Ball End Mill

Abstract

To improve machinability to inhibit chip and wear of bottom blades.SOLUTION: A ball end mill 1 includes a cutting blade part 3 made of cBN at a tip side of a tool body rotatable around a center axis O. An apical surface 4 of the cutting blade part 3 includes: a pair of R blades 5 which is disposed facing each other at 180 degrees and formed into a substantially quarter arc shape; a pair of gash grooves 7, each gash groove being formed at a front side as seen in a rotation direction of the R blade 5 and forming a rake surface 8 of the R blade 5; and a chisel 18 connecting of center axis side end parts of the pair of R blades 5. The pair of R blades 5 is formed so as to be lowered from the center of a workpiece. The lowered amount from the center is set larger than 0% of a radius R of the R blade 5 and equivalent to or smaller than 6%. A diameter t of an inscribed circle of an extended flank surface 18a having the chisel 18 is set small in a range from 0.5% to 2.0%. An axial rake angle of the R blade 5 is set in a range from -10° to +15°.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a ball end mill having a tip surface of a tool body on which a plurality of generally arc-shaped end cutting edges are formed. [Background technology]

[0002] In the field of precision machining, ball end mills, for example, are generally used to cut dies, parts, etc. For example, in a ball end mill 100 shown in Fig. 10, two quarter-arc-shaped R blades 102 are formed on the tip surface of a tool body 101 and arranged 180 degrees apart. This ball end mill 100 is rotatable around a central axis O. A gash groove 103 that forms a cutting face 102a of the R blade 102 is formed on the front side of each R blade 102 in the rotational direction.

[0003] The two R blades 102 are formed with the center raised, and each extends from the outer peripheral surface side to the opposite side passing near the central axis O. The two R blades 102 intersect via a chisel 104 overlapping the central axis O. Moreover, each gash groove 103 is provided extending from the outer peripheral side along the R blade 102 in the direction of the central axis O to the opposite side beyond the central axis O in a plan view. Therefore, a pair of gash grooves 103 intersect with each other within a range of length k. Such a ball end mill is disclosed in, for example, Patent Document 1 and the like. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2000-117522 A Summary of the Invention [Problem to be solved by the invention]

[0005] When cutting a workpiece with this ball end mill 100, the cutting resistance increases in this area because the chisel 104 with a dull blade is provided near the central axis O. Moreover, in the conventional ball end mill 100, in order to prevent chipping of the chisel 104 and ensure the strength of the cutting edge, not only was the R blade 102 set to be center-up, but the width of the thick-walled part having the chisel 104, which is an extension of the flank of the opposing R blade 102, was made wider and the rake angle was set to be negative. However, even in this case, the low cutting speed causes an excessive load on the chisel 104, resulting in large cutting resistance, and the problem of heat generation and abnormal wear cannot be solved.

[0006] The present invention has been made in consideration of the above-mentioned situation, and aims to provide a ball end mill that improves the cutting performance of the bottom cutting edge and suppresses damage and wear of the bottom cutting edge and chisel or recess. [Means for solving the problem]

[0007] The ball end mill according to the present invention is a ball end mill having a cutting edge portion on the tip side of a tool body that can rotate around a central axis, and the tip surface of the cutting edge portion is formed in a substantially arc shape. Complex and a number of bottom blades, and a front side of the bottom blade in the direction of rotation Crossing each other formation It has been Between the plurality of gash grooves and the plurality of end cutting edges The gashes are connected to each other. A recess; a second flank formed on the rear side of the end cutting edges in the rotation direction, the flank angle of which changes as it moves rearward in the rotation direction. .

[0008] In addition, in a ball end mill having a recess on the tip surface of the tool body, it is preferable that the multiple gash grooves are arranged to intersect with each other and communicate with the recess, and the diameter (d) of the inscribed circle between the bottom cutting edges is set in the range of 1% to 3% of the radius R of the bottom cutting edges. Multiple gash grooves formed ahead of the multiple bottom blades in the direction of rotation intersect with each other within a range of 1% to 3% of the radius R, and a recess is formed in the center between the overlapping bottom blades. This makes it less likely for the recesses between the bottom blades to wear or break during cutting, resulting in high cutting performance.

[0009] In addition, a ball end mill having a chisel on the tip surface of the tool body may have a shape in which multiple gash grooves do not intersect with each other on the tip surface of the tool body, and the chisel may be formed between the bottom cutting edges. A chisel is provided between the bottom blades, and because the bottom blades are made of high hardness and are formed with a core-down shape, the bottom blades have high cutting ability and wear and damage to the chisel between the bottom blades can be reduced.

[0010] Moreover, it is preferable that the diameter (t) of the inscribed circle of the portion having the chisel is set in the range of 0.5% to 2.0% of the radius R of the end cutting edge. When cutting with the cutting edge, the part with the chisel is hard and thin, so even if it is pressed against the workpiece, wear and damage to the chisel can be reduced.

[0011] Moreover, the axial rake angle of the bottom cutting edge is preferably set in the range of -10° to +15°. The axial rake angle of the bottom cutting edge is formed on the square side in the range of -10° to +15°, which, combined with the center lowering, provides high cutting performance. Effect of the Invention

[0012] According to the ball end mill of the present invention, a cutting edge portion made of cBN, which is a high hardness material, is used, A chisel or recess is provided near the central axis between the bottom blades, and the amount of center depression of the bottom blade is formed to be greater than 0% and not more than 6% of the radius R of the bottom blade, which not only improves the cutting ability of the bottom blade but also provides excellent resistance to chipping and wear of the bottom blade and the chisel and recess between the bottom blades. [Brief description of the drawings]

[0013] [Figure 1] FIG. 2 is a tip end view showing a cutting edge portion of the ball end mill according to the first embodiment of the present invention. [Diagram 2] FIG. 2 is a side view of the ball end mill shown in FIG. [Diagram 3] FIG. 2 is a side view of a ball end mill showing the axial rake angle of the R blade. [Figure 4]FIG. 11 is a tip end view showing a cutting edge portion of a ball end mill according to a second embodiment. [Diagram 5] FIG. 5 is a side view of the ball end mill shown in FIG. [Figure 6] FIG. 2 is a side view of a ball end mill showing the axial rake angle of the R blade. [Figure 7] These show conventional examples, where (a) is a diagram of the flank near the center of the R blade before machining, (b) is a contour projection of the R blade before machining, (c) is a diagram of the flank near the center of the R blade after machining, and (d) is a contour projection of the R blade after machining. [Figure 8] FIG. 1 shows Example 1, where (a) is a diagram of the flank of the chisel before machining, (b) is a contour projection of the R blade before machining, (c) is a diagram of the flank of the chisel after machining, and (d) is a contour projection of the R blade after machining. [Figure 9] This shows Example 2, where (a) is a diagram of the flank near the center of the R blade before machining, (b) is a contour projection of the R blade before machining, (c) is a diagram of the flank near the center of the R blade after machining, and (d) is a contour projection of the R blade after machining. [Figure 10] FIG. 1 is a view showing a tip surface of a cutting edge portion of a conventional ball end mill. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Ball end mills according to the embodiments of the present invention will be described below with reference to the accompanying drawings. Figures 1 to 3 show a ball end mill 1 according to a first embodiment of the present invention. In Figures 1 and 2, the ball end mill 1 according to this embodiment includes a tool body 2 formed in a substantially cylindrical shape and rotated around a central axis O, and a cutting edge portion 3 formed at the tip of the tool body 2. At least the cutting edge portion 3 of the ball end mill 1 is formed of a cBN sintered compact made of a high hardness material. Alternatively, PCD may be used as the material for the cutting edge portion 3 of the ball end mill 1 instead of cBN. This ball end mill 1 is used for cutting hard materials such as machine parts and dies. In this specification, the side of the cutting edge 3 along the central axis O of the tool body 2 is referred to as the tip side or tip, and the opposite side connected to the spindle is referred to as the base side or base.

[0015] 1 and 2, the ball end mill 1 has a plurality of, for example, two R blades 5 formed at positions facing each other at 180 degrees as bottom blades having a substantially quarter-arc shape on the substantially hemispherical tip surface 4 of the cutting blade portion 3. When the outer diameter of the tool body 2 is D and the radius of the R blade 5 is R, 2R≧D is satisfied. Moreover, each R blade 5 is formed so as to be center-down. In the cutting edge portion 3, a gash groove 7 is formed on the front side in the rotation direction of each R blade 5. The gash surface formed in the gash groove 7 is made into a rake face 8 of the R blade 5, and the rake face 8 may be formed into any of a flat surface, a concave curved surface, and a convex curved surface. In this embodiment, the rake face 8 is, for example, a convex curved surface.

[0016] In Fig. 3, the rake angle α of the rake face 8 of the R blade 5 relative to the central axis O is set in the range of -10° to +15°. The rake angle α of the R blade 5 is set to an axial rake angle α. If the rake angle α of the R blade 5 is smaller than -10°, the cutting edge strength is high but the cutting performance is significantly reduced, and if it is larger than +15°, the cutting performance is high but the cutting edge strength is reduced. A second flank 9 and a third flank 10 having positive clearance angles are formed in sequence on the rear side of the R blade 5 in the rotation direction. The clearance angle of the second flank 9 is set to a positive angle of +10° to +25°. This clearance angle may be a constant angle, or may gradually increase or decrease from the R cutting edge 5 side toward the rear in the direction of rotation. The clearance angle of the third clearance face 10 is larger than the clearance angle of the second clearance face 9.

[0017] A peripheral blade 13 is formed on the base end side of the R blade 5. A flute groove 14 is formed on the front side in the rotation direction of the peripheral blade 13. A cutting face 15 of the peripheral blade 13 is formed on the flute groove 14. The peripheral blade 13 and the flute groove 14 have a helix angle that gradually twists spirally backward in the rotation direction from the tip side to the base end side. In a side view of the tool body 2, the R blade 5 and the peripheral blade 13 are twisted rearward in the direction of rotation from the tip end to the base end. The peripheral blade 13 has a twist angle twisted rearward at the same angle as or greater than that of the R blade 5. The gash groove 7 of the R blade 5 and the flute groove 14 of the peripheral blade 13 are also twisted rearward in the direction of rotation from the tip end to the base end, similar to the R blade 5 and the peripheral blade 13.

[0018] In the tip surface view of the cutting blade portion 3 shown in FIG. 1, a pair of R blades 5 are formed with the center lowered. The R blades 5 may be formed in a convex curved shape or a straight shape that curves and protrudes forward in the rotation direction. The end of each R blade 5 on the central axis O side extends to a position close to the central axis O, and these ends are connected to a thick extended flank 18a where the extended parts of the second flank 9 are connected to each other. A chisel 18 is formed in the center of this extended flank 18a, overlapping with the central axis O. The diameter (thickness) t of the inscribed circle of the extended flank 18a (part having the chisel 18) having the chisel 18 is set in the range of 0.5% to 2.0% of the radius R of the R blade 5. If the diameter t of the inscribed circle is smaller than 0.5%, it is significantly prone to chipping during cutting, and if it is larger than 2.0%, the cutting resistance increases, causing abnormal wear. The chisel 18 corresponds to a dead spot. The extended flank 18a of the chisel 18 overlaps with the central axis O, and the ridge between the rake face and the extended flank 18a serves as a cutting edge for cutting when the tool body 2 rotates. However, since the chisel 18 is in the vicinity of the central axis O, the cutting speed is low and cutting performance is poor.

[0019] Furthermore, the amount of center drop s, which is the distance between the pair of R blades 5, is set in the range of more than 0% to 6% of the radius R of the R blade 5. If the amount of center drop s is 0%, the R blade 5 cannot be set to center drop and the cutting performance of the R blade 5 decreases, and if it exceeds 6%, the cutting performance is high but the cutting edge strength decreases. Therefore, it is preferable to set the amount of center drop s of the pair of R blades 5 in the above range in order to ensure cutting performance and cutting edge strength. In order to ensure cutting balance by the pair of R blades 5, it is preferable that the distance from the center axis O of each of the amount of center drop s is s / 2.

[0020] In addition, the two gash grooves 7 formed on the front side of each of the pair of R blades 5 in the rotational direction do not intersect with each other, and a gap of the diameter t of the inscribed circle of the extended flank 18a of the chisel 18 is set. Since the cutting edge portion 3 made of cBN has high hardness, if the chisel 18 is present near the central axis O, it will generate large resistance and will be easily chipped. In this embodiment, the range of the diameter t of the inscribed circle of the extended flank 18a of the chisel 18 is narrowed to the above range, thereby improving cutting performance and suppressing wear.

[0021] The ball end mill 1 according to this embodiment has the above-mentioned configuration, and its cutting method will now be described. When the ball end mill 1 is rotated around the central axis O and the cutting blade 3 is fed vertically in the direction of the central axis O, the cutting resistance increases because the central chisel 18 cannot cut, and the extended flank 18a located on the tip surface 4 of the cutting blade 3 is worn. However, the diameter t of the inscribed circle of the extended flank 18a of the chisel 18 is small, ranging from 0.5% to 2.0% of the radius R, so the amount of wear on the extended flank 18a is small. The ball end mill 1 is then fed laterally to cut the vertical wall of the machining surface with the R blade 5. The lateral feed of the ball end mill 1 reduces the cutting resistance during cutting. The workpiece material in the portion of the chisel 18 that could not be cut is cut by the R blade 5.

[0022] Moreover, the R blade 5 of the cutting portion 3 is made of cBN and has high hardness, and in addition, the diameter t of the inscribed circle of the extended flank 18a having the chisel 18 is small, so that the cutting performance of the R blade 5 can be improved and wear and chipping of the extended flank 18a can be suppressed.

[0023] As described above, according to the ball end mill 1 of this embodiment, the cutting edge portion 3 is made of cBN and has high hardness, and the axial rake angle α of the pair of R blades 5 is inclined to the positive side, and the diameter t of the inscribed circle of the extended flank 18a portion of the chisel 18 sandwiched by the R blades 5 is small. Therefore, the cutting ability of the R blades 5 is high, and the wear resistance and chipping resistance of the R blades 5 and the chisel 18 portions are excellent.

[0024] Although the ball end mill 1 according to the embodiment of the present invention has been described above, it goes without saying that the present invention is not limited to such an embodiment, and various different forms and configurations can be adopted without departing from the spirit of the present invention. All of these are included in the technical scope of the present invention. Other embodiments and modifications of the present invention will be described below, and the same reference numerals will be used to describe parts and components that are the same as or similar to those of the above-described embodiments.

[0025] 4 to 6 show a ball end mill 20 according to a second embodiment of the present invention, which has a similar configuration to the ball end mill 1 according to the first embodiment. The ball end mill 20 has a plurality of, for example, two R blades 5 formed at positions facing each other at 180 degrees as bottom blades having a substantially quarter-arc shape on the tip surface 4 of the cutting portion 3. The outer diameter of the tool body 2 is D, and the radius of the R blade 5 is R, so that 2R≧D is satisfied. Moreover, each R blade 5 is formed so as to be center-down. In the cutting edge portion 3, a gash groove 7 is formed on the front side in the rotation direction of each R blade 5. The gash surface of the gash groove 7 serves as a rake face 8 of the R blade 5. The rake face 8 is, for example, a convex curved surface.

[0026] The axial rake angle α, which is the rake angle of the rake face 8 of the R blade 5 relative to the central axis O, is set in the range of -10° to +15°. If the rake angle α of the R blade 5 is smaller than -10°, the cutting edge strength is high but the cutting performance is significantly reduced, and if it is larger than +15°, the cutting performance is high but the cutting edge strength is reduced. A peripheral cutting edge 13 is formed on the base end side of the R cutting edge 5, and a flute groove 14 is formed on the front side of the peripheral cutting edge 13 in the rotational direction. A rake face 15 of the peripheral cutting edge 13 is formed on the flute groove 14. A second flank 9 and a third flank 10, each having a positive clearance angle, are formed in this order on the rear side of the R cutting edge 5 in the rotational direction. The clearance angle of the second flank 9 is set to a positive angle of +10° to +25°. The clearance angle of the second flank 9 is set to a constant angle or a variable clearance angle.

[0027] A recess 21 communicating with the gash groove 7 is formed in a region including the central axis O between the two opposing R blades 5. Although the recess 21 is formed in a substantially conical shape in Fig. 4 and Fig. 5, the shape of the recess 21 is arbitrary. Therefore, no chisel 18 or dead spot is formed in the region including the central axis O between the two R blades 5. In addition, on the tip surface 4 of the cutting blade portion 3, the gash grooves 7 formed on the front side of the rotation direction of the R blade 5 extend beyond the central axis O to the region on the opposite side in the radial direction. The two gash grooves 7 overlap and intersect with each other at the recesses 21 in the region of the central axis O. The diameter d of the inscribed circle (recesses 21) between the center side ends of the opposing R blades 5 shown in FIG. 4 is set in the range of 1% to 3% of the radius R of the R blade 5. If the diameter d of the inscribed circle between the R blades 5 on the central axis O side is smaller than 1%, there is a drawback in that chips adhere to each other and abnormal wear occurs. Also, if it is larger than 3%, the diameter of the recesses 21 during vertical wall machining by the cutting blade portion 3 becomes too large, and the diameter of the convex portion remaining without cutting increases, and the cutting load of the convex portion by the R blade 5 during lateral feeding increases, resulting in deterioration of the machined surface roughness. There are some drawbacks.

[0028] The ball end mill 20 according to this embodiment has the above-mentioned configuration, and its cutting method will now be described. For example, when performing contour rough cutting by cutting vertically and feeding horizontally while rotating the cutting blade portion 3 of the ball end mill 1 around the central axis O, the recessed portion 21 formed in the center of the two R blades 5 cannot cut during vertical feeding. This causes a convex portion to remain on the workpiece due to the recessed portion 21. Thereafter, by feeding the ball end mill 1 laterally, even if there is no blade in the recess 21 on the central axis O of the cutting portion 3, the remaining convex portion that could not be cut during cutting is cut by the R blade 5. Moreover, since the R blade 5 of the cutting portion 3 is made of cBN and has high hardness, and the diameter of the recess 21 is small, cutting performance can be improved and wear and chipping can be suppressed.

[0029] As described above, according to the ball end mill 20 of the second embodiment, the cutting edge portion 3 is made of cBN and has high hardness, and the axial rake angle of the pair of R blades 5 is inclined toward the positive side, so that the remaining cutting material in the recess 21 sandwiched between the R blades 5 can be cut by lateral feed. Therefore, the cutting ability of the R blade 5 is high, and wear and chipping can be suppressed at the R blade 5 and the recessed portion 21. Moreover, since there is no chisel 18 in the recessed portion 21 between the R blades 5, the cutting resistance can be further reduced.

[0030] Next, a cutting test for rough contour cutting was carried out for the ball end mill 1 according to the first embodiment and the ball end mill 20 according to the second embodiment described above. In each test example, the ball end mill 1 according to the first embodiment was used as Example 1, the ball end mill 20 according to the second embodiment was used as Example 2, and the conventional ball end mill 100 shown in Fig. 10 was used as the conventional example, and die cutting was carried out on a workpiece made of a high-hardness material. In each of the examples 1 and 2, the pair of R blades 5 are center-down, while in the conventional example, they are center-up. In the example 1, a chisel 18 with an inscribed circle diameter t is formed near the central axis O of the cutting portion 3, while in the example 2, a recess 21 is formed near the central axis O of the cutting portion 3. In the conventional example, a chisel 104 with a thickness greater than the chisel 18 is formed near the central axis O.

[0031] The cutting conditions were: rotation speed n = 120000 min-1, feed rate Vf = 1050 mm / min, ap (cutting depth in the Z-axis direction) = 0.005 mm, ae (cutting depth in the lateral direction) = 0.005 mm. Oil mist was used as the coolant. As comparative test results, contour projection photographs are shown showing the wear condition of the flank near the center of rotation of each ball end mill 1, 20, 100 and the amount of wear of the R blades 5, 102 before and after cutting the workpiece for 10 hours.

[0032] Contour rough cutting of the workpiece was carried out for 10 hours for Example 1, Example 2, and the conventional example. In Figures 7 to 9, (a) and (b) show a contour projection photograph of the R blade and the portion near the central axis O of the R blade before cutting. Figures 7 to 9 (c) and (d) show a contour projection photograph of the R blade and the portion near the central axis O of the R blade after 10 hours of cutting. In the contour projection photograph of the R blade after 10 hours of cutting, the black portion indicates the remaining contour of the R blade, and the gray portion indicates the worn portion of the R blade.

[0033] In the conventional example shown in Figures 7(a) and (b), compared to the flank of the chisel 104 and the R blade 102 before cutting, after cutting as shown in Figures 7(c) and (d), the flank of the chisel 104 has worn significantly and the cutting edge of the R blade 102 has also worn significantly. In contrast to this, in Example 1 shown in Figures 8(a) and (b), compared to the extended flank 18a of the chisel 18 and the R blade 5 before cutting, after cutting as shown in Figures 8(c) and (d), the extended flank 18a of the chisel 18 is slightly worn and the cutting edge of the R blade 5 is only slightly worn.

[0034] In Example 2 shown in Figures 9(a) and (b), compared to the recess 21 and R blade 5 before cutting, after cutting as shown in Figures 9(c) and (d), the second flank 9 of the R blade 5 on both ends of the recess 21 is slightly worn and the cutting edge of the R blade 5 is also only slightly worn. From these test results, compared to the results of the conventional example, in Examples 1 and 2, the wear at the center portions of the pair of R blades 5 was small, and the wear at the cutting edges of the R blades 5 was also small. Therefore, it was confirmed that Examples 1 and 2 could improve cutting performance and suppress wear and chipping.

[0035] In the ball end mills 1 and 20 according to the above-mentioned embodiments, a small relief may be provided on the second flank 9 side of the R blade 5. In this case, mirror finishing can be performed without causing chipping on the machined surface. Alternatively, a honed cutting edge may be provided instead of the small relief. In the ball end mills 1 and 20 according to the above-described embodiments, the number of R blades 5 (bottom blades) formed on the cutting edge portion 3 is not limited to two, and may be three or four or more. When three or more R blades 5 are provided, these multiple R blades 5 are arranged at equal pitches, but may also be arranged at unequal pitches. [Explanation of symbols]

[0036] 1, 20 Ball end mill 2 Tool body 3 Cutting edge 5 R blade 7 Gash groove 8. Scooping surface 9 Second relief face 13 Peripheral blade 14 Flute Groove 15 Scooping face 18 Chisel 21 Recess O center axis

Claims

1. A ball end mill having a cutting edge portion at the tip end of a tool body that can rotate around a central axis, A plurality of bottom blades formed in a substantially arcuate shape on a tip surface of the cutting blade portion; A plurality of gash grooves are formed so as to intersect with each other on the front side in the rotation direction of the bottom cutting edge; a recess formed between the plurality of bottom cutting edges and including the central axis line, the recess communicating with the plurality of gashes; a second flank formed on a rear side of the end cutting edges in a rotational direction, the flank angle of which changes as the flank angle moves rearward in the rotational direction; The diameter of an inscribed circle between the multiple bottom cutting edges centered on the central axis is set to be within the range of 1% to 3% of the radius R of each bottom cutting edge.

2. 2. The ball end mill according to claim 1, wherein each of the plurality of bottom cutting edges is set to be center-down, and the amount of center-down between the bottom cutting edges is greater than 0% and not greater than 6% of the radius R of each bottom cutting edge.

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