In-situ Droplet Inspection and Control System for Liquid Metal Jet 3D Printing Process

Liquid Metal Jet Printing (LMJP) is a revolutionary 3D printing technique in fast but low-cost additive manufacturing. The driving force is produced by magneto-hydrodynamic property of liquid metal in an alternating magnetic field. Due to its integrated melting and inkjeting process, it can achieve 10x faster at 1/10th of the cost as compared to current metal 3D printing techniques. However, the jetting process may be influenced by many uncertain factors, which imposes a significant challenge to its process stability and product quality. To address this challenge, we present a closed-loop control mechanism using vision technique to inspect droplet behaviours. This system automatically tunes the drive voltage applied to compensate the uncertain influence based on vision inspection result. To realize this, we first extract multiple features and properties from both frozen and dynamic images to capture the droplet behaviour. Second, we use a voting-based decision making technique to determine how the drive voltage should be adjusted. We test this system on a piezoelectric-based inkjeting emulator, which has very similar jetting mechanism to the LMJP. Results show that significantly more stable jetting behaviour can be obtained in real-time. This system can also be applied to other droplet related applications due to its universally applicable characteristics.