3D measurement of temperature and metal vapor concentration in MIG arc plasma using a multidirectional spectroscopic method

Abstract

Tweetable abstract3D measurement for MIG arc plasma was developed with 12 cameras equipped with 3 types of interference filters.Spectroscopic measurements for metal inert gas (MIG) arc plasma have been recently performed. The studies have reported that the central core of the MIG arc has low temperature owing to the high radiation loss of iron vapor. In these studies, it was assumed that the MIG arc phenomenon is axially symmetric because of the measurement method using Abel inversion. GMA welding, including MIG arc welding, is normally performed with a travel speed and most of the phenomena become axially asymmetric. Tomographic measurement is required to obtain the internal emission intensity distribution of axially asymmetric phenomena. This study reports on a multi-directional and heterochromatic measurement system that can capture such axially asymmetric plasma. The proposed system is composed of 12 CCD cameras with three types of narrowband interference filters (one Ar I line and two Fe I lines). Each line intensity distribution was obtained using an image reconstruction method. We converted the line intensities into plasma temperature and iron vapor concentration by using the relative intensity method, absolute sensitive calculation, and solving the Saha equation under the LTE assumption. We measured a pulsed MIG welding process and observed that the temperature of the central area of the MIG arc plasma was lower than the outer area, as shown in recent conventional studies. We found such temperature and iron vapor distributions were drawn backwards along the welding line, and the time variation of the iron vapor concentration corresponded to the current pulse shape. We achieved the 3D measurement of the MIG arc through error estimation and comparison with the previous 2D studies.