Investigation On Forming Process Of Additive Manufacturing Based On Rotating Arc

With the advantages of low cost,high deposition rate,and the ability to manufacture large metal structure parts in a short time,gas metal arc additive manufacturing has been widely used.However,this method is characterized by large heat input and uneven distribution of arc heat,which can easily lead to forming quality problems such as poor fusion between beads,poor surface flatness and excessive remelting between layers of formed components.To address the above problems,this thesis proposed an additive manufacturing method based on gas metal rotating arc by applying it to additive manufacturing with the characteristics of large thermal area and uniform heat distribution.The physical processes such as arc shape,droplet transfer behavior and overlapping behavior of molten metal were deeply investigated,and the forming quality and forming characteristics of the method under different process parameters were explored,which provided a basis for the application of the additive manufacturing method of gas metal rotating arc.Firstly,the arc shape and droplet transfer behavior of rotating arc additive manufacturing were investigated.The arc acting area is larger than that of conventional arc and the arc acting position varies periodically.As the rotating frequency increases within the range of 5～15 Hz,the droplet transfer behavior does not change,and the droplet transfer position gradually concentrates on the end of the molten pool,which makes the droplet transfer frequency gradually increase and the droplet size gradually decrease.Secondly,the effect of each process parameter and its coupling on the forming quality of single deposition bead was explored,and the process window of rotating arc additive manufacturing was obtained.The relationship between the forming size of the deposition bead and the process parameters was investigated.The results show that the deposition bead is still well-formed under the large wire feed speed of 7m/min and the travel speed of 120～300 mm/min.With the increase of rotating frequency in the range of 5～15 Hz,the width,height and penetration of deposition bead gradually decrease.The deposition layer forming characteristics of the rotating arc additive manufacturing method were investigated.The arc acts on the previous deposition bead periodically to enhance the overlapping capability of the molten metal,and the deposition layer had good fusion between beads,the surface flatness was improved and penetration of deposition layer was reduced significantly.With the increase of arc rotating frequency,the transverse heat conduction is inhibited,the heat affected zone between beads is reduced,the overlapping ability of molten metal is decreased,the surface flatness will gradually deteriorate,and the penetration will gradually increase.The results show that when the rotating arc method with the rotating frequency of 5 Hz is used,the surface flatness of the deposition layer is the best,which is only 30% of that of the conventional arc method,and the penetration is the least,which is only 49% of that of the conventional arc method.To verify the theories obtained in this thesis,multi-layer single-bead straight walled components and multi-layer multi-bead stepped components were formed using conventional arc and rotating arc additive manufacturing methods,respectively.The results show that the straight walled components with rotating arc additive manufacturing method are well-formed and uniform in width,the deposition efficiency reaches 94.3%,which is12.9% higher than the conventional arc method,the surface waviness is 0.67 mm,which is only 21% of the conventional arc method.The stepped components with rotating arc additive manufacturing method have tight bonding and small penetration.The surface flatness of each layer is better than that of the conventional arc method,and the width range of each deposition layer is 1.86 mm,which is only 39% of that of the conventional arc method.The rotating arc additive manufacturing method achieves an effective improvement in the forming quality of the formed components while maintaining the forming efficiency.