On the potential of ultrasonic time of flight instrumentation for the monitoring of thermal phenomena in laser powder bed fusion

The present paper describes a proof of concept showing the ability of ultrasound time of flight measurements to complement existing temperature measurements in a laser powder bed fusion additive manufacturing process. To this end, two printers (a 3D Systems ProX DMP 320 and a Farsoon FS 271M) were instrumented with ultrasonic transducers, as well as with thermal cameras and thermocouples. The obtained results show that the time of flight signals can provide information that is both consistent and complementary with the data from the standard thermal camera and thermocouple systems. Such a conclusion is shown to be valid at both the macroscopic (i.e., whole fabrication) and the microscopic (individual layer melting and solidification) time scales. The present work shows that ultrasound time of flight data are a useful in situ diagnostic measurement. In addition, we discuss how it could be used for the validation of layer scale numerical models of the thermal phenomena during the printing process.