Advanced Thermal Imaging Sensors for Monitoring the Laser Powder Bed Fusion Processes

Advanced thermal imaging sensors have been developed to examine melt pool metrics for monitoring the laser powder bed fusion process. A Design of Experiments, DOE, was developed with major process parameters as variables, including laser power, scan velocity and hatch spacing. Thermal monitoring utilized both ThermaViz and spectral sensors. ThermaViz measures a true temperature by two wavelength imaging pyrometry. Spectral sensing provides temperature using full spectrum calibration with Planck based analysis. Both sensors utilize thermal calibration with a blackbody radiator linked to Planck based analysis. The ThermaViz sensor provides a high spatial resolution, 30 micron, image of the melt pool using fast exposures, 10-100 microseconds, and high frame rates, 100-4000 Hz. The Spectral sensor collects melt pool radiation from a larger diameter region, 25 mm, with wavelength resolution of about 1 nm, spanning from 400 to 1000 nm. The DOE spanned laser powers from 100 to 400 watts, scan velocities from 500 to 4000 millimeters per second and hatch spacings of 80 to 100 microns. The test article was a square cube with 1 x 1 cm dimensions and was built using 718 Plus powder. Thermal and dimensional metrics are derived from both sensors and compared with porosity data from the test articles. Sensors have demonstrated that the melt pool temperatures are very close or up to the boiling point of the material. Sensor measurements can be used to monitor the process and enunciate if and or when the process deviates from the set conditions, as well as possibly anomalous behavior of the melt due to the randomness of the powder spreading and resulting powder coverage over the part.