Arcam AB in Sweden recently patented an electron-beam melting (EBM) technique that additively builds complex parts out of titanium. The process economically builds parts at relatively low volumes. EBM is thus suitable for the orthopedics and aerospace and defense industries. Similar to other additive techniques, a “sliced” CAD model of the component is transferred to the working memory of the machine. The production chamber is loaded with metal powder and a high vacuum is drawn. A high-power (3.4-kW), computer-controlled electron beam melts thin layers of the metal powder, based on each CAD layer, gradually building up the part. The vacuum ensures melt purity and good end-part material properties.
In principle, users can use any metal or metal alloy, says Arcam President Magnus René. “But because most manufacturers use the machines to build hip and knee implants and aerospace parts, we keep the focus on titanium.” Arcam has commercialized several titanium alloys that comply with current industry specs. Customers can also use alloys from different suppliers.
Electron-beam melting lends itself well to orthopedic implants that are designed to have specific lattice structures. “The bone grows into the lattice spaces and fixes the implant in a stronger way than do conventional machined implants,” says René. “Today, roughly 2% off all hip implants worldwide are manufactured on an Arcam machine. For additive manufacturing, that is a large number.” The technique can also be used to build perfectly dense implants. Roughly 1.2 million hip and knee-implant procedures are carried out worldwide every year.
“Most people think that EBM is used mainly to make patient-specific implants,” says René. “But it is also widely used to make standard implants,” he says. “Companies compete for a slice of that market with many different products. For example, divide the 1.2 million into, say, 10 different manufacturers, divide the result into maybe two or three designs, and then divide every design into 10 different sizes — what comes out is around 4,000 implants/company/year.”
In aerospace, electron-beam melting is still at the stage where companies are mostly making prototypes and manufacturing low-volume parts for defense, says René. “A big advantage is weight savings. To produce a part with a conventional manufacturing method and make it lighter means more machining. More machining means higher costs. But with electron- beam melting, only the material necessary to build the part is used. So it is less costly and faster to use electron-beam melting for certain aerospace parts than it would be to, say, CNC cut them on a multiaxis machine tool. Parts are not only less costly, they are just as strong,” adds René.
Also important in aerospace is that EBM can generate parts difficult to build using any other technique. “For example, electronbeam melting can use titanium aluminide, a material notoriously difficult to machine,” says René.
The machines can produce parts from about 12-in. diameter by 10-in. high down to ½ × ½ × ¼ in. (for spinal implants).
“Like all other manufacturing technologies, engineers must design for the process,” says René. “Those skilled at designing for an additive technology will have no problem designing for electronbeam melting. For example, for parts that will be cut, it might not make sense to design in a lot of detailed features. In contrast, electron-beam melting imposes no penalty whatsoever to design with lot of curves or intricate shapes.
