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