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
  • B23K26/02—Positioning or observing the workpiece, e.g. with respect to the point of impact; Aligning, aiming or focusing the laser beam
  • B23K26/04—Automatically aligning, aiming or focusing the laser beam, e.g. using the back-scattered light
  • B23K26/046—Automatically focusing the laser beam
• • 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
• • 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
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B19/00—Condensers, e.g. light collectors or similar non-imaging optics
  • G02B19/0004—Condensers, e.g. light collectors or similar non-imaging optics characterised by the optical means employed
  • G02B19/0009—Condensers, e.g. light collectors or similar non-imaging optics characterised by the optical means employed having refractive surfaces only
  • G02B19/0014—Condensers, e.g. light collectors or similar non-imaging optics characterised by the optical means employed having refractive surfaces only at least one surface having optical power
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B19/00—Condensers, e.g. light collectors or similar non-imaging optics
  • G02B19/0033—Condensers, e.g. light collectors or similar non-imaging optics characterised by the use
  • G02B19/0047—Condensers, e.g. light collectors or similar non-imaging optics characterised by the use for use with a light source
  • G02B19/0052—Condensers, e.g. light collectors or similar non-imaging optics characterised by the use for use with a light source the light source comprising a laser diode
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
  • G02B27/09—Beam shaping, e.g. changing the cross-sectional area, not otherwise provided for
  • G02B27/0938—Using specific optical elements
  • G02B27/095—Refractive optical elements
  • G02B27/0955—Lenses
  • G02B27/0966—Cylindrical lenses
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
  • G02B27/30—Collimators
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
  • G02B27/40—Optical focusing aids

Definitions

• the invention relates to a particular optical configuration implemented in a solid-state laser cutting head, in particular to fiber, which makes it possible to control the problems of focal drift and laser damage of the optics of the focusing head, and on a laser installation equipped with such a focusing head, in particular an ytterbium fiber laser installation. .
• a fiber laser cutting facility comprises a laser source and optical devices for transporting the laser beam to a cutting head, also referred to as a focusing head, which focuses the beam in the thickness of a piece to cut.
• the laser source is a ytterbium doped fiber laser (Yb), equipped with at least one beam conveying optical fiber, and the cutting head comprises optical collimation, redirection and focusing devices for bring a focused laser beam to a workpiece.
• Yb ytterbium doped fiber laser
• Optical devices such as the focusing lens, of a laser cutting head must withstand high surface power densities, typically between 1 and 10 kW / cm 2 depending on the characteristics of the laser source and the beam diameter on the laser beams. optical, and this, while operating in polluted environments that weaken them.
• optical damage In the continuous laser emission regime, optical damage generally manifests itself in the form of a gradual degradation of optical performance, initially without visible damage, which results essentially from thermal phenomena.
• Contamination of the optical surface by the environment, ie dust, metallic projections or moisture, and their aging are factors that increase the absorption of the lenses and progressively worsen the phenomenon. warming up, leading to an increase in the amplitude of the focal drift over time.
• the phenomena described above show that the durability of the performance of a cutting process is strongly related to the resistance of the optical devices ensuring the propagation of the laser beam. Since the positioning of the focal point is an important parameter in the fiber laser cutting process, it is essential that the focal position of the beam is as stable as possible and that the deviations remain within the tolerances allowed.
• the thermal distortions experienced by high power optical elements must be minimal to avoid damage. All these requirements must be taken into account when choosing the optics constituting the focusing system of a laser cutting head.
• the focusing head of the invention may comprise one or more of the following features:
• the reflecting mirror is made of silica.
• the invention also relates to a laser beam cutting apparatus comprising:
• a conveying fiber connecting the solid-state laser device to the focusing head so as to convey the laser beam emitted by the solid-state laser device to the focusing head.
• the installation of the invention may include one or more of the following features:
• the solid laser device is of fiber type, preferably of ytterbium fibers.
• the solid laser device emits a laser beam of power between 1 and 5 kW in continuous mode, quasi-continuous or pulse, preferably in continuous mode.
• the conveying fiber has a diameter of 50 ⁇ and a BPP of between 1.6 and 2.2 mm.mrad
• the collimating lens has a focal length of between 70 and 120 mm
• the focusing lens has a focal length of between 200 and 450 mm. More specifically, in the case of a conveying fiber diameter 50 ⁇ , BPP of which is between 1.6 and 2.2 mm.mrad, the focal length of the collimating lens is between 70 and 120 mm, preferably between 70 and 90 mm.
• the focal focusing distance is advantageously between 200 and 300 mm, preferably between 220 and 280 mm, while for cutting a material whose thickness is greater or equal to 10 mm, the focal length of focus is advantageously between 350 and 450 mm, preferably between 380 and 420 mm.
• the focal length of focus is advantageously between 200 and 300 mm, preferably between 220 and 280 mm, whereas for cutting a material whose thickness is greater than or equal to 10 mm, the focal length of focusing is advantageously between 350 and 450 mm, preferably between 380 and 420 mm.
• the focusing lens has a focal length of between 200 and 450 mm.
• the invention also relates to a laser beam cutting method of a metal part, in which is implemented a focusing head or a laser beam cutting system according to the invention.
• FIG. 3 schematizes the operating principle of an installation and a method of laser cutting according to the invention
• FIG. 4 represents a comparison of the evolution of the position of the focal point of the beam during the laser irradiation of a ZnS or fused silica (S) lens system
• FIG. 5 is a comparison of the evolution of the focal point position of the focused beam by a ZnS lens system comprising a collimation lens with a thickness of 2 or 7 mm.
• the cutting head 3 comprises, in a conventional manner, optical devices for collimating, redirecting and focusing the laser beam.
• the laser beam is emitted by a device or solid-state laser generator, preferably an ytterbium doped fiber laser (Yb).
• a device or solid-state laser generator preferably an ytterbium doped fiber laser (Yb).
• Yb ytterbium doped fiber laser
• the laser effect that is to say the phenomenon of amplification of the light used to generate the laser radiation, is obtained by means of an amplifying medium preferably pumped by laser diodes and consisting of one or more typically doped optical fibers, preferably silica doped with ytterbium.
• the wavelength of the radiation emitted at the output of the laser device is between 1.06 and 1.10 ⁇ , and the laser power is between 0.1 and 25 kW, typically between 1 and 5 kW.
• the laser can operate in continuous, quasi-continuous or pulsed mode, but the present invention is particularly advantageous when working in continuous mode because it is the most severe irradiation mode for the optics of a laser head. cutting.
• BPP Beam Parameter Product
• the BPP is determined by the characteristics of the laser source SL and the diameter of the FDC conveying fiber. It is expressed as the product of the wo ray at the neck of the laser beam focused by its divergence half-angle ⁇ , as shown in Figure 2.
• the BPP is also defined by the product of the radius w > of the optical conveying fiber emitting the laser beam by the divergence half-angle of the beam at the fiber exit ⁇ 3 ⁇ 4.
• the BPP of the beam is typically between 1.6 and 2 mm.mrad
• the BPP is typically between 2.7 and 4 mm.mrad.
• the focussing system of the laser cutting head is successively composed, in the direction of circulation of the laser beam, of at least one collimation lens LC making it possible to obtain a collimated beam FC from FIG. a divergent beam FD, and at least one focusing lens LF making it possible to obtain a focused beam FF and to concentrate the energy of the laser on the piece to be cut.
• the focal lengths of collimation and focusing are chosen so as to obtain a focal spot, also called a focal spot, having a suitable diameter to have the power density necessary for cutting the part.
• the diameter of the beam 2wo in the plane of focus is defined as the product of the diameter 2wm of the fiber by the optical magnification G of the focusing system and is expressed:
• G is given by the ratio between the focal length F foc of the focusing lens FC and the focal length F co i of the collimation lens LC.
• the characteristic radius w is the distance from the optical axis where the intensity drops to 1 / e 2 (about 13.5%) of its maximum value, which means 86.5% of the beam power is included in the radius disc w. All beam parameters are defined according to this criterion.
• the beam radius radiating the collimation and focusing optics is given by the following relation:
• This type of source is characterized by low BPP and therefore by beams having a divergence ⁇ 3 ⁇ 4 lower output fiber.
• This parameter reflects the far-field expansion velocity of the beam emitted by the conveying fiber and determines the beam diameter on the system optics.
• Table 1 below gives a comparison of the typical beam characteristics for different lasers, as well as the power densities obtained on the optics for a power of 2 kW and a focal length of the collimating lens equal to 100. mm.
• optical system of the invention combines the specificities described below, according to the diagram presented in FIG.
• the cutting head 3 consists of optical devices working in transmission, that is to say here lenses 13, 14, used for collimation operations (in 13) and focusing (in 14) of the laser beam FL from of the conveying fiber and generated by the solid laser source SL.
• Zinc sulphide is advantageously used as a substrate for the collimating and focussing lenses 14.
• the amplitude of the thermal gradient established in the lenses under laser irradiation is inversely proportional to the thermal conductivity of the material. constituting the lenses.
• the thermal conductivity of ZnS (0.272 W / cm / ° C) is of the order of 20 times that of fused silica (0.0138 W / cm / ° C). This higher thermal conductivity reflects a greater ability of ZnS to remove heat, and limits the magnitude of gradients and thermal distortions induced at the lens by high power irradiation.
• the thickness and the diameter of the lenses 13, 14 also have an influence on their thermal behavior.
• thick lenses i.e., having a thickness at the edges of at least 5 mm, are used solely to carry out the focusing operations. Indeed, the assist gas is injected directly after the focusing lens, which exposes them to high pressures.
• the focusing lenses must therefore be thick to have good mechanical strength.
• thick lenses are used for both collimation and focusing of the beam.
• the cutting head 3 is made of lenses whose thickness at the edges is at least 5 mm, and preferably between 6 and 8 mm. Just as greater thickness provides better thermal behavior, larger diameter optics better dissipate heat to their edges. Whatever the size of the beam impacting on the optics of the cutting head, the cutting head 3 therefore implements lenses whose diameter is between 35 and 55 mm.
• a reflective component 15 is placed in the path of the laser beam 10 between the collimating lens 13 and the focusing lens 14. This component is a plane mirror and does not modify the propagation parameters of the beam.
• the mirror substrate is made of fused silica.
• At least one side of the mirror is coated with a reflective treatment.
• This coating consists of thin optical layers and reflects the wavelength of the cutting laser beam as well as wavelengths between 630 and 670 nm.
• the processing is transparent for part of the visible or infrared spectrum, including the wavelength of a lighting system, for example a laser diode. In this way, it allows the connection of a process control device (camera or photodiode type) to the back of the mirror. It operates at an angle of incidence of between 40 and 50 °, preferably equal to 45 °.
• the thickness of the mirror is between 3 and 15 mm, preferably between 8 and 12 mm. This mirror firstly reduces the vertical size of the head to gain mechanical stability.
• the conveying fiber is maintained horizontally, which reduces the risk of dust introduction during assembly and disassembly of the fiber or collimator.
• the integration of a reflective component in the path of the beam compensates for a portion of the focal drift induced by the lenses. Indeed, the longitudinal displacement of the focal point induced by a reflective component takes place in the opposite direction to the focal drift induced by a transmissive component.
• the lenses of the cutting head 3 are also characterized by specific focal lengths, adapted to the BPP of the conveyor fiber used. These focal lengths are necessary to obtain the appropriate focal spot diameter 2wo for cutting the treated material.
• the BPP of the beam is typically between 1.6 and 2.2 mm.mrad.
• the focal length of the collimating lens is between 70 and 120 mm, preferably between 70 and 90 mm. The choice of the focal length of collimation then conditions that of the focal length of focusing, depending on the desired optical magnification to cut the thickness of the treated material.
• the focal length of focus is between 200 and 300 mm, preferably between 220 and 280 mm.
• the focal length of focus is between 350 and 450 mm, preferably between 380 and 420 mm.
• the focusing head 3 is supplied with assist gas via a gas inlet 5 arranged in the wall of said focusing head 3, whereby a gas or gas mixture under pressure from a gas source, for example a or a plurality of gas cylinders, a storage capacity or one or more gas pipes, such as a gas distribution network, is introduced upstream of the nozzle 4 and is evacuated by this nozzle 4 in the direction of the part 30 to be cut by laser beam.
• a gas or gas mixture under pressure from a gas source for example a or a plurality of gas cylinders, a storage capacity or one or more gas pipes, such as a gas distribution network
• the assist gas serves to drive the molten metal out of the cutting groove 12 obtained by melting the metal by means of the laser beam FL which is focused at the position 11 relative to the surface of the workpiece 10 to be cut.
• gas is based on the characteristics of the material to be cut, including its composition, its shade, its thickness.
• air, oxygen, nitrogen / oxygen or helium / nitrogen mixtures can be used for steel cutting, while nitrogen, nitrogen / hydrogen, or argon / nitrogen mixtures can be used. be used to cut aluminum or stainless steel.
• the piece 10 to be laser cut can be formed of different metallic materials, such as steel, stainless steel, mild steel or light alloys, such as aluminum and its alloys, or even titanium and its alloys, and have a thickness typically between 0.1 mm and 30 mm.
• the laser beam can be focused (in 11) in the thickness, or on or in the immediate vicinity of one of the surfaces of the part 10, that is to say outside and a few mm above or below the upper surface 10a or lower 10b of the part 10, or on the upper face 10a or lower 10b.
• the position 11 of the focal point is between 5 mm above the upper surface 10a and 5 mm below the lower surface 10b of the part 10.
• the caustic of the laser beam focused by each system could be recorded using a beam analyzer.
• This device measures the radius of the beam for which 86% of the power of the laser is contained in a disk of this ray and this in successive propagation planes lying on a distance of about 10 mm on either side of the neck focused beam.
• each optical system was exposed for about 30 minutes.
• the beam had a diameter of 9.6 mm on the lens, leading to a power density of the order of 2.8 kW / cm 2 to 2 kW.
• Figure 4 presents a comparison of the evolution of the focal point position of the focused beam by a ZnS or fused silica (S) lens system.
• the first point corresponds to the position taken during a first beam analysis performed at 200 W.
• the focal shift induced by the thermal lens effect is negligible. It can be considered that the measured position corresponds to the position where the focal point of the beam is located instantaneously after the ignition of the laser.
• Figure 5 shows a comparison of the evolution of the focal point position of the focused beam by the two systems, according to the method described above.
• the combination of the optical devices of the invention makes it possible to guarantee the durability of the performances of the laser cutting process, in particular in the case of a laser cutting method obtained with a solid-state laser, in particular a fiber laser, thanks to a control of the amplitude of the phenomenon of focal drift and the problems of damage of the optics

Landscapes

• Physics & Mathematics (AREA)
• Optics & Photonics (AREA)
• Engineering & Computer Science (AREA)
• General Physics & Mathematics (AREA)
• Plasma & Fusion (AREA)
• Mechanical Engineering (AREA)
• Laser Beam Processing (AREA)
• Lenses (AREA)
• Optical Elements Other Than Lenses (AREA)
• Lasers (AREA)
• Optical Couplings Of Light Guides (AREA)

Priority Applications (10)

Applications Claiming Priority (2)

Publications (1)

Family

ID=42105843

Family Applications (1)

Country Status (13)

Cited By (3)

Families Citing this family (18)

Citations (5)

Family Cites Families (14)

• 2009
  • 2009-09-01 FR FR0955949A patent/FR2949618B1/fr not_active Expired - Fee Related
• 2010
  • 2010-08-17 JP JP2012527368A patent/JP2013503751A/ja active Pending
  • 2010-08-17 US US13/393,280 patent/US20120154922A1/en not_active Abandoned
  • 2010-08-17 PL PL10762988T patent/PL2473315T3/pl unknown
  • 2010-08-17 RU RU2012112398/02A patent/RU2553152C2/ru not_active IP Right Cessation
  • 2010-08-17 EP EP10762988.3A patent/EP2473315B1/fr not_active Not-in-force
  • 2010-08-17 PT PT107629883T patent/PT2473315E/pt unknown
  • 2010-08-17 CN CN201080038783.2A patent/CN102481665B/zh not_active Expired - Fee Related
  • 2010-08-17 IN IN926DEN2012 patent/IN2012DN00926A/en unknown
  • 2010-08-17 BR BR112012004680A patent/BR112012004680A2/pt not_active IP Right Cessation
  • 2010-08-17 WO PCT/FR2010/051723 patent/WO2011027065A1/fr not_active Ceased
  • 2010-08-17 ES ES10762988.3T patent/ES2457231T3/es active Active
  • 2010-08-17 DK DK10762988.3T patent/DK2473315T3/da active

Patent Citations (5)

Non-Patent Citations (1)

Also Published As

Similar Documents

Legal Events