Off-axis monitoring of the melt pool spatial information in Laser Metal Deposition process

Laser Metal Deposition (LMD) is one of the most promising Additive Manufacturing (AM) technologies for the fabrication, coating and repair of metal components. Although, due to the high number of factors influencing the process, defects may arise, as geometrical and dimensional inaccuracies, high residual stresses and internal voids, with effects on the quality and the mechanical performances of the produced parts. Thus, the need for in-process monitoring systems capable of timely detecting the onset of defects and process anomalies emerged.

In this work, an in-process monitoring system suitable for LMD was presented. It consisted of an industrial CMOS camera placed in the LMD machine chamber and set for the acquisition of images showing the melt pool area. Through the use of properly developed image processing algorithms, the monitoring system was capable to extract in-process the melt pool 2D spatial coordinates and to depict the geometry of the fabricated samples. Moreover, specific indexes related to the deposited height were computed in order to evaluate the quality of the process/product. The potentiality of such monitoring method lies in the simplicity of the equipment, and, mostly, in the possibility of monitoring the spatial evolution of the melt pool without interrupting the process and enabling, eventually, a further control of the LMD process. The monitoring system was tested on two 316L thin-walled components and results were validated by comparing the data obtained from the monitoring with a consolidated post-process 3D scanning method.