Probably nothing gets shop personnel cursing faster than trying to machine Inconel 718. The hard alloy rapidly chews through cutting tools. Casting Inconel is not much better because about 70% of the material gets wasted in mold gates. Yet Inconel is a favored metal for aerospace and turbine parts because it withstands temperatures from cryogenic up to 1,400°F and has excellent tensile and impact strength.
EOS of North America
Fortunately, there are fabricators that have mastered the art of making Inconel parts. Morris Technologies in Cincinnati, Ohio, for example, builds metal parts using direct metal-laser sintering (DMLS) and EOS 718, an additive-fabrication material that is equivalent to Inconel 718. EOS 718 is made by EOS of North America Inc., Novi, Mich.
One recent aerospace part Morris built is a stator ring. “A complex part like this would traditionally get cast, not machined,” says a Morris spokesperson. “But DMLS produces net or near-net-shape parts. This reduces the machining needed and thus cuts part costs by 50%. The ring does need secondary operations such as stress relieving, heat treatment, postmachining work, and hand polishing. However, most cast Inconel 718 parts would need to go through these operations anyway.”
Build time depends on several factors, according to Morris. “From strictly a build perspective, the larger the part, the more time it takes to build. However, if we must hold a certain tolerance, we might need to first go through a calibration build to find out the machine’s accuracy. We would then dial-in operating parameters to hold the needed tolerance. Casting the stator ring would probably have taken four to five weeks, best case. In contrast, making the part using DMLS took only four days. Additional processing took another four days. That’s about one week for building as compared to a month for casting.”