Materials and Melt Pool Characterization During Selective Laser Melting Through a Scanning Modulated Laser

A novel technique to measure thermal properties during selective laser melting will be presented. This is achieved by modulating the energy source periodically and measuring the transient temperature response that allows detection of certain defects. This technique has an additional benefit of providing time dependent thermal conductivity information which relates to microstructure and material properties. The measurement heating frequency can limit the thermal interrogation depth, and so is relatively insensitive to geometry compared to conventional thermography. To demonstrate this work, we built a benchtop printer that uses a blue laser as a melting and thermal interrogation source. The temperature oscillations are measured by a photodiode connected to a lock-in amplifier. By altering the frequency range, different depths into the print can be assessed, yielding insight into the microstructure via the thermal characteristics of the materials. Applications to powder properties, melt pool, and post-printed sensing and validation experiments will be discussed.