Process for manufacturing parts by laser cutting metallic-glass strips

Abstract

Disclosed is a process for cutting a metallic-glass strip, comprising applying, to the strip, a pulsed laser beam of wavelength shorter than or equal to 555 nanometres, the pulsed laser beam being formed of a succession of pulses each having a duration shorter than 10 picoseconds, and advantageously shorter than 1 picosecond, the crystallization temperature of the metallic glass being below 500°C, and the light energy of the laser beam incident on the strip being comprised between 1 and 10 microjoules per pulse.

Description

[0001] PROCESS FOR MANUFACTURING PARTS BY CUTTING METALLIC GLASS SLATS WITH A LASER

[0002] Technical field

[0003] The present invention generally relates to a method for cutting metallic glass blades using a laser, and it relates more particularly to a method for producing parts or blanks by cutting metallic glass blades using a pulsed laser beam. The present invention relates in particular to such a method which is suitable for producing parts or blanks of watchmaking micromechanical parts made of metallic glass.

[0004] State of the art

[0005] Metallic glasses or amorphous metals are metal alloys whose atomic structure is not crystalline. These alloys are generally produced by cooling sufficiently rapidly to prevent the formation of crystalline structures. The amorphous structure of the constituent material of these alloys gives them mechanical properties radically different from those of crystalline metals. In general, metallic glasses have mechanical, physical, and chemical properties that have promising applications. Indeed, parts made of bulk metallic glass (BMG) generally have higher yield strength, endurance strength, tensile strength, corrosion resistance, hardness, and wear resistance than parts made of crystalline metal.These differences make metallic glasses the materials of choice for the production of small parts, particularly in the field of watchmaking. In particular, the resistance of metallic glasses to wear and their ability to store a significant amount of energy through elastic deformation are two extremely interesting characteristics.

[0006] Metallic glasses are, however, difficult to work with. They are fragile materials with a limited, or sometimes non-existent, plastic deformation range. These materials therefore tend to fracture as soon as their elastic limit is exceeded. Indeed, since they do not have a crystalline structure, metallic glasses also do not have dislocations. However, it is these dislocations that, as they move, propagate plastic deformations and give the metal its ductility. Furthermore, metallic glasses have relatively low crystallization and melting temperatures. When working with these glasses, it is therefore important to limit heat inputs so as not to risk heating them to their crystallization temperature, otherwise their mechanical properties could be altered. Finally, the low thermal conductivity of metallic glasses makes it very difficult to cool them "to the core" quickly.It will be understood from the above that the machining methods traditionally used in watchmaking are not suitable for these new materials.

[0007] Machining amorphous metals is a recent issue, with many discoveries concerning their production having been made in the 1990s. Therefore, there are currently no established protocols guaranteeing non-crystallization of shaped parts. Furthermore, this family of materials is vast, and there are wide disparities in properties.

[0008] A laser is a generator of monochromatic and coherent electromagnetic radiation. Laser blade cutting, mentioned in the preamble, is a machining process that appeared in the 1960s. Laser cutting makes it possible to shape parts from materials of various types. This process consists of cutting the material using a large amount of energy produced by a laser and concentrated on a very small surface. The focusing of the laser beam makes it possible to raise the temperature of a small area of ​​material, until vaporization. The heat-affected zone (HAZ) of the laser beam is relatively small, which explains the little deformation undergone by the cut parts. The main disadvantages of laser cutting are the formation of zones where the quality of the machined material is altered by heat, as well as the formation of burrs at the edge of the cut.

[0009] Pulsed lasers are now available that are capable of generating series of extremely short pulses with high instantaneous power. This allows the heat generation to be confined to extremely short time intervals. The ability of the machined material to cool between each pulse limits the temperature rise compared to a continuously operating laser. This feature can be an advantage for cutting metallic glasses, since it could potentially keep the temperature of the amorphous material below its crystallization temperature.

[0010] It is worth mentioning that some known laser cutting processes are carried out using an assist gas. This gas can be reactive (e.g. oxygen) and used to enhance the material removal from the surface to be machined. Alternatively, the gas can be non-reactive (e.g. argon). A non-reactive gas will generally lead to better cutting quality and will also help remove material particles.

[0011] Despite the progress made, those skilled in the art still do not have a process for manufacturing parts by cutting metallic glass blades using a pulsed laser beam, which guarantees that the cut metallic glass does not crystallize.

[0012] Publication WO 2022 / 234155 describes a cutting method for metallic glasses having:

[0013] - a critical diameter (De) less than 5 millimeters, preferably less than 3 millimeters, and / or

[0014] - a difference (A x) between the crystallization temperature (Tx) and the glass transition temperature (Tg) less than 60°C, and / or

[0015] - a quotient (A Tx / (Tl-Tg)) of the difference (A Tx) 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) less than 0.12, preferably less than 0.1. The amorphous metal alloys described in publication WO 2022 / 234155 are nickel-based. These amorphous metal alloys have crystallization temperatures above 650°C. This document does not provide any information on the behavior of amorphous metal alloys having low crystallization temperatures, in particular below 650°C.

[0016] Disclosure of the invention

[0017] An object of the present invention is to overcome the drawbacks of the prior art which have just been explained. The present invention achieves this and other objects by providing a method for cutting a metallic glass blade comprising the application to the blade of a pulsed laser beam with a wavelength less than or equal to 555 nanometers, the pulsed laser being formed from a succession of pulses each having a duration of less than 10 picoseconds, and advantageously less than 1 picosecond.

[0018] According to the invention, the metallic glass has a crystallization temperature of less than 500°C, and the light energy of the laser beam incident on the blade is between 1 and 10 microjoules per pulse.

[0019] The present invention also relates to a method for cutting a metallic glass blade, said method comprising the steps: a) providing equipment comprising at least one laser arranged to produce a pulsed laser beam with a wavelength less than or equal to 555 nanometers, the pulsed laser beam being formed from a succession of pulses each having a duration of less than 10 picoseconds, and advantageously less than 1 picosecond, and a laser beam attenuation module arranged to be able to adjust the quantity of light energy of the incident laser beam; b) providing a sample of metallic glass to be cut;(c) adjusting the attenuation module so that the light energy of the laser beam incident on the blade is between 1 and 10 microjoules per pulse if the metallic glass to be cut has a crystallization temperature below 500°C, and so that the light energy of the laser beam incident on the blade is between 15 and 80 microjoules per pulse if the metallic glass to be cut has a crystallization temperature above 500°C;and d) cutting the blade by applying to said sample of metallic glass the laser beam whose light energy has been adjusted according to step c) by implementing the cutting method as defined above if the metallic glass has a crystallization temperature lower than 500°C, or by applying to the sample of metallic glass said laser beam whose light energy is between 15 and 80 microjoules per pulse if the metallic glass has a crystallization temperature higher than 500°C.;

[0020] Brief description of the drawings

[0021] Other characteristics and advantages of the present invention will appear on reading the description which follows, given solely by way of non-limiting example, and made with reference to the appended drawing which schematically illustrates by way of example a laser system capable of being used to implement the methods of the invention.

[0022] Embodiments of the invention

[0023] A method of cutting a metallic glass slide according to the invention comprises applying to the slide a pulsed laser beam with a wavelength less than or equal to 555 nanometers, the pulsed laser beam being formed of a succession of pulses each having a duration of less than 10 picoseconds, and advantageously less than 1 picosecond, said metallic glass having a crystallization temperature of less than 500°C, and the light energy of the laser beam incident on the slide being between 1 and 10 microjoules per pulse. This method of cutting a metallic glass slide having a crystallization temperature of less than 500°C can be implemented in a more global method of cutting a metallic glass slide using equipment making it possible to cut a metallic glass slide regardless of the crystallization temperature of the metallic glass to be cut. For this purpose,this method comprises the steps: a) providing equipment comprising at least one laser arranged to produce a pulsed laser beam with a wavelength less than or equal to 555 nanometers, the pulsed laser beam being formed from a succession of pulses each having a duration of less than 10 picoseconds, and advantageously less than 1 picosecond, and a laser beam attenuation module arranged to be able to adjust the quantity of light energy of the incident laser beam; b) providing a sample of metallic glass to be cut; c) adjusting the attenuation module so that the light energy of the incident laser beam on the blade is between 1 and 10 microjoules per pulse if the metallic glass to be cut has a crystallization temperature of less than 500°C,and such that the light energy of the laser beam incident on the blade is between 15 and 80 microjoules per pulse if the metallic glass to be cut has a crystallization temperature above 500°C; and d) cutting the blade by applying to said sample of metallic glass the laser beam whose light energy has been adjusted according to step c) by implementing the cutting method as defined above if the metallic glass has a crystallization temperature below 500°C,or by applying to the metallic glass sample said laser beam whose light energy is between 15 and 80 microjoules per pulse if the metallic glass has a crystallization temperature above 500°C. The central element of the equipment allowing the implementation of the methods of the invention is of course the laser. The attached figure schematically illustrates by way of example a laser system capable of being used to implement the methods of the invention. In this figure, reference 1 designates a femtosecond laser, reference 2 designates a laser beam attenuation module which comprises a rotating half-wave delay plate 3 and a polarized semi-reflecting mirror 4, reference 5 designates a quarter-wave plate making it possible to change the linear polarization of the laser beam into circular polarization, reference 6 designates an aperture diaphragm (or iris),reference 7 designates an afocal system consisting of a set of optical elements 7a, 7b associated in a telescope configuration, reference 8 designates a device for measuring the light power, reference 9 designates a telecentric objective (or optical deflection system) which makes it possible to control the scanning of the working plane by the laser beam. Finally, reference 10 designates the metallic glass slide which must be cut using the methods of the invention.,

[0024] The laser referenced 1 is an ultra, or quasi-ultra, short pulse laser, the duration of the laser pulses being between 100 femtoseconds and 10 picoseconds, and preferably between 100 femtoseconds and 1 picosecond. The pulse repetition rate of the laser (the cadence) is between 5 kHz and 1 MHz, advantageously between 5 kHz and 30 kHz, preferably between 5 kHz and 25 kHz, typically 5, 10, 15, 20, 25 kHz.

[0025] Preferably, when the metallic glass to be cut has a crystallization temperature below 500°C, the light energy of the laser beam incident on the blade is between 1 and 10 microjoules per pulse, and the pulse repetition rate of the laser (the cadence) is between 5 kHz and 30 kHz, preferably between 5 kHz and 25 kHz.

[0026] The wavelength of the laser beam is less than or equal to 555 nanometers. According to a first variant, the light emitted by the laser 1 is green, its wavelength being between 490 and 555 nanometers. It may, for example, be equal to 513 or 515 nanometers. According to a second variant, the laser 1 emits in a blue-violet range, its wavelength being between 380 and 490 nanometers, preferably between 405 and 450 nanometers. It may, for example, be equal to 405, 445, 447 or 450 nanometers. According to a third variant, the laser 1 emits in the ultraviolet, its wavelength being between 330 and 380 nanometers. It may, for example, be equal to 343 nanometers. Note that the wavelengths of 515 nm (green) and 343 nm (ultraviolet), cited as examples, can both be produced from the same laser.Indeed, these two wavelengths can be obtained respectively by doubling and tripling the fundamental frequency of the same laser, the fundamental frequency of the laser corresponding to a wavelength of 1030 nm.

[0027] The attenuation module (referenced 2) allows the amount of energy contained in the pulses produced by the laser system in the attached figure to be adjusted. At the output of the laser 1, the beam intensity is maximum. The beam then passes through an attenuation module 2 which allows its intensity to be attenuated and adjusted or, in other words, the energy of each pulse in the beam to be attenuated and adjusted. The attenuation module 2 allows, for example, the energy of the pulses to be adjusted in a range between 0 and 150 microjoules. It will be understood that the energy contained in the laser pulses is responsible for the increase in the temperature of the metallic glass slide. To avoid crystallization of the metallic glass, it is preferable to keep the temperature of the slide below the crystallization temperature. Under these conditions, the lower the crystallization temperature of the metallic glass, the more the laser beam energy should be attenuated.Thus, when the crystallization temperature of the metallic glass of the blade 10 is less than 500°C, a first embodiment of the method of the invention will preferably be used, according to which the energy of the pulses of the laser beam incident on the blade is between 1 and 10 microjoules, corresponding to a fluence of less than approximately 8 J / cm. 2(with a laser of wavelength 515 nm, pulse duration 230 fs, spot size 13 pm, frequency 25 kHz and scan speed 5 mm / s). An energy between 10 and 14 microjoules per pulse could also be used. For this purpose and advantageously, the attenuation module 2 was previously adjusted according to step c) of the process depending on the crystallization temperature of the metallic glass to be cut. For example, the metallic glass cut using the first method of implementation could advantageously be a TibalanceZr35.0Cu17.0S8.0 alloy (atomic percentages) such as Medalium T1 distributed by Amorphous Metal Solutions GmbH, a ZrbalanceCu17.9Ni14.6AI10.0Ti5.0 alloy (atomic percentages) such as Medalium Z2 distributed by Amorphous Metal Solutions GmbH, or a Zr59.3Cu28.8AI10.4Nb1 alloy.5 (atomic percentages) such as TAMZ4 distributed by Heraeus Group, all three of which have a crystallization temperature below 480°C. On the other hand, when the crystallization temperature of the metallic glass of the blade 10 is above 500°C, a second method of implementing the method will preferably be used, according to which the energy of the pulses of the laser beam incident on the blade is between 15 and 80 microjoules. For this purpose, and advantageously, the attenuation module 2 has been adjusted beforehand according to step c) of the method as a function of the crystallization temperature of the metallic glass to be cut. For example, the metallic glass cut using the second method of implementation could advantageously be a NibalanceNb38 alloy.0 (atomic percentage) such as Medalium N1 distributed by Amorphous Metal Solutions GmbH or a Ni(57-67)Nb(28-38)Zr(0-10) (atomic percentages) alloy such as Vulkalloys® distributed by Vulkam, notably Ni1 which both have a crystallization temperature above 600°C.

[0028] At the output of the laser 1, the beam is linearly polarized. A disadvantage of having a linearly polarized beam is that the efficiency of the ablation may depend on the angle between the direction of advancement of the point of incidence and the direction of polarization. The quarter-wave plate (referenced 5 in the attached figure) makes it possible to change the linear polarization of the beam into a circular polarization, and thus to eliminate this undesirable effect. Reference 7 in the attached figure designates an afocal system comprising a diverging lens 7a and a converging lens 7b associated in a telescope configuration. The telescope configuration makes it possible to enlarge the size of the beam emerging from the iris 6.

[0029] The blade 10 that is to be cut using the method of the invention is a thin blade. Its maximum thickness does not exceed 1 millimeter. It is even preferably less than 500 microns. It is worth specifying further that the blade referenced 10 in the attached figure is not necessarily a blade of constant thickness. It may just as well be a blade whose thickness varies from one place to another on the blade.

[0030] The sample of metallic glass to be cut provided in step b) is generally in the form of a plate.

[0031] Preferably, the metallic glasses used in the present invention have a critical diameter (De) greater than or equal to 5 mm. The metallic glass rods obtained after molding are cut into slices (cross section of the cylinder, preferably located towards the middle of the bar) with a thickness of between 1 and 10 millimeters. The slices obtained are analyzed by X-ray diffraction to determine whether they have an amorphous or partially crystalline structure. The critical diameter is then determined as the maximum diameter for which the structure is amorphous. This means that the critical diameter can be defined as the diameter above which an X-ray diffraction analysis clearly highlights crystallinity peaks. Such an evaluation of the amorphous character of a metallic alloy is detailed in the article Cheung et al., 2007 “Thermal and mechanical properties of Cu-Zr-AI bulk metallic glasses” doi:10.1016 / j.jallcom.2006.08.109).

[0032] The cutting of the metallic glass blade is done by ablation and therefore progressive digging of a 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 blade 10. The optics of the laser system are preferably adjusted so as to focus the laser beam on the surface of the blade. The diameter of the point of incidence therefore corresponds to the diameter of the beam at its focal point. Since the blade is thin and the opening angle of the laser beam is also small, it is not necessary to change the focal length during the process to take into account the depth of the groove.

[0033] By convention, in the present application, the size of the laser beam is measured by measuring its width (its diameter) at 1 / E 2(i.e. approximately 13.5%) of the maximum intensity. It is known that the light intensity (power) is maximum on the beam axis and decreases as one moves away from this axis. The diameter of the point of incidence of the laser beam on the blade (measured according to this convention) is preferably between 5 and 15 microns. Based on the same convention, the energy density (fluence) of the incident laser pulses can also be calculated by dividing the energy of a pulse by the area of ​​the point of incidence.

[0034] The width of the groove in the blade 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 groove to be obtained, and it is moved circularly by a rotating optic (called a trepanning head).

[0035] It will further be understood that various modifications and / or improvements obvious to a person skilled in the art may be made to the embodiments which are the subject of the present description without departing from the scope of the present invention defined by the appended claims.

Claims

Demands 1. A method for cutting a metallic glass blade, comprising applying a pulsed laser beam of wavelength less than or equal to 555 nanometers to the blade, the pulsed laser beam being formed of a succession of pulses each having a duration of less than 10 picoseconds, and advantageously less than 1 picosecond, characterized in that the metallic glass has a crystallization temperature of less than 500°C, and in that the light energy of the laser beam incident on the blade is between 1 and 10 microjoules per pulse.

2. A method for cutting a metallic glass blade, characterized in that it comprises the steps: a) acquiring equipment comprising at least one laser (1) arranged to produce a pulsed laser beam of wavelength less than or equal to 555 nanometers, the pulsed laser beam being formed of a succession of pulses each having a duration of less than 10 picoseconds, and advantageously less than 1 picosecond, and an attenuation module (2) of the laser beam arranged to be able to regulate the amount of light energy of the incident laser beam; b) acquiring a sample of metallic glass to be cut;(c) adjust the attenuation module (2) so that the light energy of the laser beam incident on the blade is between 1 and 10 microjoules per pulse if the metallic glass to be cut has a crystallization temperature below 500°C, and so that the light energy of the laser beam incident on the blade is between 15 and 80 microjoules per pulse if the metallic glass to be cut has a crystallization temperature above 500°C; and (d) cut the blade by applying to said metallic glass sample the laser beam whose light energy has been adjusted according to step (c) by implementing the cutting process according to claim 1 if; The metallic glass has a crystallization temperature below 500°C, or by applying said laser beam, the light energy of which is between 15 and 80 microjoules per pulse, to the metallic glass sample if the metallic glass has a crystallization temperature above 500°C. A cutting method according to claim 1 and 2, characterized in that the wavelength is between 490 and 555 nanometers. A cutting method according to claim 1 and 2, characterized in that the wavelength is between 380 and 490 nanometers, and advantageously between 405 and 450 nanometers. A cutting method according to claim 1 and 2, characterized in that the wavelength is less than 380 nanometers, and advantageously greater than 330 nanometers.A method according to any one of claims 2 to 5, characterized in that the attenuation module (2) comprises a rotating half-wave delay blade (3) and a polarized semi-reflective mirror (4). A cutting method according to any one of the preceding claims, characterized in that the laser beam is circularly polarized. A method according to any one of claims 2 to 6, characterized in that the laser beam produced by the laser is linearly polarized and in that the equipment comprises a quarter-wave blade (5) arranged to change the linear polarization of the laser beam to circular polarization. A cutting method according to any one of claims 2 to 8, characterized in that the crystallization temperature of the metallic glass is greater than 600°C. Cutting method according to claim 9, characterized in that the metallic glass is an alloy NiNb38.0 (atomic percentage) or an alloy Ni(57-67)Nb(28-38)Zr(0-10) (atomic percentages). A cutting method according to any one of the preceding claims, characterized in that the crystallization temperature of the metallic glass is less than 480°C, the metallic glass being selected from an alloy of TiZr35.0Cu17.0S8.0 (atomic percentages), an alloy of ZrCu17.9Ni14.6Al10.0Ti5.0 (atomic percentages), and an alloy of Zr59.3Cu28.8Al10.4Nb1.5 (atomic percentages). A cutting method according to any one of the preceding claims, characterized in that the repetition rate (or cadence) of the pulsed laser beam is between 5 and 30 kHz, preferably between 5 kHz and 25 kHz, typically 5, 10, 15, 20, or 25 kHz. Cutting method according to any one of the preceding claims, characterized in that the metallic glass blade has a thickness not exceeding 1 millimeter, preferably not exceeding 500 microns.A cutting method according to any one of the preceding claims, characterized in that the metal-glass blade has a thickness that is not constant but varies from one point to another along the blade. A cutting method according to any one of the preceding claims, characterized in that applying the pulsed laser beam to the blade creates at least one groove having a width between 5 and 25 microns. A cutting method according to any one of the preceding claims, 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. A cutting method according to any one of the preceding claims, characterized in that the laser beam is focused onto a diameter smaller than the width of the groove to be obtained, and in that the laser beam is moved circularly by a rotating optical system (called a trepanning head).

18. Watchmaking micromechanical part obtained by implementing the process according to one of claims 1 to 17.

Images