Abstract: Arc pressure and heat density outputted in a single cathode-arc-anode arcing system are coupled, it restricts the precise control the thermal-force balance in the melting pool. Modification should be done to release such a force-heat coupling effect. A novel arcing technology, named as two-layers-arc coaxial hybrid technology, is introduced. Based on a plasma arc welding torch, new nozzle is designed by embedding a ring shape tungsten into the bottom surface of the ordinary cooper nozzle. Ring shape arc forms from the ring tungsten cathode and is coaxial posited to the center constraint arc to form a hybrid arc. Arcing tests are done, the result show that the stable hybrid arc can be formed in the developed hybrid arc torch, the arc width is related to the ring arc current level. Primary welding tests are done with the ordinary plasma arc and the hybrid arc, stable keyhole welding processes are successfully achieved, keyhole behaviour and the resultant weld surfaces are observed to be similar with the both arc sources. Experimental results tell that it is possible to achieve stable keyhole welding process by using the proposed hybrid arc system, it also lay basic for the further improving of keyhole stability.

Key words: hybrid arc, keyhole welding, plasma arc, thermal-force properties in arc source