WO2016151394A2

WO2016151394A2 - Method for manufacturing an anisotropic micromechanical component

Info

Publication number: WO2016151394A2
Application number: PCT/IB2016/000391
Authority: WO
Inventors: David Candaux; Julien STERVINOU
Original assignee: Convergence Composite Sa
Priority date: 2015-03-26
Filing date: 2016-03-29
Publication date: 2016-09-29
Also published as: CH710914A1; WO2016151394A3

Abstract

A method for manufacturing, by moulding, a micromechanical component (4B, 4E, 4A) produced on the basis of an anisotropic composite material made up of at least two immiscible components, at least one being a reinforcing fibre and one a binding matrix, the reinforcing fibre being embedded in the binding matrix, involves a first step in which successive layers of reinforcing fibres, which are impregnated with matrix and hereinafter referred to as plies (2) are layered in a mould. Each ply (2) is made up of a single-direction web or of woven plies (2) or of multidirectional web. Each ply (2) has a given thickness ranging from 0.010 mm to 0.6 mm, and the layering of the plies (2) forms a rough form (1) the external dimensions of which are up to 50 or even 60 mm in length and up to 50 or even 60 mm in width. The rough form (1) comprises at least one zone referred to as the final zone (11) corresponding to part of the micromechanical component (4B, 4E, 4A) and at least one zone referred to as the sacrificial zone (10) intended for machining operations. A second step involves applying mechanical compression to the layer stack of plies (2) that forms the rough form (1) so as to compress the materials, said mechanical compression being associated with a temperature cycle or even, if appropriate, with an air evacuation cycle with a view to extracting gases that have built up between the reinforcing fibres. A third step involves machining the sacrificial zone or zones (10) of the rough form (1) so as to end up with the micromechanical component (4B, 4E, 4A). The rough form (1) formed in the first step has a specific anisotropic nature dependent on the orientations of the fibres and on the thickness of each ply (2), this specific anisotropic nature of the rough form (1) being chosen according to the features of the micromechanical component that is to be produced. The nature, form and aesthetic appearance of the micromechanical component (4B, 4E, 4A) come from the shape of the mould, from the type of layering and from the machining operations taking account of the specific anisotropic nature of the rough form (1), which specific anisotropic nature is found again in the finished micromechanical component (4B, 4E, 4A).

Description

METHOD FOR MANUFACTURING A MICROMECHANICAL COMPONENT

ANISOTROPIC

The present invention relates to a method of manufacturing by molding a micromechanical component made from a composite material.

In general, the most frequently used micromechanical components are machined in a metallic material, such as iron, nickel silver, copper, brass, or the like, and by bar turning in the end of a bar, or by cutting off a profile, or by stamping or punching a plate, or by milling a raw form. Some components may also be molded of thermosetting or thermoplastic synthetic material as long as their geometry is suitable for the production of a mold. The essential advantage of these techniques is their low cost of producing series of components.

The current trend is for components to be stronger, lighter, and more aesthetic. Composite materials, in the sense of reinforcing fiber and binder matrix, meet these criteria. Areas such as aeronautics, nautical, rail or automobile have taken advantage of the advantages of such materials and have developed a set of implementation processes adapted to their needs, generally summarized as follows: large, durable and lightweight parts with more or less lefts.

However, for micromechanical components, the conventional methods for implementing composite materials have significant disadvantages that make it difficult to produce micromechanical components. The commonly used methods of implementation are generally unsuited to the particular constraints of small components. Therefore, a commonly used practice is to implement processes adapted to the size of the components to be produced but which, not taking into account the specificities of the composite materials, especially in terms of anisotropy, do not necessarily allow, because too random , to make the most of these materials. For example, the machining in the mass of a material Fibrous composite resulting in a massive cut of fibers removes the mechanical advantage of using such fibers.

It is also known from the state of the art a method using composite materials for the production of watch components and including watch cases. This process, called NTPT (Noth Thin Ply Technology), is also explained in a video on "YouTube" (https://www.voutube.com/watch?v=30UOopxBxu) in which is explained the constitution of a roughing, then a material removal operation, by machining, to obtain a watch case. It is clearly seen in the constitution of the blank, that the geometry of the latter is not precisely adapted to the geometry of the finished part, so that the removal of material by machining results in a massive cut of the fibers, in all the plans. The aesthetic aspect of the piece shows in every point of the room, an exposure of the different layers, thus illustrating their massive cut, both longitudinal and transverse. This method could be defined as a machining in the mass of a laminated block.

FIG. 8 of the NTPT method illustrates a first step A which consists of a stack of fibers, which are positioned in a mold according to a fiber arrangement of (07-45 / 90/45 / 07-45 / 90) given as a 'example. This stack is then fired in a step B on an open mold, without constraint of the thickness of the blank with respect to the thickness of the watch case. In a step C, the blank of the watch case is machined to a final geometry in any point different from that of the blank.

A disadvantage of this method is that the sacrificial zone constitutes the major part of the blank. Moreover, this machining makes lose the mechanical benefit offered by the use of long fibers because the integrity of long fibers is no longer respected, as explained in more detail in the following paragraphs. Moreover, it is no longer possible to guarantee the symmetry of orientation of the folds in the thickness of the finished part with a strong and hardly predictable incidence of the evolution of the geometry of the part. Thus, to benefit from the exploitation of composite materials, anisotropy must be taken into account at all stages of design and manufacture of the micromechanical component. The choices of the fiber / matrix pair, the determination of the orientation of the fibers at each point of the micromechanical component and the taking into account of the operations necessary for the manufacture of the component, for example a machining operation, which have been the subject of of a theoretical study are complicated to implement, from a practical point of view. Indeed, the process respecting this succession of operations allowing the conformity of the theoretical choices throughout the production until the micromechanical component is difficult to implement.

For example, in the case of materials commonly used for producing watchmaking or micromechanical components, it is sufficient to know the nature of the material and the possible treatments it may have undergone to accurately predict the final behavior of the component. The designer will choose, according to his needs, from a table of materials with well-known properties. In the case of the use of a composite material, the knowledge of the fiber / matrix pair is not sufficient to allow the designer to predict the final behavior of the component to be produced, as the behavior of the latter can vary, for a same fiber / matrix pair chosen, depending on the position and orientation of these fibers. Moreover, the conventional methods consisting of an overlay of plies implemented in an open mold are not compatible with the level of precision required for a micromechanical component. They can nevertheless allow the realization of a component with a surplus of material. This surplus will then be removed by a material removal process. Given the non-isotropic nature of the consolidated composite material, depending on the nature of the geometry of the removal of material, the latter can be quite detrimental to the mechanical integrity of the component. Indeed, the machining in the mass, whatever the process, without taking into account very fine of the internal constitution, in the sense of the precise knowledge of the nature, the thickness, the constitution, the position and orientation of each fold is therefore highly hazardous as to the quality of the component thus produced. In particular, closed-mold molding processes, particularly compression molding, allow the production of components with more complex shapes, which may, for example, limit the necessity of resorting to subsequent operations of removal of material. However, in this case, obtaining complex shapes is made possible in particular by the application of high pressure on the composite material during implementation. This high pressure will allow creep of the matrix in the viscous state and inevitably causes a displacement of the fibers, without precise knowledge of the position of each fold at the end of the process. This type of process is no longer suitable since it is desired a fixed position of each fold from the beginning to the end of the implementation process, whether for mechanical or aesthetic reasons in particular.

The present invention relates to a method of manufacturing by molding a micromechanical component made of a composite material respecting the anisotropy of said composite material. According to the invention, a method of manufacturing by molding a micromechanical component made of an anisotropic composite material composed of at least two immiscible components, including at least one reinforcing fiber and a binder matrix, the fiber reinforcement being embedded in the binder matrix, comprises a first step consisting in stacking, in a closed mold adapted to the shape of the finished part, successive layers of reinforcing fibers, impregnated with matrix, hereinafter folds, each fold consisting of a unidirectional web in which the reinforcing fibers are arranged parallel to each other, or woven plies, in which the reinforcing fibers are woven in two directions, or of multidirectional web, in which the reinforcing fibers are arranged without privileged orientation. Each fold can have a given thickness ranging from 0.010 mm to 0.6 mm, the stack of plies forming a blank, the external dimensions of which are up to 50 or even 60 mm in length and up to 50 or even 60 mm in width. The blank comprises at least one so-called final zone corresponding to a part of the micromechanical component and at least one so-called sacrificial zone intended for machining operations. A second step is to apply a mechanical compression on the stack of plies forming the blank to ensure the compression of materials, said mechanical compression being associated with a temperature cycle. Preferably, the thickness of the blank obtained and compressed corresponds to the thickness of the micromechanical component. Optionally this second step can be completed by the application of an air vacuum cycle in order to extract gases accumulated between the reinforcing fibers. Finally, a third step is to remove material on the sacrificial zone or zones of the blank, so as to lead to the micromechanical component. The blank formed in the first step has a specific anisotropic character, according to the fiber orientations and the thickness of each fold, this specific anisotropic character of the blank being chosen as a function of the characteristics of the micromechanical component to be produced. The nature, shape and aesthetic appearance of the micromechanical component come from the shape of the mold, the type of stack and the material removal operations taking into account the specific anisotropic nature of the blank, which specific anisotropic character is taken over. in the micromechanical component produced.

When the thickness of the micromechanical component does not correspond to the thickness of the blank obtained during the second step, removal of material is possible with an identical removal thickness both on the top and on the bottom of the 'draft. This material removal thickness may correspond to an integer number of folds or to a thickness not corresponding to an integer number of folds. This removal of symmetrical material on the top and bottom of the blank allows in particular to ensure the flatness of the micromechanical component by maintaining the balance of interlaminar voltages. This removal may be necessary for example when the tolerance of the thickness of the blank is not sufficient compared to the tolerance of the thickness of the finished part. In this case, a mechanical removal of material can achieve the desired tolerance. Ensuring this removal of material symmetrically on the top and bottom of the blank will avoid degrading the flatness of the component.

In a first embodiment, the reinforcing fiber is a dry or pre-impregnated fiber and the binder matrix is a liquid or semi-liquid matrix. The material removal operation may for example consist of a bore, a cutting, a tapping, a drilling, a milling, a thread, a grinding and / or grinding, grinding, water jet cutting, laser cutting and engraving, laser / jet combination.

In another embodiment, the blank is of thickness close to the desired final thickness, slightly greater or to an integer close to fold, so as to be made to a desired thickness and flatness by a grinding or milling.

In order not to weaken the micromechanical component, the realization of tapping or a driving operation in a local area of said micromechanical component, can be done only if the fibers are arranged in said local area, in different directions, so as to locally create a quasi isotropic behavior.

According to another aspect of the invention, a manufacturing method by molding a rocker is made from a blank in which the rocker has a serge in which at least two spaced connecting arms are connected to said serge by a their ends, said connecting arms being interconnected by their other end by an annular element in the center of said serge. The blank comprises at least one reinforcing fiber with a high Young's modulus of between 100 and 900GPa.

According to this other aspect of the invention, the blank comprises a stack of successive layers of reinforcing fibers, impregnated with matrix, in a flat or quasi-flat mold, the reinforcing fibers taking the form of the mold. The stack of successive layers of reinforcement fibers, hereinafter plies, comprises one or more so-called final zones corresponding to a portion of the balance, the link arms of the balance being composed of fibers oriented radially and the central annular portion being composed of fibers whose orientation is varied.

Preferably, the blank is made from a carbon fiber and an epoxy resin, the carbon fiber being embedded in the epoxy resin.

Additional elements can be integrated in the blank before ^being subjected to mechanical compression. According to a completely different aspect of the invention, a method of manufacturing by molding a top and / or bottom member of a vortex cage made from a blank, wherein said upper and / or lower member of a tourbillon cage has at least two arms. Each arm has two ends, said arms being distributed around an end by which said arms are connected, the reinforcing fibers being oriented, longitudinally, in a number of orientations at least equal to the number of arms.

According to this other aspect of the invention, the blank is made from a carbon fiber and an epoxy resin, the carbon fiber being embedded in the epoxy resin.

The characteristics of the invention will appear more clearly on reading the description of several embodiments given solely by way of example, in no way limiting with reference to the schematic figures, in which: FIG. 1 represents a perspective view a stack of plies of composite materials constituting a type of blank;

- Figure 2 shows an exploded perspective view of a stack of plies of composite materials, the plies having unidirectional fibers in precise and varied orientations;

FIG. 3 represents an exploded perspective view of a stack of plies of composite materials, plies having different thicknesses, unidirectional fibers and woven fibers;

FIG. 4 is an exploded perspective view of a stack of plies of composite materials and two metal sheets disposed at each end for sandwiching plies having unidirectional fibers and woven fibers;

FIG. 5 represents a partial schematic view of the production of a balance from a stack of plies of composite materials comprising fibers in four orientations, the folds being then compressed to form a blank from which the balance is extracted;

FIG. 6 represents a partial schematic view of the embodiment of a vortex cage element from a stack of plies of composite materials comprising fibers in three orientations, the plies then being compressed to form a blank from which is extracted the element of tourbillon cage; FIG. 7 represents a blank from which three indicator hands are extracted;

FIG. 8 represents a known method NTPT; and - Figure 9 shows a method according to the present invention.

The following description concerns horological applications and more particularly, a manufacturing process by molding a balance 4B, a tourbillon cage element 4E and needles 4A from a blank 1.

The machining of watch components (for example 4B FIG. 5, 4E FIG. 6, 4A FIG. 7) is done via the use of blanks 1. These blanks 1 have a standard external shape for which the component manufacturers equip their centers with machining of adapted positions, allowing easy positioning and location, as well as sometimes, a suitable gripping mode for palletizing for serial work. The component (s) 4 can then be machined and taken from this blank 1.

The realization of a blank 1 whose constitution is precisely known (nature of the fiber / matrix pair, but also the position and orientation of the fibers) makes it possible to predict the final mechanical behavior according to the blank 1 chosen and whose external dimensions are known for allow the machinist in micromechanics to work in a conventional manner according to the rules of the art of his field.

It is here admitted that the fibers are grouped in the form of plies 2 that is to say having two and a half dimensions (a plane and a thickness) and that these fibers are pre-impregnated with a binder matrix. We will now talk about folds 2. As illustrated in Figure 1, the blank 1 consists of a stack of plies 2 of composite materials.

The blank 1 thus advantageously combines a strict compliance with the orientations and positions of the fibers, decided according to the type of component 4B, 4E, 4A to be produced from the blank 1, as well as a precision of the component 4B , 4E, 4A then taken from the blank 1 known according to the capability of the machine used. In the example illustrated in FIG. 2, the blank 1 is made from a stack of plies 2 of composite materials, the plies 2 having unidirectional fibers in various orientations, for example according to the arrangement illustrated in FIG. Figure 2 (0 / -45 / 45/0/0/0/45 / -45 / 0).

In another example illustrated in FIG. 3, the blank 1 is made from a stack of plies 2 of composite materials, the plies 2 having different thicknesses, unidirectional fibers 2U and woven fibers 2T, either in this case. example three folds 21) arranged between two folds 2T. In another example illustrated in Figure 4, the blank 1 is made from a stack of plies 2 of composite materials and two metal sheets 3 arranged at each end to sandwich pleats 2 having unidirectional fibers 2U and in the center of the 2T woven fibers.

This blank 1, for example of FIG. 3 or of FIG. 4, once consolidated, can be machined on a machining center with known precision capabilities in order to produce a micromechanical component with the desired advantages of the composite materials constituting it and with great repeatability from one manufacture to another.

The blank 1 will advantageously have a high accuracy of thickness and flatness, compatible with the tolerances required according to these criteria on the component 4B, 4E, 4A finished. In fact, the machining will generally take place in two operations, the work being carried out on the face from above, then from below. The intervention on the underside will require a flipping of the component 4B, 4E, 4A, following which the precise knowledge of thickness and flatness of the blank 1 allow a respect of the same tolerances on the component 4B, 4E, 4A. This respect of tolerance of thickness and flatness will be guaranteed by the phase of implementation and consolidation of the blank 1 (stack of a known number of folds 2 of a known thickness of folds) and the pressure / temperature conditions to ensure a final thickness of the blank 1.

Depending on the desired thickness of the final thickness, it is possible that the pitch of the folds 2 does not allow exact compliance with this thickness (the final thickness corresponds to a whole number of folds that can, for their part, be of different thicknesses ). In such a case, it is advisable to produce a blank 1 of approximate thickness of the final thickness, in slight excess, to an integer close to fold 2. Then, a thickness setting operation must be performed to guarantee the tolerance of thickness and flatness. This operation can be carried out on a platen machine (single-sided or double-sided), for example by grinding or milling.

The first step in the development of the present invention is to define its constitution, in terms of choice of the nature, type, number and orientation of each ply 2 of prepreg. This choice will be different according to the purpose of the component 4B, 4E, 4A which will be machined in the present invention, whether the purpose is mechanical, aesthetic or otherwise.

In general, a variable moment-inertia rocker comprises a wheel-shaped part comprising a serge, connecting elements between the serge and the axis of the balance and a certain arrangement of screws nuts or flyweights fixed on the serge of the pendulum that allow by adjusting their positions to change the unbalance and the moment of inertia of the pendulum.

The accuracy of a watch equipped with a sprung balance depends essentially on the frequency stability of its sprung balance. Different parameters affect the frequency stability of a sprung balance whose amplitude variations of the pendulum oscillations. These amplitude variations are notably related to the positions of the watch, to the loss of the moment of force, to the friction, in particular with the pivots of the balance shaft and the unbalance of the latter. This has the effect of causing a lack of isochronism of the sprung balance, this isochronism defect having an impact on the precision of the timepiece. Moreover, among the other important criteria for a pendulum we can mention in particular the mass, the resistance, the coefficient of friction, the coefficient of thermal expansion, the amagnetism, the hardness, ... It is extremely rare and not very likely that only one material alone can satisfy all the expected characteristics. The present invention aims to select and combine different materials that best meet each function of the balance.

In a watch clock, the axis of rotation must have specific features to reduce friction, it will usually be made of brass. The weights must have a high density, that is to say a concentrated mass for a small volume, more precisely a minimized outer surface to limit the friction of the air to which the pendulum will be subjected during oscillations. These masses can be made for example platinum. Thus, the characteristics of the axis and flyweights being defined, it is expected that the part mechanically connecting them to be the most transparent in terms of mass, deformation, elongation. The use of a composite material based on carbon fibers and epoxy resin has these advantages, with a very high strength / mass ratio.

This very high ratio is made possible thanks to the intrinsic characteristics of the composite material, but also to its non-isotropic use, that is to say with a fiber orientation in a precise direction, as a function of the forces exerted by the weights on the hub, namely their own mass and the centrifugal force in motion. This precise determination of the forces makes it possible to choose a fiber with a high Young's modulus, between 100 and 900GPa, a binding matrix making it possible to transit the forces in the fiber, and a precise orientation of the fibers, this resulting in a mechanical connection between weights and hub for a minimized mass. This mass gain makes it possible, with a given inertia, to produce a complete balance wheel of reduced mass, or of equal mass, to be able to increase its inertia by allocating the mass gained to the flyweights. This orientation will be predominantly radial, in order to limit the boom to stop due to the mass of the weights and bending the arms, and limit the elongation during oscillations, due to the centrifugal force of traction exerted by the weights. This radial distribution is made possible by the use of unidirectional sheets or son.

The conventional assembly of hunting to assemble materials of different nature will be made possible by the local orientation of the particular fibers. Indeed, we have seen that the mechanical considerations led to a preferred fiber orientation along radial axes. These orientations of fibers on such small thicknesses do not allow the driving, the driven axis exerting a uniformly distributed pressure in all directions of the plane, which leads to delamination, separation of the fibers. By arranging fibers in different directions in the area near the hunting, the fibers will be allowed to counter this pressure exerted by the driven axis. This method of assembly can be used to fix the weights on the joining part made of composite materials.

The high ratio of resistance / mass associated with a judicious orientation of the fibers makes it possible to limit the overall mass of the pendulum. Thus, according to another approach, inertia and balance mass defined with a "standard" balance, it is possible to achieve a balance using these composite materials, with equal performance, but with a larger size. Thus, if the available volume authorizes it, the present invention makes it possible to design a visually larger balance and to provide a sensible differentiation.

In the case of using a balance, a major feature is its dimensional stability over time and depending on external conditions, particularly the impact of temperature, to ensure a constant isochronism. The present invention makes it possible to ensure a very high dimensional stability thanks to a lower coefficient of thermal expansion than the conventionally used materials. For this, it will be appropriate to choose a particular carbon fiber, having this specificity of thermal expansion almost zero, while retaining its mechanical characteristics, specifically in terms of Young's modulus, particularly important in this case of use. Moreover, the arrangement of the fibers will be extremely important for the respect of the criterion of thermal elongation. Indeed, if the appropriately selected fiber can have a coefficient of thermal expansion almost zero, this is not the case of the binder matrix, the family of polymers. Thus, the consolidated composite material will have an almost zero elongation in the longitudinal direction of the fibers, while it will be non-negligible in the transverse direction. Therefore, the radial orientation favored by the mechanical aspects is also suitable for thermal aspects. Virtually zero elongation ensures constant inertia as a function of temperature. Elongation, which we can not avoid, in the transverse direction of the fibers, will have no impact on the inertia of the balance.

The accuracy of the calibres depends on the quality of their regulating organ, and the obtaining of very high oscillation frequencies, for example of 10 Hz, to be compared to the usual frequencies of 2.5 to 4 Hz, can only be obtained with the design of suitable regulating members, particularly with regard to the pendulum.

In the case of use of a balance, subject to high frequency oscillations, for example 10 Hz, the aerodynamic aspects have a significant impact on the performance, which can be seen in particular through the value of the quality factor. The fundamental parameter qualifying any resonator is its Q quality factor. It is a dimensionless number that can be interpreted in two different but closely related ways. We can first consider Q as the ratio between the internal energy W of the resonator and the energy dissipation Δ \ Λ / due to Joule losses during an oscillation cycle. A high quality factor resonator will thus require less energy for its maintenance than an identical resonator but with a low quality factor. Another interpretation of the quality factor, a little more abstract but important to understand, says that the stability of a resonator is proportional to its quality factor. The stability of a time base is therefore directly related to the quality factor of its resonator: the higher it is, the more the resonator is insensitive to its maintenance mechanism. In order to maximize the latter, it is necessary to reduce the friction on the moving parts. An aerodynamic study of the pendulum in motion shows that it is necessary to limit the wet surface and to minimize the coefficient of drag. One solution is to minimize the front surface and give the arms a shape with leading and trailing edges with a suitable profile. At the scale considered, it is not obvious to produce such shapes by conventional machining methods. The The present invention proposes to advantageously use the molding capacity of the fibers by producing this profile in a molding tool which will in turn move the fibers during their implementation and ensure compliance with this aerodynamic profile, guaranteeing a better performance. aerodynamic than a rectangular section.

The composite material selected for the present invention also has advantageous non-magnetic characteristics in the case of use of a balance, thus limiting its influence to external magnetic disturbances and ensuring a constancy of isochronism. The composite material selected for the present invention also has a high corrosion resistance.

In the example illustrated in FIG. 5, a rocker 4B is made from a blank 1 consisting of a stack of seven plies 2 of composite materials comprising fibers in four orientations. The folds 2 are compressed to form a blank 1 from which the balance 4B is extracted after a machining operation. In this example, the balance 4B taken includes a serge 5, discontinuous, in which four connecting arms 6 spaced apart from each other are connected to said serge 5 by one end of said arms 6. The link arms 6 are interconnected by their other end by an annular element 7 in the center of said serge 5. The four connecting arms 6 and the serge 5 are made of a composite material based on carbon fibers and epoxy resin having a very high strength / strength ratio. mass. The fibers are oriented radially with respect to an axis of rotation around the annular element 7 and whose orientation of the fibers in the annular element is achieved by arranging the reinforcing fibers in different directions. The stack of folds 2 is made with unidirectional fibers according to the illustrated arrangement comprising four different orientations, a first orientation at 0 °, a second orientation at 90 °, a third and a fourth orientation determined by the arrangement of the connecting arms 6, the value 0 ° corresponding to fibers oriented along the bisector of an angle between two successive arms 6 connected by a serge portion 5. In this example, the angle β is the bisector of the angle between the two arms 6 successive. In other words, the angle between said successive arms 6 connected by a serge portion 5 is 2 β °. In this example the angle β can take a value between 10 ° and 90 ° for example. Optionally, the balance 4B may comprise additional elements, for example flyweights, which are directly integrated during the production phase of the blank 1.

Thus, in the case of the production of a balance 4B, the blank 1 is made of an anisotropic composite material composed of carbon fibers and epoxy resin having a very high strength / mass ratio. The method comprises a first operation consisting in stacking, in a mold, successive layers of carbon fibers, impregnated with epoxy resin, hereinafter plies 2, each ply 2 consisting of a unidirectional layer in which the carbon fibers are arranged. parallel to each other, each ply 2 having a given thickness ranging from 0.010mm to 0.6mm, the stack of plies 2 forming a blank 1, the external dimensions of which are up to 60mm in length and up to 60mm in width .

The blank 1 comprises a so-called final zone 11 corresponding to the shape of the balance 4B and a so-called sacrificial zone 10 intended for machining operations.

Then, the application of a mechanical compression on the stack of folds 2 forming the blank 1 ensures the compression of materials, said mechanical compression being associated with a temperature cycle.

Finally, a machining operation of the sacrificial zone 10 of the blank 1 makes it possible to extract the balance 4B.

The balance 4B with variable moment of inertia comprises a serge 5, discontinuous, in which four spaced apart connecting arms 6 are connected to said serge 6 by one end of said arms 6, said connecting arms 6 are connected by one of their end to a central ring 7 and at their other end, two by two, at a serge portion 5. The link arms 6 and the serge 5 are made of a composite material using a carbon fiber, with a high Young's modulus between 100 and 900GPa, whose fibers are oriented radially with respect to an axis of rotation around the annular element 7 and whose orientation of the fibers in the annular element 7 is made by arranging the reinforcing fibers in different directions. According to another aspect of the invention, the method is implemented to manufacture another watch component 4, such as an upper or lower element of tourbillon cage 4E for a watch movement, illustrated in FIG. composite materials. The tourbillon, while improving the performance of a mechanical movement in terms of isochronism, nevertheless has an impact on the operation of said movement by its energy consumption, a direct impact on the power reserve and potentially on the isochronism according to its mass.

Like any moving element of a mechanical movement, the tourbillon cage has every interest in having a minimized total mass. The use of a low density material is therefore preferred. Nevertheless, because of their geometric shape, the upper and lower cages generally have slender arms. This slenderness, which imposes a weak section, therefore requires a high resistance. It is a material with a high ratio of rigidity / mass that will be suitable. A composite material in the reinforcing fiber sense, such as a carbon fiber and a binder matrix such as an epoxy resin, has intrinsic mechanical properties superior to the materials conventionally used for producing tourbillon cages, particularly in terms of specific Young's modulus. that is, the module brought back to the ground. In a fibrous material, which is not isotropic in nature, the value of the modulus varies considerably according to the orientation of the fibers. It is therefore necessary, to ensure the desired rigidity, to precisely orient the fibers in certain strategic places of the tourbillon cage.

For the realization of the arms, a study of resistance of nonisotropic materials will highlight the need to have a maximum of fibers in the longitudinal direction of the arms.

In the case of use of a tourbillon cage, a major feature of the latter is its dimensional stability over time and depending on external conditions, particularly the impact of temperature, to ensure a constant isochronism. The present invention makes it possible to ensure a very great dimensional stability thanks to a coefficient of thermal expansion lower than conventionally used materials. For this, it will be necessary to choose a particular carbon fiber, having a thermal expansion specificity of almost zero, while retaining its mechanical characteristics, specifically in terms of Young's modulus, particularly important in this case of use. Moreover, the arrangement of the fibers will be extremely important for meeting this criterion of thermal elongation. Indeed, if the appropriately selected fiber can have a coefficient of thermal expansion almost zero, this is not the case of the binder matrix of the family of polymers. Thus, the consolidated composite material will have an almost zero elongation in the longitudinal direction of the fibers, while it will be non-negligible in the transverse direction. Therefore, the radial orientation favored by the mechanical aspects is also suitable for thermal aspects. Virtually zero elongation ensures constant inertia as a function of temperature. Elongation, which can not be avoided, in the transverse direction of the fibers, will have no impact on the inertia of the cage. The composite material selected for the present invention also has advantageous non-magnetic characteristics in the case of use of a vortex cage, thus limiting its influence to external magnetic disturbances and ensuring consistency of the isochronism.

The composite material selected for the present invention also has a high corrosion resistance.

The realization of such a component will be made possible by the preliminary development of a blank 1, the constituent folds will be epoxy carbon prepreg, and whose grammages and orientations will depend on the geometry of the cage bridges. In the widespread case of a vortex cage element 4E with three arms 8, it will be necessary to arrange the fibers in each direction of the arms 8, so that the element of the cage 4E has a homogeneous mechanical behavior.

As illustrated in FIG. 6, the upper and / or lower element of a tourbillon cage 4E for a timepiece is obtained from a blank 1. The element 4E comprises three arms 8 distributed around a end 9 by which said arms 8 are connected, the arms 8 being made of a composite material using a reinforcing fiber, the fibers are oriented longitudinally in three orientations. The stack of folds 2 is made with unidirectional fibers having an orientation of 60 ° relative to each other. The stack of folds 2 is made with unidirectional fibers according to the following arrangement: (0/60 / -60 / 0/60 / -60 / 0/60 / -60). In theory, a mirror symmetry should be respected in the stack, but in the present case, an identical distribution of the orientations in each arm 8 is favored in order to have a homogeneous mechanical behavior from one arm 8 to the other.

In another example, illustrated in FIG. 7, needles 4A of a watch are made from a blank 1, consisting of a stack of folds 2 whose reinforcing fibers are oriented, longitudinally, according to FIG. least two orientations. In this example, there are three folds 2.

As illustrated in FIG. 9, the shape of the mold in which the stack according to the invention is made is closely adapted to the shape of the finished part, so that the sacrificial zone does not constitute the major part of the blank . The nature of the stack and in particular the orientations of the folds is determined by the mechanical aspects. They differ from one room to another and are not necessarily a variation of 45 ° every fold. A very important element concerns the symmetry of orientations in the stack: interlaminar constraints are created between the layers. Since two contact layers are oriented in different directions, this constraint could result in a negative impact on the flatness and unless taking countermeasures, the piece will go into "chips". One method to overcome this problem is to make a stack "mirror", that is to say a stack symmetrical with respect to the neutral fiber: in general the medium (in the thickness) of the room. Thus, if a 0 ° fold is deposited at the bottom of the mold for mechanical reasons, then a fold at 30 ° and another at -30 °, it will be necessary to finish stacking a fold at -30 °, the following at + 30 ° and the last at 0 °. This basic rule of laminates should not be undermined by material removal. Thus, we will concentrate the sacrificial zones in the flanks (XY plane) and as little as possible in the Z-shaped thickness, which would break this symmetry. The use of a closed compression mold, guaranteeing a geometry of the blank on all the surfaces, associated with the control of a compression process taking into account the creep parameters of the resin during its heating (decrease of its viscosity) and its compression, make it possible to guarantee the roughing a precise thickness. The final area is therefore guaranteed in thickness. The area sacrificial is concentrated on the periphery, its removal does not disturb the Z symmetry of the laminate, and therefore not disturb the flatness of the finished part.

In the field of watchmaking, taking into account the mechanical and / or aesthetic constraints, other watch components can be manufactured according to the method described, such as for example a stamp / hammer, a cog, a vortex, a spring / jumper , a mass support, a watch case without ice, a watch bezel and many other components

Moreover, the coloring of the material is not described, but it is possible in an additional step of the process. The present invention aims to ensure, in each place of a micromechanical component produced, an optimum arrangement of the constituent fibers, according to the considerations required by the need, whether mechanical or aesthetic, for example.

The examples described above highlight the advantages of the method and its application for watch components. However, the present invention also allows the manufacture of a micromechanical component for other fields such as medical, automotive, mobile telephony, aviation, space, robotics, jewelery or leather goods.

Claims

1. Method of manufacturing by molding a micromechanical component (4B, 4E, 4A) made based on an anisotropic composite material composed of at least two immiscible components, including at least one reinforcing fiber and a binder matrix, the reinforcing fiber being embedded in the binder matrix, the method comprising the following operations:

a) Stacking, in a closed mold adapted to the shape of the finished part, successive layers of reinforcing fibers, impregnated with matrix, hereinafter folds (2), each fold (2) consisting of a unidirectional layer in which the reinforcement fibers are arranged parallel to each other, or folds (2) woven, wherein the reinforcing fibers are woven in two directions, or multidirectional web, wherein the reinforcing fibers are arranged without preferred orientation, each fold (2) having a given thickness ranging from 0.010 mm to 0.6 mm, the stack of folds (2) forming a blank (1), the external dimensions of which are up to 50 or even 60 mm in length and up to 50 or even 60 mm width, said blank (1) comprising at least one so-called final zone (11) corresponding to a portion of the micromechanical component (4B, 4E, 4A) and at least one so-called sacrificial zone (10) intended for machining operations, b) Apply a compr mechanical pressure on the stack of folds (2) forming the blank (1) to ensure the compression of the materials, said mechanical compression being associated with a temperature cycle, the thickness of the blank obtained and compressed corresponding preferably to the thickness of the micromechanical component, c) Where appropriate, apply an air vacuum cycle for the purpose of extracting gases accumulated between the reinforcing fibers, and d) Machining the sacrificial zone or zones (10) of the blank (1), so as to lead to the micromechanical component (4B, 4E, 4A), characterized in that the blank (1) formed in step a) has a specific anisotropic character, according to the fiber orientations and the thickness of each fold (2), this specific anisotropic character of the blank (1) being chosen according to the characteristics of the micromechanical component (4B, 4E, 4A) to be produced, and the nature, shape and aesthetic appearance of the micromechanical component (4B, 4E, 4A) comes from the shape of the mold, the type of stacking and machining operations taking into account the specific anisotropic nature of the blank (1), which specific anisotropic character is taken up in the micromechanical component (4B, 4E, 4A) produced.

The method of claim 1, wherein the reinforcing fiber is a dry or preimpregnated fiber and the binder matrix is a liquid or semi-liquid matrix.

A method as claimed in claim 1 or 2, wherein the machining operation includes reaming, cutting, tapping, drilling, milling, threading, grinding and / or grinding.

Method according to one of the preceding claims, wherein the blank (1) is of thickness close to the desired final thickness, slightly greater or to a whole number near folds (2) and the blank is set to a thickness and flatness desired by a grinding or milling operation.

Method according to one of the preceding claims, wherein the fibers are arranged, in a local area of the micromechanical component (4B, 4E, 4A), in different directions, so as to locally create a quasi-isotropic behavior, for the realization of tapping or a driving operation.

Method according to one of the preceding claims for manufacturing by molding a pendulum (4B) of a watch mechanism from a blank (1), the balance (4B) comprising a serge (5) in which at least two connecting arms (6) spaced are connected to said serge (5) by one of their ends, said connecting arms (6) being interconnected by their other end by an annular element (7) in the center of said serge, l blank (1) comprising at least one reinforcing fiber with a high Young's modulus of between 50 and 900GPa.

7. Method according to claim 6, wherein the blank (1) comprises a stack, in a mold, of successive layers of reinforcing fibers, planar or quasi-planar, impregnated with matrix, the said so-called final zones (11). ) corresponding to a portion of the beam (4B), the link arm (6) of the beam (4B) being composed of radially oriented fibers and the central annular portion (7) being composed of fibers whose orientation is varied.

8. The method of claim 6 or 7, wherein the blank (1) is made of a carbon fiber and an epoxy resin by embedding the carbon fiber in the epoxy resin.

9. Method according to one of claims 6, 7 or 8, wherein additional elements are integrated in the blank (1) before undergoing mechanical compression.

10. Method according to one of claims 1 to 5 of manufacturing by molding of an upper element and / or lower (4E) of a vortex cage made from a blank (1), said upper element and / or lower (4E) a vortex cage having at least two arms (8), each arm (8) having two ends, said arms (8) being distributed around an end by which said arms (8) are connected , the reinforcing fibers being oriented longitudinally in a number of orientations at least equal to the number of arms (8).

11. The method of claim 10, wherein the blank (1) is made based on a carbon fiber and an epoxy resin by flooding the carbon fiber in the epoxy resin.

12. Method according to one of claims 1 to 9 for manufacturing a watch component, medical, automotive, mobile telephony, aviation, space, robotics, jewelery or leather goods.

13. Pendulum (4B) with a variable moment of inertia for a timepiece obtainable according to the method of one of claims 1 to 9, comprising a serge (5) in which at least two spaced connecting arms (6) are connected to said serge (5) by one end of said arms (6), said connecting arms (6) being interconnected by their other end by an annular element (7) in the center of said serge (5), characterized in that that the connecting arms (6) and the serge (5) are made from a composite material using a reinforcing fiber, with a high Young's modulus, of between 50 and 900GPa, the fibers of which are oriented radially with respect to an axis of rotation around the annular element (7) and whose orientation of the fibers in the annular element (7) is achieved by arranging the reinforcing fibers in different directions.

14. Pendulum (4B) according to claim 13, wherein the serge (5) is discontinuous.

15. Pendulum (4B) according to one of claims 13 or 14, comprising four connecting arms (6), the connecting arms (6) being connected by one end to a central ring (7) and their other end, two by two, to a portion of serge (5).

16. Pendulum (4B) according to one of claims 13 to 15, wherein an axis of the beam (4B) is driven into the annular element (7) in the center of said serge (5).

17. Pendulum (4B) according to one of claims 13 to 16, wherein additional elements, for example flyweights, are integrated.

18. Pendulum (4B) according to one of claims 13 to 17, wherein weights are arranged on the connecting arms (6) and / or on the serge (5). 9. Pendulum (4B) according to one of claims 13 to 18, wherein the stack of folds (2) is made with unidirectional fibers in an arrangement comprising four different orientations, a first orientation at 0 °, a second orientation at 90 °, a third and a fourth orientation determined by the arrangement of the connecting arms (6), the value 0 ° corresponding to fibers oriented along the bisector of an angle between two arms ( 6) connected by a serge portion (5).

20. Upper and / or lower element (4E) of a tourbillon cage for a timepiece obtainable according to the method of one of claims 10 or 11, the element (4E) comprising at least two arms (8). distributed around an end by which said arms (8) are connected, the arms (8) being made of a composite material using a reinforcing fiber, the fibers of which are oriented, longitudinally, according to a number of orientations at least equal to the number of arms (8).

21. Element (4E) according to claim 20, said element (4E) having three arms (8) evenly distributed, the stack of folds (2) being made with unidirectional fibers having an orientation of 60 ° relative to the other.

22. Element (4E) according to claim 20 or 21, said element (4E) having three arms (8) regularly distributed, the stack of folds (2) being made with unidirectional fibers according to the following arrangement: (0 / 60 / -60 / 0/60 / - 60/0/60 / -60).