Keyhole pores reduction in laser powder bed fusion additive manufacturing of nickel alloy 625

Abstract

Keyhole pores are common in additively manufactured parts and can badly deteriorate the part's performance. In this study, we demonstrated that the keyhole pores formation in the laser powder bed fusion additive manufacturing process can be significantly reduced by the constant laser power density scan strategy. The constant laser power density is implemented on a custom-built testbed by continuously varying the laser power with the laser scan speed through the time-stepped digital commands developed. Two cubic nickel alloy 625 parts of identical geometry were built, one with the constant laser power density scan strategy, and another with the conventional constant laser power scan strategy. The X-ray computed tomography (XCT) measurement shows a 67% porosity reduction in the part built with constant laser power density. However, the mechanisms for defect formation are not easily distinguishable in XCT, which gives a ‘total’ count of pores. To further investigate the effect of scan strategies on pore formation, two digital twins of process monitoring (DTPM), meltpool intensity volume (MPIV) and melt pool area volume (MAV), were created. The DTPM not only helps to distinguish the keyhole pores from the lack of fusion defects but also provides a foundation for the future development of machine learning models.