增材制造中粉体铺展及传热特性的离散元模拟研究

Selective Laser Sintering (SLS) is one of the representative additive manufacturing technologies which are regarded as the next generation advanced manufacturing technology focused by the world's main countries with powerful manufacturing. The SLS is also the key task for the construction of the national manufacturing innovation system of China. Numerical simulation and optimization investigation of the SLS process has rapidly become a hot researching topic and the frontier of granular flow research area. In this project, the discrete element modelling will be employed to investigate the powder spreading process in the SLS together with experimental validation. The micro contact mechanics model between the solid particles will be proposed. The effects of the powder physical properties and temperature on the fluidity will be clarified. The effects of the powder fluidity and spreading process parameters on the powder thickness and uniform distribution of density will be fully discussed. The laser-powder interaction will be analyzed. The quality index system for the powder spreading process will be established integrating the powder bed movement, granular distribution and heat transfer characteristics. The optimization model for the powder spreading process will be developed taking the powder structure parameters, powder coating process parameters, powder physical parameters and heat transfer parameters as the key variables. The results of this project will play an active role in promoting the progress of China's additive manufacturing technology.

以选择性激光烧结（SLS）为代表的增材制造技术是世界各制造强国重点发展的下一代先进制造技术，也是我国国家制造业创新体系建设的重点任务。开展SLS工艺的数值模拟与优化研究已迅速成为热点课题，也是颗粒流研究的前沿课题。本项目以SLS工艺中的铺粉工艺为中心，采用离散元模拟和实验研究相结合的方法，建立粉体颗粒间的接触力学模型，阐明粉体物性参数及温度对粉体流动性的影响，探讨粉体流动性与铺粉工艺参数对粉层厚度、密实度均匀分布的影响规律，并分析激光—粉体相互作用关系，构建综合考虑粉层运动、粉层分布和传热特性的铺粉工艺质量指标体系，发展以铺粉机构参数、铺粉工艺参数、粉体物性参数和传热参数为变量的铺粉工艺优化模型。该项目研究成果对促进我国增材制造工艺进步将发挥积极的作用。

本项目以增材制造铺粉工艺为背景，采用实验和DEM模拟相结合的研究手段，开展粉体流动性表征、铺粉工艺优化与颗粒传热特性研究。针对粉体流动性影响因素和评价指标较多的问题，选用12种粉末材料为研究对象，表征了粉体的粒径粒形特征，采用FT4粉体流变仪研究12中粉体的压缩、剪切、流动能参数，基于主成分分析法对粉体堆积、剪切、流动能参数进行分析，得到粉体流动性的综合评价指标。采用该指标对12种粉体流动性进行了评价，并与粉体的可铺展性进行相关性分析。针对铺粉工艺的研究，研究粉体物性参数（颗粒摩擦特性、表面特性和粒径分布）、铺粉器结构参数（刮刀几何形状和滚筒直径）和铺粉工艺参数 (铺粉层厚和铺粉器平移速度) 对铺粉质量（粉床密度、粉床平整度和覆盖率）的影响规律；以颗粒填充理论为指导，建立铺粉过程的颗粒级配优化模型；研究铺粉器结构参数和铺粉工艺参数对颗粒动力学行为及粉床密实化的作用机理，并优化铺粉器的结构设计和匹配铺粉工艺参数。针对增材制造的颗粒传热过程，基于离散元理论构建了粉体颗粒间多种传热模型，并考虑了高温下粉体颗粒的粘弹性力学性质和颗粒间烧结力，模拟了颗粒间在不同阶段的传热过程，以理解其中的传热、烧结规律，为工艺参数的选择、工艺过程的优化提供理论指导。