Arc welding

About: Arc welding is a research topic. Over the lifetime, 25393 publications have been published within this topic receiving 168182 citations.

Thermal plasma properties for Ar–Al, Ar–Fe and Ar–Cu mixtures used in welding plasmas processes: I. Net emission coefficients at atmospheric pressure

Abstract: This article is devoted to the calculation of the net emission coefficient (NEC) of Ar?Al, Ar?Fe and Ar?Cu mixtures at atmospheric pressure for arc welding processes. The results are given in data tables for temperatures between 3?kK and 30?kK, for five plasma thicknesses (0, 0.5, 1, 2, 5?mm) and ten concentrations of metallic vapours (pure gas, 0.01%, 0.1%, 1%, 5%, 10%, 25%, 50%, 75% and pure metal vapours in mass proportions). The results are in good agreement with most of the works published on the subject for such mixtures. They highlight the influence of three parameters on the radiation of the plasma: the NEC is directly related to temperature and inversely related to plasma radius and is highly sensitive to the presence of metal vapours. Finally, numerical data are supplied in tables in order to develop accurate computational modelling of welding arc and to estimate both qualitatively and quantitatively the influence of each metallic vapour on the size and on the shape of the weld pool.

Laser stabilisation of arc cathode spots in titanium welding

Abstract: Cathode spot formation is very pronounced during arc welding of titanium and titanium alloys. The dynamic behaviour of these spots was observed to interfere with metal transfer during welding, this interference being a fundamental cause of poor weld quality in these alloys. In the present work, stabilisation of the arc cathode spot with a focused Nd–YAG laser beam during pulsed gas metal arc welding of titanium was investigated. The laser beam was focused near the leading edge of the weld pool and the laser power and focus spot size were varied to determine the values required to confine the cathode spot to the laser focus position. The results showed that, for fixed welding conditions, the laser power required to prevent cathode spot motion varied as a function of focus spot size. The required laser power was minimised at 200 W for a spot size of 0.6 mm. The laser stabilised arcs had lower voltage but approximately the same current density as stabilised arcs. Increased welding speeds required mar...

Mechanism of ripple formation during weld solidification

Abstract: The formation of ripples on the surfaces of GTA spot and seam weld surfaces in thin metal sheet was investigated by high speed motion pictures. The ripples are observed to form solely due to oscillation of the weld pool during solidification; no other mechanism for ripple formation was found. Weld pools were melted through thin metal sheets while a high speed camera observed the melting and solidification events on the bottom surface of the pool opposite the arc. When welding power is supplied from storage batteries, the weld pool surface shows virtually no oscillation while the arc is on. Shutting off of this arc suddenly releases the plasma pressure which was stretching the pool surfaces, setting the pool into oscillation like a struck drumskin. Solidification during this oscillation results in rippled surfaces. When a single phase full-wave rectified conventional dc welding power supply is used, the pool surface is observed to oscillate at 120 hertz. When this arc is shut off, the pool changes oscillation frequency in a fraction of a second from the frequency imposed by the pulsating plasma pressure to its own natural frequency. Pool oscillation periods after the arc is shut off are measured on the film strips. If the pool is considered to be a stretched membrane with surface tension providing the stretching force, a theoretical surface tension can be calculated from the oscillation period, pool mass and pool geometry. Agreement of the calculated surface tension values with published surface tension values for several metals demonstrates that the stretched membrane model adequately describes the pool oscillations. By counting the number of pool oscillations in the films and counting the number of ripples on solidified spot welds afterwards, a one-to-one correlation is established between ripples and pool oscillations. When a seam weld is made using storage batteries as the welding random disturbances of the pool surface are observed. Each disturbance leaves a few ripples before it damps out.

Variable polarity plasma arc welding on the Space Shuttle external tank

Abstract: Variable polarity plasma arc (VPPA) techniques used at NASA's Marshall Space Flight Center for the fabrication of the Space Shuttle External Tank are presentedd. The high plasma arc jet velocities of 300-2000 m/s are produced by heating the plasma gas as it passes through a constraining orifice, with the plasma arc torch becoming a miniature jet engine. As compared to the GTA jet, the VPPA has the following advantages: (1) less sensitive to contamination, (2) a more symmetrical fusion zone, and (3) greater joint penetration. The VPPA welding system is computerized, operating with a microprocessor, to set welding variables in accordance with set points inputs, including the manipulator and wire feeder, as well as torch control and power supply. Some other VPPA welding technique advantages are: reduction in weld repair costs by elimination of porosity; reduction of joint preparation costs through elimination of the need to scrape or file faying surfaces; reduction in depeaking costs; eventual reduction of the 100 percent-X-ray inspection requirements. The paper includes a series of schematic and block diagrams.

Method for operation of a welding unit welding unit and welding torch for such a welding unit

Abstract: The invention relates to a method for operation of a welding unit (1), for the execution of welding processes with a welding device (2) and a welding torch (10), whereby operational states for the welding processes are recorded and, depending on the operational state, vibrations which may be felt are generated and a welding unit (1) and a welding torch (10), for carrying out said method. According to the invention, the possibility of providing feedback about particular operational states to people involved in the welding process, in particular, the welder, without the same having to look away from the welding spot or the arc (15) may be achieved, whereby, in particular, the welding current (I) or the welding voltage (V) are modulated, depending on the operational state, to generate acoustic vibrations in the arc occurring during welding, or, depending on the operational state, mechanical vibrations are generated. The vibrations can also be felt by the welder without looking away from welding spot or the arc (15).