Online monitoring of an additive manufacturing environment using a time-of-flight mass spectrometer

Abstract

Laser-based Directed Energy Deposition (L-DED) is a promising additive manufacturing technology, which has broad application prospects and practical value in many fields. The nondestructive testing technology of L-DED work piece quality monitoring requires high accuracy and capability for real-time process. This work developed an online monitoring system based on a miniature electron impact ion source time-of-flight mass spectrometer (EI-TOF) and a high-speed camera, which monitored the atmosphere above the molten pool area. The number of spatters was measured using a high-speed camera. The composition of the samples and spatters was measured by using element analyzer, inductively coupled plasma mass spectrometry, and electron spectroscopy. The variation in the atmosphere was measured using EI-TOF, and the results confirmed that the O2, N2 and H2O content decreased during the L-DED process. At the laser power of 400 W, the oxygen consumptions were 92.5% and 86.4% compared with those at the laser power of 500 W and 600 W, respectively. During the L-DED process, the number of spatters decreased when the laser power was increased from 400 W to 600 W. And at the laser power of 600 W, the average number of spatters was reduced to 59.3% compared with the laser power of 400 W. It can be found that dust contained a large amount of virgin powder and little spatters. It also can be found that at the laser power of 400 W, 500 W and 600 W, the amount of oxygen in the dust was 0.544%, 0.242% and 0.159%, respectively. The relative content of oxygen in the cross section of the seam was 35.58%, 43.79% and 44.30%, respectively. The deviation of the monitoring results (H2O, N2, O2) are significant at the same power when different materials was used as the substrate.