JP7419060B2 - ball end mill - Google Patents

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, ball end mills, for example, are used to cut molds, parts, and the like. For example, in the ball end mill 100 shown in FIG. 10, two 1/4 arc-shaped R blades 102 are formed on the distal end surface of the tool body 101, facing each other by 180 degrees. This ball end mill 100 is rotatable around a central axis O. A gash groove 103 that forms a rake face 102a of each R blade 102 is formed on the front side in the rotational direction of each R blade 102.

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 passing through the vicinity of the central axis O. The two R blades 102 intersect with each other via a chisel 104 that overlaps the central axis O. Moreover, each gash groove 103 is provided along the R blade 102 from the outer peripheral side in the direction of the central axis O in a plan view, extending to the opposite side beyond the central axis O. Therefore, the pair of gash grooves 103 intersect with each other within a range of length k. Such a ball end mill is also disclosed in Patent Document 1, for example.

Japanese Patent Application Publication No. 2000-117522

When cutting a workpiece with this ball end mill 100, since the chisel 104 having an uncut blade is provided near the central axis O, cutting resistance increases at this portion. 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 the R blade 102 is set to be centered, but also the chisel 104 has an extended flank surface of the opposing R blade 102. The width of the thick wall portion with 200 mm was increased, and the rake angle was set to a negative value.
However, even in this case, since the cutting speed is low, the load applied to the chisel 104 is excessive, resulting in large cutting resistance, which has not improved the problem of causing heat generation and abnormal wear.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a ball end mill that improves the cutting performance of the bottom blade and suppresses chipping and wear of the bottom blade, chisel, or recess. do.

The ball end mill according to the present invention has a cutting blade made of cBN or PCD on the distal end side of a tool body that is rotatable around a central axis, and the distal end surface of the cutting blade is formed in a substantially arc shape. A plurality of bottom blades that are set downward from the core, a plurality of gash grooves that are formed on the front side of the bottom blade in the rotational direction and form the rake face of the bottom blade, and a plurality of gash grooves that are provided between the plurality of bottom blades. and a chisel or a recessed portion including a central axis, and the amount of center drop between the bottom blades is set to be greater than 0% and 6% or less of the radius R of the bottom blades.
The ball end mill according to the present invention has a chisel near the center axis or a substantially arc-shaped bottom blade that includes a recess. Since it is formed to have a core drop of more than 0% and less than 6% of the radius R, the cutting performance of the bottom blade is high, and wear and damage of the bottom blade, chisel, or recess can be reduced.

In addition, in a ball end mill that has a recess on the tip surface of the tool body, the gash grooves are arranged to cross 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 preferable to set it in the range of 1% to 3% of R.
A plurality of gash grooves formed at the front of a plurality of bottom blades in the rotational direction intersect with each other within a range of 1% to 3% of the radius R, and a recess was formed in the center between the overlapping bottom blades. The recess between the blades is less prone to wear and chipping, and has high cutting performance.

Further, a ball end mill having a chisel on the tip surface of the tool body may have a shape in which the 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 blades.
A chisel is provided between the bottom blades, and since the bottom blades are made of high hardness and are formed downward from the core, the cutting performance of the bottom blades is high, and wear and tear of the chisel between the bottom blades can be reduced.

Further, the diameter (t) of the inscribed circle of the portion having the chisel is preferably set within a range of 0.5% to 2.0% of the radius R of the bottom blade.
When cutting with the cutting edge, the part with the chisel has high hardness and small thickness, so even if it is pressed by the workpiece, wear and chipping of the chisel can be reduced.

Further, it is preferable that the axial rake angle of the bottom blade is set in the range of -10° to +15°.
Since the axial rake angle of the bottom blade is formed on the regular side in the range of -10° to +15°, combined with center drop, the cutting performance is high.

According to the ball end mill according to the present invention, a cutting blade made of cBN, which is a highly hard material, is used, and a chisel or a recess is provided near the center axis between the bottom blades, and the amount of center drop of the bottom blade is determined by the radius of the bottom blade. Since the R is formed to be greater than 0% and less than 6%, the cutting performance of the bottom blade can be improved, and the bottom blade and the chisel and recess between the bottom blades have excellent chipping resistance and wear resistance.

FIG. 2 is a front end view showing the cutting edge portion of the ball end mill according to the first embodiment of the present invention. 2 is a side view of the ball end mill shown in FIG. 1. FIG. It is a side view of the ball end mill showing the axial rake angle of the R blade. It is a front end view which shows the cutting edge part of the ball end mill by 2nd embodiment. 5 is a side view of the ball end mill shown in FIG. 4. FIG. It is a side view of the ball end mill showing the axial rake angle of the R blade. This shows a conventional example: (a) is a diagram of the flank surface near the center of the R blade before machining, (b) is a projected outline of the R blade before machining, and (c) is the center of the R blade after machining. (d) is a diagram of the surrounding flank surface, and (d) is a contour projection diagram of the R blade after machining. Embodiment 1 is shown, (a) is a diagram of the flank surface of the chisel before machining, (b) is a contour projection diagram of the R blade before machining, (c) is a diagram of the flank surface of the chisel after machining, (d) is a contour projection diagram of the R blade after processing. Embodiment 2 is shown. (a) is a diagram of the flank surface near the center of the R blade before machining, (b) is a contour projection diagram of the R blade before machining, and (c) is a diagram of the R blade after machining. A diagram of the flank surface near the center, and (d) a contour projection diagram of the R blade after machining. FIG. 3 is a front end view of a cutting edge portion of a conventional ball end mill.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Ball end mills according to embodiments of the present invention will be described below with reference to the accompanying drawings.
1 to 3 show a ball end mill 1 according to a first embodiment of the present invention. In FIGS. 1 and 2, a ball end mill 1 according to the present 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 thereof. , is equipped with. 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 as the material for the cutting blade 3 of the ball end mill 1 instead of cBN.
This ball end mill 1 is used for cutting high hardness materials such as machine parts and molds. In this specification, the side of the cutting edge 3 along the central axis O of the tool body 2 will be referred to as the distal end side, and the opposite side connected to the main shaft will be referred to as the base end side.

In FIGS. 1 and 2, the ball end mill 1 has a plurality of approximately 1/4 arc-shaped bottom blades, for example two R blades 5, facing each other at 180 degrees on the approximately hemispherical tip surface 4 of the cutting blade 3. formed in position. When the outer diameter of the tool body 2 is D, and the radius of the R blade 5 is R, 2R≧D is set. Furthermore, each R blade 5 is formed with a downward center.
In the cutting edge portion 3, a gash groove 7 is formed on the front side of each R blade 5 in the rotational direction. The gash surface formed in the gash groove 7 is used as the rake surface 8 of the R blade 5, and the rake surface 8 may be formed in 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.

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 strength of the cutting edge is high but the cutting performance is significantly reduced, and when it is larger than +15°, the cutting performance is high but the strength of the cutting edge is reduced.
A second flank face 9 and a third flank face 10 having a positive clearance angle are sequentially formed as flank faces on the rear side in the rotational direction of the R blade 5. The clearance angle of the second clearance surface 9 is set to a positive angle of +10° to +25°. This clearance angle may be a constant angle, or it may change so that it gradually increases or decreases as it goes toward the rear in the rotational direction from the R blade 5 side. The clearance angle of the third flank face 10 is larger than the clearance angle of the second flank face 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 cutter 13 in the rotational direction. A rake face 15 of the peripheral cutting edge 13 is formed in the flute groove 14 . The outer peripheral blade 13 and the flute groove 14 have a helical angle such that they are gradually twisted in a spiral shape toward the rear in the rotational direction from the distal end toward the proximal end.
In a side view of the tool body 2, the R blade 5 and the peripheral blade 13 are twisted rearward in the rotational direction from the distal end side to the base end side. The peripheral blade 13 has a helix angle that is twisted backward at the same angle as the R blade 5 or an angle greater than that. Like the R blade 5 and the peripheral blade 13, 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 rotational direction from the distal end to the proximal end.

In the front end view of the cutting edge portion 3 shown in FIG. 1, the pair of R blades 5 are formed downward from the center. Note that the R blade 5 may be formed in a convex curved shape that curves and protrudes forward in the rotational direction or in a straight line shape. The end of each R blade 5 on the center axis O side extends to a position close to the center axis O, and these ends are connected to a thick extended flank 18a where the extensions of the second flank 9 are connected. It is connected to the. A chisel 18 that overlaps the central axis O is formed at the center of this extended flank 18a. The diameter (thickness) t of the inscribed circle of the extended flank 18a having the chisel 18 (the portion 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%, chipping is likely to occur during cutting, and if it is larger than 2.0%, cutting resistance will increase, causing abnormal wear.
Chisel 18 corresponds to a dead spot. The extended flank surface 18a of the chisel 18 overlaps the central axis O, and the ridge line between the rake surface and the extended flank surface 18a can be used as a cutting edge to cut when the tool body 2 rotates, but it is in the vicinity of the central axis O. Therefore, the cutting speed is low and machinability is poor.

Further, the center drop amount s, which is the interval between the pair of R blades 5, is set in a range greater than 0% and 6% or less of the radius R of the R blades 5. If the center drop amount s is 0%, the center drop cannot be set and the cutting performance of the R blade 5 is reduced, and if it exceeds 6%, the cutting performance is high but the cutting edge strength is reduced. Therefore, it is preferable to set the center drop amount s of the pair of R blades 5 within the above range in order to ensure machinability and cutting edge strength. In order to ensure the cutting balance between the pair of R blades 5, it is preferable that the center drop amount s is a distance of s/2 from the center axis O, respectively.

Further, the two gash grooves 7 formed on the forward side in the rotational direction of the pair of R blades 5 do not intersect with each other, and a gap equal to the diameter t of the inscribed circle of the extended flank surface 18a of the chisel 18 is set. There is. Since the cutting blade 3 made of cBN has high hardness, if the chisel 18 is present near the central axis O, it will create a large resistance and will easily break. In this embodiment, the range of the diameter t of the inscribed circle of the extended flank 18a of the chisel 18 is reduced to the above range to improve cutting performance and suppress wear.

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

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

As described above, according to the ball end mill 1 according to the present embodiment, the cutting blade 3 is made of cBN and has high hardness, and the axial rake angle α of the pair of R blades 5 is inclined toward the positive side. The diameter t of the inscribed circle of the extended flank 18a portion of the chisel 18 sandwiched between the chisel 18 and the chisel 18 is formed to be small. Therefore, the cutting performance by the R blade 5 is high, and the R blade 5 and the chisel 18 have excellent wear resistance and chipping resistance.

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 aspects can be adopted without departing from the spirit of the present invention. Needless to say. All of these are included within the technical scope of the present invention.
Other embodiments and modifications of the present invention will be described below, and parts and components that are the same as or similar to those of the above-described embodiments will be described using the same reference numerals.

4 to 6 show a ball end mill 20 according to a second embodiment of the present invention, which has the same configuration as the ball end mill 1 according to the first embodiment. The ball end mill 20 has a plurality of approximately 1/4 arc-shaped bottom blades 5, for example, two R blades 5, which are formed on the tip surface 4 of the cutting blade 3 at positions facing 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. Furthermore, each R blade 5 is formed with a downward center.
In the cutting edge portion 3, a gash groove 7 is formed on the front side of each R blade 5 in the rotational 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 strength of the cutting edge is high but the cutting performance is significantly reduced, and when it is larger than +15°, the cutting performance is high but the strength of the cutting edge is reduced.
A peripheral blade 13 is formed on the base end side of the R blade 5, and a flute groove 14 is formed on the forward side of the peripheral blade 13 in the rotational direction. A rake face 15 of the peripheral cutting edge 13 is formed in the flute groove 14 . A second flank face 9 and a third flank face 10 having a positive clearance angle are sequentially formed as flank faces on the rear side in the rotational direction of the R blade 5. The clearance angle of the second clearance surface 9 is set to a positive angle of +10° to +25°. The clearance angle of the second clearance surface 9 is set to a constant angle or a variable clearance angle.

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 FIGS. 4 and 5, the shape of the recess 21 is arbitrary. Therefore, no chisel 18 or dead spot is formed in the area including the central axis O between the two R blades 5.
Further, in the tip surface 4 of the cutting edge portion 3, the gash grooves 7 formed on the forward side in the rotational direction of the R blade 5 each extend beyond the central axis O to a region on the opposite side in the radial direction. The two gash grooves 7 overlap and intersect with each other in the recess 21 in the region of the central axis O. The diameter d of the inscribed circle (recess 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 blades 5. If the diameter d of the inscribed circle between the R blades 5 on the side of the central axis O is smaller than 1%, there is a drawback that chips adhere to each other and cause abnormal wear. If it is larger than 3%, the diameter of the concave portion 21 when machining the vertical wall by the cutting edge 3 becomes too large, and the diameter of the convex portion that remains without cutting increases, and the convex portion is cut by the R blade 5 when horizontally feeding. The disadvantage is that the load increases and the machined surface roughness deteriorates.

The ball end mill 20 according to this embodiment has the above-described configuration, and a cutting method thereof will be described next.
For example, when contour roughing is performed by rotating the cutting blade part 3 of the ball end mill 1 around the central axis O while cutting in the vertical direction and feeding it horizontally, a rough cut is formed at the center of the two R blades 5 during vertical feeding. Cutting cannot be performed at the recess 21. Then, a convex portion remaining after cutting due to the concave portion 21 is formed on the workpiece.
Thereafter, by horizontally feeding the ball end mill 1, even if there is no blade in the recess 21 at the center axis O portion of the cutting edge 3, the R blade 5 cuts the remaining convex portion that could not be cut during cutting. . 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, cutting performance 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 blade part 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. The uncut portion of the concave portion 21 sandwiched between the blades 5 can be cut by horizontal feeding.
Therefore, the cutting performance of the R blade 5 is high, and wear and damage at the R blade 5 and the recess 21 can be suppressed. Furthermore, since there is no chisel 18 in the recess 21 between the R blades 5, cutting resistance can be further reduced.

Next, a contour line rough cutting cutting test was conducted 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 was used as Example 1, the ball end mill 20 of the second embodiment was used as Example 2, and the conventional ball end mill 100 shown in FIG. 10 was used as a conventional example. We performed mold machining for the workpiece material.
In Examples 1 and 2, the pair of R blades 5 are of a downward center, whereas in the conventional example, the center of the blades 5 is upward. In the first embodiment, a chisel 18 having an inscribed circle diameter t is provided near the central axis O of the cutting blade 3, and in the second embodiment, a recess 21 is formed near the central axis O of the cutting blade 3. In the conventional example, a chisel 104 that is thicker than the chisel 18 is formed near the central axis O.

The cutting conditions were as follows: rotation speed n was 120000 min ^-1 , feed rate Vf was 1050 mm/min, ap (depth of cut in the Z-axis direction) was 0.005 mm, and ae (depth of cut in the lateral direction) was 0.005 mm. Oil mist was used as the coolant.
As a comparison test result, the wear condition of the flank face near the rotation center of each ball end mill 1, 20, and 100 before and after cutting the workpiece material for 10 hours, and the wear amount of the R blades 5 and 102 were determined. A contour projection photograph is shown.

For Example 1, Example 2, and the conventional example, contour line rough cutting of the work materials was performed for 10 hours. In FIGS. 7 to 9, (a) and (b) show a portion near the central axis O of the R blade before machining and a contour projection photograph of the R blade. FIGS. 7 to 9(c) and (d) show a portion near the center axis O of the R blade after 10 hours of cutting processing and a contour projection photograph of the R blade. In the contour projection photograph of the R blade after 10 hours of processing, the black part shows the remaining outline of the R blade, and the gray part shows the worn part 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 different from the clearance surface of the chisel 104 after the cutting process shown in FIGS. 7(c) and 7(d). The surface was greatly worn, and the cutting edge of the R blade 102 was also greatly worn.
On the other hand, in Example 1 shown in FIGS. 8(a) and 8(b), the extended flank 18a of the chisel 18 and the R blade 5 before cutting are cut as shown in FIGS. 8(c) and 8(d). After machining, the extended flank 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), with respect to the recess 21 and R blade 5 before cutting, the R on both ends of the recess 21 after cutting shown in FIGS. 9(c) and 9(d) is The second flank face 9 of the blade 5 was slightly worn, and the cutting edge of the R blade 5 was 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 portion of the pair of R blades 5 was small, and the wear at the cutting edge of the R blades 5 was also small. Therefore, it was confirmed that in Examples 1 and 2, machinability could be improved and wear and chipping could be suppressed.

Further, in the ball end mills 1 and 20 according to each of the embodiments described above, a small relief may be provided on the second flank face 9 side of the R blade 5. In this case, mirror finishing can be performed without causing chipping on the machined surface. Alternatively, a cutting edge honing may be provided in place of the small relief.
In addition, in the ball end mills 1 and 20 according to each of the embodiments described above, the number of R blades 5 (bottom blades) formed in the cutting edge portion 3 is not limited to two, but may be three or four or more. When three or more R blades 5 are arranged, the plurality of R blades 5 are arranged at equal pitches, but may be arranged at uneven pitches.

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

Claims (2)

In a ball end mill that has a cBN or PCD cutting edge on the tip side of the 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 blade portion and set downward from the center;
a plurality of gash grooves formed on the front side of the bottom blade in the rotational direction and forming a rake face of the bottom blade;
a recess provided between the plurality of bottom blades and including the central axis;
The center drop amount between the bottom blades is set to be greater than 0% and 6% or less of the radius R of the bottom blade,
On the tip surface of the tool body, the plurality of gash grooves are arranged to intersect with 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 blade. A ball end mill characterized by being set in the range of % . The ball end mill according to claim 1, wherein the axial rake angle of the bottom blade is set in a range of -10° to +15°.

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