Metal deposition technology is at the core of metal additive manufacturing (AM), and the materials are generally deposited in powder form. The powder is deposited layer by layer, melted and bound together by the heat from a laser. Because the metal additive manufacturing industry is still in its infancy, few companies are handling high volumes of powdered metal yet. But as production rates and applications increase, so, too, will safety concerns for materials handling.
Some fine metal powders are between 15 and 45 microns in size. If they become airborne, these particles represent a health hazard, either from inhaling or absorption through the skin. Mishandling of the powders could lead to respiratory problems or heavy metal poisoning. Particulate filters become necessary for manual handling, along with breathing gear designed to protect operators from the gas exhaust that’s created during the deposition phase. For many metal powders, fires and explosions are also a real concern for improperly handled materials.
|Schematic showing raw material loading and return to use, as well as build box unloading. Image source: Volkmann|
Currently, small containers of metal powders can be used and handled in manual processes with some basic safety precautions. Soon, however, companies planning to increase their usage of metal AM will need to gain a better understanding of bulk powder handling techniques and the containment procedures that make it safe. This will include ensuring that appropriate safety wear is used, safety procedures, and safety standards are being followed, and an abundance of caution is applied when workers are in contact with metal powders. This is particularly true when it comes to the transfer of unused materials from 3D printers to bulk storage.
Volkmann, which is known for its pneumatic vacuum technology, recently introduced its Additive Manufacturing Material Handling System (AMMHS) designed specifically for 3D printing processes that involve the handling of metal powders or toxic materials. The system, which can either be a mobile unit or fixed to the shop floor, enables a three-step process that recovers any unused material from the printer, screens it and returns it to the machine for immediate reuse or to a container for storage.
Pneumatic vacuum technology allows AM materials to be safely transferred from pick-up locations to the manufacturing unit, as well as for the capture, integrated screening and return-to-use stations processes. The system has been used to handle a variety of materials, including tungsten, cobalt, silver powder, iron, stainless steel, aluminum oxide (alumnia), nickel chrome, copper and carbide dust, with bulk densities ranging from 93 to 341 pounds per square foot. It’s designed to work in both a normal air environment and under an inert gas, and is compatible with any powder-based additive manufacturing system. This high level of containment solves any potential environmental issues, and addresses worker safety in all steps of the manufacturing process.
The National Fire Protection Association (NFPA) maintains a number of standards that cover the safe handling of metal and toxic powders. Nick Hayes, president of Volkmann USA, told Design News that companies are managing fairly well in meeting these standards with small volumes of production, but may find themselves struggling as they scale up or apply processes to new applications (larger parts, etc.).
“Companies follow safety procedures that are established, be they for potential operator exposure, explosion protection or other risk analysis-related concerns,” said Hayes. “Standards exist and are used. The real issue for them as the industry matures will be the scale of material handling. The inert transfer operation the system offers provides new options to companies using metal AM techniques, particularly when using more volatile substrates.”
For companies that use inert gas in their AM processes, the AMMHS unit employs a closed loop that saves and then recycles the gas, which keeps costs down and prevents waste. A specialized electric pump keeps temperature and containment stabilized.
“Many metal powders are affected by oxidization, which can also affect the metallurgical properties of the component being produced,” Hayes told Design News. “Other powders are potentially explosive, which means they require transfer in an oxygen-free system. The use of inert transfer overcomes these issues.”
According to Volkmann, the Additive Manufacturing Material Handling System can create opportunities for improved return on investment for AM. Manual processes often result in a lot of waste of very expensive materials. Volkmann’s system builds new efficiencies into the unloading and return to use of metal powders from and to the build box, increasing the conveying rate, screening rate and the practicality of recovering unused metal powder efficiently from printers. Given the high value of the metal powders and the relative difficulty in screening them with existing manual procedures, it makes economic sense to automate more of the system.
“Volkmann began developing their AMMHAS in 2015 to serve a new business segment that had developed within the aerospace and research and development-related markets,” said Hayes. “Just as the additive manufacturing sector has grown exponentially, so too has the need for a process that improves efficiency by consolidating machinery, reducing the amount of manual labor involved and limiting downtime.”