Study On Metal Additive Manufacturing Method By Selective Melting Using Microbeam Arc

There are many kinds of metal additive manufacturing technologies,each of which has its own advantages and disadvantages,each with its own suitable processing occasions.In this paper,powder bed bedding and arc heat source are combined to propose and study a new metal additive manufacturing method-microbeam arc selective melting metal additive manufacturing method.The method can obtain higher processing resolution and processing precision than the wire and arc additive manufacturing while preserving the low cost advantage of the wire and arc additive manufacturing,and is more suitable for 3D forming of parts with complex shapes and small dimensions than the wire and arc additive manufacturing technology.In addition,the method can form a gradient material part,and can realize miniaturization and desktopization of the forming equipment,and has great development potential.The process of the method is: using a layer-by-layer layering method,a layer of powder is laid on the powder bed,and the layer powder is scanned according to the crosssectional shape of the part by a direct current microbeam arc(current 5A or less),and the powder in the cross-section area is melted and cooled to be solidified.Then,the powder bed is lowered by one layer,and then a layer of powder is applied,and the above process is repeated until a three-dimensional part is formed.A prototype device for microbeam arc selective melting additive manufacturing has been developed,which can continuously and stably form the parts.Through the observation of the interpolar phenomenon,it is found that the viscous resistance of the positive electrode to the arc is greater than that of the negative electrode,and the negative polarity processing should be used in the process of microbeam arc selective melting additive manufacturing.The formation and sublimation of tungsten oxide on the surface of the tungsten electrode causes the shape change and material loss at the end of the electrode.The arc is often discharged on the side of the electrode,which is why the thinner electrode can be self-sharp.Self-sharpening of the electrode can improve the forming accuracy.It has been found through experiments that if the scanning speed is too large,spheroidization will occur and the forming will fail.Moderate scanning speed and current give the best surface quality and dimensional accuracy.The single-pass melting width,decreases as the arc scanning speed increases,and increases as the arc current increases.The additive rate increases with the increase of arc scanning speed and current.Through simulation analysis,it is found that the molten pool depth decreases as the scanning speed increases.As the arc current increases,the cross-sectional area of the arc column increases greatly,the arc energy density decreases,and the overall trend of the molten pool depth decreases.As the scanning speed increases,the volume of the molten pool,the volume of the boiling pool,and the proportion of gasification decrease.As the arc current increases,the volume of the molten pool increases first,then decreases,which is the result of the combined action of the total energy of the arc and the energy density of the arc.The boiling pool occurs when the arc current is small,because the small current has a large energy density.In general,the powder boiling gasification amount is a small proportion of the melting amount,and does not adversely affect the forming quality.According to the experimental and simulation results,the reasonable single-layer single-pass forming process parameter combination was clarified.Through experimental research,it is found that when a certain planar area is melted,changing the parallel track pitch,the channel does not change in shape size,and the flat band width between the channels is changed,and the wider parallel track pitch can improve the overall forming surface and increasing the additive rate.Single-layer single-pass samples,single-layer multi-pass flat samples and multi-layer single-pass thin-wall sample are formed,wherein the multi-layer single-pass thin-wall sample has a single-sided precision of 200 ?m.