PROCESS CONTROL AND DEFECTS IN Ti-6Al-4V ADDITIVE MANUFACTURING, USING PLASMA TRANSFERRED ARC (PTA) TECHNIQUES

Defects during Plasma Transfer Arc (PTA) beam fusion additive manufacturing (AM) processing of Ti-6Al-4V, including lack of fusion, porosity variations, and solidification cracking, have been monitored using near infrared (1.62 μm) imagery at 300 Hz, 300 μm spatial resolution and melt pool sizes of greater than 12μ. The temperature evolution exhibits a periodic temperature modulation of more than 300 K, correlated with the scan rate reflecting several phenomena: (1) variations in plate translation speed and arc dwell time, (2) non-uniform, patterned substrate features, (3) heat transfer variation near the ends of the substrate, and (4) changes in plasma conditions as the arc approaches or surpasses the end of the substrate. Melt pool temperatures reveal differences in thermal conduction associated with subsurface or prior deposit layer structures. With these new monitoring capabilities, coupled with closed loop insitu feedback control provides manufacturing complex geometries with known microstructures, potentially void free, functionally graded materials, and selective reinforcement of metal structures appears likely.