Study On Droplet Transfer Behavior And Microstructure And Properties Of GMAW Under Magnetic Field

As a kind of metal part manufacturing technology,arc additive manufacturing has the advantages of simple equipment,high material utilization rate and high production efficiency,which is widely used in the field of industrial manufacturing.However,there are some defects in the manufacture of arc additive,such as rough forming size.The transfer behavior of droplet is very important to the welding quality.It is one of the important ways to control the transfer process of droplet by external magnetic field.In this paper,the welding process of arc additive manufacturing is controlled by the external alternating longitudinal magnetic field,and the droplet transition behavior under different magnetic fields is studied by using the high-speed camera system;the influence of magnetic field on the microstructure and properties of additive manufacturing specimen after heat treatment is analyzed by means of the instrument and equipment;the surface forming size of specimen is measured,and the influence of magnetic field on the forming accuracy of specimen is analyzed.The welding technology of cmt-pa is used in the arc additive manufacturing system.The process is characterized by the combination of AC CMT process and pulse MIG process.In AC CMT welding,after applying alternating longitudinal magnetic field,the droplet volume increases and the shape changes from the original round ball shape to the flat ball shape;the arc changes from the left and right swing shape to the rotating shape,which has the electromagnetic stirring effect on the molten pool.The charged particles in the arc do the spiral motion,and the arc rotation direction changes with the change of magnetic field direction,and the rotation speed will accelerate with the increase of excitation current The increase of excitation frequency makes the arc radius of rotation decrease.During pulsed MIG welding,under the action of alternating longitudinal magnetic field,the droplet rotates,the direction of rotation changes with the direction of magnetic field,the droplet becomes flat ball,the necking duration is greatly shortened,and the droplet is easier to transition;the shape of arc changes from cone-shaped to bell shaped,the upper part contracts and the lower part expands,and the energy density of arc is more concentrated.Under the action of alternating longitudinal magnetic field,the microstructure grain of the specimen is finer and more uniform,and the surface is more flat.When the excitation current 4A is 50 Hz,the mechanical properties reach the peak value,the tensile strength is increased by70 MPa,the yield strength is increased to 9Mpa,and the hardness is increased by 24.9hv;when the excitation current 6a is 50 Hz,the elongation is increased by 8%.The surface forming of the specimen has also been greatly improved.When the excitation current is 4A and the excitation frequency is 70 Hz,the maximum difference of layer width is reduced by 1.8mm;when the excitation current is 6a and the excitation frequency is 50 Hz,the maximum difference of layer height is reduced by 2.8mm.