WO2005030432A1 - Procede et appareil d'usinage de pieces de precision par impulsion laser - Google Patents

Procede et appareil d'usinage de pieces de precision par impulsion laser Download PDF

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Publication number
WO2005030432A1
WO2005030432A1 PCT/US2004/004581 US2004004581W WO2005030432A1 WO 2005030432 A1 WO2005030432 A1 WO 2005030432A1 US 2004004581 W US2004004581 W US 2004004581W WO 2005030432 A1 WO2005030432 A1 WO 2005030432A1
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WO
WIPO (PCT)
Prior art keywords
pulse
workpiece
laser
micro
energy
Prior art date
Application number
PCT/US2004/004581
Other languages
English (en)
Inventor
David E. Stucker
Original Assignee
Stucker David E
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from US10/444,350 external-priority patent/US6706997B1/en
Application filed by Stucker David E filed Critical Stucker David E
Publication of WO2005030432A1 publication Critical patent/WO2005030432A1/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
    • B23K26/02—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
    • B23K26/382—Removing material by boring or cutting by boring
    • 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
    • B23K2103/00—Materials to be soldered, welded or cut
    • B23K2103/50—Inorganic material, e.g. metals, not provided for in B23K2103/02 – B23K2103/26
    • 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
    • B23K2103/00—Materials to be soldered, welded or cut
    • B23K2103/50—Inorganic material, e.g. metals, not provided for in B23K2103/02 – B23K2103/26
    • B23K2103/52—Ceramics

Definitions

  • the present invention relates to a method and apparatus for producing a laser pulse having a relatively low initial energy followed by a number of high energy spikes or variation thereof for use, as an example, in drilling workpieces, especially thin workpieces such as metal layers, with holes having dimensionally accurate entrance and exit shapes with close tolerances.
  • the invention can be applied to the high speed manufacture of products requiring fine tolerances, such as injector spray holes, filter screens, cooling apertures, valve seats, dies and molds or various other applications requiring cutting or welding.
  • the erbium doped YAG laser yielded encouraging results by demonstrating the capacity to perform as an efficiently drilling laser while incurring relatively low levels of collateral damage to the surrounding workpiece material, provided that low pulse rates of less than about three pulses per second were applied to the target material.
  • These Er:YAG systems operating in the microsecond pulse duration regime, have been successfully applied with minimal attendant thermal damage to the surrounding material in several areas of application in material processing and medicine.
  • the combination of high absorption, relatively short pulse duration and low pulse repetition rates enables minimization of collateral workpiece damage for those workpieces having high absorption at the Er:YAG wavelength of 2900 nm.
  • the geyser of workpiece material erupting through the exit surface can result in an exit surface exhibiting far greater damage than the surface adjacent the entrance hole, making the use of pulsed or continuous wave high power lasers less attractive for drilling and/or cutting in situations where both precision entrance and exit holes are desired.
  • high volumetric material removal rates are typically achieved through the use of high laser pulse rates, which lead to considerable thermal and mechanical collateral damage, as discussed above.
  • increasing power leads to plasma decoupling of the beam, e.g., incident laser energy is wasted in heating the ambient in front of the target. This is inherent to the process regardless of the laser type or wavelength chosen and thus leads to a manipulation of the energy within the applied laser pulse to yield higher material removal rates.
  • UV ultraviolet
  • UV excimer lasers that emit high intensity pulses of ultraviolet (UV) light as cutting and/or drilling tools.
  • Both the short wavelength characteristic of the UV light and the short nanosecond range pulse durations arising from the excimer lasers contribute to a different regime of laser- workpiece interaction.
  • Short wavelength ultraviolet photons are energetic enough to directly break chemical bonds in a wider range of workpiece materials.
  • UV excimer lasers can often vaporize a material target with minimal thermal energy transfer to adjacent workpiece material.
  • the resultant ablatant (the vaporization product) is ejected away from the target surface, leaving the target relatively free from melt, recast, or other evidence of thermal damage.
  • lasers in the UV wavelength machine some materials preferably to others, such as the polymers PFTE and PMMA versus the various steels, and the methods of UV laser machining are typically masks imaged onto the workpiece.
  • Laser machining tools have been used to machine organic, inorganic, metals and non- metals such as ceramic materials, but have been largely commercially unsuccessful over the broad materials range due to their inability to produce the desired fine tolerances in commercial products such as valve seats, dies and molds and their tendency to degrade the substrate material due to the formation of microcracks.
  • strength of the laser-machined parts is reduced considerably due to the formation of microcracks in the workpiece during the laser machining process.
  • microcracks are caused by thermal expansion and rapid cooling at the surface of the material exposed to and heated by the laser beam. These microcracks also serve as fracture initiators and result in fracturing or catastrophic failure of the workpiece during subsequent use.
  • Various other laser-machining techniques are known in the art. For instance, U.S. Pat. No. 4,638,145, issued Jan. 29, 1987, describes a laser machining apparatus for performing high quality cuts on plate type work pieces wherein the laser output is varied according to the traversing speed of the laser beam. The object is to minimize burn-through loss when machining soft steel workpieces. The output and velocity of the laser are controlled according to a predetermined formula dependent on the thickness and type of material.
  • the lasers used for the bulk of machining or material processing applications are typically high-power solid-state lasers. These high-power solid-state lasers are typically used in a pulsed mode of operation for workpiece machining applications, such as cutting, welding and drilling. Ideally, lasers used for this purpose should have variable pulse lengths and variable pulse formats. For these applications, the pulse length typically selected is in the range of about 0.4 ms to about 1 ms, achieved through the duration of the applied pump source to the gain medium. Typically, well-designed solid-state lasers produce pulses at a natural relaxation oscillation frequency when subjected to a short burst of pump energy.
  • Control can be effected either by modulating the laser itself or by controlling laser pumping, which inputs energy to the laser cavity.
  • Intracavity laser modulation usually requires the selective insertion of losses in the cavity to suppress lasing.
  • a conventional Q-switch for example, operates periodically to suppress lasing completely while the device continues to be pumped, and then suddenly removes the inserted loss and switches the laser on, which allows a large pulse to be emitted by the laser.
  • the pulse length obtained is approximately 5-50 ns (nanoseconds), which is usually too short for most machining operations, and the pulses typically have a peak intensity that is too high for precision machining use.
  • acousto-optic (A.O.) Q-switching results in longer length pulses that still exhibit high peak intensity, but are suitable for precision machining applications.
  • free running, long pulse length lasers produce pulses with insufficient intensity for efficient precision cutting and drilling applications. Control of laser output by controlling the duration and timing of pumping energy also affords a degree of control of the output pulse waveform.
  • Nos. 3,747,019 and 4,959,838, have disclosed relatively complex techniques for modulating the laser output to achieve a more desirably uniform sequence of output pulses. These techniques require some form of control system wherein the output beam is monitored and used to feed back a modulator control signal. Basically, the feedback control systems are needed because variations in the laser pump rate require commensurate variations in the modulation rate to maintain stable operation and produce the desired output pulse characteristics. However, sequential modulation of output pulses does not significantly improve the machining precision of the laser, especially with regard to the entrance surface topography of laser-drilled holes or laser cut sections (i.e., incident surface damage).
  • the present invention relates to a method and apparatus for producing a machined workpiece.
  • the method includes the steps of producing a laser pulse and directing the laser pulse through the workpiece.
  • the laser pulse is characterized by a first relatively low energy portion and at least two relatively high-energy spikes subsequent to the first relatively low energy portion.
  • One object of the present invention is to provide an improved laser machining process. Related objects and advantages of the present invention will be apparent from the following description.
  • FIG. 1 is a graph of pulse energy vs. time for a typical spiked laser pulse produced according to a first embodiment of the present invention.
  • FIG. 2 is a graph showing the relation between a laser pump signal, the Q-switching signal and the resultant spiked laser output pulse according to the embodiment of FIG. 1.
  • FIG. 3 A is a schematic representation of a first embodiment of a laser system for producing the laser pulse of FIG. 1.
  • FIG. 3B is a schematic representation of a second embodiment of a laser system for producing the laser pulse of FIG. 1.
  • FIG. 3C is a schematic representation of a third embodiment of a laser system for producing the laser pulse of FIG. 1.
  • FIG. 4 is a graph illustrating the relationship between the output of an unmodified continuous wave laser, a continuous wave laser modified by a first Q-switching circuit, and a continuous wave laser modified by a first and a second Q-switching circuit.
  • the present invention relates to a method and apparatus for using a pulsed laser beam to form precision apertures or holes in a workpiece.
  • the apertures so formed have high tolerances regarding the shape and dimensions of both the entrance and exit surfaces, as well as of the shaft formed therebetween.
  • a series of precision laser pulses is used to penetrate a workpiece, producing an aperture therethrough characterized by, in this particular case, a right circular cylindrical shaft and substantially identical circular entrance and exit holes.
  • the entrance and exit holes are preferably formed with tolerances of less than about 0.01X relative to the hole diameter, and more preferably with tolerances of less than about 0.00 IX. As illustrated in FIG.
  • each precision laser pulse may be characterized as having a first relatively low energy portion and a second relatively high-energy portion characterized by at least one relatively high energy spike.
  • the second relatively high-energy portion includes at least two relatively high-energy spikes. More preferably, the high-energy spikes are substantially identical regarding their shapes and peak energies.
  • the first portion of the pulse serves to begin to desolidify (i.e., melt and/or vaporize and/or excite to form a plasma) the workpiece.
  • the second portion of the precision laser pulse interacts with the desolidified matter to further energize the desolidified matter such that the desolidified matter is readily removed from the workpiece via the entrance aperture.
  • the mechanism of penetration of the workpiece relies less on an explosion of pressurized gas erupting from the exit surface and more on direct desolidification of the exit surface via interaction (direct and/or indirect) with the precision laser pulse, resulting in precision machining of the workpiece to very high tolerances.
  • right circular cylindrical apertures may be formed through a workpiece by orienting the laser source to impinge pulses onto the workpiece, wherein each pulse travels to the workpiece via a beam delivery from the laser oriented perpendicular to the workpiece.
  • the laser pulse in this example is characterized by a first relatively low-energy portion and at least two subsequent relatively high-energy portions, although the pulse may have other shapes, such as that of a square-wave macro-pulse containing a plurality of spiked micro-pulses.
  • the incident pulse first desolidifies a portion of the workpiece, and then energizes the desolidified portion to facilitate its departure from the surface of the workpiece. Each successive pulse therefore desolidifies and removes a successive portion of the workpieces, until a right circular cylindrical aperture is formed therethrough.
  • the pulsed laser may be used to form right circular cylindrical apertures through a workpiece, such that the aperture is characterized by a substantially circular entry hole, a substantially circular exit hole, and a circular cylindrical opening extending therebetween.
  • the entry and exit holes may be formed having tolerances of less than 0.0 IX and, more preferably, less than 0.00 IX.
  • the diameters of the entry and exit holes are preferably between 0.99X and 1.01X, and more preferably between 0.999X and 1.001X.
  • the aperture orientation is generally determined by angle of incidence between the laser beam and the workpiece, while the shape of the aperture is a function of various parameters, such as pulse pattern, energy, duration and spacing.
  • pulse pattern such as pulse pattern, energy, duration and spacing.
  • a high gain pulsed laser 10 such as a solid state diode pumped laser
  • the RF (or E.O.) driver 20 may drive a Q-switch or any convenient modulation device capable of providing similar operation. Such devices are typically electro-optic or acousto-optic in nature.
  • the pump signal is preferably split such that a portion of the pump signal is routed to the RF driver 20 and a portion is routed to the lasing pump 30 (i.e., the diodes, lamps or the like used to create a population inversion or "pump" the laser).
  • the RF driver 20 thus becomes synchronized with the pump pulse.
  • the RF driver 20 produces the Q-switching (either A.O. or E.O.), which in turn produces a series of energy spikes within the "macro" laser pulse.
  • the energy spikes are substantially identical in energy and shape.
  • a delay generator 35 is connected between the pump signal generator 25 and the RF driver 20, such that the Q-switching effect may be delayed until after the initial energy surge characteristic of an unmodified pulse.
  • the spiking or micro-pulsing may be delayed to take advantage of the natural relaxation surge that occurs in the first portion of an unmodified pulse produced by the laser.
  • the spikes produced by this technique are regularly typically spaced in time.
  • laser pulses produced by the above-described method have widths between about 50 microseconds and 20 milliseconds.
  • the pulse widths available from a given laser system are partially dependent upon the choice of electronics incorporated into the system.
  • diode-pumped lasers typically produce pulses with durations from about 50 microseconds to about 1 millisecond, while lamp-pumped lasers typically produce longer pulses with durations tending towards 20 milliseconds.
  • micro-pulses or spikes formed within the overall macro-pulse have durations that are dependent upon the switching method (i.e., acousto- optic or electro-optic.)
  • Electro-optically switched lasers micro-pulses may be as short as about 20 nanoseconds, while acousto-optical switching may be used to produce micro-pulses with durations from about 80 to about 300 nanoseconds.
  • One preferred micro-pulse duration is about 100 nanoseconds, and such micro-pulses are preferably produced with an acousto-optically switched laser system.
  • the durations of the micro-pulses are also gain and hold-off dependent, i.e. they are functions of the strength of the acousto-optic/electro-optic modulation.
  • the preferred pulse energy output of a typical laser system of the present invention is workpiece-dependent. In other words, factors such as the workpiece material composition, specific material properties, the thickness of the workpiece, and the like must be considered when determining the optimum pulse energy delivered by the laser. Also important are the duty cycle of the laser and its maximum energy output. In general, thin materials require pulse energies in the milliJoule range, while thicker materials require energies in the Joule range. One preferred micro-pulse energy is about 10 milliJoule. Likewise, the micro-pulses typically have energies in the milliJoule range, although they may have energies ranging from microJoules to Joules.
  • the energies of the micro-pulses are likewise dependent upon the same workpiece and laser system factors as listed about regarding the pulse energies.
  • the preferred timing between pulses and the preferred timing between micro-pulses are likewise workpiece composition and laser system dependent , and are also dependent upon the duration and energy of each pulse. For example, for a given pulse duration and a given workpiece thermal conductivity, higher energy pulses may require greater lag times between pulses to allow dissipation of thermal energy within the workpiece. Likewise, for workpiece compositions that easily generate ablative clouds when laser-worked, longer lag times between pulses may be required to allow for dissipation of the ablative material.
  • micro- and macro-pulse duration, energy, pattern sequencing and timing are interdependent upon each other as well as upon the workpiece material characteristics and are also governed by the energy output and duty cycle limitations of the particular laser system used to produce them.
  • the time between micro-pulses is preferably between about 5 to about 20 microseconds, although it can vary from a few nanoseconds to milliseconds.
  • FIG. 4 A second method of producing a pulse having a series of internal spikes is illustrated in FIG. 4. This method relates to the modification of a continuous wave (C.W.) laser to produce a spiked pulse. Two A.O. signals are simultaneously imposed on the C.W. laser output, such that the first A.O.
  • C.W. continuous wave
  • the spiked pulse output has proven advantageous in producing high-precision cuts and/or holes in a variety of target workpiece materials. For example, highly reflective metallic targets have been easily cut despite their almost total reflectivity at the laser wavelengths. The entry and exit surfaces are cleaner due to the increased efficiency of material removal.
  • Each spike has enough energy to desolidify or disintegrate target workpiece material, but is of such short duration that a cloud of material plasma or vapor does not form.
  • clouds are unwanted, as they tend to temporarily block the beam, causing the beam to defocus above the workpiece.
  • clouds of vaporized workpiece material absorb a portion of the beam, preventing that portion from striking and cutting through the intended workpiece.
  • the intercepted energy is transduced into heat by the cloud, resulting in superheated vapor/plasma debris at the workpiece surface.
  • the superheated plasma/vapor may then cause more surface damage, such as uncontrolled melting and/or resolidification.
  • ceramic materials have been cut with greatly reduced loss of strength.
  • the spiked pulses deliver enough energy with each spike to vaporize some of the target material, but are short enough in duration so as not to unduly heat the surrounding ceramic workpiece.
  • the result is efficient material disintegration and removal without undue heating, and attendant microcracking, of the workpiece.
  • improved welds may be affected with a "spiked" laser pulse, since more target workpiece material is transformed due to the inherent "keyhole” formed during the incident laser pulse and it is also surmised that smoother weld surfaces should result from the tailoring of the trailing end of the pulse to soften the energy applied.
  • such enhanced laser power output control lends itself to other fields where precise cutting with reduced damage to the surrounding material is required, such as medical, surgical, and dental applications.

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  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Plasma & Fusion (AREA)
  • Mechanical Engineering (AREA)
  • Laser Beam Processing (AREA)

Abstract

La présente invention concerne un procédé de production de pièces usinées avec précision au moyen d'un ensemble laser pulsé, une impulsion laser étant produite avec cet ensemble laser pulsé et ensuite dirigée à travers la pièce. Cette impulsion laser comprend une première partie de relativement faible énergie et au moins deux micro impulsions de relativement haute énergie suivant cette première partie. L'ensemble laser pulsé comprend un générateur d'impulsion, une pompe laser connectée de manière opérationnelle au générateur d'impulsion et, au moins un commutateur connecté de manière opérationnelle au générateur d'impulsion et à la pompe laser. Le commutateur est synchronisé avec l'impulsion de pompe et actionne la séparation de l'impulsion laser en une pluralité de micro impulsions discrètes.
PCT/US2004/004581 2003-05-23 2004-02-17 Procede et appareil d'usinage de pieces de precision par impulsion laser WO2005030432A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US10/444,350 US6706997B1 (en) 2002-05-24 2003-05-23 Method and apparatus for drilling high tolerance holes with laser pulses
US10/444,350 2003-05-23

Publications (1)

Publication Number Publication Date
WO2005030432A1 true WO2005030432A1 (fr) 2005-04-07

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Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4870244A (en) * 1988-10-07 1989-09-26 Copley John A Method and device for stand-off laser drilling and cutting
US6340806B1 (en) * 1999-12-28 2002-01-22 General Scanning Inc. Energy-efficient method and system for processing target material using an amplified, wavelength-shifted pulse train

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4870244A (en) * 1988-10-07 1989-09-26 Copley John A Method and device for stand-off laser drilling and cutting
US6340806B1 (en) * 1999-12-28 2002-01-22 General Scanning Inc. Energy-efficient method and system for processing target material using an amplified, wavelength-shifted pulse train

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