Design and Development of a 30kN Rocket Engine Component Using the Selective Laser Melting Process

Small Launcher R&D Office of Korea Aerospace Research Institute (KARI) has been investigating the effectiveness of using additive manufacturing technology in developing a 30 kN-class liquid rocket engine, with an emphasis on cost-cutting ideas. In this end, a thrust chamber assembly composed of a mixing head, a chamber cylinder and a nozzle throat have been printed only in three parts, for which Inconel 718 powder was used with a selective melting process to build their internal flow channels. In our design, the expansion ratio of the printed nozzle throat was kept low as the building volume of then available machine was limited. The chamber cylinder and the nozzle throat will be printed as a single component when a larger machine becomes available. A radiatively-cooled nozzle extension will be manufactured in a conventional method of forming and welding with a refractory material, and mechanically fastened to the nozzle throat for extra expansion required for the vacuum application. The buildup directions of the additively manufactured parts have been carefully chosen to minimize undesired distortion and anisotropic properties. Due to the low thermal conductivity of Inconel 718, the inner wall of the chamber body had to be designed very thin for efficient cooling, which caused many problems such as warpage, cracking, and distortion. To improve the quality of the printed parts, accounting for deformation in the part geometry, designing for enhanced support, and adjusting wall thickness have been conducted. A hot-firing test was performed at a range of 8% to 40% of the design pressure, confirming that the thrust chamber burns stably without instability even at the low pressure and showing no sign of mechanical damage after several tests.