Research On Design For Additive Manufacturing Of Lightweight Complex Component Manufactured By Selective Laser Melting

With the development of Additive Manufacturing(AM)technology,the design method of components has also changed.Benefiting from the layer-by-layer forming method of AM,the design freedom of components has been greatly liberated.Design constraints of traditional manufacturing process are no longer the primary consideration in the design process.How to improve the performance of components by design is more important,especially in lightweight design.The traditional method of model design is no longer applicable for AM.There is an urgent need for tailor-made design methods which fully consider the forming features of AM process.However,in fact,AM cannot carry out a free design in the true sense,because constraints of the process cannot be completely ignored.How to combine lightweight design with additive manufacturing and bring into play their respective advantages is an important issue for AM in practical applications.This dissertation focused on the more systematic research on design for additive manufacturing of lightweight complex component manufactured by selective laser melting(SLM).The following parts were included in this dissertation:1)The forming geometry constraints of SLM technology were summarized.The corresponding structural optimization design criteria were proposed.A design method for improving the topology optimized component to make them suitable for the SLM process was proposed to obtain components with ideal forming accuracy and performance.Case studies of antenna bracket and locking devices showed that SLM-based structural optimization technology was effective,which could also be used for optimization design of other components.2)A performance-based lightweight design method for lattice structure was proposed.Three different lattice units(FCC,VC,and ECC)were obtained through topology optimization for three specific compression load conditions.Mechanical properties of topology optimization lattice structures were evaluated after they were manufactured by SLM.The SLM 316 L stainless steel topology optimization lattice structures were superior to the common lattice structure in terms of mechanical properties,which verified the feasibility of the lattice unit selection by topology optimization technology.Thus,an available method for lattice unit selection was provided.3)The size effect of the FCC lattice structure obtained by topology optimization was explored.The mathematical models about "Young’s modulus-unit size-porosity" of FCC lattice structures with four different unit sizes were derived.Aiming at the deficiencies of mathematical models,the free node effect was proposed to explain the impact of the size effect on the mechanical property of the lattice structure: the performance of the lattice structure was affected by the ratio of the number of the free node at the outer boundary to the total number of the node.The mathematical model of "Young’s modulus-unit size-porosity" was modified under the consideration of the free node effect.The result showed that the theoretical derivation model was more consistent with the experimental data.The modified mathematical model could be used to predict the mechanical properties.4)By studying the influencing factors of laser delay on the forming performance of fine structure manufactured by SLM,the mechanism of laser delay parameters was proposed.The influence of laser delay on the density,hardness and mechanical properties of the fine structure was discussed.By establishing the mathematical model of the track overlapping,the relationship between the overlap ratio and the laser delay,the mathematical model of weld line spacing and scanning line spacing and laser spot radius,the optimized laser delay parameter of lattice structure manufactured by the SLM was obtained.When the laser delay was in the range of 350 μs ~ 450 μs,better lap,density,hardness,and mechanical property were obtained.5)Aiming at the problem that the single lattice unit was difficult to meet the stress gradient distribution of porous implants,a porous implant design based on stress distribution optimization was proposed.Local lattice structures based on stress distribution was obtained after the shape optimization of lattice structures inside the porous implant.The performance of lightweight design for the single lattice structure was improved.And the porous implant based on the stress distribution was obtained.At the end of this dissertation,the feasibility of this design method was verified by an interbody cage.