Investigation of Direct Metal Deposition Processes Using High-Resolution In-line Atomic Emission Spectroscopy

Abstract

AbstractProcess monitoring and control methods during direct metal deposition (DMD) ensure consistent manufacturing quality of the product. Naturally occurring optical process emissions provide selective and specific element lines, which can be investigated by optical spectrometers. However, DMD processes are mainly characterized by thermal conduction. Hence, the resulting optical emission lines have low intensities. The aim of this work is to investigate the spectral lines and determine the required resolution of the spectrometer. Two spectrometers coupled by a bifurcated optical fiber were used simultaneously (resolution = approx. 47 pm FWHM at 522 nm and 55 pm FWHM at 407.5 nm and resolution = 0.73 nm FWHM). A parameter study with varying process parameters using Co-Cr-based (MetcoClad21) powder on low-alloyed tool steel C45W (1.1730) substrate material was conducted. Peaks occurring in spectral data were assigned to specific element emission lines by using data from the NIST atomic spectra database. All identified element lines were non-ionized elements. Cr I, Fe I and Mn I lines in particular were frequently observed. The occurrence of element emission lines as well as the peak intensity ratios for specific elements was compared with the cross-sectional dimensions including height, weld depth and dilution. It has been shown that the occurrence and intensity of emission lines correlate with the process parameters, especially the laser power. Furthermore, the dilution of a deposition track correlates with the occurrence and intensity of an identified Fe I emission line, represented by a Fe-Cr peak intensity ratio.