Trimming for alumina-based ceramic casting cores for turbine blade by double picosecond laser scanning

Ceramic cores determine the moulding accuracy of a turbine blade's cavity, which strongly affects thermal diffusion performance and the service life of a turbine engine. To get a high quality ceramic core after the preliminary process, this paper deals with a laser trimming technology for ceramic casting cores via double picosecond laser scanning for the first time. Instead, the core ceramic foils were firstly machined at a combination of different laser processing parameters to determine the necessary laser trimming technology. Three different laser pulse duration regimes including femto-, pico- and nanosecond were examined and picosecond laser was selected for trimming of the core considering a serious recast layer occurrence in nanosecond laser processing and large amounts of faintly bonded aerosols on the side-wall of the machined surface in femtosecond laser processing. The removal profiles of the machined ceramic foils were characterized in terms of depth, deviation of linearity and surface morphology, which exhibited high dependence on the picosecond laser processing parameters. Double picosecond laser scanning for trimming was further put forward, schematically analysed and experimentally verified. Compared to the conventional trimming ways, the proposed technology allows a much smoother and denser edge and side-wall of the machined surface of ceramic casting cores, which helps to form high accuracy turbine blades cavity. What is more, it also provides a novel view for high quality laser micro-machining.