Heat and pressure characteristics in hollow cathode centered negative pressure arc column

Highlights: • Thermal-force output in HCCNPA is significantly smaller than conventional GTA. • Comparing to GTA, the arc energy density of HCCNPA increases but arc pressure decreases. • The zero-speed dividing line is first found in HCCNPA process. • The total force can be adjusted based on the negative pressure in the hollow cathode. -- Abstract: Arc characteristics are found greatly changed by the negative pressure from the hollow cathode. These changes affect the distribution of arc pressure, arc plasma flow and temperature along the arc column. The characteristics of HCCNPA (hollow cathode centered negative pressure arc) along the arc column were investigated in this study to understand the changes and influences. It was found that the negative pressure applied to the cathode reduced the arc pressure and the arc radius, and complicated the plasma flow distribution with a clear zero-speed dividing line in the arc column. Above the boundary line, the plasma in the middle of the arc column flowed to the cathode, and the peripheral plasma flowed to the anode, presenting two peak values in the arc pressure distribution. The inner negative pressure also could adjust the total arc force acting on the work-piece. Under the same inner negative pressure conditions, the difference in arc force between GTA (gas tungsten arc) and HCCNPA did not change at varying arc lengths.