Formation of microstructures and their impact on the hole quality during percussion drill-ing with ultrashort laser pulses (Formidable)

超短激光脉冲微钻孔是一个高度复杂的过程，涉及在非常小的时间和空间尺度上的极端条件下多种机制的相互作用。在金属钻井过程中会出现几个问题，例如孔内和入口处的碎屑、孔壁上的条纹、多孔的形成和出口的磨损。由于微孔的边缘质量和形状精度是大多数应用的相关标准，因此上述现象限制了工艺的适用性。随着商业上可获得的激光脉冲能量的稳步增加，这一点变得更加重要，因为激光脉冲能量可以产生非常深的孔。该项目将通过综合诊断和广泛的数值模拟来研究冲击钻井中上述质量降低、相互依存现象的形成。因此，通孔的钻孔过程分为三个阶段：(1)钻孔开始时表面结构的出现；(2)钻孔过程中孔的形状和孔壁结构的演变；(3)通孔出口几何形状的形成。在激光微加工过程中，由于超短激光脉冲与材料的相互作用，形成了自组织的纳米和微结构。在激光冲击钻孔中，结构的形成贯穿于上述钻孔阶段，并且假设结构的形成受前面的结构的显著影响。本文讨论的问题是，在冲击钻井中，这种微观结构的生长是如何导致通常有限的孔质量的。因此，该项目的目标是确定在三个钻井阶段控制微观结构形成和发展的基本机制和相应的加工参数，特别是澄清前面结构的影响。这将允许确定壁质量和冲击钻孔的孔出口对加工参数的依赖关系。为此，仪器仪器和仪器技术必须结合起来，即综合诊断和复杂的数值模拟。现有的数值模型已经包括了激光加工过程中的物理效应。因此，通过调整模型来重现所测量的结构的增长将允许确定决定性的物理效应。也就是说，IFSW和IFT相互补充，可以更好地理解潜在的物理机制。该项目的愿景是，了解上述现象的物理原因将有可能大大减少其影响，并允许在高精度应用中使用非常高效和快速的冲击钻井工艺。

Micro drilling with ultrashort laser pulses is a highly complex process involving a multitude of mechanisms interacting at extreme conditions on very small temporal and spatial scales. Several issues occur during drilling in metal, such as debris inside the hole and at the entrance, striations on the hole wall, the formation of multi-holes and frayed exits. Since the edge quality and shape accuracy of microholes are relevant criteria for most applications, the mentioned phenomena are limiting the process applicability. This becomes even more relevant with the steadily increasing commercially available laser pulse energy which allows very deep holes. The formation of the mentioned quality-reducing, mutually interdependent phenomena will be in¬vestigated in this project for percussion drilling with comprehensive diagnostics and extensive numerical simulations. The process of drilling through-holes is therefore divided into three stages: (1) emergence of surface structures at the beginning of drilling, (2) evolution of the hole shape and structures on the hole walls during the drilling, and (3) formation of the geometry of the exit of the through-hole. The formation of self-organized nano- and microstructures in laser micro processing is inherent due to the interaction between the ultrashort laser pulse and the material. In laser percussion drilling, the structures develop throughout the above-mentioned drilling stages and it is assumed that the formation of structures is significantly influenced by the preceding structures. The herein addressed question is how the growth of such microstructures is responsible for the resulting and often limited hole quality in percussion drilling. The objective of the project is therefore to identify the fundamental mechanisms and the corresponding processing parameters that rule the formation and development of microstructures during the three drilling stages and in particular to clarify the influence of the preceding structures. This will allow determining the dependence of the quality of the walls and the hole exit of percussion-drilled holes on the processing parameters. For this, the skills of the IFSW and the IFT shall be combined, i.e. comprehensive diagnostics and sophisticated numerical modelling. The existing numerical model already includes the physical effects during laser processing. The model tuning to reproduce the measured growth of the structures will allow therefore to identify the decisive physical effects. I.e. IFSW and the IFT complement each other perfectly for gaining a better understanding of the underlying physical mechanisms. The project vision is that the understanding of the physical causes for the above-mentioned phenomena will make it possible to significantly reduce their influence and allows using the very efficient and fast percussion drilling process for high-precision applications.