| Arc fuse wire 3D printing is a kind of manufacturing technology based on three-dimensional model of parts.It uses arc as heat source to melt metal wires and deposits parts layer by layer.It is a new important way to form some large and complex components which are not easy to shape with traditional method due to its free of mold and dense microstructure.However,nowadays most of arc fuse wire 3D printing processes use common wires for welding as filling materials.There is no wire specially for arc fuse wire 3D printing.It is known to all that welding process considers both base material and welding material,but arc fuse 3D printing only needs to consider the composition and properties of deposited metal.They are different in many aspects.So it is necessary to develop metal wire specially for arc fuse 3D printing.Metal powder type flux cored wire is made of a steel strip coated with mixed alloy powder,and then strip is reduced to a certain diameter after many drawing.Compared with solid wire and mineral cored wire,it has the advantages of no slag or less slag,high efficiency and easy to control composition.It is one of the most promising wires for arc fuse 3D printing.In view of the characteristics of arc fuse 3D printing,an alloying system for 780 MPa metal core wire was determined.To increase strength of deposited metal,different contents of V was added.In addition,0.5 to 1 percent of NaF was added to the wire to improve process performance.Single-layer single-pass deposition and multi-layer multi-pass deposition tests were conducted using developed metal wire.It was found that deposited metal was well shaped and no undercut,gas hole and slag were discovered.Spatter rate remained below 2.5% when current changed from 155 to 250 A,and most of the spatter particle diameter was below 2mm.The microstructure and mechanical properties of deposited metal were studied when V content was 0%,0.07%,0.15% and 0.22%.With the increment of V content,composition of optical microstructure were not changed which consisted of ferrite and granular bainite.With the help of TEM,it was found that with addition of V,precipitates were discovered in ferrite.The more V content was,the more precipitates were found.And average size of precipitates increased from 5.59 nm to 9.14 nm when V content increased from 0.07% to 0.22%.Precipitates distribution was evenly dispersed.According to diffraction spots of precipitates,it could be known that precipitates were VC.In addition,bath bainite was discovered in all the four groups of wire.High density dislocation could be found in lath bainite.As V content changed from 0% to 0.22%,yield strength of deposited metal of developed wire increased 99 MPa and tensile strength increased just 42 MPa,which was benefical from precipitation strengthen of V.And the increase of strength was accompanied by a reduction in plasticity.Meanwhile,addition of V caused the impact energy decreased about 20 J.But more V content could not affect the toughness any more.Scanning electron microscopy was used to observe the impact fracture.The fracture was a mixed of ductile and brittle fracture,which was composed of dimple and dissociation step.Inclusions could be found at the bottom of the dimple.And with the increase of V content,dimple became more and more dense and its size became smaller.According to mechanical performance standard required of propeller bracket,metal power flux cored wire with 0.15% V content of deposited metal was finally used for 3D printing of propeller bracket simulator.According to structural characteristic of propeller bracket simulator,a corresponding block printing strategy was formulated.Programs were written in java language for hierarchical slicing and path planning.In the actual printing process,arc was stable and there was less spatter.Size deviation between the final printed size and the target size was within 1mm.Microstructure and mechanical properties of printed parts were all similar to those of developed metal power flux cored wire. |
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