Twin-Wire Narrow Gap GMAW Welding System And Welding Procedure

Narrow gap welding (NGW) has gained increasing application in thick plate welding because it has many technical and economic advantages such as low heat input and high production efficiency. And twin-wire NGW can largely improve the deposition efficiency and solve the problem of lack of sidewall fusion which exists in single wire GMAW-NG. However, there is few research about the twin-wire NGW method which processed with only one welding pool at the present time. This paper systematically investigated the appearance of weld and welding stability of twin-wire MAG-NG on the base of the fully new self-designed torch of twin-wire GMAW-NG.Firstly, this paper designed a new torch of twin-wire GMAW-NG which has a nice appearance and simple construction and is portable and reliable. This torch has the characteristic of the adjustability of the space between two wires, the angle of the two wires and the distance between wire and edge. The practicability of the welding torch has been validated by flat plate welding experiment. Secondarily, the appearance of weld of twin-wire MAG-NG has been studied. The results indicate that the appearance of weld is fairly well when the space of the two wires is between 5mm and 15mm, and deteriorated when the space above 20mm; When the distance between the wire and the edge is 2.5mm, the appearance of weld can avoid forming finger penetration and obtain adequate sidewall fusion. But when the distance is less than 1.5mm, the appearance of weld is deteriorated; The appropriate arrangement of the two wire is parallel mode. If the wire inclines backwards, the appearance of weld has been spoiled; The pulse time and welding speed should been set to a reasonable level. When the pulse time exceed 3.4ms, undercutting formation of bead occurs. And when the welding speed is less than 350mm/min, the edge on the bottom of bead has not enough fusion. The research of parameter interval under different conditions of current indicates that the method of the twin-wire one-welding-pool adopted alternating pulse is only suitable to high welding current condition.Finally, the investigation has been carried systematically aiming at exploring the influence of welding parameters on the twin-wire MAG-NG welding stability and the influence of different pulse modes on the welding stability. The results indicate that when the space between wires is less than 20mm, the welding stability is good. However when the space is between 20mm and 50mm, the welding stability is worsened. When the space between wires is narrower(about 5mm), the pulse modes have little influence on the welding stability. But when the space is wider(about 30mm), the synchronizing pulse mode adopted can make the welding process be more stable.