Abstract
Metal 3D printing has many potential uses within prototyping and manufacturing. Selective laser melting (SLM) is a process that uses metal powders in the micrometer range as printing material. The particle release from the entire SLM printing process is not well-studied. While the 3D printing itself often occurs in a sealed chamber, activities related to the process can potentially release harmful metal particles to the indoor working environment through resuspension of the printing powder or via incident nanoparticles generated during printing. The objective of this study was to improve the understanding of particle exposure in work processes associated with 3D printing and potential needs for interventions by a case study conducted in a 3D printing facility. In this setting, direct release and dispersion of particles throughout the workspace from processes related to metal 3D printing was investigated. The release from five activities were studied in detail. The activities included post-printing cleaning, object annealing, and preparation of new base substrate for the next printing was. Three of the five measured activities caused particles number concentrations in the working environment to increase above background levels which were found to be 8·102 cm−3. Concentrations during chamber emptying and the open powder removal system (PRS) cleaning processes increased to 104 and 5·103 cm−3, respectively, whereas grinding activity increased number concentrations to 2.5·105 cm−3. Size distributions showed that particles were mainly smaller than 200 nm. Respirable mass concentrations were 50.4 μg m−3, collected on filters. This was corroborated by respirable mass measured with a DustTrak of 58.4 μg m−3. Respirable mass concentrations were below the occupational exposure limits in Denmark for an 8 h time-weighted average.
Highlights
Additive manufacturing (AM), known as 3D printing, has increased in popularity during the last decade
Total particle number concentrations measured in the breathing zone (BZ), near field (NF), and far field (FF) are shown in Figures 2A,B, respectively
Size distributions showed that particles released as a result of the activities were mainly below 200 nm in diameter, with average particle size in the BZ being between 53 and 70 nm as measured by the DiscMini
Summary
Additive manufacturing (AM), known as 3D printing, has increased in popularity during the last decade. In liquidbased AM, polymers are chemically activated and polymerized using lithography and direct light based techniques to form each layer. Solid based AM covers fused deposition, where heat is used to melt solid plastics or polymers and fuse it to subsequent layers. Powder-based AM covers metal and ceramics 3D printing, where Laser Powder Bed Fusion (L-PBF), which is the process used in selective laser melting (SLM) and direct metal laser sintering (DMLS), is the most used method [5]. Feedstock powders fusing in layers by selective illumination with a laser by either melting the powder completely for SLM or partially melting it and sintering it in the case of DMLS. The powder is generally layered in thicknesses down to 20–50 μm using powder with a median grain size of 40–150 μm [6]
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