As Additive Manufacturing (“AM” or 3D printing) continues to grow across industries, more facilities are introducing new materials, powders, and post-processing systems into their operations. Manufacturers are also continuing to introduce newer, larger, and more capable printers and supporting equipment with expanded applications and capabilities.
One common question we hear at Harrington Group, Inc. is whether these systems create combustible dust hazards. The answer depends largely on the technology and materials being used, as well as the existing mitigation strategies.
Some AM systems present little to no combustible dust risk, while others require careful evaluation of the existing hazard mitigation measures as well as additional recommendations for hazard mitigation. In this first “Ask the Dust Guy” post, we’ll provide a high-level overview of where combustible dust concerns may exist within additive manufacturing systems.
Technologies with Little to no Combustible Dust Risk
Some materials used in AM for creating the finished products (such as sand and ceramics) do not pose combustible dust risks (although they may pose health risks). Other materials, such as thermoplastic filaments (used in Material Extrusion printers) or liquid photopolymer resins (used in Vat Photopolymerization or Material Jetting printers) may pose limited fire risks, but do not use powders or create dust, so again no combustible dust hazards (dust fires, flash fires, or explosions) are posed during the printing process. Depending on the post-processing steps, some combustible dust hazards may be introduced and will be discussed in a later post.
Technologies with Limited Combustible Dust Concerns
Along with the technologies listed in the previous paragraph, some technologies used in AM present little to no risk of combustible dust hazards, such as Sheet Lamination (aka Selective Deposition Lamination or Laminated Object Manufacturing) and Binder Jetting. Sheet Lamination Printers use sheets of paper, composites, or certain metals, along with adhesives, pressure, and heat to create the final products. Most of these have a cutting stage that could create some dust, and the heating source (for curing the adhesive under pressure) could be an ignition source; however, with a properly designed and specified dust collection system combined with hoods near the point of dust generation, combustible dust risks are very low. Binder Jet Printers use liquid bonding agents/adhesives deposited at certain locations on a bed of powders, such as sand, ceramics, and metals (most commonly stainless steel) to create parts by layers. Binder Jet printers using metals (yes, even some stainless steel alloys with a small enough particle size have been shown to be explosible in testing) mainly present combustible dust hazards in their filling and reclaim sifting (pre-processing) stages, and in their post-processing (cleaning, sintering, and blasting, grinding, or polishing) stage. Again, these hazards can be mitigated using proper dust collection or conducting post-production in an inert environment (oxygen concentrations below the Limiting Oxygen Concentration (“LOC”) plus a safety factor).
Technologies with More Significant Combustible Dust Hazards
The last two AM printer technologies covered in this post are Powder Bed Fusion (“PBF”) and Directed Energy Deposition (“DED”). DED printers use either lasers or electron beams to melt wire or powder (metal or plastic) deposited on a surface. Wire DED printers act in similar ways to a wire-feed welder, except instead of using an electrical arc to melt and fuse the metal, they use a laser or electron beam.
PBF printers use a laser or electron beam to melt and fuse specific areas of a bed of powder (metal or plastic). The bed technology can vary by manufacturer or model (rising/lowering bed, redeposit, etc.).
Both types of printers, using either lasers or electron beams with either plastic or metal powder, can present numerous combustible dust hazards, which can include issues with the recycled material sifters/sieves and filters, powder loading systems, inerting systems, metal condensate hazards, post processing hazards, etc.
Because AM systems can vary significantly by technology, materials, and process design, understanding the potential combustible dust hazards often requires a case-by-case evaluation.
More detailed discussions around these hazards, along with more detailed pre- and post-processing considerations for other AM technologies will be discussed in the next Ask the Dust Guy post.
Until then, if you have any questions about a proposed or existing AM system, give HGI a call. We will be happy to discuss your system, the hazards associated with your system, and the Dust Hazards Analysis (“DHA”) process to both identify and mitigate these hazards.
Stay Safe!