2:45pm - 3:00pm
High-rate laser machining for large-area and high-throughput surface profiling and functionalization
University of Applied Sciences Mittweida, Germany
High-rate laser machining will be introduced as key technology for large-area surface texturing and bio-inspired functionalization. In fact, the polygon-mirror based scan technique allowing high-precision laser beam raster-scanning at hundreds meters per second is the core feature to bring high optical powers from kilowatt class lasers to industrial production. This is favourable for power scaling in micro machining as processing rate and throughput scale-up with higher pulse repetition frequency and laser powers. The great advantage of ultrafast beam movements is that unfavourable effects can easily be avoided, such as high thermal loads to the substrates and subsequent material melting as well as laser beam shielding by interactions with the previously induced plasma/particle plume. Inspired by sharks´ skin, this will be demonstrated by the example of riblet-like surface profiles and their replications in plastic materials thus providing a high potential for drag reduction in turbulent flows in technical applications.
3:00pm - 3:15pm
Laser polishing of laser micro weld seams on Cu-ETP and CuSn6 with green laser radiation
1RWTH Aachen University, Germany; 2Politecnico di Milano, Italy
Copper and copper alloys used for example in electrical applications can be contacted by laser micro welding. The achievable roughness of these micro weld seams can be too large for some applications (like sealing surfaces or to minimize surface oxidation). Up to now laser polishing, which smoothens the surface due to surface tension in the molten state, of copper could not be demonstrated successfully with industry common infrared high power laser systems typically used for laser polishing. This study investigates the use of green 515 nm wavelength high power laser sources for laser polishing of pure copper (Cu-ETP) and a widely used copper alloy (CuSn6). A suitable process window is identified by variation of process parameters (laser beam diameter, scanning speed, laser power) for single and overlapping remelting tracks. The best parameters are tested on laser micro weld seams created with the same setup to smoothen their rough surface.
3:15pm - 3:30pm
Laser texturing of heat exchanger tubes for nucleate boiling regime promotion
1AIMEN, Spain; 2INTEGASA, Spain
Titanium tubes of 16 mm diameter and 0.8 mm thickness, were textured using a CW, single mode, 1070 nm fibre laser. The laser beam was guided by a galvanometer scanner. Textures of homogeneous, parallel grooves of 60-80 µm width and 70-110 µm depth were generated on the exterior tubular surface. A wide range of parameters: laser power, laser speed, tube rotating speed or focal distance was studied to improve the homogeneity of the generated textures. These tubes were later tested in both controlled and industrial environments, along with non textured tubes, and their heat transfer behaviour was analysed under an ammonia nucleate boiling regime. Results indicate that laser textured tubes show a consistent increase of 60% of their heat transfer coefficient, when compared to original smooth tubes. These results prove that laser texturing is a suitable technique to significantly increase performance of heat exchangers that work under nucleate boiling regime
3:30pm - 3:45pm
Ultrashort laser coloration on titanium coatings
1TEKNIKER, Polo Tecnológico de Eibar, Calle Iñaki Goenaga 5, 20600, Gipuzcoa, Spain; 2INVESTPLASMA, Polígono Industrial Riu Sec, 105, 1, 12190 Borriol, Castellón, Spain
This study reports on the fabrication of structural and intrinsic colors from the oxide layers via ultrashort laser pulses on titanium coatings deposited on glass substrate. Surface modifications are tuned by adjusting laser parameters of wavelength, pulse length, scanning speed and energy per pulse. Two thickness (up to 1µm) of titanium coatings were deposited on glass substrates by physical vapor deposition. A comprehensive study of the physical and chemical measurements leading to the different appearances is presented. Different physical modifications, at micro and nanoscale levels, were identified depending on laser processing conditions. Quantitative analysis regarding chromaticity coordinates of the generated colors as well as phase composition of oxide layers were characterized by spectrophotometer and x-ray diffraction, respectively. Uniform and repetitive color palette on titanium coatings was developed by ultrashort laser processing.
3:45pm - 4:00pm
Direct laser-writing of metal nanostructures from the gas phase by two-photon absorption process
1Fraunhofer-Institut für Mikrotechnik und Mikrosysteme IMM, Mainz, Germany; 2Institut für Angewandte Physik, Technische Universität Darmstadt, Darmstadt, Germany
The fabrication of metallic 3D-nanostructures has received a lot of attention through new applications in plasmonics, e.g. metamaterials with a negative refractive index for optical cloaking and non-diffraction-limited optics. A new approach for the generation of three-dimensional metal nanostructures is introduced, based on two-photon-absorption of fs-laser radiation on silver-precursor molecules in the gas phase. A process chamber has been set up, allowing for evaporating a liquid organometallic silver-precursor under controlled temperature and pressure conditions. An inverse microscope objective of NA=0.65 and a working distance of 0.57 mm is used to focus the beam. The focus is moved in space by means of piezo-driven stage with nm-resolution. First two-dimensional structures with dimensions in the sub-micrometer range, are successfully deposited from the gas phase on glass substrates. The deposition parameters with respect to pressure, temperature and laser power, are going to be optimized to reach nm-resolution in structure size and building up 3D structures.