CUTTING TOOL

Description

Scope of the invention

[0001] The invention relates to a cutting tool intended for machining by grinding a part and, in particular, a ceramic watch component. Background of the invention

[0002] The choice of design and material for a cutting tool is crucial for the tool's lifespan, machining cycle time, and the quality of the machined part.

[0003] Documents EP 0251264 and EP 0731751 describe cutting tools made of tungsten carbide. These tools are efficient due to their high density, which reduces vibration, and their rigidity, which prevents tool deflection during machining. However, they have the disadvantage of being extremely hard, which complicates tool manufacturing. Cutting tools may include openings for coolant circulation. In particular, they may have a circular opening extending along the tool axis and radial openings leading to the active part of the cutting tool. It is important that the tool geometry be perfectly axisymmetric and, therefore, that the circular opening be perfectly centered to avoid imbalance during machining.It can be difficult to guarantee this centering when the cutting tool material is too hard.

[0004] Document EP 3 363 571 A1 discloses a cutting tool made of a hard material comprising 95% by weight tungsten and 5% by weight of a metallic binder including iron, nickel, and copper. Tools made of high-strength steels are also known. These tools have lower hardness than tungsten carbides, which simplifies their manufacture. However, their lower density can lead to the aforementioned vibration phenomena. Summary of the invention

[0005] The present invention aims to overcome the aforementioned drawbacks by providing a grinding tool made from a material that meets all of the following criteria: Very high rigidity with a Young's modulus greater than or equal to 300 GPa, Ease of machining with a hardness less than or equal to 450 HV, High density with a density greater than 15 g / cm³.

[0006] To this end, the present invention relates to a grinding tool comprising a body made of a sintered material comprising by weight between 90 and 99.5% of W in metallic form and not of carbides, and between 0.5 and 10% of a binder formed of one or more metallic elements chosen from Co, Mo and Cr.

[0007] The tool in this material has a hardness between 300 and 450 HV, a stiffness between 300 and 450 GPa and a density between 16 and 20 g / cm³.

[0008] According to the invention, the active part of the grinding tool body is coated with an abrasive bonded with one or more elements selected from Ni, Co, and Mo. The binder in the grinding tool material provides excellent adhesion to the binder in the abrasive layer, thus limiting the risk of peeling.

[0009] Other features and advantages of the present invention will become apparent from the detailed description below, which refers to the following figures. Brief description of the figures

[0010] THE Figures 1A and 1B represent respectively a side view and a cross-sectional view of the grinding tool according to the invention. Description of the invention

[0011] The invention relates to a grinding tool for machining a workpiece. For example, the workpiece could be a watch case or movement component such as a case, case back, bezel, crown, pusher, bracelet link, bracelet, pin buckle, dial, hand, dial marker, gear, axle, pinion, spring, bridge, mainplate, screw, or balance wheel. While not limited to this application, the grinding tool is particularly well-suited for machining ceramic parts.

[0012] The grinding tool shown in Figures 1A and 1Bis equipped with a body 1 which includes an active part 2, also called the head, intended to be in contact on its lateral surface with the workpiece. In the illustrated example, the grinding tool has a central orifice 4 coaxial with the longitudinal axis of the grinding body and a multitude of radial orifices 5 opening into the coating 3, also called the layer, of the head 2 of the body 1. A row of orifices having an angle α between 0 and 90° can be considered so as to allow the front face of the tool to be cooled.

[0013] According to the invention, the body of the grinding tool is made of a material comprising tungsten and a binder selected from one or more of the following elements: Co, Mo, and Cr. The material comprises, by weight, between 90 and 99.5% W and between 0.5 and 10% of one or more elements selected from Co, Mo, and Cr. Preferably, it comprises, by weight, between 93 and 99% W and between 1 and 7% of one or more elements selected from Co, Mo, and Cr. More preferably, it comprises between 95 and 98% W and between 2 and 5% of one or more elements selected from Co, Mo, and Cr.

[0014] The body has a hardness between 300 and 450 HV, preferably between 300 and 400 HV. It has a Young's modulus between 300 and 450 GPa, preferably between 300 and 400 GPa. It has a density between 16 and 20 g / cm³.

[0015] The head 2 of the body 1 is coated with a layer 3 comprising an abrasive and a metallic binder. The abrasive may be a ceramic based on oxides, carbides, or nitrides, such as cubic boron nitride, or an element such as diamond. The binder comprises one or more elements selected from Ni, Co, and Mo.

[0016] According to the invention, the grinding tool is made by sintering a mixture of tungsten powders and a metallic binder. More specifically, the manufacturing process for the grinding tool comprises a first step consisting of mixing the various powders, possibly in a humid environment. The starting powders preferably have a d50 less than 45 µm. Optionally, a second mixture comprising the aforementioned mixture and an organic binder system (paraffin, polyethylene, etc.) can be prepared. The process then includes a step of forming a blank by shaping the mixture into the desired tool body, for example, by injection molding. (MIM: Metal Injection Molding), by pressing or 3D printing. The blank is then sintered under partial gas pressure, vacuum, or atmospheric pressure at a temperature between 800 and 1500°C for a time between 10 minutes and 20 hours. This step may be preceded by a debinding step at a temperature range of 60 to 500°C if the mixture contains a binder system. The process may then include a finishing step to shape the tool body, and in particular to create the body's openings, using conventional methods such as drilling, milling, grinding, etc. The body head is then coated with the Ni, Cr, and / or Mo layer containing the abrasive by electroplating.

[0017] Comparative tests were carried out between a high-strength steel grinding tool such as 1.3346, 1.3343 and 1.3255 and a grinding tool with the material according to the invention comprising tungsten and nickel and iron as a binder.

[0018] The tests consisted of machining a ceramic (ZrO₂) watch case. The tests were carried out using a grinding tool with a 6 mm diameter body and a head coated with an abrasive layer containing diamond and nickel. Machining was performed at a cutting speed of 660 m / min. The tool's lifespan was determined based on the number of parts machined without degradation of the abrasive layer. With the grinding tool according to the invention, 24 watch cases were machined, compared to 14 with the grinding tool made of high-strength steel.

Claims

1. Grinding tool for grinding a part, said tool comprising a body (1) made of a material comprising, by weight, between 90 and 99.5% of W and between 0.5 and 10% of one or several elements chosen among Co, Mo and Cr, in which the body (1) comprises a head (2) designed to contact the part being machined, said head (2) comprising, on its outer lateral surface, a coating (3) comprising an abrasive and a binder and in which the abrasive is chosen among ceramics and diamond, and in which the binder comprises one or several elements chosen among Ni, Co and Mo.

2. Grinding tool according to claim 1, characterised in that the material comprises, by weight, between 93 and 99% of W and between 1 and 7% of one or several elements chosen among Co, Mo and Cr.

3. Grinding tool according to claim 1 or 2, characterised in that the material comprises, by weight, between 95 and 98% of W and between 2 and 5% of one or several elements chosen among Co, Mo and Cr.

4. Grinding tool according to any of the preceding claims, characterised in that the material has a hardness comprised between 300 and 450 HV.

5. Grinding tool according to any of the preceding claims, characterised in that the material has a hardness comprised between 300 and 400 HV.

6. Grinding tool according to any of the preceding claims, characterised in that the material has a Young's modulus comprised between 300 and 450 GPa.

7. Grinding tool according to any of the preceding claims, characterised in that the material has a Young's modulus comprised between 300 and 400 GPa.