End mill

Abstract

To provide an end mill with improved R accuracy.SOLUTION: An end mill 1 includes a tool body 10 extending along an axial line O1 and a plurality of bottom blades 15 provided in a distal end portion of the tool body 10. The plurality of bottom blades 15 are arranged rotation symmetrically and intersect with the axial line O1. Intersection portions of the plurality of bottom blades 15 continue to be flush.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to an end mill. [Background technology]

[0002] 2. Description of the Related Art Conventionally, a ball end mill (end mill) having a plurality of ball blades (bottom blades) has been known (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 4448386 Summary of the Invention [Problem to be solved by the invention]

[0004] However, the ball end mill of Patent Document 1 has room for improvement in the R accuracy of the bottom cutting edge (the deviation of the actual shape of the bottom cutting edge from the designed shape of the bottom cutting edge) when manufacturing the ball end mill.

[0005] The present invention has been made in consideration of such problems, and has an object to provide an end mill with improved R accuracy (reduced deviation). [Means for solving the problem]

[0006] To solve the above problem. One aspect of the present invention is an end mill comprising a tool body extending along an axis and a plurality of bottom blades provided at the tip of the tool body, the plurality of bottom blades being arranged rotationally symmetrical about the axis and intersecting on the axis, with the intersecting portions of the plurality of bottom blades being flush with one another. The term "connected flush" as used herein means that the surface is connected flush with no steps or chisels (ridges). Therefore, no step or chisel is formed at the intersection of the multiple bottom blades due to overlapping clearance angles. This reduces the number of parts in the multiple bottom blades where the shape changes significantly locally, making it easier to process the multiple bottom blades when manufacturing them. This improves the R accuracy of the end mill. Effect of the Invention

[0007] According to the present invention, the R precision can be improved. [Brief description of the drawings]

[0008] [Figure 1] FIG. 2 is a side view of the tip side of the ball end mill according to the first embodiment of the present invention. [Diagram 2] FIG. 2 is a front view of a main part of the ball end mill. [Diagram 3] FIG. 3 is an enlarged view of part R1 in FIG. [Figure 4] 4 is a cross-sectional view taken along line A1-A1 in FIG. 3. [Diagram 5] 4 is a view seen in the direction of the arrow A2 in FIG. 3. [Figure 6] 4 is a cross-sectional view taken along line A4-A4 in FIG. 3. [Figure 7] FIG. 2 is a front view of a main part of a ball end mill according to a comparative example. [Figure 8] 8 is a cross-sectional view taken along line A6-A6 in FIG. 7. [Figure 9] 8 is a view taken in the direction of the arrow A7 in FIG. 7. [Figure 10] 1A and 1B are photographs showing the main parts of ball end mills of Examples and Comparative Examples before and after coating. [Figure 11] FIG. 13 is a diagram showing the measurement results of R accuracy of the ball end mill of the embodiment before coating. [Figure 12] FIG. 13 is a diagram showing the measurement results of R accuracy before coating of the ball end mill of the comparative example. [Figure 13] FIG. 13 is a diagram showing the measurement results of R accuracy after coating of the ball end mill of the embodiment. [Figure 14]FIG. 13 is a diagram showing the measurement results of R accuracy after coating of the ball end mill of the comparative example. [Figure 15] FIG. 4 is a front view of a main portion of a ball end mill according to a second embodiment of the present invention. [Figure 16] FIG. 16 is an enlarged view of part R3 in FIG. [Figure 17] FIG. 17 is a front view for explaining the shape of the flank in FIG. 16. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] (First embodiment) Hereinafter, the end mill according to the present invention will be described with reference to FIGS. 1 to 14, taking as an example a case where the end mill is a ball end mill. As shown in FIGS. 1 and 2, the ball end mill 1 of this embodiment includes a tool body 10 and two ball blades (bottom blades) 15. The tool body 10 is formed in a rod shape extending along an axis O1. The axis O1 is the central axis of the tool body 10. The tool body 10 is formed with two peripheral cutting edges 11 corresponding to the two ball cutting edges 15.

[0010] The two ball-shaped blades 15 are provided at an end (tip) of the tool body 10 in the direction of the axis O1. The two ball-shaped blades 15 are arranged around the axis O1 with a gap between them. It is preferable that the two ball-shaped blades 15 are arranged at equal angles around the axis O1. In other words, it is preferable that the two ball-shaped blades 15 are arranged rotationally symmetric (two-way rotational symmetry) with respect to the axis O1. 1, in this example, each bottom cutting edge 15 is quadrant-shaped in side view. The side view of the bottom cutting edge 15 means that the bottom cutting edge 15 is viewed in a direction perpendicular to the axis O1 and facing the rake face 16 or the flank face 17 of the bottom cutting edge 15. 2 and 3, the two ball-shaped blades 15 are connected to each other on the axis O1. In other words, the two ball-shaped blades 15 intersect on the axis O1.

[0011] Hereinafter, the circumferential direction of the tool body 10 is simply referred to as the circumferential direction. The direction perpendicular to the axis O1 is referred to as the radial direction. The side of the two ball-shaped blades 15 relative to the tool body 10 is referred to as the tip side, and the side of the tool body 10 relative to the two ball-shaped blades 15 is referred to as the base side. 1 and 2, two chip discharge grooves 18 are formed between the two ball-shaped cutting edges 15 in the circumferential direction. Each chip discharge groove 18 extends from the tip end side to the base end side, twisting in a spiral shape toward the rear side in the rotation direction of the ball end mill 1.

[0012] 4, the clearance angle α of the clearance faces 17 of the two ball cutting edges 15 is 0° on the axis O1. When the magnitude of the clearance angle α in this embodiment is defined as α°, it is preferably (α±0.3)° (degrees), including manufacturing errors. Generally, the clearance angle is set to a value of 0° or more in order to allow the ball-shaped cutting edge to escape from the workpiece. However, taking into account manufacturing errors, the clearance angle α in this embodiment may take a relatively small negative value.

[0013] In this embodiment, the clearance angle α is an angle of 0° or more. Therefore, at the portion (intersection 15a) where the two ball-shaped blades 15 are connected, no chisel (ridge line) is formed due to the overlap of the clearance angles α (clearance faces 17) of the two ball-shaped blades 15. In other words, the intersection 15a of the two ball-shaped blades 15 is flush with each other without any step or chisel. The clearance angle of the intersection portion 15a is substantially 0°. For example, substantially 0° means (0-0.3)° or more and (0+0.3)° or less. For example, the specification of the ball end mill 1 is "R3", that is, the radius of the two ball blades 15 is 3 mm. Fig. 5 is a side view of the main part of the ball-end mill 15. As shown in Fig. 5, in the ball end mill 1, there is no flat portion on the outer edge of the two ball-end milling blades 15, and the outer edge of each ball-end milling blade 15 is arc-shaped. Each ball-end milling blade 15 is connected to the peripheral blade 11.

[0014] Here, as shown in Fig. 1, the angle between the axis O1 and the normal line L1 to the outer edge of each ball-shaped blade 15 in a side view of the ball-shaped blade 15 is defined as a bottom blade central angle β. Hereinafter, one of the two ball-shaped blades 15 will be referred to as ball-shaped blade 15A, and the other will be referred to as ball-shaped blade 15B. Fig. 1 shows the bottom blade central angle β for the ball-shaped blade 15A. When the bottom cutting edge central angle β is in the range from 0° to less than the first angle β1, the clearance angle α of each of the ball-shaped cutting edges 15 is 0°. When the bottom cutting edge central angle β is in the range from the first angle β1, which is greater than 0°, to the second angle β2, which is greater than the first angle β1, the clearance angle α of each of the ball-shaped cutting edges 15 gradually increases from 0° to α2 (see FIG. 6). When the bottom cutting edge central angle β is greater than the second angle β2 and is equal to or less than 90°, the clearance angle α of each of the ball-shaped cutting edges 15 is constant and equal to the clearance angle α (α2) when the bottom cutting edge central angle β is the second angle β2.

[0015] That is, the clearance angle α from the intersection 15a of the two ball cutting edges 15 to the predetermined length portion 15b connected to the peripheral cutting edge 11 increases without decreasing toward the rear end (base end side) of the tool body 10. Here, "the clearance angle α from the intersection 15a to the predetermined length portion 15b increases without decreasing" means that, as the bottom cutting edge central angle β increases from the intersection 15a to the predetermined length portion 15b, "the clearance angle α does not become constant, but gradually increases," or "the clearance angle α gradually increases at least once, and the clearance angle α becomes constant at least once."

[0016] 3, the position of the outer edge of the ball-shaped blade 15A where the bottom blade central angle β is the first angle β1 is indicated by line L11. The position of the outer edge of the ball-shaped blade 15A where the bottom blade central angle β is the second angle β2 is indicated by line L12. Lines corresponding to lines L11 and L12 on the ball-shaped blade 15B are indicated by lines L13 and L14. The clearance angle α is 0° in the range surrounded by lines L11 and L13 on the clearance faces 17 of the two ball-shaped cutting edges 15. The clearance angle α gradually increases from 0° in the range surrounded by lines L11 and L12 on the clearance face 17 of the ball-shaped cutting edge 15A. Specifically, the clearance angle α is 0° on line L11 and α2 on line L12. For example, the first angle β1 is equal to or greater than 0.1° and equal to or less than 1°, the second angle β2 is 4°, and α2 is 18°. In the range of the clearance face 17 of the ball-shaped cutting edge 15A on the opposite side of the axis O1 from the line L12, the clearance angle α is constant at α2. In other words, the clearance angle α of each ball-shaped cutting edge 15 beyond the predetermined length portion 15b toward the base end side and reaching the peripheral cutting edge 11 is constant at α2. In addition, in the range on the side opposite the axis O1 from the line L12 on the clearance surface 17 of the ball cutting edge 15A (the range where the bottom cutting edge central angle β is greater than the second angle β2), the clearance angle α may gradually increase from α2 as the bottom cutting edge central angle β increases, may remain constant, or may gradually decrease from α2.

[0017] The area surrounded by lines L13 and L14 on the flank 17 of the ball blade 15B and the area on the opposite side of the axis O1 from line L14 are similar to the area surrounded by lines L11 and L12 on the flank 17 of the ball blade 15A and the area on the opposite side of the axis O1 from line L12, respectively. For example, in the cross section shown in FIG. 6 along cutting line A4-A4 between lines L11 and L12 in FIG. 3, the clearance angle α on the clearance face 17 of the ball-shaped cutting edge 15A is greater than 0° and less than α2.

[0018] [Production and measurement results of ball end mills of examples and comparative examples] 1. Specifications of Ball End Mills in Examples and Comparative Examples Here, a comparative ball end mill 2 shown in Figures 7 to 9 was examined in comparison with the ball end mill 1 (embodiment). In the ball end mill 2, the clearance angle α on the clearance face 17 of the two ball blades 15 is greater than 0° on the axis O1 for each configuration of the ball end mill 1. Therefore, a chisel 20 is formed at the portion where the two ball blades 15 are connected. As shown in FIG. 9, in the ball end mill 2, the outer edges of the two ball blades 15 have flat portions corresponding to the chisels 20. The specification of ball end mill 2 is also "R3".

[0019] The material of each of the ball end mills 1 and 2 was a cemented carbide alloy. A coating was applied to the two ball blades 15 of each of the ball end mills 1 and 2. A TiSiN-based material or a TiAlCrN-based material was used as the coating material, and the coating thickness was 1 μm or more and 10 μm or less. The condition for forming the coating was a single-layer or multi-layer hard coating.

[0020] [2. Ball end mill prototype results] FIG. 10 shows photographs of the main parts of the ball end mills 1 and 2 before and after coating. In the ball end mill 1 of the embodiment, no chisel was formed, and the coating did not peel off after coating. On the other hand, the comparative ball end mill 2 has a chisel 20. In the comparative ball end mill 2, in the portion where the chisel 20 is formed, stress is concentrated on the coating when the coating is formed, and the coating peels off at position P1.

[0021] [3. Ball end mill measurement results] The measurement results of the R accuracy of the ball end mills of the examples and the comparative example are shown in Fig. 11 to Fig. 14. In Fig. 11 to Fig. 14, the R accuracy was measured at the outer edge of the ball end mill 15 corresponding to a bottom cutting central angle β of -90° or more and 90° or less. When the bottom cutting central angle β was -90° or more and less than 0°, the R accuracy of the ball end mill 15A was measured, and when the bottom cutting central angle β was 0° or more and 90° or less, the R accuracy of the ball end mill 15B was measured. In the ball end mills 1 and 2 of the example and comparative example, the design radius of the two ball blades 15 is 3 mm. The tolerance of the two ball blades 15 is ±3 μm (micrometers) with respect to the true value V1.

[0022] First, let us consider the R accuracy of the ball end mills 1 and 2 before coating. It was found that the R accuracy of the ball end mill 1 of the embodiment shown in Fig. 11 was high at about ±1 μm. On the other hand, it was found that the R accuracy of the ball end mill 2 of the comparative example shown in Fig. 12 was low in the area where the bottom cutting edge central angle β was about -5° or more and 5° or less. Next, the R accuracy of the ball end mills 1, 2 after coating will be considered. It was found that the R accuracy of the ball end mill 1 of the embodiment shown in FIG. 13 maintains the R accuracy of the ball end mill 1 of the embodiment before coating. In other words, the R accuracy at the intersection 15a of each ball blade 15 is substantially the same before and after coating. Here, "the R accuracy is substantially the same before and after coating" means, for example, that "the ratio of the R accuracy after coating to the R accuracy before coating is 0.95 or more and 1.05 or less." It was found that the R accuracy of the comparative ball end mill 2 shown in FIG. 14 was lower than the R accuracy of the comparative ball end mill 2 before coating because the coating peeled off in the portion where the chisel 20 was formed.

[0023] When manufacturing the ball end mill 1, the clearance angle α is formed from the portions of the two ball-shaped cutting edges 15 on the axis O1 by, for example, a known grinding machine. Then, the radially outer portions of the two ball-shaped cutting edges 15 are manufactured. The ball end mill 1 is used to cut a workpiece into a predetermined shape.

[0024] As described above, in the ball end mill 1 of this embodiment, two ball blades 15 are provided at the tip of the tool body 10. The two ball blades 15 are arranged rotationally symmetrically with respect to the axis O1 and intersect on the axis O1, and the intersection portion 15a of the two ball blades 15 is flush with each other. Therefore, at the intersection portion 15a where the two ball blades 15 intersect, a chisel is not formed due to the intersection of the clearance angles α of the two ball blades 15. This reduces the portion of the two ball blades 15 where the shape changes significantly locally, making it easier to process the two ball blades 15 when manufacturing them. Therefore, the R precision of the ball end mill 1 can be improved. When a coating is applied to the ball end mill 1, peeling of the coating can be suppressed.

[0025] The clearance angle α of the intersection portion 15a is substantially 0°, which makes it possible to more reliably improve the R precision of the ball end mill 1 at the intersection portion 15a. The clearance angle α from the intersection 15a to the predetermined length portion 15b increases without decreasing toward the rear end of the tool body 10. As a result, when the clearance angle α is set to be larger than 0° on the ball-shaped blade 15 radially outside the predetermined length portion 15b, the number of portions in the two ball-shaped blades 15 that are significantly locally changed in shape is reduced, compared to when the clearance angle α from the intersection 15a to the predetermined length portion 15b is smaller, for example. This makes it easier to manufacture the two ball-shaped blades 15, and further improves the R precision of the ball end mill 1.

[0026] The clearance angle α of each ball-shaped cutting edge 15 beyond the predetermined length portion 15b toward the base end side and reaching the peripheral cutting edge 11 is a constant value of α2. Therefore, a stable clearance angle α of a constant magnitude larger than 0° can be formed in the two ball-shaped cutting edges 15. The R precision of the intersection portion 15a of each ball-shaped blade 15 is substantially the same before and after coating, and therefore the R precision of the intersection portion 15a after coating can be improved.

[0027] Second embodiment Next, a second embodiment of the present invention will be described with reference to Figs. 15 to 17. The same components as those in the above embodiment are given the same reference numerals, and the description thereof will be omitted. Only the differences will be described. As shown in FIGS. 15 and 16, the ball end mill 4 of this embodiment includes a tool body 10 (not shown) and four ball blades (bottom blades) 25. The four ball-shaped blades 25 are provided at an end of the tool body 10 in the direction of the axis O1. The four ball-shaped blades 25 are arranged around the axis O1 at intervals. Hereinafter, the four ball-shaped blades 25 are also referred to as ball-shaped blades 25A, 25B, 25C, and 25D in the counterclockwise direction.

[0028] 16, the position of the outer edge of the ball-shaped blade 25A where the bottom blade central angle β is 0° is indicated by line L16. The position of the outer edge of the ball-shaped blade 25A where the bottom blade central angle β is the first angle β1 is indicated by line L17, and the position of the outer edge of the ball-shaped blade 25A where the bottom blade central angle β is the second angle β2 is indicated by line L18. Next, the clearance angle α of the ball cutting edge 25A will be described. In the range from line L16 to line L17, where the bottom cutting edge central angle β is in the range from 0° to less than the first angle β1, the clearance angle α of the ball-shaped cutting edge 25A is 0°. In the range from line L17 to line L18, where the bottom cutting edge central angle β is in the range from the first angle β1 to the second angle β2, the clearance angle α of the ball-shaped cutting edge 25A gradually increases from 0° to α2. In the range on the opposite side of the axis O1 from line L18, where the bottom cutting edge central angle β is in the range from greater than the second angle β2 to 90° or less, the clearance angle α of the ball-shaped cutting edge 25A is constant at α2.

[0029] For example, the first angle β1 is equal to or greater than 0.1° and equal to or less than 1°, the second angle β2 is 1.5°, and α2 is 6°. The clearance angles α of the ball-shaped blades 25B, 25C, and 25D are similar to the clearance angle α of the ball-shaped blade 25A.

[0030] Fig. 17 shows the shapes of the flanks 27 of the ball-shaped blades 25A, 25B, 25C, and 25D. In Fig. 17, the flanks 27 of the ball-shaped blades 25A, 25B, 25C, and 25D are hatched differently. The flanks 27 of the ball-shaped blades 25A, 25B, 25C, and 25D are each a spherically curved surface. No chisel is formed between adjacent flanks 27 of the ball-shaped blades 25A, 25B, 25C, and 25D, and adjacent flanks 27 are smoothly connected to each other.

[0031] As described above, the ball end mill 4 of this embodiment can improve the R precision.

[0032] Although the first and second embodiments of the present invention have been described above in detail with reference to the drawings, the specific configurations are not limited to these embodiments, and the present invention also includes modifications, combinations, deletions, etc. of the configurations within the scope of the gist of the present invention. Furthermore, it goes without saying that the configurations shown in each embodiment can be used in appropriate combinations. For example, in the first and second embodiments, the clearance angle α from the intersection portion 15a to the predetermined length portion 15b may gradually increase toward the rear end portion of the tool body 10. The clearance angle α of each ball cutting edge 15 that extends beyond the predetermined length portion 15b toward the base end side and reaches the peripheral cutting edge 11 may gradually increase toward the rear end portion of the tool body 10.

[0033] The number of ball blades 15, 25 provided on the ball end mills 1, 4 is not limited as long as it is plural, and may be three, five or more. Although the end mills are described as being ball end mills 1 and 4, the end mill is not limited to this and may be a barrel end mill or the like. [Explanation of symbols]

[0034] 1,4 Ball end mill (end mill) 10 Tool body 15,25 Ball head (bottom blade) 15a Intersection 15b Predetermined length section L1 normal O1 axis α Clearance angle β Bottom edge center angle β1 1st angle β2 2nd angle

Claims

1. A tool body extending along an axis; A plurality of bottom cutting edges provided at a tip portion of the tool body; Equipped with the end cutting edges are arranged rotationally symmetrically with respect to the axis and intersect with each other on the axis, The end mill has crossing portions of the plurality of bottom cutting edges that are flush with each other.

2. The clearance angle of the intersection is substantially 0°. The end mill according to claim 1 .

3. The tool body is formed with a peripheral cutting edge, A clearance angle from the intersection of the bottom cutting edges to a predetermined length portion connected to the peripheral cutting edge increases toward the rear end of the tool body without decreasing. The end mill according to claim 2 .

4. The clearance angle of each of the bottom cutting edges extending beyond the predetermined length portion and reaching the peripheral cutting edge is a constant value. The end mill according to claim 3.

5. The plurality of end blades are a plurality of ball blades, Each of the ball-shaped blades is coated with a TiSiN-based material or a TiAlCrN-based material, The R precision at the intersection of each of the ball-shaped blades is substantially the same before and after the coating. An end mill according to any one of claims 1 to 4.

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