Patent Application
20200047314
The invention concerns a machining tool for performing a grinding operation on a workpiece, particularly made of hard material, in a machine tool.
For a grinding operation in a machine tool, it is known to change the machining tool between a rough grinding step and at least one finishing step by abrasive machining of the surface of workpieces to be machined. To grind a surface of a workpiece made of hard material, first of all, a first tool can be used with a machining band having, for example, large-diameter diamond particles in a binder—this is a rough grinding step. After this first step, a second tool can be used, with a machining band having smaller-diameter diamond particles than in the first step to form a semi-finishing step. Finally, a third tool can also be used with a machining band having diamond particles of even smaller diameter than in the second step for a final finishing step. In this case, three grinding tools must necessarily be used.
As mentioned above, it is generally necessary to perform the grinding process in several steps, since it is not possible, for example, to easily remove a scratch or rough surface condition from the workpiece to be machined with a machining band having small-diameter diamond or corundum particles. In this case, a very long and therefore expensive machining time is required to make each machined workpiece. From one step to another, the grinding tool may also have to be changed in the machine tool, or the workpiece to be machined may also have been machined twice, which prolongs the machining time further and constitutes a drawback.
For example, when placing two tools in two working positions, it takes several seconds, for example 5 seconds, to move the workpiece from a first working position to a second working position. If only one working position is used, changing the tool for each machining step can take twice as long, for example 10 seconds, as two tools in two operating positions. The machining time for each workpiece is therefore long, which constitutes a drawback.
It should also be noted that, where two surfaces are to be machined or grounded, up to 6 tools may be needed for three machining steps per surface of the workpiece to be machined. The machining time of each workpiece made of hard material is therefore too long, given that the change from one working position to another working position or the repeated changing of tools considerably slows down the machining time, which constitutes a drawback. Further, there are limitations in machining positions available in the machine tools and in the tools available.
The tool may have at least one grinding surface or band composed of abrasive particles embedded in a binder. The abrasive particles are particularly diamond particles, or particles of equal or lower hardness than the workpiece to be machined, which may be made of a material such as sapphire, zirconia, oxides, nitrides or otherwise, for machining workpieces made of hard material, since wear of the abrasive part is too rapid.
Each machining band, which includes abrasive particles in a binder, can be fixed to a tool body by sintering, brazing or bonding, and the tool support body can be made of aluminium or steel, for example. The tool attachment shaft can be inserted into a tool spindle nose or chuck to perform the machining operation.
Support part 2 can be moved in a first direction X, whereas support block 3 can be moved in a second direction Y perpendicular to first direction X and in a third direction Z perpendicular to first and second directions X and Y. Support block 3 can be rotated in a rotational direction A in the plane defined by first and second directions X and Y. Chuck 5 can be rotated during the machining of workpiece 10 in a direction of rotation C in the plane defined by second and third directions Y and Z.
During the machining of workpiece 10, the latter is first brought into contact with first grinding wheel 6, which can have a maximum diameter of 250 mm with a peripheral abrasive band having large-diameter diamond or corundum particles in a binder, for a rough grinding step. Next, the workpiece 10 to be machined must be brought into contact with second grinding wheel 7, which can also have a maximum diameter of 250 mm with a peripheral abrasive band having small-diameter diamond or corundum particles in a binder, for a finishing step.
As mentioned above, the time taken to perform these machining steps is relatively long, given that the workpiece must be moved from a first working position of first grinding wheel 6 to the second working position of second grinding wheel 7. This generally constitutes a workpiece grinding time that is too long and thus expensive at the end of the workpiece machining process. Further, the need to wait for one grinding wheel to finish rotating and then to start the other rotating results in long changeover times and requires additional energy to restart rotation, due to the inertia of the grinding wheel. These constitute drawbacks.
It is thus an object of the invention to propose a machining tool for performing a grinding operation on a workpiece in a machine tool to overcome the drawbacks of the aforementioned prior art and to reduce the machining time of each workpiece by the use thereof in a machine tool.
To this end, the invention concerns a machining tool for performing a grinding operation on a workpiece in a machine tool, which includes the features defined in the independent claim 1.
Specific embodiments of the machining tool are defined in the dependent claims 2 to 33.
One advantage of the machining tool lies in the fact that the tool includes several machining portions in the same tool. Each machining portion includes particles of a harder material than the workpiece to be machined which are embedded in a binder. The nature, size or diameter of the abrasive particles are different from one machining portion to another machining portion, and the concentration thereof in the binder can also be different. The first machining portion of the tool can include larger-diameter particles than the second machining portion in order to perform a rough machining step, and in order to use the second machining portion to perform a finish-grinding step on the workpiece.
More than two machining portions can be provided, each with abrasive particles of different diameter.
For machining workpieces made of hard material, such as for a sapphire watch glass or crystal, the abrasive particles are preferably diamond particles embedded in a binder.
Advantageously, the first and second machining portions are arranged in a same tool body in order to form a single one-piece tool to be mounted in a machine tool spindle to perform rough and finish-grinding operations. These machining portions are, for example, abrasive bands arranged on the same surface of the tool body and each forming a ring. The first annular abrasive band is coaxial to and preferably spaced apart from the second annular abrasive band. The first abrasive band is used for rough grinding and the second abrasive band, which is for example of smaller diameter, is used for finish-grinding the workpiece to be machined.
Advantageously, the grinding tool can include at least two parts which are attached to each other and can easily be disassembled in order to change one of the parts. A first part includes the first machining portion, whereas the second part includes the second machining portion. Since these parts are assembled and can be disassembled, in case of premature wear of one of the machining portions, it is possible simply to change the worn portion without having to completely change the tool.
It is also possible to have more than two complementary parts that can fit together like Russian dolls and are secured to each other to form the complete machining tool. Preferably, the last complementary secured part, which may be the first part with the first machining portion, is the part whose machining portion wears most quickly, such as during a rough machining step. This makes it easier to change this last complementary part of the tool.
The objects, advantages and features of the machining tool for performing a grinding operation on a workpiece, particularly made of hard material, in a machine tool, will appear more clearly in the following description with reference to the drawings, in which:
In the following description, the machining tool will be described as a grinding tool for grinding, for example, a surface of a workpiece to be machined, which is made of hard material. Preferably, the grinding tool is arranged, once mounted in a machine tool spindle, to be driven in rotation to make beveled edges, for example, on a workpiece, such as a watch glass or crystal, which may be made of sapphire, but without restriction to other machining possibilities.
To machine workpieces made of hard material, the various machining portions 21, 22 of machining tool 20 should preferably be made with diamond particles. It is also possible to envisage using corundum particles, but the machining portion wears more quickly with such corundum particle machining portions, since the hardness of this material is generally equal to or lower than that of the workpiece to be machined.
The diamond particles are embedded in a binder, which may be a metallic, resin, vitrified, galvanic, ceramic, bakelite or other binder. It is possible to envisage embedding the particles of machining portions 21, 22 in an identical or different binder. For each machining portion, 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. By way of example, a mean grain size on the order of 91 μm corresponds to D91, and a diamond particle concentration of 100 grains per mm3 corresponds to C100. For a machining step defined as rough machining, the particle size of one machining portion is larger than the particle size of another machining portion for a machining step defined as finish-machining. Thus, the smaller the grain size, the finer the machining operation.
The machining tool 20 shown in
Tool base body 20 may be metallic, for example made of steel or aluminium. Abrasive bands 21, 22 are fixed to front face 23 by sintering, brazing or bonding. A space is provided between each abrasive band to allow a first machining step to be performed with first abrasive band 21 without detriment to second abrasive band 22 for a second machining step. First abrasive band 21 can be defined with a particle size of between D20 and D30 for a rough machining step, while second abrasive band 22 can be defined with a particle size of between D6 and D12, for example, for a finish-machining step. It is possible to use more than two machining portions, i.e. more than two abrasive bands, 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 band has a different size of abrasive particles.
By way of non-limiting example, the dimensions of a machining tool 20 shown in
The conical machining tool 20 can also include a shaft mounted by plates (not represented) through an opening 24 in the base of the base body of tool 20. The tool shaft can be mounted on a spindle chuck of a machine tool as shown, for example, in
This machining tool 30 has at least two parts 31, 34 which are secured to each other and can easily be disassembled in order to change one of the parts. A first part 31 includes a first machining portion 32, while second part 34 includes a second machining portion 35. The size or diameter of the abrasive particles, as previously, is different from one machining portion to another machining portion, and their concentration in the binder may also be different. Since these parts are assembled and can be disassembled, in case of greater wear of one of the machining portions, it is possible simply to change the worn portion without having to completely change the tool.
The first and second complementary parts 31, 34 are configured in a generally cylindrical shape, but may have another general shape provided that they can fit one inside the other, for example.
As represented in
First part 31 includes a first machining portion 32, which is secured by sintering, brazing or bonding to a front edge of the base body of first part 31. The base body may be made of steel or aluminium for example. Preferably, this first machining portion 32 is a first abrasive band 32 of annular shape whose width may be identical to the width of the edge of first part 31. First abrasive band 32 may include particles, especially diamond particles, in a conventional binder.
In the cup base of first part 31, first holes 38 are made for positioning or attaching pins shown below with reference to
Three first holes 38 and three second holes 39 may be provided, arranged alternately on a same coaxial circle around opening 33 in the base.
The angle separating a first hole 38 from an adjacent second hole 39 is thus 60°.
By way of non-limiting example, the external diameter d1 of the first part can be 250 mm, while the inner diameter d2 can be 210 mm. The width of the abrasive band is thus in this case around 20 mm and its thickness e1 can be 5 mm. The thickness e2 of the cup base can be 15 mm and its height h1 up to first abrasive band 32 can be 45 mm. The diameter d3 of the opening in the base can be 76 mm. The diameter of first holes 38 can be 6 mm and the diameter of second holes 39 for the passage of 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 of 177 mm diameter.
As represented in
First holes 38′, identical to the first holes of the first part, are made on a portion of the height of washer 34 from a lower edge. Second threaded holes 39′ for receiving the threaded part of mounting screws are also provided on a portion of the height of the washer from the lower edge. Three first holes 38′ can therefore be provided, 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 arranged halfway between the external diameter and the internal diameter of washer 34.
By way of non-limiting example, the external diameter d4 of second part 34 can be 202 mm, while the inner diameter d5 of second part 34 can be 152 mm. Holes 38′ and 39′ are on a circle of diameter of around 177 mm.
The thickness e3 of second abrasive band 35 can be 5 mm. The height h2 of second part 34 up to the second abrasive band can be 30 mm. The depth of first holes 38′ can be 10 mm and the depth of the threaded part of second holes 39′ can be 10 mm with a non-threaded hole extension of 5 mm.
It should also be noted that second abrasive band 35 of second part 34 can be intended for a rough grinding step, while first abrasive band 32 of first part 31 can be intended for a finish-grinding step with a smaller particle size than that of second abrasive band 35.
An arrangement of a first circular plate 36, such as a stopper, and a second plate 37, such as a disc, can be provided for the mounting or attachment thereof through central opening 33 in the cup base of first part 31. First plate 36 thus includes a solid central cylindrical piece and a circular rim or shoulder. The central piece is of slightly smaller diameter than the diameter of opening 33 of first part 31. The central piece can pass through central opening 33 with the rim resting against the external surface of the cup base of first part 31. At least three mounting holes 42 can be provided in the central piece of first circular plate 36.
A second plate 37 of generally cylindrical shape, such as a disc, and of larger diameter than the diameter of central opening 33 is arranged to be secured on an inner side of the cup of first part 31 to the first plate. For this purpose, at least three mounting holes 43, for example through holes, are provided in second circular plate 37 in an identical arrangement to the three holes of first circular plate 36. Thus, the two plates can, for example, be secured by screws (not represented) that pass, for example, through the three holes of the first plate and are screwed into the three threaded holes of second plate 37, which, after attachment, rests against the inner surface of the cup base of first part 31. These two mounting plates 36, 37, made of aluminium or steel for example, are preferably connected to a shaft of machining tool 30 for mounting in a machine tool spindle chuck, as represented in
By way of variant of the second embodiment, it is possible to envisage having a second cup-shaped part 34 with a second machining portion 35, such as a second abrasive band placed on a front face or edge of second cup-shaped part 34. A solid base is provided at the bottom of the cup for this second part 34. A central opening for passage of a mounting screw shaft can be made in the cup base of second part 34 and a screw head recess can also be provided inside the cup of the second part. A central threaded hole can be made in first plate 36 to receive the threaded portion of the mounting screw. Second part 34 is directly secured with its cup base in the cup base of first part 31 by tightening a screw, which passes through the screw hole of the second part, into the threaded hole of first plate 36 whose central portion is inserted into opening 33 of first part 31. Thus, second plate 37 is no longer necessary, and there are no first holes and second holes made in first part 31 and second part 34.
Of course, in a variant of the machining tool, second part 34 can also be directly secured by means of a screw in the cup base of first part 31 without opening 33 and without first plate 36, but with a central threaded hole in the base of first part 31.
It should also be noted that the second part 34 shown in
First and second abrasive bands 32, 35 were explained above as preferably being secured to a front edge or face of each part 31, 34. However, they could also be secured to an external or internal side wall of the cup or washer-shaped first and second parts 31, 34. The same applies for the embodiments described below. Each abrasive band could also be arranged on a front face and partly continuously secured to the side walls of the cup of each part. This type of abrasive band is in the form of an annular cup.
Three first holes 38 and three second holes 39 can be provided in the cup base of second part 34, arranged alternately on the same coaxial circle. The angle separating a first hole 38 from an adjacent second hole 39 is thus 60°.
By way of non-limiting example, external diameter d4 of second abrasive band 35 can be 50 mm. The thickness of second abrasive band 35 can be 8 mm, while the width 11 of second abrasive band 35 can be 3 mm. The height h2 of second part 34 with second abrasive band 35 can be 30 mm. The diameter d5 of the placement circle of holes 38 and 39 can be 23 mm. The diameter of each first hole 38 can be 3 mm and the diameter of second hole 39 for passage of the threaded part of each mounting screw can be 4 mm, while the diameter of the screw head recess can be 7 mm. This screw head recess of each second hole is inside the cup of the second part.
As in the embodiment shown in
A second plate 37 of generally cylindrical shape and of larger diameter than the diameter of central opening 33 is arranged to be secured on an inner side of the cup of first part 31 to first plate 36. For this purpose, at least three mounting holes 43, for example through holes, are arranged in second circular plate 37 to face the three holes of first circular plate 36. The two plates can, for example, be secured by screws (not represented) that pass through the three holes 42 of first plate 36 and are screwed into the three threaded holes 43 of second plate 37, which rests, after attachment, against the inner surface of the cup base of first part 31. These two mounting plates 36, 37 are, for example, made of aluminium or steel and can be connected to a shaft of machining tool 30 for mounting in a machine tool spindle chuck, as represented in
The second part 34 is secured to second plate 37 by being housed inside a cavity of complementary shape arranged from an upper surface of second plate 37. Pins 40, mounted in holes provided for this purpose in the cavity of second plate 37, are housed in the first holes through the cup base of second part 34 when this second part 34 is attached to second plate 37. Three screws 41 are also arranged to pass through the second holes of second part 34 to be screwed into three corresponding threaded holes 44 in the cavity of second plate 37. Once this second part 34 is secured in the cavity of second plate 37, second abrasive band 35 is situated outside said cavity and more at the centre of the machining tool yet quite separate from first abrasive band 32 of first part 31. The top of second abrasive band 35 can be at the same height as the top of first abrasive band 32 after assembly and before machining.
It is also to be noted that this second abrasive band 35 of second part 34 can be intended for a rough grinding step, while first abrasive band 32 of first part 31 can be intended for a finish-grinding step with a smaller particle size than that of second abrasive band 35.
As described above with reference to a variant of the second embodiment of
As previously, second part 34 can also be secured directly by means of a screw in the cup base of first part 31 without opening 33 and without first plate 36, but with a central threaded hole in the base of first part 31.
First part 31 of
As represented in
As represented in
By way of non-limiting example of first and second parts 51 and 54 of
It should also be noted that first machining portion 52 of first part 51 can be used for a rough grinding step, while second machining portion 55 of second part 54 can be used for a finishing step.
By way of non-limiting example of first part 51 of
By way of non-limiting example of second part 54 of
It should also be noted that first machining portion 52 of first part 51 can be used for a rough grinding step, while second machining portion 55 of second part 54 can be used for a finishing step. This type of machining tool 50 can advantageously be used to make bevelled edges on workpieces and particularly bevelled edges for watch glasses or crystals, which may be made of sapphire, or for workpieces made of ceramic, zirconia, oxides or nitrides.
It should also be noted that instead of attaching first and second parts 51 and 54 once assembled via a pin or a key or a screw, it is possible to envisage making an inner thread in the tubular extension of first part 51 and an outer thread on cylindrical extension 57 of second part 54. Thus, second part 54 is secured to first part 51 by screwing its threaded cylindrical extension into the complementary thread of the tubular extension of first part 51.
The difference of this fifth variant is the means of securing first part 51 and second part 54. Thus, instead of through holes 58, 58′ in the tubular and cylindrical extensions of the first and second parts 51, 54 shown in
It is to be noted that slot 62 can be longer and extend as far as the base of the cup of first part 51. This type of attachment is simpler than the attachment means described above and makes it possible to quickly change a tool part having a worn machining portion once the tool is removed from the machine tool chuck.
Naturally, it is possible to envisage having more than two machining portions for each machining tool, for example at least three machining portions, both for a one-piece tool as described with reference to
In the case of a machining tool with various assembled parts, the part with a worn machining portion can be changed while keeping the other parts whose machining portion is not yet too worn, since the parts can be disassembled with no difficulty.
From the description that has just been given, several variants of the machining tool can be devised by those skilled in the art without departing from the scope of the invention defined by the claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 18187831.5 | Aug 2018 | EP | regional |
