Manufacturing and Testing Experience with Direct Metal Laser Sintering for Closed Centrifugal Compressor Impellers

Direct Metal Laser Sintering (DMLS) is an additive manufacturing process that utilizes a high-powered laser to build up a metal part by selectively melting thin layers of metal powder. This process is attractive for the manufacturing of parts with complex geometry such as closed centrifugal compressor impellers. DMLS allows closed impellers to be made in a single piece and eliminates the shroud joint that results from two-piece manufacturing processes. Using a monolithic impeller can allow higher tip speeds with improved fatigue characteristics compared with two-piece and three-piece designs. Prototype parts can be made more economically than investment casting when considering the tooling costs. Manufacturing costs for DMLS parts are marginally higher than for two-piece machined impellers, but qualification efforts for the braze/weld joint at the cover are circumvented. The DMLS process introduces several factors that must be considered in the impeller design to achieve a successful build with the proper strength and surface finish. This paper describes the authors’ experience with manufacturing and testing multiple closed impeller designs constructed from Inconel 718, 17-4 PH Stainless Steel, and Titanium 6Al-4V. A detailed discussion of design factors and manufacturing experience with a DMLS vendor is included for the various metals. Dimensional, post-test destructive inspection, and material test results are provided showing that the DMLS process can produce an impeller with good dimensional accuracy, surface finish, and material strength. Finally, overspeed test results up to maximum tip speeds of over 1400 ft/s (425 m/s) and aerodynamic performance test results are presented and discussed.