A study on spectral characterization and quality detection of direct metal deposition process based on spectral diagnosis

In the process of laser additive manufacturing, the transmission efficiency of laser energy and the forming quality are influenced by the plasma which plays a fundamental role in coupling the incident radiation to the material. The aim of this work is to present an effective spectral diagnosis method for quality research in laser additive manufacturing. A spectrum acquisition system for direct metal deposition (DMD) was established by using fiber optic spectrometer to collect the radiation during the forming process under different process parameters. The relationships between laser powers, powder feeding rate, traverse speed, and the radiation intensity of the plasma were found. Meanwhile, special wavelengths were chosen to establish the time-domain diagram (the relationship between the intensity and time) corresponding to the process, and some forming defects caused by the changes of processing parameters were correlated with the spectral information. What is more, to diagnose the defects automatically, statistical process control (SPC) method was used to analyze the correlations between intensity fluctuation and the forming defects. The findings of the paper will be helpful to understand the formative mechanism and influencing factors of laser-induced plasma during laser additive manufacturing and lay the foundations for automatic quality control of laser additive manufacturing process.