Welding process with hybrid arc by compositing two free arcs into constraint arc

Controlling heat output and force in the arc source is important to improve the keyhole stability during welding. In this study, a double-layer hybrid arc torch was developed by adding two outer tungsten electrodes symmetrically to the orifice in the plasma arc torch. Two free arcs forming from the two outer tungsten tips are absorbed into the center constraint arc to form a hybrid arc. The arc pressure of the hybrid arc was measured, and welding experiments were carried out to test the application possibility in the keyhole welding process. It was found that: the arc pressure of the hybrid arc with two free arcs is symmetrical. The additional heat input provided by free arcs can be transferred into the keyhole bottom, and a lower constraint arc current is needed to form a stable fully penetrated keyhole. With the left-right arranged outer tungsten electrodes, arc heat is easier to be deposited into the keyhole bottom, and less sum of arc current is needed to form a fully penetrated keyhole. With the leading-rear arranged outer tungsten electrodes, the reflected arc will bridge the weld pool and the rear tungsten, and the coupling state between the free arc and the constraint arc is disturbed. When the constraint arc current is 115A and the free arc current is 40A, a fully penetrated keyhole can be formed with the left-right arranged outer tungsten electrodes but cannot be formed with the leading-rear arranged outer tungsten electrodes. The proposed hybrid arc system has advantages over the previous model in terms of a wider range of usable arc current and symmetrically distributed arc.