Research On Cross-Structure Cladding Forming Based On Inside-Laser Powder Feeding

Cross structure is a typical form of complex metal parts,such as grid structure,central flange and internal hollow support,etc.,which has been widely used in aerospace,Marine engineering and mechanical manufacturing.CNC milling,welding and casting are often used to process cross parts.However,these methods have some problems,such as low material utilization rate or inability to process in nested structure and narrow space.Laser cladding forming is an additive manufacturing technology based on layer by layer cladding stacking.It can realize high performance complex structure metal parts forming without mold,fast and near net.Therefore,forming cross structure parts by laser cladding technology has important research value.In this paper,the experiment was carried out by using the "light inside powder feeding"nozzle independently developed by the laboratory to study the powder divergence under different tilt angles of the nozzle,establish the powder density distribution model based on probability theory,and obtain the corresponding powder density distribution under different defocus process parameters.The influence of laser power,scanning speed and defocus on the width and height of single pass cladding layer was analyzed by single factor experiment,and the optimal process range of single pass cladding layer with cross structure was obtained.In this paper,the cross-forming process of cross-shaped structures was studied by using the strategy of local acceleration at the cross-overlapped parts.Firstly,the cross-unequal height deposition process was proposed.According to the law of mass conservation,by calculating the powder mass entering the molten pool and the forming mass of the cladding layer,the influence law of the forming transverse channel first on the forming longitudinal channel height was obtained.Secondly,a mathematical model of unequal height of velocity was established.Combined with the deposition process of unequal height of cross,the scanning speed was calculated when the overlapping height of cross position was equal to the height of molten channel in the uncrossed position.Finally,according to the selfhealing effect and volume flow hypothesis,a process method is proposed to reduce the distance of the acceleration stage,which solves the problem of sag in the cross-bonding part of the molten channel after the acceleration.For such as X,ring and ring cross dislocation cross structure,half cylinder along the growth direction of oblique cutting volume change,on the basis of the mathematical function calculation according to the volume assumptions.to determine the distance of intersecting acceleration period,complete melting type compound forming "rings" cross structure,honeycomb and method on the basis of forming the cross dislocation cross structure.For multi-channel crossing,the iterative calculation of intersecting crossing model was completed to obtain the initial acceleration height of cladding layer corresponding to the crossing times at different positions of cladding layer.Based on the mathematical model of unequal height growth,the acceleration measurement of crossing one,two and three times was obtained.The optimal distance of the "meter" shaped multi-channel cross acceleration section was solved,the cladding path planning was completed,and the "meter" shaped cross structural parts were completely formed.The flow displacement of the molten pool under the space arbitrary dip Angle inclined plane was analyzed,and the mathematical model of the flow of the molten pool under the space arbitrary dip Angle inclined plane was established,which provided the corresponding theoretical support for the final forming of curved "m" shaped cross structural parts.Through the research on the key technologies in the forming,the forming of "well" type,five-ring type,"meter" type,honeycomb type,bending "meter" type cross structural parts is finally realized,and the forming of the macro-dimensional accuracy,microstructure and micromechanical properties of the parts are detected and analyzed.The results show that the maximum height size error of cross parts is within+2.81%.The overall microhardness fluctuates between 275±20HV,and the surface of the final forming part is smooth and bright,without macroscopic cracks or inclusion defects.The microstructure of the forming part is dense,and the grain size increases first and then stabilizes with the increase of the forming height.The grain size of the cross part of the same layer is slightly larger than that of other parts,and the grain growth direction is vertical confluence.