Why the Turbomachinery Industry is Increasingly Bullish on Additive Manufacturing

3D-printed metal-alloys are answering critical needs for high fluid flow, high-pressure parts.

Why the Turbomachinery Industry is Increasingly Bullish on Additive Manufacturing

There’s nothing more core to turbomachinery than moving fluid at increasingly high speeds and pressures. Whether we’re talking about industrial turbines, air breathing jet engines, or liquid-rocket space applications, the higher the pressure and the higher the flow rate, the better the performance.

An overview of various approaches to 3D printing for impellers. (Image: FT Technologies)

Using traditional manufacturing techniques to produce the complex parts needed to provide the best possible performance can be a lengthy and costly process. Additive manufacturing – specifically, advanced metal powder-bed fusion – has now reached a level of quality and repeatability that makes it a viable alternative to a variety of conventional production methodologies. Casting, with its long lead times and high upfront cost, is no longer the optimal method for prototyping, and in some cases is even preferred for production.

Materials available in additive manufacturing have been developed and qualified through their history and use in aerospace engineering. Turbopump components are generally made of nickel alloys, aluminums, and titaniums. Material selection is driven by material property requirements (such as strength and ductility), working fluid compatibility, operating temperature, and machineability, among other characteristics.

An impeller developed using additive manufacturing. (Image: FT Technologies)

Inconels maintain strength at high temperatures, have excellent oxidation resistance, and are compatible with a wide range of working fluids. Aluminum alloys offer considerable weight reduction when high strength is not required. Titanium alloys offer exceptional strength to weight ratios, though they are highly reactive with cryogenic oxygen and the two must be kept out of contact. All three material bases have been successfully employed using additive manufacturing in turbopump design with continual development on new alloys.

Particularly exciting to me, as the manufacturing engineer responsible for the space group for my company, is the ability of advanced AM to print high-speed rotating components, specifically impellers. Historically, there has been a fear in the industry over the robustness of such components due to the nature of additive manufacturing being an application of welding. We’ve been working with 3D printed high speed rotating components for quite a few years now, and with the correct procedures and processes we’ve shown it to be a very viable manufacturing method.

Impellers created with conventional manufacturing (left) and additive manufacturing (right). (Image: FT Technologies)

Another challenge in building rotating components is that, due to the necessity of using support structures to prevent warping of the part during a build, the standard AM strategy has been to print at a 45-degree angle. This approach can work in static parts, but in rotating parts at high speed this introduces small amounts of non-uniform material properties, which causes excessive vibration during operation. Lately, with the Velo3D Sapphire printer—accessed through our contract-manufacturer network—we are flat-printing titanium rotating components with exceptionally good results. This is made possible by its fully integrated solution that combines software, hardware, and unique manufacturing processes to print highly complex geometries and reduce or eliminate supports.

Another example of our success with more advanced metal powder-bed fusion came during the height of the global pandemic. We had a very tight deadline to get an Inconel combustor rig to test at a time when supply chains and manufacturing capacity was extremely limited. The ability to print with minimal supports and low overhang angles allowed us to print both the combustor liner and its housing with minimal design changes in a rapid-development process. We didn’t have to iterate the design to over multiple builds to achieve a viable part. We were able to go with our original design, print it right the first time, and produce the rig within the extremely short time-window.

A more recent application of ours, for a private space-flight application, demonstrates the multiple ways in which using more advanced AM is facilitating our ability to produce the highest-performance components that our turbomachinery customers demand. The task was to redesign a specific turbopump assembly that was originally made with a legacy AM machine in Inconel. Leveraging Velo3D’s more advanced AM system, we were able to consolidate parts, change the material from Inconel to a titanium to decrease weight, and change the build orientation of the structure to reduce build time, and thus, cost. Due to our previous experience with complex additive builds, we didn’t have a lot of confidence that this could be achieved without significant trial and error, but the early prints of the part were very successful and went on to be machined into actual test articles. That design, originally deemed a high risk, is now nearly ready for production.

Collaboration remains key towards success with such cutting-edge technology as AM. As we work with our supply chain and the equipment development team, we are continuously giving feedback on materials testing and characterization that helps improve the production printing process and build parameters. Most of the parts we are printing with advanced AM are proprietary, so we don’t show them publicly. That said, the enthusiastic response of our turbomachinery customers to our ability to use advanced AM to meet extremely challenging design goals, gives us the confidence to consider 3D printing to be one of the more powerful tools in our toolbox of engineering solutions we offer.

This article was written by Dan Dombrowski, Manufacturing Engineer, Space Group, FT Technologies/Kratos Defense. For more information, visit here .