CH718375A2 - Process for the laser treatment of a watch component aimed at blackening at least a portion thereof. - Google Patents

Abstract

The invention relates to a method for the laser treatment of a substrate (2) by means of a laser source (4, 8, 10) arranged to blacken at least a portion of the substrate (2) comprising the steps consisting in: putting in performs a first laser treatment operation, according to a first predefined set of parameters, to blacken the portion to be treated by creating microstructures and nanostructures, implement a second laser treatment operation, according to a second predefined set of parameters, to smooth the surface of the portion to be treated, implementing a third laser treatment operation, according to a third set of predefined parameters, to blacken the portion to be treated by recreating microstructures and nanostructures over essentially its entire surface.

Description

Technical area

The present invention relates to a process for the laser treatment of a metal substrate for a watch component, by means of a laser source intended to emit pulses of durations equal to or less than one picosecond and arranged to define a moving incident laser beam relative to the substrate and carry out a treatment of the latter to blacken at least a portion thereof selectively.

State of the art

[0002] Such methods of laser treatment of watch components are already known from the state of the art, and are advantageous in particular because they make it possible to dispense with the use of chromium, which is very interesting from the point of view of environmental view.

[0003] Thus, for example, patent application WO 2008/097374 A2 generally describes how the operating parameters (for example the fluence or the number of impacts of the laser beam on the same region of the substrate) implemented work to perform the laser treatment of a substrate influence the nature of structures formed on the surface of the substrate, and what is the impact on the appearance of the latter. Certain operating parameters described make it possible to blacken the surface of the portion of the substrate which is thus treated.

[0004] Furthermore, patent application EP 2825347 A1 describes another process for machining a watch component, more particularly for engraving it by means of a laser beam, the properties of which simultaneously make it possible to change the coloring of the component on the path of the laser beam, in particular to darken it. A main purpose of this process seems to reside in obtaining a satisfactory overall result in terms of visual appearance of the treated portion, that is to say both in terms of etching and coloring, while reducing the processing time of the watch components concerned, by implementing two operations in a single processing step. However, a careful visual examination of the background of an engraving made with this process makes it possible to identify microstructures due to the fact that these are relatively spaced from each other. Thus, the background of the blackened engraving does not appear as completely uniform.

Disclosure of Invention

[0005] A main object of the present invention is to propose an alternative method to the methods of treatment of watchmaking components by laser beam known from the prior art, the method according to the invention allowing the production of a black portion on the component treated watchmaker, with a good depth of black obtained and a very clean appearance, in particular a uniform surface of the treated portion, and therefore with a high perceived quality.

To this end, the present invention relates more particularly to a laser treatment method for a metal substrate for a watch component of the type mentioned above, characterized in that it comprises the steps consisting of: obtain a metal substrate comprising a portion to be treated, implement a first laser treatment operation aimed at scanning the portion to be treated with an incident laser beam, according to a first set of predefined parameters, suitable for blackening the portion to be treated by creating microstructures and nanostructures over essentially its entire surface, implement a second laser treatment operation aimed at scanning the portion to be treated with an incident laser beam, according to a second set of predefined parameters, different from the first set of predefined parameters and adapted to smooth the surface of the portion to be treated, by reduction of the roughness of the surface of the portion to be treated by at least 40%, preferably by at least 50%, implement a third laser treatment operation aimed at scanning the portion to be treated with an incident laser beam, according to a third set of predefined parameters, similar to the first set of predefined parameters and adapted to darken the portion to be treated by recreating microstructures and nanostructures over essentially its entire surface.

[0007] The substrate to be treated can be a watch component as such or only a portion of a watch component, either made in one piece with the rest of the component, or attached to the rest of the component before or after implementation of the method according to the invention, without departing from the scope of the latter.

[0008] Thanks to these characteristics, it is possible to blacken a portion to be treated with the obtaining of a deep and perfectly uniform black, thanks to the great finesse and the uniform distribution of the microstructures created. The method according to the invention makes it possible to carry out such a treatment with very precise control, therefore with good reproducibility. Indeed, the first laser treatment operation, aimed at blackening the portion to be treated, makes it possible to create a surface condition having a high capacity for absorbing the energy of the laser beam scanning the portion to be treated during the second operation. It is thus possible to obtain a new surface state, having a substantially gray coloring, perfectly suited to absorb the energy provided by the laser beam during the third treatment operation, aimed at blackening again the portion to be treated, with an improved qualitative result compared to the result obtained after implementation of the first operation.

[0009] Advantageously, provision can be made for the first set of predefined parameters to include a fluence value of between 0.05 and 0.35 J/cm<2>.

[0010] Alternatively or additionally, provision can advantageously be made for the first set of predefined parameters to include a longitudinal overlap rate value greater than or equal to 65% and strictly less than 100%, preferably between 65% and 85%.

[0011] Alternatively or additionally, provision can advantageously be made for the second set of predefined parameters to include a fluence value of between 0.15 and 1 J/cm<2>.

[0012] Alternatively or additionally, provision can advantageously be made for the second set of predefined parameters to include a longitudinal overlap rate value greater than or equal to 85% and strictly less than 100%, preferably greater than or equal to 90% and less than at 99%.

[0013] Alternatively or additionally, provision can advantageously be made for the third set of predefined parameters to include a fluence value of between 0.05 and 0.35 J/cm<2>.

[0014] Alternatively or additionally, provision can advantageously be made for the third set of predefined parameters to include a longitudinal overlap rate value greater than or equal to 65% and strictly less than 100%, preferably between 65% and 85%.

[0015]According to a preferred variant embodiment, provision can be made for the laser source to be arranged during the first operation and/or the third operation to emit laser pulses in "burst" mode, being distributed in successive groups of pulses, with a group period P, the pulses of a given group being emitted for 20 to 100% of the period P.

[0016] According to a preferred embodiment, when the portion to be treated is located in an etching previously made in the metal substrate and has an at least partially curved peripheral wall to connect the free surface of the metal substrate to the bottom of the etching, may advantageously provide that the method includes an additional step consisting in implementing a fourth laser processing operation aimed at scanning at least part of the peripheral wall with an incident laser beam, according to a fourth set of predefined parameters, different from the first, second and third sets of predefined parameters and adapted to darken the peripheral wall by creating microstructures and nanostructures over essentially its entire surface.

In this case, provision can advantageously be made for the fourth set of predefined parameters to include a fluence value of between 0.10 and 0.25 J/cm<2>.

[0018] In addition, provision can advantageously be made in this case, alternatively or additionally, for the fourth set of predefined parameters to include a longitudinal overlap rate value greater than or equal to 85% and strictly less than 100%, preferably greater than or equal to 90% and less than 99%.

According to a preferred embodiment, provision may be made for the substrate to comprise one or more of the materials taken from the group comprising: steels, including stainless steels, titanium, copper, brass, gold, silver, platinum, tungsten.

Brief description of the drawings

Other characteristics and advantages of the present invention will appear more clearly on reading the detailed description of a preferred embodiment which follows, made with reference to the accompanying drawings given by way of non-limiting example and in which : FIG. 1 represents a simplified block diagram of a laser source allowing the implementation of the method according to the present invention, and FIG. 2 represents a schematic cross-sectional view of a portion to be treated located in an engraving according to a preferred embodiment of the present invention.

Embodiment(s) of the Invention

[0021] FIG. 1 represents a simplified block diagram of an example of implementation of a method for machining a watch component according to a preferred embodiment of the present invention.

More specifically, the laser beam machining method according to the present invention aims to treat a metal substrate 2 for a watch component (not shown in its entirety), this metal substrate 2 advantageously absorbing at least partially the light of the beam laser at the wavelength of the laser beam used to perform the treatment, preferably between 500 and 1100 nm. Thus, in general, the method according to the invention may be implemented in relation to all kinds of materials capable of being machined by laser, and the substrate may comprise one or more of the materials taken from the group comprising: steels , including stainless steels, titanium, copper, brass, gold, silver, platinum, tungsten, by way of illustration not limitation.

[0023] The metal substrate 2 can directly be a watch component as such or only a portion of a watch component, either made in one piece with the rest of the component, or attached to the rest of the component, without leaving the framework of the invention.

[0024] Furthermore, provision may be made for the timepiece component to be directly visible on the corresponding timepiece, being located outside the box or inside but being visible through a glass, or it may be housed inside the box and only be at least partially visible once the latter has been opened.

In general, to carry out the machining according to the invention, a first laser source 4 is used arranged, in connection with an optical device, to define an incident laser beam 6 intended to carry out the desired treatment on the metal substrate. 2 of the watch component, that is to say a treatment aimed at darkening at least a predefined portion thereof.

More specifically, the optical device may comprise, by way of non-limiting illustration, at least one first mirror 8 arranged at the output of the first laser source 4, the latter typically being able to be associated with a galvanometric head 10 comprising a set of mirrors additional, here schematized in the form of two mirrors 12 and 14, making it possible to control the direction of propagation of the incident laser beam 6 and to cause the latter to be scanned in order to carry out the treatment required on the metallic substrate 2, according to the invention . The optical device also comprises, advantageously, a focusing device 16, schematized here in the form of a converging lens to define a desired focusing plane for the incident laser beam 6. Alternatively or in addition, it is possible to provide a movable support for the metal substrate 2, to be able to move it relative to the incident laser beam, without departing from the scope of the present invention.

Advantageously, the first laser source 4 can be associated with the optical device directly inside a multi-axis CNC machine.

When a numerically controlled machine is used, it is advantageously programmed to control the incident laser beam 6 and its movements appropriately to process the metal substrate 2 along a predefined path. The numerically controlled machine typically comprises a control device, for this purpose, taking into account the geometry of the metal substrate 2 and of the treatment to be carried out, and defining the scanning speed of the surface to be treated by the incident laser beam 6 as well as the amplitude of movement of the beam and the generation of the laser pulses, so as to obtain the desired result.

Advantageously, the first laser source is chosen such that it defines an incident laser beam 6 composed of light pulses whose duration is of the order of magnitude of a picosecond or shorter. Moreover, the optical device is preferably arranged in such a way that the incident laser beam 6 has a focal plane located substantially at the surface of the metal substrate 2.

[0030] Typically, to treat substrates such as those mentioned above, one can choose a first laser source 4 such that the incident laser beam 6 is composed of pulses having an average frequency between 1 and 200 kHz, and such that it has an average power of between 1 and 10 Watts. Furthermore, provision can advantageously be made for the incident laser beam to have a pulse energy of between 2 and 10 μJ and for the speed of the relative displacement between the incident laser beam and the substrate to be between 10 and 300 mm/s. These different parameters can advantageously be refined to take into account the exact composition of the metal substrate.

Preferably, the laser treatment according to the present invention is carried out by appropriate programming of the laser source (in its broad sense, that is to say by including the optical device and / or a mobile support allowing to 'induce a relative displacement between the incident beam and the metal substrate), in other words by defining at least one vector, preferably a plurality of vectors, each of which is delimited by a starting point and an ending point and composed of a path to be traveled by the incident laser beam 6 relative to the metal substrate 2, and a series of impacts of the incident laser beam 6 along the path.

[0032] The method according to the present invention relates equally to the implementation of single passes or multiple passes, possibly crossed ("cross-hatch").

[0033] FIG. 2 represents a schematic cross-sectional view of a portion of the metal substrate 2, illustrating the implementation of a method for treating this substrate according to a preferred embodiment of the present invention.

According to this illustrative and non-limiting preferred embodiment, the metallic substrate 2 has an etched portion, the corresponding etching 20 being carried out prior to the implementation of the treatment method according to the invention. The laser treatment method according to the present invention can of course be implemented directly on the free surface of a substrate which would not be etched beforehand, without thereby departing from the scope of the invention as defined by the claims.

[0035] The etching can for example be carried out by laser or by chemical etching. When it is produced by a conventional laser engraving process, the engraving typically has straight flanks connected to the bottom of the engraving by junctions substantially at right angles. It is possible to introduce a time shift between the start of the displacement of the laser beam, at the start of each engraving vector, and the start of the emission of the laser pulses, to curve the junction between the initial flank and the bottom of the engraving. Similarly, it is possible to stop the emission of laser pulses before the laser beam has reached the end of an engraving vector to curve the junction between the final flank and the bottom of the engraving, as shown in figure 2. An etching carried out by chemical etching also presents a profile similar to that illustrated in figure 2.

[0036] In accordance with the present invention, provision is made for the method of laser treatment of the metallic substrate 2 to comprise the steps consisting in: implement a first laser processing operation aimed at scanning the portion to be processed, marked with the letter A in FIG. 2, with an incident laser beam, according to a first set of predefined parameters, adapted to darken the portion A to be processed in creating microstructures and nanostructures over essentially its entire surface, implement a second laser treatment operation aimed at scanning the portion A to be treated with an incident laser beam, according to a second set of predefined parameters, different from the first set of predefined parameters and adapted to smooth the surface of the portion A to be treated , by reducing the roughness of the surface of portion A to be treated by at least 40%, preferably by at least 50%, implement a third laser processing operation aimed at scanning the portion A to be processed with an incident laser beam, according to a third set of predefined parameters, similar to the first set of predefined parameters and adapted to darken the portion A to be processed by recreating microstructures and nanostructures over essentially its entire surface.

Preferably, the first set of predefined parameters includes a fluence value of between 0.05 and 0.35 J/cm<2>.

[0038] Alternatively or additionally, the first set of predefined parameters preferably includes a longitudinal overlap rate value greater than or equal to 65% and strictly less than 100%, preferably between 65% and 85%.

Furthermore, the second set of predefined parameters preferably includes a fluence value between 0.15 and 1 J/cm<2>, and a longitudinal overlap rate value greater than or equal to 85% and strictly less than 100% , preferably greater than or equal to 90% and less than 99%.

[0040] Furthermore, the third set of predefined parameters preferably includes a fluence value between 0.05 and 0.35 J/cm<2>, and a longitudinal overlap rate value greater than or equal to 65% and strictly less than 100% , preferably between 65% and 85%.

When the portion A to be treated is located in an engraving and has an at least partially curved peripheral wall to connect the free surface of the metallic substrate 2 to the bottom of the engraving, as illustrated in FIG. the method comprises an additional step, consisting in implementing a fourth laser processing operation aimed at scanning at least part of the peripheral wall (the whole of the peripheral wall being identified by the letters B in FIG. 2), with an incident laser beam, according to a fourth set of predefined parameters, different from the first, second and third sets of predefined parameters and adapted to darken the peripheral wall by creating microstructures and nanostructures over essentially its entire surface.

According to a preferred embodiment, the fourth set of predefined parameters includes a fluence value of between 0.10 and 0.25 J/cm<2>.

[0043] In addition, provision can advantageously be made in this case, alternatively or additionally, for the fourth set of predefined parameters to include a longitudinal overlap rate value greater than or equal to 85% and strictly less than 100%, preferably greater than or equal to 90% and less than 99%.

Thanks to this additional operation, a relatively uniform black appearance is obtained for the treated portion of the metal substrate 2, both at the level of the bottom of the engraving and of its sides, which gives it an appearance of a very high quality level. raised.

[0045] In general, the laser source is preferably programmed in such a way that the lateral coverage rate is between 50 and 98% during the implementation of the first three processing operations of the bottom of the engraving (or of the free surface of the substrate if applicable). Typically, a single pass should be sufficient to process the peripheral wall B of the etch, but a similar side coverage rate can be implemented when multiple passes are required.

According to a preferred implementation variant of the first and third operations aimed at creating microstructures and, above all, nanostructures, a “burst” mode of the laser source 4 is preferably used. laser typically emits pulses of low energy, with a natural frequency Fosc, filtered to select pulses at a frequency Fpp which is an integer quotient of the natural frequency Fosc. These pulses are generally amplified thanks to the pumping effect, by the association of another laser source making it possible to increase the energy of the pulses thus obtained. These pulses can then be split, in burst mode, into groups of pulses of reduced energy, of frequency Fpp, the pulses within each group having a frequency Fosc. Thus, the burst mode makes it possible to split each pulse of energy E into groups of N pulses, each of which has an energy E/N. It is then possible to emit groups of pulses of reduced energy with a frequency F which is an integer quotient of the group frequency Fpp. Thus, during a period P=1/F, it is possible to transmit a maximum of R groups of pulses of reduced energy, R being equal to P/Ppp, with Ppp=1/Fpp.

The Applicant has found, during its experimental tests, that a time distribution of the energy transmitted to the substrate makes it possible to improve the quality of the black treatment carried out.

[0048] Consequently, the use of the burst mode proves to be advantageous for distributing the energy of a single pulse in the form of a group of pulses of reduced energy (the sum of which corresponds to the energy of the single pulse).

The burst mode can be modeled more finely according to requirements, by defining the number of groups of pulses emitted during each period P, with the upper limit equal to R as described above. When the number of groups of pulses is less than R, it is understood that each period P comprises a certain number of groups of pulses then a waiting period, without a pulse, until the end of the period, before the start of the following period. Thus, in comparison with the use of pulses of period P of high energy, such a burst mode makes it possible to spread the supply of the same quantity of energy to the substrate over a fraction of the same period P, instead of do so over the duration of a single pulse, while optionally preserving a rest delay to the material.

Finally, the Applicant has found that a distribution of the pulses over 20 to 100% of the duration of the period P makes it possible to obtain a result of better quality, including when each group of pulses is composed only with a single pulse.

It will be noted that the implementation of the burst mode involves a variation in the longitudinal overlap rate since the emission of the laser pulses responds to two different periods, a longer period defining the times at which groups of pulses are emitted, and a shorter period separating two successive pulses within the same group of pulses.

Thus, for example, with Fpp=1823 kHz and a relative displacement speed between the laser beam and the substrate of 50 mm/s, a distance of 0.0275 μm is obtained between two successive impacts, i.e. a rate of longitudinal overlap greater than 99% with an impact diameter of around 40 µm. However, when the working frequency of the laser beam F is fixed at 5 kHz, a distance between two successive impacts of 10 μm is obtained for the same relative displacement speed, ie a longitudinal overlap rate of only 75%. By implementing a burst mode, a different result is still obtained. By way of example, by setting N=95, the laser source emits groups of 95 pulses at a frequency of 5 kHz, the frequency of the pulses in each group being 1823 kHz. As a result, during each period of 200 µs (corresponding to the frequency F of 5 kHz), there is a first phase during which the 95 pulses are emitted at the frequency of 1823 kHz, i.e. for 52.25 µs, then a second phase extending until the end of the 200 μs period, during which no pulse is emitted. In this case, the longitudinal overlap rate is greater than 99% during the first phase, while it is rather around 80% during the second phase.

[0053] Those skilled in the art will not encounter any particular difficulty in selecting operating parameters of the laser source (in particular those for implementing a possible burst mode) according to their own needs, of the laser source that he has at his disposal, or the nature of the substrate to be treated.

The implementation of the present invention is not limited to a timepiece component forming part of the casing of a timepiece. Indeed, any timepiece component can allow the implementation of the present invention to confer a distinctive character on the timepiece component and therefore on the corresponding timepiece. A person skilled in the art will not encounter any particular difficulty in adapting the present teaching to the manufacture of watch components for coverings or of the watch movement.

The foregoing description sets out to describe a particular embodiment by way of non-limiting illustration and, the invention is not limited to the implementation of certain particular characteristics which have just been described, such as the nature of the watch component or the material in which it is made.

Claims (12)

1. Method of laser treatment of a metal substrate (2) for a watch component, by means of a laser source (4, 8, 10) intended to emit pulses of duration equal to or less than one picosecond and arranged to define a Incident laser beam (6) moving relative to said substrate (2) and processing the latter to blacken at least a portion (A) thereof selectively, characterized in that it comprises the steps consisting in: – obtain a metal substrate (2) comprising a portion to be treated, – implement a first laser processing operation aimed at scanning said portion (A) to be processed with an incident laser beam (6), according to a first set of predefined parameters, adapted to darken said portion (A) to be processed by creating microstructures and nanostructures over essentially its entire surface, – implement a second laser treatment operation aimed at scanning said portion (A) to be treated with an incident laser beam (6), according to a second set of predefined parameters, different from said first set of predefined parameters and adapted to smooth the surface of said portion (A) to be treated, by reducing the roughness of said portion to be treated (A) by at least 40%, preferably by at least 50%, – implement a third laser processing operation aimed at scanning said portion (A) to be processed with an incident laser beam (6), according to a third set of predefined parameters, similar to said first set of predefined parameters and adapted to darken said portion (A) to be processed by recreating microstructures and nanostructures over essentially its entire surface. 2. Method according to claim 1, characterized in that said first set of predefined parameters includes a fluence value of between 0.05 and 0.35 J/cm2. 3. Method according to claim 1 or 2, characterized in that said first set of predefined parameters includes a longitudinal overlap rate value greater than or equal to 65% and strictly less than 100%, preferably between 65% and 85%. 4. Method according to one of the preceding claims, characterized in that said second set of predefined parameters includes a fluence value of between 0.15 and 1 J/cm<2>. 5. Method according to one of the preceding claims, characterized in that said second set of predefined parameters includes a longitudinal overlap rate value greater than or equal to 85% and strictly less than 100%, preferably greater than or equal to 90% and less than 99%. 6. Method according to one of the preceding claims, characterized in that said third set of predefined parameters includes a fluence value of between 0.05 and 0.35 J/cm<2>. 7. Method according to one of the preceding claims, characterized in that said third set of predefined parameters includes a longitudinal overlap rate value greater than or equal to 65% and strictly less than 100%, preferably between 65% and 85% . 8. Method according to one of the preceding claims, characterized in that during said first operation and/or said third operation, said laser source (4, 8, 10) is arranged to emit laser pulses in mode „ burst“, by being divided into successive groups of pulses, with a group period P, said pulses of a given group being emitted during 20 to 100% of said period P. 9. Method according to one of the preceding claims, said portion (A) to be treated being located in an engraving (20) previously made in said metal substrate (2) and having a peripheral wall (B) at least partially curved to connect the free surface of said metal substrate (2) at the bottom of said engraving (20), characterized in that it comprises an additional step consisting in implementing a fourth laser treatment operation aimed at scanning at least part of said peripheral wall ( B) with an incident laser beam (6), according to a fourth set of predefined parameters, different from said first, second and third sets of predefined parameters and adapted to darken said peripheral wall (B) by creating microstructures and nanostructures on essentially all its surface. 10. Method according to claim 9, characterized in that said fourth set of predefined parameters includes a fluence value of between 0.10 and 0.25 J/cm2. 11. Method according to claim 9 or 10, characterized in that said fourth set of predefined parameters includes a longitudinal overlap rate value greater than or equal to 85% and strictly less than 100%, preferably greater than or equal to 90% and less than at 99%. 12. Method according to one of the preceding claims, characterized in that said metal substrate (2) comprises one or more materials taken from the group comprising: steels, including stainless steels, titanium, copper, brass , gold, silver, platinum, tungsten.