Arc Plasma Temperature Diagnosis Of Pulsed Gas Metal Arc Welding

Pulsed gas metal arc welding (GMAW-P) has been widely used in welding aluminum alloy, copper alloy and other non ferrous metal. Electric arc is the heat source of arc welding. Arc character and temperature distribution play a decisive role in welding input, profile of molten pool, temperature gradient of welding joint and microstructure gradient, and finally influence the mechanical properties of welding joint. Temperature is the most important parameter to describe arc plasma thermodynamic state. There are drastic internal physical and chemical reactions, large temperature gradient and many disturbance factors in small welding arc space, which cause many difficulties for conventional sensor test. With science development, the radiation spectrum of welding arc could reflect temperature change and electron density in arc plasma, which could also be used to characterize the temperature field. Arc radiation spectrum which is used to analyze arc plasma has been widely recognized. Various physical and chemical phenomenon and some important properties and basic process could be better understood by the research on arc plasma temperature distribution, which also provides new method to improve the quality of arc welding.An arc imaging system was set up with double agglutination lens, lens gripper, screen, aperture, slideway and precise mobile platform. And portable spectrograph HR4000CG-UV-NIR was used to acquire arc plasma spectrum information. DC GMAW and GMAW-P arc plasma were studied respectively. Basing on the analysis of the internal element's discrete spectral lines distribution, Argon II spectral lines were used as calculation lines. An inversion Abel transform was achieved by using Bockasten cubic spline interpolation method, which could recover the radiation intensity distribution to emission coefficient distribution. Boltzman method was used to calculate temperature. And comparison of different exposure time diagnosis was carried out in GMAW-P arc plasma diagnosis.The results showed that the arc imaging system is feasible with high time and special resolution. Through diagnosis on DC GMAW arc plasma, the calculation temperature distribution showed that temperature distribution in the axial direction increases from the bottom to top of arc and temperature in radial direction decreases from axis to the edge of the arc. GMAW-P arc plasma, it is periodic changing in spectral information which was consistent with current periodicity. Comparison of different exposure time diagnosis of GMAW-P showed that the difference of two different exposure time were not very much due to the window width restriction of spectrometer, arc plasma's randomness and thermal inertia.