3D printing metals has been pretty much experimental up until recently. The challenges presented by the very high operating temperatures, relative to 3D printing polymers, have been significant for quality, printing time and cost. The typical applications for 3D printed metal parts (e.g. aerospace) are usually technically demanding too, requiring strict quality assurance. GE appear to be this addressing this thorny issue by patenting a technology for monitoring the metallurgical quality of parts using an acoustic technique during the printing process. You can read more about it here.