CMT电弧增材制造过程电弧特性对熔滴过渡行为的影响机理研究

Influence Mechanism of Arc Characteristics on Droplet Transfer Behavior in CMT-based Additive Manufacturing

冷金属过渡(CMT)电弧增材制造技术具有沉积效率高、制造成本低等优势,在航空用大尺寸构件的快速成型领域应用前景广阔。对于电弧增材制造大型构件需采用大电流来进一步提高沉积效率,但在此高电流模式下电弧放电过程对熔滴过渡行为的影响机理尚不明确。因此,本研究采用高速摄像仪观察了电弧增材制造过程中电弧形态及熔滴过渡行为,同时通过建立电弧模型及熔滴过渡模型,分析了在不同电流波段及工艺参数下熔滴过渡频率及熔滴尺寸变化规律,最终揭示了电弧放电过程中电流密度、洛伦兹力等物理因素对熔滴过渡的作用机理。结果表明,电弧宽度与洛伦兹力决定熔滴在电弧放电过程中的受力大小,进而决定熔滴尺寸及其过渡频率。随着送丝速度从5.5 m/min增大至7.0 m/min时,电流峰值持续时间增加了1倍左右,同时电弧宽度与电流密度的随之增加,使得熔滴过渡过程中电磁力上升,熔滴尺寸下降14%且射滴过渡频率增加了3~4倍。当瞬时电流进入熄弧阶段时,熔滴过渡形式转变为短路过渡。随着送丝速度的增加,短路过渡频率从29 Hz减少至20 Hz。

Cold metal transition(CMT) arc additive manufacturing technology has the advantages of high deposition efficiency and low manufacturing cost,which has a broad application prospect in the rapid prototyping of large-scale components for aviation.A higher current is needed to improve the deposition efficiency for arc additive manufacturing large-scale components.However,the projected transfer behavior under the high current mode and the influence mechanism of the arc discharge process on droplet transfer frequency is not explicit.Therefore,the arc shape and droplet transfer behavior in the CMT process is observed through a high-speed camera in our study.Meanwhile,the droplet transfer frequency and droplet size under different current waveforms and process parameters are analyzed by establishing the arc discharge and droplet transfer model.Finally,the impact mechanism of physical factors such as current density and Lorentz force on droplet transfer in the arc discharge process is revealed.The results show that the arc width and Lorentz force determine the force on the droplet in the process of arc discharge and then determine the droplet size and its transition frequency.The duration of the current peak value increases by about one time when the wire feeding speed increases from 5.5 m/min to 7.0 m/min.Meanwhile,the electromagnetic force increases with the rise of arc width and current density.It causes the droplet size decreases by 14%,and the droplet transfer frequency increases by 3-4 times.When the current waveform enters the arc extinguishing stage,the droplet transfer mode changes to short-circuit transition.The short-circuit transition frequency decreases from 29 Hz to 20 Hz with the increase of wire feeding speed.