Study On Mechanical Properties Of Metal Lattice Structures Based On Selective Laser Melting

Lattice structure has the characteristics of low density,high specific strength,high specific stiffness,etc.It has a broad application in the fields of aerospace,automobile,bio-medical treatment and energy.However,due to its complex structure,it is difficult to manufacture such structure using the traditional manufacturing methods.In recent years,the development of additive manufacturing technology provides a very convenient condition for the research and application of lattice structure.As the lattice structure has good potential for integrated design of material,this dissertation focuses on the problem of the manufacturing accuracy and quality of lattice structures,and lacking of systematic research on mechanical properties.In this dissertation,a new type arch lattice structure was designed,and the laser selective melting manufacturing process and method of the structure were studied.The mechanical properties of the structure were systematically studied.Finally,the application of the design and manufacturing method of the arch lattice structure was verified based on the missile wing and a certain type of strong heat exchange structure.The main researches and results are as follows:(1)The theoretical analysis of mechanical properties of arch lattice structure:The arch structure has the characteristics of high stiffness and stronger ability to resist the compaction.The arch lattice structure with different parameters was designed based on the characteristics of arch structure,and the structure with half round axes was numerical calculated.The results show that the equivalent elastic modulus of the arch lattice structure was influenced by the elastic modulus of the substrate material,the strut diameter and radius of arc.The equivalent elastic modulus increases with the increases of strut diameter and decreases with the increases of arc radius.(2)Research on the laser selective melting process of arch truss lattice structure:The processing parameters of selective laser melting fabricate lattice structure were optimized,the laser power,scanning speed,scanning spacing,spot compensation radius and shielding gas flow rate are determined.16 different combinations of laser processing parameters(different laser power,scanning speed and scanning spacing)were designed with the energy density range of 78?82 J/mm3.The effects of different combinations of process parameters on the densification,hardness,grain size and surface roughness of the samples were analyzed,and the combination of optimized laser process parameters was selected.Six kinds of spot compensation radius in the range of 0?0.13 mm were designed,and the influence of spot compensation radius on the dimensional accuracy of the strut was analyzed.The spot compensation radius with the smallest size error was selected.Finally,with the goal of improving the reproducibility of samples quality,the mechanical properties of manufacturing samples under different shielding gas flow rates were studied.The influence of shielding gas flow rate on the reproducibility of batch production samples was analyzed,and the optimized shielding gas flow rate in the manufacturing process was obtained.(3)Research on the ultimate pose and size of the arch lattice structure by laser selective melting:Based on the optimization of manufacturing parameters,the influence of the diameter and inclination angle on the formability of the strut is analyzed.Then,linear strut samples with different diameters and inclined angles were designed and manufactured.According to the printability of the samples,the shape parameters of the arch lattice structure and the formable range of the strut diameter were determined,which provided a reference for the design of the arch lattice structure.(4)Research on the quasi-static compression performance of arch lattice structures:The influence of shape parameters,element sizes,relative densities and loading directions on the compression performance of arch lattice structure was studied.The optimal shape parameters and loading direction of the lattice structure are obtained.The quasi-static compression performance of the lattice structure with the optimal shape parameters and the optimal loading direction was studied.According to the mechanical properties of the lattice structure with different relative densities,the Gibson-Ashby model of compression performance is established,which can be used to calculate the compression performance of the lattice structure with different relative densities.(5)Research on the bending performance of arch lattice structure:The influence of shape parameters,element sizes,relative densities and loading directions on the quasi-static bending performance of arch lattice structure was studied.The optimal shape parameter and loading direction are obtained.According to the mechanical properties of the lattice structure with different relative densities,the Gibson-Ashby model of bending properties is established,which can be used to calculate the bending properties of the structural materials with different relative densities.(6)Research on dynamic compression properties of sandwich structure:The dynamic compression properties of arch lattice sandwich structure was researched.The influence of strain rate and the number of lattice structure layers on the mechanical properties of sandwich structure was studied.The research results show that arch lattice sandwich structure has obvious strain rate effect,and both the strain rate and the number of lattice layers have influences on the mechanical properties and energy absorption characteristics of sandwich structures.(7)Application verification research on design and manufacturing of arch lattice structure:Based on the characteristic of the selective laser melting and the mechanical properties of arch lattice structure,the application verification research was applied on two aircraft components.The weight of the missile wing structure filled with arch lattice structure can be reduced 8.1%under the premise of satisfying the aerodynamic and reliability requirements.The heat transfer coefficient can be increased by 277.9%?296.6%after the heat exchange channel is filled with arch lattice structure.This study provides a new train of thought for innovative design based on selective laser melting.