Overmolding method

Abstract

The invention relates to an overmolding method for producing a component (1) having a decoration (2), also referred to as an overmolded part, said decoration (2) being made of an at least partially amorphous metal alloy (8), said method comprising the following steps: providing a blank (3) having at least one through-hole (4) which opens into the overmolded part (2) to be produced, said blank (3) being made of a first material having a low thermal diffusion coefficient or being at least partially plated with a layer made of said first material; providing an injection mould (6); positioning the blank (3) inside the injection mould (6); the liquid metal alloy (8) is injected through the through hole (4), and the through hole is communicated into the cavity of the injection mold (6) and / or the cavity of the blank (3); the blank (3) with the overmolded part (2) is demolded in order to obtain the component (1).

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, on components made of materials having a low thermal diffusivity. 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 blank (ébauche) of a component made of a material with a low thermal diffusivity, so as to minimize heat absorption of the blank during the overmolding process. It is also proposed to inject via a through-hole from a surface opposite or connected to the surface intended for overmolding, the through-hole being provided within the blank 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 blank 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 blank and / or in the injection mold holding the blank.

[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] This method is particularly suitable for overmolding preforms made of materials with low thermal diffusivity, such as certain ceramics (zirconia, glass, enamel, etc.), certain metals or metal alloys (grade 2 titanium, grade 5 titanium, chromium-nickel-iron alloys, etc.), polymers (rubber, PEEK, etc.), natural materials (wood, minerals, etc.), and composites and materials with any thermal diffusivity but coated with a layer having a low thermal diffusivity. Using preforms made entirely or partially of materials with low thermal diffusivity allows for the formation of through-holes with very small cross-sections without the risk of solidification before reaching the cavity. These very small through-holes prevent the ceramic or other materials 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 molded parts, improves the reproducibility of the surface finish of the mold on the molded parts, and produces bimaterial parts with "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 decorative parts, the decoration also referred to as an overmolded part, the decoration being made of at least partially amorphous metal alloy, the method comprising the following steps: - A blank is provided having a first surface to be overmolded and a second surface serving as an inlet point for injecting the liquid metal alloy. The blank is 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 is made of a first material having a K0 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 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; - Demolding the blank having the overmolded part to obtain the component. Attached Figure Description

[0012] Figures 1 to 5 The steps of the method according to the invention for relief decoration are illustrated schematically.

[0013] Figure 6 A variation of the method for negative decoration is shown.

[0014] Figure 7 It shows Figure 3 A variation thereof, wherein the cavity for covering the molded part is made only in the blank, and the decoration is flush with the surface of the blank.

[0015] Figure 8 It shows Figure 3 Another variation involves a cavity for covering the molded part being formed in the blank and the mold, thus creating a relief decoration. Detailed Implementation

[0016] This invention relates to an overmolding method for manufacturing decorative components. The component can be, for example, a watch component. More specifically, the component can be an external component selected from a non-exhaustive list including a centerpiece, case back, bezel, crown, pushers, strap connector, strap, clasp, buckle, dial, lettering, and hands. The component can also be a movement component selected from a non-exhaustive list including an oscillating mass, slats, escapement fork, wheels, and plates. Typically, the watch component is a dial or bezel 1 (… Figure 5 This part has indicators and numbers forming decoration 2, which are also referred to below as overmolded parts. In the example shown, the decoration is embossed, also known as a positive decoration. This method is more particularly suitable for decorations made of metal alloys that are at least partially amorphous. "At least partially amorphous" means having more than 50% amorphous phase. Examples include Pt850 alloy, Pd600 alloy, Vit105 alloy, and Ni53 alloy. This part is also particularly suitable for parts made of brittle materials such as ceramics. The part 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. For example, ceramics can have 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.

[0017] The overmolding method can be used when overmolding is performed to create a positive relief, flush with the surface to be decorated, or to create a negative relief relative to the surface to be overmolded. Combinations of the above-described overmolded parts can also be produced.

[0018] This method is in Figures 1 to 6 A variant is shown in Figure 7 and 8 Other variations are shown below. The following will address... Figures 1 to 6The variation shown illustrates the method, wherein a cavity for overmolding the part is formed in an injection mold, the difference being that... Figure 6 In this case, the relief is negative, not positive. For Figure 7 and 8 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.

[0019] 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.

[0020] Figures 1 to 5 The diagram illustrates a method for overmolding a bezel with embossed indicators and numerals. It should be noted that the values ​​given below are also valid for other parts to be overmolded, and are not limited to bezels or embossed overmolded parts. Therefore, in Figure 6 In the middle, the relief is negative.

[0021] In the first step ( Figure 1 In this process, a blank 3 with one or more through holes 4 is provided. These through holes serve as injection channels and extend between a surface 3a and a surface 3b, which is the visible surface intended to be overmolded, and the surface 3b is the surface opposite to or optionally connected to the surface 3a, wherein the opposite or connected surface is preferably a hidden surface once the case has been assembled. In the example shown, the visible surface 3a is the upper surface, and the surface 3b is the opposite surface, and therefore the lower surface. The blank is the part to be overmolded and is made of a material with a low thermal diffusivity. The holes 4 open to the location where the overmolded part is to be applied and form injection channels 5 for the passage of liquid metal or alloy 8. Figure 3 Depending on the dimensions of the overmolded part to be manufactured, the blank includes one or more holes passing through the overmolded part.

[0022] Preferably, to prevent the material of the blank from becoming brittle, the through hole has a small cross-section. The cross-section of the hole can be constant or vary along its length. Preferably, the hole is tapered, such as... Figure 2The hole opens towards the lower surface 3b, allowing for finer geometry on the upper surface and anchoring the overmolded part within the preform. The hole can have a circular, elliptical, or other cross-section. For example, a hole with an elliptical cross-section can be used to increase the supply cross-section on elongated overmolded parts such as indicators. The hole can also be non-straight, having 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 the bezel or dial, the blank thickness is between 0.3 mm and 3 mm. For the through-hole between the upper and lower surfaces of the blank, this results in a hole diameter / length ratio ranging from 0.08 mm to 1.7 mm for a circular cross-section with a diameter between 0.25 and 0.5 mm. For example, for other components, this hole diameter / length ratio can typically be maintained within the range of 0.08 to 1.7 mm, or in other words, for holes extending between the upper and lower surfaces, the ratio between the maximum cross-sectional dimension of the through-hole and the thickness of the blank is between 0.08 and 1.7 mm. Furthermore, for positive relief overmolded parts, the cross-section of the through-hole in the upper surface is less than or equal to the cross-section of the overmolded part to be filled projected onto the plane of the upper surface to prevent alloy overflow from the overmolded part to be filled. Preferably, the cross-section of the through-hole in the upper surface is smaller than the cross-section of the decoration 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 in the plane of the upper surface.

[0025] In the second step ( Figure 3 In this process, the blank 3 is placed in the mold 6, which has a cavity 7 in one of its two parts. This cavity has a shape corresponding to the shape of the overmolded part to be manufactured. For a positive relief, the cavity 7 forms a hollow space. Figure 7 In a variation, the mold may have no cavity, and the blank 3 includes the cavity 10 that forms the cavity. Figure 8 In this variation, mold 6 includes cavity 7, and blank 3 also includes cavity 10, 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. -1m -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 an elastomer) allows them to precisely conform to the surface of watch components (especially the bezel in the example shown) and compensate for manufacturing tolerances of watch components, 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] 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.

[0028] exist Figure 4 In the fourth step shown, the mold is removed. The resulting blank 3, corresponding to the final or near-final part, has an amorphous metal alloy overmolded part 2 on its upper surface 3a. On its lower surface 3b, a foot 9 formed by the injection alloy 8 solidified in the injection channel remains. This foot can be retained on the final part. Alternatively, the lower surface can be trimmed to remove the excess material. Figure 5The final part 1 shown has an overmolded part 2, which requires no finishing after injection into the mold. Of course, finishing steps can still be performed on the overmolded part to obtain a specific surface finish or to machine unmoldable geometries.

[0029] It should be noted that this method also allows for the manufacture of an overmolded part 2 flush with the upper surface 3a to be decorated; in this case, the cavity in the mold 6 as described above is absent, and if necessary, the blank 3 includes a cavity 10 ( Figure 7 This method also allows for the production of negative overmolded parts, in which, instead of the cavity of the injection mold, cavity 7 is formed as a protrusion inserted into through hole 4 during injection. Figure 6 ).

Claims

1. An overmolding method for manufacturing a component (1) having a decoration (2), the decoration also referred to as an overmolded part, the decoration (2) being made of at least partially amorphous metal alloy (8), the method comprising the following steps: - A blank (3) is provided 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) is 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) forms a channel (5) for injecting the metal alloy (8). The blank (3) is made of a first material having a K0 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 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, 10) 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, 10) to obtain the blank (3) having the overmolded part (2); - Demolding the blank (3) having the overmolded part (2) to obtain the component (1).

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, When the overmolded part (2) to be manufactured is a positive relief relative to the first surface (3a) of the blank (3), 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 in the plane of the first surface (3a).

4. 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).

5. 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.

6. 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.

7. 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.

8. The overcoating method according to claim 7, 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.

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

10. The overmolding method according to any one of the preceding claims, wherein, The first material is ceramic, preferably zirconium oxide.

11. The overmolding method according to any one of claims 2 to 10, wherein, The second material is a polymer.

12. The overcoating method according to the preceding claim, wherein, The second material is silicone resin or rubber.

13. The overmolding method according to any one of the preceding claims, wherein the component (1) is a watch component.

14. The overmolding method according to any one of the preceding claims, comprising the step of removing an excess of the at least partially amorphous metal alloy (8) extending from the second surface (3b) after injection of the liquid metal alloy (8).

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