Multi-Physics Modeling of Laser Beam Drilling with Temporally Shaped Pulses

由于短脉冲激光打孔效率高，在工业上得到了广泛的应用。然而，对于质量敏感的应用，有限的加工精度越来越有必要使用效率极低的超短激光脉冲。使用时间形状脉冲进行钻孔提供了一种结合了高效率和增强精度的极具吸引力的选择。然而，尽管短激光脉冲的时间脉冲整形在提高烧蚀效率和表面质量方面的有效性已经被实验证明，但实验研究尚未导致对这一过程的深入了解。因此，在拟议的研究项目中，我们希望将数值研究和实验研究相结合，以增加对过程的理解，并开发一个分析过程模型。为了更详细地了解材料去除的过程和机制，我们希望使用这些获得的知识来根据具体情况的过程参数和钻井策略来定制脉冲形状。最后，这些结果将结合起来，为现有和潜在的工业用户制定实用的指导方针。为了实现这些目标，该项目将分为两个阶段。在第一阶段，将进一步开发用于模拟激光光束材料加工的内部预先开发的瞬变流体动力学数值模型，以实现对钻孔过程的准确建模。因此，模型中将包含多相描述和可压缩性。为了确保正在开发的模型的准确性，将在模拟的同时进行验证实验，使模拟结果和实验结果能够不断迭代比较。将使用几种实验方法，包括金相研磨、纹影摄影、泵浦-探测器设置和夹层钻探，以深入了解材料和样品上方的区域。在第二项目阶段，将使用模拟和实验来进行时间形状和高斯激光脉冲的参数研究。在此基础上，系统分析了各种工艺参数对单脉冲冲击钻削过程动力学、加工效果和效率的影响。将这些结果结合起来，将建立一个分析过程模型，用于研究任意形状脉冲激光打孔的过程动力学和效率。然后，该模型将用于调整脉冲形状，以便根据工艺参数和策略获得优化的钻孔结果，从而产生特定于应用的脉冲形状定制。在最后一步，主要结果将总结在一套用户指南中，其中将包括为工业用户提供的实用建议，以根据个别应用和工艺参数优化工艺效率和钻井质量。

Due to its high efficiency laser drilling with short pulses is widely applied in industry. However, for quality sensitive applications the limited processing accuracy increasingly necessitates the use of ultrashort laser pulses with drastically lower efficiency. Drilling with temporally shaped pulses offers an appealing alternative combining high efficiency with enhanced precision. However, although the efficacy of temporal pulse shaping of short laser pulses in terms of increasing ablation efficiency and surface quality has been experimentally proven, experimental investigations have not yet led to an in-depth understanding of the process. Therefore, in the proposed research project we would like to combine numerical and experimental investigations in order to increase process understanding and to develop an analytical process model. Understanding the process and the mechanisms of material removal in more detail, we would like to use this acquired knowledge to tailor pulse shapes depending on case-specific process parameters and the drilling strategy. Finally, the results will be combined to develop practical guidelines for current and potential industrial users.To meet these objectives, the project will be divided into two phases. In the first phase, an in-house predeveloped transient fluiddynamic numerical model for the simulation of laser beam material processing will be developed further to enable accurate modeling of the drilling process. Therefore, a multi-phase description and compressibility will be included into the model. To ensure accuracy of the model under development, verification experiments will be conducted in parallel to the simulations, enabling constant iterative comparison of simulative and experimental results. Several experimental methods, comprising metallographic grindings, Schlieren photography, pump-probe setups and drilling of sandwiched layers will be used providing deep insight into both material and the area above the sample.In the second project phase, simulations and experiments will be used to conduct parameter studies for both temporally shaped and Gaussian laser pulses. With these investigations, the influence of various process parameters onto process dynamics, processing results and efficiency will be systematically analyzed for single pulse and percussion drilling. These results will be combined to develop an analytic process model for process dynamics and efficiency of laser beam drilling with arbitrarily shaped pulses. This model will then be used to adjust pulse shapes such that an optimized drilling result is obtained depending on the process parameters and strategies, leading to application-specific pulse shape tailoring. In the final step, the main results will be summarized in a set of user guidelines, which will comprise practical advice for industrial users to optimize process efficiency and drilling quality depending on the individual application and process parameters.