Research On Characteristics Of MIG Welding Process Of Aluminum Alloy With Preheated Wire

MIG welding with preheating wire is a new process of gas metal arc welding for aluminum alloy.This process is composed of TIG DC power supply and welding wire to form the preheating circuit.The resistance heat is generated by the current flow through the welding wire,so as to reduce the arc heat required for melting the welding wire and separate the welding wire melting speed from welding current.Its advantages are to increase the droplet transfer frequency,reduce the droplet size,reduce the thermal input of the base metal and improve the welding efficiency.In this paper,1.6mm wire is used to analyze the preheating temperature,electrical parameters,arc shape,droplet transfer,base metal heat input and wire melting speed under the MIG welding of preheating wire.In this paper,a MIG welding test system of preheating wire is established,which mainly includes the following parts: welding system,wire preheating temperature measurement system,electrical signal acquisition system,high speed camera system and so on.The core of the test system is the self-designed MIG welding torch,which is divided into preheating part and welding part.These two parts are independent of each other and the MIG welding process is stable.The energy of wire melting mainly comes from these two parts,namely,the resistance heat of the preheating part and the MIG arc heat of the welding part.In this paper,the wire temperature is measured by thermocouple temperature measuring device under only wire feeding with no arc.The maximum preheating temperature can reach 487 °C,and further increasing the preheating current will lead to serious softening of welding wire,fracture of stress bending and stagnation of wire feeding process.The preheating math model is fitted with the measured data by matlab.The deviation range is-27 °C ~-30 °C,and the determination coefficient is 0.9803,which shows that this model has high reliability.In this paper,the arc shape and droplet transfer process are obtained by using high speed camera equipment,and the electrical parameters of welding process are collected by electric signal acquisition device.The results show that aluminum alloy MIG welding of preheating wire can change the electrical parameters to affect the thermal input of base metal on the one hand,and change the droplet transfer characteristics of MIG welding on the other hand,such as transfer frequency,size and transition form.The process test shows that MIG welding of aluminum alloy with preheating wire has the advantages of increasing the melting speed of welding wire and reducing the heat input of base metal.When the welding current value is fixed,the larger the preheating current is,the faster the wire feeding speed is,and the faster the welding wire melting speed is,and the welding speed is also improved accordingly,so the production efficiency is improved.When the feed speed of welding wire is constant,the larger the preheating current is,the smaller the welding current value is,and the shallower the weld penetration is,and the lower the heat input of base metal is.Also the grain size of heat affected zone is increased,so the property of heat affected zone is increased,which is of great significance for strengthening the welded joint quality of aluminum alloy softened by heat treatment,as it is easy to be affected by heat input.