Development Of MIG Pulsating Narrow Gap Automatic Welding Machine For Drill Collar

Narrow gap MIG welding is an advanced welding technic with high quality.With this welding method, We can make the welded seam have good properties and beautiful outward appearance ; we can also make use of modern-control-technology, for example,the PLC controlling to improve the welding craft and realize the welding-automation.Nowadays,this method has been used in thick work pieces and pressure vessels more and more widely.Inview of the characteristics of narrow gap MIG welding and its using in the petroleum drilling works, we designed an auto-welding machine based on PLC for narrow gap MIG welding used in the petroleum drill-collars.In this paper, we have finished the next following designing works:Arc welding power source controlled by thyristor,The hardware design of the welder,the special welding torch using for this project also been designed in this part. The difficulty of un-completed penetration of both jamb wall can be soluted;The software system is mainly the PLC controls and man-machine interface designs;besides,we also designed welding conditions.In this design the welding machine provides the pulse current and the background current separately by two independent power supply. The two power can be regulated steplessly. The background power source is direct current welding power source with falling characters. The pulse power source has a flat characteristic, and it has a good compensation effect to the fluctuation of network voltage.To the minor-diameter and thick-walled tube witch likes the drill-collar ,we must notice the deep bevel gas-protection and the sidewall-fusion. Because the current contact nozzle of ordinary welding torch cann't be able to extend to the bevel, when welding the multi-layer work piece with thick wall,the length of welding wire changes, with the increasing of welded joint layers, this will cause the welding condition to change to affect the the stability of welding process, it also causes the difficulty of arc-striking, therefore it is essential to design the special narrow gap welding torch.The welder presents good performance in stability,reliability,adaptability,and many advantages such as welding parameters presetting,memory,locking,display,and automatic arc stricking and stopping.