TECHNICAL FIELD
The present invention relates to a method for machining a raised and/or hollow structure in an injection mould and to the method for manufacturing a decorated item obtained by injection of a ceramic material or by cermet within said mould. It also relates to the item, and more particularly to a watch component such as a bezel, produced with said manufacturing method as well as to the mould obtained by the machining method.
Ceramic or cermet watch components are obtained by an injection method including a step of sintering the green body obtained after injection. These components often have a decoration, such as indexes and numbers for bezels, which is machined after the injection method. These decorations have the feature of being very fine and therefore require extreme precision to obtain a quality engraving. Generally, the decorations are made by laser ablation with engraving times that can go beyond an hour. This post-injection decoration step therefore generates additional manufacturing costs and times.
The object of the present invention is to overcome the aforementioned disadvantages by proposing a new manufacturing method where the decoration is carried out at the same time as the injection so as to avoid the engraving step after the injection.
To this end, the present invention relates to a method for manufacturing an item comprising a step of injecting the material into a mould comprising an impression with a raised and/or hollow structure which is the negative of the decoration of the item to be manufactured. According to the invention, the raised and/or hollow structure on the impression is produced by laser engraving or by micro-milling. The structure to be produced is extremely fine with at least one dimension less than or equal to 1.5 mm, preferably 1 mm and more preferably 0.5 mm.
Thus, the present invention relates to the method for machining the impression of the mould and to the method for manufacturing the item involving a step of providing the mould obtained according to this machining method.
More specifically, it relates to the method for machining by laser ablation or by micro-milling a raised and/or hollow structure on an impression of an injection mould, said structure being made of one element or several separate elements with at least one element having at least one dimension less than or equal to 1.5 mm, said dimension being selected from a minimum height or depth of the respectively raised or hollow element and a minimum distance separating two opposite faces of said element in a plane transverse to said height or depth.
More specifically, it relates to the method for manufacturing the item comprising the following steps:
Providing an injection mould which includes at least one impression with the raised and/or hollow structure,
The method for manufacturing the item according to the invention thus allows to remove the step of decorating the item after the injection. This significantly reduces manufacturing costs and times.
The item decorated during the injection is made in one piece without discontinuity between the decoration and the rest of the item, unlike an item decorated by soldering or gluing the elements of the decoration onto the item.
Compared to an item decorated by laser ablation, the item with a decoration produced during the injection has a shinier, less rough surface condition, without marks from the successive passages of the laser, which possibly allows to dispense with a final polishing step.
Other features and advantages of the present invention will appear in the following description of a preferred embodiment, presented by way of non-limiting example with reference to the appended drawings.
The present invention relates to a method for machining a hollow and/or raised structure on an impression of a mould intended for the injection of a ceramic or cermet material. It also relates to the mould obtained by this machining method. It also relates to the method for manufacturing an item by injection, making use of this mould for the injection. The present invention further relates to the decorated item resulting from the manufacturing method.
According to the invention, the decoration is raised and/or hollow on the item. The decoration can be made of a single element such as an acronym or made of several distinct elements such as indexes and numbers. It is possible that some elements are raised and others are hollow within the decoration.
The item according to the invention can be a decorative item such as a constituent element of watches, jewellery, bracelets, etc. In the watchmaking field, this item can be an external component such as a middle part, a back, a bezel, a push-piece, a bracelet link, a dial, a hand, a dial index, etc. It can also be a component of the movement such as an oscillating mass, a plate, etc. By way of illustration, the item is a bezel 1 with a raised decoration 2 formed of distinct elements 2a which are indexes, numbers, rings, triangles, diamonds, etc. as shown in
The item is made of a cermet or ceramic material. The material can thus be produced with one or more ceramics selected from nitrides, carbides and oxides such as zirconium oxide. Similarly, it can be produced with cermets including a ceramic phase with carbides, nitrides and/or oxides and a phase of a metallic binder selected, for example, from precious elements such as ruthenium, rhodium, palladium, osmium, iridium, platinum, gold and silver.
According to the invention, at least one of the elements 2a of the decoration 2 of the item is very thin with at least one dimension less than or equal to 1.5 mm, preferably 1 mm and more preferably 0.5 mm (
The distance d or the height h/depth to be considered is the minimum. This means that if the height or the depth is variable within the element, it is the smallest height/depth which must be less than or equal to 1.5 mm, preferably less than or equal to 1 mm and more preferably less than or equal to equal to 0.5 mm. In the example shown, the height h is the same within the element and for all the elements and has a value of 0.3 mm. Likewise, the element may have dimensions in the transverse plane which are variable according to the height/depth. Thus, if the minimum distance d is variable between the different planes along the height/depth, it is the smallest value that must be considered. In the example shown, the base of the decorative elements is wider than the top with a minimum distance of 0.42 mm at the top of the index. The decoration is very thin with also small radii R of curvature at the junction between the contiguous faces of the element of the decoration. Typically, the radii of curvature are less than or equal to 0.1 mm and preferably less than or equal to 0.06 mm.
The impression 4 of the mould 3 visible in
The machining of the structure of the impression of the mould is carried out by micro-milling or laser ablation. Micro-milling is preferably carried out with a toroidal or hemispherical milling cutter having a diameter comprised between 0.1 and 3 mm and an angle radius at the end of the milling cutter comprised between 0.05 and 0.5 mm. Laser ablation is preferably performed with a pulsed laser such as a picosecond, nanosecond or femtosecond laser. Typically, the mould can be made of a metal alloy such as a hardened steel having a rockwell hardness HRC greater than 50. Conventionally, the impression of the mould before engraving can be obtained by milling, turning, etc.
The cermet or ceramic item is produced by injecting material into the mould provided with the impression with the raised and/or hollow structure. The method for manufacturing the item comprises the following steps:
The method may optionally include a debinding step before the sintering step if the materials have been injected with a system of organic binders (paraffin, polyethylene, etc.).
During the injection step, the impression is heated to a temperature comprised between 50° C. and 170° C., preferably between 60° C. and 150° C., to allow good filling of the structure of the impression with the material.
The finishing step is a polishing and/or machining step. The machining at the decoration, which is optional, consists in removing the ridge of the element(s) 2a of the decoration when it is raised so as to produce marked edges at the junction between the upper face and the sides of the element of the decoration as schematically shown in
The method for manufacturing the item according to the invention does not have an engraving step subsequent to the injection step or at least the majority of the decoration of the item is carried out during the injection.
Typically, a bezel 1 according to
The manufacturing method according to the invention can also be implemented to produce items with several materials that differ, for example, by their colours. The objective is then to produce an item with a decoration of a given colour on a background of another colour. More specifically, the decoration is raised on the background. The injection step uses a first impression and a second impression respectively having a raised structure and a hollow structure machined according to the method of the invention. The first impression is used when injecting the first material and the second impression is used when injecting the second material. The green body 6 after the injection of the two materials is shown in
This first part 6a of the green body is obtained after injection of the first material into a mould provided with the first impression with a raised structure forming the decoration and the opening(s). To make recesses passing through the thickness of the first part of the green body, said structure has a height greater than the filling height of the material in the first impression.
The second part 6b of the green body is obtained by injection of the second material via the openings 8 from the upper face 6c to the lower face 6d of the first part 6a. As schematically shown in
The manufacturing method has been illustrated for an item comprising two distinct materials, but it could be an item comprising 3, 4, etc. distinct materials with the production of several decorations of different colours.
The invention also relates to the item resulting from the manufacturing method.
For a multi-coloured item obtained according to the method described above (
1. Item or Bezel
2. Decoration
3. Injection mould
4. Impression
5. Raised and/or hollow structure of the impression
6. Green body
7. Recess
8. Opening
9. Sprue
10. Base of the item
11. Upper part of the item
Number | Date | Country | Kind |
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21169506.9 | Apr 2021 | EP | regional |