielding gas. The studies analyze the effects of the inter-electrode distance and the electric current over wide ranges of variation—currents from below 10 A up to 200 A, and distances from 20 mm down to 2 mm in the modelling and to the short-circuit in the experiment. The comparison of the experimentally obtained and the computed current–voltage and arc length-voltage characteristics clearly prove the predictive capability of the advanced non-equilibrium model of the arc and the electrodes. Moreover, the self-consistent model yields the structure of the electric potential and the electric field and is capable of describing the peculiarities of the plasma-electrode interaction.

To date, several numerical models predicting the properties of TIG-arcs are available. Recently, effort has been put into testing the reliability of these models for varying process parameters by means of comparing plasma temperatures and arc voltages against measured data. However, from an engineering point of view, the goal of these models is to predict the properties of weld beads. Therefore, the heat input into and the pressure applied onto the workpiece have to be predicted. This paper deals with the comparison of measured arc pressure data and the results of an approach which couples a simplified cathode sheath model with an LTE arc model.

For aluminum joining, the gas tungsten arc welding (GTAW) and the gas metal arc welding (GMAW) processes are widely used. The GTAW process is mainly used when high quality is required whereas the GMAW process allows higher throughput at a lower quality. Therefore, aluminum fabricators have to compromise between a high quality and a high productive welding process thus far. In this paper, a new GTAW welding variant is presented that operates in DCEP polarity (electrode as the anode) at high currents up to 450 A. The use of a second gas stream ensures a strong penetration and good arc stability. The welding performance of the new GTAW variant is compared to AC GTAW and pulsed GMAW. It enables high-quality welds for a wide thickness range between 2 and 10 mm at even higher welding speeds compared to GMAW.

In arc welding, particulate and gaseous as well as electromagnetic emission are generated. Users are mostly aware of the particulate fumes and therefore their risks are questioned and discussed. Gaseous emissions like NO, NO2, and O3 were either little noticed or the extent of their toxic effect were not fully recognized in the past. However, the awareness of their hazardous potential led to a decrease of the threshold limits. A fundamental understanding is needed to be able to avoid the formation of these gaseous emissions effectively. In this article, the radiation behavior for TIG-arcs and the interaction with the ozone formation is systematically investigated for different process gas components. Furthermore, the role of metal vapor in a TIG arc is clarified and the impact on the ozone formation is studied by using molten and none molten anodes. The results of the investigation show that a helium concentration of more than 80% has a significant influence on the characteristic arc radiation and as a result on the ozone formation.

To date, several numerical models representing the tungsten inert gas (TIG) arc are available. However, little has been done on testing the reliability of these models for parameter values differing from the ones used in the respective papers. This paper deals with the comparison of measured arc welding data provided by E. Siewert from Linde AG and the results of the two most common arc and cathode sheath models. These models make different degrees of simplification of the actual processes in the arc, especially the cathode sheath. Different shapes of the electrodes, different welding currents and shielding gases are taken into account as well as the resolution of the numerical grid on which the calculations are carried out. The findings of this paper are used to show when a simplified approach still leads to valid results and when more sophisticated models have to be used.

The use and development of diagnostics for thermal plasmas is motivated by the industrial importance of thermal plasma applications like welding, cutting or thermal spraying. While the physical fundamentals of plasma diagnostics were introduced decades ago new technologies allow to perform a more detailed analysis of the mentioned applications with increased spatial and temporal resolution, enabling the investigation of complex processes thereby moving the focus from pure plasma to plasma-material diagnostics. An attempt is made to demonstrate current and future possibilities provided by technical progress using "old physics" with the help of few examples. The examples introduced here focus mostly on welding applications and include the use of high-speed cameras for the spectrally resolved analysis of plasma radiation and two-color pyrometry. In addition the use of Thomson scattering in gas metal arc welding is proposed as well as the use of magnetic field measurements for non-intrusive current density measurements.

Gas flows in and around welding arcs have a strong influence on the welding process. Atmospheric gases reach the arc due to turbulences and diffusion mechanisms and this affects the arc and the weld pool. Using optical analysis of the gas flow during welding with and without the arc present reveals possible mixing and thus the causes of contamination can be determined. The Schlieren method offers a simple way to do this. In this paper, the setup of a Schlieren measuring system and the influence of the most relevant setting parameters are described as well as their influence on the Schlieren images.

The diagnostic of thermal plasmas is the main source of knowledge about technological applications like welding, cutting or thermal spray and is an enabling technology for the development and use of numerical simulation. Numerous analytical systems have been developed and applied to determine parameters like particle density, temperature or electrode behaviour. With the advent of new challenges especially due to advances in materials science innovative diagnostic systems are needed to determine phenomena like transient plasma behaviour or electrode phenomena especially in non-rotationally symmetric systems or during interaction with materials immersed inside the plasma. Fast system are introduced in this paper enabling the determination of temperatures, densities or plasma-conductor interaction involving the use of high-speed cameras employing spectrally resolved imaging to provide temporally resolved information about transient plasma processes.

The metal transfer is a fundamental process in gas metal arc welding, which substantially determines the shape of the weld seam and strongly influences arc formation and stability. In this investigation the material transfer from the wire electrode (anode) to the workpiece (cathode) is analysed experimentally with high accuracy using various innovative diagnostic techniques for a pulsed gas metal arc welding (PGMAW) process. A high-speed two-colour pyrometer, a calorimeter, thermocouples, a stereo optical setup and a droplet oscillation technique are used to analyse a precisely defined PGMAW process. Thus, results obtained are verified by different measurement techniques and enable a comprehensive description of the material transfer procedure. The surface temperature of both electrodes as well as the droplet temperature, enthalpy and surface tension were determined. Furthermore, the geometry of the arc, wire, droplets and weld pool were extracted in three dimensions in order to describe the interaction between the material transfer and the formation of the weld seam. The experiments are performed using argon as shielding gas and pure iron as filler and base material to reduce complex chemical processes. It turned out that the wire feed rate has the biggest influence on droplet temperature and detachment. A correlation between weld pool formation and weld pool surface temperature gradient was observed, which is mainly a function of welding speed and wire feed rate. The experimental results obtained provide a detailed data pool for use in modelling.

Summary form only given. The gas metal arc welding (GMAW) process is widely used due to its universal applicability, high deposition rate and automatic feeding of the filler material. However, in order to perform process optimization and further develop this welding technique a better understanding of the complex physical and chemical transactions is required. More thorough investigation is needed, in particular to describe the droplet formation, the detachment of the droplets and the interaction of the material transfer with the weld seam formation. Numerical simulation could provide new possibilities for process understanding and development. Unfortunately important thermophysical parameters are still missing to develop and validate accurate models. Such parameters are the geometry, temperature, viscosity and surface tension of the droplet and the weld pool as a function of the filler and base material, shielding gases and welding parameters. In previous diagnostic investigations mostly only one of these quantities was measured. Due to different types of welding processes and process settings, a comprehensive description on the basis of several diagnostic studies is not given. Sensitive analyses e.g. of the influence of the wire feed rate or the gas composition are almost completely missing.

In this paper, we present an adaptation of a drop oscillation technique that enables in situ measurements of thermophysical properties of an industrial pulsed gas metal arc welding (GMAW) process. Surface tension, viscosity, density and temperature were derived expanding the portfolio of existing methods and previously published measurements of surface tension in pulsed GMAW. Natural oscillations of pure liquid iron droplets are recorded during the material transfer with a high-speed camera. Frame rates up to 30 000 fps were utilized to visualize iron droplet oscillations which were in the low kHz range. Image processing algorithms were employed for edge contour extraction of the droplets and to derive parameters such as oscillation frequencies and damping rates along different dimensions of the droplet. Accurate surface tension measurements were achieved incorporating the effect of temperature on density. These are compared with a second method that has been developed to accurately determine the mass of droplets produced during the GMAW process which enables precise surface tension measurements with accuracies up to 1% and permits the study of thermophysical properties also for metals whose density highly depends on temperature. Thermophysical properties of pure liquid iron droplets formed by a wire with 1.2 mm diameter were investigated in a pulsed GMAW process with a base current of 100 A and a pulse current of 600 A. Surface tension and viscosity of a sample droplet were 1.83 +/- 0.02Nm(-1) and 2.9 +/- 0.3mPa s, respectively. The corresponding droplet temperature and density are 2040 +/- 50K and 6830 +/- 50 kgm(-3), respectively.