How safe is additive manufacturing? That’s a question that has been asked multiple times, and has been the subject of multiple research studies. In a recent study entitled “Titanium Powders Used in Powder Bed Fusion: Their Relevance to Respiratory Health,” a group of researchers looks specifically at titanium materials used in metal additive manufacturing. Despite the fact that the build phase of metal additive manufacturing is an enclosed process, the researchers point out, 3D printer operators may be exposed through inhalation to metal feedstock powders during the pre- and post-processing phases.
Pre-processing involves tasks such as vacuum cleaning of the 3D printer’s build chamber to remove unsintered or unmelted powder, the handling of powder for size-selective powder sieving, and the loading of the powder into the feedstock bins. Post-processing includes manual removal of the printed parts from the build chamber as well as any excess powder, as well as sanding, drilling and sawing to remove supports and finish the surface of the part.
“The size and chemical composition of AM powders is of importance when considering the respiratory health of AM operators,” the researchers explain. “Particle size determines whether particles are inhalable, and if inhalable, where they may be deposited in the respiratory tract. Particles can be classified into size fractions — inhalable, extrathoracic, thoracic, or respirable — depending on the regions of penetration.”
Inhalable particles are inhaled through the nose and mouth and deposited in the nasopharyngeal region, while extrathoracic particles are inhaled but do not penetrate beyond the larynx. Thoracic particles can penetrate beyond the larynx, and respirable particles can penetrate the unciliated airways and be deposited in the alveolar region of the lungs. Possible health effects depend on the chemical composition of the metal particles; titanium and iron inhalation may lead to respiratory inhalation like coughing and sneezing, while long-term inhalation of aluminum dust may lead to pulmonary fibrosis.
“The aim of this study was to establish the particle size distribution (PSD), shape, and elemental composition of titanium powders obtained from three AM facilities located in South Africa in order to compare them with the corresponding information declared in the SDSs (safety data sheets) of these powders,” the researchers continue. “The relevance of any potential discrepancies or shortcomings in SDS information to AM operators’ respiratory health was explained, and recommendations are provided to both AM powder manufacturers/suppliers and the end users.”
Samples of virgin and used titanium powders and their respective safety data sheets were collected from three additive manufacturing facilities in South Africa. The samples were placed into separate storage vials, and particle size was evaluated using particle size distribution (PSD) and scanning electron microscopy (SEM). Particle shape was evaluated through static image analysis of dry dispersed powders, and X-ray diffraction (XRD) analysis was conducted to determine the elemental composition of the powders.
PSD analysis of the virgin powders showed particle size conformance to that stated in the SDS for only one of the three powders – that from Facility A. Overall, both the virgin and used powders from the three facilities showed thoracic and respirable particles. If inhaled, these metal-containing particles have the potential to cause adverse health effects over a long term.
“Findings from this study suggest that there are circumstances in which the inaccurate/incomplete SDS could create a false sense of protection about the AM operators’ health,” the researchers state. “It is therefore recommended that manufacturers provide accurate and comprehensive information in SDSs on, in particular, the particle size and elemental composition of the AM powders. The AM operator should be able to refer to the SDS as a guide for safe powder handling, and should be informed of the potential health risks involved.”
Authors of the paper include S. du Preez, D.J de Beer and J.L du Plessis.
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