When GE decided that additive manufacturing was the way to go for making metal fuel nozzles for its new LEAP engine, the company touched off interest in other shops to move 3D printers from the design studio to the factory floor. It also stepped up the focus on safety standards for metal AM.
That’s because the use of powdered metal – generally manufactured to spheres <100microns in size – brings with it the need for new safety awareness among those on the shop floor.
Breathing in those powders can be harmful. Aluminum, for example, can cause respiratory and neurological problems if enough dust is inhaled.
“We understand that there are unknown dangers to powders,” says Ed Tackett, director of education programs at the new UL Additive Manufacturing Competency Center at the University of Louisville. “We don’t know what the long-term effects of exposure to these powders are.”
In efforts to mitigate any negative effects from exposure to metal powders, everyone in the center’s shop area wears a National Institute of Occupational Safety and Health-approved respirator.
“Personally, no matter what machine is running, I wear a p100 myself,” Tackett says of a face piece that filters out at least 99.97% of airborne particles 5microns and larger. “No one touches a machine or opens a tray without a respirator on.”
Tackett says to go for the maximum amount of protection that’s currently available, noting that metal powder handled incorrectly can waft into unprotected eyes and cuts in the skin. He recommends wearing a fireproof lab coat, eye protection and 5 mil nitrile gloves.
Wearing personal protection gear is vital while restocking a 3D printer with metal powder. That’s because most machines require a technician to pour the powder into the machine’s reservoir from a wide-mouthed canister.
“Unfortunately, that may be your only option for the way the machines are designed,” says Paul Bates, general manager of ULMCC services. “I think in the long run we’re going to see much more contained techniques.”
Tackett says one industrial AM machine maker, SLM, has a closed-loop powder loading system that’s the safest in the industry. Jim Fendrick, vice president of SLM North America, demonstrated the powder loading process for me, and our exposure to an opened canister of metal powder was just a few seconds. The canister is connected to a closed pour mechanism to load a machine’s reservoir, which contributes to worker safety.
And don’t forget subcontractors who do post-processing finish work on AM metal parts that could have some trapped powder in them, says Tackett.
“You can’t just look at your process internally,” he says. “You have to look downstream.”
Other safety factors that Tackett and Bates say shops with metal AM machines must consider are:
O2 monitoring: Laser melting machines use argon or nitrogen gas to displace oxygen. In addition, with shop floor space at a premium, additive machines can be packed tightly together, or in a closed room, leaving little space for air to circulate.
“What happens is that argon and nitrogen displace the oxygen,” says Tackett. “It’s just like carbon monoxide poisoning.”
Tackett recommends having an O2 sensor in the AM space, and aiming for 21-25% saturation.
Static electricity and fire: Almost anything in powder form with static in the air and the right ignition source can catch fire, Bates says. A fire in powdered metal is particularly concerning because it requires a special fire extinguisher and a different technique to put it out.
To help prevent fires from happening, the UL team says elements of an electro-discharge safety program should include having all machines static grounded; using anti-static mats that are grounded to the machine’s frame; using statically grounded vacuum cleaners; applying an anti-static coating to floors; and requiring that everyone wears anti-static shoes.
In the case of a metal fire, using water or a Class A, B or C fire extinguisher not only won’t extinguish the blaze, it may help spread the danger.
“Metal fires represent a unique hazard because people are often not aware of the characteristics of these fires and are not properly prepared to fight them,” Tackett says. “Even a small metal fire can spread and become a larger fire in surrounding ordinary combustible materials.”
Shops should invest in a Class D fire extinguisher and have it in the vicinity of metal AM machines. The sodium chloride in the D-type extinguisher creates a hard shell when it’s exposed to the heat of a fire, creating an oxygen-excluding crust. The proper technique is to spray down on a metal fire, not sweep side to side as you would with non-metal combustibles.
As shops integrate metal AM into their work, it’s critical to keep Material Safety Data Sheets up-to-date and require training for operators, says the UL team.
“We are well regarded for our safety training to begin with,” says Bates. “We’ve done the research, and we’ve got the experts to provide not only the minimum amount of training but the right amount of training.”
Not surprisingly, Tackett agrees.
“Any time you’re going to put in an additive manufacturing system, site preparation and site safety are paramount,” he says. “As AM emerges to a front line manufacturing technique, I think somebody really needs to take a leadership position as far as safety, personal protection and training.
“We certify operators for CNC machines, we should train for AM.”