Acoustic monitoring for additive manufacturing process and material condition determination

Process monitoring in additive manufacturing can be achieved in a number of ways, including integrated sensors, machine parameter logging, and passive external sensors. Ensuring consistent quality and the needed process control remains a challenge for additive manufacturing, particularly for emerging additive methods and materials that require process validation and final part quality assurance. Monitoring acoustic signatures during a manufacturing process has been successfully applied in a number of processes including cutting, milling, laser processing, and to a lesser extent, additive manufacturing. Results from a proof-of-concept study for on-line real-time acoustic monitoring of a directed energy deposition (DED) process will be reported which demonstrates that signatures can be correlated with machine, process, and fabricated material state. Process noise from machine vibrations, material delivery. and heat sources can all contribute to the acoustic signatures which are related to the process state. The experimental data for process state determination and acoustic signature correlation with defects for a DED additive manufacturing process were obtained using commercially available acoustic emission sensors and a passive monitoring technique. Signal processing applied to acoustic signatures taken during deposition in a DED process are also shown to correlate well with discrete defects associated with crack initiation during deposition of dissimilar materials.