Research On Welding Equipment And Process Of Magnetically Controlled Narrow-Gap-Welding Of Thick-Plate 304 Stainless Steals

304 stainless steels are widely used in the automotive industry,gas pipeline transportation,aerospace,nuclear energy and military aspects.With the various of new structures in different fields appearing,the demands of thick-plate stainless steels are also growing rapidly.Compared with the traditional thick-plate welding method with a large section area,narrow gap welding has many advantages such as low welding heat input,reduced welding material consumption,improved welding efficiency,reduced welding deformation and thermal material stress.At present,research on narrow gap MIG/MAG welding mainly focus on the method of mechanically rotating conductive nozzle to transfer arc energy to both sades of the narrow gap.Such a structure will cause conductive nozzle abrasion and rotating electrical machinery failure in the long time service.At present,there are few studies on the magnetic controlled narrow gap MAG/MIG welding methods.In this dissertation,a new MIG/MAG welding gun adapting to narrow gap was designed to study the weld forming and welding stability.(1)Firstly,we completed the design of the water cooling system,gas protection structure,conductiive path and optimized the magnetic pole of the new narrow welding gun.T he improved welding gun c an be inserted into the narrow groove for welding and the whole structure of the gun is reliable and compact which can serve for a long time.The thickness of the welding gun is 7mm,and the maximum welding groove depth is 50 mm,which conform to the requirement of the welding standards.(2)The welding stability with transverse magnetic field in different welding modes was studied on t he plates and the influences of welding parameters such as voltages,exciting current,exciting frequency and mixture gas composition on f low capacity were also studied.At the same time,the welding electrical signal acquisition system was used to collect the current and voltage waveform under the influence of magnetic field.The changes of the droplet transition and arc forms in different transverse magnetic field were studied by high speed camera.(3)Research on narrow gap welding process was studied in 20 mm thick plates.The influences of welding voltage,exciting current,exciting frequency,welding speed and other parameters on the welding form were studied and the process parameters of narrow gap welding of austenitic stainless steels were determined finally.We studied the defects in the welding process and analyzed the possible causes.The multi-layer welding test in narrow gap was carried in 30 mm thick groove and the change of welding hardness and microstructures were analyzed too.(4)The process of narrow gap welding was simulated by ANSYS software.The heat source of the simulated welding process is determined by the results of the practical test and the heat source equation of the oscillating arc was obtained by calculations,Through the change of temperature fields in the welding process,it is found that the temperature of the oscillating heat source can fully act on the side wall of the two sodes.The highest temperature at the center of the heat source can reach more than 1700?.Compared with the temperature field without oscillation,arc oscillation can solve the side wall non-fusion problem properly.