Overmolding process

Abstract

The invention relates to an overmolding process for producing an overmolding (2) forming a decoration to be applied to an article (1) or to an article as such, said overmolding (2) being in a metallic alloy (8) at least partially amorphous, comprising the steps of: - Providing a blank (3) acting as an injection tool, said blank (3) being provided with at least one through hole (4) forming a channel (5) for the injection of the metallic alloy (8), said blank (3) being made of a first material having a thermal effusivity less than or equal to 7000 W K-1 m-2 s1 / 2 or being at least partially coated with a layer made of said first material, - Positioning the blank (3) within an injection mold (6), - Injecting the metallic alloy (8) through the through hole (4) opening into a cavity to obtain the overmolding (2),- Separation of the overmolding (2) from the blank (3) to form the decoration to be added or the article itself.

Description

Technical field of the invention

[0001] The invention relates to an overmolding process adapted to produce an overmolding in at least partially amorphous metallic alloy, the overmolding forming a decoration, also called a motif, intended to be applied to an article or forming an article as such. Technological background

[0002] Several documents describe processes for overmolding an article with amorphous alloy patterns.

[0003] Examples include documents EP 2 315 673 and CH 715 132, which describe processes for embedding amorphous metal in recesses made in the article. These processes are poorly suited for creating raised overmoldings and require a finishing step to rectify the surface of the overmoldings.

[0004] Document EP 2 370 865 describes a method for decorating an article with a relief design made of amorphous metal. The method involves using a mask through which the metal is injected. This results in excess amorphous metal in the areas to be decorated, and these areas must therefore undergo a finishing step.

[0005] In injection molding processes, several problems arise with amorphous metals. It is not possible to heat the mold to a temperature close to the melting point because the cooling rate must be sufficiently high to prevent crystallization. Furthermore, the use of conventional metal molds necessitates injection channel cross-sections similar to the thickness of the cavity to be filled, to prevent premature solidification within the channels, which would prevent the alloy from reaching the cavity. This negatively impacts the flexibility of the injected part geometries, particularly for small parts where a sheet of alloy must be used to fill an entire face of the part. Summary of the invention

[0006] The present invention aims to overcome the aforementioned shortcomings by proposing an overmolding process which, on the one hand, allows injection without solidification problems in the injection channels and without risk of crystallization of the amorphous metal and, on the other hand, provides an overmolding which does not necessarily require rectification after injection.

[0007] To this end, it is proposed to start with a blank that serves as an injection mold intended for overmolding. The blank is made of a material with low thermal effusivity or coated with a layer of a material with low thermal effusivity to minimize heat extraction during overmolding. It is also proposed to inject from a face opposite or adjacent to another face intended for overmolding via through holes machined within the blank and opening into a cavity forming the negative of the overmolding to be performed. In other words, it is also proposed to inject from a portion of a surface, opposite or adjacent to another portion of the surface intended for overmolding, via through holes machined within the blank and opening into a cavity forming the negative of the overmolding to be performed. According to the invention, the cavity can be provided in the blank and / or in the injection mold receiving the blank.

[0008] The low thermal effusivity of the blank ensures that the through-holes upstream of the cavity do not solidify, thus allowing the alloy to flow into the cavity in a liquid state. Preferably, for optimal results, it is also recommended to use an injection mold made of a material with low thermal effusivity. This allows the alloy to perfectly conform to the shape of the mold cavity and / or the blank, faithfully reproducing the geometry and surface finish of the cavity. Consequently, the overmoldings are finished, both geometrically and aesthetically, in their as-injection state, eliminating the need for any further machining.

[0009] Using a blank made entirely or partially from a material with low thermal effusivity allows for very small through holes without the risk of the metal solidifying before reaching the mold cavity. These very small through holes prevent weakening the blank and allow for the creation of small overmoldings.

[0010] In summary, the overmolding process according to the invention allows for greater flexibility in the geometry of overmoldings, improves the reproduction of the surface finish of the mold and / or blank on the overmolding, and enables the creation of "net-shape overmoldings." This process thus makes it possible to produce overmoldings with complex shapes.

[0011] More specifically, the invention relates to an overmolding process for creating an overmolding that forms a decorative element to be applied to an article or to an article as such, said overmolding being made of a metallic alloy that is at least partially amorphous, the process comprising the steps of: Provision of a blank serving as an injection tool with a first face intended to be overmolded and a second face serving as an entry point for the injection of the liquid metal alloy, said blank being provided with at least one through hole extending between the first face and the second face and opening at the level of the overmolding to be carried out, the through hole forming a channel for the injection of the metal alloy, said blank being made of a first material having a thermal effusivity less than or equal to 7000 WK-1< m-2< s 1 / 2< , preferably less than or equal to 3500 WK-1< m-2< s 1 / 2< or being at least partially coated with a layer made of said first material, Provision of an injection mold, said injection mold and / or the blank comprising an impression forming the negative of the overmolding to be carried out,Positioning of the blank within the injection mold with the through-hole aligned with the mold cavity if the injection mold has a cavity; Injection of the liquid metal alloy from the second face of the blank through the through-hole opening onto the cavity to obtain the blank with the overmolding; Demolding of the blank with the overmolding; Separation of the overmolding from the blank to form the decorative element or the finished article. Brief description of the figures

[0012] THE figures 1 to 5 schematically represent the steps of the process according to the invention. figure 6 represents the overmolding that forms a decorative element applied to a bezel. figure 7 represents overmoldings forming respectively an anchor and a wheel. figure 8 represents a variant of the figure 3 where the cavity for overmolding is formed only in the blank. The figure 9represents another variant of the figure 3 where the imprint for overmolding is made in the blank and in the mold. Detailed description of the invention

[0013] The invention relates to a method for creating an overmolding, which is either a decorative element to be applied to an article or an article in itself. The article may, for example, be a watch component. More specifically, it may be a case component chosen from the non-exhaustive list including a case, case back, bezel, crown, pusher, bracelet link, bracelet, pin buckle, clasp, dial, applique, and hands. It may also be a movement component chosen from the non-exhaustive list including an oscillating weight, mainplate bridge, pallet fork, wheel, and mainplate. For example, as shown in the figure 7The overmolding 2 forming the article itself is an anchor 11 or a wheel 12. The decoration can, again by way of example, be indices and numerals to be applied to a watch component. Typically, the overmolding 2, also called decoration, is applied to a dial or a bezel 1 ( fig.6 ).

[0014] The process is specifically suited for overmolding in a metallic alloy that is at least partially amorphous. At least partially amorphous is defined as having more than 50% amorphous phase. Examples include Pt850, Pd600, Vit105, and Ni53 alloys.

[0015] The process is illustrated in figures 1 to 5 for a variant and to figures 8 and 9 for other variants. The process will be illustrated below for the variant of figures 1 to 5 where the cavity for overmolding is formed in the injection mold. For variants of figures 8 and 9The concept of the process is the same, with the only change being that the cavity for overmolding is respectively made in the blank or in the blank and in the injection mold.

[0016] Furthermore, the process is illustrated below for a blank with a multi-faceted geometry. It is also possible to implement the process for a geometry with a single surface, such as a surface of revolution in the case of a torus. In this case, the term "face" used below will be understood beyond its geometric definition and will more generally designate a portion of the blank surface serving as the entry point for the liquid alloy relative to another portion of the blank surface serving as the exit point for the liquid alloy, with these portions being either connected or disconnected.

[0017] In a first step ( fig.1A blank 3, serving as an injection tool, is provided. This blank is made of a material with low thermal effusivity. Low thermal effusivity is defined as a value less than or equal to 7000 WK⁻¹ m⁻² s⁻¹ / ², or even less than or equal to 3500 WK⁻¹ m⁻² s⁻¹ / ². This material can be a ceramic (zirconia, Macor, etc.), a metal (titanium or titanium alloy, etc.), or a synthetic material such as a polymer, and in particular a silicone or a rubber. For example, it could be a ceramic such as zirconia, which has a thermal effusivity of 2400 WK⁻¹ m⁻² s⁻¹ / ². If the rough has a thermal effusivity greater than 7000 WK -1< m -2< s 1 / 2< , it is possible to apply at least in part a surface layer which has a thermal effusivity less than or equal to 7000 WK -1< m -2< s 1 / 2< , or even less than or equal to 3500 WK -1< m -2< s 1 / 2< .

[0018] The blank 3 is provided with one or more through holes 4. According to the invention, these through holes act as injection channels and extend between face 3a, which is the face intended to be overmolded, and another face 3b, which serves as the entry point for injection. This other face may be opposite face 3a or possibly contiguous to face 3a. In the illustrated example, face 3a is the upper face and face 3b is the opposite face, which is therefore the lower face. The hole 4 opens at the location where the overmolding is to be placed and defines an injection channel 5 for the passage of the liquid metal or alloy 8 ( fig.3Depending on the dimensions of the overmolding to be performed, the blank has one or more through holes created by overmolding. Preferably, to avoid weakening the blank material, the through holes have a small cross-section. This small cross-section hole can be created, for example, by a femtosecond laser. The cross-section of the hole can be constant or variable along its length. For example, the hole can have a conical shape flaring out towards the upper face 3a as shown in the figure. figure 2This allows, for certain variants, for easy release of the overmolding with the alloy solidified in the injection channel at the end of the process. The hole can have a circular, oblong, or other cross-section. For example, holes with an oblong cross-section are possible to increase the supply area on elongated overmoldings such as indices. The holes may also be non-straight but rather have bends or complex shapes, in order to allow for more flexible positioning of the injection entry point.

[0019] Preferably, the largest dimension of the hole's cross-section is between 0.1 and 2 mm, more preferably between 0.2 and 1 mm, and even more preferably between 0.25 and 0.5 mm. If the cross-section varies along the hole, the largest cross-section will be considered, and within that cross-section, the largest dimension will be measured.

[0020] For example, for a through hole between the top and bottom faces of the blank, with a blank thickness between 0.3 and 3 mm, the hole diameter-to-length ratio will be between 0.08 and 1.7 mm for a circular cross-section diameter between 0.25 and 0.5 mm. Generally, this hole diameter-to-length ratio of 0.08 to 1.7 mm can be maintained regardless of the blank thickness. Furthermore, the cross-sectional area of ​​through holes on the top face is less than or equal to the cross-sectional area of ​​the overmoldings to be filled, projected onto the plane of the top face, to prevent the alloy from overflowing beyond the overmolding. Preferably, the cross-sectional area of ​​through holes on the top face is less than the cross-sectional area of ​​the overmoldings projected onto the plane of the top face.More preferably, the cross-section of the through holes at the top face is smaller by a factor of at least 1.2 compared to the cross-section of the overmoldings projected into the plane of the top face.

[0021] In a second step ( fig.3 ), the blank 3 is placed in a mold 6 which, in one of its two parts, has an impression 7 forming a cavity with a shape corresponding to the shape of the overmolding to be carried out. Alternatively, for the figure 8 The mold may be without an impression, and it is the blank 3 that has an impression 13 forming a cavity. As an alternative for the figure 9 The mold 6 has an impression 7, and the blank 3 also has an impression 13, forming the cavity with the two cavities intended to communicate. The overmolding will therefore fill the cavities of the blank and the mold.

[0022] According to the invention, the mold is made of a material preferably having low thermal effusivity with a value less than or equal to 7000 WK⁻¹ m⁻² s⁻¹ / ², preferably less than or equal to 3500 WK⁻¹ m⁻² s⁻¹ / ², or it is at least partially coated with a layer of this low thermal effusivity material. According to the invention, this material can be a ceramic (zirconia, Macor, etc.), a metal (titanium or titanium alloy, etc.), or preferably a polymer such as silicone or rubber. Indeed, despite the high temperatures of the molten metal during injection, for example 700°C for a Pt850 alloy or 1200°C for a Vit105 alloy, it has been found that it is possible to use a polymer mold without degrading it. There are several advantages to using a polymer mold: Their very low thermal effusivity (< 500 W K-1 m-2 s1 / 2) allows them to fill complex geometries. Their elasticity, especially for elastomers, allows them to precisely conform to the surface of the blank and compensate for manufacturing tolerances, such as angles. Their elasticity also allows them to create 3D decorations with undercuts that would not be demoldable with a rigid mold. The manufacturing cost of a polymer mold is much lower than that of a metal or ceramic mold.

[0023] For similar reasons, the choice of polymer material will also be wise for the rough draft.

[0024] In a third stage also represented at the figure 3The liquid alloy 8 is injected through the through hole 4, acting as an injection channel 5, from the lower face 3b of the blank 3. The alloy is heated and injected at a temperature equal to or higher than its solidus temperature in the case of a conventional injection molding process. In the case of a rapid-heat injection molding process for a preform that is at least partially amorphous (> 50%), such as rapid discharge forming, the injection temperature is set so that the viscosity is less than 1000 Pa·s. During injection, the mold can be heated to a temperature lower than or equal to the glass transition temperature of the injected amorphous alloy.

[0025] In a fourth, unshown step, the mold is removed.

[0026] Next, in a fifth step visible to Figures 4 and 5For two different variants, the overmolding 2 is separated from the blank 3. Depending on the variant of the figure 4 It is detached by grinding down the few points of attachment between the overmolding and the tool. Then, the overmolding is attached to the item to be decorated, visible at the figure 6 According to the variant of the figure 5 The overmoldings 2 with the sprues 10 of the amorphous alloy from the injection channels 5 are separated from the blank. The assembly can be removed by means of the alloy shrinkage during solidification. Removal will be facilitated if the through holes have a conical geometry as shown in the figure 2These sprues can form attachment points for attaching the decoration to the article. For example, they can form attachment feet to be inserted into the article. In this variant, before removal, the foot 9 formed on the underside with the injection alloy 8 solidified in the injection channel is removed. This foot can be removed by mechanically grinding the underside.

[0027] According to the invention, it is also possible to use the process described above to manufacture overmoldings which, as such, constitute an article. Thus, the overmoldings can be functional parts such as an anchor 11 or a wheel 12 as shown in the figure 7 . Just as with the decoration to be added, the piece may have on its underside a relief resulting from the cores formed by the solidification of the amorphous metal in the injection channels.

[0028] The process may optionally include an additional, unshown finishing step on the overmoldings to obtain particular surface finishes or to machine non-moldable geometries.

Claims

1. Overmolding process for producing an overmolding (2) forming a decoration to be applied to an article (1) or to an article as such, said overmolding (2) being in a metallic alloy (8) that is at least partially amorphous, the process comprising the steps of: - Providing a blank (3) acting as an injection tool with a first face (3a) intended to be overmolded and a second face (3b) serving as an entry point for the injection of the metallic alloy (8) in a liquid state, said blank (3) being provided with at least one through hole (4) extending between the first face (2a) and the second face (3b) and opening at the level of the overmolding (2) to be produced, the through hole (4) forming a channel (5) for the injection of the metallic alloy (8), said blank (3) being made of a first material having a thermal effusivity less than or equal to 7000 W K-1 m-2 s1 / 2,preferably less than or equal to 3500 W K-1 m-2 s1 / 2 or being at least partially coated with a layer made of said first material, - Provision of an injection mold (6), said injection mold (6) and / or the blank (3) comprising a cavity (7,13) forming the negative of the overmolding (2) to be produced, - Positioning of the blank (3) within the injection mold (6) with the through hole (4) positioned opposite the cavity (7) of the injection mold (6) if said injection mold (6) has a cavity (7), - Injection in liquid state of the metal alloy (8) from the second face (3b) of the blank (3) through the through hole (4) opening onto the cavity (7,13) to obtain the blank (3) with the overmolding (2), - Demolding of the blank (3) with the overmolding (2), - Separation of the overmolding (2) from the blank (3) to form the decoration to be applied or the article as such.

2. An overmolding method according to the preceding claim, wherein said injection mold (6) is made of a second material having a thermal effusivity less than or equal to 7000 WK -1 m -2 s 1 / 2 , preferably less than or equal to 3500 WK -1 m -2 s 1 / 2 or being at least partly coated with another layer made of said second material.

3. Procédé de surmoulage selon l'une des revendications précédentes, dans lequel le surmoulage (2) et au moins une carotte (10) formée par la solidification de l'alliage liquide (8) dans le canal d'injection (5) sont désolidarisés de l'ébauche (3), l'ensemble avec le surmoulage (2) et la carotte (10) formant le décor à rapporter ou l'article en tant que tel.

4. Overmolding method according to the preceding claim, wherein the assembly is separated by detachment.

5. Overmolding method according to any one of the preceding claims, wherein the cross-section of the through hole (4) at the level of the first face (3a) is less than the cross-section of the overmolding (2) projected into the plane of the first face (3a).

6. Overmolding method according to the preceding claim, wherein the cross-section of the through hole (4) at the level of the first face (3a) is smaller by a factor of at least 1.2 compared to the cross-section of the overmolding (2) projected into the plane of the first face (3a).

7. Overmolding method according to any one of the preceding claims, wherein the largest dimension of the cross-section of the through hole (4) is between 0.1 and 2 mm, preferably between 0.2 and 1 mm.

8. Overmolding method according to the preceding claim, wherein the largest dimension of the cross-section of the through hole (4) is between 0.25 and 0.5 mm.

9. Overmolding method according to any one of the preceding claims, wherein the first face (2a) is an upper face of the blank (3) and wherein the second face (2b) is an inferior face of the blank (3) opposite said upper face (2a), the through hole (4) extending between the upper face and the inferior face through the thickness of the blank (3).

10. Overmolding method according to claim 9, wherein the ratio between the largest dimension of the cross-section of the through hole (4) and the thickness of the blank (3) is between 0.08 and 1.

7.

11. Overmolding method according to claim 9 or 10, wherein the through hole (4) forms a cone flaring from the lower face to the upper face.

12. Overmolding process according to any one of claims 2 to 11, wherein the first material and / or the second material is a polymer.

13. Overmolding process according to the preceding claim, wherein the first material and / or the second material is a silicone or a rubber.

14. Overmolding process according to any one of the preceding claims, wherein the article is a watch component.

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