Lawrence Livermore National Laboratory



Printed metal parts meet critical national needs

Additive manufacturing could cut the cost of launching payloads into space, and is being used to ensure the safety and security of our strategic deterrent.

Traditional methods of manufacturing critical components for space launch and strategic deterrence are time and cost intensive. Lawrence Livermore National Laboratory is leveraging metal-based additive manufacturing to revolutionize the manufacture of rocket engines for responsive space launch, as well as non-nuclear replacement parts as part of the National Nuclear Security Administration's Life Extension Program and to support hydrodynamic testing of weapon surrogates.

As additive manufacturing matures, it will fundamentally change the way the nuclear weapons complex produces parts. Advantages include:

  • Fabrication is many times faster and cheaper than currently in weapons complex production plants.
  • Parts can be made with extremely high fidelity.
  • Novel and difficult parts can be fabricated quickly and easily, improving innovation.
  • Development time is reduced.

Matt Wraith

  • wraith1@llnl.gov

    Group Leader, Defense Technologies Engineering Division

    This animation illustrates the launch, re-entry and landing of the proposed NX-01 Nanosat Launch vehicle. The first of its rocket motors was created for testing a using powder bed additive manufacturing process.

    Proposed NX-01 Nanosat Launch vehicle

    3D printing rocket engines whole

    To meet the U.S. requirement for on-demand, operationally responsive space launch, a low cost launch capability for small satellites becomes crucial. Lawrence Livermore is pioneering the use of additive manufacturing for the production of complete rocket engines in the thrust regimes appropriate for small satellite launch. These engines are "printed" whole, as opposed to the traditional approach of manufacturing individual components for later assembly.

    The first prototype engine was printed in 8 days at a cost of $10,000, at least an order of magnitude more cost effective than would be the case with traditional manufacturing approaches. The engines are designed to produce 5,000 pounds of thrust, with six mounted on Lawrence Livermore's proposed Nanosat launch vehicle eXperimental One (NX-01).

    NX-01 is designed to be reusable: taking the payload close to orbit, releasing an expendable second stage, re-entering the Earth's atmosphere and landing either at bases on land or on Naval platforms at sea.

    This animation illustrates how the NX-01 rocket motor throat was printed, layer-by-layer, using the powder bed additive manufacturing process.

    Each layer is the thickness of about 3 or 4 powder particles.

    The powder-bed process

    Lawrence Livermore's facility for metal-based additive manufacturing houses two powder-bed, laser-based machines. Fine powders (5-50┬Ám) are used to build parts layer by layer.

    A powder spreader spreads a thin layer of powder on the build platform. The laser melts the powder in locations where the part is to be. When the layer is complete, the build platform is moved downward by the thickness of one layer, and a new layer is spread on the previous layer. The melting and spreading process is repeated as the part is build layer by layer.

    When complete, the un-melted powder can be recovered and used again. The part can then be heat treated if necessary and removed from the build platform.

    Characteristics of additively manufactured metals

    Metals produced using additive manufacturing have structure, properties, and performance that can differ from their cast and wrought counterparts. Differences include density, residual stresses, mechanical behavior, nonequilibrium microstructure, crystallographic texture:

    Density While it is challenging to reproducibly obtain additively manufactured materials that are 100 percent of the reference density, additive manufacturing methods can yield metal densities in excess of 99 percent of the reference density. Some materials are reported to have been fabricated at full density and some have been reported with a spread of densities (e.g., 99.2 to 99.5 percent). (Murr: 2011) Density is influenced by development of pores (Wang et al.: 2009) or entrapment of un-melted powders during processing. Hot isostatic pressing is occasionally used to improve as-fabricated densities.
    Residual stresses Residual stresses can be "very high" in metal parts produced using laser-based additive manufacturing methods. (Rangaswamy et al.: 2005; Wang et al.: 2008) Mitigation and optimization strategies are required and can include changing the substrate temperature, scan direction, or the application of post-deposition processing, perhaps even including in-situ shock wave processing. (Morgan et al.: 2001) Residual stress issues can be significantly reduced or even eliminated by using electron-beam-based additive manufacturing systems.
    Mechanical behavior Generally, because of the refined microstructure of metals produced using additive manufacturing, an increase in strength and decrease in ductility is expected compared with conventional wrought alloys. Differences in fracture toughness and behavior under dynamic conditions are unknown.
    Nonequilibrium microstructures Materials produced using additive manufacturing methods can experience very high cooling rates (~103-108 K/s). (Espana et al.: 2011) At these cooling rates, several effects can be realized, depending on the material, including "suppression of diffusion-controlled solid-state phase transformations, formation of supersaturated solutions and nonequilibrium phases, formation of extremely fine, refined microstructures with little elemental segregation, and formation of very fine second-phase particles such as inclusions and carbides." (Espana et al.: 2011) In some cases, these are desirable effects but must be considered on a case-by-case basis.
    Crystallographic texture Because of the rapid cooling rates and directional solidification, significant crystallographic texture can be expected in metals made using additive manufacturing processes. The texture and its effects can be somewhat controlled by varying the scan direction during deposition. (Thijs et al.: 2010)

    Matt Wraith

  • wraith1@llnl.gov

    Group Leader, Defense Technologies Engineering Division