Overmolding method

Abstract

This invention provides an overmolding method that enables injection molding without any solidification problems within the injection channel and without any risk of crystallization of amorphous metals. [Solution] An overmolding method for making a part with decoration 2, the method comprising the steps of: providing an ébauche having at least one through-hole 4 leading onto an overmolding 2 to be made, wherein the ébauche is made from a first material having low thermal permeability, or at least partially plated with a layer made from the first material; providing an injection molding mold; positioning the ébauche inside the injection molding mold; injecting liquid metal alloy through the through-hole 4 leading into the cavity of the injection molding mold and / or into the cavity of the ébauche; and removing the ébauche with the overmolding 2 from the mold to obtain a part.

Description

[Technical Field]

[0001] The present invention relates to an overmolding method suitable for making overmoldes from at least partially amorphous metal alloys, wherein the overmoldes form a decoration, also called a pattern, on a part made from a metal having a low thermal permeability. [Background technology]

[0002] Several documents describe methods for overmolding parts with amorphous alloy patterns.

[0003] For example, European Patent No. 2315673 and Swiss Patent Invention No. 715132 describe methods for inlaying amorphous metal into recesses in parts. These methods are not suitable for creating raised overmoldes and require finishing steps to precisely shape the surface of the overmolde.

[0004] A document known as European Patent No. 2370865 describes a method for decorating parts with relief decorations made from amorphous metal. This method consists of a step using a mask from which metal is injected. This leaves excess amorphous metal in the aesthetic zone, which therefore must undergo a finishing step.

[0005] Injection molding presents several problems with amorphous metals. Because the cooling rate must be sufficiently high to prevent crystallization, the mold cannot be heated to temperatures close to the melting point. Furthermore, using conventional molds requires an injection channel with a cross-section similar to the thickness of the cavity to be filled, in order to prevent premature solidification within the channel, which could prevent the alloy from reaching the cavity. This negatively impacts the geometric flexibility of the injection-molded part, especially in small parts where an alloy layer must cover the entire surface of the part. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] European Patent No. 2315673 [Patent Document 2] Swiss Patent No. 715132 [Patent Document 3] European Patent No. 2370865 [Overview of the project] [Problems that the invention aims to solve]

[0007] The present invention aims to improve upon the aforementioned drawbacks by, on the one hand, enabling injection without any solidification problems within the injection channel and without any risk of crystallization of amorphous metals, and on the other hand, by proposing an overmolding method that produces an overmolde that does not necessarily need to be precisely shaped after injection. [Means for solving the problem]

[0008] To achieve this objective, we propose starting with an ébauche of a part made from a material with low thermal permeability, so as to minimize heat removal from the material during the overmolding process. Furthermore, we propose injecting from the opposite side of the surface intended to be overmolded or from a surface connected to the intended surface, through a through-hole provided inside the ébauche that leads to a cavity forming the negative of the overmolde to be made. In other words, we further propose injecting from a portion of the surface opposite to another portion of the surface to be overmolded, or from a portion of the surface connected to another portion, through a through-hole provided inside the ébauche that leads to a cavity forming the negative of the overmolde to be made. According to the present invention, the cavity can be formed inside the ébauche and / or inside the injection molding mold that holds the ébauche.

[0009] The low thermal permeability of the ébauche ensures that there is no solidification whatsoever in the through-hole upstream of the cavity, thus guaranteeing that the alloy is injected into the cavity in a liquid state. Ideally, to obtain optimal results, it is recommended to use injection molding molds made from materials with even lower thermal permeability. This allows the alloy to perfectly conform to the shape of the mold cavity and / or ébauche, accurately reproducing the cavity's geometry and surface finish. As a result, the overmold will have a geometrically and aesthetically pleasing finish in the injected state, requiring no further precise shaping.

[0010] This method is particularly suitable for overmolding ébauches made from materials with low thermal permeability, such as certain ceramics (zirconia, glass, enamel, etc.), certain metals or metal alloys (grade 2 titanium, grade 5 titanium, Inconel, etc.), polymers (rubber, PEEK, etc.), natural materials (wood, minerals, etc.), and composite materials and materials plated with a layer having low thermal permeability, although having any thermal permeability. By using ébauches made entirely or partially from materials with low thermal permeability, it becomes possible to create through-holes with very small cross-sections, with no risk of solidification before reaching the cavity. These very small through-holes prevent the ceramic or other material from becoming brittle, allowing for the creation of small overmoldes.

[0011] In summary, the overmolding method according to the present invention enables greater flexibility in the geometry of molded parts, improves the reproducibility of the surface finish of the mold in contact with the molded part, and makes it possible to create dual-material parts with "overmolding of the final product shape." Therefore, this method makes it possible to create overmoldes with complex shapes.

[0012] More specifically, the present invention relates to an overmolding method for producing a part with decoration, also known as overmolding, wherein the decoration is made from at least partially amorphous metal alloy, and the method is: - Providing an overmold having a first surface to be overmolded and a second surface serving as an inlet point for injecting a liquid metal alloy, wherein the overmold comprises at least one through-hole extending between the first surface and the second surface and leading to the overmold to be formed, the through-hole forming a channel for injecting the metal alloy, and the overmold is 7,000WK -1 m -2 s 1 / 2 The following, preferably 3,500WK -1 m -2 s 1 / 2 - Making the overmold from a first material having the following thermal diffusivity or at least partially plating it with a layer made from the first material; - Providing an injection mold, wherein the injection mold and / or the overmold comprises an impression forming a negative of the overmold to be formed; - When the injection mold has an impression, positioning the overmold inside the injection mold having through-holes arranged towards the impression of the injection mold; - Injecting a liquid metal alloy from the second surface of the overmold through the through-hole leading to the impression to obtain an overmold with an overmold; - Removing the overmold with an overmold from the mold to obtain a component comprising.

Brief Description of Drawings

[0013] [Figure 1] Schematically shows the method steps according to the invention for embossed decoration. [Figure 2] Schematically shows the method steps according to the invention for embossed decoration. [Figure 3] Schematically shows the method steps according to the invention for embossed decoration. [Figure 4] Schematically shows the method steps according to the invention for embossed decoration. [Figure 5]Schematically shows the method steps according to the invention for relief decoration. [Figure 6] Shows a variant of the method for negative decoration. [Figure 7] Shows a variant of Figure 3, in which the overmold impression is made only in the ébauche and the decoration is flush with the surface of the ébauche. [Figure 8] Shows another variant of Figure 3, in which the overmold impression is made in the ébauche and in the mold to form a relief decoration.

Embodiments for Carrying Out the Invention

[0014] The present invention relates to an overmold method for making decorative parts. The parts can be, for example, watch components. More specifically, the parts can be external parts selected from the non-exhaustive list comprising a central part, a back, a bezel, a lug, a button, a link of a watch band, a watch band, a pin buckle, a clasp, a dial, an appliqué, and a pointer. The parts can also be movement components selected from the non-exhaustive list comprising a resonator, a plate bar, a pallet, a gear, and a plate. Typically, the watch component is a dial or bezel 1 (Figure 5) with indices and numbers forming a decoration 2, also hereafter referred to as overmold in this specification. In the example shown, the decoration takes the form of a relief, also known as positive decoration. The method is more specifically suitable for decorations made from at least partially amorphous metal alloys. "At least partially amorphous" is interpreted to mean having more than 50% amorphous phase. Examples include Pt850 alloy, Pd600 alloy, Vit105 alloy, and Ni53 alloy. At least partially amorphous metal alloys are also particularly suitable for parts made from brittle materials such as ceramics. The parts are made from a material having a low heat penetration rate. The low heat penetration rate is 7,000 WK -1 m -2 s 1 / 2The following or even 3,500WK -1 m -2 s 1 / 2 The following values ​​are specified. For example, ceramics are 2,400 WK. -1 m -2 s 1 / 2 It may be zirconia with a thermal conductivity of 7,000 WK. -1 m -2 s 1 / 2 If the thermal conductivity is greater than 7,000 WK, at least a portion of the surface of the component should be heated to 7,000 WK. -1 m -2 s 1 / 2 The following or even 3,500WL -1 m -2 s 1 / 2 It can be covered with a layer having the following thermal permeability.

[0015] The overmolding technique can be used when overmolding to create a positive relief, when overmolding coplanar with the surface to be decorated, or when overmolding to create a negative relief on the surface to be overmolded. Furthermore, combinations of the aforementioned overmolding techniques are also possible.

[0016] This method is illustrated in Figures 1 to 6 for one variant and in Figures 7 and 8 for other variants. The variants shown in Figures 1 to 6 are illustrated below, and in this method, the overmolding impression is formed in the injection molding mold, the difference being that in Figure 6 the relief is negative rather than positive. In the variants shown in Figures 7 and 8, the concept of the method is the same, the only change being that the overmolding impression is formed in the ébauche, or in the ébauche and the injection molding mold, respectively.

[0017] In addition, the method is illustrated below with respect to ébauches having polyhedral geometric shapes. The method can also be used to obtain geometric shapes with a single surface, such as the plane of revolution in the case of a torus. In this case, the term “plane” as used below should be understood to go beyond the geometric definition of a plane, and more generally, to refer to a portion of the ébauche surface that serves as the inlet point for the liquid alloy, relative to another portion of the ébauche surface that serves as the outlet point for the liquid alloy, and these portions may or may not be connected.

[0018] Figures 1 to 5 illustrate this method with respect to a positive relief overmolded from the indices and numerals on the bezel. Note that the values ​​shown below are also valid for other parts to be overmolded and are not limited to the bezel or positive relief overmolded. Accordingly, in Figure 6, the relief is negative.

[0019] In the first step (Figure 1), an ébauche 3 is provided with one or more through-holes 4. These through-holes serve as injection channels, extending between a surface 3a, which is a visible surface intended to be overmolded, and a surface 3b, which is the opposite surface of surface 3a, or optionally a surface connected to surface 3a, the opposite or connected surface being preferably a hidden surface once the watch case is assembled. In the illustrated example, the visible surface 3a is the top surface, and surface 3b is the opposite surface, and therefore the opposite surface is the bottom surface. This ébauche is the part to be overmolded and is made from a material having low thermal conductivity. The holes 4 are open to the outside where the overmolding is to be applied, forming injection channels 5 for the liquid metal or liquid alloy 8 to pass through (Figure 3). Depending on the dimensions of the overmolding to be made, the ébauche has one or more holes that penetrate the overmolding.

[0020] Preferably, to avoid brittle the ébauche material, the through-holes have a small cross-section. The cross-section of the hole may be constant or variable along the length of the hole. Preferably, the shape of the hole is conical, opening in a bell-shaped manner toward the bottom surface 3b as shown in Figure 2, which allows for more delicate geometry on the top surface and securely fixes the overmolding within the ébauche. The hole may have a circular, oval, or other cross-section. For example, a hole with an oval cross-section can be used to increase the supply cross-section in elongated overmoldings, such as indicators. The hole may also have curved portions or complex shapes rather than being linear, resulting in more flexible positioning of the injection port.

[0021] Preferably, the maximum dimension of the hole cross-section is in the range of 0.1 mm to 2 mm, more preferably between 0.2 mm and 1 mm, and even more preferably between 0.25 mm and 0.5 mm. If the hole cross-section varies along the hole, the maximum dimension is measured within the range of that cross-section, taking the maximum cross-section into account.

[0022] In bezels or dials, the thickness of the ébauche ranges from 0.3 mm to 3 mm. As a result, for through holes between the top and bottom surfaces of the ébauche, a range of hole diameter / length ratios is obtained, ranging from 0.08 mm to 1.7 mm, for circular cross-section holes with diameters ranging from 0.25 mm to 0.5 mm. For example, in other parts, a hole diameter / length ratio ranging from 0.08 mm to 1.7 mm can generally be maintained, or in other words, the ratio of the maximum dimension of the cross-section of the through hole to the thickness of the ébauche ranges from 0.08 mm to 1.7 mm for holes extending between the top and bottom surfaces. Furthermore, in positive relief overmoldings, the cross-section of the through hole in the top surface is less than or equal to the cross-section of the overmolding to be filled, which protrudes within the plane of the top surface, so as not to cause metal to overflow from the overmolding to be filled. Preferably, the cross-section of the through hole in the top surface is smaller than the cross-section of the decoration protruding within the plane of the top surface. More preferably, the cross-section of the through-hole in the upper surface is at least 1 / 2 of the cross-section of the overmolding that protrudes in the plane of the upper surface.

[0023] In the second step (Figure 3), the ébauche 3 is placed in a mold 6 having a shape corresponding to the shape of the overmold to be made, with an impression 7 on one of the two parts. In positive relief, the impression 7 forms a cavity. In a variation of Figure 7, the mold may have no impression at all, and it is the ébauche 3 that has an impression 10 forming a cavity. In a variation of Figure 8, the mold 6 has an impression 7, and the ébauche 3 also has an impression 10 that forms a cavity with two interconnected cavities. Thus, the overmold fills the cavity in the ébauche and the cavity in the mold.

[0024] According to the present invention, the mold is preferably 7,000 WK -1 m -2 s 1 / 2 The following, preferably 3,500WK -1 m -2 s 1 / 2 The mold is made from a material having a low thermal permeability having the following values, or is at least partially plated with a layer of such material having a low thermal permeability. According to the present invention, this material may be a ceramic (zirconia, Macor, etc.), a metal (titanium or titanium alloy, etc.), or preferably a polymer such as silicone or rubber. In practice, it has been found that polymer molds can be used without any degradation of the mold, even though the molten metal during injection is at high temperatures, for example, 700°C for Pt850 alloy and 1,200°C for Vit105 alloy. There are several advantages to using polymer molds. -Polymer molds have very low thermal permeability (<500WK) -1 m -2 s 1 / 2 This makes it possible to fill complex geometric shapes. - More specifically, due to the elasticity of the polymer mold made of elastomer, the polymer mold can be precisely aligned with the surface of the watch component, particularly the bezel surface in the illustrated example, and can compensate for manufacturing tolerances of the polymer mold, such as angles. - The elasticity of polymers also allows for the creation of 3D decorations with recessed carvings that are impossible with rigid molds. - The cost of manufacturing polymer molds is much lower than the cost of manufacturing metal or ceramic molds.

[0025] In the third step, also shown in Figure 3, the liquid alloy 8 is injected from the lower surface 3b of the ébauche 3 through a through-hole 4 that serves as an injection channel 5. When using conventional injection methods, the alloy is heated and injected at a temperature above the solidus temperature of the alloy. When using rapid heating methods, such as rapid discharge forming, to inject at least partially amorphous (>50%) preforms, the injection temperature is set so that the viscosity is less than 1,000 Pa·s. During injection, the mold can be heated to a temperature below the glass transition temperature of the amorphous alloy being injected.

[0026] In the fourth step shown in Figure 4, the mold is removed. The resulting ébauche 3, corresponding to the final or near-final part, has an amorphous metal alloy overmold 2 on its upper surface 3a. On the lower surface 3b of the ébauche, a foot 9 remains, formed from the injection alloy 8 that solidified in the injection channel. This foot can be retained in the final part. Alternatively, the lower surface can be precisely shaped to remove this excess material. The resulting part 1, shown in Figure 5, has an overmold 2 that does not require any precise shaping after injection into the mold. Naturally, finishing steps can nevertheless be performed on the overmold to obtain a specific surface finish, or to machine geometry that cannot be molded.

[0027] This method also makes it possible to create an overmold 2 that is coplanar with the top surface 3a to be decorated, in which case there is no cavity in the mold 6 as described above, and the ébauche 3 is equipped with an impression 10 as needed (Figure 7). This method also makes it possible to create a negative overmold, in which case the impression 7 forms a projection that is inserted into the through hole 4 during injection molding, instead of a cavity in the injection mold (Figure 6). [Explanation of symbols]

[0028] 1. Dial or bezel, component 2. Decoration 3 Ébauches 3a Visible surface, top surface 3b The opposite side of surface 3a, the surface connected to surface 3a, the bottom surface 4 through holes 5. Injection Channel 6. Mold 7 Impressions 8. Liquid metal or liquid alloy 9 Foot 10 Impressions

Claims

1. An overmolding method for producing a part (1) with a decoration (2) also known as overmolding, wherein the decoration (2) is made from at least partially amorphous metal alloy (8), and the overmolding method is - A step of providing an ébauche (3) having a first surface (3a) to be overmolded and a second surface (3b) that serves as an inlet point for injecting a liquid metal alloy (8), wherein the ébauche (3) comprises at least one through-hole (4) extending between the first surface (3a) and the second surface (3b) and opening outwards into the overmolded (2) to be made, the through-hole (4) forming a channel (5) for injecting the metal alloy (8), and the ébauche (3) is heated to 7,000 WK －１ I understand －２ s １／２ The following, preferably 3,500 WK －１ I understand －２ s １／２ A step of making a first material having the following thermal conductivity, or at least partially plating with a layer made from the first material, - A step of providing an injection molding mold (6), wherein the injection molding mold (6) and / or the ébauche (3) comprises impressions (7, 10) that form the negative of the overmold (2) to be made, - If the injection molding mold (6) is equipped with the impression (7), the step of positioning the ébauche (3) inside the injection molding mold (6) having through holes (4) arranged toward the impression (7) of the injection molding mold (6), - The steps of injecting the liquid metal alloy (8) from the second surface (3b) of the ébauche (3) through the through hole (4) which leads over the impression (7, 10) to obtain the ébauche (3) with the overmolded (2), - The step of removing the ébauche (3) with the overmolded (2) from the mold to obtain the part (1) An overmolding method that includes [a specific feature].

2. The injection molding mold (6) is 7,000 WK －１ m －２ s １／２ The following, preferably 3,500 WK －１ m －２ s １／２ The overmolding method according to claim 1, made of a second material having the following thermal penetration rate or at least partially plated with another layer made of the second material.

3. The overmolding method according to claim 1, wherein when the overmolding (2) to be made is in the form of a positive relief with respect to the first surface (3a) of the ébauche (3), the cross-section of the through hole (4) in the first surface (3a) is smaller than the cross-section of the overmolding (2) projecting into the plane of the first surface (3a).

4. The overmolding method according to claim 3, wherein the cross-section of the through hole (4) in the first surface (3a) is at least 1.2 times the cross-section of the overmolding (2) protruding in the plane of the first surface (3a).

5. The overmolding method according to claim 1, wherein the maximum dimension of the cross-section of the through hole (4) is in the range of 0.1 mm to 2 mm, preferably between 0.2 mm and 1 mm.

6. The overmolding method according to claim 5, wherein the maximum dimension of the cross-section of the through hole (4) is in the range of 0.25 mm to 0.5 mm.

7. The overmolding method according to claim 1, wherein the first surface (3a) is the upper surface of the ébauche (3), the second surface (3b) is the lower surface of the ébauche (3) opposite to the upper surface (3a), and the through hole (4) extends between the upper surface and the lower surface, penetrating the thickness of the ébauche (3).

8. The overmolding method according to claim 7, wherein the ratio of the maximum dimension of the cross-section of the through hole (4) to the thickness of the ébauche (3) is in the range of 0.08 to 1.

7.

9. The overmolding method according to claim 7 or 8, wherein the through hole (4) forms a cone that opens in a morning glory shape from the upper surface to the lower surface.

10. The overmolding method according to claim 1, wherein the first material is ceramic, preferably zirconia.

11. The overmolding method according to claim 2, wherein the second material is a polymer.

12. The overmolding method according to claim 11, wherein the second material is silicone or rubber.

13. The overmolding method according to claim 1, wherein the component (1) is a clock component.

14. The overmolding method according to claim 1, further comprising the step of removing from the second surface (3b) any excess of the at least partially amorphous metal alloy (8) that extends from the second surface (3b) after the injection of the liquid metal alloy (8).

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