Multi-field Coupling Simulation and Experimental Research of Selective Laser Sintering of Walnut Shell Composite Powder

Author:Yu Yue Qiang

Supervisor:guo yan ling


Degree Year:2019





Selective laser sintering(SLS)is an important branch of 3D printing technology,compared with other 3D printing technologies,SLS has some advantages such as no support is needed during manufacturing,materials can be reused,and parts have high precision,which greatly improves design of the product and freedom manufacturing,and realizes personalized customization and production of product.At present,the development of materials for SLS is mainly focused on metals,ceramics and polymers at home and abroad,but a few on biomass composite materials.Compared with metal,ceramic and polymer,biomass composite material is a kind of green environmental protection,low price,good sustainability.It has advantages such as low cost,low energy consumption,low demand of molding condition,stable sintering performance and small warping deformation.In this paper,biomass composite material was studied to used for SLS.Through analyzing microstructure and performance of biomass material,walnut shell powder was used as raw material of SLS and walnut shell/Co-PES powder material was prepared.The single layer sintering test was conducted to verify the feasibility,and then the best quality proportion of walnut shell powder and Co-PES powder was obtained.Based on deeply studying the effect mechanism of laser energy on powder particles,heat transfer model of SLS powder material was established.Based on previous experience,the calculation model of thermal physical property parameters of composite material was established,and equivalent specific heat capacity method in ABAQUS finite element software was used to deal with the latent heat of phase transformation of materials in the process of laser sintering.Based on the basic theory of numerical simulation of walnut shell/Co-PES powder,finite element method was chosen and ABAQUS platform was applied The finite element analysis model of walnut shell/Co-PES powder of SLS was established.Considering the heat transfer,convection and radiation boundary conditions as a whole,multi-field coupling simulation analysis of laser sintering process of walnut shell/Co-PES powder was conducted,and it was concluded that distribution and change rule of temperature,stress and strain fields of the walnut shell/Co-PES powder in SLS process.The influence of processing parameters such as preheating temperature,laser power and scanning speed on the surface temperature distribution and variation of the powder bed,the shape and size of the sintering pool and the deformation of the formed parts were discussed.Through SLS tests and thermal imaging test,the results of multi-field coupling simulation analysis were verified,and the rationality of the finite element model,load and boundary conditions was determined.Walnut shell powder particles were used as additive and Co-PES powder particles were used as matrix to prepare walnut shell/Co-PES powder of different ingredients proportions and different particle sizes.The effect of different ingredients proportions and different particle sizes on forming performance,dimension accuracy and surface quality of walnut shell/Co-PES parts were studied.Using the orthogonal test design method of five factors and four levels,Z-dimensional accuracy,tensile strength and density of parts were used as indicators,process parameters of SLS of walnut shell/Co-PES powder were optimized and the optimum process parameters were obtained.Through analyzing internal structure of laser sintering parts and using wax-infiltrated post-processing technology,the wax-infiltrated post-processing experiment of walnut shell/Co-PES parts was carried out.The influence of different ingredients proportions and different particle sizes on density and mechanical performance of walnut shell/Co-PES wax-infiltrated parts were studied.Using the response surface method,the bending strength as index,process parameters of wax-infiltrated post-processing were optimized and prediction model were verified,as well as the optimum process parameters wax-infiltrated post-processing were obtained.Furthermore,walnut shell/Co-PES wax-infiltrated post-processing experiment was carried out using the optimum process parameters.The optimized walnut shell/Co-PES wax-infiltrated parts were used in investment casting to fabricate metal parts.Through the analysis of structure and performance of binder,walnut shell powder particles were used as additive,Co-PES and Co-PA powder particles were used as matrix to prepare walnut shell/Co-PES/Co-PA powder of different binder proportions using binders mixed technology.The influence of different binder proportions on density,dimensional accuracy and mechanical properties of walnut shell/Co-PES/Co-PA parts were researched.Walnut shell/Co-PES/Co-PA parts of high dimensional accuracy,high mechanical strength,small density were obtained in order to achieve the goal of fabricating forming parts of lightweight.