Laser-based Additive Manufacturing of Metal Parts from Powder in Microgravity

在任何深空任务中(例如，飞往火星)，都需要备件来保持航天器的运行。在执行任务期间，可以通过添加制造(AM)来生产零部件，而不是在地球上制造备件并将其带来。由于可以更灵活地对部件故障做出反应，利用AM可以大大减少任务的总质量，提高任务的安全性。然而，还没有研究的微重力下的AM工艺，能够同时只通过AM产生净形状，修复表面，并生产不同的合金。激光金属沉积技术(LMD)能够实现这些目标。在LMD过程中，激光束在工件上形成熔池。同时，将流态化的金属粉末注入熔池。当激光穿过工件时，熔池凝固，从而在工件上形成隆起的结构。研究目标是发展和表征微重力下的LMD过程。通过对制作的样品进行分析，实现了LMD过程的表征。分析了试件的以下属性：几何、金相、硬度和单轴拉伸强度。LMD过程中的主要工艺参数是光束功率、粉末属性和进给速率。为了实现研究目标，必须完成两个主要目标：送粉和基于激光的熔池创建必须在微重力下工作。对于这两个主要目标，微重力条件下的基础研究是必要的。微重力是由爱因斯坦电梯实现的，这是一种新型的落塔，其重复频率比传统传送器高得多，因此可以测试更多的样品。在研究项目中，建造了两个送粉器原型，并在爱因斯坦电梯中进行了测试：不连续的和连续的。通过数值模拟CFD和DEM分析微重力下气体和颗粒的行为，辅助原型的开发。通过将激光集成到爱因斯坦升降器中，研究了微重力下金属的激光熔化。要在爱因斯坦-升降机中操作这种激光器，需要一个提供惰性气体气氛的加工室。此外，爱因斯坦电梯还集成了便携式能源和热交换器。

During any deep space mission (e.g. flying to Mars), spare parts are needed to keep the spacecraft operational. Instead of manufacturing spare parts on Earth and bringing them along, parts can be produced during the mission by additive manufacturing (AM). By utilizing AM, the total mass of the mission is greatly reduced and its safety is increased, since it is possible to react to component failure more flexibly.Multiple AM processes have been researched that work in microgravity. However, no AM process that works in microgravity has been researched that is capable of simultaneously being able to produce net shapes solely by AM, repairing surfaces, and producing different alloys. Laser Metal Deposition (LMD) is capable of achieving these goals. During the LMD process, a laser beam creates a melting pool on the work piece. Simultaneously, a fluidized metal powder is injected into the melting pool. When the laser beam traverses the work piece, the melting pool solidifies thus creating an elevated structure on the work piece.The research goal is to develop and characterize the LMD process in microgravity. The characterization of the LMD process is achieved by analyzing the manufactured specimens. The following attributes of the specimens are analyzed: geometry, metallography, hardness and uniaxial tensile strength. The major process parameters that are varied during the LMD process are the beam power, the powder attributes, and the feed rate.To achieve the research goal two primary objects have to be accomplished: the powder feeding and the laser-based creation of the melting pool must work in microgravity. For both primary objects fundamental research under microgravity conditions is necessary. Microgravity is achieved by the Einstein-Elevator - a novel drop tower that has a much higher repetition rate than conventional conveyors and thus allows testing a higher number of specimens.Within the research project, two powder feeder prototypes are built and tested in the Einstein-Elevator: a discontinuous and a continuous one. The development of the prototypes is aided by performing numerical CFD and DEM simulations to analyze the gas and particle behavior under microgravity.Laser based melting of metals in microgravity is researched by integrating a laser into the Einstein-Elevator. To operate this laser in the Einstein-Elevator, a process chamber is required that provides an inert gas atmosphere. Furthermore, a portable energy source and a heat exchanger is integrated into the Einstein-Elevator.