A Simulation Study On Electron Beam Rapid Manufacturing Of Ti-6Al-4V Thin Walled Piece

In electron beam rapid manufacturing(EBRM),metallic feed materials are melted by an electron beam and deposited layer by layer to form a piece in vacuum.Microscopic structure of Ti-6A1-4V(TC4)piece formed in an EBRM process was observed,and many pore defects were found.Elemental analysis results indicated that A1 element evaporation can lead to the generation of the pores due to the electron beam with high energy that can also provoke undesirable distortion.Simply lowering the energy of the electron beam may cause the imperfect fusion of the materials,inducing low accuracy and void defects of the piece.Numerical analysis of two processes,i.e.,wire-fed electron beam freeforming fabrication(EBF3)and powder-fed electron beam melting(EBM),was performed to explore ways to improve the quality of the piece.In EBF3,the solid state phase change(SSPC)temperature of TC4 material was determined to be 850? by variable temperature XRD measurements.The forming process of a thin-walled TC4 piece was modeled,and the most accurate predictions were achieved with an SSPC temperature of 850 0C.The thin-walled piece can form well if the electron beam operates at a scan current from 100 to 150 mA and a speed below 100 mm/s.The distributions of the residual stress are consistent in reciprocating and unidirectional scan modes,but the former performs better in distortion.In reciprocating mode,contract distortion dominates and increases with the scan current.Two methods to decrease the distortion,i.e.,a dynamic current plan and a constant temperature constraint at the bottom of the substrate,were proposed and demonstrated.In EBM,based on the thermal model,and the accuracy to predict the temperature field and the shape of the first cladding layer was verified by reported experimental results.The influence of TC4 SSPC on the temperature field can be ignored.With the reduction of the scan power,the thickness of the cladding layer decreased and the morphology got coarser.With the increase of the relative density of powder,the required scan power to realize complete fusion increased and the morphology got coarser.To improve the quality of the morphology,increasing the scan power according to the relative density appropriately to achieve complete fusion without gasification is effective.