Study On Process Characteristics Of Basic Self-shielded Flux Cored Wire In Arc Welding

Self-shielded flux cored wire is a kind of welding material suitable for field project,which is widely used in the welding and repair of structural parts such as ships,drilling platforms,oil pipelines and mining machinery.As the most common type of flux-cored wire,basic self-shielded flux-cored wire has broad application prospects in engineering with special performance requirements for joint properties such as cold cracking sensitivity,high crack resistance,high and low temperature impact toughness.However,In the welding process of basic self-shielded flux-cored wire,there are some shortcomings such as large splash,poor welding process performance and poor weld formation,which restricts application in practical engineering to some extent.In order to improve the stability and molding precision of the basic self-shielded flux-cored wire welding process,this subject mainly studies the factors affecting the stability and molding accuracy of the welding process and how to control and optimize the welding process,so that the welding rods are replaced gradually by basic self-shielded flux cored wire.The following two aspects are mainly studied:1.Study on the stability of the welding process of basic self-shielded flux cored wire.Based on the high-speed camera and electric signal synchronous acquisition system,the influence of polarity on droplet transition and arc stability was studied,and the influence mechanism of polarity on droplet transfer was analyzed.The research shows that the basic form of droplet transfer in direct current positive connection is small drop transfer,while the basic form of droplet transfer in direct current reverse connection is repulsive transfer.When is direct current positive connected or reverse,the current and voltage are larger.Within the scope of the change,the basic form of the droplet transfer has not changed fundamentally,but the droplet size,transition frequency,arc stability and spatter rate of the droplet transfer have undergone large changes;When direct current reverse connection,there is a large splash in the reasonable process parameter interval.The process performance of direct current positive connection is better than direct current reverse connection.Therefore,when using basic self-shielded flux cored wire(brand No.JD-YGD3(Z))welding,direct current positive connection should be adopted.The reason and mechanism of the influence of polarity on droplet transfer is: the basic form of droplet transfer during direct current connection is small drop transfer.The basic phenomenon is that the arc alternates between steel and slag,and the arc is not formed when the slag is not formed.The cathode spot is at the steel skin,and the steel skin melts faster than the slag column.When the slag column leaks outside,the cathode spot contains a material with a lower work function,causing the cathode spot to jump from the steel skin to the slag column.When the slag column melts faster than the steel skin,when the slag column shrinks into the steel skin,the arc ignites to the steel skin,and the arc continuously burns between the steel skin and the slag column.When the cathode spot is at the steel skin,the steel sheet is thin and melts at a high speed,and the surface tension is small,and many fine particles are formed.Before coalescing into large drops,the arc wraps the drop and disconnects from the wire under the force of electromagnetic force.When the direct current is reversed,the basic form of the droplet transfer is characterized by a large droplet repulsive transition,the droplets are severely deformed and continuously moved at the end of the wire,and the anode spots are not expanded to be bound to the bottom of the droplet and continuously transferred in the bottom region of the droplet.During the transfer of the anode spot in the bottom region of the droplet,the direction of the force of the droplet changes continuously,so the droplet forms a couple under the action of spot pressure and gravity,causing the droplet to rotate away from the end of the wire.2.The study of the characteristics of basic self-protected flux cored wire welds.On the basis of obtaining the stable basic self-shielded flux-cored welding process,The linear and nonlinear models between the input variables(arc voltage,wire feeding speed,welding speed)and the output variables(melting width,reinforcement,melting height)were established by quadratic regression universal rotation combination design and BP neural network and the simulation and sensitivity analysis of the model.The results show that the melting width increases with the increase of voltage.The reinforcement and melting height increase first ly and then decrease with the increasement of arc voltage.The melting width,reinforcement and melting height increase firstly and then decrease with the increase of wire feeding speed.Small,gradually decreasing as the welding speed increases;The wire feeding speed is the main factor affecting the melting height.The wire feeding speed is the main factor affecting the melting width and the reinforcement at low voltage.The welding speed is the main factor affecting the melting width and the reinforcement at high voltage.