Thick Wire CO₂ Welding Process For Spiral Welded Pipe Based On Digital Welding Power Source

Since the 21st century, the spiral welded pipe has turned into the main type of oil and gas pipelines. Pre-finishing welding process (two-stages method) is the most advanced production technology in spiral welded pipe, but few studies is related in China since the development of two-stages method is relatively late. In pre-finishing welding process of the spiral welded pipe, the thick wire CO2 welding process is used in tack-welding. There are some problems in high-speed thick wire CO2 welding process of tack-welding. Firstly, as the conventional welding torch is very easy adhered by spatter which causes circulation of protective gas obstructed, the welding pool is poor protected and the weld quality cannot be guaranteed. Secondly, as the spatter adhered on the welding torch is difficult to clean which takes long time, the production efficiency is seriously restricted. These two aspects have become a bottleneck in improving the level of Pre-finishing welding process.The welding system based on digital welding power is designed as test platform for this paper. First, this paper analyzes the causes of the problems above of the conventional CO2 welding torch; the jet material is match optimally to solve the problem of adhered spatter; the cooling method and gas diverter of welding torch are designed appropriately to solve the problem of welding torch cleaning. The automatic welding gun meeting the technical requirements is obtained as result and has been successfully applied national utility model patent.Secondly, this paper analyzes the arc form and droplet transfer form using the pictures of the arc form and the molten pool metal flow form, and clarify the formation process of the spatter and humping bead. Using the experimental method, this paper studies the effect rule of related process parameters on the spatter arising and weld forming, and it is considered that large current, low voltage, oxidability of protective gas, appropriate bevel and welding position will improve thick wire high speed CO2 welding to obtain stable welding process. At the same time, this paper obtained the parameters of good weld forming through welding experiment which is important to guide the actual production.