HK1176127B - Assembly of a part that has no plastic domain - Google Patents

Description

Assembly of components without plastic domains

Technical Field

The invention relates to the assembly of parts made of materials without plastic domains to elements made of different types of materials.

Background

Existing components, including silicon-based components, are typically secured by bonding. This type of operation requires very delicate applications, which makes it costly.

EP patent 2107433 discloses a first silicon-based component assembled on an intermediate metal component and subsequently mounting the whole assembly on a metal mandrel. However, the embodiments presented in this document are not satisfactory and either cause breakage of the silicon-based components during assembly or do not allow the components to be bonded to each other sufficiently well.

In fact, in this document, one end of the intermediate part is bent over the silicon part to generate a purely axial stress, which leads to a fracture of the silicon part. Moreover, this document proposes the use of faceting (faceting) techniques, which can result in non-uniform stress distribution on the silicon and can also cause silicon parts to fracture.

Disclosure of Invention

The object of the present invention is to overcome all or part of the above drawbacks by providing an adhesive-free assembly that enables fixing of a part made of a material without plastic domains to an element made of a ductile material, such as for example a metal or a metal alloy.

The invention therefore relates to a method for assembling an element made of a first material in a component made of a second material that does not have a plastic domain. The method comprises the following steps:

a) forming the part to have a hole;

b) inserting an intermediate member into the bore without any stress, the intermediate member being made of a third material and comprising an orifice;

c) introducing the element into an aperture;

d) the intermediate part is elastically and plastically deformed by axially moving two tools towards each other on the top and bottom of said intermediate part, respectively, so as to apply radial stresses to the element and to the part walls surrounding the hole, causing the part to elastically deform in order to fix the assembly in a manner that is non-destructive to said part.

This method advantageously allows radial fixation of the elements without applying any axial stress to the components. In fact, it is advantageous according to the invention to apply only radial elastic deformations to the component.

Moreover, such a structure advantageously makes it possible to fix the assembly of component-intermediate component-element without the need to adhere to the usual precisely controlled elements, while ensuring that the component is not subjected to damaging stresses even if it is made of monocrystalline silicon, for example.

Finally, the method integrates the assembly of parts-intermediate parts-elements by adjusting the dispersion in manufacturing the various components.

According to other advantageous features of the invention:

the outer wall of the intermediate part is shaped to substantially match the aperture in the part, thereby exerting substantially radial stresses on the part walls surrounding the aperture;

the holes in the part are circular;

the part wall surrounding the hole comprises a groove which will form a micro-groove on the outer surface of the intermediate part during step d) to avoid any relative movement between the elements of the assembly;

the outer surface of the element comprises grooves which, during step d), will form microgrooves on the inner surface of the intermediate part to avoid any relative movement between the elements of the assembly;

the holes in the parts are asymmetrical so as to avoid any relative movement between the elements of the assembly;

in step b), the difference between the cross section of the hole and the outer cross section of the intermediate part is about 10 μm;

in step c), the difference between the cross section of the element and the inner cross section of the intermediate part is about 10 μm;

-in step d), deforming applies a clamping force to produce a displacement between 16 μm and 40 μm;

in step b), the intermediate part comprises a conical recess coaxial with the orifice, in order to facilitate the orientation of the stresses caused by the deformation of the intermediate part in step d);

-the second material is composed of a monocrystalline silicon based material;

-the third material is composed of a metal-based or metal alloy-based material;

the component may be, for example, a timepiece wheel set, a timepiece pallet, a timepiece balance spring, a resonator or even a MEMS.

Drawings

Further features and advantages will become apparent from the following description, given by way of non-limiting example with reference to the accompanying drawings, in which:

figures 1 and 2 are schematic views of successive steps of an assembly method according to the invention;

figures 3 and 4 are a cross-sectional front view or perspective view of an intermediate part according to the invention;

figures 5 and 6 are diagrams of optional steps of the assembly method according to the invention;

figures 7 to 10 are diagrams of various variants of the intermediate element according to the invention; and

figure 11 is an illustration of an alternative hole for a part made of brittle material.

Detailed Description

As described above, the present invention relates to an assembly and a method of assembling the assembly for integrating a brittle material (i.e., a material having no plastic domain such as a single crystal silicon-based material) and a ductile material (e.g., a metal or a metal alloy).

The assembly is designed for applications in the field of timepieces. However, other fields may also be very well applicable, notably for example aeronautics, jewellery, the automotive industry or tableware.

In the field of horology, the need for such components is due to the increasing importance of brittle materials (such as those based on silicon, quartz, corundum or, more generally, ceramics). As an example, it is possible to envisage the construction of the balance spring, balance, pallet, bridge or even wheel set, such as an escape wheel, entirely or partially by a material based on a brittle material.

However, the always available ordinary steel spindles, which already know the machining technique thereof, are in fact a constraint which is difficult to adapt to the use of components without plastic domains. In fact, when the test is carried out, the steel mandrel cannot be pushed in and this systematically damages the fragile parts, i.e. those not having a plastic domain. For example, it is apparent that shear forces generated by metal mandrels entering the holes of silicon components can systematically damage the components.

Within the horology field, there is a technical prejudice that it is intended therefore that silicon parts cannot withstand stresses higher than between 300Mpa and 450Mpa without breaking. This metric is a theoretical estimate based on the Young's modulus characterizing the elastic domain of silicon.

Accordingly, for the case of estimated stresses outside this range between 300Mpa and 450Mpa, elastic deformation devices consisting of pierced holes in silicon have been developed accordingly, such as those disclosed in EP patent No. 1445670 and in patents WO2006/122873 and WO 2007/099068.

When additional testing was conducted by deforming the intermediate component and gradually increasing the stress applied to the silicon component, it was surprisingly apparent that the silicon component was actually able to withstand much higher stresses before any incipient cracks were detected. It is therefore surprising that the test is extended to a stress range of 1.5GPa to 2GPa, i.e. a technical prejudice range well beyond 300MPa to 450MPa but still without fracture. Thus, in a broad sense, brittle materials such as silicon, quartz, corundum or more generally ceramics do not necessarily follow statistical models commonly used for brittle components.

This is why the invention relates to the assembly of an element made of a first material (for example a ductile material such as steel) in a hole in a part made of a second material (for example a silicon-based material) that does not have a plastic domain, by deformation of an intermediate part made of a third material, the intermediate part being mounted between the element and the part.

According to the invention, the intermediate part comprises an aperture for receiving said element. Furthermore, the elastically and plastically deformed intermediate part radially clamps or clamps the element and elastically presses the part to fix the assembly in a manner that is non-destructive to the part.

Furthermore, in a preferred form, the outer wall of the intermediate element is shaped to substantially match the aperture in the element so as to exert substantially uniform radial stress on the wall of the element surrounding the aperture. In fact, when conducting research, it appears preferable for the intermediate part to distribute uniformly the radial stresses caused by its deformation on the part walls surrounding the hole.

Thus, if the hole in the brittle member is circular, it is preferred for the outer wall of the intermediate member to be of a substantially continuous cylindrical shape, i.e. without radial grooves or axial perforations other than the orifice for receiving the element, so as to avoid any local stresses on the small surface area of the member wall surrounding the hole that could damage the brittle material.

Of course, the shape of the aperture in the brittle member may be different, for example asymmetric, so as to avoid any relative movement between the elements of the assembly. Thus, according to a first alternative, the asymmetrical hole may thus be, for example, substantially elliptical.

According to another alternative aimed at avoiding any relative movement, the wall of the part 3 may be provided with a recess 1 extending into the hole 4, as shown in fig. 11. Preferably, the groove 1 extends over the entire thickness of the component 3 and comprises a dome-shaped outer surface of maximum height h. Of course, the grooves 1 may or may not be substantially straight.

From this it is apparent that the height h is much smaller than the diameter e of the hole 4₁Will form micro-grooves on the outer surface of the intermediate element when it is deformed, to form a mortise and tenon type connection for rotatably fixing the walls of the hole 4 and the outer surface of the intermediate element.

It is also obvious that these grooves may also be present on the outer surface of the element 5 to obtain the same effect and further improve the rotatable connection of future components.

Thus, if the cross-section of the hole is circular, the intermediate part with the orifice (the shape of which matches the hole) can be considered as a complete ring with continuous inner and outer walls, i.e. without any grooves or more generally without any material discontinuities. Thus, by elastic and plastic deformation, the mating shape of the intermediate member is capable of generating a substantially uniform radial stress over the maximum surface area of the member wall surrounding the aperture.

Of course, such matching wall shapes may also be applied to the inner wall of the intermediate part facing the element. It is therefore evident that the shape of the inner wall can be matched to the outer shape of the element in order to cause the inner wall of the intermediate part to generate a substantially uniform radial stress over the maximum surface area of the outer wall of the element.

The assembly according to the invention may be better understood with reference to fig. 1 to 10, which show an exemplary assembly. Fig. 1 to 4 show a first embodiment according to the present invention. The first step therefore consists in shaping the part 3 with a material that does not have a plastic domain and in shaping it with the holes 4. As shown in figure 1, the hole 4 has a section e preferably comprised between 0.5mm and 2mm₁And, if appropriate, the recesses 1 in fig. 11 projecting into the holes 4 have a height of between 5 μm and 25 μm.

This step can be done by dry etching or wet etching such as DRIE (deep reactive ion etching).

Furthermore, in a second step, the method comprises forming an element, which in the example of fig. 1 and 2 is the pivot pin 5, with a main cross-section e, from a second material₂. As described above, the second step may be implemented according to a general mandrel machining process. The element 5 is preferably metal and may for example be made of steel.

In a third step, the method comprises shaping the intermediate part 7 with a third material with an orifice 8, the orifice 8 having an inner cross-section e₄And an outer section e₃The walls of which substantially match the shape of the hole 4. Whereby the third step may be performed by conventional machining and/or electroformingAnd (5) realizing the process. The intermediate part 7 may thus have a thickness of between 100 μm and 600 μm and a width I of between 100 μm and 300 μm, i.e. an outer cross-section e₃Minus the internal section e₄Then divided by 2(I = (e))₃-e₄)/2)。

Preferably, the third material is more ductile than the second material of the element 5, so that the latter deforms less or not at all during the deformation step. The intermediate part 7 is preferably metal and may thus comprise nickel and/or gold. However, any other ductile material may advantageously be added to or substituted for the third material.

Of course, the first three steps need not follow any particular order and may even be performed simultaneously.

In a fourth step, the intermediate part 7 is inserted into the hole 4 without any contact. As shown in fig. 1, this means the section e of the hole 4₁Greater than or equal to the external section e of the intermediate part 7₃。

Preferably, the cross-section e of the hole 4₁Or if appropriate the outer cross-section e of the groove 1 and the intermediate part 7₃The difference between them is about 10 μm, i.e. there is a gap of about 5 μm separating the component 3 from the intermediate component 7.

Furthermore, preferably, according to the invention, one of the tools 11,13 used for the deformation step is used 11 for fixing the intermediate element 7 in the hole 4. Finally, in a preferred manner, the tool 11 comprises a recess 12 for receiving the element 5.

In a fifth step, the element 5 is introduced without any stress into the aperture 8 of the intermediate part 7. As shown in fig. 1, this means that the section e of the orifice 8₄Greater than or equal to the external section e of the element 5₂。

Preferably, the section e of the orifice 8₄With the outer cross-section e of the element 5₂The difference between them is about 10 μm, i.e. there is a gap of about 5 μm separating the element 5 from the intermediate part 7.

Furthermore, according to the invention, by fixing the element 5 in the aperture 8 by means of said recess 12 in the tool 11, the recess 12 has a cross-section e corresponding to the element 5₂Substantially equal cross-section.

Finally, the method comprises a sixth step consisting in elastically and/or plastically deforming the intermediate part 7 by moving the two tools 11,13 towards each other in the axial direction a, so as to exert radial stresses C, B on the element 5 and on the wall of the part surrounding the hole 4, respectively, by causing the part 3 to deform elastically.

In fact, it is surprising that it is not necessary to provide perforations around the hole 4 that penetrate the thickness of the component 3 to avoid component breakage, like those disclosed in EP patent No. 1445670 and in patents WO2006/122873 and WO 2007/099068. The component 3 can thus be elastically deformed without incipient cracks even under high stress, i.e. above 450Mpa for silicon.

Thus, as shown in fig. 2, the intermediate part 7 can be caused to deform elastically and plastically by pressing the tools 13 and 11 in the axial direction a on the top and bottom, respectively, of the intermediate part 7, which deforms radially only in the directions B and C, i.e. towards the part 3 and towards the element 5. Once the stress from the tools 11,13 is released, the elastic restoring force exerted by the part 3 permanently fixes the assembly constituted by the element 5-the intermediate part 7-the part 3.

Preferably, according to the invention, the deformation parameters are set such that the clamping force is larger at the gap between the undeformed intermediate member 7 and the wall of the bore 4 on the one hand and the gap between the undeformed intermediate member 7 and the element 5 on the other hand. Preferably, the displacement by the clamping force is comprised between 16 μm and 40 μm.

Thus, elastic and plastic deformation of the intermediate part 7 is required to cause elastic deformation of the part 3 surrounding the hole 4 and to cause elastic and/or plastic deformation of the element 5 to fix the element 5, the intermediate part 7 and the part 3 to each other as shown in fig. 2. As shown in fig. 2, it may also occur that the end of the intermediate part 7 is bent slightly downwards onto the part 3 during deformation, but this does not exert any axial stress on the part 3. Finally, it should be noted that this elastic deformation automatically centers the assembly constituted by the element 5-the intermediate part 7-the part 3.

Advantageously, according to the invention, no axial forces (which by definition are easily destructive) are added to the component 3 during the process. Only a radial elastic deformation controlled according to the preset stress of the tools 11,13 is added to the component 3. It should also be noted that the use of an intermediate element 7 whose outer wall has substantially the same shape as the hole 4 allows to exert a uniform stress on the wall of the element surrounding the hole 4 during the radial deformation B of the intermediate element 7, in order to avoid damaging the element 3 made of brittle material and to adjust any dispersion of the manufacture of the various components, for example the groove 1.

As shown in fig. 3 and 4, the intermediate part 7 preferably comprises a conical recess 10 coaxial with the orifice 8, in order to facilitate the radial orientation B, C of the stresses caused by the deformation of the intermediate part 7 during the deformation step, and also to allow said stresses to be graduated. In fact, the inclined surface 9 constituting the conical recess 10 creates an initial contact surface against the tool 13, which can be reduced to a circular shape by forcing the outer wall of the intermediate element 7 to deform radially by the gradual clamping force against the wall of the element surrounding the hole 4 and against the element 5.

In the example shown in fig. 3 and 4, it can be seen that the conical recess 10 in communication with the orifice 8 constitutes a flat portion between the bevel 9 and the edge of the orifice 8. However, this feature, i.e. the communication between the conical recess 10 and the orifice 8, is not essential as shown below and the recess 10 and the chamfer 9 therein may be of different shapes and sizes.

Of course, the invention is not limited to the examples illustrated but is susceptible to numerous modifications and alternative forms, which will be apparent to a person skilled in the art. In particular, the component 3 may also be axially locked in the alternative to the first embodiment.

As an example, fig. 5 and 6 show a second embodiment of the method. Thus, the alternative shown in fig. 5 and 6, in which the element 15 differs significantly from the element 5, is that it has a flange 16. Thus, the bottom of the tool 21 no longer needs to have a recess for receiving the element 15, but similarly only has a through hole 22, the cross section of which is at least equal to or greater than the cross section of the element 15.

It is thus evident that the intermediate part 7 and, if appropriate, the part 3 can accordingly be carried by the flange 16. Moreover, the deformation of the intermediate element 7 on its bottom is no longer achieved directly by the tool 21 but by the flange 16, without losing the advantages of the method. The part 3 is thus under elastic stress at the intermediate part 7 and is locked on the flange 16 of the element 15.

As an example, fig. 7 to 10 show a third embodiment of the method. Fig. 7 to 10 thus show an alternative, in which the intermediate part 27,27',27 "' differs significantly from the intermediate part 7 in the first embodiment in that it has a flange 26,26', 26"'. Accordingly, the third embodiment uses the same tools 11,13 as the first embodiment. Thereby, the component 3 is under elastic stress at the intermediate component 27,27',27 "' and is locked on the flange 26,26', 26"'.

In a first variant, shown in fig. 7, the intermediate part 27 comprises a conical recess 30, the inclined surface 29 of which communicates directly with the orifice 28, i.e. without a flat portion.

In a second variant, it is also possible for the intermediate part 27',27 "' to comprise a conical recess 30', 30"', the inclined surface 29',29 "' of which does not communicate with the orifice 28', 28"' but is separated therefrom by a ring 31',31 "'. Whereby the height of the ring 31 'may be less than the end of the bevel 29', the height of the ring 31 "may be equal to the end of the bevel 29", or the height of the ring 31 '"may be greater than the end of the bevel 29'". Of course, for this second variant, in the variant step, the tool 13 is opposite the inclined surfaces 29',29 "' without coming into contact with the rings 31', 31"'.

The embodiments given above may be combined with each other according to the target application. Also, as a non-limiting example, the assembly may be applied to a member in a timepiece such as a pallet fork, an escape wheel, a balance spring, a balance, a bridge or, more generally, a wheel set.

The assembly disclosed above may also be used in place of the elastic means 48 or the posts 63,66 in patent WO2009/115463 (incorporated herein by reference) to fix the single-piece sprung balance resonator to the pivot pin.

Of course, it is also possible to use two different assemblies to fix two elements similar to those described above to the same spindle, thus integrating their respective movements.

Finally, the assembly according to the invention can also connect any type of horological or other element whose body is made of a material without plastic domains (silicon, quartz, etc.) to the arbour, like for example a tuning fork resonator or more generally a MEMS (micro-electromechanical system).

Claims (17)

1. A method of assembling an element (5,15) made of a first material in a part (3) made of a second material having no plastic domain, comprising the steps of:

a) forming the component (3) with a hole (4);

b) inserting an intermediate part (7,27,27',27 "') into the hole (4) without any stress, the intermediate part being made of a third material and comprising an orifice (8,28,28', 28"'), the third material being more ductile than the second material of the element (5, 15);

c) introducing the element (5,15) into the aperture (8,28,28' ' ') without any stress;

d) the intermediate part (7,27,27',27 "') is elastically and plastically deformed by axially moving two pieces of tooling (11,13,21) towards each other on the top and bottom of said intermediate part, respectively, in order to apply radial stresses (B, C) to the elements (5,15) and to the wall of the part (3) surrounding the hole (4) by causing the part (3) to elastically deform, with the aim of fixing the assembly in a manner that is non-destructive to said part.

2. A method according to claim 1, characterized in that the outer wall of the intermediate member (7,27,27',27 "') is shaped to substantially match the hole (4) in the member (3) so as to exert a substantially uniform radial stress (B) on the wall of the member (3) surrounding the hole (4).

3. A method according to claim 1, characterized in that the holes (4) of the component (3) are circular.

4. A method according to claim 1, characterized in that the wall of the part (3) surrounding the hole (4) comprises a groove (1), which groove (1) will form a micro groove on the outer surface of the intermediate part (7,27,27',27 "') during step d) to avoid any relative movement between the elements of the assembly.

5. A method according to claim 1, characterised in that the outer surface of the element (5) comprises grooves which during step d) will form microgrooves on the inner surface of the intermediate part (7,27,27',27 "') to avoid any relative movement between the elements of the assembly.

6. A method according to claim 1, characterized in that the holes (4) of the component (3) are asymmetrical to avoid any relative movement between the elements of the assembly.

7. The method of claim 1, characterized by the steps ofIn step b), the cross-section (e) of the hole (4)₁) And an outer cross-section (e) of the intermediate part (7,27,27' ' ')₃) The difference between them is about 10 μm.

8. A method as claimed in claim 1, characterized in that in step c) the cross-section (e) of the element (5,15) is₂) And an inner cross-section (e) of the intermediate part (7,27,27' ' ')₄) The difference between them is about 10 μm.

9. Method according to claim 1, characterized in that in step d) the deformation applies a clamping force to generate a displacement comprised between 16 μ ι η and 40 μ ι η.

10. The method according to claim 1, characterized in that in step B) the intermediate member (7,27,27',27 "') comprises a conical recess (10,30,30', 30"') coaxial with the orifice (8,28,28',28 "') in order to contribute to the radial orientation (B, C) of the stresses caused by the deformation of the intermediate member (7,27,27', 27"') in step d).

11. The method of claim 1 wherein the second material comprises a single crystal silicon based material.

12. The method of claim 1, wherein the third material is comprised of a metal-based or metal alloy-based material.

13. A method as claimed in claim 1, characterized in that the component (3) is a timepiece wheel set.

14. A method as claimed in claim 1, characterized in that the component (3) is a timepiece pallet.

15. A method according to claim 1, characterized in that the component (3) is a horological balance spring.

16. A method as claimed in claim 1, characterized in that the component (3) is a resonator.

17. A method according to claim 1, characterized in that the component (3) is a MEMS.