Design Method And Performance Study Of SLM Formed Sandwich Structures Based On Triply Periodic Minimal Surfaces

Sandwich structure is a new kind of multi-functional composite material with light weight and high strength,which is widely applied in many fields such as aerospace,aviation,ships and transformation.It integrates heat exchange,impact resistance,energy absorption,electromagnetic shielding and other versatility into one.The design of core structure has important influence on the formability and mechanical properties of the whole structure.The traditional metal sandwich structure often adopts the periodic lattice porous structure as its core material.However,the stress concentration at the nodes may cause damage easily during loading.Therefore complex optimization process is inevitable to prevent the stress concentration.Based on the mathematical method of triply periodic minimal surfaces,Porous structures with smooth surfaces can be directly generated through concise parameterized surface equations,which can greatly improve the efficiency of structural design.In addition,the traditional fabrication process of sandwich structure not only requires various procedures,but also is difficult to accurately process parts with complex internal structure.As a kind of typical material manufacturing technology,selective laser melting technology gets rid of the limitation of the cutting tool and moulds.It can fabricate parts with complex geometries by controlling laser to scan the metal powder layer by layer according to its section contour data,which greatly enhances the structural design freedom.SLM technology,which can form parts with good accuracy and mechanical properties,are applied in the forming of porous structure and sandwich structure.In this paper,TPMS method is applied to the core design of sandwich structure,and the SLM formability,mechanical properties and energy absorption capacity of the formed parts are studied.Firstly,two kinds of uniform sandwich structure models were established by the traditional lattice structure design method which introduced the node radius optimization with diamond cell as the prototype and the structure design method based on the three-period minimal surface equation.Then sandwich structure samples with different cell sizes were fabricated through SLM technology.The formability and mechanical properties of them and the influence of different cell sizes of core structure were investigated by the experimental method.It is proved that the performance of the sandwich structure established by the TPMS design method is comparable to that of the lattice sandwich structure with the introduction of node optimization.The relationship between cell size and their properties is revealed.Secondly,different forms of coefficient functions were introduced into the diamond TPMS equation,and three types of cell-size gradient sandwich structure design were proposed.By controlling the cell size at the interface between the surface and core,the adverse effects of heat accumulation effect and warping deformation on the surface quality of sandwich structure panel are reduced.Finally,the formability,mechanical properties and energy absorption capacity of these cell-size gradient sandwich structures were studied by morphological observation,roughness detection and compression test.The experimental results show that the formability of the sandwich structure is mainly related to the cell size at the interface between surface and core,while the mechanical properties and failure mode are affected by the cell size and its change rate through the whole structure.