WO2019162464A1 - Procédé d'usinage d'un alésage s'étendant à partir d'une paroi externe d'une pièce à travailler avec un faisceau laser guidé par jet de liquide - Google Patents

Procédé d'usinage d'un alésage s'étendant à partir d'une paroi externe d'une pièce à travailler avec un faisceau laser guidé par jet de liquide Download PDF

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Publication number
WO2019162464A1
WO2019162464A1 PCT/EP2019/054485 EP2019054485W WO2019162464A1 WO 2019162464 A1 WO2019162464 A1 WO 2019162464A1 EP 2019054485 W EP2019054485 W EP 2019054485W WO 2019162464 A1 WO2019162464 A1 WO 2019162464A1
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WO
WIPO (PCT)
Prior art keywords
liquid
jet
guided laser
jet guided
laser beam
Prior art date
Application number
PCT/EP2019/054485
Other languages
English (en)
Inventor
Jens Günter GÄBELEIN
Jeroen Hribar
Christophe PRONGUÉ
Original Assignee
Avonisys Ag
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Publication date
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Publication of WO2019162464A1 publication Critical patent/WO2019162464A1/fr

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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
    • B23K26/14—Working by laser beam, e.g. welding, cutting or boring using a fluid stream, e.g. a jet of gas, in conjunction with the laser beam; Nozzles therefor
    • B23K26/142—Working by laser beam, e.g. welding, cutting or boring using a fluid stream, e.g. a jet of gas, in conjunction with the laser beam; Nozzles therefor for the removal of by-products
    • 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
    • B23K26/03—Observing, e.g. monitoring, the workpiece
    • B23K26/032—Observing, e.g. monitoring, the workpiece using optical means
    • 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
    • B23K26/14—Working by laser beam, e.g. welding, cutting or boring using a fluid stream, e.g. a jet of gas, in conjunction with the laser beam; Nozzles therefor
    • B23K26/1435—Working by laser beam, e.g. welding, cutting or boring using a fluid stream, e.g. a jet of gas, in conjunction with the laser beam; Nozzles therefor involving specially adapted flow control means
    • B23K26/1436—Working by laser beam, e.g. welding, cutting or boring using a fluid stream, e.g. a jet of gas, in conjunction with the laser beam; Nozzles therefor involving specially adapted flow control means for pressure control
    • 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
    • B23K26/14—Working by laser beam, e.g. welding, cutting or boring using a fluid stream, e.g. a jet of gas, in conjunction with the laser beam; Nozzles therefor
    • B23K26/146—Working by laser beam, e.g. welding, cutting or boring using a fluid stream, e.g. a jet of gas, in conjunction with the laser beam; Nozzles therefor the fluid stream containing a liquid
    • 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
    • B23K26/14—Working by laser beam, e.g. welding, cutting or boring using a fluid stream, e.g. a jet of gas, in conjunction with the laser beam; Nozzles therefor
    • B23K26/1462—Nozzles; Features related to nozzles
    • B23K26/1464—Supply to, or discharge from, nozzles of media, e.g. gas, powder, wire
    • B23K26/1476—Features inside the nozzle for feeding the fluid stream through the nozzle
    • 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
    • B23K26/38—Removing material by boring or cutting
    • B23K26/382—Removing material by boring or cutting by boring
    • B23K26/389—Removing material by boring or cutting by boring of fluid openings, e.g. nozzles, jets
    • 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
    • B23K26/40—Removing material taking account of the properties of the material involved
    • 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
    • B23K26/70—Auxiliary operations or equipment
    • B23K26/702—Auxiliary equipment
    • B23K26/705—Beam measuring device
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01D—NON-POSITIVE DISPLACEMENT MACHINES OR ENGINES, e.g. STEAM TURBINES
    • F01D5/00—Blades; Blade-carrying members; Heating, heat-insulating, cooling or antivibration means on the blades or the members
    • F01D5/12—Blades
    • F01D5/14—Form or construction
    • F01D5/18—Hollow blades, i.e. blades with cooling or heating channels or cavities; Heating, heat-insulating or cooling means on blades
    • F01D5/186—Film cooling
    • 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
    • B23K2101/00—Articles made by soldering, welding or cutting
    • B23K2101/001—Turbines
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F05—INDEXING SCHEMES RELATING TO ENGINES OR PUMPS IN VARIOUS SUBCLASSES OF CLASSES F01-F04
    • F05D—INDEXING SCHEME FOR ASPECTS RELATING TO NON-POSITIVE-DISPLACEMENT MACHINES OR ENGINES, GAS-TURBINES OR JET-PROPULSION PLANTS
    • F05D2230/00—Manufacture
    • F05D2230/10—Manufacture by removing material
    • F05D2230/13—Manufacture by removing material using lasers

Definitions

  • Turbines for power generation and aerospace engines are continuously optimized. In an effort to increase fuel efficiency, the turbine must be operated at very high temperatures. For aerospace engines in particular, weight savings in addition drive perpetual design optimizations.
  • turbine blades play an important role in achieving this. Film cooling is applied to safely expose the turbine blades to temperatures that would otherwise damage the blade.
  • new materials which can be exposed to even higher temperatures are applied to make the turbine blade. Such new materials can include a combination of super hard metal alloys as well as ceramics, which make it difficult to machine the blade and to create the required film cooling openings in the blade.
  • the present invention discloses manufacturing methods and systems that enable efficient machining of film cooling openings in turbine blades.
  • US patent 4762464, US patent 5773790 and UK patent 2249279 for example disclose using a laser beam to drill a hole in turbine blade that connects the outer wall of the blade to an internal cavity of the blade.
  • One problem with laser drilling is that the laser beam can damage the back wall of the internal cavity once it passes through the outer wall.
  • UK patent 2249279 discloses that a light blocking material such as PTFE can be inserted into the internal cavity, or alternatively a ceramic casting core can be left inside the blade during the laser process that is removed after the laser process is completed.
  • European patent 2335855 discloses inserting of glass balls as filling medium into a turbine blade.
  • Modern turbine blades however are very small and have a complex internal cavity structure which makes it impossible to easily insert a light blocking material or a filling medium such as glass balls.
  • Another problem involved with laser drilling is that turbine blades that are coated with a thermal barrier layer can be adversely impacted by the laser operation. The thermal barrier layer can be damaged and peel off at the position of the film cooling opening.
  • Film cooling openings in turbine blades can also be made by spark erosion aka electric discharge machining, such as disclosed in UK patent 856983 and US patent application 2006/273073. Spark erosion requires that the machined material is electrically conductive. New turbine blade materials however can be of reduced or even non-conductive properties. Turbine blades with a ceramic thermal barrier coating pose a problem for the spark erosion process. Turbine blades that are made out of lightweight aluminum-enriched Inconel alloys also are difficult to machine by spark erosion.
  • a hybrid method for drilling film cooling openings in turbine blades is for example disclosed in US patent 6362446 and US patent application 2009/169394.
  • a blind hole in the outer wall of the turbine blade is made by a laser beam.
  • the blind hole is machined by an electric discharge machining process that forms a through hole that fluidly connects the outer wall of the turbine blade to an internal cavity.
  • a major drawback of this manufacturing method is that is requires multiple machining processes, which make it very expensive to produce the film cooling openings in the turbine blade.
  • a very high positioning accuracy of the part is required to ensure that the electric discharge machining process accurately machines at the position of the blind hole that was made by the laser beam.
  • a first problem is that a turbine blade has dozens of film cooling openings and by applying a pressurized liquid to the internal cavities of the blade, the already formed cooling openings will become like a fountain inside the liquid-jet guided laser machine and potentially harm critical components of the machine.
  • Another big problem is that the liquid-jet that is required to guide the laser light to the turbine blade can be easily disturbed by the high pressurized liquid flow. Most liquids are incompressible and thus the protective liquid will eject from film cooling openings that are immediately next to a new opening that is currently being machined. The liquid-jet of the laser system can be interfered and interrupted, resulting in faulty or partly cut openings. Also, when a cooling opening is almost completed and a first partial cut- through is made, then the protective liquid can eject from such first opening and disrupt the liquid-jet guided laser, which results in faulty or partly cut openings.
  • the present invention discloses a method of machining a bore extending from an outer wall of a workpiece, preferably a turbine blade, to an internal cavity of the workpiece with a liquid-jet guided laser, wherein a back wall of the internal cavity is protected by a phase change material or a pressurized gas vaporizing the liquid-jet.
  • the liquid-jet guided laser is at least temporarily surrounded by an air-jet.
  • the feature of the air-jet and the generation of an air-jet is enclosed in the previous applications of the inventors WO 2015/087288 A2, WO 2015/087209 A2 and WO 2017/093331 A1 are incorporated by reference.
  • the pressurized gas may be pressurized air.
  • the pressurized gas vaporizing the liquid-jet may be the air-jet.
  • the air-jet leaves a machine head of a liquid-jet guided laser CNC machine preferably physically separated from the liquid- jet.
  • the liquid-jet and the liquid-jet guided laser leave a machine head of a liquid-jet guided laser CNC machine in a first opening and the air-jet leaves the machine head of the liquid-jet guided laser CNC machine in a second opening wherein the first opening is physically separated from the second opening.
  • the air-jet may run during the first part of the ablation process until a cut through is reached towards the workpiece without interfering with the liquid-jet.
  • the air-jet may interfere with the liquid-jet at a predetermined distance from the machine head thereby reducing the laminar length of the liquid-jet.
  • the laminar length of the liquid jet may be adjusted by varying the pressure of the air-jet.
  • the laminar length of the liquid-jet may be adjusted such that the back wall is not affected or machined or destroyed by the laser.
  • the method may further comprise the step of detecting an instant of time of a cut through, preferably of a first cut through, to the internal cavity in an ablation process for machining the bore triggering an application or an increase of a pressure of the air-jet to create a controlled breakup point for the liquid-jet.
  • the cut through may be detected by an optical sensor detecting back spray or the emitted light of a plasma or by an acoustic sensor detecting a sound frequency and/or a sound amplitude.
  • the ablation process for machining of the bore may be finished with the increased pressure of the pressurized gas.
  • a compressed gas is applied to the internal cavity of the workpiece.
  • the phase change material is a ferro-fluid, preferably an oil containing particles responsive to a magnetic field.
  • the present invention discloses methods and systems to machine openings in an outer wall of a hollow workpiece, such as machining film cooling openings in turbine components.
  • a turbine blade can be mounted to a workpiece holder of a liquid-jet guided laser machine.
  • the liquid-jet guided laser beam can be aligned to be precisely parallel to the vertical Z-axis of the workpiece holder.
  • Film cooling openings that fluidly connect an outer wall of the turbine blade to an internal cavity structure can be machined by a liquid-jet guided laser.
  • a compressible medium can be provided to the internal cavity structure of the blade to vaporize the liquid-jet after it passes through an outer wall.
  • a sensor can be applied to precisely detect whether a film cooling opening is correctly and completely machined in order to allow a rapid and closed-loop controlled machining process.
  • the present invention discloses in one aspect a method of aligning a liquid-jet guided laser beam to an axis of a liquid-jet guided laser CNC machine comprising the following steps: a. determining an offset angle of the axis of the liquid-jet guided laser beam to the axis of the liquid-jet guided laser CNC machine by: i. determining the position of the liquid-jet guided laser beam in a reference plane in a first position, ii. moving the laser head of the liquid-jet guided laser CNC machine and/or the reference plane relative to each other from said first position to a second position, iii. determining the position of the liquid-jet guided laser beam in the reference plane in the second position, iv.
  • the method comprises the step of verifying the angular correction adjustment by repeating steps i to iv.
  • the axis of a liquid-jet guided laser CNC machine is a Z-axis of a workpiece holder and/or the reference plane lies in the XY plane.
  • the liquid-jet guided laser beam in a low power level or an alternative light source is used for determining the position of the liquid-jet guided laser beam in the reference plane.
  • the position of the liquid-jet guided laser beam in the reference plane is determined by a sensor.
  • the sensor comprises a viewing window in the reference plane, a detecting surface and a lens arranged between the viewing window and the detecting surface and wherein the laser light or the light of the alternative light source hitting the viewing window is guided via lens to the detecting surface.
  • the detecting surface is a CCD or a CMOS detector.
  • the method comprises the step of defining the absolute position of a liquid-jet guided laser beam within the coordinate system of the liquid-jet guided laser CNC machine, preferably wherein the absolute position is determined by use of a tactile measurement system. In one aspect, preferably multiple positions of an outer wall of the sensor are measured.
  • Fig. 1 illustrates a liquid-jet guided laser head for machining film cooling openings that fluidly connect an outer wall with an internal cavity of a turbine blade according to some embodiments.
  • Fig. 2A illustrates a liquid-jet guided laser beam aligned perfectly parallel to a Z-axis of a CNC machine center.
  • Fig. 2B illustrates a liquid-jet guided laser beam with an angle offset to a Z-axis of a CNC machine center.
  • Fig. 3A illustrates a tilted liquid-jet guided laser beam at a far distance from a reference plane.
  • Fig. 3B illustrates a tilted liquid-jet guided laser beam at a near distance from a reference plane.
  • Fig. 4A-4D illustrate a particularly favorable configuration of a sensor for measuring the offset angle of a liquid-jet guided laser beam according to some embodiments.
  • Fig. 5A-5D illustrate a particularly favorable configuration of a sensor for measuring the offset angle of a liquid-jet guided laser beam according to some embodiments.
  • Fig. 6A-6C illustrate a setup for measuring the absolute position of a liquid-jet within the coordinate system of a CNC machine tool according to some embodiments.
  • Fig. 7A-7C illustrate a basic turbine blade structure according to some embodiments.
  • Fig. 8A-8E illustrate a liquid-jet guided laser head for machining film cooling openings that fluidly connect an outer wall with an internal cavity of a turbine blade, wherein the back wall of the internal cavity is protected by a pressurized gas that vaporizes the liquid-jet according to some embodiments.
  • Fig. 9A-9C illustrate a liquid-jet guided laser head for machining film cooling openings that fluidly connect an outer wall with an internal cavity of a turbine blade, wherein the back wall of the internal cavity is protected by a phase-change material that blocks the liquid-jet according to some embodiments.
  • Fig. 10A illustrates a liquid-jet guided laser head and a liquid-jet guided laser beam that machines a film cooling opening in an outer wall of a turbine blade, wherein the opening is an unfinished blind opening and does not fluidly connect into an internal cavity in the turbine blade.
  • Fig. 10B illustrates a cross-sectional view of a liquid-jet guided beam that machines a film cooling opening in an outer wall of a turbine blade.
  • Fig. 10C illustrates a liquid-jet guided laser head and a liquid-jet guided laser beam that machines a film cooling opening in an outer wall of a turbine blade, wherein the opening is a finished through-opening and fluidly connects into an internal cavity in the turbine blade.
  • Fig. 10D illustrates a cross-sectional view of a liquid-jet guided beam that machines a film cooling opening in an outer wall of a turbine blade, wherein the liquid-jet guided beam can pass through a finished through-opening without being interrupted and without being back-sprayed.
  • Fig. 11A-1 1 C illustrate a sensor configuration to monitor a diffused back-sprayed portion of a liquid-jet guided laser beam according to some embodiments.
  • Fig. 12A-12C illustrate a sensor configuration to monitor a sound response of a turbine blade machined by a liquid-jet guided laser beam according to some embodiments.
  • Fig. 13A-13B illustrate a sensor configuration to monitor a plasma emission of a liquid-jet guided laser beam according to some embodiments.
  • Fig. 14 illustrates a closed loop process for laser machining of film cooling openings.
  • Fig. 15 illustrates a flow chart for operating a liquid-jet guided laser CNC machine tool to machine openings in a workpiece that fluidly connect an outer wall of the workpiece to an internal cavity inside the workpiece according to some embodiments.
  • Fig. 16 illustrates a liquid-jet guided laser head for machining openings that fluidly connect an outer wall with an internal cavity of a workpiece, wherein the back wall of an internal cavity is protected by a pressurized gas that vaporizes the liquid-jet and wherein a sensor detects a cut- through point based on a liquid-jet back-spray condition according to some embodiments.
  • US patent 4762464 discloses a two-step process for generating air cooling holes in airfoils of a gas-turbine engine, whereby a laser beam drills the holes in a first step and an EDM process forms a diffusor shape in a second step.
  • US patent 8993923 also discloses using a laser to create cooling passages in the surface of an airfoil. Here however the laser is guided towards the airfoil by a fluid column.
  • US patent 8993923 also primarily discloses flowing a liquid inside the airfoil to scatter the laser beam and prevent the laser beam from striking an inside surface of the airfoil.
  • US patent 6365871 also disclosed laser drilling of holes through a workpiece, into a cavity with a laser and protecting the workpiece from laser light across the cavity by providing a fluid having laser-barrier properties, thus essentially preventing the laser beam from striking the inside surface of the workpiece too.
  • a first problem is that a turbine blade has dozens of film cooling openings and by applying a pressurized liquid to the internal cavities of the blade, the already formed cooling openings will become like a fountain inside the liquid-jet guided laser machine and potentially harm critical components of the machine.
  • Another big problem is that the liquid-jet that is required to guide the laser light to the turbine blade can be easily disturbed by the high pressurized liquid flow. Most liquids are incompressible and thus the protective liquid will eject from film cooling openings that are immediately next to a new opening that is currently machine. The liquid-jet of the laser system can be interfered and interrupted, resulting in faulty or partly cut openings.
  • the protective liquid can eject from such first opening and disrupt the liquid-jet guided laser, which results in faulty or partly cut openings.
  • the present invention discloses methods to efficiently and safely protect the back wall of an internal cavity in a turbine blade during a liquid-jet guided laser process. In some embodiment, the present invention discloses methods to efficiently machine film cooling openings in turbine blades, which involves precise laser-to-part alignment, internal cavity protection, laser cut-through detection as well as closed-loop control of the liquid-jet laser machining process.
  • Fig. 1 illustrates a liquid-jet guided laser head 101 for machining film cooling openings 103 that fluidly connect an outer wall with an internal cavity of a turbine blade 100 according to some embodiments.
  • the liquid-jet guided laser head 101 can be part of a liquid-jet guided laser machine.
  • a laser source (not shown) can provide a laser beam (not shown), which can be guided to an optical head (not shown) by a fiber optic cable (not shown).
  • the optical head can contain an optical element to collimate the laser beam that is delivered by the fiber.
  • the optical head can also contain an optical element to focus the collimated laser beam into a small spot.
  • a liquid-jet guided laser head 101 can be mounted. Inside the liquid-jet guided laser head 101 , the focused laser beam can be coupled into a liquid-jet.
  • the liquid-jet guided laser head 101 can be connected to at least one liquid supply source (not shown), such as a high-pressure liquid pump to generate a liquid-jet.
  • the liquid-jet guided laser head 101 can also be connected to at least one gas-supply source (not shown), such as compressed air to generate a gas protection barrier around the liquid-jet (not shown).
  • a gas protection barrier surrounding the liquid-jet may be referred to as air jet.
  • the energy of the laser is guided to the workpiece inside a liquid-jet 102 by total internal reflection 104.
  • the liquid-jet is created by pressing a liquid, typically water, through a small nozzle (not shown) that is present inside the liquid-jet guided laser head 101.
  • a focused laser beam is guided through a window (not shown) that is present inside the liquid-jet guided laser head 101 into the center opening of the nozzle.
  • the liquid-jet guided laser machine can further contain at least one motorized and moveable axis (not shown) to move the laser head and/or the workpiece during a machining process.
  • the liquid-jet guided laser process can be used to machine film cooling openings 103 that connect an outer wall of the turbine blade 100 to an internal distribution cavity (not shown).
  • Such film cooling openings 103 can be of arbitrary shape, such as round holes, elliptical holes, or even other shapes such as disclosed in US patent application 2016/0368090.
  • these film cooling openings 103 are machined under a large angle in respect to the surface of the blade 100.
  • a multi-axis liquid-jet guided laser CNC machine center can be applied to machine film cooling openings 103 in a turbine blade at an arbitrary position and at an arbitrary angle.
  • EP2960006A1 discloses a method and apparatus for determining a position of a liquid jet through the modification of an orientation. The method determines the position of the liquid-jet by measuring the liquid-jet in a non-disturbed condition compared to a disturbed condition. Different liquid-jet nozzle diameters, for example 30pm compared to 150pm, behave different when it comes to disturbance sensitivity, hence this method is prone to measurement inaccuracies and subjective interpretation.
  • the present invention discloses different methods to precisely determine the position of the liquid-jet precisely that are not prone to the behavior of different liquid-jets and that are based on an actual laminar working condition of the jet.
  • Fig. 2A illustrates a liquid-jet guided laser beam 202 aligned perfectly parallel to a Z-axis 205 of a CNC machine center. For the laser machining operation, this is the required condition.
  • Fig. 2B illustrates a liquid-jet guided laser beam 202 with an angle offset 204 to a Z-axis 205 of a CNC machine center.
  • the angle offset 204 can have various reasons.
  • the liquid-jet guided laser head 201 itself can be mounted not perfectly perpendicular.
  • the liquid-jet nozzle that generates the liquid-jet can be subject to manufacturing tolerances that lead to a slightly non-perpendicular liquid-jet exiting from the liquid-jet guided laser head 201 toward the workpiece plane 203.
  • Fig. 3A illustrates a tilted 304 liquid-jet guided laser beam 302 at a far distance 305 from a reference plane 303.
  • a far distance 305 can for example be 50mm or 60mm.
  • the liquid-jet guided laser head 301 can be mounted to a vertical aka Z-axis of a CNC machine center. To set a far distance, the Z-axis of the CNC machine center can be moved up and away from a reference plane 303.
  • Fig. 3B illustrates a tilted liquid-jet guided laser beam 302 at a near distance 315 from a reference plane 303.
  • a near distance 315 can for example be 5mm or 10mm.
  • the liquid-jet guided laser head 301 that is mounted to the Z-axis of the CNC machine center can be moved down and towards a reference plane 303.
  • the XY coordinate of the liquid-jet on a reference plane 303 at a far distance 305 and the XY coordinate of the liquid-jet on the same reference plane 303 at a near distance 315 can be measured and mathematically derived.
  • this measurement is best performed with an optical system in which the liquid-jet incidents on a viewing window, wherein the light from the liquid-jet that hits the viewing window is projected by a lens onto a detecting surface.
  • the near distance i.e. the position of the laser head and the sensor, may be considered as first position and the far distance as second position or vice versa.
  • Fig. 4A-4D illustrate a particularly favorable configuration of a sensor for measuring the offset angle of a liquid-jet guided laser beam according to some embodiments.
  • Fig. 4A and fig. 4B illustrate a sensor 408 for measuring the XY position of a liquid-jet guided laser beam.
  • the unadjusted liquid-jet 402 can be tilted 404 from the optical axis 409 of the sensor 408.
  • the laser head 401 is positioned at a first distance 405 from a viewing window 403 of the sensor 408.
  • the liquid-jet guided laser head 401 can be mounted to a vertical aka Z-axis of a CNC machine center (not shown).
  • a first distance 405 can be chosen in such way that the liquid-jet 402 is laminar and not vaporizing and can for example be 50mm or 60mm.
  • either the laser head 401 and/or the sensor 408 can now be moved in XY direction to position the liquid-jet 402 roughly to the center of the viewing window 403.
  • At least one lens 406 projects the light guided by the liquid-jet 402 that hits the viewing window 403 onto a detecting surface 407.
  • the light guided through and by the liquid-jet 402 can be for example the laser itself that is connected to the laser head and being operated at a low power level.
  • the detecting surface 407 can for example be a CCD or a CMOS detector.
  • the detector area 417 can consist of a multitude of photo-sensitive pixels that spatially resolve in X and Y direction of the detecting surface 407.
  • the detector area 417 can contain at least 2 x 2 pixels, for example 1000 x 1000 pixels, or for example 2560 x 1920 pixels. Other aspect ratios and pixel amounts are possible too.
  • the lens 406 projects the light guided by the liquid-jet 402 that hits the viewing window 403 onto the detector area 417 as a bright round spot in a first position 412.
  • the lens 406 consist of at least 2 lens elements.
  • a first lens element can be facing towards the viewing window 403 and have its focal plane on the upper side of the viewing window 403 that faces the laser head 401.
  • the first lens element can further have a short focal length of for example 20mm.
  • a second lens element can be facing towards the detecting surface 407 and have its focal plane on the detecting surface 407.
  • the second lens element can further have a long focal length of for example 80mm.
  • the optical magnification is 1 :4 and thus the light guided by a liquid-jet 402 diameter of for example 0.05mm that hits the viewing window 403 is projected onto the detector area 417 with a diameter of 0.20mm.
  • Fig. 4C and fig. 4D illustrate the sensor 408 for measuring the XY position of a liquid-jet guided laser beam at a second measurement position.
  • the Z-axis of the CNC machine center can be moved down and towards a viewing window 403.
  • a second distance 425 can be chosen in such way that the liquid-jet 402 is laminar and not vaporizing and can for example be 5mm or 10mm.
  • the X and Y axis of the CNC machine are not moved.
  • the lens 406 projects the light guided by the liquid-jet 402 that hits the viewing window 403 onto the detector area 417 as a bright round spot in a second position 432.
  • the angle offset 404 of the liquid-jet 402 compared to the optical axis 409 of the sensor can now be precisely calculated based on the height difference between the first distance 405 and the second distance 425, in relation to the first position 412 and the second position 432 of the light spot projected onto the detector area 417.
  • Fig. 5A-5D illustrate a particularly favorable configuration of a sensor for measuring the offset angle of a liquid-jet guided laser beam according to some embodiments.
  • the laser head can now be mechanically adjusted to compensate the angle offset.
  • Fig. 5A and 5B illustrate a first position measurement of the liquid- jet 502 after the laser head 501 has been mechanically adjusted to compensate the angle offset.
  • the laser head 501 can be mounted to for example a 3-point fixation system (not shown) into the CNC machine that enables compensating an angle offset of the liquid-jet by mechanically adjusting the angle of the laser head 501 in such way that the liquid-jet 502 and the optical axis 509 of the sensor 508 are parallel to each other.
  • either the laser head 501 and/or the sensor 508 can be moved in XY direction to position the liquid-jet 502 roughly to the center of the viewing window 503.
  • the Z-axis of the CNC machine center can be moved up and away from a viewing window 503.
  • a first distance 505 can be chosen in such way that the liquid-jet 502 is laminar and not vaporizing and can for example be 50mm or 60mm.
  • the lens 506 projects the light guided by the liquid-jet 502 that hits the viewing window 503 onto the detector area 517 as a bright round spot in a first position 512.
  • 5C and 5D illustrate a second position measurement of the liquid-jet 502 after the laser head 501 has been mechanically adjusted to compensate the angle offset.
  • the Z-axis of the CNC machine center can be moved down and towards a viewing window 503.
  • a second distance 525 can be chosen in such way that the liquid-jet 502 is laminar and not vaporizing and can for example be 5mm or 10mm.
  • the X and Y axis of the CNC machine are not moved.
  • the lens 506 projects the light guided by the liquid-jet 502 that hits the viewing window 503 onto the detector area 517 as a bright round spot in a second position 532.
  • the first position 512 and the second position 532 of the bright round spot on the detector area 517 must be identical, within a set tolerance. If there is still a small angle offset of the liquid-jet 502 to the optical axis 509 of the sensor 508, then the angle of the laser head 501 can be mechanically fine-aligned and the measurement process repeated. Once the liquid- jet 502 is aligned parallel to the optical axis 509 of the sensor, the absolute position of the liquid- jet 502 within the coordinate system of the CNC machine tool can be determined.
  • FIG. 6A-6C illustrate a setup for measuring the absolute position of a liquid-jet within the coordinate system of a CNC machine tool according to some embodiments.
  • a liquid-jet guided laser head 601 can be mounted to a common structure 600 on an axis of a CNC machine tool.
  • a tactile measurement system 603, such as a touch probe, can be mounted to the same common structure 600.
  • a tactile measurement system 603 can contain a measuring shaft 605.
  • a touching body 604, such as a sapphire ball, can be mounted to an end portion of the measuring shaft 605. When the touching body 604 touches the surface of an object, the measuring shaft 605 can be displaced 613, wherein the displacement can be used to measure a distance.
  • either the axis to which the common structure 600 is mounted can be moved and/or the axis to which the position sensor 606 is mounted can be moved, in order to position the touching body 604 of the tactile measurement system 603 against an outer wall 608 of the position sensor 606.
  • the axis to which the common structure 600 is mounted can be moved and/or the axis to which the position sensor 606 is mounted can be moved, in order to position the touching body 604 of the tactile measurement system 603 against an outer wall 608 of the position sensor 606.
  • at least one outer wall 608 of the position sensor 606 is measured.
  • multiple different positions on the outer wall 608 of the sensor 606 are measured.
  • the touching body 604 can touch a vertical outer wall 608 at a first position 621 , a second position 622, a third position 623 and a fourth position 624.
  • the sensor can be rotated around the optical axis by 180 degrees and the touching body 604 can touch a vertical outer wall 608 at a first position 621 , a second position 622, a third position 623 and a fourth position 624.
  • the touching body can also touch a horizontal top side of a sensor 612 at a first position 631 , a second position 632, a third position 633 and a fourth position 634.
  • the distance 609 from the optical axis 607 of the sensor 606 to the outer wall 608 is known precisely and based on the obtained measurements, a precise absolute position 610 of the liquid-jet 602 in relation to the sensor 606 can be derived.
  • the position sensor 606 can be interchangeably mounted to a fixation mechanism 611 to which also a workpiece (not shown), such as a turbine blade, can be interchangeably mounted.
  • the fixation mechanism 61 1 can have standardized fixation points, which are the same for the sensor 606 as well as a workpiece and thus based on the combined optical and tactile measurements, a precise absolute position of the liquid-jet 602 in relation to workpiece mounted on the fixation mechanism 611 can be set. Thus, accurate machining of a workpiece using multiple axis of the CNC machine tool is possible.
  • a Turbine blade can be mounted to the fixation mechanism 61 1 of the liquid-jet guided laser CNC machine tool.
  • Fig. 7A-7C illustrate a basic turbine blade structure according to some embodiments.
  • the turbine blade 700 can have an airfoil section 701 and a mounting base 702. Feeding holes 703 in the mounting base 702 can connect into internal cavities 705 in the blade. An end portion of the airfoil can have an opening 704.
  • a liquid-jet guided laser process can be applied to machine cooling openings in the outer wall of the airfoil section 701 that fluidly connect into an internal cavity 705.
  • Fig. 8A-8E illustrate a liquid-jet guided laser head for machining film cooling openings that fluidly connect an outer wall with an internal cavity of a turbine blade, wherein the back wall of the internal cavity is protected by a pressurized gas that vaporizes the liquid-jet according to some embodiments.
  • a liquid-jet guided laser beam 802 can be provided by a liquid-jet laser head 801. The liquid-jet guided laser beam 802 can incident an outer wall 813 of a turbine blade 800 in order to machine a film cooling opening 803 that connects an outer wall 813 of the turbine blade to an internal cavity 814.
  • a pressurized gas 805 can be provided to an internal cavity 814 of the turbine blade 800.
  • the pressurized gas 805 can for example be air.
  • the pressurized gas 805 can also be one of an inert gas, for example to suppress oxidation effects in the area of the film cooling opening 803.
  • the pressurized gas 805 can have a pressure that is sufficient to vaporize 828 the liquid-jet that guides the laser beam and prevent the liquid-jet guided laser beam 802 from touching a back wall 815 of an internal cavity 814.
  • the pressure of the pressurized gas 805 can for example be in a range of 1-10 bar and preferably in a range of 1-6 bar.
  • the turbine blade has at least one opening 804 in an end portion of the blade through which the compressed gas can escape 806 from the turbine blade 806.
  • Such opening 804 can be present prior to the laser machining process.
  • Such opening 804 can also be machined by the liquid-jet guided laser beam 802, prior to machining a first film cooling opening 803.
  • a surface area of the opening 804 in an end portion of the blade can be 2-8x larger than a surface area of the largest film cooling opening 803.
  • a surface area of the opening 804 in an end portion of the blade can be 3-5x larger than a surface area of the largest film cooling opening 803.
  • the back wall 815 of the internal cavity 814 is protected by the pressurized gas of the airjet 817.
  • the airjet 817 can be configured to surround the liquid jet and run in a same direction, such as parallel or substantially parallel, with the liquid jet.
  • the airjet 817 can be produced separately from the liquid jet, e.g., the airjet 817 can run parallel to and surrounding the liquid jet while being separated from each other by a solid separation in the liquid-jet laser head 801.
  • the air jet 817 can be controlled independently without or with minimum effect on the liquid jet operation within the desired working distance.
  • the airjet 817 and the liquid jet can leave the system, e.g.
  • the liquid-jet laser head 801 at two separate openings, such as a middle opening for the liquid jet and a surrounding, preferably annular opening 817a for the airjet 817.
  • the gas pressure of the airjet 817 may be set to a value below 10 bar.
  • the process is continuously monitored with a sensor 818 for detecting a cut- through point of an opening 803.
  • a cut-through sensor 818 may be, for example, a plasma sensor, an optical sensor detecting back spray or by an acoustic sensor detecting a sound frequency and/or a sound amplitude as described below in further detail.
  • the pressure of the airjet 817 is increased promptly. The sudden increase of the airjet 817 pressure can be carried out without an influence on the pressure of the liquid-jet 802 due to the independence of the controls and separate exit openings of the liquid-jet guided laser beam 802 and the airjet 817.
  • the increase of the airjet pressure leads to a controlled reduction of the laminar length of the liquid-jet to a desired maximum working distance.
  • the AirJet forms a diverging cylindrical curtain of gas. The point where the converging portions intersect define the controlled break up point of the liquid-jet that passes through this intersecting gas curtain.
  • the increase in pressure is controlled that the laminar length of the liquid-jet 802 is reduced such that the machining of the bore 803 can be finished without an impact on the back wall 815 of the internal cavity 814.
  • the laminar length of the liquid-jet 802 is reduced to the length to the surface 800a of the workpiece, e.g. the turbine blade 800.
  • the laminar length of the liquid-jet 802 extends from inside the liquid-jet laser head 801 to the surface 800a of the workpiece 800.
  • the surface 800a of the workpiece 800 may be in one embodiment the outer wall 813 of the turbine blade 800.
  • the reduction of the laminar length to the surface 800a generally provides sufficient energy of the laser to the bore 803 for it being finished without affecting the back wall 815.
  • the process of reducing the laminar length of the liquid-jet 802 may in one embodiment be assisted by a pressurized gas 805 flowing through the internal cavity 814. This may reduce the risk to impact or destroy the back wall 815 of the internal cavity 814 further. This can be useful when particularly small diameter internal cavities, for example 0.5-2mm, are present in a workpiece.
  • FIG. 9A-9C illustrate a liquid-jet guided laser head for machining film cooling openings that fluidly connect an outer wall with an internal cavity of a turbine blade, wherein the back wall of the internal cavity is protected by a phase-change material that blocks the liquid-jet according to some embodiments.
  • a liquid-jet guided laser beam 902 can be provided by a liquid-jet laser head 901. The liquid-jet guided laser beam 902 can incident an outer wall 913 of a turbine blade 900 in order to machine a film cooling opening 903 that connects an outer wall 913 of the turbine blade to an internal cavity 914.
  • Fig. 9A-9C illustrate a liquid-jet guided laser head for machining film cooling openings that fluidly connect an outer wall with an internal cavity of a turbine blade, wherein the back wall of the internal cavity is protected by a phase-change material that blocks the liquid-jet according to some embodiments.
  • a liquid-jet guided laser beam 902 can be provided by a liquid-jet laser head 901. The liquid-jet guided laser beam 902 can incident an
  • a phase-change material in a fluid state 917 can for example be a ferro-fluid.
  • a ferro-fluid can be an oil that contains particles that are responsive to a magnetic field.
  • a ferro- fluid can be turned into a solid or semi-solid state by applying a magnetic field to the turbine blade 900.
  • a phase-change material in a fluid state 917 can also be a material that is brought into an internal cavity 914 of a turbine blade 900 in a molten stage, such as a molten wax.
  • a molten material can be turned into a solid or semi-solid state by cooling down the turbine blade 900 to a required temperature.
  • An internal cavity 914 of a turbine blade 900 can be filled up with a phase-change material in a fluid state 917 in such way that an external wall 913 and a back wall 916 are separated from each other by the phase-change material.
  • Fig 9C illustrates a cross sectional view of a turbine blade 900.
  • An internal cavity 914 can be filled with a phase-change material in a solid or semi-solid state 927.
  • a film cooling opening 903 can be machined by a liquid-jet guided laser beam 902.
  • the liquid-jet guided laser beam 902 can be obstructed by a phase-change material in a solid or semi-solid state 927.
  • a back wall 916 of an internal cavity 914 can be protected from the liquid-jet guided laser beam 902.
  • a cut-through point of an opening in a turbine blade based on a liquid-jet back- spray condition, is disclosed.
  • Fig. 10A illustrates a liquid-jet guided laser head 1001 and a liquid- jet guided laser beam 1002 that machines a film cooling opening in an outer wall of a turbine blade 1000, wherein the opening is an unfinished blind opening 1003 and does not fluidly connect into an internal cavity in the turbine blade 1000.
  • Fig. 10A illustrates a liquid-jet guided laser head 1001 and a liquid- jet guided laser beam 1002 that machines a film cooling opening in an outer wall of a turbine blade 1000, wherein the opening is an unfinished blind opening 1003 and does not fluidly connect into an internal cavity in the turbine blade 1000.
  • FIG. 10B illustrates a cross-sectional view of a liquid-jet guided beam 1002 that machines a film cooling opening in an outer wall 1005 of a turbine blade 1000.
  • a liquid-jet back-spray 1004 can be present when an opening in an outer wall 1005 of a turbine blade 1000 is an unfinished blind opening 1003.
  • Such liquid-jet back-spray 1004 can diffusely propagate a portion of the laser energy.
  • Fig. 10C illustrates a liquid-jet guided laser head 1001 and a liquid-jet guided laser beam 1002 that machines a film cooling opening in an outer wall of a turbine blade 1000, wherein the opening is a finished through-opening 1013 and fluidly connects into an internal cavity in the turbine blade 1000.
  • Fig. 10C illustrates a liquid-jet guided laser head 1001 and a liquid-jet guided laser beam 1002 that machines a film cooling opening in an outer wall of a turbine blade 1000, wherein the opening is a finished through-opening 1013 and fluidly connects into
  • FIG. 10D illustrates a cross-sectional view of a liquid-jet guided beam 1002 that machines a film cooling opening in an outer wall 1005 of a turbine blade 1000, wherein the liquid-jet guided beam 1002 can pass through a finished through-opening 1013 without being interrupted and without being back-sprayed.
  • a liquid-jet back-spray that can diffusely propagate a portion of the laser energy can be monitored by a sensor.
  • Fig. 11A-1 1 C illustrate a sensor configuration to monitor a diffused back-sprayed portion of a liquid-jet guided laser beam according to some embodiments.
  • a liquid-jet guided laser head 1 101 can generate a liquid-jet guided laser beam 1102, which can be applied to machine a film cooling opening in a turbine blade 1100.
  • An optical sensor 1105 can be applied to monitor a cut-through point of an opening based on a liquid-jet back-spray 1104 condition.
  • An optical sensor 1 105 can contain a detector that is sensitive to the wavelength of the light that is emitted by the laser, which is guided by the liquid-jet laser beam 1102.
  • the detector of an optical sensor 1 105 can detect a light intensity 1 121.
  • the detector of an optical sensor 1 105 can detect an intensity of the ambient light 1122.
  • a liquid-jet guided laser beam 1 102 can start to machine a film cooling opening in an outer wall of a turbine blade 1 100.
  • liquid-jet back-spray 1104 can be present when an opening in an outer wall of the turbine blade 1100 is unfinished and/or not cut-through.
  • Such liquid-jet back-spray 1104 can diffusely propagate a portion of the laser energy from the liquid-jet guided laser beam 1102.
  • the detector of an optical sensor 1105 can detect an intensity of the diffusely propagated laser light 1123. After cut-through, a liquid-jet back-spray 1104 can disappear 11 13 or reduce significantly.
  • an optical sensor 1 105 can detect a strongly reduced laser light intensity 1 124.
  • the detector of an optical sensor 1 105 can be used to detect when an intensity drops below a defined threshold 1 125, which can be used to create a closed-loop machining process.
  • an optical sensor 1 105 can contain one of an optical element, such as a lens, or a mechanical element, such as a tube to create a parallel or narrow field of view. The sensor can be aligned in such way that the peripheral angle of view 1 106 does not cross the liquid-jet guided laser beam
  • a sensor with a detector that is sensitive to a sound or to a sound frequency can be used to detect a cut-through point.
  • FIG. 12A-12C illustrate a sensor configuration to monitor a sound response of a turbine blade machined by a liquid-jet guided laser beam according to some embodiments.
  • a liquid-jet guided laser head 1201 can generate a liquid-jet guided laser beam 1202, which can be applied to machine a film cooling opening in a turbine blade 1200.
  • An acoustical sensor 1205 can be applied to monitor a cut- through point of a film cooling opening based on a sound response of a liquid-jet guided laser beam 1202 and a turbine blade 1200.
  • An acoustical sensor 1205 can detect a sound frequency 1226 and a sound amplitude 1221.
  • a liquid-jet back-spray 1204 can be present when an opening in an outer wall of a turbine blade 1200 is unfinished 1203 and/or not cut-through.
  • a back-spray 1204 can create a certain damped sound frequency and amplitude. After cut- through, a liquid-jet back-spray 1204 can disappear or reduce significantly.
  • the opening 1213 that connects into an internal cavity of the turbine blade can function as a resonating body, which can significantly change a sound frequency and amplitude.
  • a distinct sound 1228 can be created by the liquid-jet guided laser beam 1202 that tangents the side wall of the opening 1213.
  • the sensor 1205 can pick up a frequency 1226 and an amplitude 1221 of the distinct sound 1228. Based on an expected sound response of an internal cavity in a turbine blade 1200 interacting with a liquid-jet guided laser beam 1201 , the sensor can monitor whether a sound appears around a set frequency 1224 and/or a sound exceeding an amplitude threshold, which can be used to create a closed-loop machining process.
  • the cut through is detected by an optical sensor adapted to detect the emitted light of a plasma.
  • Laser cutting technology is based on laser ablation, i.e. the process of removing material from a solid surface by irradiating it with a laser beam.
  • a plasma In laser ablation, the surface of a workpiece is heated by the laser to such an extent that a plasma is generated.
  • the plasma generated on the surface of the workpiece emits light back into the liquid jet.
  • the light waves propagate in the liquid jet opposite to the direction of the laser beam towards the liquid-jet laser head and can be detected by a sensor.
  • Fig. 13A, B show one embodiment of a liquid-jet laser head 1301 equipped with such a sensor 1305.
  • the liquid-jet laser head 1301 comprises optics 1303 with lenses and mirrors for focusing and coupling the laser beam 1306 into the liquid jet 1302.
  • a mirror 1303a in the optics 1303 of the liquid-jet laser head 1301 is adapted to reflect the light of the laser beam 1306 but to be transmissible for the light emitted 1304 by the plasma 1304a, i.e. the wavelength of the light of the plasma 1304. Therefore it is mandatory that the wavelength of the laser light 1306 differs from the wavelength of light emitted by the plasma 1304.
  • the laser light 1306 may be invisible NIR light while the plasma light 1304 is in the range of the visible light, i.e. between 400 and 700nm.
  • the light of the plasma 1304 can such be separated from the laser light 1306 and detected by a sensor 1305.
  • the plasma 1304a is generated as long as the surface of the workpiece1300 is heated and the machining is in progress.
  • the machining is in progress as long as the bore 1307 has not been completely finished and no cut-through is reached.
  • the workpiece 1300 preferably consist of metal or a metal alloy.
  • no plasma 1304a is generated and hence, no plasma light 1304 is detected by the sensor 1305.
  • a cut-through is detected by the sensor 1305.
  • the present invention discloses a closed loop process for machining film cooling openings in a turbine blade.
  • Fig. 14 illustrates a closed loop process for laser machining of film cooling openings.
  • a laser machining process can be started.
  • the CNC laser machine tool can move the liquid-jet guided laser head to the first of an N-amount of machining positions.
  • the laser process can be activated. Once a sensor detects a cut-through signal, the laser process can run a defined amount of extra safety passes. After running a defined amount of safety passes the laser process can stop and the CNC laser machine tool can move the liquid-jet guided laser head to the next of an N-amount of machining positions.
  • the loop continues and can be completed once the last of N-amount of machining positions is finished.
  • Fig. 15 illustrates a flow chart for operating a liquid-jet guided laser CNC machine tool to machine openings in a workpiece that fluidly connect an outer wall of the workpiece to an internal cavity inside the workpiece according to some embodiments.
  • Operation 1500 calibrates a liquid-jet guided laser CNC machine, wherein an optical sensor and a tactile sensor measure the absolute position of the liquid-jet within the coordinate system of the CNC machine.
  • Operation 1510 adjusts the position of laser head, wherein the measured center axis of the liquid-jet is aligned to be parallel to the Z axis of the CNC machine workpiece fixation
  • Operation 1520 loads a workpiece into a workpiece fixation mechanism of the CNC machine, wherein the workpiece has at least one outer wall and at least one internal cavity.
  • Operation 1530 provides a flow of pressurized gas to an internal cavity of the workpiece, wherein the pressurized gas is provided through a workpieces fixation mechanism and wherein the workpiece has at least one exit opening at an end portion of an internal cavity.
  • Operation 1540 generates an opening in the workpiece that fluidly connects an outer wall to an internal cavity, wherein the opening is made by a liquid-jet guided laser.
  • Operation 1550 disrupts the liquid-jet guided laser once it passes through an opening, wherein a flow of pressurized gas inside an internal cavity is used to vaporize the liquid-jet.
  • Operation 1560 detects whether the liquid-jet guided laser passes through an opening, wherein an optical sensor monitors the scattered laser light inside the back-spray of the liquid-jet.
  • Operation 1570 stops the liquid-jet guided laser once an optical sensor detects that the liquid-jet guided laser passes through an opening.
  • the sensor detects a first cut through.
  • the laser is generally moved in a predetermined pattern over the surface of the workpiece.
  • the first cut through is may be processed at an arbitrary point on the surface during the ablation process.
  • the first cut through may be detected by a sensor and subsequently, an air-jet is applied or the pressure of the air-jet is increased in order to limit the effective length of the liquid-jet guided laser beam to such extent that the bore can be finished but the jet is vaporized at or beyond the exit point of the bore into the cavity.
  • the ablation process is continued until the bore is machined completely. Subsequently, the machining of the next bore may be started.
  • Fig. 16 illustrates a liquid-jet guided laser head for machining openings that fluidly connect an outer wall with an internal cavity of a workpiece, wherein the back wall of an internal cavity is protected by a pressurized gas that vaporizes the liquid-jet and wherein a sensor detects a cut-through point based on a liquid-jet back-spray condition according to some embodiments.
  • a liquid-jet guided laser beam 1602 can be provided by a liquid-jet laser head 1601.
  • the liquid-jet guided laser beam 1602 can incident an outer wall 1614 of a workpiece 1600 in order to machine an opening 1603 that connects an outer wall 1614 of the workpiece 1600 to an internal cavity 1614. After an opening 1603 is machined, the liquid-jet guided laser beam 1602 can pass through the internal cavity 1614 and damage a back wall of the internal cavity 1614.
  • a pressurized gas 1605 can be provided to an internal cavity 1614 of a workpiece 1600.
  • the pressurized gas 1605 can for example be air.
  • the pressurized gas 1605 can also be one of an inert gas, for example to suppress oxidation effects in the area of the opening 1603.
  • the pressurized gas 1605 can have a pressure that is sufficient to vaporize inside an internal cavity 1614 the liquid-jet that guides the laser beam and prevent the liquid-jet guided laser beam 1602 from touching a back wall of an internal cavity 1614.
  • the pressure of the pressurized gas 1605 can for example be in a range of 1-10 bar and preferably in a range of 1-6 bar.
  • the pressurized gas 1605 may hence protect the back wall of the internal cavity by reducing the laminar length of the liquid-jet in which the laser is guided.
  • the workpiece has at least one opening 1604 in an end portion of the workpiece through which the compressed gas can escape from the workpiece 1606. Such opening 1604 can be present prior to the laser machining process.
  • Such opening 1604 can also be machined by the liquid-jet guided laser beam 1602, prior to machining a first opening 1603.
  • a surface area of the opening 1604 in an end portion of the workpiece can be 2-8x larger than a surface area of the largest opening 1603 in the workpiece wall.
  • a surface area of the opening 1604 in an end portion of the blade can be 3-5x larger than a surface area of the largest opening 1603 in the workpiece wall.
  • a sensor 1608 can be applied to monitor a cut-through point of an opening 1603 based on a liquid-jet back-spray 1607 condition.
  • the sensor can be one of an optical and/or one of an acoustical sensor.
  • a liquid-jet back-spray 1607 can be present when an opening 1603 in an outer wall 1614 of a workpiece 1600 is unfinished and/or not cut-through.
  • Such liquid-jet back-spray 1607 can diffusely propagate a portion of the laser energy.
  • Such portion of laser energy can be monitored by for example a sensor 1608, which can contain a detector that is sensitive to the wavelength of the light that is emitted by the laser.
  • a liquid- jet back-spray 1607 can disappear or reduce significantly.
  • the sensor 1608 can pick up a change of the liquid-jet back-spray 1607 condition and detect when an opening 1603 fluidly connects into an internal cavity 1614 of a workpiece 1600.
  • a sensor 1608 with a detector that is sensitive to a sound or to a sound frequency can be used.
  • a liquid- jet back-spray 1607 can be present when an opening 1603 in an outer wall 1614 of a workpiece 1600 is unfinished and/or not cut-through.
  • a back-spray 1607 can create a certain damped sound frequency and amplitude. After cut-through, a liquid-jet back-spray 1607 can disappear or reduce significantly. After cut-through, the opening 1603 that connects into an internal cavity 1614 can function as a resonating body, which can significantly change a sound frequency and amplitude.
  • the sensor 1608 can pick up a change of a sound frequency and/or a sound amplitude and detect when an opening 1603 fluidly connects into an internal cavity 1614 of a workpiece 1600. Additionally or alternatively, the back wall may be protected by the air-jet 1617 surrounding the liquid-jet. In one embodiment, the air-jet 1617 exits the liquid-jet laser head 1601 from an opening other than the liquid-jet 1602. The liquid-jet guided laser 1602 is surrounded by an air-jet 1617. The air-jet 1617 leaves a machine head of a liquid-jet guided laser CNC machine preferably physically separated from the liquid-jet and runs to the workpiece 1600.
  • the air-jet 1617 touches the liquid-jet and terminates the laminar length of the liquid-jet.
  • the distance where the air-jet 1617 touches the liquid-jet and hence the laminar length of the liquid-jet may be adjusted by adjusting the pressure of the air-jet 1617.
  • the adjustment of the pressure may also include switching the air- jet 1617 on.
  • the pressure may be adjusted after the (first) cut through through the wall 1613 of the workpiece to the internal cavity 1614 such that the back wall is not affected by the laser.
  • the pressure of the air-jet may be adjusted prior to staring the ablation process such that the laminar length of the liquid-jet is shorter than the distance to the back wall and hence, the back wall is not touched by the laser.

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  • Physics & Mathematics (AREA)
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Abstract

L'invention concerne un procédé d'usinage d'un alésage (803) s'étendant à partir d'une paroi extérieure d'une pièce (800), de préférence une aube de turbine (800), vers une cavité interne (814) de la pièce à travailler (800) avec un laser guidé par jet de liquide (802). Une paroi arrière (815) de la cavité interne (814) est protégée par un matériau à changement de phase ou un gaz sous pression (805) vaporisant le jet de liquide (802) et le laser guidé par jet de liquide (802) est au moins temporairement entouré par un jet d'air (817).
PCT/EP2019/054485 2018-02-23 2019-02-22 Procédé d'usinage d'un alésage s'étendant à partir d'une paroi externe d'une pièce à travailler avec un faisceau laser guidé par jet de liquide WO2019162464A1 (fr)

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EP18158452 2018-02-23

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN114043073A (zh) * 2021-11-18 2022-02-15 哈尔滨工业大学 一种基于声学信号实时监测的水助激光加工系统及方法

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