Determining the feasible conditions for processing lunar regolith simulant via laser powder bed fusion

2020

Additive Manufacturing

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Section: Laser Powder Bed Fusion Systemmentioning

confidence: 99%

Observing molten pool surface oscillations during keyhole processing in laser powder bed fusion as a novel method to estimate the penetration depth

2020

Additive Manufacturing

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“…Laser Powder Bed Fusion system A prototype LPBF system was employed for the powder delivery and substrate positioning. The open architecture of the LPBF machine allowed for the flexible adaptation of the optical monitoring system and baseplates [22,23]. In the present experiments the system was equipped with a nozzle for localized gas supply in the laser-material interaction area.…”

Section: Methodsmentioning

confidence: 99%

Nonintrusive estimation of subsurface geometrical attributes of the melt pool through the sensing of surface oscillations in laser powder bed fusion

Journal of Laser Applications

2021

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Molten pool geometry, whose surface parameters may be extrapolated through direct process observations, has been identified as a fundamental indicator of stability in Laser Powder Bed Fusion (LPBF). However, a parameter which cannot be directly measured on industrial systems by means of conventional sensing equipment is the molten pool depth. Indeed, methods based on X-ray imaging demonstrated in literature have helped a better understanding of the process. However, retrofitting such solutions to industrial systems does not appear as a viable route currently. Within the present investigation, a non-intrusive sensing method for the indirect measurement of sub-surface molten pool geometry based upon the detection of surface oscillations is presented. The analysis of frames acquired using a high speed camera and a secondary illumination light allows the identification of the crests of molten pool capillary waves through bright reflections on the surface of the molten pool. The characteristic oscillation frequency of the surface ripples may be correlated to penetration depth or to other sub-surface geometrical parameters.Proof of concept testing of the sensing principle was conducted on two different materials, namely AISI316L and IN718, by means of single track LPBF depositions. Experiments were conducted at different levels of laser emission power to induce variations in molten pool characteristics. The process was observed employing an off-axis illumination light and a high-speed camera, which allowed acquisitions with high spatial and temporal resolution. The acquired frames were post-processed to extract the oscillation indicator and analysis of the Power Spectral Density of the signal allowed to identify the oscillation frequency.Results show that oscillation frequencies range from 3 to 5.5 kHz. Molten pool penetration depth and cross-sectional area could be correlated to the oscillation frequencies for the in-line detection of these parameters during LPBF depositions. For both materials, higher oscillation frequencies corresponded to shallower molten pool and smaller mass of molten material. Moreover, different characteristic curves of oscillation frequency variations as a function of the melt pool cross-sectional area were determined for IN718 and AISI316L.

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“…This equipment enables flexible configuration of processing and monitoring equipment. The prototypal LPBF system was presented in greater detail in previous publications [24,50,51]. For the scope of this work, the scanner head was equipped with a monitoring module which enables coaxial integration of imaging sensors as well as the illumination light.…”

Section: Lpbf Systemmentioning

confidence: 99%

External Illumination Enables Coaxial Sensing of Surface and Subsurface Molten Pool Geometry in LPBF

2022

Metals

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