JPL has been hand-welding aluminum tubing for decades in support of flight programs and ground support equipment, including thermal plates and shrouds. This hand-welding process is time-consuming, cumbersome, difficult, and unreliable in terms of repeatability and success, which leads to leaks, rework, and cost increase. Socket-style meltdown welds are difficult to inspect via traditional nondestructive evaluation (NDE) methods (radiography) since by design, there is always an inherent highstress point in the joint.
Experimentation and process development verified that orbital tube butt welding could be performed on aluminum tubes, as opposed to hand socket welds. Preliminary results were excellent with 5000 series aluminum that can be welded autogenously (without filler metal). Early results on 6000 series aluminum was initially discouraging, but further trials with 4000 series aluminum filler t-rings proved much more promising. All these welded samples passed radiographic and visual examination.
Orbital welding is a specialized area of welding whereby the arc is rotated mechanically 360° around a static workpiece, such as tubing or pipe, in a continuous process. The main components of every orbital welding system are the power source controller and the welding head. Welding of all sizes and material types will also require an internal pressure control system during the purge. There are a large number of factors that can have an influence on the welding result. These aspects include the arc length, pulse frequency of the welding current, welding speed, inert shielding gas, internal purge pressure, parent material, filler material, weld preparation, and thermal conductivity. Ultimately, a high-quality weld is achieved through detailed knowledge of how to precisely adjust all these parameters for each individual welding task. The effort proposed will be state-of-the-art development of true orbital welding capability for aluminum tubes.
This work was done by James T. Diener, Frank Q. Picha, and Dellon R. Strommen of Caltech for NASA’s Jet Propulsion Laboratory. NPO-49581
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Aluminum Gas Tungsten Arc Orbital Tube Welding
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Overview
The document discusses the development of Aluminum Gas Tungsten Arc Orbital Tube Welding technology at NASA's Jet Propulsion Laboratory (JPL), aimed at improving the welding processes for space flight fluid systems. The need for this technology arose during the Mars Exploration Rovers (MER) project, where manual welding of tube socket joints was challenging due to difficult access and a high likelihood of requiring rework. This led to schedule delays and increased costs.
The primary objective of the project is to demonstrate successful welds on Aluminum tubing that meet rigorous testing standards, including proof, leak, burst pressure testing, and various forms of inspection such as visual and radiographic examination. The proposed solution involves the development of a state-of-the-art orbital welding capability specifically for Aluminum tubes, which would significantly reduce the number of manual weld joints required for missions like the Mars Science Laboratory (MSL) Heat Rejection System (HRS). By implementing orbital welding, the project aims to eliminate 102 manual weld joints, potentially saving 10 days in schedule time and associated costs, given that approximately 20% of manual welds typically require re-welding after inspections.
The approach includes fabricating a conversion box to connect a DC weld head to an AC welding power supply, designing and fabricating weld samples for trial welding, and conducting preliminary qualification evaluations. The trials focus on 6000 series Aluminum with 4000 series filler materials, which have shown promising results in initial tests.
The document emphasizes the importance of developing a reliable welding technique that can produce leak-free welds, as traditional non-destructive testing methods struggle with inspecting certain joint designs. The research aims to provide a comprehensive data set for full welding qualification and to deliver a mechanical interface capable of performing flight-quality orbital welding on Aluminum tubes.
Overall, this initiative represents a significant advancement in welding technology for aerospace applications, with the potential to enhance the reliability and efficiency of future space missions. The document also notes that the research is conducted under NASA's sponsorship and is part of a broader effort to make aerospace-related developments available for wider technological and commercial applications.
