Effect Of Preheated Wire On Stainless Steel CMT Welding Mechanism And Droplet Transition Behavior

After the connection of stainless steel rail vehicle body lap joint by resistance spot welding,MAG welding is usually chosen to perform on the gap between the welding joints to realize the sealing of the vehicle body.Due to the large heat input during the MAG welding process,post-weld deformation is serious and welding defects are more.At the same time,solidification of the structure results in large gaps due to deformation,which greatly affects the stability of the welding process.Cai Chen et al.proposed CMT welding with low heat input,no spatter,and stable welding process features to be applied to the welding of lap welds of stainless steel rail vehicles.However,because the CMT welding heat input is still too high,more welding defects still occur,and the welding process is less stable.Since the combination of the preheating of the welding wire and the traditional MIG/MAG welding technology can effectively reduce the heat input into the base metal during the welding process and improve the welding efficiency,this subject aims to introduce the welding wire preheating in the CMT welding process and analyze the influencing mechanism of preheating welding wire on the droplet transition behavior and the welding process.The process test is also applied to prove the superiority of the preheated welding wire CMT welding.This paper first uses the principle of resistance heating to design the wire preheating device in the CMT welding process.At the same time,using finite element theory and heat transfer theory,a finite element model of wire preheating in CMT welding process was established for the special wire movement in CMT welding.Using the APDL language,the heat generation rate model was used as the heating source,and the movement of the welding wire during CMT welding was simplified,and the heating of the stainless steel wire was achieved by the movement of the heat source.The temperature distribution of the wire in the wire preheating device during the CMT welding process was obtained.Through the collection of droplet transition information in the CMT welding process,comparative analysis is done under different preheat conditions.It can be concluded that the wire preheating can significantly improve the droplet growth size,but it will not change the CMT Welding droplet transition mode.At the same time,when the temperature of the preheating wire is high,the welding wire generates a liquid bridge with the weld pool in the withdrawal stage.At the same time,the tip of the wire remains at the end of the wire after separation of the welding wire and the weld pool.These together result in more splashes in short-circuit transition phase and an arcing phase.Using the collected information of the droplet transfer image,the welding current voltage signal and the wire movement speed related information,the influence mechanism of the welding wire preheating on the CMT welding process was analyzed.It has been found that the preheating of the welding wire can increase the wire feeding speed of the CMT welder,and increase the length of the CMT welding cycle,increase the length of wire withdrawal,and reduce the frequency of wire drawing.Finally,the use of process tests proved that the wire preheating can effectively improve the deposition rate during the CMT welding process and improve the weld formation.In addition,the preheating of the welding wire can effectively improve the CMT welding efficiency and the welding stability of the stainless steel sheet lap joint.