Fusaki Koshiishi

Plasma properties of helium gas tungsten arc with metal vapour

Abstract The energy source characteristics of gas tungsten arc (GTA) strongly depend on the physical property of arc plasma. In welding processes, it has been experimentally confirmed that metal vapour evaporated from a high temperature weld pool drastically changes the property of arc plasma and decreases its temperature. However, the effect of metal vapour on the characteristics of heat flux into a base metal is still not clear owing to the difficulty in experimental studies of arc plasma. In the present paper, the energy source property of helium GTA mixed with metal vapour was numerically analysed. It was found that the intense radiation generated from dense metal vapour decreases heat flux into a base metal and contracts the current density distribution especially near the arc axis.

The Measurement of Metal Droplet Temperature in GMA Welding by Infrared Two-Color Pyrometry

The temperature of metal droplets is essential for clarifying the phenomenon of metal droplet transfer and the melting behaviour of wire; also, it governs the emission of fumes. On the other hand, in situ measurement of the temperature of a metal droplet formed at the tip of a wire during welding was difficult. Hence, this temperature was obtained in many experiences of measurements by such a way that several numbers of metal droplets were collected in a calorimeter to measure the amount of heat content of metal droplet and the heat was converted to temperature. With this way, however, the reliability of the measurement is not necessarily high because the heat loss of the metal droplet during the time when detaching from the wire tip and entering into the calorimeter has to be estimated properly. In this research, two-colour pyrometry has been conducted to obtain the temperature of metal droplets, in which metal droplets have been photographed by a high-speed camera during arc welding, two wavelengths (950 and 980 nm) of light in the infrared range have been selected from the thermal radiation light emitted from the metal droplet at the instant of arc extinguishment by using an imaging spectroscope, and the temperature has been obtained from the intensity ratio of the two waves of light. Consequently, in CO2 arc welding, it has been revealed that the constricted arc causes high-heat input density locally at the arc root portion of a metal droplet and thereby the arc root portion exhibits a higher temperature. By contrast, in MAG (80% Ar–20% CO2) arc welding, it has been disclosed that because the arc covers metal droplets, the temperature distribution in a metal droplet is relatively uniform and the average temperature is lower than in CO2 arc welding.

Measurement of surface temperature of weld pools by infrared two colour pyrometry

Abstract In this research, two colour pyrometry was conducted to obtain the surface temperature of weld pools, in which the weld pool was photographed by a high speed camera during arc welding. Two wavelengths (950 and 980 nm) of light in the infrared range were selected from the thermal radiation light emitted from the weld pool at the instant when the arc was extinguished, using an imaging spectroscope. Consequently, in gas tungsten arc welding, it was shown that the surface temperature distribution of a weld pool is affected by the sulphur content in the base metal. It is thought that this temperature distribution is determined by the balance between the driving forces of viscous drag from the cathode jet of plasma and Marangoni surface tension. In gas metal arc welding, it was seen that the surface temperature distribution becomes uniform and the temperature is 1715–1845 K, which is obviously lower than that of the metal droplet.

Spatter And Fume Reduction In Co2 Gas- Shielded Arc Welding By Regulated Globular Transfer

The CO2 gas-shielded arc welding process with solid wire is widely used in Japan due to its good weld quality, high efficiency and reasonable wire and shielding gas costs. However, this process has its drawbacks, especially in the globular transfer mode at a high welding current, where significant amounts of spatter and fume are generated. To solve this problem, the author has investigated how to control globular transfer with a special pulsed current and has developed a regulated method and power source for practical use. The present report discusses the mechanism of this new method of regulating the globular transfer of molten droplets, in which each droplet is squeezed at its upper part in peak current duration and is detached silently in base current duration. Also various effects are reported concerning this new method and its application in the welding robot system for fabricating steel frames for buildings.

Study of spatter reduction in pulsed CO2 shielded arc welding

Summary Spatter reduction in pulsed CO2 shielded arc welding is studied with special reference to rectangular pulsed waveform control and the chemical composition of the welding wire. The spatter affecting pulsed CO2 shielded arc welding is mainly due to the molten droplet on the welding wire being blown off by the arc repulsive force at peak current. Droplet blowoff depends on the up-slope of the peak current, and a rapid up-slope causes heavy spatter to increase. Droplet blowoff is also affected by the deoxidising elements. An increased content of deoxidising elements (Al, Ti, Si) in the chemical composition of the welding wire greatly reduces weldpool spatter and droplet necking. Any excess content of deoxidising elements, however, upsets the stability of one pulse one drop transfer, and the molten droplet is blown off at the peak current. When waveform control and the content of deoxidising elements in the welding wire are optimised, the amount of spatter can be reduced to 1/6th of that found in conve...

EFFECT OF FLUX RATIO IN FLUX-CORED WIRE ON WIRE MELTING BEHAVIOUR AND FUME EMISSION RATE

In GMAW, the welding wire melts itself due to the arc discharges from the electrode. Both the Joule heating and the arc heating of the electrode contribute to the melting of the wire. In general, it is said that flux-cored wire (FCW) melts faster than solid wire as the welding current flows mainly through the sheath of the FCW. FCW structure differs from solid wire and these differences affect not only the wire melting behaviour, but also the fume emission rate (FER). However, at present, no report exists which defines these effects in detail. Therefore, it is very important to clarify the effect of these differences in wire structure on the wire melting behaviour and FER in order to understand how to reduce the latter. In this study, we found that FER increased with the flux ratio of FCW. It is assumed that these results can be attributed to the state of the stability of the flux column in the arc and the heat content of the droplets.

Welding materials: an overview

Arc welding is an indispensable technology for the construction of steel-framed buildings, ship building, motor vehicle manufacture, power plants and other industries. Developments in welding processes have continued as part of the efforts to improve the stability of structural members and increase the efficiency of fabrication. Various elements constitute the welding process, depending on the materials being welded, the welding method, the welding power source, the shield gas, etc. The quality of the weldment produced is particularly dependent on the welding materials and improvement in performance is required. In this article, I describe new welding materials that achieve such improvement and outline the problems that need to be solved to achieve further progress in welding process.