Mitigating voids in AM: re-melt and parameter adjustment strategies

Laser powder bed fusion (PBF-LB) additive manufacturing (AM) enables production of complex metal parts. The PBF-LB process is, however, prone to the formation of voids, that can compromise the mechanical properties of the final product. Advancements to in-situ sensing and data processing enables the detection of void formation mid-process. If sensing data can be processed efficiently and in real-time, there is the possibility to mitigate voids in-situ, without relying on post-process methods, such as hot isostatic pressing (HIP). Mitigating defects in-situ reduces energy and material expense, limits the need for post-processing, and improves process reliability and consistency. This study investigates two in-situ strategies for targeted void mitigation in PBF-LB of Ti-6Al-4V: (1) targeted intralayer re-melt mitigation (TIRM, re-processing void regions before powder recoating) and (2) targeted interlayer parameter adjustment (TIPA, adjusting the laser power when processing in the void region on the subsequent layer after a void). For each mitigation strategy, the size of the mitigation area relative to the size of the void and the laser power used for mitigation were varied. To systematically assess mitigation success, surrogate voids were programmatically induced during part fabrication at known locations by decreasing the laser power when processing within predetermined regions over sequential layers. This work provides insight into the proper mitigation parameters to effectively heal voids and understanding into the limits of in-situ void mitigation. For both mitigation strategies, optimal mitigation parameters resulted in complete elimination of voids or a significant reduction in void volume. These results indicate that voids detected during PBF-LB AM can be reduced in volume or eliminated in-situ.