Geometry assessment of ultra-short pulsed laser drilled micro-holes
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ORIGINAL ARTICLE
Geometry assessment of ultra-short pulsed laser drilled micro-holes Matthias Putzer 1,2 & Norbert Ackerl 2 & Konrad Wegener 2 Received: 23 September 2020 / Accepted: 29 September 2020 # The Author(s) 2020
Abstract Ultra-short pulsed laser ablation enables a defined generation of micro-holes. A parameter study on the ablation characteristics of copper clearly reveals a benefit for green wavelength with lower threshold fluence, simultaneously increasing the Rayleigh length. The use of a circular drilling method allows a defined manufacturing of micro boreholes and micro through-holes with 35 μm diameter of up to 165 μm and 300 μm length. Introducing high-resolution micro-computed X-ray tomography studying the micro-hole evolution and adjacent geometrical transformations reveals micrometer resolution and high usability. The conical geometry evolving up to an aspect ratio of 5:1 fits well to established models known for percussion drilling. However, increasing the number of pulses leads to non-conical geometry evolution, and this resulting geometry is studied for the first time. Henceforth, the exact geometrical evolution from conical to cylindrical shape upon laser drilling can be resolved revealing the impact of multiple reflections at the generated steep flanks. Keywords Ultra-short pulsed laser . Micro-holes . Micro-computed tomography . Circular path drilling
1 Introduction In recent years, ultra-short pulsed laser (USP) machining is becoming a viable technology for industrial application [1]. The equipment costs have been constantly decreasing, and several benefits are leading to a strong increase in usage and application in industry. Laser pulses from such USP systems have a typical pulse duration of picoseconds to femtoseconds reaching power densities higher 1012 W cm s−2, which causes a non-linear and/or multi-photon absorption in the radiated materials. A thin and small volume on the surface gets ablated by the absorbed energy, and due to the quick heating and cooling, the heataffected zone (HAZ) is narrow whereby damage in the underlying material is negligible [2]. The small lateral size of the Peer-review Statement: Peer review under the responsibility of the scientific committee of the International Conference on Advanced and Competitive Manufacturing Technologies * Matthias Putzer [email protected] 1
inspire AG, Technoparkstrasse 1, Zurich, Switzerland
2
Department of Mechanical Engineering, IWF, ETH Zurich, Leonhardstrasse 21, Zurich, Switzerland
focused spot being several tens of square micrometers allows texturing the surface in the micrometer range, and the interaction of linear-polarized light with the matter leads to hierarchical structures in the nanometer size known as laser-induced periodic surface structures (LIPSS). Due to the low damage of the substrate below the absorbing and ablated material, structural modification and ablation of hard-to-machine and heat-sensitive materials is feasible. These include ceramics like alumina, zirconia [3–5], or glass [6, 7]. In a
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