Abstract Scope |
As a high-energy-density arc welding method, keyhole plasma arc welding (K-PAW) can achieve full penetration of medium - thickness metal materials without any groove. However, along with the increased plate thickness and deeper penetration, the weld pool and keyhole become more fragile due to complex and unstable forces, showing serious weld pool fluctuation, large spatter, and collapsing keyhole, etc. In order to maintain the dynamic balance between the long keyhole and surrounding liquid metal throughout the thickness, this research proposes a novel "controlled constant keyhole" process, during which the keyhole is controlled with nearly constant rather than opening and closing periodically under the traditional "one pulse and one keyhole" strategy. Besides, the computer-based control system shows slow response causing late adjustment of welding process parameters, in which case the efflux plasma voltage fluctuates in a large range indicating the sharply changed keyhole sizes. Therefore, a closed-loop control system based on programmable logic controller (PLC) with faster response speed and greater flexibility in regulation has been developed. The adjustment frequency is increased from the maximum 2 Hz to 6 Hz, and the efflux plasma voltage fluctuation range is reduced to about 500 mv. Deep-penetration of 14 mm thickness of 304 stainless steel butt-welding joints were realized with high-efficiency and high-quality with low heat input. The full-penetration welded joint shows excellent microstructure, mechanical properties, and corrosion resistance, indicating the great potential of this technology being widely applied in many industries. |