The MULTIPOINT main objective is to develop a high-power femtosecond laser system with a multibeam generation unit and custom beam delivery scanning and processing on the fly heads for high throughput micro-drilling of large Ti panels used in the fabrication HLFC structures in the aerospace industry.
However, although the quality and precision of these laser systems are extraordinary, productivity is still limited by current ultrashort laser sources performances. The quality using a femtosecond laser system is much better than that with the single microsecond pulse system, however, while the second one reaches production rates of up to 300 holes per second, the femtosecond laser system requires 5 seconds with a scanner using percussion drilling and beam precession movement to perform the job.
This disadvantage also extends to other applications such as surface micro-texturing. In fact, although it would be very useful in industries such as automotive for the ability to functional surfaces (for example the creation of hydrophobic surfaces for easy cleaning or micro-texturization of areas for the bonding of different materials) the current production rates (the production of few cm2 of micro-texturized area can typically take minutes) are not viable. Hence the elaboration of strategies with the aim of improving production and optimizing the process together with the development of new technologies that improve the overall capacity of femtosecond laser sources are necessary.
Reductions of at least 30% in the final cost in the fabrication of HLFC panels.
Incrementation of the quality and performance of HLFC panels.
Less environmental impact due to the elimination of chemical post-processing procedures in the fabrication of HLFC panels.
Fuel consumption reductions higher than 9% on commercial planes when HLFC panels applied.
Nowadays the micro-drilling of large Ti panels for the manufacture of HFLC (hybrid laminar flow control) structures can be carried out by means of the laser percussion drilling (PD) technique with lasers of nanosecond pulses and single pulse drilling (SPD) technique with high energy laser sources and microsecond pulses. The use of these techniques for this application is in an advanced development phase. It is expected that the first European industrial prototype capable of manufacturing 5 x 2 m panels will be available from 2019. A Ti panel for use in an HLFC structure for the aerospace industry is achieved by creating a pattern of millions of micro-holes perfectly aligned in typical pitches from 500 to 700 microns and diameters around 50-100 μm. Typical tolerances for both pitch and diameters are around 5 μm.
When these structures are used at the leading edges of aircraft wings to suck the first layers of air in contact with the wing (boundary layer), drag is reduced, and the aircraft’s support is improved. Theoretical calculations estimate a 9% reduction in fuel consumption and contaminant emissions (noise, NOX and other pollutants) for intercontinental flights. Hence, the aeronautical industry has a high interest in the development of HLFCs structures.
However, until the irruption of the laser technologies, PD and SPD for high throughput micro-drilling, the manufacture of these structures were not possible. The best production rates can be achieved by the SPD technique in which micro-drilling capacity of up to 500 holes per second has been demonstrated. The PD technique has demonstrated production rates of up to 300 holes per second. Although these production rates are very promising and provide feasibility for the industrial production of the HLFC structures, the fact is that they require chemical (etching) and mechanical (successive sanding stages) processes after laser manufacturing to eliminate burrs and non-desirable Ti microstructural phases (alpha-case) in the heat affected area surrounding the micro-holes.
Therefore, the development of a micro-drilling technique that aims to achieve production rates in an order of magnitude of 102 holes per second, offering surface qualities that do not require chemical or mechanical postprocessing, would be highly desirable. Femtosecond laser systems can meet this requirement but need to be brought to higher production rates. This is the main motivation and objectives of the MULTIPOINT project.
To provide a solution to this need, it is first necessary to develop technology by raising the average power of femtosecond sources to levels that guarantee an increase in productivity but also optimizing beam delivery in such a way as to maximize the amount of material removed versus energy supplied.
MAIN TECHNOLOGICAL CHALLENGES
- A 1.2 kW femtosecond laser source.
- A multibeam generation unit.
- Two strategies for delivering the multibeam pattern to the titanium panel
MULTIPOINT will, therefore, address the following three key challenges:
A 1.2 kW femtosecond laser source working at high pulse energy (at least 2 mJ pulses) will be developed. This laser has enough power to drive several synchronized processes of percussion drilling at the same time thus allowing maximizing the production only from a point of view of the increase of the energy provided to the material.
Secondly, a multibeam generation unit will be developed for the main beam supplied by the laser source. This unit will be optimized not only optically but will take into account process optimization and application requirements. In particular, it will be designed to optimize the energy balance per beam in a pattern determined by the particular requirements of the micro-drilling of Ti panels for the development of HLFC structures.
Finally, two strategies, based on the percussion drilling technique, for delivering the multibeam pattern to the Ti panel will be developed and tested. The first head will be a multibeam scanner based on galvanometric mirrors. Its custom design will include a sufficient optical aperture to take a number of parallel beams to the sample, within a working field determined by a focusing f-theta lens, in a closed environment by means of an inert Ar atmosphere chamber for processing protection. The second head will be a multibeam on-the-fly processing head with pulse trains in a multibeam pattern and Ar jet nozzle. These two strategies will also allow us to study the best processing approach through the development of new beam delivery technologies to optimize the process parameters and maximize production. In Figure 2 we show an illustration of the 2 heads.
By addressing these challenges, the MULTIPOINT project will provide a novel system driven by the industrial requirements of the fabrication of large micro-perforated Ti panels for the construction of HLFC structures with technology development both in the laser source and in the multibeam generation and delivery.