Investigation On The Novel Gas Tungsten Rotary Arc Additive Manufacturing Technology For Stainless Steel Materials

Compared with conventional manufacturing technologies such as milling and casting,additive manufacturing technology has the advantages of high material utilization,simplified production process,and suitable for manufacturing complex shaped parts.Among them,the arc additive manufacturing technology has higher deposition efficiency,simple equipment and low cost,so it has greater advantages in manufacturing large parts.Additive manufacturing with GTA(Gas Tungsten Arc)as the heat source has the advantages of stable deposition process,no splash,and high precision.However,there are problems such as uneven arc heat concentration,tissue coarsening and performance degradation caused by large heat input when the current is large,excessive remelting and hump defects caused by excessive arc pressure.Therefore,the GTA additive manufacturing current is usually limited to less than 200 A,which greatly limits the efficiency and performance of this additive manufacturing technology.In order to solve the above problems,our research group proposed a novel Gas Tungsten Rotary Arc Additive Manufacturing technology(GTRA-AM),in which the tungsten electrode tip is nonaxisymmetric and is driven by a motor with adjustable speed for additive manufacturing.manufacture.The rotary arc can effectively disperse the arc pressure and heat,make the heating process more uniform,reduce the arc pressure and heat input acting on the additively formed parts,and at the same time can effectively stir the molten pool to make the formed parts finegrained,the performance is improved,and the range of forming electrical parameters is expanded.The results of the research have important implications for improving the efficiency and quality of GTA additive manufacturingGTRA additive manufacturing experimental platform was built,and 304L stainless steel welding wire was used for additive manufacturing.It is calculated that the rotary arc covers a larger area than the conventional arc,the arc pressure is more dispersed,and the tungsten electrode tip is a 450 inclined plane,which is the best shape of the additive tungsten electrode tip.When the arc rotates to both sides of the accumulation layer wall,the arc will be exposed outside the wall,which effectively reduces the heat input.When the arc rotates to the side of the welding wire,the arc melts the welding wire and produces droplet transfer.Detection of electrical signals and thermal cycling indicated that the rotary arc had a lower maximum temperature during manufacture,reflecting the lower heat input to the rotary arc.When the rotary arc is deposited on the wall of the accumulation layer,the voltage presents a ’M’ shape.When the arc rotates to both sides of the wall,the arc is elongated,and the arc voltage rises to form a wave peak;when the arc rotates to the molten pool side and the welding wire side,the arc shortening,the arc voltage is reduced to form a trough,and due to the long path of the arc on both sides,a ’m-shaped’ platform will be formed at the peak of the wave.When the tungsten electrode is raised,the arc voltage of the arc increases,and the arc is not sensitive to the height difference between the middle and both sides of the molten pool.At this time,the platform disappears,showing a regular ’M’ shape.Observing the flow behavior of molten pool with high-speed camera by embedding tracer particles.It is found that the tracer particles in the molten pool rotate periodically with the rotation of the arc.Compared with the conventional arc,the tracer particles move more violently under the influence of the constantly changing arc force of the rotary arc,and the arc has an stirring effect on the molten pool.The structure in the bottom of the formed part is mainly composed of small columnar crystals and cellular crystals;the central melting zone(below the fusion line)is mainly composed of coarse columnar crystals and dendrites,and the central remelting zone(above the fusion line)is mainly columnar crystals and cellular crystals;The structure in the top is columnar crystals and dendrites with different grain orientations,and the phase composition is mainly austenite and a small amount of residual δ-ferrite.Compared with conventional GTA additive manufacturing,the formed parts produced by rotary arc additive manufacturing have finer grains,more uniform hardness,and better tensile strength,plasticity,impact toughness and corrosion resistance.With the decrease of heat input,the strength,plasticity and corrosion resistance of rotary arc formed parts increase.At the same time,due to the different residence time of different parts of the formed parts in the sensibilization temperaturel,the intergranular corrosion resistance of the samples is better at the top than at the bottom and central the intergranular corrosion resistance of the top sample is better than that of the middle and bottom samples.