Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
  • B23K26/352—Working by laser beam, e.g. welding, cutting or boring for surface treatment
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
  • B23K26/352—Working by laser beam, e.g. welding, cutting or boring for surface treatment
  • B23K26/355—Texturing
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
  • B23K26/02—Positioning or observing the workpiece, e.g. with respect to the point of impact; Aligning, aiming or focusing the laser beam
  • B23K26/06—Shaping the laser beam, e.g. by masks or multi-focusing
  • B23K26/067—Dividing the beam into multiple beams, e.g. multifocusing
  • B23K26/0676—Dividing the beam into multiple beams, e.g. multifocusing into dependently operating sub-beams, e.g. an array of spots with fixed spatial relationship or for performing simultaneously identical operations
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
  • B23K26/08—Devices involving relative movement between laser beam and workpiece
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
  • B23K26/352—Working by laser beam, e.g. welding, cutting or boring for surface treatment
  • B23K26/3568—Modifying rugosity
  • B23K26/3584—Increasing rugosity, e.g. roughening
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
  • B23K26/36—Removing material
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B64—AIRCRAFT; AVIATION; COSMONAUTICS
  • B64C—AEROPLANES; HELICOPTERS
  • B64C21/00—Influencing air flow over aircraft surfaces by affecting boundary layer flow
  • B64C21/10—Influencing air flow over aircraft surfaces by affecting boundary layer flow using other surface properties, e.g. roughness
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B64—AIRCRAFT; AVIATION; COSMONAUTICS
  • B64C—AEROPLANES; HELICOPTERS
  • B64C2230/00—Boundary layer controls
  • B64C2230/26—Boundary layer controls by using rib lets or hydrophobic surfaces
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E10/00—Energy generation through renewable energy sources
  • Y02E10/70—Wind energy
  • Y02E10/72—Wind turbines with rotation axis in wind direction

Definitions

• the invention relates to a method and a device for producing riblets and to a correspondingly producible component with riblets.
• Another known method for the production of riblets on an aircraft surface is based on a special paint system for the aircraft surface, a circulating silicone tape for impressing a riblet structure in the not yet cured paint and a subsequent UV light curing of the embossed in this way surface.
• the riblet structure is embossed as a negative image in the silicone film.
• the silicone film clings to the aircraft surface and transfers the structure into the freshly applied, still soft coating layer.
• the aircraft surface thus produced with riblets must regularly continue to cure for several hours at room temperature in order to fully cure and thus achieve the toughness and abrasion resistance required for flight operations.
• a riblet structure was introduced into a turbine blade for turbocompressors in a further process by means of laser ablation.
• a focused laser beam was guided by a scanner along the riblet grooves.
• the processing speed achieved in this example was 30 mm 2 / min. Even taking into account that a particularly tough steel has been processed in this case, an economic transfer of the process to an aircraft surface is hardly conceivable.
• the riblets are to be formed on the paint surface of an aircraft by scanning a focused laser beam, the processing speed achievable thereby is limited and may be too low for economic use in certain applications.
• a method for producing riblets wherein the riblets are introduced by laser interference structuring or DLIP - Direct Laser Interference Patterning - in a surface, in particular in an already painted and cured surface.
• Riblets are known to designate a surface geometry, also called riblet structure, with fine ribs having very sharp rib tips.
• the riblets (freely translated “small ribs” or “ribs") usually extend in a longitudinal direction.
• the longitudinal direction along a component is oriented parallel to a designated flow direction.
• Two adjacent ribs define a groove between the two adjacent ribs.
• the furrow basically has a furrow width which corresponds to the spacing of the opposite flanks of the two adjacent ribs. In principle, this refers to the clear width of the furrow, that is, for example, the distance of a right Flank of a first rib to the left flank of a arranged on the right of the first rib second rib.
• One rib has a flank on each side.
• the furrow basically has a furrow depth that corresponds to the rib height.
• two adjacent ribs are oriented in the longitudinal direction parallel or substantially parallel to each other, i. in particular with angular deviations ⁇ 5 °.
• Two adjacent furrows have a furrow spacing, which is typically measured from furrow center to furrow center of the two adjacent furrows.
• riblets have a groove depth that is approximately half of the groove spacing, with a deviation ⁇ 30%.
• Riblets have a typical groove spacing between 40 ⁇ and 200 ⁇ especially for the types of use mentioned.
• the furrow spacing should advantageously be 100 ⁇ .
• the groove spacing is about 100 ⁇ .
• the furrows should ideally be 50 ⁇ deep and have a rectangular cross-section.
• the ridges between the furrows should be as narrow as possible.
• a frequent compromise between this aerodynamic requirement and the mechanical stability has for the cross-sectional shape of the webs result in a vertical triangle, which in particular has a 30 ° flank angle at the top.
• such riblets can be used particularly effectively for reducing the flow resistance in a long-haul aircraft, ie with a typical intended speed of approximately 850 km / h at approximately 10,000 m altitude.
• riblets by laser interference structuring enables the large-area application of riblet structures with a particularly high process speed and thus enables a particularly economical, simple and flexible applicable production of riblets on aircraft, ships and wind turbines. Additional mechanical processing such as grinding accounts.
• DLIP Direct Laser Interference Patterning and is a well-known multi-beam laser interference technique that uses interference specifically for microstructuring surfaces, and tests have shown that two-beam laser interference patterning is particularly suitable
• generally enough coherent laser light is used so that it can be split into two identical sub-beams that can interfere with each other, these sub-beams are overlapped at a defined angle on the paint surface
• the distance L and thus the riblet structure with the groove spacing a can advantageously be adapted to the different fields of use. It is also advantageous that the fineness of the structure is not created by a correspondingly strong focusing of the laser beam, but that it is generated by the interference itself. As a result, it is largely independent of the working distance of the machining head or optical head.
• the overlap region of the partial beams is designed as an elongated rectangle (for example 100: 1) by using cylindrical lenses for focusing the beams.
• the method is particularly simple and flexible applicable and thereby enables the economic use of riblets in aircraft, ships and wind turbines.
• the laser light is sufficiently absorbed by the paint. That is, the wavelength of the laser overlaps with a spectral absorption band of the paint.
• the depth of the laser ablation can then be adjusted in one embodiment on the intensity and duration of exposure of the radiation.
• the exposure time can be selected in one embodiment so that the laser ablation is faster than the dissipation of energy by heat conduction.
• both topcoats for aircraft and wind turbines and underwater coatings for ships are predominantly polyurethane (PUR) systems.
• PUR polyurethane
• epoxy and acrylic systems are also used.
• the absorption spectra show more or less pronounced overlaps with the emission range of the C0 2 laser.
• This laser can be operated with selective wavelengths in the range between 9 ⁇ and 1 1 ⁇ .
• Riblet structures of 40-200 ⁇ can thus be produced in one embodiment according to the above formula with a union angle 2a in the range between 25 ° and 3 °.
• the C0 2 laser is a particularly suitable tool to structure the aforementioned paint systems.
• the exposure time of the laser radiation is ⁇ 1 msec. The process is preferably set up so that the energy absorbed by the lacquer within this time is sufficient to effect the material removal at the desired depth.
• pulse durations ⁇ 1 msec can be achieved by pulsed electrical excitation.
• the size of the processing field and the scanning speed can be matched to one another such that an exposure time of ⁇ 1 msec occurs.
• the energy that is absorbed within a certain thickness of the paint is basically dependent on the wavelength-specific absorption coefficient and the intensity of the laser light.
• the C0 2 laser typically has two particularly intense emission lines at 10.6 ⁇ and 9.6 ⁇ .
• the energy density is preferably about 1 J / cm 2 , this value being adjusted in accordance with the desired removal depth can.
• the entire structure for the surface treatment is performed as a compact, monolithic block along the paint surface.
• the advantage here is that the process works contactless and wear-free.
• the working distance is not critical, especially as long as the partial beams on the paint surface sufficiently overlap. Even free-form surfaces can therefore be processed without extremely complex path control.
• That micro-structuring of paints with millisecond pulses of a C0 2 laser or even with a continuous wave C0 2 laser is possible, is surprising for experts. There the opinion prevails that with lacquers on polymer basis (eg PUR) with the relatively slow introduction of energy contrary to the observation made, soot formation and other unwanted decomposition and melting effects occur.
• lacquers on polymer basis eg PUR
• the exposure time of the laser radiation is in particular ⁇ 1 ms so that the structuring is not "smeared" as a result of the thermal diffusion
• the geometry of the machining area is chosen appropriately or by clocking the electrical excitation of the laser.
• the riblets are subsequently introduced by means of the laser interference structuring into an already painted surface which is suitable for being exposed to a flow during operation.
• Already painted surface means that the paint has already hardened and the surface is basically ready for later operation.
• the laser is a C0 2 laser.
• a particularly high degree of absorption can thus be achieved in conventional paints, in particular in PU-based paints.
• the laser is a C02 continuous wave laser. Such lasers with corresponding focusing and coherence properties are in a power range up to multi-kilowatt for material processing in industrial applications.
• Interfering laser radiation preferably comprises two radiation beams, which are directed onto the surface in such a way that the two radiation beams interfere with one another.
• the two beams and thus the interfering laser radiation can be obtained in particular by beam splitting of the output laser beam, so that the interfering laser radiation introduces correspondingly distributed energy onto the surface.
• the interfering laser radiation generates a sinusoidal interference structure on the surface with periodically juxtaposed intensity maxima at a distance L from each other. When synchronously moving the two beams in the longitudinal direction so a plurality of juxtaposed grooves is generated.
• the sinusoidal intensity profile produces a likewise sinusoidal height profile on the paint surface.
• the riblet ridges should have a width to depth ratio of 2 to 1, and the ridges should be as thin as possible.
• the crests and valleys are extremely shallow. That means there are usually no pronounced bridges.
• such riblets can be only partially effective. If you want a sine profile with sharp peaks, so in particular the amplitude of the wave is large compared to their period set.
• the furrow width and thus the period with 100 ⁇ fixed it would result in the pit depth a theoretical value> 500 ⁇ , which in turn would be in contradiction to the functionality of the riblets.
• the basecoat finely suspended titanium dioxide pigments contains, which lead to homogenization of the light intensity and thus to blur the interference structure due to their strong scattering property.
• An essential material removal in the basecoat layer therefore does not take place. This layer therefore forms a barrier and thus limits the further depth removal in the furrows.
• the depth of the riblet grooves is thus determined by the thickness of the clearcoat layer.
• the riblets are made by a laser beam and an additional laser beam, wherein the laser beam and the additional laser beam are offset by an offset AL transverse to a feed direction or transverse to a longitudinal direction of the riblets on a surface for producing the riblets.
• the longitudinal direction of the riblets means the longitudinal direction of the ribs and / or grooves of the riblets.
• Feed direction means the direction of a relative movement of the laser beam and / or the additional laser beam relative to the surface.
• Riblets with particularly steep flanks, i. Walls, and especially slender ribs, i. Bars can be made in this way.
• the additional laser beam is emitted by an additional laser or the additional laser beam is generated by division of the laser beam or separation or branching from the laser beam.
• the additional laser beam corresponds to the laser beam, but offset in time, for example, in a later processing path over the same surface area.
• overlapping furrows can be generated, wherein the two edges of a rib between two such overlapping furrows are then offset in time or generated by different laser beams or partial beam.
• the riblets are introduced into an outer topcoat layer by means of the laser and / or a basecoat layer disposed below the topcoat layer has a low absorption coefficient for the wavelength of the laser compared to the topcoat layer, ie for the wavelength of the laser beam emitted by the laser or interfering laser radiation.
• the topcoat layer is preferably a clearcoat layer, in particular based on polyurethane.
• the basecoat film is preferably a plastic and / or resin, more preferably an epoxy resin.
• the base coat layer arranged below the topcoat layer is partially exposed by means of the laser.
• a lower layer arranged below a material layer is partially exposed by means of the laser, wherein the material layer may be the topcoat layer and / or the lower layer may be the basecoat layer.
• Partially expose means that in one or more parts the underlayer is not covered by the material layer or the basecoat layer is not covered by the topcoat layer.
• the surface can be formed on this part or parts of the lower layer or the basecoat layer.
• the absorption coefficient of the basecoat film is lower than the absorption coefficient of the topcoat film in such a way that the machining threshold or threshold intensity of the laser beam or the interfering laser radiation in the topcoat film intended for removal of material is reached or exceeded, but not in the basecoat film.
• the energy introduced into the top coat layer or material layer by the laser ensures removal of material, such that the intensity distribution of the laser beam or the interference structure with an at least approximately corresponding shape of a recess or groove in the topcoat layer or material layer is imaged.
• the intensity distribution in the basecoat film does not diminish.
• the particular flat upper side of the basecoat layer, which adjoins the topcoat layer and is at least partially exposed by the laser, can thus be preserved.
• the riblets are introduced into the surface of an aircraft, a ship or the rotor blades of a wind turbine. A particularly effective reduction of the flow resistance can thereby be made possible.
• a further aspect of the invention relates to a device for carrying out the above-described method for producing riblets with a laser or continuous wave laser, in particular C0 2 laser, set up for the production of the riblets.
• the device comprises at least one laser and one Optical head with at least one beam splitting device and at least one focusing devices.
• Riblets made by a continuous wave laser exhibit a continuously generated groove, with occasional traces of melting and / or decomposition effects observable.
• riblets with very pointed ribs with a rib tip width b T of at most 1 ⁇ or 2 ⁇ be prepared, in particular as shown in Fig. 5 measured transversely to the longitudinal direction and / or measured exactly 1 ⁇ below the highest point of the fin tip.
• riblets with very pointed ribs having a rib width of at most 30% or 40% of the groove spacing can be made, the width of the ribs meaning the dimension transverse to the longitudinal direction as measured at a distance below the highest point of the rib tip in particular one third of the groove depth or rib height.
• the riblets have flanks of ridges between grooves which map an intensity distribution of a laser beam or an intensity distribution of an interference structure, i. a section of a corresponding measurement curve of intensity I over an axis x on the surface transverse to the feed direction.
• Figure 1 Schematic representation of the production of riblets by means of a laser
• Figure 2 Schematic representation of a beam splitting and focusing device for generating an interference structure on a surface.
• Figure 3 Schematic representation of the mapping of an interference structure in a
• Figure 4 Schematic representation of the mapping of an interference structure in a
• Topcoat layer and an underlying basecoat layer are Topcoat layer and an underlying basecoat layer.
• Figure 5 Schematic representation of a production of riblets by the locally offset introduction of laser radiation in a layer of material.
• Figure 6 Schematic representation of a production of riblets by the locally offset introduction of laser radiation in a surface with a
• Figure 7 Schematic representation of an optical structure with two tiltable
• Deflecting mirrors for deflecting partial beams onto the surface
• Figure 8 Schematic representation of an optical structure with four tiltable
• Figure 9 Schematic front view of an optical structure with two tiltable deflecting mirrors and an optical deflecting body
• FIG. 10 top view of an elongate laser spot
• Figure 1 1 Schematic spatial side view of an optical structure with two tiltable deflecting mirrors and an optical deflecting body.
• a movement unit in the manner of a 5-axis robot 14 is provided, which is arranged so that a laser beam 15, interfering laser radiation 16, an additional laser beam 17 and / or additional interfering laser radiation 18 can be moved relative to the surface 3, preferably motorized by means of drive and / or automatically by means of a control for the drive.
• the movement unit 14 comprises a focusing device 20 and / or a beam splitting device 21, preferably as a compact structural unit, so that a defined spot diameter can be set on the surface 3, which in particular remains constant during the relative movement.
• the continuous wave laser 2 is connected to the focusing device 20 and / or a beam splitting device 21 via a movable beam guiding device, so that the movement unit 14 can be moved independently of the standing wave laser 2.
• the processing takes place as shown in Fig. 1 in the feed direction. 9
• Generally aircraft paints are multi-layer systems.
• such multilayer systems for aircraft coatings consist of a primer as corrosion protection and adhesion promoter, a basecoat of the basecoat film 5 in particular with color pigments and / or a clearcoat of the topcoat film 4.
• the basecoat is usually a multi-component epoxy resin coating.
• the clearcoat is preferably based on a polyurethane system (PUR). So that the visual impression of the aircraft surface is not impaired, it is advantageous to introduce the riblet structure into the especially transparent topcoat layer 4. If the top coat layer is based on polyurethane, it has an IR absorption structure in the emission range of the C0 2 laser.
• FIG. 2 shows an exemplary optical design of a beam splitting device 21 and focusing device 20 for converting a laser beam 15 into interfering laser radiation 16.
• the following explanations apply analogously to an additional laser beam 17 which is converted into an additional interfering laser radiation 18.
• the incident laser beam 15 is split into a first partial beam 6 and a second partial beam 7 on a preferably non-polarizing beam splitter, preferably a partially transmissive mirror 22.
• the incident laser beam 15 can be divided in an alternative or complementary embodiment so that two different laser beams with only one maximum intensity l max can draw a groove 13 in the surface 3.
• the partial beams 6, 7 are directed onto the surface 3 with the aid of optical mirrors 23 so that they impinge there at a predetermined angle ⁇ .
• the Equation ⁇ 2 ⁇ , ie both partial beams 6, 7 fall on the surface 3 at the same angle ⁇ .
• the entire optical setup is performed with beam splitter 21 and / or focusing device 20 as a compact, monolithic block.
• This can thus be guided particularly easily along the surface 3 of the aircraft 10 or aircraft component.
• the advantage here is that the removal process - with the exception of the roles - works contactless and wear-free.
• the movement unit is moved without contact over the surface. This even a touch of the surface is avoided by rolling.
• interfering radiation a particularly large tolerance range in terms of working distance, i. the focus position relative to the surface 3, are possible.
• the working distance over a range perpendicular to the surface 3 in the tolerance range in which the partial beams 6, 7 sufficiently overlap on the surface 3 for a scheduled ablation so for example, the intensity maxima l max still reach the desired threshold intensity.
• the intensity maxima l max still reach the desired threshold intensity.
• the distance L of the intensity maxima l max of a particular periodic distribution of the laser intensity l (x) over a transverse axis x perpendicular to the feed direction 9 or longitudinal direction 8 of the riblets can be adjusted to the surface 3.
• the particular periodic intensity distribution may be a modified sine function, sinusoidal or sinusoidal.
• FIG. 3 illustrates how the intensity l (x) at a position of the transverse axis x can correlate with the removal depth, so that this intensity distribution can be transferred into the height profile of the surface 3.
• the thickness of the topcoat layer 4, in particular of clearcoat based on PU is equal to or greater than the desired groove depth d of the riblets 1, that is to say the height of the ribs 12.
• FIG. 4 shows a surface 3, below which a The intensity l (x) of the laser radiation at an intensity maximum l max is so high that the material layer or topcoat layer 4 is partially completely removed and the lower layer or basecoat layer 5 thus partially completely uncovered. In part, this means the location of the surface 3 at which an energy of the laser is introduced with the intensity maximum l max .
• the laser radiation is in particular the interfering laser radiation 16, which was preferably obtained by conversion of the laser beam 15.
• the laser radiation is in particular the interfering laser radiation 16, which was preferably obtained by conversion of the laser beam 15.
• the wavelength of the laser light emitted by the laser light is selected in one embodiment so that it is absorbed in the topcoat layer 4, but hardly penetrates into the basecoat layer 5 due to the strong scattering of the Ti0 2 pigments, the ablation process effected by means of the laser stops on the basecoat layer 5 by itself (see Fig. 4).
• the groove depth d corresponds to the thickness of the topcoat layer 4, while the groove spacing a corresponds to the distance L of the intensity maxima l max .
• a furrow 13 with a particularly smooth sole, ie a flat furrow bottom, and steep flanks 11 of the ribs 12 can thus be achieved by utilizing the self-stopping removal process on the lower layer or base lacquer layer 5.
• 5 shows schematically a two-stage production of riblets 1 by the locally offset introduction of laser radiation 16 in a first processing stage and of additional laser radiation 18 in a second processing stage.
• the intermediate product has been shown in FIG. 5 through the first processing stage before the second processing stage is carried out.
• the first processing level and second processing level can also be simultaneously respectively.
• the two-stage machining process makes it possible to produce riblets with particularly steep flanks 11 and pointed ribs 12.
• the groove width, the groove depth, the groove spacing and / or the groove depth to groove spacing ratio may preferably be adapted to the size of the energy consuming vortices on the surface 3 of the component that would form on a smooth surface during operation of the component at a typical flow rate , Ideally, for example, in a long-haul aircraft, 2 ⁇ m wide and preferably rectangular or rectangular ribs 12 would be provided between the furrows 13.
• a component having a surface 3 with riblets 1 with 100 ⁇ furrow spacing of preferably about 100 ⁇ , and / or a groove depth of approximately 50 ⁇ can be in a long-haul aircraft in a phase reasonably constant airspeed of the total flow resistance, which is not only due to the surface friction to be reduced by up to 3%. Accordingly, fuel consumption may also decrease.
• WTs wind turbines
• up to 60% of the wind energy can be converted into mechanical energy of the rotor.
• the limitation is that behind the rotor, the wind speed is indeed reduced, but the air must continue to flow, so that the back pressure does not block the rotor.
• the riblets 1 are produced in particular by continuous or stepwise increase or reduction of the overlap angle ⁇ of the two partial beams 6, 7 so that the riblets have a decreasing or increasing groove width L, in particular transversely to the longitudinal axis 8.
• the riblets 1 on a rotor blade can be adapted particularly easily and effectively to the increasing peripheral speed with increasing distance to the hub.
• the underwater surfaces can be equipped with riblets 1 in merchant ships.
• the for the typical cruising speeds of these ships from 10 to 20 knots require riblets with furrow widths between 80 and 200 ⁇ .
• Such riblets 1 can be introduced into the underwater lacquer by means of DLIP.
• the size of the riblets 1 can be varied by a simple change of the angle ⁇ at the partial beams 6, 7,
• the groove depth d of the riblets 1 can be adjusted by the intensity and feed rate
• riblets 1 with particularly steep flanks 11, slender, pointed ribs 12 can be produced, particularly simply by slightly offset overlapping of in particular substantially identical interference structures, preferably produced by offset optical heads,
• processing can be fully automatic and / or remotely controlled
• the riblets are subsequently introduced into standard, cured coatings. This allows a particularly flexible introduction of Riblets.
• the riblet structures are generated by interfering laser radiation or interference patterning.
• riblets can be introduced with a particularly high processing speed.
• interference structures of the interfering laser radiation or the interference patterning are produced in particular shifted slightly.
• sharp and sharp riblet tips can be produced by superposition of, in particular, slightly shifted interference structures.
• a C0 2 laser is used.
• Common lacquer systems and particularly advantageous riblet sizes can thus be produced very precisely and effectively.
• a laser with a wavelength of 9.6 ⁇ is used.
• a particularly high absorption in PUR varnish can thus be made possible.
• the flow resistance on a component can be reduced overall in an improved manner during operation by adapting the introduced riblets 1 at different points of a component to the flow conditions prevailing in operation, ie flow velocity and / or air pressure.
• a particular periodic distribution of the laser intensity l (x ) over a transverse axis x perpendicular to the feed direction 9 or longitudinal direction 8 of the riblets on the surface 3 are adjusted accordingly.
• the wall friction of a flow can be reduced in this way in particular to a total extent.
• the fuel consumption can be reduced or in a wind turbine whose efficiency can be increased.
• An adaptation of at least one geometric parameter of the riblets 1-such as the size of the riblets, the furrow width correlating to the distance L or the furrow spacing a-to the local flow conditions during operation of a component is therefore of particular advantage.
• a merging angle ⁇ between the two interfering partial beams 6, 7 is selectively changed.
• the merging angle ⁇ describes the angle enclosed by the two interfering partial beams 6, 7 during the reunification of the partial beams, or in other words when crossing or meeting the partial beams.
• the point of reuniting, crossing, and meeting the sub-beams will be called “cross point.”
• the "machining distance” will be referred to as the distance of the sub-beam Cross point of at least two partial beams of the machining head or a tilting axis 27 of a fixed deflecting mirror 24th
• the cross point is placed on the surface 3.
• the merging angle ⁇ between the two interfering partial beams 6, 7 can then be measured when hitting the surface 3.
• ⁇ 2a
• a is the angle which is enclosed by the central axis 26 and the first or second partial beam 6, 7.
• the union angle ⁇ may be an interference angle or referred to as such.
• a deliberate change of the union angle ⁇ means a scheduled change to obtain a desired union angle ⁇ .
• the targeted change takes place in particular semi-automatically with the involvement of the user or fully automatically by means of a controller.
• the two interfering partial beams 6, 7 were obtained by division of a coherent laser beam 15 as described above.
• the interfering partial beams 6, 7 form the interfering laser radiation 16 and / or bring on the surface 3 correspondingly distributed energy to produce the riblets 1 by material removal.
• the targeted changing of the union angle ⁇ allows the targeted adaptation of at least one geometric parameter of the riblets 1, which are introduced into the surface 3 with the deliberately changed union angle ⁇ .
• the geometric parameters of the riblets 1, which can be specifically adapted by selectively modifying the joining angle ⁇ include the furrow spacing a, the furrow width and the ratio of furrow depth d to furrow spacing a.
• the joining angle ⁇ by deliberately changing the joining angle ⁇ , the furrow spacing a, the furrow width and / or the ratio of furrow depth d to furrow spacing a of the riblets 1 can be selectively changed.
• the joining angle ⁇ , the furrow spacing a, the furrow width and / or the ratio of furrow depth d to furrow spacing a of the riblets 1 can be specifically adapted to flow conditions which typically prevail at the area of the surface 3 to be processed during operation .
• the area to be processed is meant a locally limited area of the surface 3.
• the flow velocity and / or the air pressure can be used.
• the flow conditions that typically exist during operation can be determined by measurements, calculations, and / or estimates.
• an average value or weighted average is used for the typically prevailing flow conditions.
• a controller in which, depending on the position of a region of the surface 3 or the position of a processing point 29, a union angle ⁇ is deposited, so that when moving the machining head over the surface 3 automatically sets a union angle ⁇ using the controller which is provided for the currently processed area of the surface 3 or the current processing point 29.
• a displacement sensor is provided, so that the controller receives information about the current position of the machining head or the machining point 29 relative to the surface 3.
• the controller can control a drive for the motorized tilting of a tiltable deflecting mirror 24 for changing or adjusting the joining angle ⁇ .
• the merging angle ⁇ is increased if, for a region of the surface 3 to be machined, a smaller groove spacing a is to be planned for the riblets 1 to be produced in this region due to a greater flow velocity to be expected there during operation.
• the union angle ⁇ is reduced if, for a region of the surface 3 to be machined, a greater groove spacing a is planned for the riblets 1 to be produced in this region due to a lower flow velocity to be expected there during operation.
• the riblets 1 can be adapted in this particularly efficient and economical manner to the flow conditions prevailing at this point in operation to maximize drag reduction.
• the machining head is set up such that a laser beam 15 arriving from the laser into the machining head is split into a plurality of partial beams 6, 7 and then combined again with a desired interference structure to form the interfering interference radiation 16. In an analogous manner, this can also be implemented for the additional laser beam 17.
• the riblets can thus be produced with a particularly easy-to-handle, monolithic processing head.
• the beam splitting device or a beam splitter can be used for splitting the laser beam 15 or the additional laser beam 17 into partial beams 6, 7, the beam splitting device or a beam splitter can be used.
• tiltable deflection mirror 24 and / or an optical deflection body 30 can be used.
• the beam splitter is a Diffractive Optical Element (DOE) or the beam splitter includes a DOE.
• DOE Diffractive Optical Element
• a laser beam 15 or additional laser beam 17 can thereby be split into two or more sub-beams 6, 7 with almost no energy loss, preferably in exactly two or exactly four sub-beams 6, 7.
• Interference effects within the DOE convert an incident laser beam into two, three, four or more sub-beams 6, 7 divided.
• the two, three, four or more partial beams 6, 7 are deflected at a certain angle.
• the DOE is a transmitting DOE.
• the partial beams 6, 7 are then transmitted through the DOE.
• the DOE is a reflective DOE.
• the partial beams 6, 7 are then reflected by the DOE.
• the DOE is a reflective or transparent phase grating 25.
• a particularly compact design of the machining head can be realized thereby.
• a reflective phase grating 25 is particularly robust and has a comparatively high damage threshold.
• a transparent phase grating 25 allows a particularly slim design of the machining head.
• the reflective or transparent phase grating can be set up, in particular by appropriate selection of the grating parameters, so that the incident laser beam 15 can be divided into two, three, four or more identical partial beams 6, 7.
• the identical partial beams 6, 7 are deflected symmetrically with respect to the original beam direction of the laser beam 15.
• a reflective or transparent phase grating for the additional laser beam 17 is used in one embodiment.
• the beam splitter is a partially reflecting mirror or the beam splitting device comprises a partially reflecting mirror.
• the incident laser beam 15 is then partially transmitted and partially reflected.
• At least one tiltable deflection mirror 24 for deflecting a partial beam 6, 7 is tilted for the purpose of deliberately changing the association angle ⁇ .
• a particularly simple and reliable targeted modification of the union angle ⁇ is made possible.
• two or four tiltable deflecting mirrors 24 for deflecting a partial beam 6, 7 are tilted for purposefully changing the joining angle ⁇ .
• only one tiltable deflection mirror 24 is provided for exactly one partial beam 6, 7 in each case.
• a tiltable deflecting mirror 24 may be shaped or constructed such that two partial beams 6, 7 can thus be deflected according to plan.
• all tiltable deflecting mirrors 24 can only be tilted synchronously.
• two or four deflection mirrors 24, which can only be tilted synchronously in a synchronized manner are provided for purposefully changing the angle of union ⁇ . When tilting, a change in the tilt angle of the deflecting mirror 24 takes place by a tilt angle change ⁇ .
• the periodic distance L of the riblets 1 between two adjacent intensity maxima l max is determined by the merging angle ⁇ of the partial beams 6, 7.
• the angle ⁇ and thus the distance L selectively changed become.
• tilting of a deflecting mirror 24 takes place about a tilting axis 27.
• the tilting axis 27 is oriented perpendicular to the central axis 26.
• the two or four tiltable deflection mirrors 24 are arranged symmetrically about a central axis 26.
• One pair of mirrors or two mirror pairs of two each symmetrically arranged tiltable deflecting mirrors 24 are obtained.
• Tilting only synchronously means that tilting movements of the only synchronously tiltable deflection mirror 24 are in a fixed relationship to one another or have the same tilt angle change.
• the synchronously tiltable deflecting mirrors 24 are tilted synchronously correspondingly, preferably every two or four tiltable deflecting mirrors 24 by the same amount of tilt angle change ⁇ .
• the two tiltable deflecting mirrors 24 are preferably tilted by the same tilt angle in order to change the joining angle ⁇ in a targeted manner. If exactly two pairs of mirrors are provided, the two tiltable deflecting mirrors 24 of each mirror pair are preferably always tilted by the same tilt angle in order to change the joining angle ⁇ in a targeted manner. In principle, a tilting of the tiltable deflecting mirrors 24 of a pair of mirrors is mirror-symmetrical to the central axis 26.
• the two tiltable deflection mirrors 24 are gimbal tilting mirrors 24. Because a gimbal tiltable deflection mirror is placed about the point of impact of an incoming beam, e.g. Laser beam or partial beam, can be tilted with the mirror surface, allows the pivot point of the beam always remains the same.
• an incoming beam e.g. Laser beam or partial beam
• a drive for motorized tilting of the two tiltable deflection mirrors 24 is provided, in particular for tilting into one or more differently oriented tilting axes.
• a high level of automation can be achieved in this way.
• At least two partial beams 6, 7, in particular exactly two or exactly four partial beams 6, 7, are directed by a respective tiltable deflection mirror 24 directly onto the surface 3 for introducing the riblets 1 or onto an optical deflection body 30.
• the at least one tiltable deflection mirror 24 directs a partial beam 6, 7 on the surface 3.
• the straightening, ie the deflection, of a partial beam 6, 7 is performed directly by a tiltable deflection mirror 24 on the surface.
• a particularly simple construction of the machining head can be achieved.
• the machining head or the arrangement of the optical elements is set up so that the tilting of the tiltable deflection mirror 24 of the Machining distance changed.
• a tracking of the machining head is provided in order to compensate for a change in the machining distance as a result of the targeted changing of the joining angle ⁇ . It is thus ensured that the cross point of the partial beams 6, 7 is approximately at the level of the surface 3 and / or in the desired processing point 29.
• the focusing device is adjusted and / or tracked so that the focal positions of the partial beams 6, 7 are approximately at the level of the surface 3 and / or in the desired processing point 29.
• the focal position describes, based on the beam propagation direction, the position of the narrowest spot diameter in the beam path relative to the processing point 29 on the surface 3 to be processed.
• the spot diameter or the laser spot 36 (see FIG ) on the surface 3 to be processed.
• this will change the intensity of the interfering laser radiation 16 acting on the processing point 29, which basically is e.g. can affect the groove depth d or the gap width.
• a tracking of the machining head is not provided in order to change the groove depth d and / or the gap width of the riblets 1 in a targeted manner by a machining distance changed in this way.
• the tiltable deflecting mirrors 24 each direct a partial beam 6, 7 onto an optical deflecting body 30 for deflecting onto the surface 3.
• an optical deflecting body 30 in the beam path between the tiltable deflecting mirrors 24 and the surface 3 to be machined, a particularly compact Construction of the machining head achieved and the number of optical components can be reduced.
• it can be achieved by the optical deflecting body 30 that the machining distance remains the same during a targeted change in the joining angle ⁇ , in particular by tilting a tiltable deflecting mirror 24.
• the optical deflection body 30 for deflecting a partial beam 6, 7 comprises a two-dimensionally curved or three-dimensionally curved deflection surface 31.
• the two-dimensionally or three-dimensionally curved surface is elliptically curved. It can be achieved so that the machining distance during a targeted change in the association angle ⁇ in particular by tilting a tilting deflection mirror 24 remains the same.
• the optical deflecting body 30 and / or the deflecting surface 31 are reflective for a partial beam 6, 7, that is to say they are not transparent.
• the optical deflecting body 30 and / or the deflection surface 31 are made of metal, preferably copper.
• the optical deflecting body 30 for deflecting a partial beam 6, 7 has a two-dimensionally curved deflecting surface 31 for selectively changing the joining angle ⁇ as a function of a tilt angle change ⁇ of the tiltable deflecting mirror 24.
• the machining distance is independent of the tilt angle change ⁇ .
• a constant machining distance can be obtained even during a tilting of a tiltable deflection mirror 24 by a tilt angle change ⁇ for the purpose of selectively changing the association angle ⁇ .
• a tracking of the machining head can thus be omitted. If the machining head is moved, for example, by means of rollers at a constant distance from the surface 3 in the feed direction, the joining angle ⁇ can be changed in a targeted, continuous, rapid and reliable manner without a distance adjustment.
• the two-dimensionally curved deflecting surface 31 extends in a tilting plane of the tiltable deflecting mirrors 24, ie perpendicular to the tilting axis 27.
• the two-dimensionally curved deflecting surface 31 has an elliptical contour progression which corresponds to a section of an ellipse 32.
• this ellipse 32 has a first focal point in the tilt axis 27 of a tiltable deflection mirror 24.
• this ellipse 32 has a second focal point in a cross point of the partial beams and / or in a processing point 29 on the surface to be machined 3.
• a lens 33 is provided for focusing in the beam path in front of the beam splitter or the beam splitting device, so that only deflecting takes place without focusing through the optical deflecting body 10.
• the optical deflecting body 30 for deflecting a partial beam 6, 7 has a three-dimensionally curved deflection surface 31 for focusing the partial beam 6, 7 on the surface 3 and / or for deliberately changing the merging angle ⁇ as a function of a tilt angle change ⁇ of the tiltable deflecting mirror 24 on.
• the machining distance is independent of the tilt angle change ⁇ .
• the three-dimensionally curved deflection surface 31 has an ellipsoidal, preferably parabolic or spherical curvature.
• the three-dimensionally curved deflection surface 31 corresponds to two overlapping two-dimensional curvatures, wherein the planes of the two two-dimensional curvatures are oriented perpendicular to one another.
• the first two-dimensional curvature extends in a plane perpendicular to the tilting axis 27 and / or corresponds to the two-dimensional curvatures described above for selectively changing the joining angle ⁇ as a function of a tilt angle change ⁇ of the tiltable deflection mirror 24.
• the first two-dimensional curvature preferably comprises the first described above Focus and / or second focus of the ellipse 32 on.
• the second two-dimensional curvature extends in a plane perpendicular to the central axis 26 and / or has a preferably parabolic or circular segment-shaped contour for focusing an incident partial beam on the cross point with another partial beam and / or on the processing point 29 on the surface 3 to be processed.
• the three-dimensionally curved deflection surface 31 in a first plane perpendicular to the tilting axis 27 of the tiltable deflection mirror 24 comprises an ellipsoidal curvature and perpendicular thereto a parabolic or spherical curvature.
• the term "perpendicular thereto" means in this case in particular perpendicular to the first plane and along the surface normal at each point
• the parabolic or spherical curvature of the three-dimensionally curved deflection surface 31 serves to focus a partial beam 6, 7 on the surface 3.
• the ellipsoidal curvature corresponds in particular, the first two-dimensional curvature described above.
• a parabolic curvature has the advantage that this curvature can focus the partial beam 6, 7 by only one axis.
• a pre-focusing or a focus lens 33 for focusing a laser beam 15, which comprises the processing head and is arranged in the beam path in front of the optical deflection body 30, can thus be saved and the number of optical components can be reduced. It can also be focused by being closer to the surface.
• a spherical curvature has the advantage that a particularly precise focusing can be implemented particularly easily and reliably.
• the directed through the tiltable deflection mirror 24 on the deflection surface 31 partial beam 6, 7 can be focused with a specifically adjustable and variable union angle ⁇ on the surface 3, wherein the association angle ⁇ of the tilt angle of the tiltable deflection mirror 24 is dependent.
• the optical deflecting body 30 with a three-dimensionally curved deflection surface 31 belongs to the focusing device 20 or in one embodiment is the focusing device 20.
• the focusing device 20 and / or the optical deflecting body 30 are arranged such that the laser beam 15 has a substantially circular shape Beam cross section 34 is focused so that the interfering laser radiation 16 has an elongated beam cross section 35.
• interfering laser radiation 16 with an elongated radiation cross section 35 for introducing the riblets 1 acts.
• an elongate surface patch is exposed simultaneously by the interfering laser radiation 16.
• the result is a so-called laser spot 36, which is elongated.
• the laser spot 36 thus has a long side in the direction of this elongated extent and a short side which extends perpendicular to the long side. It may be a length of the laser spot 36 - hereinafter also called “spot length" - the long side and a width of the laser spot The width of the laser spot 36, that is to say the short side thereof, runs in the longitudinal direction 8.
• the elongate radiation cross section 35 is oval or substantially rectangular in shape.
• the elongate radiation cross section 35 in the focal position has an aspect ratio of length to width of at least 5 to 1, preferably 20 to 1 and / or at most 500 to 1, preferably 200 to 1, particularly preferably approximately 50 to 1.
• the laser spot 36 on the surface 3 in focus position is 5 cm long and 1 mm wide.
• the elongated extension of the radiation cross section 35 is oriented transversely to the longitudinal direction 8 of the riblets 1 or the grooves 13.
• the feed direction 9 is directed transversely to the direction of the elongated extent of the radiation cross section 35.
• the machining head moves over the surface 3 in the feed direction 9, which corresponds to the longitudinal direction 9 of the grooves 13, a plurality of grooves 13 next to each other and thus a plurality of parallel riblets 1 are continuously introduced into the surface 3.
• It can be prepared as a component whose surface 3 riblets 1 with a furrow spacing a, which varies continuously in the longitudinal direction 8, depending on the prevailing at the respective location in operation flow conditions.
• At least ten, preferably fifty, more preferably one hundred, and / or not more than five thousand, preferably not more than one thousand, particularly preferably not more than five hundred, parallel grooves 13 or riblets 1 are introduced simultaneously through the interference structure focused on the surface 3 to be processed.
• the number of parallel grooves 13 or riblets 1, which are introduced simultaneously by the interference structure focused on the surface 3 to be processed are adapted to the size of the laser spot 36, in particular along its length. The length of the laser spot 36 is measured perpendicular to the longitudinal direction 8 as described above, in which the machining head is moved over the surface 3.
• stain lengths per millimeter are at least five Ruts 13 and / or at most twenty furrows 13 provided.
• this may correspond to spot lengths of ten to two hundred millimeters, and thus 50 to 4000 grooves 13, which are simultaneously introduced into the surface 3.
• the focusing takes place about only one axis, so that a laser beam 15, in which a length of the beam cross section 34 corresponds approximately to the width, is converted into an elongate radiation cross section 35.
• the focusing takes place about only one axis through one or more lenses of the focusing device before or after the beam splitting or through the optical deflecting body 30.
• the curved deflection surface 31 is shaped so that a partial beam 6, 7, which falls with a substantially circular beam cross section 34 on the curved deflection surface 31 is deflected with an elongated beam cross section 35 on the surface to be processed 3 and / or focused ,
• the long axis of the laser spot 36 extends along the plane of the partial beam 6, 7 incident on the surface 3 to be processed.
• a constant machining distance with a changing joining angle ⁇ can be made possible in this way without tracking the machining head through the optical deflecting body 30.
• 31 smaller focal lengths and thus a stronger focus with a narrower spot diameter in the focus position can be made possible by a deflecting body 30 with a three-dimensionally curved deflection 31.
• the smaller focal length is possible because the optical deflecting body 30 can be arranged closer to the surface 3 compared to a lens 33 for focusing in front of the tiltable deflecting mirrors 24. With a lens 33 for focusing with a similarly small focal length, there would otherwise be little or no space between the beam splitter and the surface 3 for accommodating the optical deflecting body 30.
• the optical deflection body 30 is symmetrically shaped and / or constructed, in particular to the central axis 26 and / or the tilt axis 27.
• a plane which is spanned by the central axis 26 and the tilt axis 27, serves as a plane of symmetry for the optical deflection body 30th Preferred are two provided opposite curved deflection 31 and / or mirror-symmetrically with respect to the plane of symmetry.
• the optical deflecting body 30 is pivotally mounted, in particular about a pivot axis 28.
• the partial beams 6, 7 can be deflected in this way in the direction of feed direction 9 or counter to the feed direction 9.
• the processing point 29 can be moved on the surface 3 of the component relative to the machining head. This can be helpful, for example, to compensate for inaccuracies of the feed movement.
• the pivot axis 28 extends perpendicular to the central axis 26 and / or perpendicular tilt axis 27.
• two tiltable deflection mirror 24 at an equal distance from the optical deflecting body 30 in the direction of the pivot axis 28.
• a further aspect of the invention relates to a method for producing riblets 1, wherein the riblets 1 are introduced into a surface 3 by means of laser interference structuring or DLIP - direct laser interference patterning, in particular into a lacquered and hardened surface 3, with the aid of two interfering partial beams 6, 7 on the surface 3, which is especially painted and cured, an interference structure with intensity maxima l max is generated at a periodic distance L, wherein during the riblet production, in particular during the introduction of the riblets 1 in the surface 3, a joining angle Gezielt between the two interfering partial beams 6, 7 is selectively changed.
• Riblets 1 can thus be adapted to the prevailing flow conditions during operation and produced particularly efficiently.
• the above description also relates to this aspect of the invention.
• Another aspect of the invention relates to a device for introducing riblets 1 by means of laser interference structuring or DLIP - Direct Laser Interference Patterning - into a surface 3 of a component, in particular into a lacquered and hardened surface 3, comprising a laser, a processing head with a beam splitting device 21 and a focusing device 20 and a movement unit 14, wherein the movement unit 14 is set up such that the processing head - in particular controlled by a control and / or driven by a drive - can be moved over a surface 3 to be processed, the processing head being arranged that with the aid of two interfering partial beams 6, 7 on the surface 3, which is in particular painted and cured, an interference structure with intensity maxima l max can be generated at a periodic distance L, wherein the Device is set up so that during the riblet production, in particular during the introduction of the riblets 1 in the surface 3, a merging angle ⁇ between the two interfering partial beams 6, 7 can be selectively changed.
• riblets by means of
• Another aspect of the invention relates to a component which has been produced in particular in the manner described above, wherein a surface 3 of the component riblets 1, wherein the riblets 1 and grooves 13 between the riblets 1 continuously, so without an interruption, in a longitudinal direction 8, wherein a groove spacing a between two immediately adjacent furrows 13 changes in the longitudinal direction 8, in particular continuously.
• the riblets 1 swing continuously and / or in sections, but are not interrupted or joined together from a plurality of prefabricated pieces.
• a particularly effective reduction of the frictional resistance due to prevailing in operation currents can be made possible.
• the above description also relates to this aspect of the invention.
• FIG. 8 shows an extension of the construction shown in FIG. A phase-correct superimposition of interference structures with the periodic distances L and L / 2 is made possible with this structure.
• a transparent phase grating 33 is used, in which, however, not as in Figure 7, two symmetrical partial beams 6, 7, but two symmetrical pairs of two partial beams 6, 7 occur, i. four partial beams.
• the tilt angles of the tiltable deflection mirrors 24 are now adjusted so that for one pair the union angle ⁇ for the periodic distance L and for the other pair the union angle ⁇ for the periodic distance L / 2 results.
• FIG. 9 shows an optical structure in which the partial beams 6, 7 are each directed by a tiltable deflection mirror 24 to a respective curved deflection surface 31 and from there to the surface 3.
• the curved deflection surface 31 of the structure of FIG. 9 is curved two-dimensionally.
• a lens 33 is provided for focusing the laser radiation on the surface 3. The focusing by the lens 33 is effected by only one axis, so that in the processing point 29, an elongated shaped radiation cross section is formed, which can cause a laser spot 36 as shown in FIG.
• FIG. 11 shows an optical deflection body 30 in a spatial side view.
• the curved deflection surface 31 has the same curvature in the front plane as shown in FIG.
• the deflection surface 31 of FIG. 11 is in at least one further plane curved spherically or parabolically, as indicated in Figure 1 1.
• the optical deflecting body 30 with such a three-dimensionally shaped deflecting surface 31 thus has a dual function. A lens 33 for focusing can thereby be saved.
• the joining angle ⁇ can be selectively changed as a function of a synchronous tilt angle change ⁇ of the tiltable deflection mirror 24 and thus the riblet size, in particular the groove spacing a, continuously to a previously determined target value during the machining process be adjusted.
• FIG. 10 shows an oblong laser spot which images the intensity distribution of the interfering laser radiation.
• the laser spot can be determined by baking into a substrate, for example at the level of the surface 3 or by a device for the position-resolved detection of the intensity distribution of laser radiation or the interfering laser radiation. By determining the distance between two intensity maxima l max , the distance L can also be determined from this.
• the laser spot 36 on the surface has a spot width of at least 0.3 mm and / or at most 3 mm, preferably about 1 mm. In the constructions shown in FIGS.
• Riblet production affects the entire manufacturing process.
• the machining head is initially set so that riblets can be created with the desired geometry.
• an adaptation of the machining head takes place continuously during the insertion of the riblets during riblet production.
• the riblets are introduced into a surface, in particular into a lacquered and hardened surface, by means of laser interference structuring or DLIP.
• the riblets are introduced into a lacquer layer 4, 5 applied to the surface and hardened.
• the surface is generally a surface of a component. If a surface has been painted, the surface has at least one paint layer 4, 5 of a paint system.
• a paint system can be a paint with multiple ingredients or components.
• topcoat layer 4 and basecoat layer 5 different lacquer systems are preferably provided.
• a painted and cured surface 3 is a painted surface of a component whose paint system has cured or its paint systems are cured. The riblets are thus introduced only after the curing of a paint or paint system.
• the paint system of the surface 3 based on polyurethane, epoxy and / or acrylic components and / or the surface of a component was painted with a paint system based on polyurethane, epoxy and / or acrylic components.
• the paint system of this embodiment serves to form a topcoat layer 4.
• the paint system of this embodiment relates to the painted and cured surface, i. it can be used for painting the surface with subsequent curing.
• the laser has sufficient spatial and temporal coherence, so that its beam can be divided into identical partial beams 6, 7, which generate regular interference structures on subsequent superimposition.
• a laser that has sufficient spatial and temporal coherence refers to a laser beam source that can produce a beam with sufficient spatial and temporal coherence. With beam here the laser beam 15 and / or the additional laser beam 17 are meant.
• the interference structures correspond to the interfering laser radiation 16 and / or the additional interfering laser radiation 18.
• the laser is continuously excited and / or operated in continuous wave or pulsed with pulse durations ⁇ 1 ms. Soot formation can thus be avoided, in particular when using a C0 2 laser and / or when introducing the riblets into a lacquer layer.
• the pulse duration is> 0.1 ⁇ , preferably> ⁇ ⁇ ⁇ $. Foaming of the material can thus be reduced, suppressed and / or completely prevented, in particular when using a C0 2 laser and / or when introducing the riblets into a paint layer.
• a laser operated in continuous wave is generally a continuous wave laser 2, that is to say a continuously excited laser which, in contrast to a pulsed laser, continuously emits a laser beam. It is basically possible for the continuous wave laser 2 to be set up in such a way that a pulsed laser beam is emitted.
• the laser is a CO 2 laser, the emission of which, in particular, is adapted to the wavelengths 9.3 ⁇ , 9.4 ⁇ , 9.6 ⁇ or 10.6 ⁇ depending on the paint system.
• emission is meant the laser beam 15 and / or the additional laser beam 17.
• An adjustment of the laser or its emission depending on the paint system takes place as a function of a corresponding absorption characteristic of the paint system, such that of several possible wavelengths for the emission exactly that wavelength is selected for the setting of a peak wavelength or a wavelength range with relative large absorption in accordance with the wavelength-dependent absorption characteristics of the paint system comes closest.
• the riblets 1 are produced with the aid of interfering laser radiation 16, 18, ie the interfering laser radiation 16 and / or the additional interfering laser radiation 18.
• an interference structure with intensity maxima is generated on the paint surface with the aid of two interfering partial beams 6, 7 l max at periodic distance L.
• the interference structure corresponds to the interfering laser radiation 16 and / or the additional interfering laser radiation 18.
• parallel grooves 13 on the paint surface and thus riblets 1 in the flow direction are formed by lateral movement of the interference structure with simultaneous laser removal. The furrows 13 thus obtained form a furrow system.
• two adjacent furrows have a furrow spacing a, which is generally measured from furrow center to furrow center of the two adjacent furrows, in particular transversely to the longitudinal direction 8.
• Lateral movement means the feed movement, in particular in the feed direction 9 and / or in the longitudinal direction 8 of the grooves 13.
• the flow direction is basically oriented parallel to the longitudinal direction 8 of the grooves 13.
• the paint surface means an already painted and cured surface 3.
• the riblets 1 are introduced into the outer topcoat layer 4, wherein a base coat layer 5 arranged below the topcoat layer 4 is a comparatively has low absorption for the corresponding laser wavelength.
• the degree of absorption of the basecoat film 5 is preferably lower than the absorption coefficient of the topcoat film 4 for the wavelength of the laser beam 15 or of the additional laser beam 17.
• the base coat layer 5 arranged below the top coat layer 4 is partially exposed by means of the interfering laser radiation 16, 18.
• the original laser beam 15 is split into at least three or four partial beams 6, 7, preferably identical partial beams 6, 7, and these partial beams 6 , 7, preferably identical partial beams 6, 7, in turn for generating interference structures, a first interference structure and a second interference structure, brought on the paint surface to overlap.
• a phase grating 25 is provided for dividing the original laser beam into partial beams.
• the first interference structure and the second interference structure are separated.
• the two interference structures are separated so that there is no interference of the two interference structures.
• the two interference structures are directed locally offset to the surface 3 to be processed.
• each of two of the four sub-beams generates an interference structure in two separate optical units and / or the separate furrow systems thus created may be shifted or be relative to each other.
• the interference structure is generated by means of two interfering partial beams 6, 7 on the paint surface with intensity maxima l max at periodic distance L.
• the furrow systems are formed by parallel furrows on the lacquer surface and thus riblets in the flow direction are generated by lateral movement of the interference structure with simultaneous laser ablation.
• the distance L between two intensity maxima l max can be determined by means of a device for measuring the radiation intensity.
• the spacing period, that is to say the distance a, of the two furrow systems is 2L in each case, and the two furrow systems are displaced transversely to the furrow 13, ie transversely to the longitudinal direction 8, by the distance L, so that therefrom superposition of the interference structures results in a riblet structure with the period L and / or with significantly steeper edges than in the case of the two-beam interference.
• period L and distance L is meant a shift with the amount of the distance L between two adjacent, spaced apart intensity maxima l max .
• the riblets 1 are introduced into the surface 3 of an aircraft 10, a ship or the rotor blades of a wind turbine.
• the device is set up in particular for carrying out the above-described method for producing riblets 1.
• the device comprises a C0 2 laser set up to produce the riblets 1.
• the device further comprises a monolithic machining head, which can also be called optical head.
• a monolithic machining head which can also be called optical head.
• one or two beam splitters, in particular the beam splitting device 21 are integrated.
• One or more finely adjustable, refractive and / or reflective optical elements, in particular the focusing device 20 are also integrated in the machining head.
• the processing head also has a semi-automatic or fully automatic manipulator.
• the manipulator is a movement unit which is set up so that a laser beam 15, interfering laser radiation 16, an additional laser beam 17 and / or additional interfering laser radiation 18 can be moved relative to the surface 3.
• the moving unit is a multi-axis axis robot 14 with multiple axes of movement.
• FIGS. 5 and 6 show how a first intensity distribution (x) of the interfering laser radiation 16 and a separate second intensity distribution l 2 (x) of the additional interfering laser radiation 18 are shifted by a local offset AL, in particular in the direction transverse to the longitudinal direction 8 of the grooves 13 and / or transverse to the feed direction 9.
• the interfering laser radiation 16 may also be referred to as a first interference structure.
• the additional interfering laser radiation 18 may also be referred to as a second interference structure.
• the first interference structure is shifted relative to the second interference structure by L 2.
• the local offset AL thus corresponds to half the periodic distance L.
• the first interference structure and the second interference structure have the same periodic distance L of the respective intensity maxima Lax.
• the unprocessed, smooth surface areas can thereby be provided, in particular centered between the grooves of the first processing stage, that is to say by the first intensity distribution ⁇ circumflex over (l) ⁇ , with furrows of the second processing stage, that is to say through the second intensity distribution l 2 (x).
• Riblets with a groove depth d which corresponds approximately to half of the groove spacing a, can be produced in this way in a particularly simple and precise manner.
• FIG. 6 shows a two-stage production process with provision of a material layer and a lower layer or a topcoat layer 4 and a basecoat layer 5, wherein the intensity distributions (x) and l 2 (x) are adjusted such that the lower layer or the basecoat layer 5 is partially is exposed.
• the two-stage production process can be implemented by two processing heads that are directly connected to one another but offset by the offset AL, each of which comprises at least one focusing device 20.
• the two-stage production process can be performed by a machining head with one or two beam-splitting devices 21 and at least two Realize focusing devices 20.
• the interfering laser radiation 16 and an additional interfering laser radiation 18 offset by the offset AL can be obtained from only one incoming laser beam 15 by beam splitting or beam splitting.
• the laser radiation of the first processing stage is in particular the interfering laser radiation 16 or a first interference structure, which was preferably obtained by conversion of the laser beam 15.
• the additional laser radiation of the second processing stage is in particular the additional interfering laser radiation 18 or a second interference structure, which was preferably obtained by conversion of the laser beam 17.

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  • 2018-04-25 EP EP18720234.6A patent/EP3615258A1/de active Pending

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