Adaptive powder nozzle for additive manufacturing processes

增材制造过程成本节约的一个重要范围在于增材材料的高效和经济使用。以激光粉末堆焊为例，这对应于要使用的粉末的精确计量使用。在这个项目的框架内，为了避免引入的粉末不受控制的扩散，并确保这种添加剂材料的有效使用，我们在实验和数值上研究了各种概念。为了预测潜在的材料效率和焊缝质量，对不同喷嘴配置下的焊接过程进行了实验和数值研究，包括激光束的热输入。为了提高粉末效率，需要设计自适应粉末喷嘴。这有助于确定粉末光斑直径对激光光斑直径的适应性。自适应粉末喷嘴由三个与激光束同轴布置的单喷嘴组成。它们与衬底表面的距离和工作角度可以进行可变调节。除了粉末喷嘴的位置对粉斑直径的大小有影响外，喷嘴的位置还对粉末流中粒子与激光束的相互作用周期有影响。过长或过短的相互作用时间都会对工艺效率或焊头质量产生负面影响。本项目的目的是确定粉斑直径大小的相关工艺参数以及制造小型或大型单轨的相互作用周期。所获得的工艺知识将用于高精度生产大型多轨道结构。伴随着实验研究，基于欧拉/拉格朗日描述，粉末颗粒的运动以及周围空气作为载体相的运动进行了数值模拟。喷嘴内的颗粒/壁面相互作用和喷嘴出口尾迹中的大规模湍流结构对粉末扩散和待描述过程的材料效率有重大影响。粒子相的动力学通过粒子胞内（PIC）方法进行了相应的映射，该方法考虑了与载流子相的相互作用以及与粒子相互碰撞的多分散粒子相的相互作用。利用这一改进的概念，结合新的模拟方法来描述固体颗粒的相变，可以预测湍流和多分散多相流中的扩散过程，以便更好地聚焦堆焊过程中的粉末流动。

An essential scope in the cost savings of additive manufacturing processes lies in the efficient and economical use of additive materials. Using the example of laser powder build-up welding, this corresponds to the precisely metered use of the powder to be used. In the framework of the project presented here, various concepts are investigated both experimentally and numerically in order to avoid uncontrolled diffusion of the introduced powder and to ensure effective use of this additive material. With the aim of predicting the underlying material efficiency and the quality of the weld, the welding process in different nozzle configurations including the thermal input of the laser beam is investigated both experimentally and numerically.For a higher powder efficiency an adaptive powder nozzle will be designed. This contributes a defined adaption of the powder-spot diameter to the diameter of the laser-spot. The adaptive powder nozzle consists of three single nozzles which are arranged coaxially to the laser beam. Their distance to the substrate surface and their working angle could adjusted variably. Besides the influence of the powder nozzle position on the size of the powder-spot diameter the position has also amongst others an impact on interaction period between the particles out of the powder stream and the laser beam. Both a very long and a very short interaction period can have a negative impact on process efficiency or welding bead quality. Aim of this project is to identify the relevant process parameters for the size of the powder-spot diameter as well as the interaction period to manufacture small or large single tracks. The gained process knowledge will be transferred for producing large multi-track structures with a high precision.Accompanying the experimental investigation, based on an Euler / Lagrange description, the motion of the powder particles as well as that of the surrounding air as a carrier phase are numerically modeled. The particle / wall interaction within the nozzle and large-scale turbulent structures in the wake of the nozzle exit have a significant influence on the powder diffusion and accordingly the material efficiency of the process to be described. The dynamics of the particle phase are correspondingly mapped by a particle-in-cell (PIC) method, which takes into account both the interaction with the carrier phase and the interaction of the polydispersed particle phase with respect to mutual particle collisions.With this improved concept, in combination with new simulation approaches to describe the phase transition of solid particles, diffusion processes in turbulent and polydisperse multiphase flows are to be predicted in order to enable a better focusing of the powder flow of build-up welding processes.