HK1224025B - One-piece electroformed metal component - Google Patents

Description

One-piece electroformed metal parts

Technical Field

The present invention relates to a one-piece electroformed metal component, particularly such a component having enhanced wear resistance.

Background Art

It is known to form one-piece metal parts by means of the LIGA process, ie a process combining the formation of a mould, for example by photolithography, and the filling of said mould by means of electroforming.

However, these electroformed parts are often too soft and have unsatisfactory wear resistance.

Summary of the Invention

An object of the present invention is to overcome all or part of the above-mentioned drawbacks by proposing a one-piece electroformed component having improved wear resistance while maintaining a relative magnetic permeability of less than 10 and the ability to be tight-fitted or press-fitted, and a manufacturing method including a surface hardening step, the depth of which can be easily controlled.

To this end, the invention relates to a one-piece component comprising an electroformed metal body containing trapped hydrogen, characterized in that the outer surface of said body dissipates the trapped hydrogen only over a predetermined depth, resulting in a hardening relative to the rest of the body in order to improve the wear resistance of the one-piece component while maintaining a relative magnetic permeability of less than 10 and the ability to be tight-fitted or press-fitted.

Surprisingly, therefore, such surface hardening of the electroformed metal body, advantageously according to the invention, makes it possible to improve the wear resistance of the one-piece component while maintaining a relative magnetic permeability of less than 10 and retaining the ability to be tight-fitted or press-fitted.

According to other advantageous variants of the invention:

- the predetermined depth is between 0.1% and 10% of the total thickness of the one-piece component;

- the metal is electroformed in an amorphous form and the outer surface comprises at least a partial crystalline phase of the electroformed metal or comprises a larger grain size than the electroformed metal of the remainder of the body;

- Electroforming metals include nickel, gold or platinum, such as nickel-phosphorus alloys, nickel-tungsten alloys or nickel-cobalt-phosphorus alloys.

Furthermore, the invention relates to a timepiece, characterized in that it comprises a component according to any one of the aforementioned variants, said component forming part of the exterior of the timepiece or part of a timepiece movement.

Finally, the invention relates to a method for producing a one-piece component, comprising the following steps:

a) forming a mold on a conductive substrate;

b) filling the mold by electroforming to form at least one integral metal part;

c) releasing the at least one integral metal component from the base plate and from the mold;

Characterized in that the method further comprises:

d) achieving desorption of hydrogen trapped in the at least one integral metal component during electroforming so as to produce another form of electroformed metal by causing hardening relative to the rest of the body only at a predetermined depth of the outer surface of the body.

Surprisingly, controlling hydrogen desorption in the obtained one-piece metal part makes it possible to harden the outer surface of the obtained one-piece metal part at a depth that is easily controlled. It can therefore be understood that the hardening front from the outer surface towards the center of the part can be easily achieved and controlled.

This surprising possibility overcomes the technical prejudice that heat treatment is always homogeneous, ie, in particular for timepiece components whose thickness rarely exceeds 200 μm, the hardening being effective between the outer surface and the core of the component.

According to other advantageous variants of the invention:

- the predetermined depth is between 0.1% and 10% of the total thickness of the one-piece component;

the metal is electroformed in step b) in amorphous form and the outer surface comprises at least part of a crystalline phase of the electroformed metal or has a larger grain size than the metal electroformed in step b);

- the metal electroformed in step b) comprises nickel, gold or platinum, such as a nickel-phosphorus alloy, a nickel-tungsten alloy or a nickel-cobalt-phosphorus alloy;

- step d) is carried out in a controlled atmosphere with a low hydrogen partial pressure, the controlled atmosphere being formed by 95% of dinitrogen and 5% of dihydrogen at atmospheric pressure;

- step d) is performed in vacuum;

- step d) is at a temperature between 250°C and 450°C for 15 to 240 minutes.

BRIEF DESCRIPTION OF THE DRAWINGS

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

1 to 4 are simplified diagrams of the steps of the method according to the present invention;

FIG5 is a graph intended to explain the results of factor variations in the desorption step of the method according to the present invention;

FIG6 is a schematic diagram of an external part of a clock and watch in which the present invention is applied;

7 and 8 are diagrams showing the application of the present invention to a timepiece movement.

DETAILED DESCRIPTION

As mentioned above, electroformed parts are very satisfactory in terms of their dimensions, especially when they are obtained by the LIGA process, but they are generally too soft and also have unsatisfactory wear resistance.

According to recent developments described further below, it has been found that surprisingly the outer surface of an electroformed component can be hardened at or to a depth that is easily controlled.

This surprising possibility overcomes the technical prejudice that heat treatment is always uniform, ie effective hardening between the outer surface and the core of the component, especially for timepiece parts whose thickness rarely exceeds 200 μm.

Advantageously and according to the invention, the one-piece part constituted by the electroformed body comprises an external surface comprising the dissipation of trapped hydrogen only to or up to a predetermined depth in the electroformed metal body, causing hardening relative to the rest of the body.

In fact, depending on the materials used, it is possible to electroform metal parts that are insensitive to magnetic fields. However, hardening causes the surface of the metal, which was initially electroformed in a homogeneous manner, to transform into a different form that may be sensitive to magnetic fields but may also restrict its plastic range to the point where a tight or press fit is not possible.

Thus, by means of surprising surface hardening of the electroformed metal body, it is advantageously possible according to the invention to improve the wear resistance of the one-piece component while maintaining a relative magnetic permeability of less than 10 and the ability to be tight-fitted or press-fitted.

The manufacturing method according to the invention comprises a first step a) for forming a mould 1 on a conductive substrate 3, as shown in Figure 1. The substrate 3 may be conductive itself, such as steel or doped silicon, or coated with a conductive layer, such as silicon coated with gold and/or chromium, or glass or ceramic.

In the example shown in Figure 1, mold 1 is formed from a resin obtained by photolithography to form a central portion 2 and a peripheral portion 4. The gap between the central portion 2 and the peripheral portion 4 will be used to accurately form the negative pattern 5 of the future integrated component. Of course, the advantage of this mold is that it is not limited to a single pattern 5. Therefore, multiple patterns 5 can be advantageously formed on the same substrate, and these multiple patterns can be the same or different.

The method then proceeds to a second step b) of filling the mold 1 by electroforming to form at least one integral metal part. The electroforming is performed by connecting the conductive surface of the base plate 3, which forms the bottom of the negative shape 5. Preferably, the metal electroformed in step b) comprises nickel, gold, or platinum.

Even more preferably, nickel-phosphorus alloys, nickel-tungsten alloys or nickel-cobalt-phosphorus alloys have been found to be particularly advantageous for forming timepiece components, such as a timepiece exterior or a part of a timepiece movement.In the example shown in FIG1 , bottom moulding 5 is in the shape of a wheel.

The method comprises a third step c) of releasing the at least one integral metal component 7 from the substrate 3 and from the mold 1, as shown in FIG2 . In this figure, it can be seen that the integral metal component 7 thus comprises a through hole 6 and a toothed ring 8, thereby forming a wheel. Step c) depends on the type of substrate 3 and mold 1 used. Selective chemical etching is typically used to preserve the at least one integral metal component 7 obtained.

Advantageously, according to the invention, the method further comprises a final step d) for desorbing hydrogen trapped in the at least one integral metal part during the electroforming of step b). In fact, recent research has shown that hydrogen is trapped during the electroforming step.

Therefore, surprisingly, controlling the desorption of hydrogen in the at least one obtained integral metal component 7 allows the outer surface of the at least one obtained integral metal component 7 to be hardened at a depth that is easily controlled. It can therefore be understood that the hardening front from the outer surface of the component towards the center of the component can be easily achieved and controlled.

As shown in FIG4 , it is thus clear that a composite component 17 is obtained from component 7. Thus, outer surface 19 comprises only a predetermined depth _E1 of the other electroformed metal, which has been hardened relative to the rest of body 20 initially electroformed in step b). Component 17 advantageously retains its original shape, namely toothed ring 18 and through-hole 16.

Thus, experiments have shown that a predetermined depth E ₁ between 0.1% and 10% of the total thickness _ET of the one-piece component 17, i.e. 2·E ₁ = 0.1% - 10%· _ET , surprisingly produces a component whose wear resistance is increased by 30% while still maintaining a relative magnetic permeability _μR of less than 10 and the ability to be tight or press fit.

Depending on the material chosen, the outer surface may include an increase in grain size relative to the remainder of the body, or a change in phase relative to the remainder of the body, such as a change from an amorphous phase to an at least partially crystalline phase.

According to the invention, step d) can be performed in a controlled atmosphere with a low hydrogen partial pressure or in a vacuum, so that the trapped hydrogen can escape from component 7. As a non-limiting example, one possible controlled atmosphere can consist of a fluid composed of 95% dinitrogen and 5% dihydrogen at atmospheric pressure. Finally, step d) can last for 15 to 240 minutes at a temperature between 250° C. and 450° C., depending on the materials used.

Advantageously, according to the present invention, the hardening front can be easily controlled from the outer surface of the component towards the center of the component. In fact, FIG7 shows an exemplary application of the present invention to a coaxial one-piece wheel 27 made of a nickel-phosphorus alloy and comprising a lower toothed ring 24, an upper toothed ring 28 and a through hole 26.

As shown in Figure 5, the parameters of step d) have been modified to generate a graph showing their effect on the integral component 27. The abscissa represents the duration in hours (H) of step d), which is performed at 300°C in a controlled atmosphere formed by 95% dinitrogen and 5% dihydrogen at atmospheric pressure. The ordinate represents the Vickers hardness (HV) on the left and the relative magnetic permeability ( _μR ) on the right.

The line marked with triangles (Δ) represents the Vickers hardness (HV 0.01) under a load of 10 g, the line marked with circles (○) represents the Vickers hardness (HV 0.5) under a load of 500 g, and the line marked with squares (□) represents the hardness difference between the experiment under a load of 10 g and the experiment under a load of 500 g. The line marked with crosses (×) represents the evolution of relative magnetic permeability μ _R.

Observing the curve marked with triangles (Δ), it can be seen that the external hardness of component 27 increases rapidly during the first hour of desorption at 300°C, then approaches an asymptote approaching 1000 HV. In comparison, the curve marked with circles (○), which represents the hardness at a depth of approximately 3 μm, remains essentially stable until after one hour of desorption at 300°C. It is therefore clear that a very gentle transformation front is achieved, as shown by the curve marked with squares (□). The curve marked with squares (□) also shows that the extreme value, representing a difference approaching 300 HV, is reached after 75 minutes of heating.

As previously mentioned, one objective of the present invention is to increase wear resistance while maintaining a relative magnetic permeability μ _R of less than 10, while also retaining the ability to provide a tight or press fit between the components. FIG. 5 shows a surface bounded by dashed lines to represent the range in which these conditions are observed. It can be seen that the duration of step d) at 300° C., which provides a favorable compromise for the one-piece nickel-phosphorus alloy component 27, ranges from 15 to 90 minutes. However, it is clear that, depending on the application and the materials used, this range could be from 15 to 240 minutes.

According to the tests, the one-hour duration of step d) at 300°C appears to be optimal for the one-piece nickel-phosphorus alloy component 27, as the hardness of the outer surface is approximately 850 HV, formed by the dendritic phase transformation front that gradually propagates towards the interior of the component as hydrogen escapes, while the hardness at a depth of approximately 3 μm remains unchanged at approximately 600 HV, formed by the amorphous phase. Furthermore, the relative magnetic permeability remains limited to 1.5, which makes the one-piece component insensitive to magnetic fields. Finally, after the tests, it became clear that the one-piece component 27 can still be fitted or press-fit onto an arbour using conventional methods to form a timepiece wheel set.

Step d) according to the invention differs from conventional metal heat treatments, which are usually performed at about 200°C in order to relieve internal stresses. As an example, in the case of nickel-phosphorus alloys, the phenomena described above only occur at temperatures significantly above 250°C.

Of course, the invention is not limited to the examples shown, but is capable of various variations and modifications that may occur to a person skilled in the art. In particular, identical experiments must be carried out depending on the application, temperature, materials used and duration of step d) in order to determine the optimal parameters for the component to be manufactured.

In the example shown in FIG8 , a timepiece spring, such as mainspring 37, does not need to be tight-fitted or press-fitted like a wheel set, but is simply engaged, via its eyelet 36, on a hook in the core of an arbour (not shown). It can thus, of course, withstand a longer duration of step d), i.e., for example, between 90 and 240 minutes, in order to provide the timepiece with a longer power reserve. Furthermore, since mainspring 37 is electroformed, strap 34 can have a variable cross-section for providing a substantially constant elastic torque during the relaxation of mainspring 37, and/or include a bridle 38 integral with strap 34.

Similarly, as shown in FIG6 , the application of the present invention is not limited to a portion of a timepiece movement, but can also be advantageously applied to the exterior of the timepiece. Indeed, while the back cover 41 and bezel 43 of a timepiece are typically tight-fitting or press-fitting, this is not the case with the case middle 45, the strap 47, the push-buttons 42, or the crown 44.

Thus, in a non-limiting manner, case middle part 45 or links 46 of bracelet 47 could of course be subjected to step d) for a longer time, i.e., for example between 90 and 240 minutes, in order to provide improved wear resistance and thus the timepiece forming fewer marks during wear.

The method can also be modified without departing from the scope of the invention. Thus, it is conceivable to deposit a certain sacrificial volume in the hole 6 before step d), so that the advancement of the hardening front in the wall of the hole 16, 26 can be limited, thereby making it easier to subsequently fit the one-piece component 17, 27 tight or press-fit.

Claims (17)

1. A one-piece component (17,27,37,41,42,43,44,45,47) comprising an electroformed metal body containing trapped hydrogen, characterized in that the hydrogen trapped on the outer surface (19) of the body is dissipated only up to a predetermined depth (E ₁ ), resulting in hardening relative to the rest of the body to improve the wear resistance of the one-piece component (17,27,37,41,42,43,44,45,47) while maintaining a relative permeability (μ _R ) of less than 10 and the ability to be tightly fitted. 2. The integral component (17,27,37,41,42,43,44,45,47) according to claim 1, characterized in that the predetermined depth ( _E1 ) is 0.1% to 10% of the total thickness ( _ET ) of the integral component (17,27,37,41,42,43,44,45,47). 3. The integral component (17,27,37,41,42,43,44,45,47) according to claim 1, characterized in that the metal is electroformed in an amorphous form, and the outer surface (19) comprises at least a portion of the crystalline phase of the electroformed metal. 4. The integral component (17,27,37,41,42,43,44,45,47) according to claim 1, characterized in that the outer surface (19) has a larger grain size than the electroformed metal of the rest of the body. 5. The integrated component (17,27,37,41,42,43,44,45,47) according to claim 1, characterized in that the electroformed metal is a nickel-phosphorus alloy, a nickel-tungsten alloy, or a nickel-cobalt-phosphorus alloy. 6. A clock, characterized in that the clock comprises an integral component (17,27,37,41,42,43,44,45,47) according to any one of claims 1 to 5. 7. The clock according to claim 6, wherein the integral component forms part of the outer portion of the clock. 8. The watch according to claim 6, wherein the integral component forms part of the movement of the watch. 9. A method for manufacturing an integral component (17,27,37,41,42,43,44,45,47), comprising the following steps: a) Forming a mold (1) on a conductive substrate (3); b) Fill the mold (1) by electroforming to form at least one integral metal part; c) Release the at least one integral metal component from the conductive substrate and from the mold; The method is characterized by further comprising the following steps: d) Desorption of trapped hydrogen in the at least one integral metal component during electroforming is achieved so that hardening relative to the rest of the body is formed only at a predetermined depth (E ₁ ) on the outer surface (19) of the body. 10. The method according to claim 9, wherein the predetermined depth ( _E1 ) is 0.1% to 10% of the total thickness ( _ET ) of the at least one integral component (17,27,37,41,42,43,44,45,47). 11. The method according to claim 9 or 10, wherein the metal is electroformed in an amorphous form in step b), and the outer surface comprises at least a portion of the crystalline phase of the electroformed metal. 12. The method according to claim 9 or 10, wherein the outer surface comprises a larger grain size than the metal electroformed in step b). 13. The method according to claim 9 or 10, wherein the metal electroformed in step b) is a nickel-phosphorus alloy, a nickel-tungsten alloy, or a nickel-cobalt-phosphorus alloy. 14. The method according to claim 9 or 10, characterized in that step d is performed in a controlled atmosphere having a low hydrogen partial pressure. 15. The method according to claim 14, wherein the controlled atmosphere is formed of 95% nitrogen and 5% hydrogen at atmospheric pressure. 16. The method according to claim 9 or 10, characterized in that step d) is performed in a vacuum. 17. The method according to claim 9 or 10, wherein step d) is sustained at a temperature between 250°C and 450°C for 15 to 240 minutes.