Assessment of trapped powder removal and inspection strategies for powder bed fusion techniques

Abstract

The issue of trapped powder within a part made using powder bed fusion additive manufacturing (AM) is one of the 'dirty secrets' of AM, yet it has not received significant attention by the research community. Trapped powders limit the application of AM for complex geometries, including heat exchangers and dies with conformal cooling channels. Being able to detect and remove trapped powder from the build is a necessary step to avoid downstream processing and performance challenges. In this work, 'powder challenge geometries' with complex internal features were fabricated via laser powder bed fusion (L-PBF) and electron beam selective melting (EBSM) and were used to assess the effectiveness of several powder removal and inspection methods. Hand-held ultrasonic polishing was explored as a powder removal technique and was shown to effectively clear extremely elongated channels that grit-blasting (the current industry standard) cannot clear. X-ray computed tomography (XCT) and weighing were used to inspect and quantitatively assess the effectiveness of powder removal techniques on the challenge geometries. Using the lesser known 'vacuum boiling' powder removal process and the more common ultrasonic bathing process, trapped L-PBF powder was easily removed from the deep channels. Conversely, trapped EBSM powder was difficult to remove using ultrasonic polishing as the powder was sintered inside the channels. It was shown that the powder recovered by the ultrasonic polishing process had size distributions, surface chemistry, morphology and porosity similar to the virgin powder. It is suggested, on these bases, that the recovered powder could likely be recycled without detrimental effects on the process operation.

Influence of Postprocessing on Wear Resistance of Aerospace Steel Parts Produced by Laser Powder Bed Fusion

“…Hunter, L.W. [51] reported on the inability to assemble functional parts due to the presence of trapped powder within a part made using powder bed fusion additive manufacturing that was not, up to now, researched enough by the scientific community, especially regarding the parts with complex surfaces and inner channels. By the opinion of the authors, the problem of trapped raw powder granules limits the application of additive manufacturing methods for complex geometries like heat exchangers and dies with conformal cooling channels.…”

Osteoconductivity of bioactive Ti-6Al-4V implants with lattice-shaped interconnected large pores fabricated by electron beam melting

“…Especially when the implant is fabricated with EBM, the complete removal of the metal powder from small pores of the implants during the manufacturing process is extremely difficult due to pre-heating or the partial consolidation of the powder. 16,25 We therefore developed a new type of porous Ti-6Al-4V implant with relatively large, lattice-shaped, interconnected pores of 880–1400 μm. This porous implant allows for the easy removal of metal powder from pores with currently available removal techniques, such as manual processes, liquid immersion, and ultrasonic cleaning, 25 owing to its relatively large geometric pattern of pores.…”

“…16,25 We therefore developed a new type of porous Ti-6Al-4V implant with relatively large, lattice-shaped, interconnected pores of 880–1400 μm. This porous implant allows for the easy removal of metal powder from pores with currently available removal techniques, such as manual processes, liquid immersion, and ultrasonic cleaning, 25 owing to its relatively large geometric pattern of pores. Furthermore, if enough bone ingrowth is observed in the implant with a lager pore size, then a stronger bonding between metal and bone can be expected.…”

“…The larger pore size of the implant allows for the complete removal of any metal powder from the small pores of 3D printed implants. 16 , 25 We therefore developed a new type of porous Ti-6Al-4V implant with lattice-shaped interconnected pores measuring 880–1400 μm, which allows for the easy removal of metal powder using current removal processes, such as manual processes, liquid immersion, and ultrasonic cleaning. 25…”

Mapping Spatial Distribution of Pores in an Additively Manufactured Gold Alloy Using Neutron Microtomography

“…The Archimedes method [8] has been used in different studies to evaluate the relative density of parts [9,10]. In L-PBF processing, due to the geometrical constraints and/or partial consolidation of powder particles, there might be particles left inside of pores after build completion [11]. Since the used immersion liquid cannot wet rough surfaces efficiently and also does not take these internally trapped powders into consideration, the Archimedes method is not a very reliable technique to precisely measure the porosity content in L-PBF samples.…”