| Laser 3D printing technology is a new advanced manufacturing technology which combines rapid prototyping theory in recent years.Because it can realize the rapid,die-free and near-net-shape manufacturing of metal parts with arbitrary free-form structure,high density and excellent performance,it has a wide application in aerospace,intelligent automobile,new chemical energy and other high-tech industries.In recent years,systematic analysis of this technology has become a research hotspot.Firstly,the main process parameters affecting the quality of laser 3D printing are quantitatively processed by using the unified dimension method.Through systematic experimental research,the optimum single-channel printing process parameters satisfying the set conditions are obtained:laser power P=2200W,scanning speed v=480mm/min,spot diameter d=3mm,powder feeding speed f=18g/min,heat input value lambda=275W.S/mm.Then,using single-channel optimum process parameters,large-scale metal thin-walled parts with different gradients of 10,20 and 30 layers were printed.The characterization and analysis of the 30-layer wall parts system showed that the microstructure of the samples was mainly composed of columnar dendrites grown by directional epitaxy,and the direction of dendrite grain growth was 45-65 degrees with the direction of laser beam scanning.With the increase of the number of printing layers,the microstructure of dendrites grew 45-65 degrees with the increase of the number of printing layers There is a process of transformation from fine cellular crystals to cellular dendrites to dendrites,which conforms to the theory of rapid solidification and is consistent with the research results obtained by key research institutes at home and abroad.It is also found that with the increase of height,the longitudinal gradient structure of the specimen is not uniform,and the tensile strength at different gradient positions is obviously inconsistent.In order to solve these problems,based on ABAQUS 6.14.1 CAE,the evolution process of transient temperature field of laser 3D printing large-sized thin-walled parts was dynamically simulated by using "life and death element method".The influence of main process parameters on the evolution of molten pool was obtained by implicit solution and iterative calculation.It was found that laser 3D printing process was a rapid heating and cooling process.The peak temperature of each analysis step in the printing layer is higher than that in the previous one,but the increase will be smaller and smaller until it remains stable.With the increase of the number of printing layers,the temperature of the molten pool will accumulate seriously,the heat affected zone will expand significantly,and the remelting zone of the molten pool will also increase.In order to solve these problems,a dynamic adaptive layer-by-layer power reduction processing scheme is proposed to alleviate the thermal accumulation effect in the process of laser 3D printing of thin-walled parts,so that the structure of the printed parts is more uniform and the performance is further improved.In order to find the boundary value of this scheme,a layer-by-layer 20W and layer-by-layer 30W reduction scheme for minimizing heat input is designed and simulated.By comparing the thermal cycle curves of the relevant feature points,it is found that this scheme can significantly reduce the thermal accumulation effect in printing process.According to the new design scheme,the related forming experiments were carried out and the system comparison analysis was carried out.The characterization results show that the performance of thin-walled parts formed by the new scheme is better and more uniform,and the structure is more uniform.The process design and performance optimization of 3D printing metal thin-walled parts are carried out systematically. |
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