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THERMOCOUPLE PROCESS MONITORING FOR ADDITIVE MANUFACTURING BY SHANT KENDERIAN*†, TAIT MCLOUTH*, DHRUV PATEL*, AND JULIAN LOHSER* ABSTR ACT To understand the thermal history of parts manufactured in a laser powder bed fusion system, eight thermocouple sensors were imbedded at key locations with respect to the parts being built. The design comprised eight vertical cylinders 2.54 cm (1 in.) and 1.27 cm (0.5 in.) in diameter and four 2.54 cm (1 in.) horizontal cylinders. The temperature signature collected at the eight locations reveals the time intervals of depositing and melting each layer and the cooling trend associated with the stoppage required for filter cleaning. The temperature profile also reveals a fast rate of heat accumulation at the start of the process. As more layers are melted and the part becomes taller, the dissipation path for heat deposited by the laser increases prior to reaching the build plate. The heat accumulation, therefore, increases rapidly at first, then decreases, plateaus, and then drops slightly toward the end. Distortions due to residual stresses and resultant part separation from the build plate can be deduced from the thermal signature as detected by the thermocouple sensors. This allows the manufacturer to make adjustments or abort the process if necessary. Otherwise, these distortions that render the part a reject are discovered hours or days later upon completion of the additively manufactured part. KEYWORDS: additive manufacturing, process monitoring, thermocouples Introduction With the increased application and acceptance of additively manufactured parts in various industries, including the aero- space industry, a widespread effort has been dedicated toward nondestructive evaluation (NDE) applications for additively manufactured parts during the last decade. Different efforts of NDE techniques have been approached for additively manufactured parts worldwide. The additive manufacturing (AM) process itself went through phases as it was identified first as “3D printing” and “rapid prototyping” before it became known as “additive manufacturing.” However, the strong interest in NDE did not arise until late in 1999 (Griffith et al. 1999 Martinez-Anton et al. 1999). Additionally, although there may have been a number of conference presentations on NDE for AM in the past, the first entire conference session organized by the American Society for Nondestructive Testing (ASNT) on this topic was during the 2016 Annual Conference. Since 2016, there have been one or two sessions held during every ASNT Annual Conference and Research Symposium. In 2018, the European Conference on Nondestructive Testing (ECNDT) organized three sessions on NDE for AM. It is not always easy to determine what should be included in the AM NDE category. For example, it may be argued that post-process NDE on AM parts is nothing more than NDE, if it were not unique to AM. What follows are some observations regarding the NDE efforts that have been reported for AM: Most NDE techniques reported in literature were applied to the part after removal from the AM machine. Therefore, these applications are not used as AM process control, but rather as materials characterization tools to better under- stand the influence of the AM process on materials prop- erties of the product. Some examples to this are computed tomography (CT) (Slotwinski and Garboczi 2014 Smith et al. 2016 Beshears 2017) and neutron radiography (Brooks et al. 2017 Thiede 2018 Bilheux et al. 2016 Rodriguez et al. 2012 Watkins et al. 2013) applications. Some applications are not necessarily “nondestructive” or practical. The micro-CT technique, for example, requires cutting very small coupons from the AM part (Zhou et al. 2015). Some techniques were adapted so that they may potentially be used for AM, such as laser ultrasound (Everton et al. 2015 Cerniglia et al. 2015 Helvajian et al. 2016 Manzo et al. 2016 Klein and Sears 2004 Edwards et al. 2012 Kube 2016). * Space Materials Laboratory, The Aerospace Corp., El Segundo, CA 90245 USA † shant@aero.org Materials Evaluation 80 (4): 30–36 https://doi.org/10.32548/2022.me-04243 ©2022 American Society for Nondestructive Testing ME | TECHPAPER 30 M A T E R I A L S E V A L U A T I O N • A P R I L 2 0 2 2