Case Study: Additive Manufacturing

3D printing a rocket engine

| Editor: Steffen Donath

The structural cooling design, developed by Cellcore, provides an optimal relationship between stability and mass application of the thrust chamber.
The structural cooling design, developed by Cellcore, provides an optimal relationship between stability and mass application of the thrust chamber. (Source: SLM)

SLM and Cellcore collaborated for a rocket propulsion engine. The production utilises 3D printing and selective laser melting and showcases potential for the aerospace industry.

The manufacture of rocket components requires many criteria factors be taken into consideration. Not only is consequent, lightweight construction essential, materials must also be able to withstand particularly high stresses and temperatures. Additionally, the manufacturing costs for their complex geometries are very high when limited to conventional manufacturing processes.

The engine manufactured by Cellcore and SLM Solutions consists of a thrust chamber, the core element of a liquid-propellant engine with a combustion chamber wall, fuel inlet and an injection head with oxidant inlet. The chemical reaction in the combustion chamber creates gas that expands due to the heat development that is then ejected with enormous force, generating the thrust required to drive the rocket through recoil. Extremely high temperatures are created in the chamber during the combustion process, requiring the wall to be cooled to prevent it from burning, too. To achieve this, the liquid fuel (e.g. kerosene or hydrogen) is fed upwards through cooling ducts in the combustion chamber wall before entering through the injection head. There, the fuel mixes with the oxidant and is lit by a spark plug. In conventional constructions, the cooling ducts are countersunk in a blank and subsequently sealed through multiple working steps. With selective laser melting, the cooling is integrated into the wall as part of the design and created together with the chamber in one process. Due to the engine‘s complexity, the traditional manufacturing process is cost-intensive, requiring half a year minimum. In the 3D printed engine, Cellcore demonstrates the possibilities the SLM technology can offer for the aerospace industry, as the additive manufacturing process takes fewer than five days to build, while creating a functionally optimised component.

Filigree structural cooling to increase efficiency

The single-piece rocket propulsion engine, combining the injector and thrust chamber, reduces numerous individual components into one, with multi-functional lightweight construction achievable only with the selective laser melting process. The internal structure developed by Cellcore is the fundamental element of the engine and cannot be manufactured by traditional methods. It is not only suited for heat transport, but also improves the structural stability of the component. The cooling properties of the Cellcore design considerably outperform conventional approaches, such as right-angled, concentrically running cooling ducts, according to SLM. It offers an optimised relationship between stability and mass application and exhibits low current resistance with a simultaneously high reaction surface, making it more efficient while integrating additional functions and reducing weight compared to conventionally manufactured components.

SLM Solutions collaborated with Cellcore in the preparation of this highly complex component to ensure success by optimising the selective laser melting process. SLM Solutions customer success team developed specific parameters for the geometry, focusing on downskin optimisation. Build plate orientation was recommended after consultation with the SLM Solutions’ application engineering team and critical sections of the part were identified for test-builds to guarantee success of the manufacturing job. To satisfy the aerospace industry’s high material requirements, the engine was manufactured in the nickel superalloy IN718 on the SLM 280 selective laser melting machine.

The one-piece assembly is printed in just over three days on the SLM 280.
The one-piece assembly is printed in just over three days on the SLM 280. (Source: SLM)

IN718 is a precipitation hardening nickel-chromium alloy with exceptional tensile, fatigue, creep and breaking strength up to 700°C, making it an important material for aircraft and gas turbine components, as well as numerous other high-temperature applications, such as rocket propulsion engines. When processed conventionally, the hard material is difficult to machine and causes extreme tool wear. This concern is mitigated through the additive process, as powder material is melted into the end-geometry.

Despite its complex structure, post-processing is minimised, thus avoiding high levels of tool wear. SLM technology saves considerable costs by reducing expensive, time-consuming manufacturing steps and simplifying the engine‘s structure. Selective laser melting offers aerospace companies the opportunity to increase their competitive position by optimising rocket system functionality while maintaining exceptional quality, as well as lightweighting and drastically reducing development, testing and production timeframes.

Summary

  • Simplified manufacturing: Minimal post-processing despite complex structure to avoid tooling wear when processing too difficult to machine nickel based alloy (IN718)
  • Innovation: Direct integration of multiple parts and internal features, e.g. internal ducts
  • Improved function: Cooling due to innovative lattice structure, which also increases stability
  • Efficiency: Minimisation of individual process steps while combining multiple individual parts into one component; production time reduced from months to days
  • Lightweight construction: Considerable weight reduction due to lattice structures
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