Abstract
Powder bed fusion of polymers is becoming increasingly adopted by a variety of industries to tailor the strength, weight and functionality of end-use products. To meet the high standards of the modern manufacturing industry, parts built with powder bed fusion require consistent properties and to be free of defects, which is intrinsically connected to the quality of the powder bed prior to melting. The hypothesis of this work is that the roughness of the top surface of an unmelted powder bed can serve as a proxy for the powder bed density, which is known to correlate with final part density. In this study, a laser line scan profilometer is integrated onto the recoater arm of a custom powder test bench, which is able to automatically create layers of powder. A diverse group of polymers was investigated including polyamide 12 (PA12), polyamide 11 (PA11), polypropylene (PP), and a thermoplastic elastomer (TPU) under different recoating speed in order to increase the variance of the dataset. Data analytics were employed to compare roughness to measured powder bed density and a statically significant correlation was established between them.
Highlights
Laser powder bed fusion is the most industrialized additive manufacturing technology available on the market
The hypothesis of this work is that the roughness of the top surface of an unmelted powder bed can serve as a proxy for the powder bed density, which is known to correlate with final part density
Process monitoring in polymer powder bed fusion is generally absent in industrial-grade commercial systems and remains an expensive yet unproven option even in metal laser powder bed fusion, for example with the optical tomography (OT) monitoring systems provided with either visible or infrared recording such as the EOS EOSTATE Exposure OT [6]
Summary
Laser powder bed fusion is the most industrialized additive manufacturing technology available on the market. Utilizing polymer or metal feedstock in powder form, complex geometries are fabricated striking the balance of mechanical performance versus weight in a layer-by-layer manner, even without support structures in the case of polymer powders. For this generation of manufacturing technology to be more widely adopted in industrial applications, quality assurance will be crucial as material properties and part geometry are realized simultaneously. Proper in situ measurements are required to provide insights on the quality of the produced parts by ensuring the process is within specification. If not corrected in time, these process anomalies can lead to reduced yield with consequences in both environmental and profitability terms
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