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In the last years, a new generation of developed laser systems with optic fiber as the active medium, the so-called fiber lasers, have made possible that laser technologies whose precision and quality were not so relevant in the production of micro-perforations now become in high-throughput quality solutions in new fields of application. In this work we present a study of the Single Pulse Micro-Drilling (SPMD) technique for the production of large micro-perforated titanium panels needed in the aerospace industry for developing Hybrid Laminar Flow Control (HLFC) structures at production rates as high as 300 holes per second.
DOI: 10.2961/jlmn.2019.01.0010
Keywords: laser drilling, single pulse drilling, HLFC, micro-holes
1.Introduction
In the last years, it has been stablished that the most appropriate fabrication technique to fulfill the requirements of the manufacturing of large skin Ti panels for hybrid laminar flow control (HLFC) in the aerospace industry is mainly the application of pulsed lasers [1, 2]. The HLFC is a technique that prevents the formation of a turbulent boundary layer at the leading edges of the aircraft wings by sucking through the skin surface a small amount of air. With this technology the transition of the boundary layer from laminar to turbulent flow can be delayed and hence skin friction drag reduced [3]. Since skin friction drag accounts for nearly 50% of the total drag of a civil jet transport aircraft in cruise, technologies that enable laminar flow control offer potential for enormous economic and environmental benefit [4].
Nowadays there are two laser techniques that fulfill the high rate production requirements (drilling rates larger than 200 Hz) for the fabrication of micro-perforated Ti sheets for HLFC applications: the percussion micro-drilling (PMD) [5] and the single pulse micro-drilling (SPMD) techniques [6, 7]. Here we focus on the SPMD technique. In this technique, a pulsed laser with pulse width in the order of hundreds of microseconds is focused on a Ti sample. Then, a hole is produced by sending one single laser pulse. By applying a constant speed to the laser head and setting a certain pulse repetition rate for matching the required hole pitch (hole separation), a line of micro-holes is produced. An X-Y gantry then makes a matrix of holes by drilling several lines. The resulting pitch...