Research On Compulsively Constricted Wire Arc Additive Manufacturing

Wire and arc additive manufacturing(WAAM),as one of the most advanced manufacturing technology,is generally regarded as the most promising method for reliable and economical additive manufacturing of metal parts.It's paticularly suitable for the rapid prototyping in the fields of ship,aviation,and aerospace due to its advantages such as lower cost,higher efficiency and higher density compared to conventional metal additive manufacturing with high energy beam.A novel compulsively constricted wire arc additive manufacturing(CC-WAAM)method was proposed and investigated in this paper.It's aimed to solve the challenges confronting traditional WAAM such as low accurancy and poor machanical properties of the parts due to excessive heat input and "stair stepping" in the process of the welding.Compared with traditional WAAM,the indirect arc burns between a metallic wire and a tungsten electrode rather than between a wire and workpiece.The proposed technology could provide compulsive constriction on arc plasma and liquid metal droplets using a CBN(cubic boron nitride)ceramic nozzle.The surrounding arc was ejected out of the nozzle and offers extra heating and good shielding environment during the whole manufacturing process.The trajectory of the droplets can be regulated by the ceramic nozzle for high accurancy at the same time.The wide-range adjustable heat input can control the state of the metallic formation ranging from solid metal balls to overheated droplets,making it possible to have an accurate control of microstructure and properties.The geometrical dimensions of each layer were effectively controlled via regulating the travelling speed.An innovatively designed torch based on the compulsive constriction producing constricted arc and liquid metal was employed for additive manufacturing.Preliminary experiments showed that the torch could meet the principle of CC-WAAM with stable welding process and integration of the torch.The additive manufacturing with low alloy steel was produced on the baseplate to explore the morphology under different gas flows,travelling speeds,electrical parameters and nozzle outlet diameters.Meanwhile,a double-layer AM layer was deposited continuously with the process parameters researched.The microstructures of the cross-section shown that the AM layers produced by the novel method had homogeneous and fine grains consisted of acicular ferrite and granular bainite.However,no coarse column-like grains in the sections were found,which is attributed to the low heat input of this novel arc constricted WAAM method.In addition,the micro-hardness distribution indicated that the micro-hardness distribution of the both AM layers is homogeneous which ranges from 240HV to 300HV.In addition,the shape of constricted arc and liuquid pool,droplet transfer behavior under differert process parameters were observed and analyzed with high speed camera.The influences of various factors on these were explored to provide a theoretical basis for the control of CC-WAAM morphology.