High-precision and complex geometry helical drilling by adapted energy deposition

High-precision microholes are widely used as, for example, nozzles and venting holes in the automobile and consumer electronics industries. Owing to the development of modern devices and applications, the requirements on such holes have increased, not only in terms of geometric complexity but also of high precision. The helical drilling technology using ultrashort pulsed lasers is able to meet such requirements since it can generate higher precision in the hole geometry: through the layer-by-layer ablation strategy thanks to the helical movement of the laser pulses. Moreover, it is easier to control and more flexible in fabricating microholes with adjustable diameters, greater conicity and higher complexity. This work aims to investigate and clarify the behavior and influence of laser energy deposition on the fabrication of microholes with the ultrashort-pulsed-laser helical-drilling process. In order to quantify the laser energy deposition in the helical drilling process, I investigated the superposed laser intensity on the helical path. These paths are illustrated and visualized by means of numeric simulation and camera-based experimental acquisition. The three-dimensional helical path is rotationally symmetric and determined by the parameter setting of the helical optics - the parallel offset and the tilt angle of the focused laser beam. A classic and dynamic helical process can be defined depending on the dimension of the helical path. For classic helical drilling, I have investigated how the parameters of laser pulses and helical optics, as well as the process ambient conditions influence the morphological and metallurgic properties of the boreholes. With the specified laser beam sources, a maximum hole aspect ratio of 10:1 in 1 mm thick stainless steel plate can be achieved. A dynamic helical drilling process can be performed when the helical path is changed during the drilling process. With this change, the hole entrance can be shaped to a designated profile and, thus, the complexity of hole geometry enhanced. Indeed, the maximum hole aspect ratio can be increased to 50:1. In addition to that, a reduced model for dynamic helical ablation was built by investigating the development of ablation depth at varied processing parameters over the whole helical diameter. The drilling results with adapted laser energy deposition on the helical path agree well with the simulation by the reduced model. Moreover, thanks to the advantages of the dynamic helical drilling process with adapted energy deposition, the performance of the helical optics can be enhanced, with respect to drilling precision, complexity and productivity.