Thermocouple Process Monitoring for Additive Manufacturing

To understand the thermal history of parts manufactured in a laser powder bed fusion system, eight thermocouple sensors were imbedded at key locations with respect to the parts being built. The design comprised eight vertical cylinders 2.54 cm (1 in.) and 1.27 cm (0.5 in.) in diameter and four 2.54 cm (1 in.) horizontal cylinders. The temperature signature collected at the eight locations reveals the time intervals of depositing and melting each layer and the cooling trend associated with the stoppage required for filter cleaning. The temperature profile also reveals a fast rate of heat accumulation at the start of the process. As more layers are melted and the part becomes taller, the dissipation path for heat deposited by the laser increases prior to reaching the build plate. The heat accumulation, therefore, increases rapidly at first, then decreases, plateaus, and then drops slightly toward the end. Distortions due to residual stresses and resultant part separation from the build plate can be deduced from the thermal signature as detected by the thermocouple sensors. This allows the manufacturer to make adjustments or abort the process if necessary. Otherwise, these distortions that render the part a reject are discovered hours or days later upon completion of the additively manufactured part.