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

Abstract

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.

The effects of metal vapour in arc welding

“…Wilhelm et al [45] investigated GMAW operating in the dip transfer mode. A steel wire, and carbon dioxide and argon-oxygen shielding gases, were used, and the cold metal transfer process was adopted, in which the current was controlled so that it was minimum during the short circuit and rapidly increased after separation of the wire and workpiece.…”

“…It should be noted, however, that the concentration of metal vapour in a stationary arc will tend to increase with time, particularly in the first few tens of seconds after arc initiation, so that the measurement is not steady state. A method adopted [42,[44][45][46] for the case of a moving arc is to measure the emission along the line of motion of the arc. In this case the arc is symmetric in the plane perpendicular to the optical axis.…”

Use of radiative properties to determine temperature and vapours concentration in MAG welding arc (Ar–CO2–Fe plasmas)

“…The iron content under argon shielding gas was also estimated. Wilhelm et al [9] diagnosed the arcs in pure CO 2 and 92%Ar-8%O 2 mixture with a steel wire operating in cold metal transfer (CMT) arc process. The temperature and the iron vapour concentration were determined by the analysis of the line emission coefficients from shielding gas (Ar I or O I) and iron vapour (Fe I).…”

Sterowanie spawarek MIG/MAG

“…Z tego powodu fizycy zajmują się filmowaniem przechodzenia kropli w łuku, pomiarem rozkładu temperatury łuku spawalniczego, ciśnienia łuku, stopnia jonizacji, ilości oparów itd. [1,2]. Z kolei dla technologa istotna jest stabilność procesu i jakość połączenia, a dla energoelektronika i konstruktora urzą-dzeń istotne jest zrozumienie i hierarchiczne poukłada-nie tych spraw.…”

“…Aby ograniczyć niekorzystne narastanie prą-du, w latach 80. zastosowano mechaniczne odrywanie kropli na skutek wibracji uchwytem -"wibrostyk" stosowany do regeneracyjnego napawania wałów autobusów, a współcześnie odciąganie drutu szybkim mikrosilniczkiem (funkcja CMT Fronius, rys. 1b) [2]. Niemiecka firma NWM opracowała tranzystorowe źródło pozwalające obniżyć prąd po rozwarciu do wartości przed zwarciem (funkcja cold arc, rys.…”