Method for manufacturing a micromechanical fastening element, forming tool for creating a recess for a micromechanical fastening element, and micromechanical fastening element - Patents.com

Abstract

To provide a method for manufacturing a fastening element, and specifically, a method for producing a micromechanical fastening element, such as a screw or other tightening element, comprising an impression designed to cooperate with a tightening tool for applying a tightening torque, while controlling the condition of visible surfaces of the impression.SOLUTION: The method includes a step of producing a blank of the fastening element with a head and a shank connected to each other, and a subsequent step of forming an impression in the head. The forming step includes an operation of machining the impression, carried out with a cutting member (11) and an operation of matting a target surface of the impression carried out with a matting member (12).SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to the manufacture of micro-mechanical parts, and more particularly to a forming tool for creating recesses for micro-mechanical fastening elements, a method for manufacturing a micro-mechanical fastening element, and a micro-mechanical fastening element.

[0002] The invention has advantageous applications in the field of watchmaking. [Background technology]

[0003] In the field of micromechanics, and in particular in the field of watchmaking, the aesthetic appearance of the mechanical parts of an assembly such as a watch movement or a watch case is of great importance: in particular, the condition of the visible surfaces of the parts that make up the assembly must be controlled.

[0004] For this purpose, some flat surfaces are polished or decorated by removing material to give particular reliefs such as guilloching, sunburst or circular graining.

[0005] However, some difficult-to-contact surfaces of the components are left machined due to their very small dimensions, such as the inner faces of recesses in micro-mechanical fastening elements, such as the inner faces of screw holes.

[0006] The final surface condition of the inner faces of these cavities is then determined solely by the machining conditions of the cavities, and among other things this surface condition depends on vibration phenomena occurring during machining, which are very difficult to control due to the very small dimensions of the cutting tools and the parts to be machined, and many of the inner faces of the cavities of the machined parts do not have a surface condition that is compatible with the manufacturing requirements.

[0007] If the fastening elements are intended for the fine watchmaking industry, the number of rejects is even higher, since the requirements regarding the finish and surface quality are very high.

[0008] It is therefore necessary to produce fastening elements in which the condition of all visible surfaces is controlled in order to meet the most stringent demands. Summary of the Invention [Problem to be solved by the invention]

[0009] The present invention proposes a solution to the aforementioned disadvantages by manufacturing micro-mechanical fastening elements, such as screws or other fastening elements, with recesses designed to cooperate with a tightening tool for applying a tightening torque, while controlling the condition of the visible surface of the recesses.

[0010] Furthermore, it is an object of the present invention to reduce the manufacturing costs of the fastening element. [Means for solving the problem]

[0011] To this end, one aspect of the invention relates to a method for manufacturing a micro-mechanical fastening element, comprising the steps of manufacturing a blank of the fastening element with a head and a shank connected to one another, followed by forming a recess in the head, the step of forming the recess comprising a machining operation of the recess performed with a cutting member and a matting operation of the target surface of the recess performed with a matting member.

[0012] Advantageously, the matting process makes it possible to modify the state of the object surface after machining so as to meet the manufacturing requirements, in particular by plastic deformation of the material under the effect of the local pressure generated by the matting member during the manufacture of the fastening element, improving the state of the object surface, i.e. minimizing the geometrical defects of said surface on the micrometer scale.

[0013] In specific embodiments, the invention may further comprise one or more of the following features, taken alone or in any technically possible combination:

[0014] In a particular embodiment, the step of forming the recess in the head portion is performed using a single forming tool having a cutting member and a matting member disposed therein.

[0015] In certain embodiments, the fastener elements are held in the same position throughout the entire recess forming process and only the forming tool is moved.

[0016] In a particular embodiment, the surface to be matted is the inner surface of a depression, and the matting operation is performed such that at the end of the forming process, said inner surface has an Ra of 0.01 μm to 0.1 μm.

[0017] In certain embodiments, the forming tool is driven in different rotational directions when performing machining and matting operations, and the cutting members and matting members are located on a single disk of the forming tool.

[0018] In a particular embodiment, during the machining and matting operations, the blank is machined by cutting members and matted by matting members each constituted by a disk of a forming tool, said disks being parallel and coaxial.

[0019] In certain embodiments, the matting operation is performed by multiple successive passes of the matting member over the target surface, each pass being performed to a penetration depth of 0.1 μm to 2 μm or 0.5 μm to 1.5 μm.

[0020] According to another object, the invention relates to a forming tool for producing recesses of micromechanical fastening elements, said forming tool being advantageously adapted to carry out the manufacturing method described above.

[0021] The forming tool comprises a body extending along a longitudinal axis, the tool being intended to rotate about the longitudinal axis, and further comprises cutting members arranged at the longitudinal ends of the body, the cutting members having cutting edges intended to remove material from the fastener element as the tool rotates to form a recess, and a matting member having an active surface intended to matt a target surface of the recess as the tool rotates.

[0022] In certain embodiments, the cutting member and matting member are in the form of a single disk configured such that when the tool is driven in a first rotational direction, the cutting member is activated and the matting member is inactivated, and when the tool is driven in a second rotational direction opposite the first rotational direction, the cutting member is inactivated and the matting member is activated.

[0023] In a particular embodiment, the disk comprises a plurality of regularly distributed peripheral teeth, each tooth having at its apex a relief surface forming the working surface of the matting member, said relief surface further defining, together with the leading surface of each tooth, a cutting edge of the cutting member.

[0024] In a particular embodiment, each of the cutting member and matting member is in the form of a disk, the disks being arranged parallel and coaxially, and the cutting edge and working surface, respectively, being disposed around the periphery of said disk.

[0025] In a particular embodiment, the working surface of the matting member has a circular cross section.

[0026] In a particular embodiment, the working surface of the matting member has a polygonal cross-section consisting of arcs joined by rounded vertices.

[0027] In certain embodiments, the arc has a concave curvature.

[0028] Another aspect of the invention relates to a micromechanical fastening element, made of a metallic material, preferably produced by implementing the manufacturing method according to the invention, having a shank connected to a head, the head having a recess extending from an opening to a rear face, said fastening element being characterized in that the rear face has an Ra of 0.01 μm to 0.1 μm.

[0029] In a particular embodiment, the recess is intended to cooperate with a tightening tool for transmitting torque and the shank is provided with a screw thread. [Brief description of the drawings]

[0030] Other characteristics and advantages of the invention will become apparent upon reading the following detailed description, given by way of non-limiting example and with reference to the attached drawings, in which: [Figure 1] 1 shows a schematic plan view of a forming tool according to a first embodiment of the invention; [Diagram 2] 2 is a cross-sectional view along cutting axis AA of the cutting member of the forming tool of FIG. 1. [Diagram 3] 2 is a cross-sectional view of the matting member of the forming tool of FIG. 1 along cutting axis BB. [Figure 4] FIG. 4 shows a schematic plan view of a forming tool according to a second embodiment of the invention; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0031] Please note that the drawings are not necessarily drawn to scale for clarity.

[0032] A first aspect of the invention relates to a method for manufacturing a micromechanical fastening element intended to be visible to the user, such as a screw, preferably a watch screw, made of a metallic material such as steel, titanium, etc., preferably intended for the watchmaking sector, but generally adaptable for use in all micromechanical sectors.

[0033] The method includes the steps of manufacturing a blank for the fastener element having a head and a shank connected to one another, and then forming a recess in the head.

[0034] The recess extends from the opening to the back face and is designed to conveniently receive the head of a fastening tool, such as a screwdriver, to apply torque to the fastener element. In this example, the process of manufacturing the blank may include a thread preparation operation to create a screw thread on the shank of the blank. As an alternative example, the recess may be merely decorative.

[0035] In either case, the head of the fastening element, and therefore the recess, is intended to be visible to the user. The recess may be of any suitable shape, for example a cross, a polygonal cross section, etc., or in the shape of a straight slot.

[0036] Advantageously, the step of forming the recess includes both machining the recess, performed with a cutting member 11, and matting the target surface of the recess, performed with a matting member 12. The target surface of the recess is intended to be visible to the user and preferably corresponds to the depth of the recess.

[0037] Thanks to these features, the surface of the depression, especially the inner part of the depression, has a controlled surface condition, the surface is polished etc., making it possible to meet the most stringent requirements regarding appearance. In practice, the matting operation is carried out in such a way that the inner surface has an Ra of 0.01 μm to 0.1 μm, preferably 0.02 μm to 0.05 μm at the end of the depression formation process.

[0038] These features also make it possible, thanks to the method according to the invention, to industrially produce micromechanical fastening elements with excellent reproducibility, which makes it possible to significantly reduce or eliminate production rejects. Furthermore, the fact that the machining and matting operations are carried out in the same step of the method makes it possible to optimize the manufacturing time of the fastening elements and thus to keep their costs down.

[0039] The machining operation is performed such that the indentation has a depth of between 0.05 and 0.5 mm, for example between 100 μm and 200 μm, for example 170 μm, and can achieve that goal in one or more passes of the cutting member 11. In particular, the machining operation can be performed by an empty pass followed by a finishing pass, the finishing pass being a few micrometers deep, for example 2 μm.

[0040] The matting operation is performed by making several successive passes, for example three passes, of the matting member 12 over the target surface, each pass being made to a pass depth of 0.1 μm to 2 μm, preferably 0.5 μm to 1.5 μm, for example 1 μm. In that way, the material of the target surface is cold worked by the matting member 12, making it possible to substantially planarize the target surface on the micrometer or sub-micrometer scale, thereby improving its surface condition.

[0041] Advantageously, the step of forming the recesses is carried out using a single forming tool 10, described in detail below according to another aspect of the invention, in which a cutting member 11 and a matting member 12 are arranged. Such a forming tool 10 is intended to be fixed in a tool holder of a machining centre so that it can be rotated to make the recesses of the fastening elements.

[0042] The method may include a finishing step of polishing the exterior surface of the head, i.e., the surface of the head excluding the surface of the cavity.

[0043] As can be seen in Fig. 1, the forming tool 10 comprises a body, for example in the form of a post, extending along a longitudinal axis which corresponds to the axis of rotation of the tool. The cutting member 11 and the matting member 12 are arranged at the free ends of the body. The cutting member 11 comprises a cutting edge 110 intended to remove material from the head of the fastener element so that a recess is formed when the tool is rotated. The matting member 12 comprises an action surface 120 for matting the target surface of the recess when the tool is rotated.

[0044] Advantageously, the fastener element is held in the same position during all operations in the recess forming process and only the forming tool 10 moves and passes differently, which allows for better adaptation to machining tolerances.

[0045] In a first embodiment, the cutting member 11 and the matting member 12 are each constituted by a disk of a forming tool 10, said disks being parallel and coaxial. The design of such a forming tool 10 is shown in figure 1. As can be seen in figures 2 and 3, the cutting edge 110 and the working surface 120 are respectively arranged on the circumference of said disk. By way of example, the disk may have a diameter of a few millimeters, for example 4 mm.

[0046] As can be seen in Fig. 2, the cutting member 11 has the shape of a circular milling cutter. This cutting member 11 has a plurality, for example 16, of regularly distributed peripheral teeth, each tooth being provided at its apex with a relief surface 111. Together with the leading surface of each tooth, the relief surface 111 defines a cutting edge 110 of the cutting member 11.

[0047] In this embodiment, the matting member 12 may have a generally polygonal cross section, consisting of arcs 122 connected to one another by rounded vertices 121, as shown in Figure 3. Preferably, the matting member 12 has 14 vertices 121, the radii of which are a few tenths of a millimeter. The arcs 122 may be straight or may have a concave curvature dimensioned such that the maximum deviation from a theoretical circle through which the vertices 121 pass is a few hundredths of a millimeter, as shown in detail in Figure 3.

[0048] Alternatively, in an embodiment of the invention not shown, the working surface 120 of the matting member 12 may have a circular cross-section.

[0049] In a second embodiment of the invention shown in Figure 4, the cutting member 11 and the matting member 12 are in the form of a single disc. This disc has substantially the same shape as the disc of the first embodiment constituting the cutting member 11 shown in Figure 2. This disc is configured such that when the tool is driven in a first rotational direction, the cutting member 11 is active and the matting member 12 is inactive, and when the tool is driven in a second rotational direction opposite to the first rotational direction, the cutting member 11 is inactive and the matting member 12 is active. More precisely, the relief surface 111 becomes the working surface 120 of the matting member 12.

[0050] More generally, it should be noted that the implementations and embodiments discussed above have been described as non-limiting examples, and thus other variations are possible.

Claims

1. A method for manufacturing a micromechanical fastening element for a watch, comprising the steps of manufacturing a blank for said fastening element having a head and a shank connected to each other, and then forming a recess in said head, said step of forming the recess in said head comprising a machining operation for machining said recess using a cutting member (11) and a matting operation for matting a target surface of said recess using a matting member (12); The step of forming a recess in the head portion is carried out using a single forming tool (10) in which the cutting member (11) and the matting member (12) are arranged, CHARACTERIZED IN THAT, WHEN PERFORMING THE MACHINING OPERATIONS AND THE MATING OPERATIONS, THE FORMING TOOL (10) IS DRIVEN IN DIFFERENT ROTATIONAL DIRECTIONS, AND THE CUTTERING MEMBERS (11) AND THE MATING MEMBERS (12) ARE ARRANGEMENT ON A SINGLE DISCRETE OF THE FORMING TOOL (10).

2. A method for manufacturing a micromechanical fastening element for a watch, comprising the steps of manufacturing a blank of the fastening element having a head and a shank connected to each other, and then forming a recess in the head, the step of forming the recess in the head comprising a machining operation for machining the recess using a cutting member (11) and a matting operation for matting a target surface of the recess using a matting member (12); The step of forming a recess in the head portion is carried out using a single forming tool (10) in which the cutting member (11) and the matting member (12) are arranged, 13. A method according to claim 12, wherein during said machining and matting operations, said blank is machined by said cutting member (11) and matted by said matting member (12), said cutting member (11) and said matting member (12) each being constituted by a disk of said forming tool (10), said disks being parallel and coaxial with each other.

3. 3. The method according to claim 1 or 2, wherein the fastening element is kept in the same position and only the forming tool (10) is moved during the entire step of forming the recess in the head.

4. 3. The method according to claim 1 or 2, wherein the target surface to be matted is the inner surface of the recess, and the matting operation is carried out such that at the end of the step of forming a recess in the head, the inner surface has an Ra of 0.01 μm to 0.1 μm.

5. 3. The method according to claim 1 or 2, wherein the matting operation is performed by multiple successive passes of the matting material (12) over the target surface, each pass being performed to a penetration depth of 0.1 μm to 2 μm or 0.5 μm to 1.5 μm.

6. A forming tool (10) for creating a recess in a micromechanical fastening element for a watch, comprising a body extending along a longitudinal axis, the forming tool intended to rotate around the longitudinal axis, the forming tool comprising cutting members (11) arranged at the longitudinal ends of the body, the cutting members having cutting edges intended to remove material from a fastening element as the forming tool rotates to form a recess, and a matting member (12) having an action surface (120) intended to matt a target surface of the recess as the forming tool rotates, said cutting member (11) and said matting member (12) being in the form of a single disk configured such that, when said forming tool is driven in a first rotational direction, said cutting member (11) is active and said matting member (12) is inactive, and when said forming tool is driven in a second rotational direction opposite to the first rotational direction, said cutting member (11) is inactive and said matting member (12) is active; A forming tool (10), characterized in that the disk comprises a plurality of regularly distributed peripheral teeth, each tooth having at its apex a relief surface (111) forming an active surface (120) of the matting member (12), said relief surface (111) further defining, together with the leading surface of each tooth, a cutting edge (110) of the cutting member (11).

7. A forming tool (10) for creating a recess in a micromechanical fastening element for a watch, comprising a body extending along a longitudinal axis, the forming tool intended to rotate around the longitudinal axis, the forming tool comprising cutting members (11) arranged at the longitudinal ends of the body and provided with cutting edges intended to remove material from a fastening element to form a recess as the forming tool rotates, and a matting member (12) provided with an action surface (120) intended to matt a target surface of the recess as the forming tool rotates, each of said cutting member (11) and said matting member (12) being in the form of a disk, said disks being arranged parallel and coaxially, said cutting edge (110) and said working surface (120) being respectively arranged around the periphery of said disk; A forming tool (10), characterized in that the working surface (120) of said matting member (12) has a circular cross section or a polygonal cross section consisting of arcs (122) connected by rounded vertices (121).

8. The forming tool (10) of claim 7, wherein the arc (122) has a concave curvature.

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