Identification of effective control technologies for additive manufacturing

Abstract

Additive manufacturing (AM) refers to several types of processes that join materials to build objects, often layer-by-layer, from a computer-aided design file. Many AM processes release potentially hazardous particles and gases during printing and associated tasks. There is limited understanding of the efficacy of controls including elimination, substitution, administrative, and personal protective technologies to reduce or remove emissions, which is an impediment to implementation of risk mitigation strategies. The Medline, Embase, Environmental Science Collection, CINAHL, Scopus, and Web of Science databases and other resources were used to identify 42 articles that met the inclusion criteria for this review. Key findings were as follows: 1) engineering controls for material extrusion-type fused filament fabrication (FFF) 3-D printers and material jetting printers that included local exhaust ventilation generally exhibited higher efficacy to decrease particle and gas levels compared with isolation alone, and 2) engineering controls for particle emissions from FFF 3-D printers displayed higher efficacy for ultrafine particles compared with fine particles and in test chambers compared with real-world settings. Critical knowledge gaps identified included a need for data: 1) on efficacy of controls for all AM process types, 2) better understanding approaches to control particles over a range of sizes and gas-phase emissions, 3) obtained using a standardized collection approach to facilitate inter-comparison of study results, 4) approaches that go beyond the inhalation exposure pathway to include controls to minimize dermal exposures, and 5) to evaluate not just the engineering tier, but also the prevention-through-design and other tiers of the hierarchy of controls.

Keywords: Ultrafine particles; filtration; indoor air quality; particle emission; volatile organic compounds.

Figure 1.

Tested controls organized according to our version of the hierarchy of controls and additive manufacturing (AM) process category. The number of published articles for each tier is indicated in parentheses. Sub-classification of the engineering and administrative control tiers is also indicated. Note that the total number of articles given in Figure 1 (45) was greater than the total number of citations that met the inclusion criteria of this review (42) because some citations included results for more than one control type. ME = material extrusion, DED = directed energy deposition, MJ = material jetting, PBF = powder bed fusion, VP = vat photopolymerization, and BJ = binder jetting.

Figure 2.

Median % efficacies of controls for particle (n = 148 values) and gas emissions (n = 68 values) for all AM process categories by hierarchy tier.

Figure 3.

Median % efficacies of controls for particle number-based data only (n = 94 values) and gas emissions (n = 58 values) for select AM processes by hierarchy tier. ME = FFF 3-D printers, MJ = material jetting.

Figure 4.

Median % efficacies of controls for particle and gas emissions for select AM processes by type of engineering control: (a) medians for particles calculated from number-based data only (n = 65 values), (b) medians for gases calculated from all sample data (n = 51), (c) medians for particles calculated for fine size fraction only (n = 38 values), and (d) medians for particles calculated for ultrafine size fraction only (n = 24 values). ME = material extrusion (FFF 3-D printers only), MJ = material jetting.

Figure 5.

Median % efficacies of engineering controls for particle number-based data only (n = 65 values) from material extrusion-type FFF 3-D printers by: (a) implemented by-design or retrofit, and (b) studied in a test chamber or real-world setting.