Powder paving is an intermediate process of selective laser sintering(SLS).The dimensional accuracy and mechanical properties of sintered components are directly affected by the quality of the powder paving process,wh...Powder paving is an intermediate process of selective laser sintering(SLS).The dimensional accuracy and mechanical properties of sintered components are directly affected by the quality of the powder paving process,which is closely related to the flow characteristics of the powder and the process parameters of powder paving.This study investigated the simulation and optimization of the nylon powder paving in SLS by combining a discrete-element-method numerical simulation with a process test.A dynamic model was established to describe the flow and paving process of nylon powder at a preheating temperature considering mesoscopic van der Waals and electrostatic forces.The effects of the physical parameters and ambient temperature on the flow characteristics of nylon powder were analyzed,and the intrinsic relationship between the physical parameters of nylon powder,the process parameters of powder paving,and the quality of the powder paving were explored.A multi-objective regression model of the quality of powder paving was established using the response surface methodology,and a genetic algorithm was adopted to optimize the quality of the powder paving.A scientific and intelligent database of the nylon powder paving process in SLS was constructed by matching the process parameters of powder paving and physical parameters of the nylon powder,and the level of the SLS process was improved.展开更多
The chemical structure of polyamide 6(PA6)dictates that only 50%of hydrogen bonds participate in crystallization during the crystallization process,resulting in the properties of its products being significantly depen...The chemical structure of polyamide 6(PA6)dictates that only 50%of hydrogen bonds participate in crystallization during the crystallization process,resulting in the properties of its products being significantly dependent on the molding process.Therefore,the design and development of nucleating agents suitable for PA6 holds great practical significance for high-performance PA6 materials.Amide-based nucleating agents can effectively improve the crystallization rate by increasing intermolecular hydrogen bond density.Further introduction of hydroxyl groups can enhance the hydrogen bonding interactions between the nucleating agent and PA6.In this study,a hydroxyl-containing amidebased nucleating agent,BHT,was designed and synthesized using a tyramine-based biomass as the raw material.These results demonstrated that BHT exhibited good structural compatibility with PA6.After adding 1 wt%BHT,the crystallization temperature of PA6 increased from 170.9℃to 193.3℃,the crystallinity increased 16.6%,the heat distortion temperature and Vicat softening temperature rose to 89.5 and 187.8℃,respectively,the haze decreased to 46%,achieving the synergistic optimization of mechanical,thermal,and optical properties.The in situ time-resolved FTIR results indicated that the addition of BHT increased the enthalpy of hydrogen bond formation during the nucleation stage,facilitated the segmental conformation adjustment of PA6,and enhanced the molar concentration of trans-conformations,ultimately leading to an improvement in the crystallization rate.展开更多
基金Supported by National Natural Science Foundation of China(Grant Nos.52375466,51975504)Guangdong Provincial Basic and Applied Basic Research Foundation(Grant No.2022A1515110862)+1 种基金Jiangsu Provincial Key Laboratory of Precision and Micro-Manufacturing Technology(Grant No.JSKL2223K06)Hunan Provincial Excellent Youth Project of Education Department(Grant No.22B0109).
文摘Powder paving is an intermediate process of selective laser sintering(SLS).The dimensional accuracy and mechanical properties of sintered components are directly affected by the quality of the powder paving process,which is closely related to the flow characteristics of the powder and the process parameters of powder paving.This study investigated the simulation and optimization of the nylon powder paving in SLS by combining a discrete-element-method numerical simulation with a process test.A dynamic model was established to describe the flow and paving process of nylon powder at a preheating temperature considering mesoscopic van der Waals and electrostatic forces.The effects of the physical parameters and ambient temperature on the flow characteristics of nylon powder were analyzed,and the intrinsic relationship between the physical parameters of nylon powder,the process parameters of powder paving,and the quality of the powder paving were explored.A multi-objective regression model of the quality of powder paving was established using the response surface methodology,and a genetic algorithm was adopted to optimize the quality of the powder paving.A scientific and intelligent database of the nylon powder paving process in SLS was constructed by matching the process parameters of powder paving and physical parameters of the nylon powder,and the level of the SLS process was improved.
文摘The chemical structure of polyamide 6(PA6)dictates that only 50%of hydrogen bonds participate in crystallization during the crystallization process,resulting in the properties of its products being significantly dependent on the molding process.Therefore,the design and development of nucleating agents suitable for PA6 holds great practical significance for high-performance PA6 materials.Amide-based nucleating agents can effectively improve the crystallization rate by increasing intermolecular hydrogen bond density.Further introduction of hydroxyl groups can enhance the hydrogen bonding interactions between the nucleating agent and PA6.In this study,a hydroxyl-containing amidebased nucleating agent,BHT,was designed and synthesized using a tyramine-based biomass as the raw material.These results demonstrated that BHT exhibited good structural compatibility with PA6.After adding 1 wt%BHT,the crystallization temperature of PA6 increased from 170.9℃to 193.3℃,the crystallinity increased 16.6%,the heat distortion temperature and Vicat softening temperature rose to 89.5 and 187.8℃,respectively,the haze decreased to 46%,achieving the synergistic optimization of mechanical,thermal,and optical properties.The in situ time-resolved FTIR results indicated that the addition of BHT increased the enthalpy of hydrogen bond formation during the nucleation stage,facilitated the segmental conformation adjustment of PA6,and enhanced the molar concentration of trans-conformations,ultimately leading to an improvement in the crystallization rate.
