Cladding and Freeform Deposition for Coolant Channel Closeout

LWDC technology enables an improved channel wall nozzle with an outer liner that is fused to the inner liner to contain the coolant. It is an additive manufacturing technology that 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, Material #1, is cladded with an interim Material #2 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. The micrograph on the left shows the quality of the bond at the interface of the channel edge and the closeout layer; on the right is a copper channel closed out with stainless. 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. As such, NASA 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 new Laser Wire Direct Closeout (LWDC) capability reduces the time to fabricate the nozzle and allows for real-time inspection during the build. 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. Hot-fire testing is complete&#8212the parts were exposed to extreme combustion chamber temperatures and pressure conditions for 1,000+ seconds. Micro-graph examination of the hot-fired test article has verified that the coolant channel closeout bonds are reliable and that there is very little deformation to the coolant channels. The picture above was taken during the hot-fire testing of a nozzle.