Adaptive process control for selective laser melting to compensate for pore formation

随着产品定制化程度的不断提高，增材制造发挥着至关重要的作用，而耗时、成本密集型的工具制造变得过时，复杂几何形状的直接生产成为可能。基于粉末床的工艺，如选择性激光熔化（SLM/PBF-LB/M），是工业上相关且广泛的增材制造形式。在这个过程中，以激光束形式输入的能量熔化粉末层，该粉末层在随后的固化过程中变成固体化合物。该过程逐层重复，直到形成三维部件。为此，数字工艺准备通过虚拟3D模型提取层的数据，并进行激光路径的路径规划，为增材制造机器提供部件的相关几何信息。然而，在构建阶段期间，制造参数、粉末和机器特性、环境条件和操作员相关因素之间的复杂相互作用部分导致不可预见的过程结果。这些问题以部件性能缺陷的形式变得明显，这极大地限制了工艺的盈利能力。与传统方法相比，当前用于定义稳定工艺窗口的合适制造参数的试错法减少了直接增材制造的时间优势。达到高达100%的部件最大材料密度以实现最佳材料特性是增材制造的重要质量特征。然而，与工艺相关的孔隙的形成和熔合的缺乏（它们中的每一个以不同的方式影响部件密度以及静态和动态强度）是实现该目标的基本问题。同时，这些不同的过程误差以互补的方式部分地取决于过程中的能量输入。过程中复杂的相互作用以及当今使用的控制系统不提供实时人工干预和界面的事实的结果是，当前机器控制的动态参数调整不用于增材制造。因此，工艺参数，如激光功率和扫描速度，通常保持恒定。为了克服这一局限性，研究考虑瞬态过程状态的高动态控制和调节概念是必要的。因此，它是本研究项目的目标是开发一个自适应控制系统，它确定适当的制造参数受相关的过程和测量因素。因此，可以确保最佳的工艺状态，并且可以提高最终的部件质量。

With the increasing customization of products, additive manufacturing plays a crucial role while time-consuming, cost-intensive toolmaking becomes obsolete and the direct production of complex geometries is made possible. Powder bed-based processes, like selective laser melting (SLM/PBF-LB/M), are an industrially relevant and widespread form of additive manufacturing. In this process, the energy input in the form of a laser beam melts a layer of powder that turns into a solid compound during the subsequent solidification. This process is repeated layer-by-layer until a three-dimensional component has been formed. For this, digital process preparations extract data of the layers through a virtual 3D model, and a path planning for the laser path is made to provide the additive manufacturing machine with the relevant geometric information of a component. However, the complex interaction between manufacturing parameters, powder and machine characteristics, ambient conditions, and operator-dependent factors during the build phase leads in part to unforeseeable process results. These become evident in the form of faulty component properties, which immensely limit the profitability of the process. Current trial-and-error approaches for the definition of suitable manufacturing parameters for stable process windows reduce the time advantage of direct additive manufacturing compared to conventional methods. Reaching a maximum material density of the component of up to 100 % to achieve optimal material properties is a significant quality feature in additive manufacturing. However, the formation of process-related pores and lack of fusion, each of which worsens the component density as well as the static and dynamic strength in a different way, is a fundamental problem in reaching this goal. At the same time, these different process errors partly depend on the energy input in the process in a complementary way. The consequence of the complex interaction in the process and the fact that control systems used today do not provide real-time manual intervention and interfaces is that a dynamic parameter adjustment of current machine controls is not used in additive manufacturing. Therefore, process parameters, like laser power and scanning speed, are usually kept constant. In order to counteract this limitation, the research of highly dynamic control and regulation concepts in consideration of transient process states is essential. Hence, it is the goal of this research project to develop a self-adapting control system, which determines suitable manufacturing parameters subject to relevant process and measurement factors. Thereby, optimal process states can be ensured and the resulting component quality can be increased.