Description:

The focus of the project is to develop advanced Friction Stir Welding (FSW) Techniques for welding light weight, difficult to weld aluminum alloys in a complex three-dimensional geometry. The primary application for this technology is to weld geometries that are capable of radially accommodating essential human spaceflight capabilities (e.g., docking ports, hatches, windows, etc.). With the completion of this project Boeing plans to implement this capability into their habitat product line. Initial designs for this product line were funded by the NextSTEP program at NASA.

The primary enabling technology for this development program is retractable pin tool friction stir welding, which is an advancement on conventional friction stir welding pioneered at Marshall Space Flight Center (MSFC). With Retractable Pin Tool FSW, welds can be conducted with no need of close out procedures which are common for other FSW processes. This feature allows for welding additional items onto existing hardware. An example of this would be welding a window into an existing habitat module. RPT-FSW is conventionally used on flat panels and curved panels, however it has not been used on three-dimensional shapes which require 6-axis or more of tool motion. This project is aiming to use the complex tool path capabilities of MSFC's Robotic Weld Tool (RWT), housed in MSFC Bldg 4755, to demonstrate the ability to weld a port bulkhead into a barrel panel for a Mars transit habitat. This technology will be applicable and relevant for all future generation habitats for earth's orbit, the lunar surface, and deep space human transportation.

Benefits: The primary benefit of this technology is enabling the ability to conduct very complex geometry welds to join similarly complex components onto a habitat's primary structures, like a docking port. Traditionally, these features have been welded using fusion-based processes. Fusion-based welding processes are generally difficult to conduct on advanced lightweight aluminum structures as these aluminums exhibit severe weld cracking behaviors. This was shown during welding of the super light weight external tank for the space shuttle program. The weld team had difficulty welding aluminum-lithium alloy 2195 using conventional fusion welding methods. Due to these issues, FSW was incorporated into NASA's welding technology tool belt with the specific intent to weld 2195 for the external tank program. NASA and Boeing plan to use similar aluminum-lithium alloys on future space vehicles and therefore plan to use FSW on these applications. In addition to the reduction in weld cracking, FSWs have been shown to have superior mechanical behavior. This enables the team to utilize thinner weld joints and provides an overall weight reduction on the entire space vehicle or habitat. This weight reduction is imperative for reducing launch weight as many of these structures will need to be launched from earth's surface to orbit to get to their destination.