Impact Innovations, a German-based leader in industrial cold spray additive manufacturing (CSAM) systems, has teamed up with UK-based propulsion system designer Airborne Engineering (AEL) to prove the concept of manufacturing propulsion system components via CSAM technology.
The partners worked together to design a combustion chamber demonstrator to test a 3D printed demo inlet manifold – the part of an engine that supplies fuel to the cylinders – and demonstrate the advantages of the CSAM process over other additive manufacturing techniques.
Cold spray 3D printing
CSAM is a material deposition process that involves the acceleration of solid powder particles using a supersonic gas jet. Particles are fired through a nozzle onto a substrate at four times the speed of sound, whereby they behave like a liquid and cool, forming an atomic bond with the substrate.
The process differs from laser-based, electron beam and wire-arc 3D printing processes as it does not require high temperatures. As such, this means a protective atmosphere during the printing process is not required, eliminating the impact of thermal residual stresses on the printed part.
In December last year, Impact Innovations developed a new CSAM process especially for the titanium alloy Ti-6Al-4V which uses nitrogen gas as a propellant. The alloy had previously been challenging to print via cold spray deposition due to its high critical velocities which ultimately lead to high porosity in printed parts, however the firm’s new method achieved Ti-6Al-4V parts with porosity levels below 0.2 percent.
Impact Innovations is not alone in its development of CSAM technology, with other variations of the process having been developed by the likes of GE to repair a gearbox on its GE90 engine, and SPEE3D, which has commercialized its cold spray technology in the form of its LightSPEE3D 3D printer. SPEE3D’s technology has since been utilized by the Australian Army for various field tests and is also being deployed to fabricate low-cost metal 3D printed rocket engines.
Over the past few years, cold spray 3D printing processes have also been explored for the fabrication of high-performance magnets for electric motors, and there has been multiple initiatives to further the research and adoption of CSAM and develop new materials for the technology.
Proving CSAM for combustion chamber manufacturing
In recent years increasing attention has focused on developing fast and low-cost additive manufacturing processes for the production of commercial rocket engines. Powder bed fusion (PBF) technologies, in particular, have been explored for this application, due to its design freedom and prevalence on the market.
However, as Impact Innovations points out, PBF 3D printing does face challenges in regards to combustion chamber manufacturing, namely limited build envelopes and processing of metals and alloys, in addition to high surface roughness, specifically in the cooling channel inner walls, which can reduce cooling efficiency within the component.
Impact Innovations is seeking to address these limitations with its CSAM technology, and has turned to AEL to prove the process for manufacturing combustion chamber components. With guidance from Impact Innovations, AEL designed a combustion chamber demonstrator suitable for testing a CSAM-printed inlet manifold comprised of a regeneratively cooled liner made of a high-strength Cu-alloy and an Inconel outer jacket.
The partners fabricated a demo sample of the inlet manifold component via CSAM, which they claim proves the suitability of the process for the manufacture of combustion chambers with notable benefits over other 3D printing technologies.
CSAM advantages over other AM technologies
According to Impact Innovations and AEL, one advantage of the CSAM process over other additive manufacturing technologies is that no protective atmosphere is required during the printing process. CSAM also provides a simple joining technique of dissimilar materials and alloys, with additional parts able to be joined without welding.
The process also delivers negligible thermal stress to parts, while negating the issue of surface roughness in a component’s cooling channels. Additionally, powder is only required for the material to be deposited, in contrast to PBF processes where it is required to fill the entire build volume.
The demo sample of a combustion engine manifold’s cooling channels was manufactured to determine the mechanical properties of the part’s Cu-alloy and Inconel. The CSAM process had a deposition rate of 10 kg per hour for the Cu-alloy and 6.7 kg per hour for Inconel, which is reportedly more than 20 times faster than comparative PBF 3D printing processes.
At Impact Innovation’s spray-lab, the firm’s spray lathe allows the manufacture of components up to 1.5 meters in diameter and two meters in length with a max weight of 1,500 kg. A full-size combustion chamber is currently being manufactured via the CSAM process at the company’s facility, and will soon be fire tested at AEL’s site.
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Featured image shows a demo sample of the combustion chamber inlet manifold fabricated via CSAM. Image via Impact Innovations.
