Additive manufacturing is key for engineering Inconel rocket engine injectors
Components in rocket thrusters used to boost satellites into Earths orbit have to withstand exceptionally tough operating conditions; for example, functioning in harsh oxygenated environments at temperatures of around 1,000°C for extended periods.
We were approached by DELTACAT, a spin-off company from the University of Southampton, to engineer an innovative design of injector nozzle for a new trial rocket thruster. Due to the harsh operating environment, the injector had to be manufactured from Inconel 625. This is a super-alloy produced from austenitic nickel-chromium, containing percentages of molybdenum and niobium, which is designed to maintain its tensile strength at temperatures that would render other metals pliable.
Manufacturing parts from Inconel using conventional machining techniques can, however, be a tough challenge. The hardness of the metal has the potential to deform or break cutting tools, while under extreme conditions the machining process can degrade the surface properties of the base metal.
Traditional engineering methods
With a traditional machining approach, producing the freeform injector shape would require multiple setups on a 5-axis CNC mill, with at least one operation on an EDM machine. This is time consuming and, even with the unrivalled experience of our machinists, carried the risk of tool-breakages and higher cost. Alternatively, the nozzles could have been produced in two sections and vacuum brazed together. Although this option would reduce machining time the braze would have been of different material, creating a potential weakness along the seam, with the risk of failure in service – clearly, this is an unacceptable risk in a critical satellite component.
Metal Additive Manufacturing offers a solution
Although each injector nozzle had a relatively simple design, it lent itself well to production using additive manufacturing technology, enabling multiple parts to be easily printed simultaneously in Inconel 625. Additionally, the flexibility of the additive manufacturing process enabled our engineers to work with the team from DELTACAT to optimise the design of the injector nozzles for manufacture without compromising their performance characteristics. This helped to reduce overall time and cost.
Using our advanced Renishaw metal additive manufacturing system, we are able to produce each injector nozzle in a single piece, thus eliminating any weak points. The nozzle was also designed to be built without any support structures, which dramatically reduced the post-build finishing required. The parts only needed to be wire cut from the platform and then inspected before delivery.
Cost and time saving
The ability to create the injector nozzles in Inconel 625 using additive manufacturing played an important role in reducing overall production time and unit cost for DELTACAT. Perhaps as importantly, our ability to provide detailed technical advice and support throughout the project, together with our knowledge of Inconel machining, helped the customer optimise both the design of and in-service performance of each part.
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