On the Nature of Material Lot Variability in Laser Powder Bed Fusion

Metal additive manufacturing (AM) and the laser powder bed fusion (PBF-LB) AM process have gained recent prevalence due to their unique capabilities that nullify a variety of design constraints. However, it has been observed that material defects, often appearing to be unpredictable in their occurrence, can introduce high scatter in the mechanical properties of manufactured workpieces nominally produced under the same process conditions. This lack of process repeatability defies the typical concept of a ‘material lot,’ which implies that materials which share a common manufacturing pedigree should also share similar quality levels and properties. This work has studied the precise nature and causal factors of material lot variability in PBF-LB. To better understand the origination of material defects, PBF-LB process signals that contribute to defect formation were measured and analyzed with a focus on capturing the fundamental behaviors of spatter redistribution. To advance process monitoring capabilities key to understanding such process signals, novel approaches to powder bed topography measurement were examined in detail and quality metrics were proposed. Finally, the scope and nature of material lot variability in PBF-LB, particularly as related to fatigue, was quantified and studied. A model capable of predicting material lot variability as a function of material defects was also developed. In total, these efforts have enabled a more comprehensive understanding of process phenomena formerly treated as unpredictable in nature, creating causal links between the process and material.

Date

2023-04-25

Resource Type

Text

Resource Subtype

Dissertation

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