CH711914A2 - Process for producing a carbon fiber watch case and a carbon fiber watch case - Google Patents

Abstract

The present invention relates to a method for manufacturing a carbon fiber watch case comprising the steps of: a) forming an upper piece, a bottom piece, two side pieces and an inner piece (15) made of molding carbon fiber prepregs (10) between a forming tool (T5) and a compression counterpart (C5) complementary to a mold (M5), the inner part (15) defining a central bore for the middle part watch case comprising a net, and preferably a bezel, on an inner surface of the inner piece (15) during molding thereof, and b) assembly of the upper piece, the lower piece and the two side pieces around an outer surface of the inner piece (15) with additional carbon fiber prepregs interfaced with said upper piece, bottom piece, two side pieces and the inner piece (15) and molding of these to form a single molded carbon fiber watch case assembly. The invention also relates to a carbon fiber watch case comprising a caseband comprising an internal thread formed integrally, and preferably a bezel formed integrally.

Description

Description TECHNICAL FIELD [0001] The present invention relates to the field of watchmaking. In particular, it relates to a method for manufacturing a carbon fiber watch case and a carbon watch case obtained with this method.

STATE OF THE ART [0002] The use of fiber reinforced materials for making watch cases and / or other consumer articles is very well known in the art. In particular, JP 60 125 583 A discloses a process for manufacturing parts of a watch case from prepregs of fiber-reinforced polymeric materials and watch cases comprising these reinforced portions. However, this document only teaches the manufacture of watch case parts and says nothing about the manufacture of a watch case made entirely from a carbon fiber material.

[0003] EP 2 805 066 A2 further discloses a process for molding articles of polymeric composite material comprising reinforcing fibers in a polymeric matrix material. Surface characteristics are created during hot molding of the polymeric composite material to form the article, and the surface features include polymeric matrix material and reinforcing fibers therein. The molding process involves placing the composite material in a mold and molding the composite material using bladder inflation molding to push the reinforcing fibers into the surface feature of a cured portion of a mold.

Although bladder inflation molding works very well for molding polymeric materials into articles of simple, regular shapes, it is rather unsuitable for molding articles of complex shapes made entirely of fiber-reinforced materials because that it can not guarantee the simultaneous and homogeneous application of pressure from the bladder to all sides and all parts of the article to be molded, such as shoulders, threads and horns in a housing of watch, thereby creating parts of lesser mechanical strength than the others, which is unacceptable.

An object of the invention is thus to overcome at least partially some of the disadvantages mentioned above of the prior art, to obtain the manufacture of carbon fiber watch cases having shapes and characteristics identical to those metal-based watch cases, in particular having a thread integrally formed in the middle of the watch case without the need for any metal insert to ensure the waterproof assembly of a case back on the build.

PRESENTATION OF THE INVENTION [0006] Accordingly, a first object of the invention relates to a method for manufacturing a carbon fiber watch case comprising the steps of: a) forming an upper piece, a lower piece , two side pieces and an inner part by molding carbon fiber prepregs between a forming tool and a compression counterpart complementary to a mold for each piece, the inner part defining a central bore for the middle part watch case comprising a net, and preferably a bezel for supporting a glass, on an internal surface of the inner part when molding it, and b) assembling the upper part, the lower part and two side pieces around an outer surface of the inner part with additional carbon fiber prepregs interfaced with said upper part, lower part A pair of side pieces and the inner piece and molding thereof to form a single molded carbon fiber watch case assembly.

The two-step process of the invention is particularly advantageous in that it comprises molding each part (or part) of the watch case individually from pre-impregnated carbon fibers so that each of these parts has optimum mechanical strength due to the optimum orientation of the reinforcing carbon fibers in each individual part, and also thanks to the relatively simple shape of each individual part, which does not require complex mold shapes and therefore does not require does not require the machining of the parts for their assembly in the second step, nor for the subsequent assembly of the watch elements in and on the watch case. Indeed, the geometry of the individual parts of the watch case molded in the first step of the process is essentially their final geometry, with little need, if any, for further improvement when mounting the watch elements in the housing of shows.

Once the individual parts of the watch case are molded individually, they are even easier to assemble with each other in the second stage with additional prepregs added at the interfaces between the pieces to bind them to each other. others in the second molding stage. Again, the final watch case product obtained after the second molding step requires little machining, only the excess material to be removed at the joints between the individual pieces joined together.

A watch case of integral carbon fiber material is thus obtained using a very simple manufacturing process, although efficient and cost-effective.

[0010] According to the invention, in step a) the molds are heated for at least about 30 minutes at a temperature of at least 130 ° C to allow the prepregs to cure.

According to the invention, in step a) each of the upper piece, the lower piece, the two side pieces and the inner piece is individually formed in a custom mold by depositing and adjusting the prepregs on forming tool and compressing them on said forming tool with the complementary compression counterpart during molding.

According to the invention, in step a) a pressure of at least 5 bars is applied to the prepregs and the forming tool by the complementary compression counterpart. It has been found that this pressure helps to ensure the proper curing and forming of the carbon fiber prepregs while avoiding the formation of bubbles or wrinkles in the individual molded parts, which could change the mechanical strength of these parts.

Advantageously, in step a) the forming tool and the complementary compression counterpart of each mold are constrained by an assembly. The use of an assembly is particularly preferred to ensure the application of a correct and constant pressure on the prepregs in the molds during their heating.

According to the invention, the forming tool is made of a heat resistant material, preferably a metal or a metal alloy, and preferably the complementary compression counterpart is made of silicone rubber. .

Advantageously, the pressure is applied to the forming tool and the pre-impregnated by the thermal expansion of the complementary compression counterpart during the heating of the molds.

It has been found that the silicone rubber counterparts for the molding of the individual part are particularly advantageous in that they extend homogeneously during heating in all the dimensions of the space, thereby applying uniform pressure on the prepregs in the mold.

Advantageously, the tool for forming the mold to form the inner part comprises a cylindrical shutter comprising a thread on an outer surface thereof, and preferably a shoulder to form a bezel in said inner part.

Advantageously, the complementary compression counterpart is removed from the forming tool between step a) and step b).

According to the invention, step b) comprises the following sub-steps: - adjustment of a band of additional carbon fiber prepregs around the inner part held on its forming tool, and - d inserting additional carbon fiber prepregs into the recesses arranged for this purpose in the forming tool for the upper part or in the forming tool for the lower part to form the horns of the watch case, and - positioning and adjusting the forming tools of each mold supporting the upper piece, the lower piece and the individual side pieces molded in step a) relative to each other and around the forming tool of the inner piece of so that said upper piece, lower piece and side pieces held on their forming tool interfere with the additional carbon fiber prepregs on the piece this internal and in the recesses, and - keeping all the forming tools together by mounting, and - heating the forming tools in the assembly at a temperature of at least 130 ° C for at least 30 minutes to allow the additional prepregs to cure and mold the top piece, bottom piece, and individual side pieces and the inner piece together to form a single molded carbon fiber watch case assembly.

Advantageously, the substeps consisting of the insertion of additional carbon fiber prepregs into the recesses comprise, for each recess: the cutting of the individual prepreg pieces and the gluing thereof the others for forming a stack of prepregs having first and second ends, and - inserting a first end of the prepreg stack into the recess so that said end is oriented toward the inner part, and - the folding the stack of prepregs on itself so that the second end thereof is also directed towards the inner part and the fold is oriented outwards.

[0021] Advantageously, after molding, the assembly and the forming tools are removed from the single molded carbon fiber watch case assembly.

Advantageously, after step b) the excess material of the molded single carbon fiber watch case assembly is removed and the horns are drilled to form through holes designed to receive a bar to secure a bracelet to the watch case.

A second object of the invention relates to a carbon fiber watch case comprising a middle part comprising an internal thread formed in one piece, and preferably also a bezel.

Advantageously, the carbon fiber watch case of the invention further comprises horns extending outwards from the middle part and in one piece with it, the horns comprising through holes designed to receive a bar for attaching a bracelet to the watch case.

BRIEF DESCRIPTION OF THE DRAWINGS Further details of the invention will now be described in connection with the figures, in which: FIG. 1 illustrates a watch case according to the invention in perspective view; figs. 2 to 4 respectively show a right side view, a top view and a bottom view of the watch case of the invention as shown in FIG. 1; figs. 5A and 5B illustrate a mold for making the side pieces of a watch case according to the process of the invention; fig. Figure 6 illustrates a mold for making an upper part of a watch case according to the process of the invention; fig. Figure 7 illustrates a mold for making a lower part of a watch case according to the process of the invention;

fig. 8 illustrates a mold for making an inner part of a watch case according to the process of the invention; fig. 9 illustrates the steps of preparation before a second step of molding a watch case according to the process of the invention; figs. 10 and 11 respectively illustrate a mold as used for a second step of molding a watch case according to the process of the invention.

Embodiments of the Invention [0026] The present invention provides a novel process for manufacturing a unitary watch case 1 as shown in FIG. 1, which consists entirely of a hot-molded composite material, particularly epoxy resin-impregnated carbon fiber prepreg sheets, commonly referred to as prepreg (singular) or prepregs (plural) throughout the present disclosure.

The watch case 1 of the invention comprises, as shown in FIGS. 1.3 and 4 in particular, a substantially tubular middle section 2 of circular section comprising, on an upper inner face, a telescope 21, and on a lower inner face, a thread 22, respectively for adjusting and assembling in a substantially sealed manner water and pressure-resistant, a glass and a caseback, not shown in the figures. The watch case 1 further comprises, on its outer surface and extending outside on the opposite sides, two pairs of horns 3 for attaching a bracelet by means of bars (not shown) inserted in holes 4 drilled to through the ends of the horns 3 as shown in FIGS. 1 and 2 in particular.

Finally, as shown in Figs. 1 and 2, the middle part 2 of the watch case 1 preferably comprises one or more recesses 5 and through holes 6 machined on at least one side of the middle part 2 between the opposite horns 3 to allow the insertion and positioning of buttons. pushers and other time setting members for the watch.

According to the invention, the watch case 1 consists entirely of a composite material reinforced with carbon fibers, with the thread 22 and the bezel 21 in the internal lateral face of the middle part 2 formed integrally of the material. composite during the hot molding of said composite material and without any machining. This integral formation of the bezel 21 and the net 22 provides a very precise geometry for the middle part 2 in a repeatable way and at a very low cost due to the absence of a necessary machining after the molding. This is further advantageous for the subsequent assembly of a glass and a case back for the construction of a watch using the watch case 1 of the invention since these can be mounted on the case. watch case 1 using standard seals and without intermediate pieces or metal adjustment rings, thus ensuring excellent water tightness and resistance to pressure.

The watch case 1 of the invention is manufactured according to a 2-step process described hereinafter with reference to FIGS. 5 to 11.

The method according to the invention essentially comprises the steps of: a) forming an upper piece 11, a lower piece 12, two lateral pieces 13, 14 and an inner piece 15 by the molding of carbon fiber prepregs between a forming tool T1, 12, T3, T4, T5 and a complementary compression counterpart C1, C2, C3, C4, C5 of a custom mold M1, M2, M3, M4, M5 for each of the individual pieces 11, 12, 13, 14, 15, the inner piece defining a central bore for the middle of the watch case comprising a thread and preferably a shoulder on an inner surface of the inner piece during molding thereof, and b) assembling the upper piece, the bottom piece and the two side pieces around an outer surface of the inner piece with additional carbon fiber prepregs interfaced with said upper piece, piece lower, two side parts and the inner piece and molding thereof to form a single molded carbon fiber watch case assembly.

In the first step a), the parts or elementary parts are manufactured according to the invention from components 7, 8, 9, 10 made of composite material consisting of pre-impregnated carbon fibers which are impregnated with an epoxy resin. reactive, commonly referred to as "prepregs", which are cut into a suitable shape determined by the shape of the watch case 1 to be made from the sheets and / or strips of prepreg material. Examples of prepregs suitable for carrying out the invention are commercially available from the German manufacturer Krem-pel-Group under the reference KGBX 0909 or from the German manufacturer SGL Group under the reference SIGRAPREG® C W200-Tw2 / 2E323 - 45% .

The prepreg components 7, 8, 9, 10 cut are arranged on a forming tool T1, T2, T3, T4, T5 corresponding molds and covered with a compression counterpart C1, C2, C3, C4 , C5 respectively of a shape complementary to the corresponding forming tool and designed to homogeneously press the prepreg components 7, 8, 9, 10 on the forming tool T1, T2, T3, T4, T5 during the first step of molding the process of the invention.

The shape of the upper part 11, the lower part 12 and the two side parts 13, 14 is determined by the watch manufacturer according to the design of the watch case 1 selected. Consequently, the corresponding molds M1, M2, M3 and M4 and in particular the forming tool T1, 12, 13, 14 thereof can vary significantly and must be adapted to the design of the watch case 1. In a somewhat opposite manner, the dimensions of the inner part 15 may vary, but it must generally remain in the standard formally as a substantially tubular part defining a central bore for the middle part 2 of the watch case comprising at least one thread on a lower internal surface obtained during molding thereof, and at least one shoulder on a substantially greater internal surface to form a telescope 21 of the middle part 2. To allow this formation of the telescope 21 and the thread 22 in the inner part 15,1 'forming tool T5 comprises a cylindrical shutter comprising a thread on an outer surface thereof and a shoulder around which the strip material impregnated 10 is wound to form the inner part 15.

The forming tools T1, T2, T3, T4, T5 molds M1, M2, M3, M4, M5 are preferably made of a hard heat resistant hard metal material such as cast stainless steel and machined to include a form of molding in the specific form of the part 11,12,13,14,15 of the watch case 1 for the molding of which it is dedicated. The compression counterparts C1, C2, C3, C4, C5 of each mold M1, M2, M3, M4, M5 consist of a substantially soft, deformable and expandable material such as silicone rubber, a preferable material being preferably marketed under the name Neukasil RTV 20, by the German manufacturer Altropol Kunststoff GmbH.

Once the prepreg components 7, 8, 9, 10 are deposited on the forming tool T1,12,13,14,15 of each of the individual molds M1, M2, M3, M4, M5, they are covered with a flexible protective sheet (not shown in the figures for the sake of clarity) and pressed against the forming tool by means of the complementary compression counterpart C1, C2, C3, C4, C5 corresponding. Finally, each of the molds M1, M2, M3, M4, M5 is locked using a mounting, which is not shown either in the figures, designed to constrain the counterpart C1, C2, C3, C4, C5 on the forming tool T1, T2, T3, T4, T5 of the molds M1, M2, M3, M4, M5 to guarantee the correct compression on the prepreg components 7, 8, 9, 10 by the expansion of the material of the counter- parts during hot molding.

When all the individual molds M1, M2, M3, M4, M5 are locked in their assembly, they are then fired at a temperature of at least 130 ° C for at least 30 minutes to allow the resin components of prepregs to bake and harden into the shape given by the respective molds M1, M2, M3, M4, M5. Preferably, the baking of the prepregs / heating of the molds is carried out using infrared heating, which allows a homogeneous distribution of heat in the molds, both in the forming tool and in the compression counterparts. .

After cooking, the molds M1, M2, M3, M4, M5 and their assemblies are allowed to cool to room temperature and then the counterpart C1, C2, C3, C4, C5 of each mold is removed from the forming tool T1, T2, T3, T4, T5 as well as the protective sheet of the now-molded carbon fiber reinforced part 11, 12, 13, 14, 15 of composite material, which is based on the tool of forming.

At this point, the molded parts 11, 12, 13, 14, 15 of composite material are then prepared for the second and final molding step without removing them from forming tools T1, T2, T3, T4, T5 molds M1, M2, M3, M4, M5 individual and without machining to remove excess material from castings.

The preparation for the second molding step b) comprises a plurality of sub-steps, a first of which consists in depositing and arranging additional prepreg components on parts of the moldings 11, 12, 13, 14, 15 so as to provide a bonding material identical to that of the molded parts themselves to allow their assembly in the second molding step of the process of the invention.

As shown in FIG. 9, at least one additional prepreg 16 is added specifically around the circumference of the inner part 15 molded on the mold forming tool T5 of the mold M5 to allow assembly of the upper, lower and side pieces 11, 12, 13, 14 on the inner part 15 in the second molding step to form the middle part 2 of the watch case 1.

In addition, at a second substep, specially prepared prepreg components 17 are inserted into recesses 18 arranged for this purpose on the forming tool T1 for the upper part 11 and / or the forming tool. T2 for the lower part 12 for the formation of the horns 3 of the watch case 1 on the middle part 2 in the second molding step. These prepreg components 17 act to assist in bonding the various parts of the watch case to each other, and also as filler material so as not to leave cavities in the structure. However, if desired, cavities may be left in the structure of the watch case.

The prepreg components 17 specially prepared are advantageously constituted by multiple prepregs stacked on each other, preferably between about 5 and 15 pieces of prepregs depending on the shape of the watch case 1 and its components. horns. These layered prepreg components 17 have a substantially rectangular shape and they are inserted into the recesses 18 so that a first end is brought into abutment against the inner part 15 and the second end is then folded on this first end in abutment against the inner part 15 also so that a fold 19 extends outwardly from the inner part 15 between the two ends of the prepregs 17 in layers.

This particular arrangement of the layered prepregs 17 is intended to produce tensile resistant horns 3 made integrally of a composite material and anchored to the middle part 2 of the watch case 1. More specifically, the prepreg components 17 are assembled so that the carbon fibers in each layer thereof extend in the longitudinal direction of the components 17. This orientation of the fibers in the prepreg components 17 results in the fibers forming a loop or a fold along the the entire length of the horns 3, starting from the middle at one end of the prepregs 17 and back to the middle at the other end of the prepregs 17. This folded orientation of the fibers in the horns 3 contributes significantly to the resistance of the horns 3 to the tensile forces at their free ends where the bars to fix a bracele t are inserted in holes 4 as shown in Figs. 1 and 2. Indeed experiments have shown that it is not necessary to provide metal bushings in the holes 4, since the composite material has a sufficient mechanical strength to allow direct interaction with the ends of the bars.

As can be seen in FIG. Also, the additional prepregs 17 are positioned in the recesses 18 of the forming tool T1 when the forming tool T5 of the mold M5 for the inner part 15 with said inner part 15 thereon inserted in a corresponding through hole. arranged in said forming tool T1 for this purpose as will be better understood below from the description of the second molding step of the process of the invention.

With the additional prepregs 16, 17 in place as described above, the second molding step b) of the process of the invention then comprises, at a third substep, the assembly of the upper part 11, the lower part 12 and the two lateral parts 13, 14 around an outer surface of the inner part 15 by means of the additional prepregs 16, 17 in a modular mold M6.

The modular mold M6 is formed by positioning and adjusting the forming tools T1, T2, T3, T4 used in the first step a) with the corresponding individual pieces 11, 12, 13, 14 on them one after the other. relative to the others and around the forming tool T5 of the inner part 15 so that said upper part 11, lower part 12 and side parts 13, 14 held on their forming tool T1, 12, T3, T4 s' interface with the additional carbon fiber prepregs 16, 17 on the inner part 15 and in the recesses of the forming tool T1.

Once this is done, all the forming tools are held against each other in position by another assembly, represented by means of arrows F in FIGS. 10 and 11.

Then, the mold M6 in the assembly is heated to a temperature of at least 130 ° C for at least 30 minutes to allow the pre-impregnated 16, 17 additional cook and mold the upper part 11, lower part 12 and parts 13, 14 and the inner member 15 together to form a single molded carbon fiber watch case assembly.

Claims (16)

Preferably, this second hot molding step is performed using a heating technique different from the infrared heating of the first step a) since the mold M6 consists entirely of the heat-resistant steel of the individual forming tools. It is therefore preferred to use induction heating to effect this final molding of the watch case assembly. After the second molding step b), the assembly and forming tools T1, 12, 13, 14 and T5 are allowed to cool to room temperature and are then removed from the fiber watch case assembly. of unique molded carbon obtained at this stage. It is only necessary to remove any excess material from the single molded carbon fiber watch case assembly by cutting off this excess material and then finishing the watch case 1 by delimiting the horns 4 and forming through holes 4 therein and also by machining for example the recesses of push buttons 5 and the corresponding holes 6. However, these last two finishing steps should not be performed directly after molding, but can be performed anytime later, especially when assembling and assembling an entire watch. The above description has been made with reference to a particular example of a watch case 1 consisting entirely of a composite material of carbon fibers according to the process described here. However, obvious changes in the shape of the watch case so as to perform any of the molding steps may be arranged by a person skilled in the art without departing from the scope of the invention. claims A method of manufacturing a carbon fiber watch case (1) comprising the steps of: a) forming an upper piece (11), a lower piece (12), two side pieces (13), , 14) and an inner part (15) by molding carbon fiber prepregs (7, 8, 9, 10) between a forming tool (T1, 12, T3, T4, T5) and a counterpart of compression (C1, C2, C3, C4, C5) complementary to a mold (M1, M2, M3, M4, M5) for each piece, the inner piece (15) defining a central bore for the middle part (2) of the watch case comprising a thread (22), and preferably a bezel (21) for supporting a glass, on an internal surface of the inner part during the molding thereof, and b) assembly of the upper part, the bottom piece and the two side pieces around an outer surface of the inner piece with additional carbon fiber prepregs (16, 17) the top piece, bottom piece, two side pieces and the inner piece and molding thereof to form a single molded carbon fiber watch case assembly. The method of claim 1, wherein in step a), the molds are heated for at least about 30 minutes at a temperature of at least 130 ° C to allow the prepregs to cook. A method according to claim 1 or 2, wherein in step a) each of the upper piece, the bottom piece, the two side pieces and the inner piece is individually formed in a custom mold by depositing and adjusting the prepregs on the forming tool and compressing them on said forming tool with the complementary compression counterpart during molding. 4. Method according to any one of claims 1 to 3, wherein, in step a), a pressure of at least 5 bar is applied to the prepregs and the forming tool by the compression counterpart complementary. 5. Method according to any one of claims 1 to 4, wherein in step a), the forming tool and the complementary compression counterpart of each mold are constrained by a mounting. The method of any one of claims 1 to 5, wherein the forming tool is made of a heat resistant material, preferably a metal or a metal alloy. The method of any one of claims 1 to 6, wherein the complementary compression counterpart is made of silicone rubber. 8. A method according to claims 4 and 7, wherein the pressure is applied to the forming tool and the prepregs by the thermal expansion of the complementary compression counterpart during the heating of the molds. The method of any one of claims 1 to 8, wherein the mold forming tool for forming the inner part comprises a cylindrical shutter comprising a thread on an outer surface thereof. The method of any one of claims 1 to 9, wherein the complementary compression counterpart is removed from the forming tool between step a) and step b). 11. A method according to any one of the preceding claims, wherein step b) comprises the following sub-steps: - adjusting a band of carbon fiber prepregs (16) around the inner part maintained on its forming tool, and - inserting additional carbon fiber prepregs (17) into recesses (18) arranged therein in the forming tool (T1) for the upper part or in the tool forming for the lower part (T2) to form the horns of the watch case, and - positioning and adjustment of the forming tools of each mold supporting the upper piece, lower piece and individual side pieces molded in step a ) relative to one another (T1, 12, T3, T4) and around the forming tool (T5) of the inner part (15) so that said upper part, lower part and side parts held on their out they form interfacing with the additional carbon fiber prepregs on the inner part and in the recesses, and - holding all the forming tools together with one another, and - heating the forming tools in the assembly at a temperature of at least 130 ° C for at least 30 minutes to allow additional prepregs to bake and mold the top piece, bottom piece, and individual side pieces and the inner piece together to form a unique molded carbon fiber watch case assembly. The method according to claim 11, wherein the sub-step of inserting additional carbon fiber prepregs (17) in recesses (18) comprises, for each recess: cutting the individual prepreg pieces and their stacking on one another to form a prepreg component (17) having first and second ends, and - inserting a first end of the prepreg component (17) into the recess (18) so that said end is oriented towards the inner part (15), and - the folding of the prepreg component (17) on itself so that the second end thereof is also oriented towards the inner part (15) and that the fold is outward facing. The method of any one of claims 11 and 12, wherein after molding, the fixture and the forming tools are removed from the single molded carbon fiber watch case assembly. A method according to any one of claims 1 to 13, wherein after step b), the excess material of the molded single carbon fiber watch case assembly is cut and the horns (3) are drilled to form through holes (4) adapted to receive a bar for attaching a bracelet to the watch case. 15. A carbon fiber watch case (1) comprising a caseband (2) having an integral internal thread (22) and preferably a telescope (21). 16. A carbon fiber watch case according to claim 15, further comprising horns (3) extending outwardly from the middle (2) and in one piece with it, the horns. comprising through holes (4) adapted to receive a bar for attaching a bracelet to the watch case.