Generation of rotationally symmetric stellite micro tools using ultra-short laser pulsesWednesday (24.06.2020) 17:40 - 18:00 Room 3
We report on the fabrication of rotationally symmetrical geometries with focused ultra-short laser pulses with the laser impinging the work piece, which in turn is under constant rotation, in a tangential manner. This particular micro machining geometry is referred to as laser turning, upon which the laser beam is, in general, oriented perpendicularly to the rotational axis and tangentially to the work piece. The target geometry is realized by moving the constantly rotating specimen according to the specified geometry under the focused laser spot. Additionally a trepanning optic moves the laser spot in a circular motion with an adaptable diameter in order to spatially distribute the laser power. In contrast to mechanical turning, laser turning induces a minimized amount of lateral forces through friction that might deteriorate the geometry. Furthermore, laser turning is capable of generating parts with better roundness as compared to manual lathing  and has already been successfully used to fabricate dental ceramic implants . Moreover, tangentially ablated tools offer advantages regarding machining forces as well as wearing .
In this study, laser turning is examined for stellite, a hard alloy on cobalt-chromium base, with a diameter of 1 mm. In particular, we present a comprehensive parameter study to improve ablation rate and surface roughness. The applied pulse energy is found to increase the achievable ablation rate linearly. By tuning the speed of the laser spot alongside the work piece and by progressively decreasing the distance between rotational axis and laser focus, an explicit impact on the process results can be observed. With a peak ablation rate of 3.2 mm³/min and a minimum surface roughness of 0.13 µm, laser turning combines both, fast processing and high surface quality. The maximum feasible feed rate as well as the ablation rate are found to be influenced by a variation of the trepanning diameter. Furthermore, the effects of the geometric layout of the work piece upon the process regarding fracture and soiling are shown.
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