Method for producing part by laser cutting metal-glass strip

Abstract

Disclosed is a method for cutting a metal-glass strip, comprising: applying a pulsed laser beam having a wavelength of less than or equal to 555 nanometers to the strip, the pulsed laser beam being formed from a series of pulses, each pulse having a duration of less than 10 picoseconds, and advantageously less than 1 picosecond, the crystallization temperature of the metal glass being less than 500 DEG C, and the light energy of the laser beam incident on the strip is between 1 microjoule / pulse and 10 microjoule / pulse.

Description

Technical Field

[0001] The present invention generally relates to a method for laser cutting of metal-glass ribbons, and more specifically to a method for producing components or blanks by cutting metal-glass ribbons by means of a pulsed laser beam. In particular, the present invention relates to a method for producing components or blanks suitable for watchmaking micromechanical components in metallic glass. Background Art

[0002] Metallic glasses or amorphous metals are metal alloys whose atomic structure is a non-crystalline structure. Such alloys are usually manufactured by cooling rapidly enough to prevent the formation of a crystalline structure. The amorphous structure of the constituent materials of such alloys gives them mechanical properties that are completely different from those of crystalline metals. In general, metallic glasses have mechanical, physical and chemical properties that offer a wide range of applications. In fact, parts made of metallic glass (bulk metallic glass (BMG)) often have higher elastic limits, durability limits, tensile strength, corrosion resistance, hardness and wear resistance than parts made of crystalline metals. These differences make metallic glass a material of choice for the manufacture of small parts in the watchmaking sector. In particular, the wear resistance of metallic glass and its ability to store large amounts of energy through elastic deformation are two very attractive properties.

[0003] However, metallic glasses are difficult to process. In fact, metallic glasses are brittle materials, the range of their plastic deformation is limited, and sometimes even non-existent. Therefore, once the elastic limit of metallic glasses is exceeded, these materials tend to break. In fact, since metallic glasses do not have a crystalline structure, they do not have dislocations. At present, it is these dislocations that propagate plastic deformations by moving and provide ductility to metals. On the other hand, the crystallization temperature and melting temperature of metallic glasses are relatively low. Therefore, when processing these metallic glasses, it is important to limit the heat input so as not to heat the metallic glasses to the crystallization temperature, otherwise the mechanical properties of these metallic glasses will change. Finally, the low thermal conductivity of metallic glasses makes it difficult to cool them quickly to the "core". Based on the above, it can be understood that the traditional processing methods used for watchmaking are not suitable for these new materials.

[0004] There have been a lot of discoveries about making amorphous metals in the 1990s, but the processing of amorphous metals is a recent problem. Therefore, to date, there is no established procedure to ensure that the molded parts will not crystallize. In addition, due to the wide variety of amorphous metal materials, there are also great differences in properties.

[0005] A laser is a generator of monochromatic coherent electromagnetic radiation. The laser cutting of strips mentioned in the preamble is a processing method that appeared in the 1960s. Laser cutting can be used for component forming of various materials. The method includes: using a large amount of energy generated by a laser and concentrated on a very small surface to cut the material. Focusing the laser beam makes it possible to raise the temperature of a small area of ​​the material to the vaporization point. The heat affected zone (HAZ) of the laser beam is relatively small, which is why the amount of deformation suffered by the cut part is small. The main disadvantages of laser cutting are: the formation of an area where the quality of the processed material changes due to heat, and the formation of burrs on the cut edge.

[0006] Today, there are pulsed lasers that are able to generate a series of pulses of very short duration at high instantaneous power. This makes it possible to limit the generation of heat to very short time intervals. The possibility of cooling the processed material between each pulse makes it possible to limit the temperature increase compared to a laser operating continuously. This property is an advantage when cutting metallic glasses, since it can potentially keep the temperature of amorphous materials below their crystallization temperature.

[0007] It is worth mentioning again that the implementation of some known laser cutting methods is accompanied by the use of an auxiliary gas. Such a gas may be a reactive gas in nature (e.g. oxygen), the purpose of which is to be used to enhance the removal of material from the surface to be processed. Alternatively, such a gas may be a non-reactive gas in nature (e.g. argon). In principle, a non-reactive gas may achieve a better cutting quality and also help remove material particles.

[0008] Despite the progress that has been made, to date, those skilled in the art still lack a method for producing components by cutting metal-glass ribbons by means of a pulsed laser beam, which method is required to ensure the amorphization of the cut metallic glass.

[0009] Patent document WO2022 / 234155 describes a method for cutting metallic glass having: a critical diameter (Dc) less than 5 mm, preferably less than 3 mm, and / or a difference (Δx) between a crystallization temperature (Tx) and a glass transition temperature (Tg) less than 60°C, and / or a quotient of the difference (ΔTx) between the crystallization temperature (Tx) and the glass transition temperature (Tg) and the difference between the liquidus temperature (Tl) and the glass transition temperature (Tg) (ΔTx / (Tl-Tg)) less than 0.12, preferably less than 0.1.

[0010] The amorphous metal alloy described in patent document WO2022 / 234155 is nickel-based. The crystallization temperature of such amorphous metal alloy is higher than 650° C. The patent document does not provide any information on the behavior of amorphous metal alloys with lower crystallization temperatures (especially below 650° C.). Summary of the invention

[0011] An object of the present invention is to remedy the disadvantages of the prior art described above. The present invention achieves the above and other objects by providing a method for cutting a metal-glass ribbon. The method comprises applying a pulsed laser beam having a wavelength less than or equal to 555 nanometers to the ribbon, the pulsed laser beam being formed by a series of pulses, each pulse having a duration of less than 10 picoseconds, and advantageously less than 1 picosecond.

[0012] According to the present invention, the crystallization temperature of the metallic glass is lower than 500° C., and the light energy of the laser beam incident on the ribbon is between 1 microjoule / pulse and 10 microjoules / pulse.

[0013] The present invention also relates to a method for cutting a metal-glass ribbon, the method comprising the following steps.

[0014] a) Providing an apparatus, the apparatus comprising: at least one laser arranged to generate a pulsed laser beam having a wavelength less than or equal to 555 nanometers, the pulsed laser beam being formed by a series of pulses, each pulse having a duration less than 10 picoseconds and advantageously less than 1 picosecond, and a laser beam attenuation module arranged to be able to adjust the light energy of the incident laser beam.

[0015] b) Providing a metal-glass sample to be cut.

[0016] c) adjusting the attenuation module so that: if the crystallization temperature of the metallic glass to be cut is lower than 500° C., the light energy of the laser beam incident on the strip is between 1 microjoule / pulse and 10 microjoules / pulse; and, if the crystallization temperature of the metallic glass to be cut is higher than 500° C., the light energy of the laser beam incident on the strip is between 15 microjoules / pulse and 80 microjoules / pulse.

[0017] d) if the crystallization temperature of the metallic glass is below 500° C., cutting the ribbon by applying a laser beam to the metal-glass sample to cut the ribbon, the light energy of the laser beam having been adjusted according to step c) by implementing the above-mentioned cutting method, or, if the crystallization temperature of the metallic glass is above 500° C., cutting the ribbon by applying a laser beam to the metal-glass sample to cut the ribbon, the light energy of the laser beam having been adjusted according to step c). BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Other features and advantages of the invention will emerge from reading the following description made with reference to the accompanying drawings, which are provided by way of non-limiting example only. In the accompanying drawings, a laser system which can be used to implement the method of the invention is schematically shown by way of example. DETAILED DESCRIPTION

[0019] A method for cutting a metal-glass ribbon according to the invention comprises applying a pulsed laser beam having a wavelength less than or equal to 555 nanometers to the ribbon, the pulsed laser beam being formed by a series of pulses, each pulse having a duration less than 10 picoseconds, and advantageously less than 1 picosecond. The crystallization temperature of the metallic glass is less than 500° C., and the light energy of the laser beam incident on the ribbon is between 1 microjoule / pulse and 10 microjoules / pulse.

[0020] This method for cutting a metal-glass ribbon having a crystallization temperature below 500° C. can be implemented in a more general process for cutting a metal-glass ribbon. The method uses an apparatus so that the metal-glass ribbon can be cut regardless of the crystallization temperature of the metallic glass to be cut. To this end, the method comprises the following steps.

[0021] a) Providing an apparatus, the apparatus comprising: at least one laser and a laser beam attenuation module. The at least one laser is arranged to generate a pulsed laser beam with a wavelength less than or equal to 555 nanometers, the pulsed laser beam being formed by a series of pulses, each pulse having a duration less than 10 picoseconds and advantageously less than 1 picosecond. The attenuation module is arranged to be able to adjust the light energy of the incident laser beam.

[0022] b) Providing a metal-glass sample to be cut.

[0023] c) adjusting the attenuation module so that: if the crystallization temperature of the metallic glass to be cut is lower than 500° C., the light energy of the laser beam incident on the strip is between 1 microjoule / pulse and 10 microjoules / pulse; and if the crystallization temperature of the metallic glass to be cut is higher than 500° C., the light energy of the laser beam incident on the strip is between 15 microjoules / pulse and 80 microjoules / pulse.

[0024] d) if the crystallization temperature of the metallic glass is below 500° C., the above-mentioned cutting method is performed by applying a laser beam to the metal-glass sample to cut the ribbon, the light energy of the laser beam having been adjusted according to step c), or, if the crystallization temperature of the metallic glass is above 500° C., the ribbon is cut by applying a laser beam to the metal-glass sample to cut the ribbon, the light energy of the laser beam being between 15 μJ / pulse and 80 μJ / pulse.

[0025] Of course, the laser is the central element of the device that enables the implementation of the method of the invention. In the attached figure, a laser system that can be used to implement the method of the invention is schematically shown by way of example. In this figure, reference numeral 1 denotes a femtosecond laser. Reference numeral 2 denotes an attenuation module for the laser beam, which comprises a rotating half-wave delay band 3 and a polarizing semi-reflecting mirror 4. Reference numeral 5 denotes a quarter-wave band capable of converting the linear polarization of the laser beam into a circular polarization. Reference numeral 6 denotes an opening stop (or iris). Reference numeral 7 denotes an afocal system of a telescope configuration consisting of a set of associated optical elements 7a, 7b. Reference numeral 8 denotes a device for measuring the optical power. Reference numeral 9 denotes a telecentric objective (or optical offset system) that makes it possible to control the scanning of the laser beam on the working plane. Finally, reference numeral 10 denotes the metal-glass strip to be cut with the aid of the method of the invention.

[0026] The laser indicated by reference numeral 1 is an ultrashort pulse or quasi-ultrashort pulse laser, the duration of its laser pulse is between 100 femtoseconds and 10 picoseconds, and preferably between 100 femtoseconds and 1 picosecond. The repetition rate (cadence) of the laser pulse is between 5 kilohertz (kHz) and 1 megahertz (MHz), advantageously between 5kHz and 30kHz, preferably between 5kHz and 25kHz, typically 5kHz, 10kHz, 15kHz, 20kHz, 25kHz.

[0027] Preferably, when the crystallization temperature of the metallic glass to be cut is lower than 500°C, the light energy of the laser beam incident on the strip is between 1 microjoule / pulse and 10 microjoules / pulse, and the repetition rate (rhythm) of the laser pulse is between 5kHz and 30kHz, preferably between 5kHz and 25kHz.

[0028] The wavelength of the laser beam is less than or equal to 555 nanometers (nm). According to a first variant, the light emitted by the laser 1 is green light, and its wavelength is between 490 nanometers and 555 nanometers. The wavelength may be, for example, equal to 513 nanometers or 515 nanometers. According to a second variant, the light emitted by the laser 1 is in the range of blue-violet light, and its wavelength is between 380 nanometers and 490 nanometers, preferably between 405 nanometers and 450 nanometers. The wavelength may be, for example, equal to 405 nanometers, 445 nanometers, 447 nanometers or 450 nanometers. According to a third variant, the light emitted by the laser 1 is in the range of ultraviolet light, and its wavelength is between 330 nanometers and 380 nanometers. For example, the wavelength may be equal to 343 nanometers. It should be understood that the light with the wavelength of 515 nanometers (green light) and 343 nanometers (ultraviolet light) illustrated by the same laser can be generated. In fact, the above two wavelengths can be obtained by doubling and tripling the fundamental frequency of the same laser, respectively, and the wavelength corresponding to the fundamental frequency of the laser is 1030 nanometers.

[0029] The attenuation module (indicated by the reference numeral 2) makes it possible to adjust the energy contained in the pulses generated by the laser system of the figure. At the exit of the laser 1, the intensity of the light beam is maximum. Then, the light beam passes through the attenuation module 2, which can attenuate and adjust the intensity of the light beam, or in other words, the energy of each pulse of the light beam. The attenuation module 2 can adjust the energy of the pulses, for example, within a range between 0 and 150 microjoules. It will be understood that the energy contained in the laser pulses will increase the temperature of the metal-glass strip. In order to avoid crystallization of the metallic glass, it is preferred to keep the temperature of the strip below the crystallization temperature. Taking these conditions into account, the lower the crystallization temperature of the metallic glass, the more the energy of the laser beam must be attenuated. Therefore, when the crystallization temperature of the metallic glass of the strip 10 is lower than 500° C., it is preferred to use the first embodiment of the method of the invention, according to which the energy of the laser beam pulses incident on the strip is between 1 microjoule and 10 microjoules, corresponding to a fluence of less than about 8 J / cm 2(Laser wavelength 515 nm, pulse duration 230 femtoseconds (fs), spot size 13 μm, frequency 25 kHz, scanning speed 5 mm / s). Energy between 10 μJ / pulse and 14 μJ / pulse can also be used. For this purpose, the attenuation module 2 is advantageously adjusted in advance according to the crystallization temperature of the metallic glass to be cut, using step c) of the method. For example, the metallic glass cut using the first embodiment can advantageously be: alloy TibalanceZr35.0Cu17.0S8.0 (atomic percent), such as Medalium T1 distributed by Amorphous Metal Solutions GmbH; alloy ZrbalanceCu17.9Ni 14.6Al10.0Ti5.0 (atomic percent), such as Medalium Z2 distributed by Amorphous Metal Solutions GmbH; or alloy Zr59.3Cu28.8Al10.4Nb1.5 (atomic percent), such as AMZ4 distributed by Heraeus Group. All three of the above alloys have a crystallization temperature below 480° C. In contrast, when the crystallization temperature of the metallic glass of the strip 10 is above 500° C., the second embodiment of the method will preferably be used, according to which the energy of the laser beam pulses incident on the strip is between 15 microjoules and 80 microjoules. To this end, the attenuation module 2 is advantageously adjusted in advance according to the crystallization temperature of the metallic glass to be cut, using step c) of the method. For example, the metallic glass cut using the second embodiment can advantageously be: alloy NibalanceNb38.0 (atomic percentage), such as Medalium N1 distributed by Amorphous Metal Solutions LLC; or alloy Ni(57-67)Nb(28-38)Zr(0-10) (atomic percentage), such as distributed by Vulkam Especially Ni1. The crystallization temperatures of these alloys are all above 600℃.

[0030] At the exit of the laser 1, the beam is linearly polarized. A disadvantage of a linearly polarized beam is that the ablation effect may depend on the angle between the direction of advance and the polarization direction at the point of incidence. A quarter wave band (indicated by reference numeral 5 in the drawings) makes it possible to change the linear polarization of the beam into a circular polarization, thereby eliminating this undesirable effect.

[0031] In the figures, an afocal system is indicated by reference numeral 7, which comprises a diverging lens 7a and a converging lens 7b associated in a telescopic configuration. Such a telescopic structure makes it possible to enlarge the size of the light beam emerging from the aperture 6.

[0032] The strip 10 intended to be cut using the method of the invention is a thin strip. The maximum thickness of the thin strip does not exceed 1 mm, preferably even less than 500 microns. In addition, it is worth pointing out that the thickness of the strip indicated by the reference numeral 10 in the figures is not necessarily constant. The strip can also be a strip whose thickness can vary from one position to another.

[0033] The metal-glass sample to be cut provided in step b) is usually in the form of a plate.

[0034] The critical diameter (Dc) of the metallic glass used in the present invention is preferably greater than or equal to 5 mm. The metal-glass rod obtained after molding is cut into thin slices with a thickness between 1 mm and 10 mm (a cross section of a cylinder, preferably located in the middle of the rod). The obtained thin slices are analyzed by X-ray diffraction to determine whether these thin slices have an amorphous structure or a partially crystalline structure. Then, the critical diameter is determined as the maximum diameter of the amorphous structure. This means that the critical diameter can be defined as the diameter that clearly shows a crystallinity peak after X-ray diffraction analysis. In the article "Thermal and mechanical properties of Cu-Zr-Al bulk metallic glasses" written by Cheung et al. in 2007 (doi: 10.1016 / j.jallcom.2006.08.109), this evaluation of the amorphous properties of metal alloys is described in detail.

[0035] The metal-glass ribbon is cut by ablation, whereby a groove is gradually dug out. The width of the groove is at least as large as the diameter of the point of incidence (or spot) of the laser beam on the surface of the ribbon 10. The optics of the laser system are preferably adjusted to focus the laser beam on the surface of the ribbon. Thus, the diameter of the point of incidence corresponds to the diameter of the beam at its focus. Due to the thinness of the ribbon and the small opening angle of the laser beam, it is not necessary to change the focal length during processing to take into account the depth of the groove.

[0036] By convention, in the present invention, the intensity is maximized by 1 / E 2 The size of the laser beam is measured by measuring the width of the laser beam (its diameter) at about 100 μm (i.e., about 13.5%). As is well known, the light intensity (power) is greatest on the axis of the beam and tapers off away from the axis. The diameter of the point of incidence of the laser beam on the strip (measured according to this convention) is preferably between 5 μm and 15 μm. Based on the same convention, the energy density (fluence) of the incident laser pulse can additionally be calculated by dividing the energy of the pulse by the surface area of ​​the point of incidence.

[0037] The width of the grooves in the strip is preferably between 5 and 25 microns. According to an advantageous variant, the laser beam is focused on a diameter smaller than the width of the grooves to be obtained and is set in a circular motion by rotating optics, known as a trepanation head.

[0038] Furthermore, it is to be understood that various modifications and / or improvements obvious to a person skilled in the art may be made to the embodiments that are the subject of this description without departing from the scope of the invention as defined by the appended claims.

Claims

1. A method for cutting a metallic glass ribbon, comprising: A pulsed laser beam having a wavelength less than or equal to 555 nanometers is applied to the ribbon, the pulsed laser beam being formed by a series of pulses, each pulse having a duration of less than 10 picoseconds, and advantageously less than 1 picosecond, characterized in that the crystallization temperature of the metallic glass is lower than 500° C., and the light energy of the laser beam incident on the ribbon is between 1 microjoule / pulse and 10 microjoules / pulse.

2. A method for cutting a metallic glass strip, characterized in that: The following steps are involved: a) providing a device, comprising: at least one laser (1) arranged to generate a pulsed laser beam having a wavelength less than or equal to 555 nanometers, the pulsed laser beam being formed by a series of pulses, each pulse having a duration less than 10 picoseconds and advantageously less than 1 picosecond; and a laser beam attenuation module (2) arranged to be able to adjust the light energy of the incident laser beam; b) providing a metallic glass sample to be cut; c) adjusting the attenuation module (2) so that: if the crystallization temperature of the metallic glass to be cut is lower than 500° C., the light energy of the laser beam incident on the strip is between 1 microjoule / pulse and 10 microjoules / pulse; and if the crystallization temperature of the metallic glass to be cut is higher than 500° C., the light energy of the laser beam incident on the strip is between 15 microjoules / pulse and 80 microjoules / pulse; and d) if the crystallization temperature of the metallic glass is lower than 500° C., cutting the ribbon by applying the laser beam to the metallic glass sample, the light energy of the laser beam having been adjusted according to step c), or, if the crystallization temperature of the metallic glass is higher than 500° C., cutting the ribbon by applying the laser beam to the metallic glass sample, the light energy of the laser beam being between 15 μJ / pulse and 80 μJ / pulse.

3. The cutting method according to claim 1 or 2, characterized in that: The wavelength is between 490 nanometers and 555 nanometers.

4. The cutting method according to claim 1 or 2, characterized in that: The wavelength is between 380 and 490 nanometers, and advantageously between 405 and 450 nanometers.

5. The cutting method according to claim 1 or 2, characterized in that: The wavelength is less than 380 nanometers and advantageously greater than 330 nanometers.

6. The method according to any one of claims 2 to 5, characterized in that The attenuation module (2) comprises: a rotating half-wave delay band (3) and a polarizing half-reflecting mirror (4).

7. The cutting method according to any one of the preceding claims, characterized in that The laser beam is circularly polarized.

8. The method according to any one of claims 2 to 6, characterized in that The laser beam generated by the laser is linearly polarized, and the device comprises a quarter wave band (5) arranged to change the linear polarization of the laser beam into a circular polarization.

9. The cutting method according to any one of claims 2 to 8, characterized in that: The crystallization temperature of the metallic glass is higher than 600°C.

10. The cutting method according to claim 9, characterized in that: The metallic glass is alloy NiNb38.0 (atomic percentage) or alloy Ni(57-67)Nb(28-38)Zr(0-10) (atomic percentage).

11. The cutting method according to any one of the preceding claims, characterized in that The crystallization temperature of the metallic glass is lower than 480° C., and the metallic glass is selected from the following: alloy TiZr35.0Cu17.0S8.0 (atomic percentage), alloy ZrCu17.9Ni14.6Al10.0Ti5.0 (atomic percentage) and alloy Zr59.3Cu28.8Al10.4Nb1.5 (atomic percentage).

12. The cutting method according to any one of the preceding claims, characterized in that The repetition rate (or rhythm) of the pulsed laser beam is between 5 kHz and 30 kHz, preferably between 5 kHz and 25 kHz, typically 5 kHz, 10 kHz, 15 kHz, 20 kHz, or 25 kHz.

13. The cutting method according to any one of the preceding claims, characterized in that The thickness of the metallic glass ribbon is no more than 1 mm, preferably no more than 500 μm.

14. The cutting method according to any one of the preceding claims, characterized in that The thickness of the metallic glass ribbon is not constant, but varies from one location on the ribbon to another.

15. The cutting method according to any one of the preceding claims, characterized in that When the pulsed laser beam is applied to the strip, at least one groove is dug out, and the width of the groove is between 5 micrometers and 25 micrometers.

16. The cutting method according to any one of the preceding claims, characterized in that The diameter of the laser beam incident on the plate at the focus point (spot size) is between 5 microns and 15 microns.

17. The cutting method according to any one of the preceding claims, characterized in that The laser beam is focused on a diameter smaller than the width of the groove to be obtained and is set in a circular motion by rotating the optical device (called drilling head).

18. A watchmaking micromechanical component obtained by implementing a method according to any one of claims 1 to 17.

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