RU2691483C1 - End mill - Google Patents

Abstract

FIELD: technological processes.SUBSTANCE: invention relates to a metal cutting tool, in particular, to end mills used for machining articles from high-strength steels and hard-to-machine materials, as well as for aluminum processing. Cutter comprises working part arranged around axis of rotation with cutting edges formed at intersection of front and rear surfaces and arranged alternating with chip removal grooves. Wearproof coating is applied on working part, consisting of at least one layer, which contains phase with at least one of elements V, Cr, Nb, Ti, Ta, Zr, Hf, Al, Si, C, N, O and has residual compressive stresses, wherein the wear-resistant coating has a non-uniform thickness along the surface of the working part of the mill. Thickness of wear-resistant coating on front and rear surfaces, as well as surfaces of chip removal grooves in each cross-section by working part plane has variable value within 0.2…5.0 mcm and more in direction from cutter axis to cutting edges.EFFECT: working capacity and durability of a mill increases.10 cl, 9 dwg

Description

The field of technology.

The present invention relates to a metal-cutting tool, in particular, to end mills used for machining various surfaces primarily in high-strength steel products and difficult-to-work materials, as well as for machining aluminum.

The level of technology.

For processing products that have a different shape of the treated surface, end mills of different diameters are used, the working part of which is made of a hard alloy with a wear-resistant coating. Wear-resistant coating, taking into account its intended purpose, can significantly improve the performance and durability of the cutters in relation to specific processed materials and cutting conditions.

In the process of milling the working part of the end mills is subjected to significant mechanical and thermal effects. At the same time, it is subjected to shock loads and periodically experiences a bend with torsion, being in a complex stress-strain state. This may cause vibrations, accompanied by a decrease in the resistance of the cutters and the deterioration of the machined surfaces, which is especially important when processing parts of aircraft.

When developing designs of mills, usually uneven loading of end mills along their working part is taken into account, which is connected with their cantilever fastening in the spindle of the metalworking machine. In this case, as a rule, do not take into account the console arrangement of the teeth of the cutters in the radial direction relative to their axis. To increase the rigidity of the working part of the end mills, various shapes and sizes are used, both of the working part itself, and the shapes and sizes of chip grooves and teeth located along the working part of the mills. For mills with wear-resistant coatings for these purposes also use the properties of wear-resistant coatings with residual compressive mechanical stresses.

Known design end mills, for example, patents of the Russian Federation for the invention №262731 and №27617827, containing located around the axis of rotation of the working part with cutting edges, alternating with chip grooves. In this case, the working part of these cutters is made of a hard alloy with a wear-resistant coating, in which at least one layer has residual compressive stresses. In these structures, the properties of wear-resistant coatings with compressive residual stresses are used to increase the rigidity of the working part of the cutters. In this case, given the ratio of length and / or surface area with a wear-resistant coating and the size of the working part of the cutters to reduce vibrations in the processing of products from difficult-to-process materials. The design of these end mills provides for a different thickness of the wear-resistant coating on the surface of the working part, which allows to take into account the peculiarity of the cantilever loading of the mills as a whole.

However, the above technical solutions are aimed at increasing the rigidity only in the whole working part of end mills, taking into account its cantilever loading. They do not take into account the console arrangement and the variable section of the teeth of the cutters in the radial direction relative to the axis of rotation. At the same time, it should be noted that it is the teeth of the cutters that first of all perceive the shock load that occurs at the time of cutting the cutting edges into the material being processed. At the same time, the cutting edges, being the tip of the teeth, furthest from the axis of rotation of the cutters, are subjected to maximum dynamic loads and experience maximum tangential stresses that affect the performance and durability of end mills.

It is known that with cantilever positioning, cantilever beams of equal resistance, having a variable cross section, are most capable of withstanding impact loads. Existing tooth shapes also have a variable cross section in the radial direction relative to the axis of the end mills. These forms depend primarily on the cutting angles, as well as on the shape and size of the chip grooves and the working part as a whole of the end mills themselves. These parameters are decisive, since the performance of end mills depends on them in principle.

At the same time, the existing dimensions and shapes of the teeth of the end mills do not take into account the features of beams of equal resistance. In this case, as a rule, the sections of the teeth in their bases are significantly larger in area than the sections located closer to the cutting edges. Moreover, this difference is not commensurate with the distance from the corresponding section to the axis of rotation of the cutters, which determines the magnitude of the bending moment in the corresponding section. As a result, sections that are located closer to the cutting edges experience significantly greater mechanical stresses and associated loads than sections that are located closer to the axis of rotation of the cutters. This leads to non-uniform loading of the teeth along their length in the radial direction and thereby the loss of the properties of the beams of equal resistance.

Improvement of the design of end mills due to the selection of the sizes and shapes of their teeth and chip removal grooves, taking into account the requirements for beams of equal resistance, is largely exhausted. New features reveals the use of wear-resistant coatings with residual compressive stresses and allowing to reduce the negative impact of shock loads on the cutting part of end mills.

The present invention is to improve the performance and durability of the end mills through the use of wear-resistant coatings with residual compressive stresses and different thickness over the surface of the working part of the milling machine in the radial direction relative to its axis of rotation.

Technical result: increased efficiency and durability of the cutter.

Disclosure of the invention.

This technical result is achieved by a combination of features that are given in the respective claims.

The end milling cutter contains a working part located around the axis of rotation with cutting edges formed at the intersection of the front and rear surfaces and arranged alternately with the chip grooves. A wear-resistant coating is applied to the working part, consisting of at least one layer that contains a phase with at least one of the elements V, Cr, Nb, Ti, Ta, Zr, Hf, Al, Si, C, N , Oh and has residual compressive stresses. In this case, the wear-resistant coating has an uneven thickness over the surface of the working part of the cutter.

According to the invention, the thickness of the wear-resistant coating on the front and rear surfaces in the cross-sectional view by the plane of the working part in the radial direction from the axis of rotation of the cutter to its cutting edges has a variable value in the range of 0.2-5.0 μm and it is larger in the direction from the axis of rotation of the cutter to cutting edges.

In accordance with one preferred embodiment of the milling cutter, its working part is made of removable hard alloy.

In accordance with another preferred embodiment of the milling cutter, the thickness of the wear-resistant coating is inversely proportional to the angle between the normal to the corresponding surface and the radius of the working part of the milling cutter passing through this surface and is directly proportional to the distance from the axis of rotation of the milling cutter to the said surface.

In accordance with another preferred embodiment of the milling cutter, the wear-resistant coating comprises a layer of superhard amorphous carbon.

In accordance with another preferred embodiment of the cutter, the thickness of the layer of superhard amorphous carbon is in the range of 0.5-1.6 μm, and the residual compressive stresses in the wear-resistant coating are in the range of 4-10 GPa.

In accordance with another preferred embodiment of the milling cutter in the cross sectional view by the plane of its working part, the thickness of the wear-resistant coating is equal to areas of the front and rear surfaces of the teeth that are located on circles equidistant to the circles passing through the cutting edges that are furthest from the axis of the cutter; equal to each other.

In accordance with another preferred embodiment of the milling cutter, the thickness of the wear-resistant coating on the rear surfaces is greater than on the front.

In accordance with another preferred embodiment of the milling cutter, its wear-resistant multi-layer coating with a thickness in the range of 1.5-5 microns.

In accordance with another preferred embodiment of the milling cutter, the thickness of the wear-resistant coating is not uniform along the length of the cutting part.

In accordance with another preferred embodiment of the milling cutter, the thickness of the wear-resistant coating along the length of the cutting part is less in the direction from its end to the shank.

Brief description of the drawings.

FIG. 1a, b shows a side view of the end mill, respectively, with a solid and removable cylindrical working part;

in fig. 2 shows an end view of an end mill as depicted in FIG. one;

in fig. 3 shows a fragment of a cross section of the plane along the line A-A of the cutter tooth end shown in FIG. 1, with wear-resistant coating;

in fig. 4a, b shows schematically a fragment of the cutter tooth section, respectively, along the line I-I and IV-IV shown in FIG. 3;

in fig. 5a, b schematically shows a fragment of a cross-section of the tooth of the cutter, respectively, along the line II-II and III-III, shown in FIG. 3;

in fig. 6 shows a fragment of the cross-section of the face of the cutter tooth, along the line A-A shown in FIG. 1, indicating the angles between the normal to the corresponding surface with a wear-resistant coating and the radius of the circumference of the working part, passing through this surface;

in fig. 7a, b, c schematically show fragments of a cross-section of the cutter tooth shown in FIG. 6, respectively, through lines V-V, VI-VI and VII-VII;

in fig. 8 shows a fragment of a cross-section of the face of the cutter tooth, along the line A-A shown in FIG. 1, with the indication of the cutting planes of the cutter's tooth parallel to its axis along the lines B-B and C-C;

in fig. 9a, b depict fragments of sections of the tooth of the cutter shown in FIG. 8, along the lines B-B and C-C.

Detailed description of the drawings.

FIG. 1a shows, as an example, a end milling cutter 10 with a cylindrical working part 14, four teeth and a screw arrangement of cutting edges 16 around an axis 12 with alternation with chip removal grooves 22. In this case, the number of teeth of the milling cutter may be different, and its working part may be, for example, cone-shaped.

The working part 14 may be made of hard alloy or high-speed steel. It can also be detachable 14a and attached to the shank 12a of the cutter using a threaded connection, as shown in FIG. 1b. FIG. 2 shows an end view of the working portion 14 and 14a of the milling cutter 10 with the image of the end teeth 22a extending in the radial direction from the axis 12 of the milling cutter 10.

A wear-resistant coating 24 is applied to the working part 14, 14a, for example, by vacuum-arc spraying. Moreover, wear-resistant coating 24 consists of at least one layer 26, which contains a phase with at least one of the elements V, Cr, Nb, Ti, Ta, Zr, Hf, Al, Si, C, N, O and has residual compressive stresses.

The elements specified in the list, as a rule, are included in wear-resistant coatings that have residual compressive stresses and are used to increase the durability of the cutting tool, depending on the material being processed and processing modes. For example, Nb, Ta, Hf are used in high-temperature coatings of tools used in surface treatment of products from difficult-to-process materials.

In this case, the wear-resistant coating 24 may be single-layer 26, for example, made of amorphous carbon, or be multi-layered and deposited on the surface of the working part by the PVD method. Further, to simplify the understanding of the essence of the invention, a single-layer wear-resistant coating 26 is considered. The thickness of the wear-resistant coating 26 on the surface of the working part 14 and 14a is not uniform and is made with regard to the cantilever arrangement of the cutter teeth relative to its axis 12.

Thus, in accordance with the invention, the thickness of the wear-resistant coating 26 h1 ... h7 on the front 18 rear 20 surfaces in a cross-sectional view with the plane of FIG. 1a along the line A-A of the working part 14 of the milling cutter 10 in the radial direction from the axis 12 of rotation of the milling cutter 10 to its cutting edges 16 has a variable value in the range of 0.2-5.0 μm. Moreover, this value is greater in the direction from the axis 12 of the cutter to its cutting edges 16.

As an example, consider FIG. 4a, b and fig. 5a, b. Here are schematically depicted fragments of the tooth sections shown in FIG. 3, the milling cutters 10, respectively, along the lines I-I, IV-IV and II-II, III-III. In this case, for example, the thickness of the wear-resistant coating 26 in sections I-I and IV-IV located closer to the cutter axis, respectively h1 and h4 is less than sections II-II and III-III, located further from the cutter axis, respectively h2 and h3.

In accordance with one of the preferred versions of the cutter, the thickness of the wear-resistant coating is also inversely proportional to the angle between the normal to the corresponding surface and the radius of the circumference of the working part of the cutter passing through this surface.

As an example, consider FIG. 6. Here is a schematic representation of a fragment of the cross-section of the cutter tooth plane along the line A-A shown in FIG. 1, indicating the angles between the normal to the corresponding surface with a wear-resistant coating and the radius of the circumference of the working part 14 passing through this surface. In this case, the radii drawn from the axis 12 of the cutter 10 to the corresponding sections are depicted in the form of broken lines, which is associated with the scale of the image of the fragment.

From FIG. 6 that the above angles α1 ... α3 of the surfaces of working honor 14 in this case, the cutter teeth, respectively, are different in sections V-V ... VII-VII.

From FIG. 7 a, b, c that these angles of inclination correspond to the thickness of the wear-resistant coating 24. In particular, the smallest angle of inclination α1 corresponds to the greatest for this example thickness h7 of the wear-resistant coating, located in section VII-VII (Fig. 7b). At the same time, the largest angle of inclination α3 corresponds to the smallest thickness h5 of the wear-resistant coating located in the section V-V (Fig. 7a). In this case, the thickness of the wear-resistant coating h6, corresponding to the angle of inclination α2, occupies an intermediate value.

Next, consider FIG. 8, where a fragment of the cross-section is shown by the plane of the cutter's tooth, along the line A-A shown in FIG. 1, with the indication of the cutting planes of the cutter's tooth parallel to its axis along the lines B-B and C-C, and FIG. 9a, b, where fragments of sections of FIG. 6 respectively along the lines bb and cc.

From FIG. 9a, b, it can be seen that the fragment of area S1, corresponding to section B-B, is substantially larger than the fragment of area S2, corresponding to section C – C of FIG. 8. As a result, even taking into account the cantilever loading of the cutter teeth, sections located closer to the cutting edges 16 experience significantly greater mechanical stresses and associated loads than sections located closer to the axis of rotation 12 of the normal cutters. This leads to uneven loading of the teeth along their length in the radial direction and thereby loss of properties of the beams of equal resistance. Therefore, in one of the preferred versions of the proposed cutter design, this negative factor is compensated for by a wear-resistant coating having residual compressive stresses and different thickness over the surface of the working part 14, including taking into account the change in the tooth cross-sectional area from the mill axis.

This ensures the equalization of stresses in the specified sections along the length of the teeth in the radial direction, i.e. in the direction from the axis of the cutter to its cutting edges in order to obtain a beam of equal resistance, due to a certain compensation of a significant difference in the areas of the specified sections along the length of the teeth in the radial direction. At the same time, the greatest thickness of the wear-resistant coating on the surface of the working part of the cutter, which is furthest from the axis of rotation, makes it possible to reduce stresses in the coating that result from the effect of the greatest tangential stresses when the working part is twisted.

It should be understood that to obtain a technical result of a given value for cutters with a specific tooth shape in the cross-sectional view of the working part of the cutters with the plane taking into account specific materials of wear-resistant coatings, cutting conditions and materials being processed, the thickness of the wear-resistant coating in the radial direction from the cutter axis will be within 0.2-5.0 microns.

For example, for end mills with the traditional shape of the teeth and with a wear-resistant coating of amorphous carbon, the range of variation of the coating thickness from 0.5 to 1.6 μm is most preferable. In this case, the residual compressive stresses in the wear-resistant coating should be in the range of 4-10 GPa.

For end mills with a multi-layer wear-resistant coating, most preferably the coating thickness should be in the range of 1.5-5 microns. Such a multi-layer wear-resistant coating may contain layers of NbN or TiB2, having residual compressive stresses.

To obtain a higher resistance of the proposed cutter design in accordance with one of the preferred versions of the cutter in the cross-sectional view by the plane of the working part 14 of the cutter 10, the thickness of the wear-resistant coating 24 on the front and rear surfaces of the teeth located on circles 28 (Fig. 6) with radius Ri circles 30 with a radius Rmax, passing through the parts of the cutting edges 16 that are most distant from the axis 12 of the cutter, should not be equal to each other. It is most preferable that the thickness of the wear-resistant coating on the rear surfaces of the 20 teeth be greater than on the front 18.

Further, it should be taken into account that in existing structures of end mills, as a rule, their teeth on one side have an exit to the end of the working part 14 with the formation of end teeth 22a, and on the other hand, together with chip grooves, extend onto the cylindrical part of the cutter shaft 12a. As a result, along the length of the working part of the cutter, the teeth also have non-uniform rigidity. Moreover, it increases in the direction from the end of the cutter to its shank.

In connection with this, in accordance with one of the preferred versions of the cutter, the end thickness of the wear-resistant coating is not uniform along the length of its cutting part. At the same time, depending on the specific technological problem being solved, the thickness of the wear-resistant coating, for example, may decrease from the end of the cutter to its shank, as shown in the fragments of sections shown in FIG. 9a and 9b. This allows you to compensate for the uneven rigidity of the teeth along the working part.

This design solution is particularly effective, for example, for cutters with a large working section length, made with a variable core section, which compensates for the console fixing of the cutter in the machine spindle. This ensures the greatest rigidity of the teeth of the cutter near its end, which allows you to work with increased feed per tooth, increasing productivity and durability of the cutters.

An uneven thickness of wear-resistant coatings on the surfaces of the working parts of end mills can be obtained, for example, in vacuum-arc spraying installations using the PVD method as follows. When applying a wear-resistant coating in these installations, as a rule, end mills are placed in the cassettes working up part. In this case, the cutters rotate with the cassettes and planetary movement in the volume of the vacuum chamber, rotating about its axis.

To obtain a non-uniform thickness of the coating on the surface of the teeth and the chip removal grooves in the radial direction, it is most preferable to arrange the plasma sources in the installation horizontally opposite the working parts of the end mills perpendicular to their axis. Moreover, to obtain the most preferred execution of the proposed cutter, the axes of the plasma sources must coincide with the ends of the working part of the cutters. At the same time, the most remote from the sources, but closer to the axis of rotation of the cutters, the surface areas of the working part of the cutters will have a smaller thickness of the wear-resistant coating, i.e. an increase in the thickness of the wear-resistant coating on the surface of the teeth in the radial direction from the axis of the mills to their cutting edges will be provided. In this case, wear-resistant coating will also have an uneven thickness along the length of the working part. Moreover, the coating thickness will decrease in the direction from the end of the working part.

When placing plasma sources above the working part of the cutters at an angle to their axis of rotation or the cutters themselves in the cassettes at an angle to the horizontally positioned electrodes, the thickness of the wear-resistant coating over the surfaces of the teeth and chip removal grooves will also be uneven, both in the radial direction relative to the axis of the cutters and direction along the axis of the cutters.

At the same time, by changing the angle of the sources and / or the mills themselves, a wear-resistant coating can be obtained with a corresponding gradient of its thickness, both in the radial direction and along the working part of the mills. The magnitude of the mutual angle of the axes of the cutters and plasma sources in the vacuum-arc installation is chosen depending on the geometrical dimensions and configuration of the working part of the cutters, as well as on the material of the wear-resistant coating, the material being processed and the cutting conditions.

In the process of milling, the working part of the end mills is subjected to considerable shock loads and periodically undergoes bending with torsion, being in a complex stress-strain state. At the same time, in the end mills of the proposed construction, due to the uneven distribution of the thickness of the wear-resistant coating having residual compressive stresses over the surfaces of the teeth and the chip removal grooves in the radial direction relative to the mill axis and along the mill axis, the stresses of equal resistance are equalized. This provides increased efficiency and durability of end mills.

Although the present invention has been described with a certain degree of detail, it should be understood that its various changes and modifications can be made without departing from the essence and scope of the invention set forth in the claims below.

Claims (10)

1. End milling cutter containing a working part located around the axis of rotation with cutting edges formed at the intersection of the front and rear surfaces and interleaved with chip removal grooves, while a wear resistant coating is applied to the working part consisting of at least one layer that has residual compressive stresses and contains a phase with at least one of the elements V, Cr, Nb, Ti, Ta, Zr, Hf, Al, Si, C, N, O, characterized in that the wear-resistant coating has an uneven thickness over the surface the working part, while the thickness of the wear-resistant coating on the front and rear surfaces in the cross section of the working part in the radial direction from the axis of rotation of the cutter to its cutting edges has a variable value in the range of 0.2 to 5.0 μm and increases in the direction from the axis of rotation of the cutter to cutting edges. 2. End milling cutter according to claim. 1, characterized in that its working part is made of hard alloy and removable. 3. End milling cutter according to claim 1 or 2, characterized in that the thickness of the wear-resistant coating is inversely proportional to the angle between the normal to the corresponding surface and the radius of the working part of the cutter passing through this surface and is directly proportional to the distance from the axis of rotation of the cutter to the said surface. 4. End milling cutter according to claim 1 or 2, characterized in that the wear-resistant coating contains a layer of superhard amorphous carbon. 5. End milling cutter according to claim 4, characterized in that the thickness of the layer of superhard amorphous carbon is in the range of 0.5-1.6 microns, and the residual compressive stresses in the wear-resistant coating are in the range of 4-10 GPa. 6. End milling cutter according to claim 1 or 2, characterized in that in the cross section of the working part of the cutter the thickness of the wear-resistant coating on the parts of the front and rear surfaces of the teeth that are equidistant from the cutter axis are located on circles equidistant to the cutters passing through the cutter most distant from the axis areas of cutting edges are not equal to each other. 7. End milling cutter according to claim 6, characterized in that the thickness of the wear-resistant coating on the rear surfaces is greater than on the front. 8. End milling cutter according to claim 1 or 2, characterized in that the wear-resistant coating is made multi-layer with a thickness in the range of 1.5-5 microns. 9. End milling cutter according to claim. 1, characterized in that the thickness of the wear-resistant coating along the length of the working part is uneven. 10. End milling cutter according to claim. 9, characterized in that the thickness of the wear-resistant coating along the length of the working part decreases from its end to the shank.

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