Increase in process efficiency of laser chemical machining by preventing the gas bubble related removal disturbances

激光化学加工(LCM)是对电化学加工技术的进一步发展，它是基于激光诱导的阳极材料在工件-电解液界面上的溶解。因此，该工艺的特点是它的灵活性和多样性，它的温和和无残留物的去除，以及它对工件的低热负荷。使用合适的材料-电解液组合和能量输入结构&lt；50μm，可以实现高达0.1μm的表面粗糙度。然而，低处理速度(&lt；1·e-2mm3/min)仍然是LCM工艺的主要缺点，并对工业应用构成了障碍。这可以归结为这样一个事实，即纯激光化学加工是在一个非常有限的工艺窗口中进行的，该窗口受到电解液沸点快速达到的限制。由于诱导温度高，沸腾气泡的强化形成在相互作用区起到屏蔽作用，导致材料去除的扰动，因此本项目的目的是进一步提高激光化学去除的工艺效率和质量。为了避免形成气泡，该工艺应在较高的环境压力下进行。因此，假设由于环境压力的升高而导致的电解液沸点的升高导致气泡尺寸的减小以及去除速率的增加。因此，可以拓宽无干扰激光化学去除的工艺窗口。为此，应开发合适的工艺单元，以确保在高环境压力下的安全加工。根据工艺相关参数，例如环境压力，应确定激光化学去除的特性(去除深度、宽度和表面质量)。此外，还将识别可在其内实现无干扰去除的压力依赖的工艺窗口。为了更好地了解去除机理，应可视化沸腾区域的温度相关转变以及相互作用区在有和没有激光束曝光的情况下的行为。因此，沸腾性质和由此产生的去除扰动之间的关系可以被证明和澄清。然后，将获得的发现应提供给对LCM去除机制的类似模型的描述，该描述应基于对工件表面的激光诱导的温度场的分析计算及其与所产生的去除几何形状的直接关联。

Laser chemical machining (LCM) is a further development of the electrochemical processing and is based on the laser-induced anodic material dissolution at the interface workpiece-electrolyte. Thereby, the process is characterized by its flexibility and variety, its gentle and residue-free removal as well as its low thermal load on the workpiece. Using suitable material-electrolyte combinations and energy inputs structures of < 50 μm and surface roughness of up to 0.1 μm can be realized. However, the low processing speed (<1·e-2 mm3/min) is still representing the main disadvantage of LCM-process and poses an obstacle for an industrial application. This can be reduced to the fact that purely laser chemical machining takes place in a very restricted process window, which is limited by the rapid achievement of the electrolyte boiling point. Due to high induced temperatures the intensified formation of boiling bubbles exerts a shielding effect in the interaction zone and leads to a disturbance of the material removal.The aim of this project is therefore to further increase process efficiency and quality of the laser chemical removal. In order to avoid the formation of gas bubbles the process should be carried out in higher ambient pressures. Thereby it is assumed that the increase of the electrolyte boiling point due to rising ambient pressure leads to a reduction in gas bubble size as well as to an increase in the removal rates. Thus, the process window for disturbance-free laser chemical removal can be broadened.For this purpose, a suitable process cell should be developed to ensure a safe processing at high ambient pressures. In dependence of the process relevant parameters, e.g. ambient pressure the properties of the laser chemical removal (removal depth, width, and surface quality) should be then characterized. Besides, the pressure-dependent process windows, within which a disturbance-free removal can be realized reproducibly, are to be identified. For a better understanding of the removal mechanisms the temperature-related transitions of the boiling regimes as well as the behavior of the interaction zone with and without laser beam exposure should be visualized. Thus, the relationships between the boiling properties and the resulting removal disturbances could be demonstrated and clarified. The findings to be obtained should then feed into a model-like description of the LCM removal mechanisms, which should be based on the analytical computation of the laser-induced temperature fields on the workpiece surface and their direct correlation with the resulting removal geometries.