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 forming decoration on a part, comprising the step of providing an ébauche 3 to be used as an injection tool, wherein the ébauche 3 has at least one through hole 4 that forms a channel 5 for injecting a metal alloy 8, and 7,000WK -1 m -2 s 1 / 2 The process includes the steps of: making a first material having the following thermal conductivity, or at least partially plating it with a layer made from the first material; positioning the ébauche 3 inside an injection molding mold 6; injecting a metal alloy 8 through a through hole 4 leading into a cavity to obtain an overmold 2; and separating the overmold 2 from the ébauche 3 to form any additional decorations or the part itself.

Description

[Technical Field]

[0001] The present invention relates to an overmolding method suitable for making overmoldes in at least partially amorphous metal alloys, wherein the overmolde forms a decoration, also known as a pattern, designed to be added to a part, or forms the part itself. [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 to be used as an injection molding tool designed for overmolding. The ébauche is made from a material with low thermal permeability, or plated with a layer of a material with low thermal permeability, to minimize heat removal due to low thermal permeability during the overmolding process. Furthermore, we propose injection from a surface opposite to or connected to the other surface intended for overmolding, 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 injection from a portion of the surface opposite to or connected to the other portion of the surface to be overmolded, 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] By using ébauches made entirely or partially from materials with low thermal permeability, it becomes possible to create through-holes with extremely small cross-sections, eliminating any risk of the metal solidifying before reaching the cavity in the mold. These very small through-holes prevent the ébauches from becoming brittle and allow for the creation of small overmoldes.

[0011] In summary, the overmolding method according to the present invention enables greater flexibility in the geometry of the overmold, improves the reproducibility of the surface finish of the mold and / or ébauche in contact with the overmold, and makes it possible to create an "overmold of the final product shape." Therefore, this method makes it possible to create overmolds with complex shapes.

[0012] More specifically, the present invention relates to an overmolding method for forming an overmolding to be added to a part, or for making the part itself, wherein the overmolding is made from at least partially amorphous metal alloy, and the method is - Providing an overmold having a first face to be overmolded and a second face serving as an inlet point for injecting a liquid metal alloy, wherein the overmold comprises at least one through-hole extending between the first face and the second face and leading to the overmold to be formed, the through-hole forming a channel for injecting the metal alloy, and the overmold has a thermal conductivity of 7,000WK [Figure 4] , 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 conductivity or at least partially plating it with a layer made from the first material<​​​​​​​​​​​​​​​​​​​​​​​​​​​The steps in the method according to the present invention are outlined below. [Figure 5] The steps in the method according to the present invention are outlined below. [Figure 6] This shows the overmolding that forms the decorative elements to be added to the bezel. [Figure 7] These show the overmoldings that form the pallet and gear, respectively. [Figure 8] Figure 3 shows the modified form, in which the overmolding impression is created only within the ébauche. [Figure 9] Figure 3 shows another variant, in which the overmolding impression is created both within the ébauche and within the mold. [Modes for carrying out the invention]

[0014] The present invention relates to a method for creating an overmold that is either a decoration to be added to a component or the component itself. A component can also be, for example, a watch component. More specifically, a component can be an external component selected from a non-exclusive list of central parts, backs, bezels, crowns, buttons, watch band links, watch bands, pin buckles, clasps, dials, appliqués, and hands. A component can also be a movement component selected from a non-exclusive list of oscillators, plate bars, palettes, gears, and plates. For example, as shown in Figure 7, the overmold 2 that forms the component itself is a palette 11 or a gear 12. In another example, a decoration can be an indicator and numeral to be added to a watch component. Typically, the overmold 2, also known as a decoration, is added to a dial or bezel 1 (Figure 6).

[0015] This method is more specifically suitable for overmolds 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.

[0016] This method is illustrated in Figures 1 - 5 for one variant form and in Figures 8 and 9 for other variant forms. This method is illustrated below with respect to the variant form shown in Figures 1 - 5, in which an impression for the overmold is formed with an injection molding mold. In the variant forms of Figures 8 and 9, the concept of the method is the same, and the only difference is that the impression for the overmold is formed either in an evosh or in an evosh and in an injection molding mold, respectively.

[0017] In addition, this method is illustrated below with respect to an evosh having a multi - faceted geometry. This method can also be used to obtain geometries having a single surface, such as a rotating surface in the case of a toroid. In this case, the term "surface" used below should be understood to go beyond the geometric definition of a surface and, more generally, refers to a part of the evosh surface that serves as an inlet point for the liquid alloy with respect to another part of the evosh surface that serves as an outlet point for the liquid alloy, and these parts may or may not be connected.

[0018] In the first step (Figure 1), an evosh 3 used as an injection tool is provided. This evosh is made of a material having a low heat penetration rate. The low heat penetration rate is defined as the following value or even further as 3,500 WK -1 m -2 s 1 / 2 below or even 3,500 WK -1 m -2 s 1 / 2 below. This material can be a ceramic (such as zirconia, Macor, etc.), a metal (such as titanium or titanium alloy, etc.), or a synthetic material such as a polymer, specifically silicone or rubber, for example. This material can be 2,400 WK-1 m -2 s 1 / 2 It may be a ceramic such as zirconia with a thermal permeability of 7,000 WK. -1 m -2 s 1 / 2 If the thermal conductivity is greater than that, at least a portion of the surface of the ébauche is heated to 7,000 WK. -1 m -2 s 1 / 2 The following or even 3,500WK -1 m -2 s 1 / 2 It can be covered with a layer having the following thermal permeability.

[0019] The ébauche 3 has one or more through holes 4. According to the present invention, these through holes serve as injection channels and extend between a surface 3a, which is the surface to be overmolded, and another surface 3b, which serves as the injection entrance point. This other surface 3b may be the surface opposite to surface 3a, or may optionally be connected to surface 3a. 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. 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. Preferably, to avoid brittle the material of the ébauche, the through holes have a small cross-section. These holes with a small cross-section can be made, for example, using a femtosecond laser. The cross-section of the hole may be constant or variable along the length of the hole. For example, the hole may have a conical shape that opens towards the top surface 3a in a bell-shaped manner, as shown in Figure 2, which in certain deformation forms allows for easy release of the overmolded with the solidified alloy in the injection channel at the end of the process. 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 overmoldeds, such as indexes. The hole may also have curved portions or complex shapes rather than being linear, resulting in more flexible positioning of the injection inlet point.

[0020] 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.

[0021] For example, with respect to a through hole between the top and bottom surfaces of an ébauche, for ébauche thicknesses in the range of 0.3 mm to 3 mm, the range of the hole diameter / length ratio is between 0.08 mm and 1.7 mm for a circular cross-section with a diameter in the range of 0.25 mm to 0.5 mm. In general, this hole diameter / length ratio in the range of 0.08 mm to 1.7 mm can be maintained regardless of the ébauche thickness. Furthermore, the cross-section of the through hole in the top surface is less than or equal to the cross-section of the overmold to be filled, which protrudes in the plane of the top surface, in order to prevent the alloy from overflowing from the overmold 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 in the plane of the top surface. More preferably, the cross-section of the through hole in the top surface is at least 1.2 times the cross-section of the overmold protruding in the plane of the top surface.

[0022] 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 forming a cavity in one of the two parts. In a variation of Figure 8, the mold may have no impression at all, and it is the ébauche 3 that has the impression 13 forming a cavity. In a variation of Figure 9, the mold 6 has the impression 7, and the ébauche 3 also has the impression 13 forming a cavity with two interconnected cavities. Thus, the overmold fills the cavity in the ébauche and the cavity in the mold.

[0023] 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 / 2The 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, the elasticity of the polymer mold made of elastomer allows the polymer mold to precisely conform to the surface of the ébauche, 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.

[0024] For similar reasons, polymer materials are also a good option for ébauches.

[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 a fourth step (not shown), the mold is removed.

[0027] Next, in the fifth step, which can be understood in Figures 4 and 5 for two different modification forms, the overmold 2 is separated from the ébauche 3. According to the modification form in Figure 4, the overmold 2 is separated by grinding down the few attachment points between the overmold and the tool. Then, as shown in Figure 6, the overmold is attached to the part to be decorated. According to the modification form in Figure 5, the overmold 2, with the amorphous alloy press 10 derived from the injection channel 5, is separated from the ébauche. When the alloy is removed during solidification, the entire part can be ejected. Ejection is easier if the through-hole is conical, as shown in Figure 2. These presses can form mounting means for adding decoration to the part. For example, these presses can form fixing feet to be inserted into the part. In this modification form, before ejection, the feet 9 formed on the bottom surface, with the injection alloy 8 solidified in the injection channel, are removed. These feet can be removed by mechanically shaping the bottom surface.

[0028] According to the present invention, an overmold that forms a part itself can also be manufactured using the method described above. Thus, the overmold may be a functional part such as a pallet 11 or a gear 12 as shown in Figure 7. As with any decoration to be added, the part may have reliefs on its underside formed by the press created by the solidification of the amorphous alloy within the injection channel.

[0029] The present invention may optionally include additional steps (not shown) for finishing the overmold to obtain specific surface conditions or to machine unformable geometric shapes. [Explanation of Symbols]

[0030] 1. Dial or bezel 2 Overmolding 3 Ébauches 3a Surface to be overmolded, visible surface, top surface 3b Another surface that serves as the injection port / inlet point, the opposite surface of 3a, the bottom surface 4 through holes 5. Injection Channel 6. Mold 7 Impressions 8. Liquid metal or liquid alloy, injection alloy 9 Foot 10 Pusher 11 Palettes 12 gears 13 Impressions

Claims

1. An overmolding method for forming an overmold (2) to be added to a part (1), or for making the part itself, wherein the overmold (2) is made from at least partially amorphous metal alloy (8), and the overmolding method is - A step of providing an ébauche (3) to be used as an injection tool, comprising a first surface (3a) to be overmolded and a second surface (3b) which 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 leading outward onto 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 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, 13) 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, 13) to obtain the ébauche (3) with the overmolded (2), - The step of removing the ébauche (3) with the overmolding (2) from the mold, - The steps of separating the overmolding (3) from the ébauche (3) and forming the decoration to be added or the part itself. An overmolding method that includes [a specific feature].

2. The injection mold (6) has 7,000 WK －１ m －２ s １／２ or less, 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 the overmolding (2) and at least one press (10) formed by the solidification of the liquid metal alloy (8) in the injection channel (5) are separated from the ébauche (3), and the overmolding (2) and the press (10) together form the decoration to be added or the part itself.

4. The overmolding method according to claim 3, wherein the entire part can be separated by ejecting the entire part.

5. The overmolding method according to claim 1, wherein the cross-section of the through hole (4) in the first surface (3a) is smaller than the cross-section of the overmolding (2) protruding in the plane of the first surface (3a).

6. The overmolding method according to claim 5, 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).

7. 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.

8. The overmolding method according to claim 7, 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.

9. 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).

10. The overmolding method according to claim 9, 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.

11. The overmolding method according to claim 9 or 10, wherein the through hole (4) forms a cone that opens in a morning glory shape from the upper surface to the lower surface.

12. The overmolding method according to claim 2, wherein the first material and / or the second material is a polymer.

13. The overmolding method according to claim 12, wherein the first material and / or the second material is silicone or rubber.

14. The overmolding method according to claim 1, wherein the aforementioned component is a clock component.

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