2018 Volume 36 Issue 1 Pages 39-48
Recently, many studies have reported the distribution of temperature and metal vapor concentration in MIG arc plasma by the optical emission spectroscopy. However, these studies required the assumption of axial symmetry of the plasma. Most of MIG welding phenomena are not axially symmetric, therefore, a tomographic approach is required. In this study, we constructed the simultaneous and multidirectional measurement system by 12 detectors to measure 3D distribution of temperature and iron vapor concentration. The detectors consisted of the CCD cameras equipped with the interference filters, which acquired the spectral line intensities for one Ar I line and two Fe I lines. Each spectral line intensity was laterally integrated with 4 directions and converted into 3D distribution by image reconstruction method. In metal plasma region, we used the relative intensity method for temperature and Saha equation for iron vapor concentration. In Ar plasma region, temperature were calculated by using absolute intensity calibration. We measured MIG arc plasma in globular, globular to spray, and spray transfer mode. As a result, increasing welding current caused the enlargement of high iron vapor concentration region and the expansion of high temperature region of the outer arc plasma. It was found that there was large deviation of Ar plasma region although Fe plasma still exits near the center of arc axis and symmetrical arc plasma were captured by one-side measurement. In addition, this state has a possibility to be measured as a symmetrical-like state by one-side measurement.