| Variable cross-section special-shaped thin-walled structures are widely used in equipment in aerospace,ocean-going machinery,and biomedical fields.Such components have structural characteristics such as large-angle torsion overhang and cross-sectional space anisotropic growth.The traditional processing methods are mostly Processes such as CNC milling,hydraulic filling and split forming of stamping and tailor welding are the main processes.Such processing methods have a long manufacturing cycle,serious waste of raw materials,and the performance of formed parts is difficult to meet the needs of specific working conditions.Additive manufacturing technology can achieve near-net-shape of complex parts,but there are problems such as small size,high cost,and complicated support in selective powder bed melting,and the inclination angle of the existing fused deposition nozzle is too small.Therefore,based on the laser internal powder feeding cladding forming technology,this paper studies the direct forming process of variable cross-section specialshaped thin-walled structural parts.In this paper,by analyzing the optical powder coupling characteristics and distribution mode of the optical powder feeding technology,the optimal defocus amount range of the cladding plane theory is obtained,and the influence trend of different process parameters on the shape of the molten channel is studied through the basic single-channel experiment.Explore the best forming parameters and build a process window for cladding with internal powder feeding.Based on the typical application scenarios of variable-section special-shaped thinwalled structures,three parts models with more representative structural features and forming difficulties are designed(including open curved and twisted structural parts,closed variable-section bending-torsional structural parts,and variable-section large-scale Aiming at the geometric characteristics and slicing difficulties of this type of structural parts,a discrete gradient layering method is proposed to complete the slicing process,and a series of discrete units with different shapes and orientations are obtained.According to the position and direction information of the discrete units obtained by slicing the structural parts,the trajectory planning of the nozzle is completed and the preliminary accumulation experiment is carried out.Aiming at the flow and displacement phenomenon of the molten pool when the variable-section special-shaped thin-walled structural parts are stacked,the force model of the liquid molten pool on the inclined surface of the space is established by establishing a force model of the liquid molten pool.,a process method for controlling the displacement of the overhanging molten pool is obtained;in order to solve the problem of light leakage at the corner of the structural member due to the lack of matrix support,the position of the light spot is compensated with reference to its transformation base point during the process of changing the attitude of the nozzle,so that the diameter of the light spot is related to the shape of the beam.The wall thickness of the parts is uniform to eliminate light leakage defects.In order to realize the unequal height accumulation of structural parts in the continuous variable attitude cladding process of the nozzle,a spatial variable angle weld channel unequal height growth process model was established,and the cladding inclination was introduced as an input variable to conduct a single-channel orthogonal experiment,and the fitting results were obtained.The mapping relationship between scanning speed and cladding inclination angle and layer height under different powers,the stacking unequal height overhanging structural parts are designed to verify the applicability of the model in the process of stacking growth between layers of variable-angle melt channels,and the matching logic is completed according to the model parameters.Cladding forming of two kinds of variable-section special-shaped thin-walled structural parts,open and closed.Based on the existing equipment,in order to realize the direct forming of large-scale structural parts with variable cross-section,this paper proposes a vertical normal cladding forming method,and solves the problem of nozzle load during long-term continuous cladding by optimizing the structural materials of the protective gas cover and the powder discharge pipe;the design""The path planning strategy of "from small to large,necking first" combined with the synchronous compensation scheme of nozzle lift and offset in the later stage of forming,completed the laser cladding forming of large parts.During the cladding process,the deposition rate reaches 24.8 g/min,the size error of the formed parts is between-1.6%and 2.18%,and there is no obvious macroscopic crack defect on the surface.The follow-up inspection of the camber twisted structural parts shows that the formed parts have high precision,the dimensional error is between-1.89%and 3.05%,and the surface roughness is between 1.323 μm and 9.638 μm;the overall distribution of microhardness is relatively uniform,and the mechanical The performance is good,the upper yield strength and maximum tensile strength are 340.52 MPa and 765.81 MPa,respectively,and the elongation after fracture is 11.2%;the microstructure is dominated by uniform and dense fine dendrites,without obvious pores and inclusion defects. |
PDF Full Text Request