Plasma Arc Welding for Large Titanium Aerospace Structures

Plasma arc welding produces butt-type joints satisfactorily in titanium as thick as 5/16 of an inch and in three common welding positions. The Keyholing technique accomplishes this in one pass. Without a filler wire addition this results in weld bead reinforcement that has slight undercutting at the weld edges. Undercutting could be prevented by filler wire addition or corrected by a second ‘wash’ pass.

Much higher depth-to-width weld bead ratios and much higher welding rates can be achieved by plasma instead of by conventional welding methods.

Tooling for plasma arc welding requires a deeper under-bead gap and wider holddown clearance than for conventional welding methods.

Joint evaluation revealed excellent results. X-ray quality was defect-free (“water-clear”). Joint strength approximated 100% for mill-annealed material. Joint ductility was also high relative to parent material. This was established by Elongation and by Bend Radii determinations relative to parent material.

Plasma arc welding may be an optimum choice between conventional TIG / MIG and Electron Beam methods for some large structures involving thick joints.