Toward In-Situ Sensing of Powder Bed Packing Density in Metal Binder Jetting via Recoating-Force and Acoustic Signals: A Comparison

Metal binder jetting (MBJ) is an additive manufacturing (AM) process that offers advantages such as high speed, low cost, and low residual stress, compared to the prevalent fusion-based metal AM methods. However, a major barrier to MBJ is the low density of manufactured parts, which restricts part quality and limits its applications. One key process parameter that affects part density is the packing density of the powder bed. In general, a higher packing density is preferable in MBJ. Although research has been conducted to enhance the packing density ex-situ, most proposed approaches lack robustness when applied to real-world printing, where environmental variations and stochastic powder behavior introduce inconsistencies. An in-situ sensing method for packing density can mitigate these issues in several ways. It enables the implementation of feedback control strategies to regulate packing density during printing, contributes to comprehensive in-situ process monitoring, and provides quantitative data to support post-processing analysis and optimization. However, effective in-situ methods for accurately sensing packing density remain limited. To fill this research gap, two methods, namely ultrasound (acoustic) and recoating-force sensing, are proposed as potential approaches for in-situ sensing of powder packing density. Using a dedicated test platform, their responses to different powder bed packing densities are measured and compared. The results show a strong correlation between packing density and the sensor measurements, with differing levels of estimation confidence, demonstrating promising potential for their implementation as in-situ packing density sensors. Furthermore, the concept of sensor fusion is tested by combining the force-sensing and acoustic-sensing data, leading to improvements in the estimation confidence.