基于离散单元的多维功能梯度零件激光近净成形机理研究

Compared with homogeneous material, the functionally graded parts have many perfect performances, thus, it has been widely applied in aerospace field, as well as in special working environment. Since the material attributes are very complex, the traditional processes are difficult to be adopted to fabricate multi-dimensional functionally graded parts(MFGP). The technology of Laser Engineered Net Shaping(LENS) has the potential to fabricate such complex material, however, the mechanism is still not clear, thus, the LENS technology has not been adopted yet..This project aims to realize the fabrication of MFGP efficiently and accurately and explore LENS mechanism for MFGP. This project will (1) construct discrete units with three characters (self-adaption, non-uniform and variable size) driven by multiple elements, whose material and geometry attributes are inherited from the geometry-material coupling model of MFGP and are stored by proposed topological store algorithm; (2) create discrete tool paths via connecting these discrete units under the proposed material equivalent conditions; (3)implement the discrete tool paths planning with multi-strategies for the slice of heterogeneous object based on graph theory, to obtain “time-sequence” map for discrete tool paths which can improve the fabrication efficiency and quality of MFGP..This research provides effective method and tool for MFGP design and fabrication, and it has significant theory and application value for developing the fabrication processes of MFGP.

功能梯度材料具有均质材料不具备的众多优异特性，广泛应用于航空航天等重大装备、特殊服役环境零件的制造。多维功能梯度零件材料属性非常复杂，难以应用电化学等传统制备工艺,激光近净成形技术为其制备提供了可能，但由于机理尚不明确，尚未应用于多维功能梯度零件的制备。.本项目以多维功能梯度零件的高效精密制造为目标，探索该类零件激光近净成形机理，为此，在多维功能梯度零件几何材料耦合模型的基础上构建多因素共同作用下自适应非均匀变尺寸离散单元模型，对离散单元继承而来的材料和几何属性提出拓扑存储算法；基于所提出的材料等值条件将离散单元进行有效连接生成离散扫描路径，在此基础上，基于图论理论研究异质材料切片区域多策略离散路径规划，获得离散路径时序图谱，为提高成形制造的效率与质量奠定基础。.本研究有望为多维功能梯度零件的设计与制造，提供有效的工具，对发展多维功能梯度零件制备工艺，具有重要的理论意义与应用价值。

功能梯度材料具有均质材料不具备的众多优异特性，广泛应用于航空航天等重大装备、特殊服役环境零件的制造。本项目探究了该类零件的增材制造原理及工艺，主要研究内容有：.1）建立了多因素共同作用下自适应非均匀变尺寸离散单元模型.究了单一维度变化、多维相互独立变化、多维复合叠加变化下的材料空间与几何空间的映射关系，提出了一种面向制造的将材料模型附加在几何模型上的多维功能梯度材料实体模型表征方法，进而提出了非规则实体离散化方法，获得了多因素共同作用下自适应非均匀变尺寸的离散单元模型。.2）构建了基于材料等值条件的离散扫描路径.基于四连通、六连通、八连通研究了离散单元扫描路径生成方法，构建了多材料离散扫描路径。.3）研究了异质材料切片区域多策略离散路径规划.采用遗传算法和蚁群算法对不同数量离散扫描路径进行规划，提出了多材料离散路径规划方法。.4）研究了功能梯度材料增材制造材料混合机理及机构构型设计.进行了功能梯度材料增材制造过程模拟仿真分析，包括送粉系统粉末汇聚过程仿真研究、成形过程温度场和应力应变场仿真，在此基础上，设计了异质材料增材制造系统，研制了异质材料增材制造同轴送粉系统物理样机，联合研制了基于SLM工艺的金属材料3D打印机。.主要结论及科学意义有：.1）提出的非规则实体离散化单元模型可以根据性能要求、尺寸要求、材料要求等调节其单元尺寸大小，提高异质材料零件3D打印尺寸精度和材料精度，其材料属性可以从设计阶段识别并由制造阶段继承，实现了异质材料3D打印设计阶段与制造阶段无缝衔接。.2）离散扫描路径及其规划获得时间-序列图谱（时序图）以指导多喷嘴协同运行，实现了空行程最短、减少了成形过程中材料的混合和切换次数，提高3D打印效率。.3）数值模拟获得了最优的流道倾角及粉末利用率变化曲线、工艺参数对温度场及成形试件性能的影响，对送粉装置设计优化、成形工艺优化与性能提升具有重要的指导意义。