A method of manufacturing a component by laser cutting a metallic glass strip

Abstract

A method of cutting a metallic glass strip, the method comprising applying a pulsed laser beam having a wavelength of 555 nanometers or less to the strip, the pulsed laser beam being formed from a series of pulses each having a duration shorter than 10 picoseconds, preferably shorter than 1 picosecond, the crystallization temperature of the metallic glass being less than 500 °C, and the optical energy of the laser beam incident on the strip being comprised between 1 and 10 microjoules per pulse, a method of cutting a metallic glass strip is disclosed.

Description

Technical Field

[0001] Generally, the present invention relates to a method for laser cutting a metallic glass strip, and more particularly, to a method for manufacturing parts or blanks by cutting a metallic glass strip with a pulsed laser beam. In particular, the present invention relates to such a method suitable for manufacturing parts or blanks of micromechanical parts for manufacturing timepieces made of metallic glass.

Background Art

[0002] Metallic glass or amorphous metal is a metal alloy whose atomic structure is non-crystalline. These alloys are generally produced by cooling rapidly enough to prevent the formation of a crystalline structure. The amorphous structure of the constituent materials of these alloys gives the alloys mechanical properties that are fundamentally different from those of crystalline metals. Generally, metallic glasses have mechanical, physical, and chemical properties that can be expected to be applied. In fact, parts made from metallic glass (bulk metallic glass (BMG)) generally have an elastic limit, endurance limit, tensile strength, corrosion resistance, hardness, and wear resistance, all of which are higher than the elastic limit, endurance limit, tensile strength, corrosion resistance, hardness, and wear resistance of parts made from crystalline metals. Due to these differences, metallic glass has been selected as a material for manufacturing small parts, particularly in the field of watchmaking. The wear resistance of metallic glass and its ability to store a significant amount of energy, particularly by elastic deformation, are two very attractive features.

[0003] However, metallic glasses are difficult to handle. In fact, metallic glasses are brittle materials, and their range of plastic deformation is limited or, in fact, often non-existent. Therefore, these materials tend to break as soon as they exceed their elastic limit. In fact, metallic glasses do not have a crystal structure and thus do not have dislocations. Here, it is these dislocations that, by moving, propagate plastic deformation and impart ductility to metals. On the other hand, metallic glasses have relatively low crystallization and melting temperatures. Therefore, when handling these metallic glasses, it is important to limit the heat input so as not to risk heating the metallic glass up to its crystallization temperature, otherwise the mechanical properties of the metallic glass will change. Finally, the low thermal conductivity of metallic glasses makes it very difficult to rapidly cool the metallic glass "to its core". From the above, it should be understood that the machining methods conventionally used in watchmaking are not suitable for these new materials.

[0004] Machining amorphous metals has been a challenge in recent years, and there have been many discoveries regarding products made in the 1990s. Therefore, there is no established protocol to guarantee the non-crystallization of the formed parts. Furthermore, due to the wide range of this family of materials, there are significant differences in properties.

[0005] A laser is a generator of monochromatic and coherent electromagnetic radiation. Laser cutting of strips, mentioned in the introduction, is a machining method that emerged in the 1960s. Laser cutting makes it possible to form parts from various types of materials. This method consists of cutting the material using a large amount of energy generated by the laser and concentrated on a very small surface. 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 deformation suffered by the cut part is small. The main disadvantages of laser cutting are the formation of regions where the quality of the machined material changes due to heat and the formation of jagged edges at the cut edges.

[0006] Currently, there are pulsed lasers that can generate a series of pulses with extremely high instantaneous power over an extremely short period. This makes it possible to limit the generation of heat to an extremely short time interval. The possibility that the machined material cools between each pulse makes it possible to limit the temperature rise compared to a continuously operating laser. This characteristic can potentially keep the temperature of the amorphous material below its crystallization temperature, so it can be an advantage when cutting metallic glass.

[0007] It is worth mentioning again that the implementation of certain known laser cutting methods is achieved by the use of assist gas. This gas can be essentially reactive (e.g., oxygen) and can be used for the purpose of enhancing the removal of material occurring on the surface being machined. Alternatively, the gas can be essentially non-reactive (e.g., argon). In principle, non-reactive gas enables better cutting quality and, in addition, contributes to the removal of material particles.

[0008] Despite the advantages brought, those skilled in the art still do not currently have a method for manufacturing components by cutting metallic glass strips with a pulsed laser beam that guarantees the non-crystallization of the cut metallic glass.

[0009] International Publication No. WO 2022 / 234155 of the publication discloses a critical diameter (Dc) of less than 5 millimeters, preferably less than 3 millimeters, and / or a difference (Δx) of less than 60 °C between the crystallization temperature (Tx) and the glass transition temperature (Tg), and / or a ratio (ΔTx / (Tl - Tg)) of less than 0.12, preferably less than 0.1, between the difference (Δx) 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) for a method of cutting metallic glass having the above characteristics.

[0010] The amorphous metal alloys described in International Publication No. WO 2022 / 234155 of the Gazette are nickel-based. These amorphous metal alloys have a crystallization temperature above 650 °C. This document provides no information whatsoever on the behavior of amorphous metal alloys having a low crystallization temperature, particularly below 650 °C.

Prior Art Documents

Patent Documents

[0011]

Patent Document 1

Non-Patent Documents

[0012]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0013] One object of the present invention is to improve the disadvantages of the conventional techniques just described.

Means for Solving the Problems

[0014] The present invention achieves this object and other objects by providing a method for cutting a metallic glass strip, the method including applying a pulsed laser beam having a wavelength of 555 nanometers or less to the strip, the pulsed laser beam being formed from a series of pulses each having a duration shorter than 10 picoseconds, preferably shorter than 1 picosecond.

[0015] According to the present invention, the metallic glass has a crystallization temperature of less than 500°C, and the optical energy of the laser beam incident on the strip is included between 1 and 10 microjoules per pulse.

[0016] The present invention also relates to a method for cutting a metallic glass strip, comprising the following steps, namely a) providing a facility including at least one laser arranged to generate a pulsed laser beam with a wavelength of 555 nanometers or less, the pulsed laser beam being formed from a series of pulses each having a duration shorter than 10 picoseconds, preferably shorter than 1 picosecond, and a laser beam attenuation module arranged to be able to adjust the amount of optical energy of the incident laser beam; b) providing a metallic glass sample to be cut; c) adjusting the attenuation module such that when the metallic glass to be cut has a crystallization temperature of less than 500°C, the optical energy of the laser beam incident on the strip is included between 1 and 10 microjoules per pulse, and when the metallic glass to be cut has a crystallization temperature of more than 500°C, the optical energy of the laser beam incident on the strip is included between 15 and 80 microjoules per pulse; d) cutting the strip by applying the laser beam to the metallic glass sample, the optical energy of the laser beam being adjusted according to step c) by implementing the cutting method as defined above when the metallic glass has a crystallization temperature of less than 500°C, or by applying the laser beam with an optical energy included between 15 and 80 microjoules per pulse to the metallic glass sample when the metallic glass has a crystallization temperature of more than 500°C. relates to a method for cutting a metallic glass strip, including the above steps.

Brief Description of the Drawings

[0017]

Figure 1

Embodiments for Carrying Out the Invention

[0018] The method for cutting a metallic glass strip according to the present invention includes applying a pulsed laser beam having a wavelength of 555 nanometers or less to the strip, the pulsed laser beam being formed from a series of pulses each having a duration shorter than 10 picoseconds, preferably shorter than 1 picosecond, the metallic glass having a crystallization temperature of less than 500 °C, and the optical energy of the laser beam incident on the strip being included between 1 and 10 microjoules per pulse.

[0019] This method of cutting a metallic glass strip having a crystallization temperature of less than 500 °C can be implemented in a more comprehensive way by using equipment that enables cutting of the metallic glass strip regardless of the crystallization temperature of the metallic glass to be cut. For this purpose, the method comprises the following steps, namely a) providing equipment comprising at least one laser arranged to generate a pulsed laser beam having a wavelength of 555 nanometers or less, the pulsed laser beam being formed from a series of pulses each having a duration shorter than 10 picoseconds, preferably shorter than 1 picosecond, and a laser beam attenuation module arranged to be able to adjust the amount of optical energy of the incident laser beam; b) preparing a metallic glass sample to be cut; c) When the metallic glass to be cut has a crystallization temperature of less than 500 °C, adjusting the attenuation module so that the optical energy of the laser beam incident on the strip is between 1 and 10 microjoules per pulse, and when the metallic glass to be cut has a crystallization temperature of more than 500 °C, adjusting the attenuation module so that the optical energy of the laser beam incident on the strip is between 15 and 80 microjoules per pulse; d) Cutting the strip by applying a laser beam to the metallic glass sample, wherein the optical energy of the laser beam is, when the metallic glass has a crystallization temperature of less than 500 °C, by implementing the cutting method as defined above, or when the metallic glass has a crystallization temperature of more than 500 °C, by applying the laser beam with an optical energy between 15 and 80 microjoules per pulse to the metallic glass sample, the laser beam being adjusted according to step c); comprising.

[0020] Of course, the central element of the equipment enabling the implementation of the method of the present invention is the laser. The accompanying drawings schematically show a laser system that can be used to implement the method of the present invention 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 includes a rotating half-wavelength retardation strip 3 and a polarization semi-reflective mirror 4, reference numeral 5 denotes a quarter-wavelength strip capable of changing the linear polarization of the laser beam into circular polarization, reference numeral 6 denotes an aperture stop (or iris), reference numeral 7 denotes an afocal system consisting of a set of related optical elements 7a, 7b in a telescopic configuration, reference numeral 8 denotes a device for measuring the optical power, reference numeral 9 denotes a telecentric objective lens (or optical deflection system) capable of controlling the scanning of the working surface by the laser beam. Finally, reference numeral 10 denotes the metallic glass strip that needs to be cut by the method of the present invention.

[0021] The laser with reference sign 1 is an ultrashort pulse laser or a quasi-ultrashort pulse laser, and the duration of the laser pulse is between 100 femtoseconds and 10 picoseconds, preferably between 100 femtoseconds and 1 picosecond. The repetition rate (frequency) of the laser pulse is between 5 kHz and 1 MHz, advantageously between 5 kHz and 30 kHz, preferably between 5 kHz and 25 kHz, and typically 5, 10, 15, 20, 25 kHz.

[0022] Preferably, when the metallic glass to be cut has a crystallization temperature of less than 500 °C, the optical energy of the laser beam incident on the strip is between 1 and 10 microjoules per pulse, and the repetition rate (frequency) of the laser pulse is between 5 kHz and 30 kHz, preferably between 5 kHz and 25 kHz.

[0023] The wavelength of the laser beam is 555 nanometers or less. According to the first modification example, the light emitted by the laser 1 is green, and its wavelength is included between 490 and 555 nanometers. The wavelength can be made equal to, for example, 513 nanometers or 515 nanometers. According to the second modification example, the laser 1 emits light in the range from blue to violet, and its wavelength is included between 380 and 490 nanometers, preferably between 405 and 450 nanometers. The wavelength can be made equal to, for example, 405 nanometers, 445 nanometers, 447 nanometers or 450 nanometers. According to the third modification example, the laser 1 emits light in the ultraviolet range, and its wavelength is included between 330 and 380 nanometers. The wavelength can be made equal to, for example, 343 nanometers. It should be noted that the wavelengths of 515 nm (green) and 343 nm (ultraviolet) cited as examples can both be generated from the same laser. In fact, these two wavelengths can be obtained by doubling and tripling the fundamental frequency of the same laser respectively, and the fundamental frequency of the laser corresponds to a wavelength of 1030 nm.

[0024] The attenuation module (having reference numeral 2) makes it possible to adjust the amount of energy contained in the pulses generated by the laser system of the attached drawings. At the exit of laser 1, the intensity of the beam is at its maximum. The beam then passes through an attenuation module 2 that makes it possible to attenuate and adjust its intensity or, in other words, to attenuate and adjust the energy of each pulse of the beam. The attenuation module 2 makes it possible to adjust the energy of the pulses, for example, in a range included between 0 and 150 microjoules. It should be understood that the energy contained in the laser pulses causes an increase in the temperature of the metallic glass strip. In order to avoid crystallization of the metallic glass, it is preferable to keep the temperature of the strip below the crystallization temperature. Under these conditions, the lower the crystallization temperature of the metallic glass, the more the energy of the laser beam will need to be attenuated. Thus, if the crystallization temperature of the metallic glass of strip 10 is less than 500 °C, preferably the first embodiment of the method of the present invention is used, according to which the energy of the pulses of the laser beam incident on the strip is approximately 8 J / cm (for a laser with a wavelength of 515 nm, a pulse duration of 230 fs, a spot size of 13 μm, a frequency of 25 kHz and a scanning speed of 5 mm / s). 2It is included between 1 and 10 microjoules corresponding to a flow rate amount less than. Energy included between 10 and 14 microjoules per pulse can also be used. For this purpose, advantageously, the attenuation module 2 is pre-adjusted according to step c) of the method according to the crystallization temperature of the metallic glass to be cut. As an example, the metallic glass cut using the first example is advantageously an alloy such as TibalanceZr35.0Cu17.0S8.0 (atomic percentage), such as Medalium T1 supplied by Amorphous Metal Solutions GmbH, an alloy such as ZrbalanceCu17.9Ni14.6Al10.0Ti5.0 (atomic percentage), such as Medalium Z2 supplied by Amorphous Metal Solutions GmbH, or an alloy such as Zr59.3Cu28.8Al10.4Nb1.5 (atomic percentage), such as AMZ4 supplied by Heraeus Group, and all three of these have a crystallization temperature of less than 480 °C. In contrast, when the crystallization temperature of the metallic glass of the strip 10 is above 500 °C, preferably the second example of the method is used. According to the second example, the energy of the pulse of the laser beam incident on the strip is included between 15 and 80 microjoules. For this purpose, advantageously, the attenuation module 2 is pre-adjusted according to step c) of the method according to the crystallization temperature of the metallic glass to be cut. As an example, the metallic glass cut using the second example is advantageously an alloy such as NibalanceNb38.0 (atomic percentage), such as Medalium N1 supplied by Amorphous Metal Solutions GmbH, or an alloy such as Ni(57 - 67)Nb(28 - 38)Zr(0 - 10) (atomic percentage), such as Vulkalloys® supplied by Vulkam, especially Ni1, and both of these have a crystallization temperature above 600 °C.

[0025] At the exit of laser 1, the beam is linearly polarized. A disadvantage of having a linearly polarized beam is that the effectiveness of ablation can depend on the angle between the forward direction of the point of incidence and the polarization direction. A quarter-wave strip (having reference numeral 5 in the attached drawings) makes it possible to change the linear polarization of the beam to circular polarization and thus makes it possible to eliminate this undesirable effect.

[0026] Reference numeral 7 in the attached drawings indicates an afocal system including a related diverging lens 7a and a converging lens 7b of a telescopic configuration. The telescopic configuration makes it possible to enlarge the size of the beam emerging from iris 6.

[0027] The strip 10 intended to be cut using the method of the present invention is a thin strip. Its maximum thickness does not exceed 1 millimeter. The maximum thickness is preferably even less than 500 microns. Furthermore, it is worth noting that the strip having reference numeral 10 in the attached drawings is not necessarily a strip of constant thickness. The strip may be a strip whose thickness varies from one location to another on the strip.

[0028] The metallic glass sample to be cut prepared in step b) is generally in the form of a plate.

[0029] The metallic glass used in the present invention preferably has a critical diameter (Dc) of 5 mm or more. The metallic glass rod obtained following shaping is cut into slices (preferably cylindrical cross-sections located at the center of the rod) having a thickness included between 1 and 10 millimeters. The slices obtained are analyzed by X-ray diffraction in order to determine whether the slices have an amorphous structure or a partially crystalline structure. The critical diameter is then determined as being the largest diameter for which the structure is amorphous. This means that the critical diameter can be defined as a diameter such that, beyond that diameter, the X-ray diffraction analysis clearly shows a crystallinity peak. Such an evaluation of the amorphous characteristics of metallic alloys is detailed in the 2007 paper "Thermal and mechanical properties of Cu-Zr-Al bulk metallic glasses" by Cheung et al., doi:10.1016 / j.jallcom.2006.08.109).

[0030] The metallic glass strip is cut by ablation and thus by progressive excavation of the groove. 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 strip 10. The optical lens of the laser system is preferably adjusted to focus the laser beam on the surface of the strip. Thus, the diameter of the point of incidence corresponds to the diameter of the beam at its focus. The strip is thin and the aperture angle of the laser beam is also small, so there is no need to vary the focal distance during the method in order to take into account the depth of the groove.

[0031] According to convention, in the present application, the size of the laser beam is the 1 / E of maximum intensity 2It is measured by measuring its width (its diameter) at (i.e., at approximately 13.5%). It can be seen that the light intensity (power) is maximum on the axis of the beam and decreases as it moves away from this axis. The diameter of the incident point of the laser beam on the strip (measured according to this convention) is preferably included between 5 and 15 microns. Based on the same convention, furthermore, the energy density (flow rate amount) of the incident laser pulse can be calculated by dividing the energy of the pulse by the surface area of the incident point.

[0032] The width of the groove in the strip is preferably included between 5 and 25 microns. According to an advantageous variant, the laser beam is focused to a diameter smaller than the width of the resulting groove and is moved in a circular motion by a rotating optical lens (referred to as a perforating head).

[0033] Furthermore, it should be understood that various changes and / or improvements obvious to those skilled in the art can be made to the examples that are the subject matter of this specification without departing from the scope of the invention as defined by the appended claims.

Claims

1. A method for cutting a metallic glass strip, the method comprising applying a pulsed laser beam having a wavelength of 555 nanometers or less to the strip, wherein the pulsed laser beam is formed from a series of pulses, each having a duration of less than 10 picoseconds, preferably less than 1 picosecond, the metallic glass having a crystallization temperature of less than 500°C, and the light energy of the laser beam incident on the strip is between 1 and 10 microjoules per pulse.

2. A method for cutting a metallic glass strip, comprising the following steps: a) Providing equipment comprising at least one laser (1) arranged to generate a pulsed laser beam with a wavelength of 555 nanometers or less, wherein the pulsed laser beam is formed from a series of pulses, each having a duration of less than 10 picoseconds, preferably less than 1 picosecond, and a laser beam attenuation module (2) arranged to adjust the amount of light energy of the incident laser beam; b) A step of preparing a metallic glass sample to be cut, c) Adjusting the attenuation module (2) so that, if the metallic glass to be cut has a crystallization temperature of less than 500°C, the light energy of the laser beam incident on the strip is between 1 and 10 microjoules per pulse, and if the metallic glass to be cut has a crystallization temperature greater than 500°C, the light energy of the laser beam incident on the strip is between 15 and 80 microjoules per pulse; d) A step of cutting the strip by applying the laser beam to the metallic glass sample, wherein the light energy of the laser beam is adjusted according to step c), and if the metallic glass has a crystallization temperature of less than 500°C, the cutting method according to claim 1 is performed, or if the metallic glass has a crystallization temperature of more than 500°C, the cutting method is performed by applying the laser beam to the metallic glass sample, wherein the light energy is between 15 and 80 microjoules per pulse, A method for cutting a metallic glass strip, characterized by including [a certain element].

3. The cutting method according to claim 1 or 2, characterized in that the wavelength is between 490 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 preferably between 405 and 450 nanometers.

5. The cutting method according to claim 1 or 2, characterized in that the wavelength is shorter than 380 nanometers, and preferably longer than 330 nanometers.

6. The method according to claim 2, characterized in that the attenuation module (2) includes a rotating half-wavelength delay strip (3) and a polarization semi-reflective mirror (4).

7. The cutting method according to claim 1 or 2, characterized in that the laser beam is circularly polarized.

8. The method according to claim 2, characterized in that the laser beam generated by the laser is linearly polarized, and the apparatus includes a quarter-wavelength strip (5) arranged to convert the linear polarization of the laser beam to circular polarization.

9. The cutting method according to claim 2, characterized in that the crystallization temperature of the metallic glass is greater than 600°C.

10. The cutting method according to claim 9, characterized in that the metallic glass is an alloy NiNb 38.0 (atomic percentage) or an alloy Ni(57-67)Nb(28-38)Zr(0-10) (atomic percentage).

11. The cutting method according to claim 1 or 2, characterized in that the crystallization temperature of the metallic glass is less than 480°C, and the metallic glass is selected from 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 claim 1 or 2, characterized in that the repetition rate (or frequency) of the pulsed laser beam is between 5 and 30 kHz, preferably between 5 kHz and 25 kHz, and typically 5, 10, 15, 20, and 25 kHz.

13. The cutting method according to claim 1 or 2, characterized in that the metallic glass strip has a thickness not exceeding 1 millimeter, preferably not exceeding 500 microns.

14. The cutting method according to claim 1 or 2, characterized in that the metallic glass strip has a thickness that is not uniform but varies from one point on the strip to the other.

15. The cutting method according to claim 1 or 2, characterized in that the application of the pulsed laser beam to the strip excavates at least one groove having a width between 5 and 25 microns.

16. The cutting method according to claim 1 or 2, characterized in that the diameter of the laser beam incident on the plate (spot size) is between 5 and 15 microns at the focal point.

17. The cutting method according to claim 1 or 2, characterized in that the laser beam is focused to a diameter smaller than the width of the groove to be obtained, and the laser beam is moved in a circular motion by a rotating optical lens (called a drilling head).

18. A miniature mechanical component for watchmaking obtained by carrying out the method described in claim 1 or 2.

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