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

• Applicant: Professor Dr.-Ing. Frank Vollertsen
• Subject Area: Production Automation and Assembly Technology
• Term: from 2018 to 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 403820352

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.

• DFG Programme: Research Grants