In situ monitoring of material jetting additive manufacturing process via impedance based measurements

In this paper, the authors explore the use of impedance-based monitoring techniques for in-situ detection of additive manufacturing build defects. By physically coupling a piezoceramic (PZT)sensor to the part being fabricated, the measured electrical impedance of the PZT can be directly linked to the mechanical impedance of the part. It is hypothesized that one can detect build defects in geometry or material properties in-situ by comparing the signatures collected during printing of parts with that of a defect-free control sample. In this paper, the authors explore the layer-to-layer sensitivity for both PZT sensors embedded into printed parts and for a fixture-based PZT sensor. For this work, this concept is evaluated in context of material jetting. A set of control samples is created and used to establish a baseline signature. (e.g., internal voids)are fabricated and their layer-to-layer signatures are compared to a control sample. Using this technique, the authors demonstrate an ability to track print progress and detect defects as they occur. For embedded sensors the defects were detectable at 2.28% of the part volume (95.6 mm³)and by fixture-based sensors when it affected 1.38% of the part volume.