Arc-based ultra-short laser pulse assisted workpiece machining

金属零件的连接、切割、组织或成形加工有着悠久的传统，但在当今的研究中仍在进行深入的研究。然而，对于某些应用，只出现了几种不同的处理技术。例如，在远程激光加工中，激光束被快速检流计扫描仪偏转，并通过工件上的成像光学元件聚焦，从而提供了高加工速度，并允许加工具有空间范围的工件。缺点主要是系统技术性质的，如努力产生足够功率的激光并将光束引导到工件上。与远程加工相反的是，出现了各种电弧技术，这些技术提供高功率，但必须紧密地引导到工件表面。因此，任何自动化都必须使用机器人或门户系统，并要求工件具有平坦的表面几何形状，以防止由于曲面产生的不适当电场梯度而导致的电弧偏转。拟议的项目研究了一种将激光远程处理的速度和易用性与电弧处理的高功率利用率的优势相结合的技术。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细丝。等离子体细丝可以充当长通道，将高功率的电放电精确地传输到工件的任意位置，因为它们显著降低了连接电极和工件之间的间隙所需的击穿电压。此外，虽然细丝将作为不同极性的电极之间的导电通道，但它们也可以作为由于电极上的高电位而引起的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，即使是用于隔离材料。这些特性可用于快速、远程和高功率加工。为此，超短脉冲激光光束将使用检流计扫描仪进行偏转。为了聚焦，使用了一种改进的成像系统，该成像系统独立于激光在工件侧的实际偏转为其提供固定的会聚点。因此，可以将电极放置在会聚点附近，以确保由附近的激光产生的等离子体灯丝触发和引导电放电的沟道。此外，激光可以以这样一种方式预聚焦，即在会聚点处产生灯丝。该项目的目的是调查拟议的技术，以评估灯丝诱导的放电在焊接或切割等材料加工中的适用性。

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.