Acoustic emission monitoring of multi-phase fluid flow in laser-engineered net shaping process (LENS)

Advisors: Federico Sciammarella.Committee members: Matthew Gonser; Abhijit Gupta.The Laser Engineered Net Shaping (LENS) Process uses an argon stream to direct metallic particulates at a molten pool created by a high-power Yb-fiber laser. The LENS process uses numerical control (NC) to manipulate the laser beam heat source in 3-dimensional space so parts can be built additively, layer-by-layer. The metal powder that is carried by the stream of argon gas creates a two-phase fluid, which can make measurement of mass flow rate difficult using conventional sensors. Maintaining a specified mass flow rate is essential in the quality control of this additive manufacturing process. An alternative device, an acoustic emission (AE) sensor, is proposed to monitor the rate of the metal powder flowing through the machine's nozzles. Pressure waves are created by the collisions of the powder with one another as well as the walls of the channel. This pressure is transduced by the piezo-electric element in the base of the AE sensor into electro-motive force. A mount was designed and created to facilitate non-intrusive flow monitoring using AE. The actual mass is monitored using a scale and a powder capture apparatus. The real mass over time and the RMS of the AE signal are compared and found to correlate closely. The system will be implemented in Optomec's LENS 850-M machine in order to provide feedback to the machine's operator regarding the condition of the powder delivery system. The relationship between the AE RMS and the actual flow rate will be characterized and used to estimate the actual flow using only AE. Further research is conducted on the frequency spectrum of the AE waveform, and a control system will be proposed.M.S. (Master of Science