JP2021104573A - Ball end mill - Google Patents

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

The present invention relates to a ball end mill in which a plurality of substantially arcuate bottom blades are formed on the tip surface of a tool body.

Generally, in the field of precision machining, for example, a ball end mill is used for cutting a mold, a part, or the like. For example, in the ball end mill 100 shown in FIG. 10, two 1/4 arc-shaped R blades 102 are formed so as to face the tip surface of the tool body 101 180 degrees. The ball end mill 100 is rotatable around the central axis O. A gash groove 103 forming a rake face 102a of the R blade 102 is formed on the front side of each R blade 102 in the rotation direction.

The two R blades 102 are formed so as to be centered, and each extends from the outer peripheral surface side to the opposite side through the vicinity of the central axis O. The two R blades 102 intersect via a chisel 104 that overlaps the central axis O. Moreover, each gash groove 103 is provided along the R blade 102 in a plan view from the outer peripheral side toward the central axis O and extends to the opposite side beyond the central axis O. Therefore, the pair of gosh grooves 103 intersect each other within a range of length k. Such a ball end mill is also disclosed in, for example, Patent Document 1.

Japanese Unexamined Patent Publication No. 2000-117522

When cutting the work material with the ball end mill 100, a chisel 104 having an inseparable blade is provided near the central axis O, so that the cutting resistance at this portion increases. Moreover, in the conventional ball end mill 100, in order to prevent the chisel 104 from being damaged and secure the cutting edge strength, not only the R blade 102 is set to be raised, but also the flank surface of the opposing R blade 102 is extended. The width of the thick part with the blade was increased, and the rake angle was set to the negative.
However, even in this case, since the cutting speed is low, the load applied to the chisel 104 is excessive and the cutting resistance is large, and the problem of causing heat generation and abnormal wear cannot be improved.

The present invention has been made in view of such circumstances, and an object of the present invention is to provide a ball end mill capable of improving the machinability of the bottom blade and suppressing chipping and wear of the bottom blade and the chisel or recess. do.

The ball end mill according to the present invention is a ball end mill provided with a cBN or PCD cutting edge portion on the tip end side of a tool body that can rotate around the central axis, and is formed in a substantially arc shape on the tip surface of the cutting edge portion. It is provided between a plurality of bottom blades set to lower the center, a plurality of gash grooves formed on the front side in the rotation direction of the bottom blade and forming a rake face of the bottom blade, and a plurality of bottom blades. It is characterized in that it is provided with a chisel or a recess including a central axis, and the amount of center drop between the bottom blades is set to 6% or less, which is larger than 0% of the radius R of the bottom blades.
The ball end mill according to the present invention has a high hardness and an arcuate bottom blade because the cutting edge is made of cBN or PCD when cutting with a substantially arcuate bottom blade including a chisel or recess near the central axis. Is formed so as to have a center drop of 6% or less, which is larger than 0% of the radius R, so that the machinability of the bottom blade is high and the wear and loss of the bottom blade and the chisel or the recess can be reduced.

Further, in a ball end mill having a recess on the tip surface of the tool body, a plurality of gash grooves are arranged so as to intersect each other and communicate with the recess, and the diameter (d) of the inscribed circle between the bottom blades is the radius of the bottom blade. It is preferably set in the range of 1% to 3% of R.
A plurality of gosh grooves formed forward in the rotation direction of the plurality of bottom blades intersect each other within a range of 1% to 3% of the radius R, and a recess is formed in the center between the bottom blades overlapping the same, so that the bottom is formed during cutting. The recesses between the blades are less likely to cause wear and chipping, and have high machinability.

Further, the ball end mill having a chisel on the tip surface of the tool body may have a shape in which a plurality of gash grooves do not intersect each other on the tip surface of the tool body, and a chisel may be formed between the bottom blades.
Although the chisel is provided between the bottom blades, since the bottom blade is formed to have a high hardness and a lower core, the machinability of the bottom blade is high and the wear and chipping of the chisel between the bottom blades can be reduced.

Further, 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 bottom blade.
When cutting with the cutting edge portion, the portion having the chisel has high hardness and a small thickness, so that the wear and chipping of the chisel can be reduced even when pressed by the work material.

Further, the axial rake angle of the bottom blade is preferably set in the range of −10 ° to + 15 °.
Since the axial rake angle of the bottom blade is formed on the conformal side in the range of -10 ° to + 15 °, the machinability is high in combination with the center drop.

According to the ball end mill according to the present invention, a cutting edge portion made of cBN made of a high hardness material is used, a chisel or a recess is provided near the central axis between the bottom blades, and the amount of centering of the bottom blade is determined by the radius of the bottom blade. Since it is formed to be larger than 0% and 6% or less of R, the machinability of the bottom blade can be improved, and the chisel and recess between the bottom blade and the bottom blade are excellent in chipping resistance and abrasion resistance.

It is a front end view which shows the cutting edge part of the ball end mill by 1st Embodiment of this invention. It is a side view of the ball end mill shown in FIG. It is a side view of the ball end mill which shows the axial rake angle of an R blade. It is a front end view which shows the cutting edge part of the ball end mill by 2nd Embodiment. It is a side view of the ball end mill shown in FIG. It is a side view of the ball end mill which shows the axial rake angle of an R blade. In the conventional example, (a) is a view of the flank surface near the center of the R blade before machining, (b) is a contour projection drawing of the R blade before machining, and (c) is the center of the R blade after machining. The figure of the flank surface in the vicinity, (d) is the contour projection view of the R blade after processing. Example 1 is shown, where (a) is a view of the flank surface of the chisel before machining, (b) is a contour projection view of the R blade before machining, and (c) is a view of the flank surface of the chisel after machining. (D) is a contour projection drawing of the R blade after processing. Example 2 is shown, where (a) is a view of a flank near the center of the R blade before machining, (b) is a contour projection drawing of the R blade before machining, and (c) is a view of the R blade after machining. The figure of the flank surface near the center, (d) is the contour projection view of the R blade after processing. It is a front view of the cutting edge portion of a conventional ball end mill.

Hereinafter, the ball end mill according to each embodiment of the present invention will be described with reference to the accompanying drawings.
1 to 3 show a ball end mill 1 according to the first embodiment of the present invention. In FIGS. 1 and 2, the ball end mill 1 according to the present embodiment includes a tool body 2 formed in a substantially columnar shape and rotated about a central axis O, and a cutting edge portion 3 formed at the tip thereof. , Is equipped. At least the cutting edge portion 3 of the ball end mill 1 is formed of a cBN sintered body made of a high hardness material. Alternatively, PCD may be used instead of cBN as the material of the cutting edge portion 3 of the ball end mill 1.
This ball end mill 1 is used for cutting high-hardness materials such as machine parts and dies. In the present specification, the cutting edge portion 3 side along the central axis O of the tool body 2 is referred to as the tip side and the tip, and the opposite side connected to the spindle is referred to as the proximal end side and the proximal end.

In FIGS. 1 and 2, a plurality of ball end mills 1 have a substantially hemispherical tip surface 4 of a cutting edge portion 3 and a plurality of substantially 1/4 arcuate bottom blades, for example, two R blades 5 facing each other by 180 degrees. It is formed at the position. When the outer diameter of the tool body 2 is D, the radius of the R blade 5 is set to R and 2R ≧ D. Moreover, each R blade 5 is formed so as to be centered.
In the cutting edge portion 3, a gash groove 7 is formed on the front side of each R blade 5 in the rotation direction. The gash surface formed in the gash groove 7 is a rake surface 8 of the R blade 5, and the rake surface 8 may be formed on any of a flat surface, a concave curved surface, and a convex curved surface. In the present embodiment, the rake face 8 is, for example, a convex curved surface.

In FIG. 3, the rake angle α of the rake face 8 of the R blade 5 with respect 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 the axial rake angle α. When the rake angle α of the R blade 5 is smaller than −10 °, the cutting edge strength is high but the machinability is remarkably lowered, and when it is larger than + 15 °, the machinability is high but the cutting edge strength is lowered.
On the rear side of the R blade 5 in the rotation direction, a second flank surface 9 and a third flank surface 10 having a positive flank angle are sequentially formed as flanks. The clearance angle of the second flank surface 9 is set to a conformal angle of + 10 ° to + 25 °. The clearance angle may be a constant angle, or may be changed so as to gradually increase or decrease from the R blade 5 side toward the rear in the rotation direction. The flank angle of the third flank surface 10 has a flank angle larger than the flank angle of the second flank surface 9.

An outer 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 of the outer peripheral blade 13 in the rotation direction. A rake face 15 of the outer peripheral blade 13 is formed in the flute groove 14. The outer peripheral blade 13 and the flute groove 14 have a helix angle so as to be spirally twisted to the rear side in the rotational direction from the tip end side to the base end side.
When viewed from the side of the tool body 2, the R blade 5 and the outer peripheral blade 13 are twisted from the tip end side toward the base end side toward the rear side in the rotational direction. The outer peripheral blade 13 has a helix angle twisted rearward at an angle equal to or greater than that of the R blade 5. Like the R blade 5 and the outer peripheral blade 13, the gash groove 7 of the R blade 5 and the flute groove 14 of the outer peripheral blade 13 are also twisted to the rear side in the rotational direction from the tip end side toward the base end side.

In the front end view of the cutting edge portion 3 shown in FIG. 1, the pair of R blades 5 are formed so as to be centered. The R blade 5 may be formed in a convex curve shape or a straight line shape that curves forward in the rotation direction and protrudes. 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 thick extension flanks 18a to which the extension portions of the second flank 9 are connected to each other. It is connected to the. A chisel 18 that overlaps the central axis O is formed in the center of the extension flank surface 18a. The diameter (thickness) t of the inscribed circle of the extension flank surface 18a (the portion 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 likely to be significantly damaged during cutting, and if it is larger than 2.0%, the cutting resistance increases and causes abnormal wear.
The chisel 18 corresponds to a dead spot. The chisel 18 has an extension flank surface 18a that overlaps the central axis O, and can be cut when the tool body 2 is rotated using the ridgeline between the rake face and the extension flank surface 18a as a cutting edge, but is in the vicinity of the center axis O. Therefore, the cutting speed is low and the machinability is poor.

Further, the core lowering amount s, which is the distance between the pair of R blades 5, is set in a range larger than 0% of the radius R of the R blades 5 and 6% or less. If the center lowering amount s is 0%, the center lowering cannot be set and the machinability of the R blade 5 is lowered, and if it exceeds 6%, the machinability is high but the cutting edge strength is lowered. Therefore, it is preferable to set the center lowering amount s of the pair of R blades 5 in the above range in order to secure machinability and cutting edge strength. The centering amount s is preferably s / 2 at a distance from the central axis O in order to secure the cutting balance between the pair of R blades 5.

Further, the two gash grooves 7 formed on the front side of the pair of R blades 5 in the rotation direction do not intersect with each other, and a gap corresponding to the diameter t of the inscribed circle of the extension flank surface 18a of the chisel 18 is set. There is. Since the cutting edge portion 3 made of cBN has a high hardness, if the chisel 18 is present in the vicinity of the central axis O, it becomes a large resistance and easily chipped. In the present embodiment, the range of the diameter t of the inscribed circle of the extension flank surface 18a of the chisel 18 is reduced to the above range to improve machinability and suppress wear.

The ball end mill 1 according to the present embodiment has the above-described configuration, and the cutting method thereof will be described next.
When the ball end mill 1 is rotated around the central axis O and the cutting edge portion 3 is vertically fed in the central axis O direction, the cutting resistance increases because the central chisel 18 cannot cut, and the tip surface 4 of the cutting edge portion 3 increases. The extension flank 18a located at is worn. However, since the diameter t of the inscribed circle of the extension flank surface 18a of the chisel 18 is as small as 0.5% to 2.0% of the radius R, the amount of wear of the extension flank surface 18a is small. After that, by laterally feeding the ball end mill 1, the standing wall of the machined surface is cut by the R blade 5. By the lateral feed of the ball end mill 1, the work material of the part of the chisel 18 that could not be cut at the time of cutting is cut by the R blade 5.

Moreover, since the R blade 5 of the cutting edge portion 3 is made of cBN and has a high hardness and the diameter t of the inscribed circle of the extension flank surface 18a having the chisel 18 is small, the machinability by the R blade 5 can be improved and extended. Wear and chipping of the flank 18a can be suppressed.

As described above, according to the ball end mill 1 according to the present 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. The diameter t of the inscribed circle of the extended flank surface 18a portion of the chisel 18 sandwiched between 5 is formed to be small. Therefore, the machinability by the R blade 5 is high, and the wear resistance and the chipping resistance at the parts of the R blade 5 and the chisel 18 are excellent.

Although the ball end mill 1 according to the embodiment of the present invention has been described above, the present invention is not limited to such an embodiment, and various different forms and modes can be adopted without departing from the spirit of the present invention. Needless to say. All of these are within the technical scope of the present invention.
Other embodiments and modifications of the present invention will be described below, but the same or similar parts and parts of the above-described embodiments will be described using the same reference numerals.

4 to 6 show the ball end mill 20 according to the second embodiment of the present invention, and have the same configuration as the ball end mill 1 according to the first embodiment. A plurality of ball end mills 20 are formed on the tip surface 4 of the cutting edge portion 3 as substantially 1/4 arcuate bottom blades, for example, at positions where two R blades 5 face each other by 180 degrees. The outer diameter of the tool body 2 is D, and the radius of the R blade 5 is R, and 2R ≧ D is set. Moreover, each R blade 5 is formed so as to be centered.
In the cutting edge portion 3, a gash groove 7 is formed on the front side of each R blade 5 in the rotation direction. The gash surface of the gash groove 7 is the rake surface 8 of the R blade 5. The rake face 8 is, for example, a convex curved surface.

The axial rake angle α, which is the rake angle of the rake face 8 of the R blade 5 with respect to the central axis O, is set in the range of −10 ° to + 15 °. When the rake angle α of the R blade 5 is smaller than −10 °, the cutting edge strength is high but the machinability is remarkably lowered, and when it is larger than + 15 °, the machinability is high but the cutting edge strength is lowered.
An outer peripheral blade 13 is formed on the base end side of the R blade 5, and a flute groove 14 is formed on the front side in the rotation direction of the outer peripheral blade 13. A rake face 15 of the outer peripheral blade 13 is formed in the flute groove 14. On the rear side of the R blade 5 in the rotation direction, a second flank surface 9 and a third flank surface 10 having a positive flank angle are sequentially formed as flanks. The clearance angle of the second flank surface 9 is set to a conformal angle of + 10 ° to + 25 °. The clearance angle of the second flank surface 9 is set to a constant angle or a variable clearance angle.

A recess 21 communicating with the gash groove 7 is formed between two R blades 5 facing each other in a region including the central axis O. The recess 21 is formed in a substantially conical shape in FIGS. 4 and 5, but the shape of the recess 21 is arbitrary. Therefore, the chisel 18 and the dead spot are not formed in the region including the central axis O between the two R blades 5.
Further, on the tip surface 4 of the cutting edge portion 3, the gash grooves 7 formed on the front side in the rotation direction of the R blade 5 extend beyond the central axis O to a region on the opposite side in the radial direction. The two gosh grooves 7 overlap each other at the recess 21 in the region of the central axis O. The diameter d of the inscribed circle (recess 21) between the central end portions 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 that chips adhere to each other and abnormal wear occurs. If it is larger than 3%, the diameter of the concave portion 21 during vertical wall machining by the cutting edge portion 3 becomes too large, and the diameter of the convex portion remaining by non-cutting increases, and the convex portion is cut by the R blade 5 when laterally fed. There is a drawback that the load increases and the roughness of the machined surface deteriorates.

The ball end mill 20 according to the present embodiment has the above-described configuration, and the cutting method thereof will be described next.
For example, when the contour line roughing process of cutting the cutting edge portion 3 of the ball end mill 1 in the vertical direction while rotating it around the central axis O and feeding it horizontally is performed, it is formed at the center of the two R blades 5 during vertical feeding. Cannot cut in the recess 21. Then, the work material has a convex portion remaining after cutting due to the concave portion 21.
After that, by laterally feeding the ball end mill 1, even if there is no blade in the concave portion 21 of the central axis O portion of the cutting edge portion 3, the remaining convex portion that could not be cut at the time of cutting is cut by the R blade 5. .. Moreover, since the R blade 5 of the cutting edge portion 3 is made of cBN and has high hardness and the diameter of the recess 21 is small, machinability can be improved and wear and chipping can be suppressed.

As described above, according to the ball end mill 20 according to 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 to the positive side. The uncut portion of the recess 21 sandwiched between the blades 5 can be machined by lateral feed.
Therefore, the machinability of the R blade 5 is high, and wear and chipping at the portions of the R blade 5 and the recess 21 can be suppressed. Moreover, since there is no chisel 18 in the recess 21 between the R blades 5, the cutting resistance can be further reduced.

Next, a cutting test for contour roughing was performed on 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 of the first embodiment is set to Example 1, the ball end mill 20 of the second embodiment is set to Example 2, and the conventional ball end mill 100 shown in FIG. 10 is used as a conventional example from a high hardness material. The work material was machined.
In the first and second embodiments, the pair of R blades 5 are centered down, and the conventional example is centered up. In the first embodiment, there is a chisel 18 having an inscribed circle diameter t near the central axis O of the cutting edge portion 3, and in the second embodiment, a recess 21 is formed near the central axis O of the cutting edge portion 3. In the conventional example, a chisel 104 having a thickness larger than that of the chisel 18 is formed near the central axis O.

The cutting conditions were such that the rotation speed n was 120,000 ^min-1 , the feed speed Vf was 1050 mm / min, the ap (cut amount in the Z-axis direction) was 0.005 mm, and the ae (cut amount in the lateral direction) was 0.005 mm. Oil mist was used as the coolant.
Then, as a result of the comparative test, the wear state of the flanks near the rotation centers of the ball end mills 1, 20 and 100 before and after cutting in which the work material was cut for 10 hours, and the wear amount of the R blades 5 and 102 were determined. The contour projection photograph shown is shown.

Contour roughing of the work material was performed for 10 hours for Example 1, Example 2, and Conventional Example. 7 to 9 show the portions (a) and (b) in the vicinity of the central axis O of the R blade before processing and the contour projection photograph of the R blade. 7 to 9 (c) and 9 (d) show contour projection photographs of the vicinity of the central axis O of the R blade and the R blade after cutting for 10 hours. In the contour projection photograph of the R blade after processing for 10 hours, the black portion shows the contour of the R blade, and the gray portion shows the worn portion of the R blade.

In FIGS. 7 (a) and 7 (b), in the conventional example, the clearance surface of the chisel 104 and the R blade 102 before the cutting process are opposed to the relief surface of the chisel 104 after the cutting process shown in FIGS. The surface was greatly worn, and the cutting edge of the R blade 102 was also greatly worn.
On the other hand, in the first embodiment shown in FIGS. 8 (a) and 8 (b), the extended flank surface 18a and the R blade 5 of the chisel 18 before cutting are cut according to the drawings (c) and (d). After processing, the extension flank surface 18a of the chisel 18 was slightly worn, and the cutting edge of the R blade 5 was only slightly worn.

In Example 2 shown in FIGS. 9 (a) and 9 (b), the recesses 21 and the R blade 5 before cutting are opposed to the R on both ends of the recesses 21 after cutting shown in FIGS. 9 (c) and 9 (d). The second flank 9 of the blade 5 is slightly worn, and the cutting edge of the R blade 5 is also slightly worn.
From these test results, the wear of the central portion of the pair of R blades 5 was smaller and the wear of the cutting edge of the R blades 5 was smaller than the results of the conventional example in Examples 1 and 2. Therefore, it was confirmed that in Examples 1 and 2, the machinability could be improved and wear and chipping could be suppressed.

Further, in the ball end mills 1 and 20 according to the above-described embodiments, a small relief may be provided on the second flank surface 9 side of the R blade 5. In this case, mirror surface processing can be performed without causing chipping on the processed surface. Alternatively, a cutting edge honing 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 arranged, these plurality of R blades 5 are arranged at equal pitches, but they may be arranged at unequal pitches.

1, 20 Ball end mill 2 Tool body 3 Cutting edge 5 R blade 7 Gash groove 8 Scoop surface 9 Second flank surface 13 Outer blade 14 Flute groove 15 Scoop surface 18 Chisel 21 Recess O Central axis

Claims (5)

In a ball end mill equipped with a cBN or PCD cutting edge on the tip side of a tool body that can rotate around the central axis.
A plurality of bottom blades formed in a substantially arc shape on the tip surface of the cutting edge portion and set to lower the center,
A plurality of gash grooves formed on the front side in the rotation direction of the bottom blade and forming a rake face of the bottom blade,
A chisel or recess provided between the plurality of bottom blades and including the central axis,
The ball end mill is characterized in that the amount of center drop between the bottom blades is set to 6% or less, which is larger than 0% of the radius R of the bottom blades. On the tip surface of the tool body, the plurality of gash grooves are arranged so as to intersect each other and communicate with the recess, and the diameter of the inscribed circle between the bottom blades is 1% to 3% of the radius R of the bottom blades. The ball end mill according to claim 1, which is set in the range of%. The ball end mill according to claim 1, wherein the plurality of gash grooves do not intersect each other on the tip surface of the tool body, and the chisel is formed between the bottom blades. The ball end mill according to claim 1 or 3, wherein the diameter 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 bottom blade. The ball end mill according to any one of claims 1 to 4, wherein the axial rake angle of the bottom blade is set in the range of −10 ° to + 15 °.

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