Low-cost, large-scale liquid rocket engines with regeneratively cooled nozzles will enable reliable and reduced-cost access to space. Coolant contained under high pressure circulates through a bank of channels within the nozzle to properly cool the nozzle walls to withstand high temperatures and prevent failure. It has been a challenge to affordably manufacture and close out the intricate nozzle channels.
NASA Marshall developed a robust and simplified additive manufacturing technology to build the nozzle liner outer jacket to close out the channels within and contain the high-pressure coolant. The Laser Wire Direct Closeout (LWDC) capability reduces the time to fabricate the nozzle and allows for realtime inspection during the build.
LWDC technology enables an improved channel wall nozzle with an outer liner that is fused to the inner liner to contain the coolant. It builds upon large-scale cladding techniques that have been used for many years in the oil and gas industry and in the repair industry for aerospace components. LWDC leverages wire freeform laser deposition to create features in place and to seal the coolant channels. It enables bimetallic components such as an internal copper liner with a superalloy jacket.
LWDC begins when a fabricated liner made from one material is cladded with an interim material that sets up the base structure for channel slotting. A robotic and wire-based fused additive welding system creates a freeform shell on the outside of the liner. Building up from the base, the rotating weld head spools a bead of wire, closing out the coolant channels as the laser traverses circumferentially around the slotted liner. This creates a joint at the interface of the two materials that is reliable and repeatable. The LWDC wire and laser process is continued for each layer until the slotted liner is fully closed out without the need for any filler internal to the coolant channels.
One variation enables a bimetallic part (copper/super-alloy, e.g.) to help optimize material where it is needed. The manufacturing process has been demonstrated on a series of different alloys. In hot-fire testing, the parts were exposed to extreme combustion chamber temperatures and pressure conditions for 1,000+ seconds. Micrograph examination of the hot-fired test article verified that the coolant channel closeout bonds are reliable and that there is very little deformation to the coolant channels.