Occupational exposure during metal additive manufacturing: A case study of laser powder bed fusion of aluminum alloy

Abstract

Occupational exposure during metal additive manufacturing (Laser Powder Bed Fusion) using an aluminum alloy (AlSi10Mg) was assessed. Background aerosols before manufacturing, powder sieving, machine loading, manufacturing, machine unloading, powder unpacking, and machine cleaning were analyzed. Measurements were taken simultaneously at the source, in the near field, and on the operator during five manufacturing cycles. Aerosol measurement devices and physico-chemical techniques were used to determine the particle number or mass concentration (DiSCmini, core particle counter and sampling cassette), particle size distribution (NanoScan, optical particle detector and impactor), and the shape/size and chemical compositions of the inhalable particles (laser diffraction, inductively coupled plasma spectroscopy, scanning electron microscopy, energy dispersive X-ray microanalysis, and Brunauer–Emmett–Teller Method). The laser powder-bed fusion machine emitted in the additive manufacturing room an inhalable fraction of 2.37 ± 0.35 mg/m³, with an aerosol number concentration ranging from 2 × 10⁴ to 10⁵ #/cm³ and a mass mean aerodynamic diameter of 318 nm. A relatively low concentration level was observed in the near field of the machine with an aerosol number concentration of ∼10⁴ #/cm³. A higher concentration level on the operator was attained during the unpacking and cleaning steps, showing an inhalable fraction of 1.73 ± 0.30 mg/m³. Al and Mg nanoparticles were aerosolized at the source (inside the laser powder-bed fusion machine) with a particle size distribution of 153 nm for Al and 117 nm for Mg and an aerosol number concentration reaching ten times that of the background aerosol level. The number or mass concentration of particles in the room atmosphere was increased to double that of the background aerosol level at specific workstations during manufacturing. Metal additive manufacturing is a source of potential occupational exposure to airborne metal nanoparticles. Particle-counting instruments showed high numbers of nanoparticles and some important peaks of particles ranging from 10 nm to 10 µm or larger at specific work tasks in the Additive Manufacturing (AM) environment. A multimetric approach was used to characterize the particle emissions resulting from this type of additive manufacturing.

Keywords:

• Additive manufacturing
• aerosol
• AlSi10Mg;
• laser powder bed fusion
• metal nanoparticles
• occupational exposure
• selective laser melting

Acknowledgments

The authors thank Mr. Philippe Bertrand from ENISE for his support during the use of the additive manufacturing machine. Authors also acknowledge Mrs. Lara LeClerc and Mrs. Coralie Laurent from Ecole des Mines de Saint-Etienne, Mr. Davy Rousset, Mr. Sébastien Bau, and Mrs. Hélène Poirot from INRS for off-line sample analysis and technical support for the physicochemical characterization.