Off-axis optical system for the monitoring of the Laser Metal Deposition process

The Laser Metal Deposition (LMD) is emerging among the additive manufacturing (AM) technologies of metals for its versatility. It takes advantage of the flexibility of a laser source and a powder flow to fabricate or repair components with very complex features. The challenging process conditions that characterize the processing of metallic materials (temperatures and stresses) underlie the occurrence of several defects that plague such AM processes. Thus, the necessity to develop monitoring systems that can comprehensively analyze the production phase arises. In the present work, an innovative off-axis optical system consisting of three cameras with appropriate filters is proposed for the monitoring of LMD process. The peculiarity of this system lies in the capability of monitoring the spatial evolution of the melt pool, enabling eventually a complete control of the deposition process. In fact, through the use of properly developed image processing algorithms, the system enables the tridimensional definition of the size and shape of the melt pool and at the same time the reconstruction of each deposited layer. The potential of the monitoring system was tested on a series of thin-walled components. Subsequently, the analysis results were validated by comparison with 3D scanning of the parts and analyses performed using a coaxial monitoring system.