Arc-based ultra-short laser pulse assisted workpiece machining

通过连接、切割、结构化或成形来加工金属工件具有悠久的传统，但尽管如此，在当今的研究中仍在进行深入的研究。然而，对于某些应用，只有少数不同的处理技术已经出现。例如，其中激光束被快速检流计扫描器偏转并被成像光学器件聚焦在工件上的远程激光处理提供了高处理速度并允许处理具有空间范围的工件。缺点主要是系统的技术性质，例如产生足够功率的激光和将光束导向工件的努力。与远程处理相反，存在各种电弧技术，其提供高功率但必须紧密地引导到工件表面。因此，任何自动化都必须利用机器人或入口系统，并且需要具有平坦表面几何形状的工件，以便防止由于源自弯曲表面的不适当的电场梯度而引起的电弧偏转。本项目将研究一种技术，该技术将激光远程加工的速度和易于访问的优点与电弧加工的高功率可用性相结合。所提出的技术是基于使用具有高脉冲能量的超短激光脉冲在空气或其他气体中产生导电等离子体丝。等离子体丝可以用作长通道以将高功率放电精确地输送到工件的任意点上，因为它们显著地降低了桥接电极和工件之间的差距所需的击穿电压。此外，虽然细丝将充当具有不同极性的电极之间的导电通道，但是它们也可以充当用于由于电极上的高电势而由场电离引发的放电的引导通道，而不需要具有相反极性的第二电极。这使得新的加工方法成为可能，即使是隔离材料。这些特性可用于工件的快速、远程和高功率处理。为此，将使用检流计扫描仪偏转超短脉冲激光束。为了聚焦，使用改进的成像系统，其在工件侧上独立于其实际偏转为激光束提供固定的会聚点。因此，电极可以被放置在会聚点附近，确保放电的通道被附近的激光产生的等离子体丝引发和引导。此外，激光可以以在会聚点处产生灯丝的方式预聚焦。该项目的目的是调查拟议的技术，以评估材料加工（如焊接或切割）的磁感应放电的适用性。

The processing of metallic workpieces by joining, cutting, structuring or forming has had a long tradition but is, nonwithstanding, still being intensively investigated in present-day research. Nevertheless, for certain applications only few distinct processing technologies have emerged. For instance remote laser processing where the laser beam is deflected by a fast galvanometric scanner and focused by imaging optics on the workpiece offers a high processing speed and allows to process workpieces that have spatial extents. The disadvantages are mainly of system technological nature such as the effort to generate the laser of sufficient power and to guide the beam towards the work piece. In opposition to remote processing various electric arc techniques are present that offer high power but have to be guided closely to the workpieces surface. Consequently, any automation must utilize robot or portal systems and requires workpieces with flat surface geometry in order to prevent a deflection of the electric arc due to an inappropriate electric field gradient originating from a curved surface. The proposed project investigates a technology that combines the advantages of speed and ease-of-access of laser remote processing with those of high power availability in electric arc processing. The proposed technology is based on the generation of electrically conductive plasma filaments in air or other gases using ultrashort laser pulses with high pulse energy. The plasma filaments can act as long channels to deliver high power electrical discharges precisely onto an arbitrary spot of the workpiece, since they significantly reduce the breakdown voltage necessary to bridge the gap between an electrode and the workpiece. Moreover, while the filaments will act as conductive channels between electrodes with different polarity, they can also act as guiding channels for electrical discharges initiated by field ionization due to a high potential on an electrode, without the need to have a second electrode with opposite polarity. This makes new processing methods possible, even for isolating materials. These properties can be utilized for a fast, remote and high-power processing of the workpiece. For this purpose an ultrashort pulsed laser beam will be deflected using a galvanometric scanner. For focusing a modified imaging system is used that provides a fixed convergence point for the laser beam, independently on its actual deflection, on the workpieces side. Thus, an electrode can be placed near to the convergence point ensuring the channeling of electrical discharges is set off and directed by a nearby laser generated plasma filament. Furthermore, the laser can be prefocused in such a way that the filament is generated at the convergence point. The aim of this project is to investigate the proposed technology in order to assess the suitability of filament-induced electrical discharges for material processing such as welding or cutting.