Overmolding method

Abstract

The invention relates to an overmolding method for manufacturing an overmolded part (2) forming a decoration to be added to a part (1) or the part itself, said overmolded part (2) being made of an at least partially amorphous metal alloy (8), the method comprising the following steps: providing a blank (3) for use as an injection tool, a blank (3) having at least one through-hole (4) forming a channel (5) for injecting the metal alloy (8), the blank (3) being made of a first material having a thermal diffusion coefficient of less than or equal to 7000 W K-1 m-2 s 1 / 2, or being at least partially plated with a layer made of the first material; positioning the blank (3) in an injection mould (6); injecting the metal alloy (8) through the through-hole (4) opening into the cavity in order to obtain the overmolded part (2); the overmolded part (2) is separated from the blank (3) in order to form the trim or the part itself to be added.

Description

Technical Field

[0001] The present invention relates to an overmolding method suitable for manufacturing overmolded parts from at least partially amorphous metal alloys, the overmolded parts forming decorations, also known as patterns, which are designed to be added to or form part itself. Background Technology

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

[0003] For example, documents EP2315673 and CH715132 describe methods for embedding amorphous metals into grooves in components. These methods are not well-suited for manufacturing embossed overmolded parts and require finishing steps to smooth the surface of the overmolded parts.

[0004] Document EP2370865 describes a method for decorating components using relief decorations made of amorphous metal. The method involves using a mask through which metal is injected. This leaves excess amorphous metal in the aesthetic areas, necessitating finishing steps.

[0005] Injection molding presents several challenges when dealing with amorphous metals. The mold cannot be heated to near its melting point because the cooling rate must be high enough to prevent crystallization. Furthermore, using conventional metal molds requires injection channels with a cross-section similar to the thickness of the cavity to be filled to prevent premature solidification within the channels, which would hinder the alloy from reaching the cavity. This negatively impacts the flexibility of the injected part's geometry, especially for small parts that must be filled with an alloy layer covering the entire surface of the part. Summary of the Invention

[0006] The purpose of this invention is to overcome the above-mentioned disadvantages by proposing an overmolding method that, on the one hand, allows injection to be performed without solidification problems in the injection channel and without the risk of amorphous metal crystallization, and on the other hand, produces overmolded parts that do not require trimming after injection.

[0007] To this end, it is proposed to begin with a preform (ébauche) used as an injection tool, which is designed to be overmolded. This preform is made of a material with a low thermal diffusivity, or coated with a layer of a material with a low thermal diffusivity, in order to minimize heat absorption of the preform during the overmolding process. It is also proposed to inject via a through-hole from a surface opposite or connected to the other side intended for overmolding, the through-hole being provided within the preform and opening into a cavity of the mold forming the overmolded part to be manufactured. In other words, it is also proposed to inject via a through-hole from a portion of a surface opposite or connected to another portion of the surface to be overmolded, the through-hole being provided within the preform and opening into a cavity of the mold forming the overmolded part to be manufactured. According to the invention, this cavity may be formed in the preform and / or in the injection mold holding the preform.

[0008] The low thermal diffusivity of the preform ensures no solidification occurs in the through-hole upstream of the cavity, allowing the alloy to be injected 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 a low thermal diffusivity. This allows the alloy to perfectly conform to the shape of the mold cavity and / or the shape of the preform, accurately reproducing the cavity geometry and surface finish. As a result, the overmolded part is geometrically and aesthetically finished in its injection state without the need for further finishing.

[0009] Using blanks made entirely or partially of a material with a low thermal diffusivity allows for the formation of through-holes with very small cross-sections, eliminating the risk of metal solidification before reaching the cavity in the mold. These very small through-holes prevent the blanks from becoming brittle and enable the formation of small overmolded parts.

[0010] In summary, the overmolding method according to the present invention enables greater flexibility in the geometry of overmolded parts, improves the reproducibility of the surface finish of the mold and / or preform on the overmolded part, and produces "net-shape overmolded parts". Therefore, this method makes it possible to produce overmolded parts with complex shapes.

[0011] More specifically, the present invention relates to an overmolding method for manufacturing an overmolded part that forms a decoration to be added to a component or the component itself, the overmolded part being made of a metal alloy that is at least partially amorphous, the method comprising the following steps: - A blank for use as an injection tool is provided, the blank having a first surface to be overmolded and a second surface serving as an entry point for injecting the liquid metal alloy, the blank being provided with at least one through-hole extending between the first and second surfaces and opening to the overmolded part to be manufactured, the through-hole forming a channel for injecting the metal alloy, the blank being made of a first material having a K0 of less than or equal to 7000 WK. -1 m -2 s 1 / 2 Preferably less than or equal to 3500W K -1 m -2 s 1 / 2 The thermal diffusivity, or the blank being at least partially coated with a layer made of the first material; - Provide an injection mold, the injection mold and / or the preform including a cavity, the cavity forming a female mold of the overmolded part to be manufactured; - If the injection mold includes a cavity, the preform is positioned within the injection mold, wherein the through hole is arranged to face the cavity of the injection mold; - The liquid metal alloy is injected from the second side of the blank through the through hole opening into the cavity to obtain the blank having the overmolded part; - Demold the blank having the overmolded part; - Separate the overmolded part from the blank to form the decoration to be added or the part itself. Attached Figure Description

[0012] Figures 1 to 5 The steps in the method according to the invention are illustrated schematically.

[0013] Figure 6 The overmolded part forming the decoration added to the bezel is shown.

[0014] Figure 7 The overmolded parts forming the escapement fork and the wheel are shown.

[0015] Figure 8 It shows Figure 3 A variant in which the cavity for covering the molded part is made only in the blank.

[0016] Figure 9 It shows Figure 3 Another variation, in which the cavity for covering the molded part is made in the blank and in the mold. Detailed Implementation

[0017] This invention relates to a method for manufacturing an overmolded part, which is either a decoration to be added to a component or the component itself. For example, the component could be a watch component. More specifically, the component could be an external component selected from a non-exhaustive list including a centerpiece, case back, bezel, crown, pushers, strap connector, strap, clasp, buckle, dial, inlay, and hands. The component could also be a movement component selected from a non-exhaustive list including an oscillating mass, slats, escapement fork, wheels, and plates. For example, such as... Figure 7 As shown, the overmolded part 2 forming the component itself is the escapement fork 11 or the wheel 12. As another example, decoration could be indicators and numerals to be added to watch components. Typically, the overmolded part 2, also called decoration, is added to the dial or bezel 1 (…). Figure 6 ).

[0018] This method is particularly suitable for overmolded parts made of at least partially amorphous metallic alloys. "At least partially amorphous" means having more than 50% amorphous phase. Examples include Pt850 alloy, Pd600 alloy, Vit105 alloy, and Ni53 alloy.

[0019] This method is in Figures 1 to 5 A variant is shown in Figure 8 and 9 Other variations are shown below. The following will address... Figures 1 to 5 The variation shown illustrates the method, wherein a cavity for overmolding the part is formed in an injection mold. For Figure 8 and 9 The concept of this method remains the same, except that cavities for overmolding the part are formed either in the preform or in the injection mold.

[0020] Furthermore, the method is illustrated below for blanks with multifaceted geometries. This method can also be used for geometries with a single surface (e.g., a rotating surface in the case of a toroid). In this context, the term "face" as used below should be understood beyond its geometric definition and more generally refers to the portion of the blank's surface that serves as an inlet point for the liquid alloy, relative to another portion of the blank's surface that serves as an outlet point for the liquid alloy, wherein said portion may or may not be connected.

[0021] In the first step ( Figure 1 In this invention, a blank 3 is provided for use as an injection tool. This blank is made of a material with a low thermal diffusivity. A low thermal diffusivity is defined as less than or equal to 7000 W / K. -1 m -2 s 1 / 2 or even less than or equal to 3500W K -1 m-2 s 1 / 2 The value of the material can be ceramic (zirconia, machinable glass ceramics, etc.), metal (titanium or titanium alloys, etc.), or synthetic material, such as polymer, especially silicone resin or rubber. For example, the material can be ceramic, such as having a value of 2400W K. -1 m -2 s 1 / 2 Zirconia with a thermal diffusivity greater than 7000 W / K. -1 m -2 s 1 / 2 If the thermal diffusivity is such that at least a portion of its surface can be coated with a material having a thermal diffusivity of less than or equal to 7000 W / K, then... -1 m -2 s 1 / 2 Or even less than or equal to 3500W K - 1 m -2 s 1 / 2 The thermal diffusivity of the layer.

[0022] The blank 3 has one or more through holes 4. According to the 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 inlet point. This other surface can be the opposite surface 3a or optionally connected to surface 3a. In the example shown, surface 3a is the upper surface, while surface 3b is the opposite surface, and therefore the lower surface. The holes 4 open to the location where the overmolded part is to be applied and form an injection channel 5 for the passage of liquid metal or alloy 8. Figure 3 Depending on the dimensions of the overmolded part to be manufactured, the preform includes one or more holes passing through the overmolded part. Preferably, to prevent the preform material from becoming brittle, the through holes have a small cross-section. For example, such holes with small cross-sections can be fabricated using a femtosecond laser. The cross-section of the hole can be constant or vary along its length. For example, the hole can have a tapered shape opening toward the upper surface 3a, such as... Figure 2 As shown, for certain variations, this allows for easy release of overmolded parts containing an alloy that solidifies in the injection channel at the end of the process. The orifice can have a circular, elliptical, or other cross-section. For example, an orifice with an elliptical cross-section can be used to increase the supply cross-section on elongated overmolded parts such as indicators. The orifice may also not be straight, but rather have a curved or complex shape, allowing for more flexible positioning of the injection inlet point.

[0023] Preferably, the maximum dimension of the hole 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 maximum cross-section will be considered, and the maximum dimension will be measured within that cross-section.

[0024] For example, for a through hole between the upper and lower surfaces of a blank, for a blank thickness between 0.3 and 3 mm, for a circular cross-section with a diameter between 0.25 and 0.5 mm, the hole diameter / length ratio will range between 0.08 and 1.7 mm. Typically, this hole diameter / length ratio can be maintained within the range of 0.08 to 1.7 mm regardless of the blank thickness. Furthermore, the cross-section of the through hole in the upper surface is smaller than or equal to the cross-section of the overmolded part projected onto the plane of the upper surface to prevent alloy overflow from the overmolded part. Preferably, the cross-section of the through hole in the upper surface is smaller than the cross-section of the overmolded part projected onto the plane of the upper surface. More preferably, the cross-section of the through hole in the upper surface is at least 1.2 times smaller than the cross-section of the overmolded part projected onto the plane of the upper surface.

[0025] In the second step ( Figure 3 In the process, the blank 3 is placed in the mold 6, which has a cavity 7 formed in one of its two parts, the cavity having a shape corresponding to the shape of the overmolded part to be manufactured. Figure 8 In a variation, the mold may have no cavity, and the blank 3 includes cavity 13 that forms the cavity. Figure 9 In this variation, mold 6 includes cavity 7, and blank 3 also includes cavity 13, thus forming a cavity with two cavities designed to be connected. Therefore, the overmolded part will fill the cavity of the blank and the cavity of the mold.

[0026] According to the present invention, the mold is preferably made of a material having a low thermal diffusivity, the value of which is less than or equal to 7000 W K. -1 m -2 s 1 / 2 Preferably less than or equal to 3500W K -1 m -2 s 1 / 2 Alternatively, the mold may be at least partially coated with a layer of such a material having a low thermal diffusivity. According to the invention, this material may be ceramic (zirconia, machinable glass ceramics, etc.), metal (titanium or titanium alloys, etc.), or preferably a polymer (e.g., silicone or rubber). Indeed, although the temperature of the molten metal during injection is high, for example 700°C for Pt850 alloy or 1200°C for Vit105 alloy, it has been found that polymer molds can be used without deterioration. Using polymer molds has several advantages: -Their very low thermal diffusivity (<500 W K) -1 m -2 s 1 / 2 This allows it to fill complex geometric shapes; - Their elasticity (especially elasticity in elastomers) allows them to precisely conform to the surface of the blank and compensate for the blank's manufacturing tolerances, such as angles; Their elasticity also allows for the creation of 3D decorations with recessed reliefs, which is impossible in rigid molds; - The cost of manufacturing polymer molds is much lower than the cost of manufacturing metal or ceramic molds.

[0027] For similar reasons, polymer materials are also a good choice for preforms.

[0028] In the third step, also as Figure 3 As shown, liquid alloy 8 is injected from the lower surface 3b of the preform 3 through a through-hole 4 serving as an injection channel 5. When using conventional injection methods, the alloy is heated and injected at a temperature equal to or higher than its solidus temperature. When using a rapid heating method to inject a preform that is at least partially amorphous (>50%), such as rapid electrical discharge molding, the injection temperature is set so that the viscosity is below 1000 Pa·s. During injection, the mold can be heated to a temperature below or equal to the glass transition temperature of the injected amorphous alloy.

[0029] In the fourth step (not shown), the mold has been removed.

[0030] Then, in the fifth step, as Figure 4 and Figure 5 As shown, for the two different variations, the overmolded part 2 has been separated from the blank 3. According to... Figure 4 The variation involves separating the overmolded part from the tool by grinding several attachment points between the overmolded part and the tool. Then, as... Figure 6 As shown, the overmolded part is attached to the component to be decorated. According to... Figure 5 In the variant, the overmolded part 2, with an amorphous alloy gate 10 from injection channel 5, has been separated from the blank. The entire part can be discharged during solidification as the alloy is removed. If the through-hole is tapered, such as... Figure 2 As shown, effluent discharge will be easier. These gates can form attachment devices for adding decorations to the component. For example, these gates can form fastening feet to be inserted into the component. In this variation, before effluent discharge, the foot 9 formed on the lower surface where the injection alloy 8 is cured in the injection channel is removed. The foot can be removed by mechanically trimming the lower surface.

[0031] According to the present invention, the above method can also be used to manufacture overmolded parts that form their own components. Therefore, the overmolded part can be a functional component, for example... Figure 7The escapement fork 11 or wheel 12 is shown. Similar to any decorative elements to be added, the component may include an embossed design on its lower surface, formed by a gate created through the solidification of amorphous metal in an injection channel.

[0032] The method may optionally include additional steps, not shown, namely, finishing the overmolded part to obtain specific surface conditions or machining non-moldable geometries.

Claims

1. A method for manufacturing an overmolded part (2), the overmolded part forming a decoration or part itself to be added to a component (1), the overmolded part (2) being made of at least partially amorphous metal alloy (8), the method comprising the following steps: - A blank (3) is provided for use as an injection tool, the blank having a first surface (3a) to be overmolded and a second surface (3b) serving as an entry point for injecting the liquid metal alloy (8), the blank (3) being provided with at least one through hole (4) extending between the first surface (2a) and the second surface (3b) and opening to the overmolded part (2) to be manufactured, the through hole (4) forming a channel (5) for injecting the metal alloy (8), the blank (3) being made of a first material having a content less than or equal to 7000 W K. -1 m -2 s 1 / 2 Preferably less than or equal to 3500W K -1 m -2 s 1 / 2 The thermal diffusivity, or the blank being at least partially coated with a layer made of the first material; - Provide an injection mold (6), the injection mold (6) and / or the blank (3) including cavities (7, 13) that form a female mold for the overmolded part (2) to be manufactured; - If the injection mold (6) includes a cavity (7), the blank (3) is positioned inside the injection mold (6), wherein the through hole (4) is arranged to face the cavity (7) of the injection mold (6). - The liquid metal alloy (8) is injected from the second surface (3b) of the blank (3) through the through hole (4) opening into the cavity (7, 13) to obtain the blank (3) having the overmolded part (2). - Demold the blank (3) having the overmolded part (2); - Separate the overmolded part (2) from the blank (3) to form the decoration to be added or the part itself.

2. The overcoating method according to the preceding claims, wherein, The injection mold (6) is made of a second material having a yield of less than or equal to 7000 W / K. -1 m -2 s 1 / 2 Preferably less than or equal to 3500W K -1 m -2 s 1 / 2 The thermal diffusivity, or the injection mold is at least partially coated with another layer made of the second material.

3. The overcoating method according to any one of the preceding claims, wherein, The overmolded part (2) and at least one gate (10) formed by the solidification of the liquid alloy (8) in the injection channel (5) are separated from the blank (3), and the overmolded part (2) and the gate (10) together form the decoration to be added or the part itself.

4. The overcoating method according to the preceding claims, wherein, The entire part can be separated by discharging it.

5. The overcoating method according to any one of the preceding claims, wherein, The cross-section of the through hole (4) in the first surface (3a) is smaller than the cross-section of the overmolded part (2) projected onto the plane of the first surface (3a).

6. The overcoating method according to the preceding claims, wherein, The cross-section of the through hole (4) in the first surface (3a) is at least 1.2 times smaller than the cross-section of the overmolded part (2) projected onto the plane of the first surface (3a).

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

8. The overcoating method according to the preceding claims, wherein, The maximum cross-sectional dimension of the through hole (4) is between 0.25 mm and 0.5 mm.

9. The overcoating method according to any one of the preceding claims, wherein, The first surface (2a) is the upper surface of the blank (3), and the second surface (2b) is the lower surface of the blank (3) opposite to the upper surface (2a), and the through hole (4) extends through the thickness of the blank (3) between the upper surface and the lower surface.

10. The overcoating method according to claim 9, wherein, The ratio between the maximum cross-sectional dimension of the through hole (4) and the thickness of the blank (3) is between 0.08 mm and 1.7 mm.

11. The overcoating method according to claim 9 or 10, wherein, The through hole (4) is formed into a cone shape that opens from the lower surface to the upper surface.

12. The overcoating method according to any one of claims 2 to 11, wherein, The first material and / or the second material are polymers.

13. The overcoating method according to the preceding claim, wherein, The first material and / or the second material is silicone resin or rubber.

14. The overmolding method according to any one of the preceding claims, wherein, The component in question is a watch component.

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