Joshua Evans, Applications Engineer and Head of Learning at BOFA International, delves into best practices for maintaining a healthy and productive environment in additive manufacturing environments.
Around this time last year, additive manufacturing (AM) hit the general public at the start of the pandemic, when progressive manufacturers joined forces with 3D printing hobbyists to respond to the demand for protective equipment for health and care workers on the front lines.
Of course, we know that because of its ability to shorten production cycles, lower tooling costs and reduce waste, AM has long been a cornerstone of advanced manufacturing in sectors such as automotive, defense, aerospace, medical devices and electronics.
Given the increasing adoption of AM in a range of materials and applications, the manufacturer should be reminded that the associated health risks for employees from air pollutants must be regularly reviewed. This is especially important not only for corporate responsibility reasons, but also to meet existing and emerging occupational exposure standards.
Some health, safety and environmental laws and guidelines have been realigned to accommodate this evolving industry and more changes are likely to occur over time.
So watch this room as they say, as many studies confirm the presence of smoke, gases and particulates in AM processes and highlight the need for effective methods of capturing potentially harmful emissions.
For example, Vat polymerization and material jet Usually use either UV light or digital light processing to cure photopolymer resin. The resin is photoreactive and then hardens when hit by light. This process offers several possibilities for gas release. First, there is the resin itself, which can contain some compounds that can’t wait to evaporate, even at room temperature. Then some printers heat the resin, which obviously increases the temperature and provides more energy for other harmful gases to escape. Finally, there is the photoreaction itself, where even more energy can lead to other undesirable chemical by-products (AB Stefaniaka, 2019).
Some of these released gases, such as acrylic acid and cumene hydroperoxide, can be dangerous to humans. Some gaseous emissions are classified as slightly irritating and others as completely toxic. These chemicals can have a variety of effects, from headaches to much more serious health conditions.
In another example Powder bed fusion (PBF) and directed energy deposition Processes use a high energy source to melt certain areas of material. This can be done in the form of a powder bed or solid wire in a variety of different materials from polymers to titanium. When the high energy source hits the material, it can result in very fine particle emission. An example would be the laser from a PBF process that hits a metal powder bed. The laser’s ablation mechanism instantly boils and then condenses the metal powder, creating a cloud of ultrafine particles.
To keep these processes under control, the atmosphere inside the printer is usually sealed and sometimes made up of an inert gas. Or, if this is not possible, an inert source is directed at the target area for deposition.
Due to the closed nature of the process, the risk to the health of the user during printing is greatly reduced. However, this can lead to particle residue on the devices which can affect the quality. In addition, any build-up of particles can create premature durability concerns and post-printing risk to the user when handling finished components. Similar risks can exist in post-processing, for example when removing powder.
in the Material extrusionThe material is forced through a heating nozzle so that it becomes pliable, and the printer then layers the molten material until the final object is ready. The combined shear force and the combined heating process of polymers will degrade the material but unfortunately give off a smoke that is a health hazard for employees. The emitted particle sizes are very small and well below 1 micron (Health and Safety Executive, 2019). The particle emission rate increases with the nozzle temperature.
That brings me to one critical factor that AM users need to consider – the size of the particles emitted from the process. This is key to understanding the potential health effects, particularly how far a particular airborne contamination can penetrate the human body.
30 micron particles are roughly what you can see with the human eye. at 10 microns, particles enter your mouth and nasal cavity; at 5 microns, particles enter your airways; At 2.5 microns they can get into your lungs, and particles around 1 micron reach the extremities of your lungs (Praznikar, 2012).
Nanoparticles deserve special mention because, if they are not captured in an extraction process, they have the ability to enter the human body through membranes (Ostiguy C, 2008).
The key to success is specifying an extraction technology that has been proven to capture vapors, particles and nanoparticles associated with the materials being processed, for example using data sheets. The volume of the generated particles in the air must also be taken into account in order to determine the most suitable filter system for the application.
From a productivity standpoint, if you don’t control particles, such as particle size, can negatively impact AM printer efficiency and increase the risk of product contamination. B. by the formation of sticky plastic droplets on critical components. This can lead to quality and reliability problems, costly, unscheduled downtime and, in the worst case, the replacement of devices.
Given these risks, I would urge manufacturers to choose a smoke evacuation system that includes a pre-filter (to remove larger particles and thus protect the more expensive main filter), a HEPA filter (to remove nanoparticles), and a pre-filter, an activated carbon filter ( for removing vapors and gases). Intelligent operating systems can also regulate the air flow and monitor the filter condition in order to optimize the filter life and ensure a timely replacement.
It is also worth considering the high temperatures encountered in some AM processes. Here, a sealed filter replacement design can eliminate the risk of thermal events in pyrophoric material operations. In certain circumstances, manufacturers might also consider whether an application of refractories for the enclosure and filter, spark arrestor, and thermal shutdown protection would benefit to reduce the risk of burning particles entering the exhaust system.
- AB Stefaniaka, LN (2019). Particle and vapor emissions from three-dimensional printers with vat polymerization.
- Occupational health and safety officer. (2019). RR1146 – Measurement and control of emissions from 3D desktop printers made of polymer filaments. London: Crown.
- Ostiguy C, SB (2008). Health effects of nanoparticles.
- Praznikar. (2012). The effects of particulate air pollution on respiratory and cardiovascular health.
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