Development of a monitoring device based on the thermal emission in laser direct metal deposition

Laser Direct Metal Deposition (LDMD) is an additive technology based on the continuous material feeding mechanism. The material is progressively melted with the aid of laser and, layer after layer, is aggregated in order to obtain 3D complex components. Due to the numerous advantages this new approach to building objects is showing, the technology is becoming widely used for a wide range of applications such as Aerospace, Automotive and motorsports, Oil & Gas, Military, Medical and Jewelry. However, the complexity of the overall process, and the need for cross-disciplinary competences, requires the development of new scientific works which touch upon most of the aspects this technology deals with. In order to better understand the overall deposition process, its monitoring represents one of the main targets. The response variables which could be monitored are different. However, monitoring the thermal emission of the process represents one of the most promising responses, as the mechanical proprieties of the material (and thus its metallurgy and the morphology of the deposited layer) are connected to this. This work represents the development of a monitoring and control device based on the multimode fiber laser architecture. The design of the monitoring and control device is based on Planck’s emission law, and the developed system is compared with other temperature measurement instruments such as thermal camera and thermocouples. The signals deriving from the different instruments show good agreement with each other, as well as correlation with the morphology of the deposited layer. Information deriving from the designed monitoring device is firstly used to understand and select proper process parameters during the deposition of AISI 316, and later to used improve the uniformity of the deposition using it as input for closed loop control over the laser power.