基于离散单元法的激光选区熔化粉末铺设机制与成形件性能调控研究

The properties of part manufactured via selective laser melting (SLM), such as strength, reliability, and surface roughness, can not reach the standard of the ones made by traditional processing technology due to the forming defects such as holes, cracks and ballings. And this becomes the main bottleneck which restrict the development of SLM technique. Powder-layering as one of the basic processings of SLM has currently received little attention, although it makes significant influences on the parts from SLM. In this project, the powder layering will be investigated in order to improve the properties of parts from SLM. And the discrete element method (DEM) will be innovatively employed to study the processing of SLM concerning the discountious feature of powder used in the processing. The DEM simulations combined with experimental tests would be conducted to study flowing and deposition of powder during layering, and the forming mechanism of powder bed in SLM processing will be revealed. Then the melting and solidification of powder in SLM will be investigated to reveal the effects of powder layering on the properties of part such as densitification, surface roughness and strength. The quantitative relationship of the processing parameters of powder-layering and the characterists of powder particles to the properties of parts will be obtained. In this project, a innovative performance control theory and technological scheme for SLM will be proposed from the perspective of powder-layering. And it is of great signficance to break through the technology bottleneck of SLM and develop a SLM technology with high-performance.

激光选区熔化（SLM）容易产生孔隙、裂纹、球化等成形缺陷，导致成形件的致密度、力学性能、表面粗糙度等性能指标无法达到传统加工技术的标准，成为制约SLM发展的主要瓶颈。粉末铺设是SLM的基本环节，对成形过程具有重要影响，但目前受到的关注甚少。本项目提出从SLM粉末铺设环节的研究入手，进而获得成形件性能提升方案的研究思路；并针对粉末的离散特性，创新性地将离散单元法（DEM）用于SLM的研究。结合DEM模拟与实验测试：从颗粒层面研究粉末铺设的流动与沉积机制，揭示粉末床的堆积形成规律；研究粉末颗粒堆积状态对粉末熔化-凝固过程的影响机制，揭示粉末铺设对成形件致密度、力学性能、表面粗糙度等性能指标的影响规律；以此明确SLM铺粉工艺、粉末特性与成形件性能之间的映射关系。项目有望从粉末铺设的角度提出新的SLM成形件性能调控理论，对突破SLM技术瓶颈，发展高性能的SLM成形制造具有重要意义。

项目针对激光选区熔化/烧结（SLM/SLS）粉末铺设工艺的基础科学问题：1）基于离散单元法（DEM）理论，建立了球形/非球形粉末的动力学模型，从颗粒尺度实现了的SLM/SLS粉末铺设过程的计算模拟与预测。2）结合DEM计算与原位监测实验，研究了金属粉末的铺设过程，阐明了金属粉末铺设过程的速度分布、轨迹演变、压力分布等微观动力学特征，揭示了壁面效应、粘结效应和渗流效应3种主导粉末铺设的内在机制，以此得出了铺粉工艺参数（粉末物性、铺粉机构结构参数、运动参数等）与粉末床质量（致密度、粗糙度、均匀度等）之间的关系。研究了非球形短纤维/高分子复合粉末的铺设过程，重点揭示了短纤维导致的铺粉粘滞与阻塞规律，明确了短纤维铺设过程的空间取向特征分布规律。3）揭示了粉末床铺设质量与最终成形件性能之间的关系。SLM成形金属零件，调整铺粉工艺不但能增加成形效率，而且由于铺粉补偿效应，还可以降低孔隙和裂纹等成形缺陷。SLS成形短纤维/高分子复合粉末，通过层厚、铺粉速度、滚筒转速等工艺参数调控铺粉过程的剪切效应，可以改善成形件的各向异性。基于以上基础研究，参加增材制造国际学术会议1次。在SLM/SLS工艺建模及成形方案方面申请了发明专利2项，授权2项。在《Acta Materialia》、《Int J Machine Tools & Manufacture》、《机械工程学报》等学术期刊上发表论文9篇。本研究从粉末铺设工艺角度出发，丰富了SLM/SLS成形的基础理论体系，对高效率、高性能的SLM/SLS成形具有工程指导意义。