Keyhole Welding with Hybrid Plasma-Free Arc Source

Improving the keyhole welding process window is challenging work because the force and thermal state in the weld pool are hard to control. A hybrid plasma-free arc source was developed based on a plasma arc torch, sided tungsten was added close to the constraint orifice to form a free arc, and hybrid arcs formed after the free arc was fully absorbed into the constraint arc. In such a one-anode, twocathode hybrid arc system, the added free arc acts in an assistant role to adjust arc heat output without influencing the arc pressure peak, and the constraint arc acts as the guiding arc to control the arc pressure and slightly incline to the free arc side. Bead-on welding experiments were done to test keyhole welding process behavior with the hybrid arc source, including arc column, keyhole state, weld surface performance, and melting state in the weld pool. Results showed that (1) the hybrid arc can enlarge the stable keyhole welding process window in aspects of welding current and welding speed, and a more-obvious improving effect is obtained with the leading-sided tungsten; (2) the hybrid arc with the rear-sided tungsten has a smooth front weld surface; (3) the increased heat will enlarge the weld cross-section area with no obvious influence to the backside weld width; and (4) the leading keyhole wall is related to the outer tungsten position. The research gives a new method for improving keyhole welding stability.