JP7527796B2 - Multi-blade ball end mill and machining method thereof - Google Patents

Description

The present invention relates to a multi-blade ball end mill with three or more bottom cutting edges formed on the cutting edge portion at the tip of the tool body, and a machining method for the multi-blade ball end mill.

In the field of precision machining, ball end mills and other tools are generally used to cut high-hardness materials such as molds and precision parts. Furthermore, cutting of workpieces requires high-precision, highly efficient cutting that can produce a stable machined surface for a long period of time.

For example, in the three-blade ball end mill described in Patent Document 1, three arc-shaped cutting edges are formed at equal intervals in the circumferential direction on the tip surface of the approximately hemispherical cutting edge portion of the tool body. A chisel blade is formed on the chisel portion provided on the inner periphery of each arc-shaped cutting edge from the inner end of each arc-shaped cutting edge toward the central axis of the tool body. This chisel blade is formed within a range that does not exceed the hemispherical shape formed by the rotational trajectory of the arc-shaped cutting edge, and the width of the chisel blade in the central axis direction is formed to gradually decrease as it moves along the chisel blade toward the central axis.

Patent No. 4677722

However, the ball end mill described in the above-mentioned Patent Document 1 cuts the workpiece using three equally spaced chisel blades and three arc-shaped cutting edges, so if there are too many cutting edges in contact with the machining surface, vibrations increase, which can reduce machining accuracy.

The present invention was made in consideration of the above-mentioned circumstances, and aims to provide a ball end mill and a machining method for a multi-blade ball end mill that suppresses vibration during cutting and enables high-precision cutting even when the ball end mill has three or more blades.

The multi-blade ball end mill according to the present invention is a multi-blade ball end mill having a cutting edge portion at the tip side of a tool body rotatable around a central axis, and is characterized in that it comprises three or more bottom blades having an arc-shaped portion formed on the tip surface of the cutting edge portion, a gash groove formed on the front side of the bottom blade in the rotational direction and having a rake surface of the bottom blade, a relief surface formed on the rear side of the rotational direction of the bottom blade, and three or more chisel blades each formed at the tip end of the bottom blade, extending in the direction of the central axis, and having a rake surface that is concavely curved so as to suppress changes in blade thickness in the direction of the central axis, and the bottom blades are unequally divided in shape, the angular difference between adjacent bottom blades is set to within 20° , the relief angle of the bottom blades is set to 18° or more, and the rake angle of the bottom blades is set in the range of more than 0° to 15° .
According to the present invention, the cutting can be performed efficiently by rotating the tool body at high speed with the bottom blade and the chisel blade. Moreover, the bottom blade is unequally divided to prevent resonance during cutting and suppress vibration, and the angle difference between the bottom blades is set to within 20° to ensure balance in cutting.

The multi-blade ball end mill according to the present invention is a multi-blade ball end mill having a cutting edge portion at the tip side of a tool body rotatable around a central axis, and is characterized in that it comprises three or more bottom blades having an arc-shaped portion formed on the tip surface of the cutting edge portion, a gash groove formed on the front side of the rotation direction of the bottom blades and having a rake surface of the bottom blade, a relief surface formed on the rear side of the rotation direction of the bottom blade, and a recess formed on the tip end of the bottom blade and having no blade formed therein, wherein the bottom blades are unequally divided and the angular difference between adjacent bottom blades is set to within 20° , the relief angle of the bottom blades is set to 18° or more, and the rake angle of the bottom blades is set in the range of more than 0° to 15° .
According to the present invention, a recess is formed in the center side region of the bottom blade provided in the cutting edge portion, so that the recess leaves a part of the cutting edge when cutting in the axial direction, but the part of the cutting edge can be cut off by lateral feeding, resulting in high finishing accuracy. In addition, the bottom blade is unequally divided, so that resonance during cutting can be prevented, vibration can be suppressed, and cutting balance can be ensured.

It is also preferable that the clearance angle of the bottom cutting edge is set to 18° or more.
The rake angle of the bottom cutting edge is preferably set in the range of from more than 0° to 15°.
Therefore, the cutting ability of the bottom cutting edge can be improved and the cutting resistance can be reduced.

The machining method for a multi-blade ball end mill according to the present invention comprises the steps of: machining the tip surface of the cutting blade portion into a concave shape in a multi-blade ball end mill having a cutting blade portion at the tip side of a tool body rotatable around a central axis, forming a gash groove to form three or more bottom blades into an unequally divided shape; and further machining the tip side of the gash groove into a concave groove shape with laser light, thereby forming three or more chisel blades in the chisel portion at the tip side of the bottom blade, the rake surface of which is concavely curved, thereby suppressing the change in blade thickness in the direction of the central axis, and wherein the clearance angle of the bottom blade is set to 18° or more, and the rake angle of the bottom blade is set in the range of more than 0° to 15° .
According to the present invention, since laser light has a higher processing accuracy than a grinding wheel, by processing the tip side of the gash groove with laser light, a chisel blade can be formed in which change in blade thickness in the direction of the central axis is suppressed.Even if the chisel blade wears during cutting, the increase in blade thickness can be suppressed, so that high cutting accuracy can be achieved, cutting resistance can be suppressed, and rigidity can be ensured.

According to the multi-blade ball end mill of the present invention, the bottom blade and chisel blade are unequally divided and the angle difference between adjacent bottom blades is set to within 20°, so that vibration of the ball end mill due to resonance during cutting is suppressed, resulting in a balanced, highly precise finished surface.
According to the processing method for a multi-blade ball end mill of the present invention, the tip side of the gash groove is processed into a concave groove shape using laser light, and a chisel blade is formed so that the increase in blade thickness is suppressed even if it wears during cutting, thereby ensuring high processing accuracy and rigidity.

1 is a side view showing a cutting edge portion of a ball end mill according to a first embodiment of the present invention. FIG. FIG. 2 is a view showing a tip surface of the ball end mill shown in FIG. 1 . FIG. 2 is a perspective view of a main part of a cutting blade portion of a ball end mill according to an embodiment. FIG. 2 is an enlarged view of a chisel blade portion of a ball end mill. 1 shows test examples of an embodiment and a conventional example, and is a diagram of the tip surfaces of the bottom cutting edge and chisel cutting edge of a ball end mill before and after machining. 1 shows a ball end mill according to a modified example of the first embodiment, in which (a) is a side view of a chisel blade portion, and (b) is a cross-sectional view taken along line A-A in FIG. FIG. 4 is a side view of a ball end mill according to a second embodiment of the present invention. FIG. 8 is a tip surface view showing the bottom cutting edge of the ball end mill shown in FIG. 7 . FIG. 11 is a perspective view of a main part of a cutting blade portion of a ball end mill according to a second embodiment.

Hereinafter, a ball end mill according to each embodiment of the present invention will be described with reference to the accompanying drawings.
1 to 5 show a three-blade multi-blade ball end mill 1 according to a first embodiment of the present invention. In Fig. 1 to 4, the ball end mill 1 according to this embodiment includes a tool body 2 formed in a substantially cylindrical shape and rotated about a central axis O, and a cutting blade portion 3 brazed to or integrally formed at the tip of the tool body 2. The cutting blade portion 3 can be made of cemented carbide, cBN, PCD (sintered diamond), or the like. The ball end mill 1 according to this embodiment is used for small-diameter ball end mills 1 in which the maximum outer diameter D of the cutting blade portion 3 is less than 0.3 mm.
This ball end mill 1 is used for cutting high-hardness materials such as small precision machine parts and dies, non-ferrous metals, general steel materials, etc. In this specification, the side of the cutting edge portion 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.

In Figures 1 and 2, the cutting edge 3 of the ball end mill 1 has a tip formed in an approximately hemispherical shape, and multiple, for example, three, gash grooves 4 are formed in a concave shape at predetermined intervals in the circumferential direction from the base end side to the tip end side. A clearance surface 6 is formed behind the gash groove 4 in the rotation direction of the cutting edge 3 centered on the central axis O, and an arc-shaped bottom cutting edge 5 is formed at the intersection ridge of the gash groove 4 and the clearance surface 6. The bottom cutting edge 5 is formed with the center raised. The surface of the gash groove 4 facing forward in the rotation direction of the tool body 2 forms the rake surface 7 of the bottom cutting edge 5.

In the case of conventional ball end mills, the rake angle of the rake face 7 of the bottom cutting edge 5 is set in the range of -20° to 0°, but in this embodiment, the rake angle is set to a regular angle in the range of more than 0° to 15°. By setting the rake angle to be stronger than in the past, cutting performance can be improved and cutting resistance can be reduced, and since the bottom cutting edge 5 is formed with the center raised, wear resistance and chipping resistance can be improved.
On the other hand, if the rake angle is less than 0°, the above effect cannot be achieved, and if it exceeds 15°, there is a drawback in that the cutting edge becomes easily chipped due to the small cutting edge angle.

In addition, the clearance angle of the clearance face 6 formed on the rear side of the bottom cutting edge 5 in the rotation direction is set to 18° or less in conventional ball end mills, but in this embodiment, it is set to a positive angle of more than 18°. By setting the clearance angle larger than that of conventional products, it is possible to improve the cutting ability of the bottom cutting edge 5, reduce the cutting resistance, and reduce the thrust force. Also, if the clearance angle is 18° or less, there is a disadvantage that the cutting ability of the bottom cutting edge 5 is reduced and the cutting resistance increases.
The gash groove 4 having the rake face 7 of the bottom cutting edge 5 in the cutting edge portion 3 is connected to the flute groove 9 at its base end, and the flute groove 9 is twisted backward in the rotation direction by the same or a larger twist angle as the gash groove 4. Therefore, the chips flow from the gash groove 4 to the outside, or smoothly flow into the flute groove 9 and are discharged to the outside.

In addition, the three bottom blades 5 are set to have unequal divisions with the circumferential angles between adjacent bottom blades 5 being θ1, θ2, and θ3. In this case, at least one of the angles θ1, θ2, and θ3 needs to be different from the other angles, and the angle difference is limited to 20° or less. In a multi-blade ball end mill 1 having three or more bottom blades 5, if the number of bottom blades 5 in contact with the machining surface of the workpiece increases, resonance occurs and the vibration of the tool body 2 increases.
However, by setting the intervals between the bottom blades 5 in the circumferential direction to unequal angles, it is possible to suppress vibration so as not to cause resonance. In this case, by setting the difference in the angles θ1, θ2, and θ3 between the bottom blades 5 to 20° or less, it is possible to ensure a balance of the load during cutting work, and it is possible to suppress imbalance and vibration during cutting work due to the difference in the intervals between the bottom blades 5.

2, a chisel portion 10 including a central axis O is provided in the inscribed circle of the central region formed between the inner ends of the three bottom blades 5. The chisel portion 10 has three chisel blades 11 extending from the inner ends of the bottom blades 5 toward the central axis O. Each chisel blade 11 shown in FIG. 3 and FIG. 4 is formed in a concave curve in the rotational direction of the tool body 2. The chisel blade 11 may be linear or convex.
Each chisel blade 11 is formed along or within a substantially hemispherical locus drawn by rotation around the central axis O of the arc-shaped bottom blade 5. The three chisel blades 11 are formed so that their inner ends join on the central axis O, but the chisel blades 11 do not need to intersect on the central axis O and may be offset from each other.

The ball end mill 1 according to this embodiment has the above-mentioned configuration. Next, a method for machining the chisel blade 11 will be described.
In the cutting blade portion 3 of the ball end mill 1 according to this embodiment, the gash groove 4 is ground from the tip end side to the base end side, for example, by a grindstone. Also, the flank 6 on the rear side of the gash groove 4 in the rotation direction is ground. By grinding the rake face 7 and flank 6 of the gash groove 4, a bottom blade 5 is formed at the intersecting ridge line. Moreover, the arc-shaped bottom blade 5 is not formed in the central region of the tip of the cutting blade portion 3, and this central region becomes a chisel portion 10. Since the three bottom blades 5 rotate at high speed, the cutting performance of the peripheral region of the cutting blade portion 3 can be improved.
The chisel portion 10 including the central axis O is a low-speed rotating region formed in a substantially triangular pyramid shape, and as shown in FIG. 4, three chisel blades 11 are formed by a grindstone into, for example, a concave curved shape in a plan view.

Next, a cutting method for a workpiece using the ball end mill 1 will be described.
While rotating the ball end mill 1 around the central axis O, a vertical wall is machined perpendicular to the workpiece by the contour machining method. When cutting, the workpiece is cut by the bottom cutting edge 5 of the cutting edge portion 3, and the generated chips travel along the rake face 7 of the gash groove 4, flow toward the base end, and are discharged to the outside.
In this case, the bottom blade 5 formed on the outer peripheral surface of the cutting edge portion 3 has a rake angle in the range of more than 0° to 15° and a clearance angle of more than 18°, so that even in rough machining with high cutting resistance, the bottom blade 5 has high cutting ability, reduces cutting resistance, and improves wear resistance and chipping resistance. In addition, the three bottom blades 5 are unequally divided, so vibration during machining can be suppressed.

In addition, at the chisel portion 10 at the tip of the cutting blade portion 3, a chisel blade 11 is connected to the inner end of the bottom blade 5. These chisel blades 11 are rotated at a low speed, but because the chisel portion 10 is a small area, the rigidity of the entire bottom blade 5 is ensured. In addition, during finishing, the cutting depth is small and the cutting resistance is small, so that the wear of the central chisel blade 11 is eliminated, resulting in a finished surface with low surface roughness.

Next, cutting tests carried out on the example of the ball end mill 1 according to the embodiment and a conventional example will be described with reference to FIG.
In this test example, the three-blade ball end mill 1 according to the embodiment was used in the example, and a two-blade ball end mill was used in the conventional example, and each was attached to a machine tool to perform contour machining. The rotation speed of the machine tool was 40,000 min ^-1 , the feed rate of the example was 750 mm/min, and the feed rate of the conventional example was 500 mm/min, and in both cases the feed rate per blade was 0.00625 mm/tooth, ap (cut amount in the Z-axis direction) was 0.013 mm, and ae (cut amount in the horizontal direction) was 0.036 mm. Oil mist was used as the coolant.

The workpiece HAP40 (65HRC) was machined for 10 minutes for both the Example and the Conventional Example, and the amount of wear on the cutting edges after machining was compared to before machining, as shown in Figure 5. Comparing the amount of wear on the cutting edges after machining, it can be seen that the chisel blade and the bottom blades on both sides of it in the Conventional Example are largely worn overall, whereas in the Example, although the chisel blade is worn, the amount of wear on the three bottom blades 5 is small.

As described above, according to the ball end mill 1 of this embodiment, the bottom blade 5 and the chisel blade 11 are unequally divided and the angle difference between adjacent bottom blades is set to within 20°, so that vibration of the ball end mill 1 is suppressed during cutting, resulting in good cutting balance of the bottom blade 5 and a highly accurate machined surface.
Furthermore, since the bottom blade 5 is formed with the center raised, the cutting precision and processing precision of the chisel blade 11 and the rigidity of the bottom blade 5 and the chisel blade 11 can be ensured.

Although the ball end mill 1 and the machining method thereof according to the embodiment of the present invention have been described above, the present invention is not limited to such an embodiment, and it goes without saying that other embodiments and modifications 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 or similar parts as those in the above-described embodiment will be described using the same reference numerals.

6(a) and (b) show a modified example of the ball end mill 1 according to the first embodiment. In this modified example, additional processing was performed with a laser beam on the chisel blade 11 formed on the inside of the bottom blade 5 having three blades, which has the same configuration as the embodiment.
Each chisel blade 11 has a flank 11a formed on the extension of each flank 6 of the bottom blade 5 formed with the center raised. Moreover, the inner end of the gash groove 4 is further cut into a concave groove shape by laser light toward the central axis O side, as shown by the hatched area in Fig. 6(a). As a result, a rake face 11b is formed in which the rake angle of the chisel blade 11 is larger in the normal angle direction. In particular, the gash groove 4 is extended inward and cut into an approximately V- or U-shape, forming a concave curved chisel blade 11.

Each chisel blade 11 is formed along or within a substantially hemispherical locus drawn by the rotation of the arc-shaped bottom cutting edge 5 about the central axis O. Moreover, as shown in Figures 4 and 6, each chisel blade 11 is formed at the intersection of a flank 11a, which is an extension of the flank 6 of the bottom cutting edge 5, and a rake face 11b, which cuts the inner end of the gash groove 4 further toward the central axis O in a concave groove shape.
As shown in the cross-sectional view of Fig. 6(b), the chisel blade 11 is formed to have a thickness such that the cutting surface 11b is carved into a concave curved shape so that the thickness of the blade can be prevented from increasing even if the blade is worn during cutting. The chisel blade 11 is formed to stand upright forward in the direction of the central axis O while preventing any change in the thickness of the blade.

Figure 6 (a) is a side view of the chisel portion 10 of the cutting blade portion 3 shown in Figure 4. By using a ball end mill 1 equipped with such a chisel blade 11 to cut a workpiece, even if the chisel blade 11 at the tip is worn as shown by the two-dot chain line a, the blade thickness of the chisel blade 11 is prevented from increasing as shown in Figure 6 (b). Therefore, the cutting resistance of the chisel blade 11 does not increase. Moreover, since only partial wear and tear of the chisel blade 11 occurs, the rigidity and strength of the entire bottom cutting edge 5 is maintained.

On the other hand, in a conventional ball end mill, as the wear of the chisel blade 11 progresses during cutting, the thickness of the chisel blade 11 increases and the cutting resistance increases because the gash groove 4 is not additionally machined on the side of the central axis O in the chisel portion 10. This is a disadvantage.
In this modified example, the three chisel blades 11 are formed so that their inner ends are joined on the central axis O, but the chisel blades 11 do not need to intersect on the central axis O and may be offset from each other.

According to the ball end mill 1 of this modified example, the chisel portion 10 including the central axis O is in the low-speed rotation region, but is formed in a roughly triangular pyramid shape with three chisel blades 11 (see FIG. 4). Furthermore, the machining accuracy of the chisel blades 11 can be improved by additionally machining the chisel portion 10 side of the gash groove 4 into a concave groove shape using laser light. The machining accuracy of the grindstone is approximately 0.015 mm in diameter at minimum, but the laser light has a diameter of approximately 0.005 mm, so machining can be performed with high precision closer to the tip.

Therefore, according to this modified example, by cutting the tip side of the gash groove 4 into a concave groove shape with laser light, the area of the rake face 11b of each chisel blade 11 and the flank face 11a of the adjacent chisel blade 11 can be machined with high precision to form a predetermined blade thickness that protrudes the chisel blade 11 in the direction of the central axis O. As a result, even if each chisel blade 11 is worn down by cutting the workpiece, the blade thickness of the chisel blade 11 can be suppressed from increasing, and the rigidity of the chisel blade 11 can be secured.
In addition, since the chisel portion 10 is a small area, the rigidity of the entire bottom cutting edge 5 is ensured. During finish machining, the cutting depth is small and the cutting resistance is small, so that the wear of the chisel edge 11 in the center is eliminated and a finished surface with small surface roughness can be obtained.

In addition, according to the machining method of the ball end mill 1, the rake face 11b and the clearance face 11a of the chisel blade 11 can be machined with high precision from the tip side of the gash groove 4 using laser light. Therefore, even if the chisel blade 11 wears, the increase in the blade thickness of the chisel blade 11 and the cutting resistance can be suppressed.

7 to 9 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 according to this embodiment differs from the ball end mill 1 according to the first embodiment in the chisel portion 10, but the remaining configuration is the same. In this second embodiment, a recess 21 is formed at the inner end of each of the three bottom blades 5 of the ball end mill 20, and no chisel blade 11 is formed. This recess 21 is formed and connected to three gash grooves 4 formed on the outer peripheral surface of the cutting blade portion 3. The recess 21 is formed recessed from the tip of the cutting blade portion 3 toward the base end in the direction of the central axis O. The inner peripheral end of the bottom blade 5 is not connected at the center on the tip side. The bottom blade 5 is formed with the center down.

Therefore, according to the ball end mill 20 of the second embodiment, the recess 21 is formed at the tip including the central axis O of the cutting blade portion 3 which rotates at a low speed, so that the bottom blade 5 is not worn when feeding and cutting in the direction of the central axis O. At that time, the three bottom blades 5 provided on the peripheral portion of the recess 21 perform high-speed cutting, so that the bottom blade 5 is not damaged and cutting performance can be improved. Also, during feed cutting in the direction of the central axis O, cutting cannot be performed at the recess 21 of the ball end mill 20, so the workpiece remains as a convex portion, but by feeding the ball end mill 20 laterally, cutting can be performed including the remaining convex portion.
Therefore, the ball end mill 20 according to this embodiment can perform high-precision machining not only in rough cutting but also in finish cutting.

In the ball end mills 1 and 20 according to the above-mentioned embodiments, the number of bottom edges 5 formed on the cutting edge portion 3 is not limited to three, but may be four or more, forming a multi-edge ball end mill.

Reference Signs List 1, 20 Ball end mill 2 Tool body 3 Cutting edge portion 4 Gash groove 5 Bottom cutting edge 6 Flank surface 7 Rake surface 10 Chisel portion 11 Chisel blade 11a Flank surface 11b of chisel blade Rake surface 21 of chisel blade Concave portion O Central axis

Claims (3)

In a multi-blade ball end mill having a cutting edge portion on the tip side of a tool body that can rotate around a central axis,
Three or more bottom blades each having an arc-shaped portion formed on a tip surface of the cutting blade portion;
A gash groove is formed on a front side of the bottom cutting edge in a rotational direction and has a rake face of the bottom cutting edge;
A flank surface formed on a rear side of the end cutting edge in a rotation direction;
and three or more chisel blades each formed at a tip end of the bottom cutting edge, extending in the direction of the central axis, and having a concavely curved rake surface that suppresses a change in blade thickness in the direction of the central axis,
The bottom cutting edge is unequally divided, and the angle difference between adjacent bottom cutting edges is set to within 20° .
The clearance angle of the end cutting edge is set to 18° or more,
A multi-blade ball end mill characterized in that the rake angle of the bottom cutting edge is set in the range of from over 0° to 15° . In a multi-blade ball end mill having a cutting edge portion on the tip side of a tool body that can rotate around a central axis,
Three or more bottom blades each having an arc-shaped portion formed on a tip surface of the cutting blade portion;
A gash groove is formed on a front side of the bottom cutting edge in a rotational direction and has a rake face of the bottom cutting edge;
A flank surface formed on a rear side of the end cutting edge in a rotation direction;
A recess is formed at the tip end of the bottom cutting edge, and no cutting edge is formed therein.
The bottom cutting edge is unequally divided, and the angle difference between adjacent bottom cutting edges is set to within 20° .
The clearance angle of the end cutting edge is set to 18° or more,
A multi-blade ball end mill characterized in that the rake angle of the bottom cutting edge is set in the range of from over 0° to 15° . In a multi-blade ball end mill having a cutting edge portion on the tip side of a tool body that can rotate around a central axis,
A step of forming three or more bottom blades into an unequal divided shape by forming a gash groove by processing a tip surface of the cutting blade portion into a concave shape;
and forming three or more chisel blades each having a concavely curved rake surface and standing upright while suppressing a change in blade thickness in the direction of the central axis, by further processing the tip side of the gash groove into a concave groove shape with a laser beam ,
The clearance angle of the end cutting edge is set to 18° or more,
A method for machining a multi-blade ball end mill, characterized in that the rake angle of the bottom cutting edge is set in the range of from greater than 0° to 15° .

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