Laser turning system, laser turning method using the system and component obtained by the method

Abstract

The application describes a laser turning system (1) for producing a timepiece component, the system comprising a rotating spindle (3) for moving a material rod (50) and a galvanometer scanner (12) capable of emitting a femtosecond laser beam scanning a generated contour of the component to be machined in the material rod (50).

Description

TECHNICAL FIELD

[0001] The present invention relates to a laser turning system. The present invention also relates to a laser turning method. Finally, the present invention relates to an assembly obtained using such a system or implementing such a method. BACKGROUND

[0002] In order to produce assemblies comprising one or more revolution shapes, it is known to implement a machining method of the turning type based on material removal. Traditionally, the removal of material is done using a cutting tool which acts on a bar of material which is made to rotate and which is intended to give rise to the assembly.

[0003] The production of small-size revolution clock assemblies (for example, clock axles) of high precision is generally performed by turning, in particular by continuous bar turning of the assembly in a metal bar. This takes into account the industrial productivity, but presents some drawbacks related to the nature of the material on which the machining is performed.

[0004] While bar turning is relatively easy for materials particularly suitable for this technique (for example, bar turning steels comprising a chip breaking element such as sulphur), bar turning of parts made of ceramic and of hard metal leads to a severe wear of the tool, which makes this technique less effective than its application to more suitable materials. Moreover, bar turning of hard materials generally causes vibrations of the bar, which do not allow to achieve the required surface roughness.

[0005] Laser turning performed with a continuous laser source (for example, a CO2 laser) has been widely developed in industry, but the precision which it is able to achieve is only of the order of a few tenths of a millimetre, which can prove insufficient for certain applications, and the thermal shock which it generates on the obtained assembly can cause local hardening which damages the microstructure of the material, or, even worse, can generate thermal deformations which affect the dimensions of the assembly, in particular in the case of small-volume assemblies. Therefore, it has not been kept as an advantageous alternative to the traditional turning for average-size parts, or for micrometric-size parts.

[0006] The documents EP 2 314 412 A2, EP 2 374 569 A2, EP 2 489 458 A1 and WO 2016 005 133 A1 describe different types of apparatuses which can be machined using a laser.

[0007] Several studies have been published relating to texturing by femtosecond laser.

[0008] In a study titled "Development of Laser Turning Using Femtosecond Laser Ablation" (Yokotani, A., Kawahara, K., Kurogi, Y., Matsuo, N., Sawada, H., and Kurosawa, K. (2002), Proceedings of SPIE, Vol. 4426, pp. 90-93), it was demonstrated that laser technology can achieve lower or intentionally higher surface roughness on flat surfaces.

[0009] In a study titled "Optimization of Nd:YAG Laser Micro Turning Process Using Response Surface Methodology" (Kibria, G., Doloi, B., Bhattacharyya, B. (2012), International Journal of Precision Technology, Vol. 3, Issue 1), the effect of pulse speed and energy parameters on surface roughness was observed using a rotating cylindrical ceramic part made of alumina that was radially impacted by a Nd:YAG laser. In this setup, no drilling was used and the coverage was driven only by the part rotation speed of no more than 600 rpm. The part was radially impacted by nanosecond pulses. SUMMARY

[0010] It is an object of the present invention to provide a laser turning system that remedies the above-mentioned drawbacks and enhances the laser turning systems known in the art. In particular, the present invention proposes a laser turning system that is competitive compared to the known turning systems.

[0011] In a first aspect, a turning system according to the present invention comprises a rotating spindle for moving a material rod and a galvanometer scanner capable of emitting a femtosecond laser beam that scans the generated profile of the component to be machined in the material rod with an angle of incidence tangent to the material rod.

[0012] In the above-mentioned first aspect, the galvanometer scanner is configured to displace the focal point of the laser at a speed of 0.5 m / s or more or 10 m / s or more or 20 m / s or more and / or an acceleration of 5 m / s2or more or 500 m / s2or more or 5000 m / s2or more or 50000 m / s2or more.

[0013] In the above-mentioned first aspect, the galvanometer scanner is mounted on a translation axis that is orthogonal to the axis of the rotating spindle.

[0014] In the above-mentioned first aspect, the rotating spindle is capable of rotating at a speed of 20000 rpm or more or 50000 rpm or more or 100000 rpm or more.

[0015] In the above-mentioned first aspect, the laser turning system comprises a secondary spindle.

[0016] In the above-mentioned first aspect, the laser beam has a frequency of 50 kHz or more.

[0017] In the first aspect described above, the laser turning system comprises an automation module comprising a measuring element for measuring in real time at least one dimension of the component.

[0018] In the first aspect described above, the laser turning system comprises a module for servo-controlling the parameters of the laser and / or the displacement of the laser beam as a function of the measurements performed by the measuring element.

[0019] In the first aspect described above, the laser turning system comprises a rotary encoder configured to continuously know the angular position of the rotary spindle, in particular the absolute angular position of the rotary spindle.

[0020] In the first aspect described above, the laser turning system comprises a synchronization module configured to synchronize the pulses of the laser with the angular position of the rotary spindle.

[0021] In the first aspect described above, the laser turning system comprises a feeder. In a second aspect, a turning method according to the invention comprises using the turning system of the first aspect described above.

[0022] In a third aspect, a component according to the invention is obtained from the turning method of the second aspect described above.

[0023] In a fourth aspect, a timepiece according to the invention comprises the component of the third aspect.

[0024] In the fourth aspect described above, the timepiece can be a watch, in particular a wristwatch. BRIEF DESCRIPTION OF DRAWINGS

[0025] The drawings illustrate by way of example embodiments of a turning system according to the invention and embodiments of a timepiece according to the invention.

[0026] Figure 1 is a schematic view of an embodiment of a turning system according to the invention.

[0027] Figure 2 is a schematic view of a trajectory of a laser beam according to the invention.

[0028] Figure 3 is a schematic view of an embodiment of a timepiece according to the invention. DETAILED DESCRIPTION

[0029] The following description refers to Figure 1 An embodiment of a turning system 1 for producing a component is described below.

[0030] The system comprises:

[0031] - a rotary spindle 3 for moving the material rod 50; and

[0032] - a galvanometer scanner 12 capable of guiding the femtosecond laser beam along a trajectory that scans the generated profile of the part to be machined in the material rod. Preferably, the scanning is performed in the tangential direction of the material rod 50 or according to an angle of incidence that is tangent to the material rod 50.

[0033] More generally, the system comprises a module 2 for moving the material rod, in particular for rotating the material rod according to a first axis X. This module for moving the material rod comprises a main spindle 3 on the first axis X. Preferably, the main spindle 3 is rotatable at a speed of more than 20000 rpm or more than 50000 rpm or more than 100000 rpm. For example, the main spindle 3 is an electric spindle. Preferably, the main spindle 3 is equipped with a clamping chuck, in particular of the pneumatic type.

[0034] The moving module 2 preferably also comprises a secondary spindle 4 for rotating. This secondary spindle 4 allows the correction of the part when it is separated from the main spindle 3. The secondary spindle 4 allows rotation on the first axis X. Preferably, the secondary spindle 4 is rotatable at a speed of more than 20000 rpm or more than 50000 rpm or more than 100000 rpm. For example, the secondary spindle 4 is an electric spindle. Preferably, the secondary spindle 4 is equipped with a clamping chuck, in particular of the pneumatic type. In addition, the secondary spindle 4 is movable in translation on the first axis X with respect to the main spindle 3. For example, such a secondary spindle can perform a separation machining of the assembly to separate it from the rod. With traditional separation methods, the separation face of the assembly from the rod is usually subject to burrs when it is separated.

[0035] The moving module 2 also comprises elements 5 allowing the displacement of the main spindle 3 and of the secondary spindle 4 in a plane X-Y containing the first axis X and a second axis Y at right angles to the first axis X.

[0036] The system comprises elements 29 for generating the laser beam. The laser beam for performing the machining is a laser beam comprising light pulses having a pulse duration of between 100 fs and 10 ps. It can have a frequency of more than 50 kHz, that is to say emit pulses or impacts at a frequency of more than 50 kHz.

[0037] The scanner 12 is placed on the path of the laser beam between the output of the elements 29 for generating the laser beam and the part to be machined.

[0038] The galvanometer scanner 12 is an electromechanical device containing 1 to 3 axes of rotation and possibly axes of translation, on which optical elements of the mirror or lens type are mounted. Voltage-controlled actuators control the movement of these axes and are capable of producing extremely fast and accurate displacements of the laser beam on two or three axes. The galvanometer scanner 12 comprises focusing means capable of focusing the laser at a focal point. The fine management of the synchronization between the movement of the optical elements and the triggering of the laser impacts makes it possible to form a generator of revolution machined parts.

[0039] The galvanometric scanner is different from a polygon scanner which allows scanning in a single direction.

[0040] Preferably, the scanner 12 is arranged and / or configured to displace the focal point of the laser at a speed of more than 0.5 m / s or more than 10 m / s or more than 20 m / s. The scanner 12 is arranged and / or configured to displace the focal point of the laser at a speed of more than 5 m / s 2 or more than 500 m / s 2 or more than 5000 m / s 2 or more than 50000 m / s 2 or more than 50000 m / s

[0041] Advantageously, the scanner 12 is mounted to be able to move in translation along a third axis Z which is orthogonal to the first axis X and to the second axis Y. In other words, the scanner is mounted on a translation axis which is orthogonal to the first axis X. Thus, the galvanometric scanner can position the focal point of the laser beam at the desired point, in particular on a tangent lying on the horizontal median plane of the rod of material being machined.

[0042] The system advantageously comprises an automation module 6 which can control the machining method or the method for operating the system.

[0043] The automation module 6 comprises an element 7 for measuring at least one dimension, in particular the diameter, of the assembly in real time. The addition of this element is decisive for producing assemblies comprising diameters of a few tens of microns within a tolerance of about 1 micron.

[0044] Indeed, the diameter of the focused femtosecond laser beam is generally about 20 microns and the depth of field is the same amount.

[0045] In the machining method with radial incidence of the laser beam, the laser impacts hit the layer of material located under the direct ablation layer. This is due to the incompressible depth of field of the laser beam. This physical limitation leads to not being able to produce a revolution part with a diameter precision less than the order of magnitude of the size of the beam, i.e. 20 microns.

[0046] This limitation is overcome using a tangential incidence of the laser beam. The ablation is performed using only the edge of the Gaussian profile of the laser beam. In this particular case, successive laser impacts do not cause additional ablation. Thus, the precision of the diameter size is defined by the positioning precision of the laser beam and not by its size. The positioning precision of the laser beam itself is defined by the positioning precision of the scanner 12 and of the element 5 for displacing the spindle 3 on the axis Y and is about 1 micron.

[0047] The servo-control of the diameter dimension by the measuring element 7, which has a measurement accuracy of approximately 1 micron, combined with the tangential beam ablation method, makes it possible to produce turned parts on the profile generator with a precision of the same order of magnitude (i.e. 1 micron).

[0048] The automation module 6 also advantageously comprises a module 8 for servo-controlling the parameters of the laser and / or the displacement of the laser beam as a function of the measurements performed by the measuring element 7.

[0049] The automation module 6 drives the plurality of actuators of the system, including the main shaft 3 and / or the secondary main shaft 4 and / or the laser beam generation element 29. This control can in particular be performed as a function of the measured values of the dimensions of the part being machined. For example, the servo-control module 8 can servo-control the rotation speed of the main shaft 3 or of the secondary main shaft 4 as a function of the dimensions of the part to be machined, in particular the diameter of the part to be machined. Thus, for example, the speed of the main shaft and of the secondary main shaft can be varied as a function of the theoretical value of the diameter to be machined, so as to make the laser strike with the same width coverage (as a function of the rotation speed of the main shaft, of the diameter being machined and of the laser frequency). More generally, the speed of the main shaft and of the secondary main shaft can be varied as a function of the diameter and / or of the portion of the assembly in order to obtain a variable or constant coverage, so as to obtain a particular surface texture, for example with different surface textures on different portions of the assembly.

[0050] The measuring element 7 can be an optical micrometer.

[0051] In addition, the automation module 6 comprising the measuring element 7 can track the production in order to correct any deviations in the machining method. By acquiring data via the measuring element 7, it is possible to improve the repeatability of the machining of the assembly. By acquiring data via the measuring element 7, it is possible to achieve the final dimensions of the assembly with very high precision, which would not be possible without such servo-control, in particular because of the deviations in the machining and / or the very high rotation speed of the main shaft.

[0052] The automation module 6 advantageously comprises a rotary encoder 9 configured to continuously know the angular position of the main shaft, in particular the absolute angular position of the main shaft.

[0053] Furthermore, the automation module 6 advantageously comprises a synchronization module 10 configured to synchronize the pulses of the laser with the angular position of the main shaft.

[0054] It is thus possible to synchronize this angular position with the scans of the scanner. It is thus possible to envisage producing parts comprising surfaces that do not revolve on the first axis, for example surfaces with a pitch, teeth, radial boreholes, flat surfaces, grooves, surfaces with a non-circular cross-section, etc.

[0055] The system advantageously comprises a feeder 11. The feeder included in the system can simply automate the insertion of the material rod into the main spindle without performing a rotation of the secondary spindle. The material rod is then inserted into the space between the main spindle and the secondary spindle and is then pushed into the clamp of the main spindle by the secondary spindle.

[0056] A laser turning method, in particular a way of performing laser bar turning, is described hereafter.

[0057] The method can obtain a watch component from a material rod. The method comprises using the laser turning system previously described.

[0058] The displacement of the laser beam L is controlled by the activation of the galvanometer scanner 12. This allows the laser beam to be displaced very quickly. Consequently, the impact coverage of the laser beam on the part to be machined is reduced and the machining quality is higher. This coverage is defined as the ratio between (i) the surface area of the intersection of two successive impacts of the laser beam on the part and (ii) the surface area of one impact of the laser beam on the part.

[0059] The laser beam is preferably focused on a horizontal median plane X-Y of the part, which corresponds to a horizontal plane passing through the first rotation axis X of the main spindle. The beam is also oriented to be tangentially incident or substantially tangentially incident with respect to the rotating bar, that is to say oriented on or substantially on the third axis Z and displaced on a trajectory T following the desired final profile of the component, as shown in Figure 2

[0060] In this way, the material of the relevant radius of the part to be machined is completely ablated and no additional ablation is produced with continued laser impact. This does not happen in the case where the laser is not tangentially incident, in particular where the laser beam is radially incident. Indeed, in this hypothesis, additional impacts would lead to additional ablation.

[0061] Furthermore, in the case where the laser beam is tangentially incident, the material that is ablated is ejected in the direction away from the beam and does not return into the beam and interrupt it as in the case of radial incidence.

[0062] This configuration allows perfect control of the machining passes. In addition, the edge of the Gaussian profile of the beam comes into contact with the surface of the part to be machined. The energy applied to the surface of the part is below the ablation threshold, so the surface of the part is equivalent to having undergone a finishing pass, thus levelling the residual material.

[0063] ​Advantageously, the profile generating line of the part to be machined is produced by the system 6. During machining of the part, the focal point of the laser beam is displaced along the profile constituted by this line, along the trajectory T in the plane X-Y, by action of the galvanometer scanner 12. Furthermore, in order to carry out machining of the part, the part is rotated about the first axis X and is displaced in the plane X-Y, in particular on the second axis Y, by the elements 5, in particular using the movement module 2, so as to bring the generating line progressively closer to the first axis X. The different passes of the generating line produced by the laser beam each constitute one machining pass.

[0064] Implementation of the method described previously makes it possible to obtain an embodiment of an assembly, in particular a watch assembly 60, in particular a watch arbor. Preferably, this assembly has a diameter of less than 3 mm and / or a length of less than 15 mm.

[0065] Figure 3 An embodiment of a watch 100, in particular a watch, in particular a wristwatch, is shown. This watch comprises the watch assembly 60 described previously.

[0066] The laser machining technique makes it possible to overcome the tool wear described above, but also to provide the following advantages:

[0067] - the range of materials that can be machined is greatly widened, since it is no longer necessary to take into account the behaviour of the chips (in particular compared with bar turning steels traditionally containing sulphur as chip breakers).

[0068] - the cutting forces are negligible and the bar does not vibrate. Indeed, the frequency of the laser impacts can be servo-controlled so that the eigenmodes of the part being machined are never changed as the machining progresses.

[0069] - no lubricant is necessary, machining by femtosecond laser is athermal.

[0070] - hardening of the surface and / or texturing of the surface can be carried out at the same time as the machining.

[0071] In this document, the words "bar", "part" and "assembly" are used to designate an assembly at different stages of production. The word "bar" preferably designates the bar of material 50 before and at the start of the laser machining. The word "part" preferably designates the bar or assembly during the laser machining. The word "assembly" preferably designates the assembly 60 at the end of the laser machining and after the laser machining.

Claims

1. A laser turning system (1) for producing a watch component (60), the laser turning system comprising a rotary spindle (3) for moving a material bar and a galvanometer scanner (12) capable of emitting a femtosecond laser beam that scans the generated profile of the component to be processed in the material bar at an incident angle tangential to the material bar, wherein the laser turning system further comprises a sub-spindle (4) capable of correcting the material bar during laser processing when the material bar is separated from the rotary spindle (3) during laser processing, and capable of performing separation processing of the component to separate the component from the material bar.

2. The laser turning system according to claim 1, wherein, The galvanometer scanner is configured to focus the laser at a speed of 0.5 m / s or more, or 10 m / s or more, or 20 m / s or more, and / or 5 m / s. 2 or above 500m / s 2 or above 5000m / s 2 or above 50000 m / s 2 The above acceleration is used for displacement.

3. The laser turning system according to any one of the preceding claims, wherein, The galvanometer scanner is mounted on a translation axis (Z) orthogonal to the axis (X) of the rotating spindle (3).

4. The laser turning system according to claim 1 or 2, wherein, The rotating spindle can rotate at speeds of 20,000 rpm or higher, or 50,000 rpm or higher, or 100,000 rpm or higher.

5. The laser turning system according to claim 1 or 2, wherein, The laser beam has a frequency of 50 kHz or higher.

6. The laser turning system according to claim 1 or 2, wherein, The laser turning system includes an automation module (6) which includes a measuring element (7) for real-time measurement of at least one dimension of the component.

7. The laser turning system according to claim 6, wherein, The laser turning system includes a module (8) for servo control of the laser parameters and / or the displacement of the laser beam based on measurements performed by the measuring element.

8. The laser turning system according to claim 1 or 2, wherein, The laser turning system includes a rotary encoder (9) configured to continuously know the angular position of the rotary spindle.

9. The laser turning system according to claim 8, wherein, The angular position of the rotating spindle is the absolute angular position of the rotating spindle.

10. The laser turning system according to claim 8, wherein, The laser turning system includes a synchronization module (10) configured to synchronize the laser pulses with the angular position of the rotating spindle.

11. The laser turning system according to claim 1 or 2, wherein, The laser turning system includes a feeder (11).

12. A laser turning method for turning a watch assembly from a material bar, the method comprising using a laser turning system according to any one of the preceding claims.

13. A watch assembly (60) obtained by performing the laser turning method according to claim 12.

14. A clock (100) comprising a clock assembly (60) according to claim 13.

15. The clock (100) according to claim 14, wherein, The clock mentioned is a watch.

16. The clock (100) according to claim 14, wherein, The clock mentioned is a wristwatch.

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