HK1172960B - Method of assembly of a part that has no plastic domain - Google Patents

Description

Method for assembling a component without a plastic domain

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-mentioned drawbacks by providing an adhesive-free assembly that enables, for example, the fixing of a part made of a material that does not have a plastic domain 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 of assembling an axially extending element made of a first material in a component made of a second material which does not have a plastic domain. The method comprises the following steps:

a) forming the part to have a hole;

b) inserting the radially expanded portion of the element into the hole without any stress;

c) the component is secured in a manner that is non-destructive to the component by elastically and plastically deforming the flared portion of the element within the bore by axially moving two-piece tooling toward each other on the top and bottom of the flared portion, respectively, thereby applying radial stress to the component wall surrounding the bore, causing the component to elastically deform.

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 a uniform radial elastic deformation to the component.

Moreover, such a structure advantageously enables the fixing of the assembly of component-elements without the need to adhere to the usual precisely controlled elements, while ensuring that the component is not subjected to damaging stresses even when it is made of, for example, monocrystalline silicon.

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

According to other advantageous features of the invention:

-the outer wall shape of the expanded portion of the element within the bore substantially matches the bore within the component, thereby exerting a substantially uniform radial stress on the component wall surrounding the bore;

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 flared portion during step c) 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 developed part of the element inside the hole is about 10 μm;

-in step c), deforming applies a clamping force to produce a displacement between 8 μm and 20 μm;

-in steps b) and c), fixing the expanded portion of the element in the hole by using one of the two tools;

in step B), the flared portion of the element inside the hole comprises a conical recess, with the aim of contributing to the radial orientation (B) of the stresses caused by the deformation of said flared portion in step c);

-the second material is a silicon-based material;

-the first 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 sectional front or perspective views of an element 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 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.

In the field of horology, 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 radially deforming the flared portion 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 was therefore surprising that the test was 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 component made of a second material (for example a silicon-based material) which does not have a plastic domain.

According to the invention, said element comprises a radially expanding and elastically and plastically deformable portion which radially grips or clamps the wall of said part surrounding the hole, thereby elastically stressing the part with the aim of fixing the assembly in a manner which is non-destructive to said part.

Furthermore, the radially developed portion of the element present in the bore is preferably shaped to substantially match the bore in the component, thereby exerting substantially uniform radial stress on the component wall surrounding the bore. In fact, when conducting research, it is obviously preferable for the development of the elements present in the hole to distribute in a uniform manner the radial stresses caused by their deformation on the wall of the part surrounding the hole.

Thus, if the hole in the brittle member is circular, it is preferred for the outer wall of the flared portion of the element present in the hole to be of substantially continuous cylindrical shape, i.e. without radial grooves or axial perforations, 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 4₁These recesses 1, when they are deformed, can form microgrooves on the outer surface of the flared portion to form a mortise and tenon type connection for rotatably fixing the walls of the hole 4 and the outer surface of the flared portion and, additionally, the outer surface of the element 5.

Thus, if the cross-section of the hole is circular, the radially developed part of the element present in the hole, the shape of which matches that of the hole, can be considered as a complete disc with a continuous outer wall, that is without any grooves or, more generally, without any discontinuities in the material. Thus, by elastic and plastic deformation, the matching shape of the developed part of the element present in the hole enables to generate a substantially uniform radial stress on the maximum surface area of the part wall surrounding the hole.

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 forming the part 3 from a material without plastic domains and in forming it with a circular hole 4. As shown in figure 1, the hole 4 has a section e preferably comprised between 0.5mm and 2mm₁And, if appropriate, the recess 1 in fig. 11 projecting into the hole 4 has a heightThe degree is 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 a second material having a main section e₂And an element of a radially developed part 7, which in the example of fig. 1 and 2 is the pivot pin 5, the radially developed part 7 being intended for deformation and having a maximum cross section e₃. The flared portion 7 may have a thickness of between 100 μm and 600 μm. 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.

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

In a third step, the radially developed portion 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 flared portion 7 of the element 5₃。

Preferably, the cross-section e of the hole 4₁(or if appropriate the groove 1) and the outer section e of the flared part 7₃The difference between them is about 10 μm, i.e. there is a gap of about 5 μm separating the component 3 with respect to the flared portion 7 of the element 5.

Moreover, preferably, according to the invention, the radially expanded portion 7 and, concomitantly, the element 5 are fixed inside the hole 4 by means of one of the tools 11,13 for the deformation step. Finally, in a preferred manner, the tool 11 comprises a recess 12 for receiving one end of the element 5.

Finally, the method comprises a fourth step consisting in elastically and plastically deforming the radially flared portion 7 of the element 5 by moving the two tools 11,13 towards each other in the axial direction a, so as to apply a radial stress B to the wall of the part surrounding the hole 4, causing the part 3 to elastically deform.

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 the component 3 breaking, 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 flaring 7 can be caused to deform elastically and plastically only radially in direction B, i.e. towards the component 3, by the tools 13 and 11 pressing in axial direction a on the top and bottom, respectively, of the deformed radial flaring 7. Once the stress from the tools 11,13 is released, the elastic return force exerted by the part 3 permanently fixes the assembly of elements 5-part 3 by means of the flared portion 7.

Preferably, according to the invention, the deformation parameters are set such that the clamping force is greater at the gap between the undeformed flared portion 7 and the wall of the hole 4. Preferably, the displacement by the clamping force is comprised between 8 μm and 20 μm.

Thus, elastic and plastic deformation of the radially flared portion 7 is required to cause elastic deformation of the part 3 around the hole 4 in order to fix the element 5, and therefore the flared portion 7 and the part 3, deformed, to each other as shown in fig. 2. As shown in fig. 2, it may also occur that the end of the flared portion 7 is slightly bent down onto the component 3 during deformation, but this does not exert any axial stress on the component 3. Finally, it should be noted that this embodiment would enable the element 5 to be automatically centred with respect to the component 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 a radially flared portion 7 whose outer wall has substantially the same shape as the hole 4 allows to exert a uniform stress on the wall of the part surrounding the hole 4 during the radial deformation B of the flared portion 7, in order to avoid damaging the part 3 made of brittle material and to adjust any dispersion of the manufacturing of the various components, for example the groove 1.

As shown in fig. 3 and 4, the radially flared portion 7 preferably comprises a conical recess 10 in order to facilitate the radial orientation B of the stresses caused by the deformation of the flared portion 7 during the deformation step, and also to make said stresses gradual. In fact, the inclined surface 9 constituting the conical recess 10 creates an initial contact surface against the tool 13, which can be restored to a circular shape by forcing the radial deformation of the outer wall of the flared portion 7 by the gradual clamping force against the wall of the part 3 surrounding the hole 4.

In the example shown in fig. 3 and 4, it can be seen that the conical recess 10 constitutes a chamfer 9 and the thickness returns to e₂Between the elements 5. However, this feature, namely the conical recess 10 and the thickness e₂The communication between the elements 5 is not essential as shown below and the recesses 10 and the bevels 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. The bottom of the tool 21 is thus modified and has a through hole 22 whose cross section is at least equal to or greater than that of the element 15.

It is thus evident that the element 5 is no longer carried by the radially developed portion 7 but can be carried by the flange 16, if appropriate also by the component 3. Moreover, the deformation of the flared portion 7 on its bottom is no longer achieved directly with the tool 21 but by the flange 16, without losing the advantages of the method. The component 3 is thus under elastic stress at the flared portion 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 radially developed sections 27,27',27 "' differ significantly from the developed section 7 of the first embodiment in that they have flanges 26,26', 26"'. Accordingly, the third embodiment uses the same tools 21,13 as the second embodiment. Thereby, the component 3 is under elastic stress at the flared portions 27,27',27 "' and is locked on the flanges 26,26', 26"'.

In a first variant, shown in figure 7, the flared portion 27 comprises a conical recess 30, the inclined surface 29 of which has a thickness e₂The element 25 of (a) is directly terminated, i.e. without a flat portion.

In a second variant, it is also possible for the flared portions 27',27 "' to comprise conical recesses 30', 30"', the inclined surfaces 29',29 "' of which do not have a thickness e₂But rather is terminated by a ring 31',31 "'. Whereby the height of the ring 31 'may be less than the height of the end of the bevel 29', the height of the ring 31 "may be equal to the height of the end of the bevel 29", or the height of the ring 31 "'may be greater than the height of the end of the bevel 29"'. Of course, for this second variant, the tool 13 faces the inclined surfaces 29',29 "' during the variant step 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 mandrel, so that their respective movements are integrated. It is evident that the same mandrel can be shaped with two radially developed portions 7,27,27',27 "' that can be deformed.

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 (16)

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

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

b) inserting the radially developed parts (7,27,27',27 "') of the elements (5,15) into the holes (4) without any stress;

c) the expanded portion (7,27,27',27 "') of the element within the hole (4) is elastically and plastically deformed by axially moving two pieces of tooling (11,13,21) towards each other on the top and bottom of the expanded portion, respectively, so as to apply radial stresses (B) to the wall of the component (3) surrounding the hole (4), causing the component (3) to elastically deform, thereby fixing the assembly in a manner that is non-destructive to the component.

2. A method according to claim 1, characterized in that the outer wall shape of the flared portion (7,27,27',27 "') substantially matches the hole (4) in the component (3) so that a substantially uniform radial stress (B) is exerted on the wall of the component (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 component (3) surrounding the hole (4) comprises a groove (1), which groove (1) will form a micro groove on the outer surface of the flared portion (7,27,27',27 "') during step c) to avoid any relative movement between the elements of the assembly.

5. 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.

6. A method as claimed in claim 1, characterized in that in step b) the cross-section (e) of the hole (4) is₁) And the external section (e) of the developed part (7,27,27' ' ') of said element inside the hole (4)₃) The difference between them is about 10 μm.

7. Method according to claim 1, characterized in that in step c) the deformation applies a clamping force to generate a displacement comprised between 8 μ ι η and 20 μ ι η.

8. A method as claimed in claim 1, characterized in that in steps b) and c) the developed part (7,27,27',27 "') of the element (5,15) in the hole (4) is fixed in the hole (4) by using one of the two tools (11,13, 21).

9. Method according to claim 1, characterized in that in step B) the flared portion (7,27,27',27 "') of the element inside the hole (4) comprises a conical recess (10,30,30', 30"') with the purpose of contributing to the radial orientation (B) of the stresses caused by the deformation of said flared portion in step c).

10. The method of claim 1, wherein the second material is a silicon-based material.

11. The method of claim 1, wherein the first metallic material is comprised of a metal-based or metal alloy-based material.

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

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

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

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

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