Machining tool for grinding a workpiece

Abstract

The machining tool (30) is used to grind a workpiece in a machining machine. The tool comprises at least a first machining portion having particles of a material harder than the workpiece material, the particles being arranged in a binder, and at least a second machining portion having particles of smaller diameter than the first machining portion, and of a material harder than the workpiece material, the particles of the second portion being arranged in a binder identical to that of the first portion or in a different binder.

Description

DOMAINE TECHNIQUE DE L'INVENTION

[0001] The invention relates to a machining tool for performing a grinding operation on a workpiece, particularly made of hard material, on a machining machine. ETAT DE LA TECHNIQUE

[0002] In a grinding operation on a machine tool, it is common practice to change machining tools between a roughing stage and at least one finishing stage involving surface abrasion of the workpiece. To grind a face of a hard material, a first tool with a grinding band containing, for example, large-diameter diamond particles in a bonding agent can be used; this is a roughing stage. After this first stage, a second tool with a grinding band containing diamond particles of a smaller diameter than the first tool can be used to define a semi-finishing stage. Finally, a third tool with a grinding band containing diamond particles of an even smaller diameter than the second tool can be used for a final finishing stage. In this scenario, three grinding tools must be used.

[0003] As mentioned above, grinding is generally required in several stages, as it is not easy to remove, for example, a scratch or a rough surface finish on the workpiece with a grinding wheel containing small-diameter diamond or corundum particles. In such cases, a very long and therefore costly machining time is required for each part. Between stages, it may also be necessary to change the grinding tool in the machine tool, or to perform two passes, thus requiring two re-machining operations on the workpiece, which further slows down the machining time and is a drawback.

[0004] For example, by placing two tools in two working positions, it takes a few seconds, such as 5 seconds, to move the workpiece from the first working position to the second. If only one working position is used, changing the tool for each machining step can take twice as long, for example, 10 seconds, compared to using two tools in two working positions. The machining time for each workpiece is therefore long, which is a drawback.

[0005] It should also be noted that for two surfaces to be machined or ground, up to six tools can be required for three machining steps per workpiece surface. Machining each workpiece in hard material is therefore excessively long, as the constant switching between working positions or the continuous tool changes significantly slow down the machining process, which is a drawback. Furthermore, there are limitations in the machining positions available on machine tools and in the tools available.

[0006] The tool may include at least one machining surface or band composed of abrasive particles embedded in a binder. The abrasive particles are typically diamond, or even particles of equal or lesser hardness than the workpiece, which may be made of materials such as sapphire, zirconia, oxides, nitrides, or others, for machining workpieces made of hard materials, as the wear of the abrasive portion is too rapid.

[0007] Each machining belt, which consists of abrasive particles in a binder, can be attached to a tool body by sintering, brazing, or bonding. The tool body can be made of aluminum or steel, for example. The tool holder can be inserted into the nose or chuck of a tool spindle to perform the machining operation.

[0008] To the figure 1 A machining center 1 is schematically represented. This machining center 1 conventionally comprises a support section 2 carrying a first spindle 8 for a first machining tool 6, such as a first grinding wheel, and a second spindle 9 for a second machining tool 7, such as a second grinding wheel. A second section 4 of the machining center 1 comprises a workpiece support block 3 for the workpiece 10. The workpiece 10 can be mounted via a workpiece retainer 10' to a clamping chuck 5 of the support block 3.

[0009] The support part 2 can be moved in a first direction X, while the support block 3 can be moved in a second direction Y perpendicular to the first direction X and in a third direction Z perpendicular to the first and second directions X and Y. The support block 3 can be rotated about a direction A in the plane defined by the first and second directions X and Y. The clamping chuck 5 can be rotated during machining of the part 10 about a direction C in the plane defined by the second and third directions Y and Z.

[0010] During the machining of part 10, it is first brought into contact with the first grinding wheel 6, which can have a maximum diameter of 250 mm and an abrasive belt on its periphery containing large-diameter diamond or corundum particles in a bonding agent, for a roughing stage. Then, the workpiece 10 must be brought into contact with the second grinding wheel 7, which can also have a maximum diameter of 250 mm and an abrasive belt on its periphery containing small-diameter diamond or corundum particles in a bonding agent, for a finishing stage.

[0011] As previously mentioned, the time required to perform these machining steps is relatively long, given that the workpiece must be moved from the first working position of the first grinding wheel 6 to the second working position of the second grinding wheel 7. This generally results in excessively long and therefore costly grinding time. Furthermore, having to wait for one grinding wheel to stop rotating and then restart the other generates long processing times and requires additional energy to restart the rotation due to the grinding wheel's inertia. These are drawbacks.

[0012] From document FR 1 049 991A, a machining tool for grinding a workpiece in a machining center is known, the tool comprising at least a first machining portion having particles of a material harder than the material of the workpiece, the particles being arranged in a binder, and at least a second machining portion having particles of a larger or smaller diameter than the first machining portion, and of a material harder than the material of the workpiece, the particles of the second machining portion being arranged in a binder identical to that of the first machining portion or in a different binder, the first and second machining portions being constituted by first and second abrasive bands arranged on at least one front face of the tool body, which is capable of being driven in rotation in a spindle of a machining center for grinding a workpiece,The first and second abrasive bands are annular and fixed coaxially to the front face of the tool body, with the front face perpendicular to the axis of rotation of the cylindrical or conical tool body. RESUMÉ DE L'INVENTION

[0013] The invention therefore aims to provide a machining tool for performing a grinding operation on a part in a machining machine to overcome the disadvantages of the aforementioned prior art and to reduce the machining time of each part by its use in a machining machine.

[0014] For this purpose, the invention relates to a machining tool for performing a grinding operation on a workpiece in a machining machine, which includes the features mentioned in independent claim 1.

[0015] Specific embodiments of the machining tool are defined in dependent claims 2 to 5.

[0016] One advantage of this machining tool is that it incorporates multiple machining sections. Each machining section contains particles of a material harder than the workpiece, bound together with a binder. The nature, size, or diameter of the abrasive particles varies from one machining section to another, and their concentration in the binder can also differ. The first machining section of the tool might contain larger diameter particles than the second machining section to perform a roughing operation, while the second machining section is used for a finishing operation, grinding the workpiece.

[0017] More than two machining sections can be planned, each with abrasive particles of a different diameter.

[0018] For machining parts made of hard material, such as for a sapphire crystal or watch glass, the abrasive particles are preferably diamond particles integrated into a binder.

[0019] Advantageously, the first and second machining portions are arranged on the same tool body to form a single, one-piece tool that is mounted in a machine tool spindle to perform roughing and finishing grinding. These machining portions are, for example, abrasive bands arranged on the same face of the tool body, each forming a ring. The first annular abrasive band is coaxial with, and preferably spaced apart from, the second annular abrasive band. The first abrasive band is used for roughing grinding, and the second abrasive band, for example, with a smaller diameter, is used for finishing the workpiece.

[0020] Advantageously, the grinding tool can comprise at least two parts fixed to one another and easily detachable for replacement. The first part comprises the first machining portion, while the second part comprises the second machining portion. Because these parts are assembled and detachable, in the event of premature wear of one of the machining portions, only the worn portion needs to be replaced without having to replace the entire tool.

[0021] It is also possible to have more than two complementary parts that fit together like Russian nesting dolls and are fixed together to form the complete machining tool. Preferably, the last complementary part fixed, which may be the first part with the initial machining portion, is the one where the machining portion wears the fastest, such as during a roughing machining step. This makes it easier to change this final complementary part of the tool. BREVE DESCRIPTION DES FIGURES

[0022] The purposes, advantages, and characteristics of the machining tool for performing a grinding operation on a workpiece, particularly one made of hard material on a machine tool, will be more clearly illustrated in the following description alongside the drawings on which: there figure 1 The already mentioned machine represents, in simplified form, a machining tool for performing grinding operations on a workpiece, particularly one made of hard material, according to the prior art. figures 2a et 2b represent a diametrical cross-sectional view and a three-dimensional view of a first embodiment of a one-piece machining tool with different abrasion bands on one face of the tool body according to the invention, figures 3a , 3b et 3c represent diametrical, top, and bottom cross-sectional views of the first and second parts having abrasive portions forming a second embodiment of the machining tool, as well as a three-dimensional exploded view of the tool with the various parts to be assembled according to the invention, the figures 4a , 4b et 4c represent diametrical and top cross-sectional views of the first and second parts having abrasive portions forming a first variant of the second embodiment of the machining tool, as well as a three-dimensional exploded view of the tool with the various parts to be assembled according to the invention, the figures 5a , 5b et 5c represent diametrical and top cross-sectional views of the first and second parts having abrasive portions forming a second variant of the second embodiment of the machining tool, as well as a three-dimensional exploded view of the tool with the various parts to be assembled according to the invention, the figures 6a, 6b And 6crepresent diametrical and top cross-sectional views of the first and second parts having abrasive portions forming a first variant of a third embodiment of the machining tool, as well as a three-dimensional exploded and assembled view of the tool to be fixed to a chuck of a spindle of a machining machine according to the invention, figures 7a , 7b et 7c represent diametrical and top cross-sectional views of the first and second parts having abrasive portions forming a second variant of a third embodiment of the machining tool, as well as a three-dimensional exploded and assembled view of the tool to be fixed to a chuck of a spindle of a machining machine according to the invention, figures 8a, 8b And 8crepresent diametrical and top cross-sectional views of the first and second parts having abrasive portions forming a third variant of a third embodiment of the machining tool, as well as a three-dimensional exploded and assembled view of the machining tool to be fixed to a chuck of a spindle of a machining machine according to the invention, figures 9a , 9b et 9c represent diametrical and top cross-sectional views of the first and second parts having abrasive portions forming a fourth variant of a third embodiment of the machining tool, as well as a three-dimensional exploded and assembled view of the machining tool to be fixed to a chuck of a spindle of a machining machine according to the invention, and the figures 10a, 10b And 10crepresent diametrical and top cross-sectional views of the first and second parts having abrasive portions forming a fifth variant of a third embodiment of the machining tool, as well as a three-dimensional exploded and assembled view of the machining tool to be fixed to a chuck of a spindle of a machining machine according to the invention. DESCRIPTION DETAILLEE DE L'INVENTION

[0023] In the following description, the machining tool will be described as a grinding tool for the purpose of grinding, for example, a face of a workpiece made of a hard material. Preferably, the grinding tool is mounted in a spindle of a machining center to be driven in rotation to create, for example, chamfers on a workpiece, such as a glass or watch crystal, which may be sapphire, but without limiting other machining possibilities.

[0024] To figures 2a et 2b A machining tool 20 is shown for grinding one or more workpieces. The machining tool is primarily designed for grinding workpieces made of hard material. The machining tool 20 mainly comprises at least one first machining portion 21 and at least one second machining portion 22. The first and second machining portions 21 and 22 each comprise particles of a material harder than the material of each workpiece. These particles are arranged or embedded in a binder. The average size or diameter of the machining particles differs for each machining portion. This allows several machining operations or steps to be performed with the same machining tool 20 without having to change the tool in a machining center for different machining steps.

[0025] For machining workpieces made of hard materials, it is necessary to machine the various machining areas 21, 22 of the machining tool 20 preferably with diamond particles. Corundum particles can also be used, but the machining area wears more quickly with such areas, as this material is generally of equal or lesser hardness than the workpiece.

[0026] Diamond particles are embedded in a binder, which can be metallic, resinoid, vitrified, galvanic, ceramic, bakelite, or another type of binder. It is possible to have the particles from machining sections 21 and 22 embedded in the same or a different binder. For each machining section, the size or diameter of the diamond particles (grains) is defined by Dxx, and the diamond concentration per mm³ in its binder is defined by Cxx. For example, with an average grain size of approximately 91 µm, this corresponds to D91, and with a diamond particle concentration of 100 grains per mm³, this corresponds to C100. For a machining step defined as roughing, the particle size of one machining section is larger than the particle size of another machining section for a machining step defined as finishing. Thus, the smaller the particle size, the finer the machining.

[0027] The machining tool 20 presented at figures 2a et 2b The system comprises a first machining portion in the form of a first abrasive strip or layer 21, and a second machining portion in the form of a second abrasive strip or layer 22. These abrasive strips 21, 22 are fixed to a face 23 of the basic body of the machining tool 20. Preferably, the face 23 is a front face 23 forming a ring to which each annular abrasive strip 21, 22 is fixed. These abrasive strips 21, 22 are fixed coaxially to each other on the front face 23 of the cylindrical or conical tool body 20 to form, in this first embodiment, a single-piece tool. Preferably, the front face 23 is perpendicular to the axis of rotation of the cylindrical or conical tool body 20 when mounted in a spindle of a machining center.

[0028] The tool's basic body 20 can be metallic, for example, steel or aluminum. The abrasive belts 21 and 22 are attached to the front face 23 by sintering, brazing, or bonding. A gap is provided between each abrasive belt to allow a first machining step to be performed with the first abrasive belt 21 without interfering with the second abrasive belt 22 for a subsequent machining step. The first abrasive belt 21 can be defined with a particle size between D20 and D30 for a roughing machining step, while the second abrasive belt 22 can be defined with a particle size between D6 and D12, for example, for a finishing machining step. It is possible to use more than two machining sections, i.e., more than two abrasive belts, which can be arranged and spaced coaxially with respect to each other on the same front face 23 or another side face, for example.Each belt contains a different size of abrasive particles.

[0029] By way of example and without limitation, the dimensions of a machining tool 20 presented to the figures 2a et 2b The diameter d1 of the tool can be 250 mm, as can the outside diameter of the first abrasive belt 21. The outside diameter of the second abrasive belt 22 can be 200 mm. The width l1 of the second abrasive belt 22 can be 6 mm, and the width l2 of the first abrasive belt can be the same as the first belt's 6 mm width or different. Thus, the spacing between each abrasive belt can be 19 mm. The thickness e1 of each abrasive belt can be the same or different, but in this case, this thickness e1 can be 5 mm.

[0030] The conical machining tool 20 may further include a shank mounted by plates (not shown) through an opening 24 in the bottom of the tool's base body 20. The tool shank may be mounted to a chuck on a spindle of a machining center, as shown, for example, in the figure 1 The diameter d3 of the inner part of the base can be 166.2 mm. The diameter d4 of the opening 24 can be 76 mm. The diameter d5 of the outer part of the base can be 219.7 mm, and the thickness e2 of the base can be 15 mm. The thickness or height h1 of the base body with the abrasive belts 21, 22 can be 50 mm. Other dimensions can be determined for the same tool shape, for example, without limitation.

[0031] THE figures 3a , 3b et 3c represent a second form of execution of the machining tool 30. In this second form of execution, the machining tool consists of different parts assembled or nested one inside the other like "Russian dolls".

[0032] This machining tool 30 comprises at least two parts 31, 34 fixed to one another and easily detachable for replacing one of the parts. A first part 31 comprises a first machining portion 32, while the second part 34 comprises a second machining portion 35. The size or diameter of the abrasive particles, as before, differs from one machining portion to another, and their concentration in the bonding agent may also vary. Because these parts are assembled and detachable, it is possible, in the event of more significant wear on one of the machining portions, to replace only the worn portion without having to replace the entire tool.

[0033] The first and second complementary parts 31, 34 are configured in the general cylindrical form, but can be of another general form provided that they can be nested one inside the other, for example.

[0034] As depicted in the figure 3a The first part 31 is in the form of a cylindrical cup with a central opening 33 in the bottom of the cup for attaching the second part 34 and two retaining plates normally connected to a machining tool shank (not shown) for mounting in a chuck of a machine tool spindle. The axis of the cylindrical cup is positioned along an axis of rotation of the machining tool.

[0035] The first part 31 comprises a first machining portion 32, which is fixed by sintering, brazing, or bonding to a front edge of the base body of the first part 31. The base body may be made of steel or aluminum, for example. Preferably, this first machining portion 32 is a first abrasive strip 32 of annular shape and width that may be identical to the width of the edge of the first part 31. The first abrasive strip 32 may comprise particles, in particular diamond particles, in a conventional binder.

[0036] In the bottom of the bowl of the first part 31, the first holes 38 are made for the positioning or fixing of the pins shown below with reference to the figure 3c , in order to position the second part, which includes equivalent holes around its periphery for mounting it in the bowl of the first part 31. Second holes 39 are also provided in the bottom of the bowl with an external recess for the placement of fixing screws for the second part 34 shown below with reference to the figure 3c .

[0037] Three first holes 38 and three second holes 39 can be provided arranged alternately on the same coaxial circle around the bottom opening 33. The angle separating a first hole 38 from a neighboring second hole 39 is therefore 60°.

[0038] By way of example and without limitation, the outer diameter d1 of the first part can be 250 mm, while the inner diameter d2 can be 210 mm. The width of the abrasive belt is therefore in this case approximately 20 mm, and its thickness e1 can be 5 mm. The thickness e2 of the base of the bowl can be 15 mm and its height h1 up to the first abrasive belt 32 can be 45 mm. The diameter d3 of the opening in the base can be 76 mm. The diameter of the first holes 38 can be 6 mm and the diameter of the second holes 39 for the threaded part of each screw can be 8.8 mm, and the diameter for the screw head can be 14.5 mm. The first and second holes 38 and 39 are on a circle with a diameter of 177 mm.

[0039] As depicted in the figure 3b The second part 34 is configured in the form of a washer and includes a second machining portion 35, which is preferably a second abrasive strip 35 fixed by sintering, brazing or bonding to an annular face of the upper edge of the body of the second part 34. The second abrasive strip 35 can have a width equivalent to the edge width of the washer 34. The body of the second part 34 can be made of steel or aluminum, for example.

[0040] First holes 38', equivalent to the first holes of the first part, are made along a portion of the height of the washer 34 from a lower edge. Second threaded holes 39', to receive the threaded portion of the fixing screws, are also provided along a portion of the height of the washer from the lower edge. Therefore, three first holes 38' can be arranged alternately with three second threaded holes 39' arranged on a central circle on the lower edge of the washer. The angle between a first hole 38' and a second hole 39' is thus 60°. This circle is located midway between the outer and inner diameters of the washer 34.

[0041] By way of example and without limitation, the outer diameter d4 of the second part 34 can be 202 mm, while the inner diameter d5 of the second part 34 can be 152 mm. The holes 38' and 39' are on a circle with a diameter of approximately 177 mm. The thickness e3 of the second abrasive belt 35 can be 5 mm. The height h2 from the second part 34 to the second abrasive belt can be 30 mm. The depth of the first holes 38' can be 10 mm, and the depth of the threaded portion of the second holes 39' can be 10 mm with a 5 mm extension of the unthreaded hole.

[0042] It should also be noted that the second abrasive belt 35 of the second part 34 can be provided for a rough grinding stage, while the first abrasive belt 32 of the first part 31 can be provided for a finishing grinding stage with a particle size smaller than that of the second abrasive belt 35.

[0043] There figure 3c This shows an exploded three-dimensional view of the various elements of the machining tool 30 according to the second embodiment. The first and second parts 31 and 34 are assembled using screws 41, the head of each screw being positioned in the recess of each second hole 39 of the first part so that they can be screwed into each second threaded hole of the second part 34. Pins 40 are fixed in the first holes of the second part 34 so that they can be positioned in the first holes 38 of the first part 31.

[0044] An arrangement of a first circular plate 36, such as a plug, and a second plate 37, such as a disc, can be provided for their mounting or fastening through the central opening 33 in the bottom of the bowl of the first part 31. The first plate 36 therefore comprises a solid cylindrical central piece and a circular rim or shoulder. The central piece has a diameter slightly smaller than the diameter of the opening 33 in the first part 31. The central piece can pass through the central opening 33 with its rim bearing against the outer surface of the bottom of the bowl of the first part 31. At least three fastening holes 42 can be provided in the central piece of the first circular plate 36.

[0045] A second plate 37, generally cylindrical in shape, such as a disc, and with a diameter larger than the diameter of the central opening 33, is intended to be fixed to the first plate on one inner side of the bowl of the first part 31. To this end, at least three through-holes 43 are provided in the second circular plate 37, arranged in a manner equivalent to the three holes in the first circular plate 36. Thus, the two plates can be fixed, for example, by screws (not shown) passing through the three holes in the first plate and screwed into the three threaded holes in the second plate 37, which, after fixing, rests against the inner surface of the bottom of the bowl of the first part 31.These two fixing plates 36, 37, made of aluminium or steel for example, are preferably connected to a rod of the machining tool 30 to be mounted in a chuck of a spindle of a machining machine as shown in the figure. figure 1 .

[0046] As an alternative to the second embodiment, a second part 34 may be provided in the form of a cup with a second machined portion 35, such as a second abrasive strip positioned on a front face or edge of the second cup-shaped part 34. A solid base is provided at the bottom of the cup for this second part 34. A central opening with a diameter sufficient for the shank of a fixing screw may be made in the bottom of the cup of the second part 34, and optionally, a recess for the screw head may also be provided inside the cup of the second part. A central tapped hole may be made in the first plate 36 to receive the threaded portion of the fixing screw.The second part 34 is fixed directly with its bowl base into the bowl base of the first part 31 by screwing a screw, passing through the screw shank passage of the second part, into the tapped hole of the first plate 36 whose central part is inserted into the opening 33 of the first part 31. Thus the second plate 37 is no longer necessary and there are no first and second holes made in the first part 31 and the second part 34.

[0047] As an alternative embodiment of the machining tool, the second part 34 can also be fixed directly by means of a screw in the bottom of the cup of the first part 31 without the opening 33 and without the first plate 36, but with a central threaded hole in the bottom of the first part 31.

[0048] It should also be noted that the second part 34 shown at the figure 3b The second part 34 can be a washer without the first holes 38' and the second holes 39'. This second part 34 can be attached to the first part 31 by means of an external thread on a lower outer area of ​​the second part 34, opposite to the attachment of the second abrasive belt 35 to the front face of the second part 34. In this case, an internal cylindrical edge, complementary to the external thread of the second part 34, can be provided at the bottom of the recess of the first part 31. The second part 34 is fixed by screwing it into the threaded hole in the internal cylindrical edge of the first part 31. Naturally, the thread is cut in the opposite direction to the rotation of the tool during machining to ensure that the two parts 31 and 34 are securely fastened to each other.

[0049] The first and second abrasive belts 32, 35 were described above as preferably fixed to an edge or front face of each part 31, 34. However, it is also possible to fix them to an outer or inner side wall of the first and second parts 31, 34 in the form of a cup or washer. The same applies to the embodiments described below. It is also possible to have each abrasive belt positioned on a front face and fixed continuously, in part, to the side walls of the cup of each part. This type of abrasive belt is in the form of an annular cup.

[0050] THE figures 4a , 4b et 4c represent a first variant of the second form of execution presented to figures 3a , 3b et 3c The same reference symbols are used for the same elements of this first variant, and for the sake of simplicity, only the elements differing from the execution form presented in the figures 3a , 3b et 3c .

[0051] There figure 4a represents the first part 31 having the first machining portion 32 in the form of a first abrasive strip 32. This first part 31 is identical in shape to the first part 31 described with reference to the figure 3a This first part 31 comprises only a central opening 33, but there are no fixing holes in the bottom of the bowl. The dimensions of this first part 31 can be the same as those of the first part 31 seen in figure 3a However, only the height h1 of the first part 31 up to the first abrasive strip 32 can be greater, for example 74 mm.

[0052] There figure 4b represents the second part 34 having a second machining portion 35 in the form of a second annular abrasive strip 35 with a thickness greater than its width. This second abrasive strip is cylindrical in shape. The second abrasive strip 35 is fixed to the outer periphery of the edge of the second part 34. This second part 34 is in the form of a basin. In the bottom of the basin of the second part 34, first holes 38 are made for the positioning or fixing of pins shown below with reference to the figure 4c , in order to place this second part 34 onto a second fixing plate explained below. Second holes 39 are also provided in the bottom of the bowl with an internal recess for the placement of fixing screws for this second part 34 onto the second plate explained below. figure 4c .

[0053] Three first holes 38 and three second holes 39 can be provided in the bottom of the basin of the second part 34, arranged alternately on the same coaxial circle. The angle separating a first hole 38 from a neighboring second hole 39 is therefore 60°.

[0054] By way of example and without limitation, the outer diameter d4 of the second abrasive belt 35 can be 50 mm. The thickness of the second abrasive belt 35 can be 8 mm, while its width l1 can be 3 mm. The height h2 of the second part 34 with the second abrasive belt 35 can be 30 mm. The diameter d5 of the circle for the placement of holes 38 and 39 can be 23 mm. The diameter of each first hole 38 can be 3 mm, and the diameter of the second hole 39 for the threaded portion of each fixing screw can be 4 mm, while the diameter of the screw head recess can be 7 mm. This screw head recess for each second hole is located inside the cup of the second part.

[0055] There figure 4c shows an exploded three-dimensional view of the various elements of the machining tool 30 according to the first variant of the second embodiment. This time the second part 34 is mounted and fixed on a second mounting plate 37 of generally cylindrical shape and not on the first part 31.

[0056] As with the execution form shown in the figure 3c A first circular fixing plate 36, shaped like a plug, comprises a solid cylindrical central piece and a circular rim or shoulder. The central piece has a diameter slightly smaller than the diameter of the opening 33 in the first part 31. The central piece can pass through the central opening 33, and the rim rests against the outer surface of the bowl bottom of the first part 31. As before, at least three fixing holes 42 can be provided in the central piece of the first circular plate 36.

[0057] A second plate 37, generally cylindrical in shape and with a diameter larger than the diameter of the central opening 33, is intended to be fixed to the first plate 36 on one inner side of the cup of the first part 31. To this end, at least three through mounting holes 43, for example, are provided in the second circular plate 37 to align with the three holes in the first circular plate 36. The two plates can, for example, be fixed by screws (not shown) passing through the three holes 42 of the first plate 36 and screwed into the three threaded holes 43 of the second plate 37, which, after fixing, bears against the inner surface of the bottom of the cup of the first part 31. These two mounting plates 36, 37 are, for example, made of aluminum or steel and can be connected to a shaft of the machining tool 30 for mounting in a chuck of a spindle of a machining center as shown in the figure. figure 1 .

[0058] The second part 34 is attached to the second insert 37 by fitting into a complementaryly shaped cavity provided from an upper surface of the second insert 37. Pins 40, mounted in holes provided for this purpose in the cavity of the second insert 37, fit into the first through holes in the bottom of the recess of the second part 34 when this second part 34 is attached to the second insert 37. Three screws 41 are also provided to pass through the second holes of the second part 34 in order to be screwed into three corresponding threaded holes 44 in the cavity of the second insert 37. After this second part 34 is attached to the cavity of the second insert 37, the second abrasive belt 35 is positioned well outside said cavity and more towards the center of the machining tool, being well separated from the first abrasive belt 32 of the first part 31.The top of the second abrasive belt 35 can be at the same height as the top of the first abrasive belt 32 after assembly and before machining.

[0059] It should also be noted that this second abrasive belt 35 of the second part 34 can be intended for a rough grinding stage, while the first abrasive belt 32 of the first part 31 can be intended for a finishing grinding stage with a particle size smaller than that of the second abrasive belt 35.

[0060] As described above in connection with a variant of the second form of execution of the figures 3a , 3b et 3c It is possible to have a second part 34 in the form of a cup with a second machined portion 35, such as a second abrasive belt placed on a front face or edge of the second cup-shaped part 34. A solid base is provided at the bottom of the cup for this second part 34, which can be fixed by means of a screw in a central tapped hole made in the first insert 36. The second part 34 is fixed directly, with its cup base, to the base of the cup of the first part 31 by screwing a screw into the tapped hole of the first insert 36, the central part of which fits into the opening 33 of the first part 31. Thus, the second insert 37 is no longer necessary, and first and second holes are not made in the first part 31 and the second part 34.

[0061] As before, the second part 34 can also be fixed directly by means of a screw in the bottom of the bowl of the first part 31 without the opening 33 and without the first plate 36, but with a central threaded hole in the bottom of the first part 31.

[0062] THE figures 5a , 5b et 5c represent a second variant of the second form of execution presented to figures 3a , 3b et 3c This second variant is largely similar to the first variant described with reference to figures 4a , 4b et 4c For the sake of simplicity, only the elements that differ from this first variant will be described.

[0063] The first part 31 of the figure 5a is entirely identical to that described in the figure 4a Similarly, the second part 34 of the figure 5b is identical in shape to that of the figure 4b The only difference is that no means, such as holes in the bottom of the bowl, are provided for attaching it to a second pad as described below. The difference lies in the fact that an external thread 34' is provided on an external area of ​​the base body of the second part 34. This thread 34' is located on the opposite side from the placement of the second abrasive belt 35. As a non-limiting example, the height h3 of this thread 34' can be 10 mm.

[0064] There figure 5c This represents a three-dimensional exploded view of the various elements of the machining tool 30 according to the second variant of the second embodiment. The second part 34 is mounted in a cavity with a complementary shape to the second, generally cylindrical, mounting plate 37. The cavity includes a thread 45 so that the second part 34, with its thread 34', can be screwed into place for fastening. The thread orientation is designed to be in the opposite direction to the rotation of the machining tool for grinding operations in a machine tool spindle. In this way, the second part 34 remains securely screwed into the threaded cavity 45 of the second plate 37. Only holes 43 are provided in the second plate for fastening to the first plate 36 by means of screws passing through the holes 42 of the first plate 36.The machining tool 30 may further include a rod fixed to the first plate 36 for mounting in a chuck of the spindle of the machining machine.

[0065] THE figures 6a, 6b And 6c represent a first variant of a third form of execution of the machining tool 50. In this third form of execution, the machining tool consists of at least two different parts assembled or nested one inside the other like "Russian dolls".

[0066] As depicted in the figure 6a The first part 51 includes a first machining portion 52, which may be in the form of a first abrasive strip arranged and fixed, for example, by sintering, brazing, or bonding, to an upper edge of a cup-shaped recess. The first abrasive strip 52 is cylindrical in shape to extend the cup-shaped recess of the first part 51, with a thickness e1 greater than its width. The recess with the first machining portion 52 includes a housing 56 for receiving the second part of the machining tool. The recess further includes an opening 53 of diameter d4 through its base with a lower tubular extension from the opening 53 in the base, arranged along a longitudinal axis of the recess. The outer diameter d5 of the tubular extension is smaller than the outer diameter d1 of the recess with the first machining portion 52.This tubular extension of the first part 51 also includes a first through opening 58 perpendicular to the central axis of the tubular extension for a means of fixing in the form of a pin, a key, a conical flush or a screw for example.

[0067] As depicted in the figure 6b The second part 54 comprises a second machining portion 55 in an upper position of the second part 54. This second machining portion 55 is in the form of a solid abrasive cylindrical block 55, forming a tool head, having a flat upper surface and a lower surface fixed, in particular by sintering, brazing, or bonding, to a flat upper surface of a cylindrical body of the second part 54. The outside diameter d12 of this cylindrical body of the second part 54 is equal to or slightly less than the outside diameter d11 of the solid abrasive cylindrical block 55. A cylindrical extension 57 extends along a central axis from a lower surface of the cylindrical body of the second part 54. This cylindrical extension 57, as well as optionally the cylindrical body, may have a centered longitudinal opening.A second through-opening 58' is also provided in the cylindrical extension 57, which is perpendicular to the central axis of the tubular extension. This second through-opening 58' is arranged to be aligned with the first through-opening of the first part once the second part 54 is fitted into the first part. The two parts can be secured by a pin, a key, a tapered punch, or a screw inserted into the two aligned through-openings, for example.

[0068] By way of example and without limitation, parts 51 and 54 of the first and second figures 6a et 6b The outer diameter d1 of the first abrasive belt 52 can be 30 mm, while the outer diameter d6 of the bowl body can be 29 mm. The inner diameter d2 of the first abrasive belt 52 can be 22 mm, resulting in an abrasive belt width of 4 mm and a thickness e1 of 15 mm. The inner diameter d3 of the bowl base can be 20 mm. The diameter d4 of the opening 53 in the bowl base can be 6 mm. The outer diameter d5 of the tubular extension of the first part can be 12 mm. The length h1 of the tubular extension can be 20 mm, with the first through-hole 58 having a diameter t1 of approximately 3 mm. This through-hole 58 is located at a distance h2 of 11 mm from the outer surface of the bowl base. The abrasive belt is fixed at a height h3 of approximately 4 mm, while an inner edge from the bottom of the bowl is at a height h4 of 2 mm.The outer diameter d11 of the abrasive cylindrical block 55 of the second part 54 can be 21 mm and its thickness e2 equal to 10 mm, for example, while the upper body of the second part 54 has an outer diameter d12, which can be 20 mm. The outer diameter d13 of the cylindrical extension 57 can be approximately 6 mm so as to be inserted into the opening 53 of the first part and slid into the opening of the tubular extension of the first part 51. The length h5 of the extension can be 30 mm. The second through opening 58' can have a diameter t2 of 3 mm and be located at a distance h6 of 14 mm from the cylindrical body of the second part 54, which has a height h7 of approximately 20 mm.

[0069] There figure 6c This represents a three-dimensional exploded and assembled view of the machining tool 50 before and after its mounting on a chuck 18 of a machine tool spindle. The second part 54, with its cylindrical extension 57, is inserted into the housing 56 of the first part 51, and the cylindrical extension 57 passes through the central opening in the bottom of the cup to slide into the opening of the tubular extension of the first part 51. Once the two openings 58 and 58' are properly aligned, a pin 61, or possibly a screw, is inserted, for example by force, into the two openings, thus making the machining tool 50 fully assembled and ready for machining operations.

[0070] It should also be noted that the first machining portion 52 of the first part 51 can be used for a roughing grinding step, while the second machining portion 55 of the second part 54 can be used for a finishing step.

[0071] THE figures 7a , 7b et 7c represent a second variant of a third embodiment of the machining tool 50. As before in this second variant of the third embodiment, the machining tool also consists of at least two different parts assembled or nested one inside the other like "Russian dolls". All the elements of this second variant are identical to those of the first variant described with reference to figures 6a, 6b And 6c Therefore, not all parts and their identical assembly will be described. There is only a dimensional difference between the first and second parts, 51 and 54.

[0072] By way of example and without limitation from the first part 51 of the figure 7a The diameter d1 can be 30 mm, the diameter d2 can be 12 mm, the diameter d3 can be 10 mm, the diameter d4 can be 6 mm, the diameter d5 can be 10 mm, and the diameter d6 can be 15 mm. The thickness e1 can be 15 mm. The length h1 can be 20 mm, the distance h2 can be 13 mm, the height h3 can be 2 mm, and the height h4 can be 2 mm. The diameter t1 of the first through opening 58 can be 3 mm.

[0073] By way of example and without limitation from the second part 54 of the figure 7b The diameter d11 can be 11 mm and the thickness e2 equal to 10 mm, the diameter d12 can be 10 mm, and the diameter d13 can be 6 mm, or even slightly less to allow the cylindrical extension 57 of the second part 54 to slide within the tube of the tubular extension of the first part 51. The length h5 of the extension can be 30 mm. The second through opening 58' can have a diameter t2 of 3 mm and be located at a distance h6 of 14 mm from the cylindrical body of the second part 54, which has a height h7 of approximately 20 mm.

[0074] THE figures 8a, 8b And 8crepresent a third variant of a third embodiment of the machining tool 50. For this third variant of the third embodiment, the machining tool 50 also consists of at least two different parts assembled or nested one inside the other like "Russian dolls". The machining tool 50 of this third variant is identical even in dimensions to the different elements described for the second variant of the figures 7a , 7b et 7c The only difference concerns the second machining portion 55 fixed to a flat surface of the cylindrical body of the second part 54. This second machining portion 55 does not end with a flat surface, but with a centered point, the point angle of which can be 120°.

[0075] THE figures 9a , 9b et 9c represent a fourth variant of a third embodiment of the machining tool 50. For this fourth variant of the third embodiment, the machining tool 50 also consists of at least two different parts assembled or nested one inside the other like "Russian dolls". This fourth variant is identical even in dimensions to the different elements described for the second variant of the figures 7a , 7b et 7c The only difference concerns the second machining portion 55 fixed to a flat surface of the cylindrical body of the second part 54. This second machining portion 55 does not end with a flat surface, but with a hemispherical shape, the radius of which can be half the diameter of the solid abrasive cylindrical block 55, i.e. 5.5 mm.

[0076] It should also be noted that the first machining portion 52 of the first part 51 can be used for a roughing grinding step, while the second machining portion 55 of the second part 54 can be used for a finishing step. This type of machining tool 50 can advantageously be used to create chamfers on parts, particularly chamfers for watch crystals or lenses, which can be made of sapphire, or even for parts made of ceramic, zirconia, oxides, or nitrides.

[0077] It should also be noted that instead of fixing the first and second parts 51 and 54 once assembled by a pin or a key or a screw, it is possible to imagine making an internal thread in the tubular extension of the first part 51 and an external thread on the cylindrical extension 57 of the second part 54. Thus the second part 54 is fixed to the first part 51 by screwing its threaded cylindrical extension into the complementary thread of the tubular extension of the first part 51.

[0078] THE figures 10a, 10b And 10c represent a fifth variant of a third embodiment of the machining tool 50, which is based on the first variant shown in figures 6a, 6b And 6c For the sake of simplicity, only the difference between this fifth variant and the first variant is explained.

[0079] The difference in this fifth variant is the means of fixing the first part 51 and the second part 54. To achieve this, instead of through holes 58, 58' in the tubular and cylindrical extensions of the first and second parts 51, 54 shown in the figures 6a et 6b A slot 62 is formed at the end of the tubular extension of the first part 51. This slot 62 is preferably formed on two diametrically opposite sides and axially. This slot can be located at a distance h2 of 11 mm from the outer surface of the bottom of the bowl. Thus, the cylindrical extension 57 of the second part 54 is inserted into the tube of the tubular extension of the first part 51 until the base of the second part is in the bottom of the bowl of the first part 51. The second part 54 and the first part 51 are held together once the tool 50 is inserted into the chuck 18. Tightening the chuck causes the slotted portion of the first part to bend, allowing the second part 54 to be fixed to the first part 51 by this tightening.

[0080] It should be noted that the slot 62 can be longer and extend to the base of the cup of the first part 51. This type of fixing is simpler than the fixing means described above and allows for quick change of a part of the tool having a worn machining portion once the tool has been removed from the chuck of the machining machine.

[0081] Of course, it is possible to have more than two machining portions for each machining tool, for example at least three machining portions for a single-piece tool as described in reference to figures 2a et 2bThis applies to a tool with different assembled or interlocking and removable parts. Each machining portion comprises particles, preferably diamond, whose size or diameter varies from one machining portion to another on the same tool. These machining portions can therefore be arranged as strips or layers around the periphery of a cylindrical or conical tool body, sufficiently spaced apart. With three machining portions, a roughing grinding step can be performed, followed by a semi-finishing grinding step, and finally a finishing grinding step.

[0082] In the case of a machining tool with different assembled parts, it is possible to change the part with the worn machining portion and keep the other parts whose machining portion is not yet too worn as the parts can be disassembled without problem.

[0083] From the description just given, several variants of the machining tool can be designed by a person skilled in the art without departing from the scope of the invention defined by the claims.

Claims

1. A machining tool (20, 30, 50) for grinding a workpiece in a machining machine (1), the tool comprising at least a first machining portion (21, 31, 51) having particles of a material harder than the material of the workpiece to be machined, the particles being dispersed in a binder, and at least a second machining portion (22, 35, 55) having particles with a larger or smaller diameter than the first machining portion, and of a material harder than the material of the workpiece to be machined, the particles of the second machining portion being dispersed in a binder identical to that of the first machining portion or in a different binder, the first and second machining portions (21, 22) being in the form of strips or layers arranged peripherally on the same tool body (20) to form a one-piece tool, and the first and second machining portions consisting of first and second abrasive strips (21, 22) arranged on at least a front face of the tool body (20), which can be rotated in a spindle on a machining machine (1) to grind a workpiece to be machined; the first and second abrasive strips (21, 22) are annular and coaxially fastened to the front face (23) of the tool body (20) while being sufficiently spaced apart, and the front face (23) is perpendicular to the axis of rotation of the cylindrical or conical tool body (20).

2. The machining tool (20, 30, 50) for grinding a workpiece made of hard material in a machining machine (1) according to claim 1, characterised in that each machining portion (21, 22, 31, 35, 51, 55) comprises diamond particles embedded in a binder.

3. The machining tool (20, 30, 50) according to claim 1, characterised in that a third machining portion in the form of a third abrasive strip is arranged on the face of the same tool body.

4. The machining tool (20, 30, 50) according to claim 3, characterised in that the third annular strip is fastened to the front face (23) coaxial to the first and second abrasive strips (21, 22), all being spaced apart from each other.

5. The machining tool (20, 30, 50) according to claim 1, characterised in that the first machining portion (21) is arranged to comprise particles with a larger diameter than the second machining portion to be able to carry out a rough machining step, and to use the second machining portion to carry out a finishing step involving grinding the workpiece.

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