Heinz Schöpp

Study of the welding gas influence on a controlled short-arc GMAW process by optical emission spectroscopy

The controlled short-arc processes, variants of the gas metal arc welding (GMAW) process, which have recently been developed, are used to reduce the heat input into the workpiece. Such a process with a wire feeding speed which varies periodically, using a steel wire and a steel workpiece to produce bead-on-plate welds has been investigated. As welding gases CO2 and a mixture of Ar and O2 have been used. Depending on the gas, the properties of the plasma change, and as a consequence the weldseams themselves also differ distinctly. Optical emission spectroscopy has been applied to analyse the plasma. The radial profiles of the emission coefficients of an iron line and an argon line or an atomic oxygen line, respectively, have been determined. These profiles indicate the establishment of a metal vapour arc core which has a broader profile under CO2 but is more focused in the centre for argon. The measured iron line emission was near to its norm maximum in the case of CO2. From this fact, temperatures around 8000 K and a metal vapour molar fraction above 75% in the arc centre could be roughly estimated for this case. Estimations of the electrical conductivity and the arc field indicate that the current path must include not only the metal vapour arc core but also outer hot regions dominated by welding gas properties in the case of argon.

Improvement of the control of a gas metal arc welding process

Up to now, the use of the electrical characteristics for process control is state of the art in gas metal arc welding (GMAW). The aim of the work is the improvement of GMAW processes by using additional information from the arc. Therefore, the emitted light of the arc is analysed spectroscopically and compared with high-speed camera images. With this information, a conclusion about the plasma arc and the droplet formation is reasonable. With the correlation of the spectral and local information of the plasma, a specific control of the power supply can be applied. A corresponding spectral control unit (SCU) is introduced.

Spectral diagnostics of a pulsed gas metal arc welding process

IntroductionPlasma properties in the pulsed arc determine the welding process. They will have influence on the consumable electrode and the weld pool. For that reason, the accurate gauging of the plasma properties is of special importance for deeper understanding of the processes.Material and methodsUsing spectroscopic methods and plasma physical diagnostics, the temperature in the arc during the high-current phase of a pulsed gas metal arc welding process is determined. With this knowledge and composition calculation, the electrical conductivity is also derived. A one-drop-per-pulse process with workpiece and wire made of steel and an argon-dominated shielding gas is considered. Boltzmann plots applied to iron lines, broadening of argon lines or the emission coefficient of optically thin lines are used for the determination of plasma parameters.ResultsIntersections of the arc at different distances from the workpiece are analysed for different times during the pulse. It is observed that the brighter central part of such an arc has a minimum in the temperature profile and contains a high amount of iron.ConclusionConsequently, the central part of the arc has lower electrical conductivity than the outer part dominated by the shielding gas argon.

Temperature profiles of welding arcs and its interpretation

Summary form only given. Pulsed gas metal arc welding is a widespread and established joining technology. Improvements of efficiency and join quality can be obtained by reducing and focusing the heat input into the workpiece. The energy transfer takes place mostly during the high-current arc phase. Its spatial distribution depends on the arc property profiles and those of the arc root at the weld pool surface. Radial temperature profiles of the arc at different distances from the weld pool in the high-current phase of several pulsed gas metal arc welding processes under different shielding gases have been determined by optical emission spectroscopy. In addition, the plasma composition and, in particular, the density profiles of metal vapour in the arc have been deduced. Therefore, the absolutely calibrated spectral radiances of atom lines of metal and shielding gas species have been recorded and analysed over the arc cross section. The arc shape, assumed as nearly rotational symmetric, and its dynamic behaviour during the spectroscopic recording have been controlled by high-speed