Study On Droplet Transfer Behavior And Forming Characteristics Of CMT-based Wire And Arc Additive Manufacturing For High Nitrogen Steel

In view of the problems of the instability of droplet transfer behavior in the CMT-based wire and arc additive manufacturing for high nitrogen steel,the experimental research on the CMT-based single and double wire and arc additive manufacturing for high nitrogen steel was carried out,and revealed the influence of different process parameters,including wire feeding speed and double wire angle,on the droplet transfer behavior and forming characteristics of high nitrogen steel.Then,the droplet transfer behavior was stable by adjusting the current waveform parameters,so as to obtain the stable process range of CMT-based wire and arc additive manufacturing for high nitrogen steel.Firstly,the droplet transfer behavior of CMT-based wire and arc additive manufacturing for high nitrogen steel was studied.The results showed that the droplet explosion mainly occurs in the current peak stage,and the droplet transfer behavior is relatively stable in the short circuit stage.When the wire feeding speed is less than 4 m/min,the droplet basically does not explode and the droplet transfer behavior is stable.Then,by adjusting the current waveform to expand the process range,it was found that the stability of droplet transfer behavior in the peak stage is mainly affected by the peak current and peak duration.When the peak current I_b is133A～193A,the peak duration t_b is 3ms～6ms,the peak wire feeding speed V_d is 32～40 m/min,and the base current I_wait is 40A～80A,the droplet transfer behavior is relatively stable.After current waveform optimization,the process range of stable droplet transfer of CMT-based single wire and arc additive manufacturing for high nitrogen steel is expanded from 70A～85A to 70A～100A.Although the droplet transfer behavior of CMT-based single wire and arc additive manufacturing for high nitrogen steel is stable under low current,the forming of deposited metal is poor.Now the single wire stable droplet transfer process was applied to the CMT-based double wire and arc additive manufacturing to improve the heat input and realized the deposition effect of high heat input under low current.The results showed that the size of the overlap area of the molten pool is different for the different double wire angle,and the oscillation of the molten pool with lager overlap area is more violent.It results in serious arc interference and worse droplet transfer stability.The double wire arc interference can be improved by adjusting the peak duration t_b.When the sum of the double wire peak duration is smaller and the difference is smaller,the droplet transfer behavior is more stable.Finally,the forming characteristics and the nitrogen pore of CMT-based double wire and arc additive manufacturing for high nitrogen steel were studied.The results showed that the minimum total wire feeding speed required for double wire eutectic pool increases with the increase of double wire angle.When the double wire angle is less than 45°,the spread of deposited metal is poor.When the double wire angle is 45°and the sum of the double wire feeding speeds is greater than 8.7 m/min,the deposited metal generally reachesⅡweld.After the current waveform is optimized,the spatter at the edge of deposited metal is significantly reduced and the porosity is basically unchanged.Then the optimized current waveform parameters were selected for lap test.It was found that the surface flatness of deposited metal layer is better when the center spacing is 8mm.