JP2022016105A - Ball-end mill - Google Patents

Abstract

To prevent strength of a bottom blade from deteriorating to prevent chipping and defect or the like, while suppressing increase of cutting resistance due to chip jamming by securing excellent performance of exhausting chips.SOLUTION: First gashes 7 are formed at a tip part of a chip exhaust groove 5 formed at an outer periphery of a tip part of an end mill main body 1 that is rotated in an end mill-rotation direction T around an axial line O. Bottom blades 8 whose rotation trajectories around the axis line O are semi-sphere shapes are formed at ridge parts at the outer periphery sides of tips of first wall surfaces 7a pointing to the end mill-rotation direction T of the first gashes 7. On the first wall surfaces 7a of the first gashes 7 are formed second gashes 9 with an interval from the bottom blades 8. The first and the second gashes 7 and 9 are twisted toward an opposite direction of the end mill-rotation direction T as approaching a rear end side in the axis line direction O, where a twist angle β of a twist line N2 of the second gash is larger than a twist angle α of a twist line N1 of the first gash.SELECTED DRAWING: Figure 4

Description

In the present invention, a chip discharge groove that opens to the tip flank of the end mill body and extends toward the rear end side in the axial direction is formed on the outer periphery of the tip of the end mill body that is rotated in the direction of rotation of the end mill around the axis. At the tip of the chip discharge groove, a concave groove-shaped gash is formed so as to cut out the bottom surface of the chip discharge groove toward the inner peripheral side of the end mill body, and the side of the outer peripheral side of the tip of the wall surface facing the end mill rotation direction of this gash. It relates to a ball end mill in which a hemispherical bottom blade having a center on the axis and convex toward the tip is formed on a ridge.

As such a ball end mill, for example, in Patent Document 1, in a ball end mill having a ball blade (bottom blade) made of a single tool material, the blade shape of the ball end mill is set in a plane including an end mill rotation axis (axis line). When projected in a direction perpendicular to the line segment connecting the cutting edge (the bottom blade) located at 45 ° with respect to the end mill rotation axis from the center of the ball, the rake angle at this position is 5 ° or more and It is described that the radius (R) of the blade bottom (gash) roundness of the end mill has a relationship of R = (0.15 to 0.3) × D with respect to the end mill diameter (D).

Japanese Unexamined Patent Publication No. 5-042410

However, like the ball end mill described in Patent Document 1, the radius (R) of the blade bottom roundness of the bottom blade located at 45 ° from the ball center of the ball blade portion with respect to the end mill rotation axis is the end mill diameter (D). ), R = (0.15 to 0.3) × D to increase the tip pocket, and the rake angle to be 5 ° or more to improve machinability, the blade angle of the bottom blade becomes smaller and the strength is improved. There is a risk that the bottom blade will be chipped or chipped.

In addition, if the gash extends to the end mill rotation center where the axis passes on the tip flank of the end mill body with the radius of the blade bottom roundness and the rake angle of the bottom blade as it is, the peripheral speed is close to 0, so large cutting is performed. Even in the vicinity of the center of rotation of the end mill on which a load acts, the strength of the bottom blade is reduced and chipping, chipping, etc. are likely to occur.

Moreover, in Patent Document 1, the tip pocket of the ball blade is normally smoothly continuous with the outer peripheral blade, whereas as described above, 45 ° from the ball center of the ball blade to the end mill rotation axis. Even if the tip pocket is enlarged with the radius (R) of the blade bottom roundness of the bottom blade located at R = (0.15 to 0.3) × D with respect to the end mill diameter (D), the ball blade portion is mainly used. It is stated that there is no problem with the joint in the molding process using the cutting edge, but when using the bottom blade on the rear end side in the axial direction from this 45 °, the joint discharges good chips. Sex may be impaired.

On the other hand, if the rake angle is made smaller and the tip pocket is also made smaller to increase the blade angle of the bottom blade, especially when cutting is performed by rotating the end mill body at high speed or cutting is performed with a large depth of cut. In that case, the chip evacuation property is impaired and chip clogging occurs, which leads to an increase in cutting resistance.

The present invention has been made under such a background, and while ensuring good chip evacuation and suppressing an increase in cutting resistance due to chip clogging, it prevents a decrease in the strength of the bottom blade and causes chipping or chipping on the bottom blade. It is an object of the present invention to provide a ball end mill having a long end mill life, which does not cause such problems.

In order to solve the above problems and achieve such an object, the present invention opens the outer periphery of the tip of the end mill body, which is rotated in the direction of rotation of the end mill around the axis, to the tip flank of the end mill body. A chip discharge groove extending toward the rear end side in the axial direction is formed, and a concave groove shape is formed at the tip of the chip discharge groove so that the bottom surface of the chip discharge groove is cut out on the inner peripheral side of the end mill body. The first gash is formed, and the rotation locus around the axis has a center on the axis at the ridge portion on the outer peripheral side of the tip of the first wall surface facing the end mill rotation direction of the first gash. A ball end mill having a hemispherical bottom blade that is convex toward the tip side. A groove bottom portion extending between the bottom surface and the first wall surface is provided, and at least the first wall surface of the first gash is spaced from the bottom blade to provide the first wall surface. A concave groove-shaped second gash is formed so as to further cut out the wall surface, and the first gash and the second gash have an end mill rotation direction toward the rear end side in the axial direction. The axis line is the groove bottom position where the distance from the axis line of the arc, which is formed so as to twist toward the opposite side and has the minimum radius of curvature in the cross section orthogonal to the axis line of the second gash, is the shortest. The distance from the axis of the arc where the twist angle of the second gash twist line connected in the direction with respect to the axis is the minimum radius of curvature in the cross section orthogonal to the axis of the groove bottom of the first gash is the shortest. It is characterized in that the position of the bottom of the groove is larger than the twist angle of the first gash twist wire connecting the groove bottoms in the axial direction with respect to the axis.

In the ball end mill configured as described above, the first wall surface is further cut on at least the first wall surface of the concave groove-shaped first gash formed at the tip of the chip discharge groove so as to face the end mill rotation direction. A concave groove-shaped second gash is formed so as to be lacking, and this second gash is formed on the peripheral edge portion on the outer peripheral side of the tip of the first wall surface facing the end mill rotation direction of the first gash. It is spaced from the bottom blade.

Therefore, the blade angle of the bottom blade can be largely secured by the first wall surface of the first gash even near the center of rotation of the end mill or on the outer peripheral side of the end mill main body, and the size of the tip pocket is also the size of the first gash. It can be largely secured by a second gash formed to cut out at least the first wall surface of the. For this reason, it is necessary to improve the chip evacuation property and suppress the increase in cutting resistance due to chip clogging, while preventing the bottom blade from being weakened due to the decrease in the blade angle of the bottom blade and causing chipping and chipping. Is possible.

Further, in the ball end mill having the above configuration, the first gash and the second gash are formed so as to be twisted toward the rear end side in the axial direction and toward the side opposite to the end mill rotation direction. The second gash twist line connecting the groove bottom positions where the distance from the axis of the arc having the minimum radius of curvature in the cross section orthogonal to the axis of the second gash is the shortest in the axial direction is the above. The groove bottom position where the distance from the axis of the arc having the minimum radius of curvature in the cross section orthogonal to the axis of the groove bottom of the first gash with respect to the axis is the shortest is connected in the axis direction. It is larger than the twist angle of the first gash twist wire with respect to the axis.

As a result, the second gash is formed so as to be twisted more toward the rear end side in the axial direction than the first gash and toward the side opposite to the rotation direction of the end mill. On the edge side, the second gash can be formed deeper with respect to the first wall surface of the first gash. Therefore, the chip discharge property can be further improved, and the drop from the bottom blade to the second gash can be increased to improve the chip fragmentation property. Moreover, since the twist angle of the second gash can be brought close to the twist angle of the chip discharge groove, it is possible to prevent the chip discharge property from being hindered by the joint between the second gash and the chip discharge groove. ..

Here, when the second gash is formed from the first wall surface of the first gash to the bottom surface beyond the groove bottom portion, the groove bottom portion and the second gash are formed. When viewed from the direction facing the first wall surface along a straight line that passes through the intersection with the first wall surface and is orthogonal to the first wall surface, the groove from the center of the hemisphere formed by the rotation locus around the axis of the bottom blade. It is desirable that the angle formed by the straight line passing through the intersection of the bottom portion and the second gash with respect to the axis extending from the center of the bottom blade toward the tip side is within the range of 40 ° to 85 °.

In such a case, the intersection of the groove bottom portion and the second gash is one of the boundary portions on the tip side in the axial direction of the first and second gashes, but this intersection is from the center of the bottom blade. If the angle formed by the straight line passing through the portion with respect to the axis extending from the center of the bottom blade to the tip side is smaller than 40 °, the second gash will be too close to the vicinity of the center of rotation of the end mill, causing chipping or chipping of the bottom blade. It may be easier.

Conversely, if the angle between the center of the bottom blade and the straight line passing through this intersection with respect to the axis extending from the center of the bottom blade to the tip side is greater than 85 °, most of the rake face of the bottom blade is first. It will be occupied by the first wall surface of the gash, and it may be difficult to improve the chip evacuation property.

It is desirable that the difference between the twist angle of the second gash twist wire with respect to the axis and the twist angle of the first gash twist wire with respect to the axis is within the range of 2 ° to 15 °. .. When the difference in the twist angle is less than 2 °, the second gash cannot be formed deeper with respect to the first wall surface of the first gash, and the chip discharge property and the chip fragmentation property are sufficiently improved. If it exceeds 15 °, the second gash becomes too deep on the rear end side, and the strength of the bottom blade and the end mill body may decrease.

On the other hand, the axis and the first in a cross section orthogonal to the second gash when the first gash twist line is extended toward the rear end side in the axis direction while maintaining the twist angle with respect to the axis. With respect to the straight line connecting the groove bottom position of 1 gash, the straight line connecting the axis line and the groove bottom position of the second gash in the same cross section may be deviated in the end mill rotation direction about the axis line. desirable.

In contrast to the straight line connecting the axis and the groove bottom position of the first gash in the same cross section orthogonal to the axis, the straight line connecting the axis and the groove bottom position of the second gash is an end mill centered on the axis. By shifting in the rotation direction and providing a phase difference at the groove bottom positions of the first and second gashes, it was generated by the bottom blade on the rear end side in the axial direction, especially when cutting with a large depth of cut. The groove bottom position of the second gash where the thick chips are curved can be kept away from the bottom blade.

Therefore, a large chip can be guided to the large chip pocket formed by the second gash and curved by the groove bottom portion to be efficiently divided. Therefore, with such a configuration, the chip pocket formed by the second gash can be effectively used, and even when the cutting amount is large, stable processing of chips can be achieved.

In this case, the intersection angle between the straight line connecting the axis and the groove bottom position of the first gash in the cross section and the straight line connecting the axis and the groove bottom position of the second gash is 5 °. It is desirable that it is within the range of ~ 30 °. If this crossing angle is less than 5 °, the groove bottom position of the second gash may not be sufficiently far from the bottom blade and the tip pocket may not be effectively used. If it exceeds 30 °, it may not be possible to make effective use of the tip pocket. On the contrary, the groove bottom position of the second gash may be too far from the bottom blade, which may lead to an increase in cutting resistance.

As described above, according to the present invention, by forming the second gash at a distance from the bottom blade, it is possible to improve the chip discharge property even when cutting with a large cutting amount. It is possible to suppress an increase in cutting resistance due to chip clogging, secure a blade angle of the bottom blade, prevent a decrease in the strength of the bottom blade, and prevent chipping, chipping, and the like.

It is a perspective view of the tip part of the end mill main body which shows one Embodiment of this invention. It is a front view which looked at the embodiment shown in FIG. 1 from the tip side in the axial direction. It is a side view of the arrow line X direction view in FIG. It is an enlarged side view of the tip part of the end mill main body in FIG. FIG. 6 is a sectional view taken along line VV in FIG. FIG. 6 is a sectional view taken along line WW in FIG. FIG. 5 is a cross-sectional view taken along the line XX in FIG. FIG. 6 is a sectional view taken along the line YY in FIG. It is a ZZ sectional view in FIG.

1 to 9 show an embodiment of the present invention. In the present embodiment, the end mill main body 1 is formed of a hard material such as cemented carbide in a substantially columnar shape centered on the axis O, and the rear end portion of the end mill main body 1 (the upper right side portion in FIG. 1). In 3, the right side portion) is a shank portion 2 that remains columnar, and the tip portion (lower left portion in FIG. 1; left portion in FIG. 3) is a cutting edge portion 3.

In such a ball end mill, the shank portion 2 is gripped by the spindle of the machine tool, and the end mill main body 1 is rotated around the axis O in the end mill rotation direction T, while being rotated in the direction perpendicular to the axis O, the axis O direction, and the axis O. The work material is grooved or shoulder-cut by the cutting edge formed on the cutting edge portion 3 by being fed diagonally in a direction perpendicular to the cutting edge portion 3.

On the outer circumference of the cutting edge portion 3, an opening is made in the tip escape surface 4, which is the tip surface of the cutting edge portion 3, and while twisting around the axis O in the direction opposite to the end mill rotation direction T, the rear end side in the axis O direction. A chip discharge groove 5 extending to the surface is formed. In the present embodiment, the four chip discharge grooves 5 are formed at intervals in the circumferential direction, and these chip discharge grooves 5 are cut off toward the outer periphery at the tip of the shank portion 2.

The outer peripheral blade 6 of the above-mentioned cutting blades having the wall surface as a rake surface is formed on the outer peripheral side ridge portion of the wall surface of the chip discharge groove 5 facing the end mill rotation direction T. The outer peripheral blade 6 in the present embodiment is formed so that the rotation locus around the axis O forms a cylindrical shape centered on the axis O, and the axis line is directed toward the rear end side in the axis O direction like the chip discharge groove 5. It is twisted around O in the direction opposite to the end mill rotation direction T.

On the other hand, at the tip of the chip discharge groove 5, the wall surface of each chip discharge groove 5 facing the end mill rotation direction T and the wall surface facing the side opposite to the end mill rotation direction T are directed toward the inner peripheral side of the end mill body 1. A concave groove-shaped first gash 7 is formed so as to be cut out. The first gash 7 has a first wall surface 7a facing the end mill rotation direction T, a bottom surface 7b facing the outer peripheral side of the end mill main body 1, and a groove bottom portion 7c extending between the first wall surface 7a and the bottom surface 7b. In this embodiment, a second wall surface 7d facing the side opposite to the end mill rotation direction T is provided, and the width between the first and second wall surfaces 7a and 7d increases toward the outer peripheral side of the end mill main body 1. It is formed so as to gradually widen.

Further, a rotation locus around the axis O is formed on the peripheral edge portion on the outer peripheral side of the tip of the first wall surface 7a where the first wall surface 7a of the first gash 7 and the tip flank surface 4 of the end mill main body 1 intersect. A hemispherical bottom blade 8 having a center P on the axis O and convex toward the tip side is formed. The outer peripheral ends of these bottom blades 8 are smoothly connected to the tips of the outer peripheral blades 6 formed on the outer peripheral side ridges of the chip discharge groove 5.

Here, as shown in FIG. 2, in the present embodiment, among the four bottom blades 8 to be formed, every other bottom blade 8 in the circumferential direction (bottom blade extending in the vertical direction in FIG. 2) 8 is A long bottom blade 8a extending to the vicinity of the end mill rotation center C through which the axis O passes on the tip flank surface 4, and every other bottom blade 8 in the remaining circumferential direction (bottom blade extending in the left-right direction in FIG. 2) 8 Is a short bottom blade 8b extending from the outer peripheral end of the tip flank surface 4 to a position spaced apart from the end mill rotation center C from the long bottom blade 8a.

In the present embodiment, in the first gash 7, the first and second wall surfaces 7a and 7d and the bottom surface 7b extend substantially linearly in a cross section orthogonal to the axis O, as shown in FIG. The groove bottom portion 7c is formed in a concave curve shape such as a concave arc having a very small radius of curvature in contact with the first wall surface 7a and the bottom surface 7b. The minimum radius of curvature R1 in the cross section orthogonal to the axis O of the groove bottom 7c is 0.005 × R to 0.15 × R with respect to the hemispherical radius R formed by the rotation locus around the axis O of the bottom blade 8. It is said to be within the range.

Further, on at least the first wall surface 7a of the first gash 7, a groove-shaped second gash 9 is formed so as to further cut out the first wall surface 7a at a distance from the bottom blade 8. ing. In the present embodiment, the second gash 9 extends from the first wall surface 7a of the first gash 7 between the first wall surface 7a and the bottom surface 7b in a cross section orthogonal to the axis O. It is formed so as to extend beyond the groove bottom portion 7c of the gash 7 and extend over the bottom surface 7b, reach the second wall surface 7d, and connect to the tip flank surface 4 adjacent to the end mill rotation direction T.

Here, the bottom surface 9a of the second gash 9 facing the outer peripheral side of the end mill body 1 is formed so as to form a concave curve as a whole as shown in FIGS. 6 to 9 in a cross section orthogonal to the axis O. There is. The concave curve formed by the bottom surface 9a of the second gash 9 in the cross section orthogonal to the axis O has the minimum radius of curvature R2 at the position of the substantially contact point between the bottom surface 9a and the circle inscribed in the bottom surface 9a about the axis O. The minimum radius of curvature R2 is within the range of 0.03 × R to 0.2 × R with respect to the hemispherical radius R formed by the rotation locus around the axis O of the bottom blade 8. Has been done.

Further, in the present embodiment, the minimum radius of curvature R2 in the cross section orthogonal to the axis O of the second gash 9 is the minimum radius of curvature in the cross section orthogonal to the axis O of the groove bottom 7c of the first gash 7. Larger than R1.

Further, a second gash 9 having a concave curved shape in a cross section orthogonal to the axis O is formed from the first wall surface 7a of the first gash 7 to the bottom surface 7b beyond the groove bottom portion 7c, and the cross section is described above. By intersecting the first wall surface 7a and the bottom surface 7b forming a linear shape in the above, the first on the tip side of the end mill main body 1 when viewed from the direction facing the first wall surface 7a as shown in FIGS. 3 and 4. The crossing ridge line L1 between the wall surface 7a and the second gash 9 and the crossing ridge line between the bottom surface 7b and the second gash 9 form a convex curved chevron shape that is convex toward the tip side in the axis O direction, and the groove bottom portion. The intersection Q between the 7c and the second gash 9 is formed in a valley shape sandwiched between the mountain shapes formed by the intersection ridge line L1 between the first wall surface 7a and the bottom surface 7b.

Here, in the present embodiment, when viewed from the direction facing the first wall surface 7a along a straight line orthogonal to the first wall surface 7a through the intersection Q of the groove bottom portion 7c and the second gash 9. A tangent line M1 tangent to the convex curve formed by the intersecting ridge line L1 between the first wall surface 7a and the second gash 9 on the tip end side of the end mill body 1 extends from the center P of the bottom blade 8 to the tip end side from the center P of the bottom blade 8. The angle θ1 formed with respect to the axis O is within the range of 35 ° to 75 °. Similarly, when viewed from the direction facing the first wall surface 7a, a straight line M2 passing from the center P of the bottom blade 8 to the intersection Q of the groove bottom portion 7c and the second gash 9 is the tip from the center P of the bottom blade 8. The angle θ2 formed with respect to the axis O extending to the side is within the range of 40 ° to 85 °.

On the other hand, the outer peripheral side of the end mill body 1 extends toward the rear end side from the tip on the tip side in the axis O direction of the crossing ridge line L1 forming a mountain shape between the first wall surface 7a of the first gash 7 and the second gash 9. The first wall surface 7a portion left between the crossed ridge line and the bottom blade 8 at which the second gash 9 is spaced extends the second gash 9 and the tip flank surface 4 as they are in the end mill rotation direction T. The chamfer surface 7e is such that the ridgeline portion, which is the bottom blade 8 when crossed, is chamfered. Therefore, the portion on the rear end side in the axis O direction with respect to the tangent line M1 is referred to as the chamfer surface 7e.

The width H in the radial direction with respect to the center P of the bottom blade 8 of the chamfer surface 7e is larger on the tip side in the axis O direction than on the rear end side, and is the widest on the tangent line M1 in the present embodiment. The width gradually narrows toward the rear end side, and the width remains narrow on the rear end side in the O-direction of the axis, and the size is constant.

Here, the intersecting ridge line between the first wall surface 7a on the outer peripheral side of the end mill main body 1 and the second gash 9 has a convex curve that is convex toward the bottom blade 8, and the width H of the chamfer surface 7e is On the front end side in the axis O direction, the ratio of narrowing becomes smaller toward the rear end side, and the width becomes constant on the rear end side in the axis O direction as described above. In the present embodiment, the width H in the radial direction of the chamfer surface 7e on the rear end side of the bottom blade 8, which is made constant in this way, is a hemisphere formed by the rotation locus around the axis O of the bottom blade 8. It is within the range of 0.03 × R to 0.25 × R with respect to the radius R of.

Further, the first and second gashes 7 and 9 are formed so as to be twisted toward the rear end side in the axis O direction and toward the side opposite to the end mill rotation direction T in accordance with the twist of the chip discharge groove 5. ing. Therefore, the first and second wall surfaces 7a, 7d and the bottom surface 7b of the first gash 7, which are substantially linear in the cross section orthogonal to the axis O, are formed in a twisted surface shape in the axis O direction.

Then, as shown in FIG. 6, the groove bottom position 7f having the shortest distance from the axis O of the arc having the minimum radius of curvature R1 in the cross section orthogonal to the axis O of the groove bottom 7c of the first gash 7 is shown in FIG. The minimum radius of curvature in the cross section orthogonal to the axis O of the second gash 9 as shown in FIG. As shown in FIG. 3, the second gash twist line N2 connecting the groove bottom position 9b having the shortest distance from the axis O of the arc to be R2 to the axis O has a large twist angle β with respect to the axis O. It is formed.

Here, in the present embodiment, the difference β−α between the twist angle β of the second gash twist line N2 with respect to the axis O and the twist angle α of the first gash twist line N1 with respect to the axis O is 2 ° to 15 °. It is within the range of °.

Furthermore, in the present embodiment, the first gash twist line N1 becomes the second gash 9 as shown in FIG. 9 when the twist angle α with respect to the axis O is extended toward the rear end side in the axis O direction. With respect to the straight line F1 connecting the axis O in the cross section orthogonal to the axis O and the groove bottom position 7f of the first gash 7, the axis O in the same cross section and the groove bottom position 9b of the second gash 9 The straight line F2 connecting the two is deviated from the axis line O in the end mill rotation direction T.

Here, in the present embodiment, as shown in FIG. 9, a straight line F1 connecting the axis O in the cross section, which is the phase difference between the straight lines F1 and F2, and the groove bottom position 7f of the first gamma 7, and the axis line. The cross-sectional angle γ of the straight line F2 connecting O and the groove bottom position 9b of the second gash 9 is within the range of 5 ° to 30 °.

In the ball end mill configured as described above, the first wall surface 7a of the concave groove-shaped first gash 7 formed at the tip of the chip discharge groove 5 facing at least the end mill rotation direction T. A groove-shaped second gash with a gap from the bottom blade 8 formed on the outer peripheral side of the tip of the wall surface 7a so as to further cut out the first wall surface 7a of the first gash 7. 9 is formed.

Therefore, the size of the chip pocket for accommodating the chips can be largely secured by the second gash 9 formed so as to cut out the first wall surface 7a of the first gash 7. On the other hand, the blade angle of the bottom blade 8 can be largely secured by the first wall surface 7a of the first gash 7 even in the vicinity of the end mill rotation center C or on the outer peripheral side of the end mill main body 1. Therefore, it is possible to prevent the strength of the bottom blade 8 from being lowered due to the small blade angle of the bottom blade 8, and to improve the chip discharge property and suppress the increase in cutting resistance due to chip clogging.

Moreover, in the present embodiment, the second gash 9 is a groove bottom portion between the first wall surface 7a of the first gash 7 facing the end mill rotation direction T and the bottom surface 7b facing the outer peripheral side of the end mill main body 1. It extends beyond 7c to the bottom surface 7b, and further reaches the second wall surface 7d facing the side opposite to the end mill rotation direction T. Therefore, since the capacity of the chip pocket by the second gash 9 can be further secured, good chip ejection property can be obtained.

Further, in the ball end mill having the above configuration, the first and second gashes 7 and 9 are twisted toward the rear end side in the axis O direction and toward the side opposite to the end mill rotation direction T as in the chip discharge groove 5. It is formed so as to be. Therefore, as the end mill main body 1 rotates during cutting, the chips generated by the bottom blade 8 are sent to the chip discharge groove 5 on the rear end side and discharged, so that good chip discharge is obtained. Can be done.

Further, in this case, in the ball end mill having the above configuration, the groove bottom position 9b having the shortest distance from the axis O of the arc having the minimum radius of curvature R2 in the cross section orthogonal to the axis O of the second gash 9 is obtained. The axis O of the arc whose twist angle β with respect to the axis O of the second gash twist line N2 connected in the axis O direction is the minimum radius of curvature R1 in the cross section orthogonal to the axis O of the groove bottom 7c of the first gash 7. The groove bottom position 7f having the shortest distance from the is formed at different twist angles so as to be larger than the twist angle α with respect to the axis O of the first gash twist line N1 connecting the axis O direction.

Therefore, the second gash 9 is twisted at a twist angle β larger than the twist angle α of the first gash 7 with respect to the axis O, and is different from the end mill rotation direction T toward the rear end side in the axis O direction. Since it is formed so as to face the opposite side, the second gash 9 may be formed so as to be deeper than the first wall surface 7a of the first gash 7 on the rear end side in the O direction of the axis. can.

Therefore, according to the ball end mill configured in this way, the capacity of the tip pocket by the second gash 9 can be further increased to further improve the chip evacuation property, and the bottom blade 8 to the second blade 8 to the second. It is possible to increase the head of the gash 9 to the bottom surface 9a to improve the chip splitting property.

Further, since the twist angle β of the second gash 9 can be brought closer to the twist angle of the chip discharge groove 5, the center P is more than the angle of 45 ° from the center P of the bottom blade 8 to the axis O on the tip side. Even in a cutting process in which the bottom blade 8 on the rear end side in the O direction of the axis is used around the center, there is no possibility that the good chip discharge property is hindered by the joint between the second gash 9 and the chip discharge groove 5. ..

Moreover, in the present embodiment, the difference β-α between the twist angle β of the second gash twist line N2 with respect to the axis O and the twist angle α of the first gash twist line N1 with respect to the axis O is 2 ° to 15 °. Since it is within the range of °, it is possible to prevent the bottom blade 8 and the end mill main body 1 from deteriorating in strength while further improving the chip discharging property and the chip breaking property.

That is, if the difference β-α between the twist angles β and α is so small that it is less than 2 °, the second gash 9 cannot be formed deeply with respect to the first wall surface 7a of the first gash 7. , There is a possibility that the chip discharge property and the chip fragmentation property cannot be sufficiently improved. On the other hand, if the difference β-α between the twist angles β and α is so large that it exceeds 15 °, the second gash 9 is carved too deeply on the rear end side in the axis O direction, and the bottom blade 8 and the end mill body 1 are cut. The strength of the blade portion 3 may decrease.

Further, in the present embodiment, as described above, the second gash 9 is formed from the first wall surface 7a of the first gash 7 to the bottom surface 7b facing the outer peripheral side of the end mill main body 1 beyond the groove bottom portion 7c. In this case, a straight line M2 passing from the center P of the bottom blade 8 to the intersection Q of the groove bottom portion 7c and the second gash 9 extends from the center P of the bottom blade 8 toward the tip end side with respect to the axis line O. The angle θ2 formed is within the range of 40 ° to 85 °. Therefore, it is possible to reliably prevent chipping, chipping, and the like of the bottom blade 8 while ensuring better chip discharge.

That is, when the angle θ2 formed by the straight line M2 passing through the intersection Q from the center C of the bottom blade 8 with respect to the axis O extending from the center P of the bottom blade 8 toward the tip side is smaller than 40 °, the second gash 9 Is too close to the vicinity of the end mill rotation center C, and the bottom blade 8 may be easily chipped or chipped.

On the contrary, when the angle θ2 formed by the straight line M2 passing through the intersection Q from the center P of the bottom blade 8 with respect to the axis O extending from the center P of the bottom blade 8 toward the tip side is larger than 85 °, the bottom blade 8 Most of the rake face will be occupied by the first wall surface 7a of the first gash 7, and it may be difficult to improve the chip discharge property.

Further, in the present embodiment, the first gash twist line N1 intersects the second gash 9 when the twist angle α with respect to the axis O is extended toward the rear end side in the axis O direction and is orthogonal to the axis O. The straight line F1 connecting the axis O in the cross section and the groove bottom position 7f of the first gash 7 has the axis O, whereas the straight line F2 connecting the axis O in the same cross section and the groove bottom position 9b of the second gash 9 has the axis O. It is offset in the end mill rotation direction T as the center.

Therefore, according to the present embodiment, the straight line F2 connecting the axis O and the groove bottom position 9b of the second gash 9 in this way is the groove bottom position of the axis O and the first gash 7 with the axis O as the center. By shifting from the straight line F1 connecting 7f to the end mill rotation direction T, that is, by providing a phase difference between the groove bottom positions 7f and 9b of the first and second gashes 7 and 9, cutting can be performed with a particularly large depth of cut. In this case, the groove bottom position 9b of the second gash 9 on which the thick chips generated by the bottom blade 8 on the rear end side in the axis O direction are curved can be kept away from the bottom blade 8.

Therefore, the large chip pocket formed by the second gash 9 is guided by the thick chip generated by the large notch and curved by the portion of the groove bottom position 9b to efficiently divide the chip. Can be done. Therefore, in the present embodiment, the chip pocket formed by the second gash 9 can be effectively used, and even when the cutting amount is large as described above, stable processing of thick chips is promoted. It becomes possible.

In this case, in the present embodiment, the straight line F1 connecting the axis O in the cross section and the groove bottom position 7f of the first gash 7 is connected to the axis O and the groove bottom position 9b of the second gash 9. The cross-sectional angle γ with the straight line F2 is within the range of 5 ° to 30 °. Therefore, while ensuring the effective use of the chip pocket by the second gash 9 as described above, it is possible to prevent the cutting resistance from increasing more than necessary due to chip clogging or the like.

That is, when this crossing angle γ is less than 5 °, the groove bottom position 9b of the second gash 9 cannot be sufficiently separated from the bottom blade 8, and the tip pocket by the second gash 9 can be effectively used. It may not be possible. On the contrary, when this crossing angle γ exceeds 30 °, the groove bottom position 9b of the second gash 9 is too far from the bottom blade 8, and the chips are long and scrape the bottom surface 9a of the second gash 9. It may cause chip clogging and increase cutting resistance.

On the other hand, in the present embodiment, the minimum radius of curvature R2 in the cross section orthogonal to the axis O of the second gash 9 is the minimum in the cross section orthogonal to the axis O of the groove bottom 7c, which is the minimum radius of the first gash 7. It is larger than the radius of curvature R1. Therefore, it is possible to prevent stress from concentrating on the bottom blade 8 by forming the second gash 9, so that the rigidity of the bottom blade 8 can be ensured and the life of the end mill can be extended. Become.

Further, in the present embodiment, the minimum radius of curvature R2 in the cross section orthogonal to the axis O of the second gash 9 is 0.03 × with respect to the radius R of the hemisphere formed by the rotation locus around the axis O of the bottom blade 8. It is within the range of R to 0.2 × R, which makes it possible to secure even better chip evacuation and reliably prevent chipping and chipping of the bottom blade 8. ..

That is, if the minimum radius of curvature R2 of the second gash 9 is smaller than the above range, the second gash 9 may become small and it may be difficult to improve the chip discharge property. On the other hand, on the contrary, when the minimum radius of curvature R2 of the second gash 9 is larger than the above range, the first gash 7 is not cut out too much, and the strength of the bottom blade 8 can be secured. It may disappear.

Further, in the present embodiment, the minimum radius of curvature R1 in the cross section orthogonal to the axis O of the groove bottom portion 7c of the first gash 7 is relative to the radius R of the hemisphere formed by the rotation locus around the axis O of the bottom blade 8. Since it is in the range of 0.005 × R to 0.15 × R, it is possible to secure good chip discharge property and surely prevent chipping and chipping of the bottom blade 8. It will be possible.

That is, if the minimum radius R1 of the groove bottom portion 7c of the first gash 7 is smaller than the above range, chips may be caught in the groove bottom portion 7c and clogging may occur. On the other hand, on the contrary, when the minimum radius R1 of the groove bottom portion 7c of the first gash 7 is larger than the above range, the strength of the bottom blade 8 on the tip side in the axis O direction is impaired compared to the second gash 9 and chipping. And defects may occur.

Furthermore, the first wall surface 7a left between the crossing ridge line between the first wall surface 7a of the first gash 7 and the bottom surface 9a of the second gash 9 and the bottom blade 8 on the outer peripheral side of the tip of the end mill main body 1. Is a chamfer surface 7e as if the ridgeline portion, which is the bottom blade 8 when the second gash 9 and the tip flank surface 4 are extended and crossed in the end mill rotation direction T as they are as described above, is chamfered. However, in the present embodiment, the width H in the radial direction of the bottom blade 8 of the chamfer surface 7e with respect to the center P is larger on the front end side in the axis O direction than on the rear end side.

Therefore, according to the present embodiment, the strength of the bottom blade 8 can be maintained on the tip side in the axis O direction on which a large cutting load acts, and the turning radius around the axis O becomes large, so that chips are generated. On the rear end side of the bottom blade 8 generated in a large amount, it is possible to promote good chip separation.

Further, in the present embodiment, when the width H in the radial direction with respect to the center P of the bottom blade 8 of the chamfer surface 7e is larger on the front end side in the axis O direction than on the rear end side, the rear end side in the axis O direction is rearward. On the end side, the width H in the radial direction with respect to the center P of the bottom blade 8 of the chamfer surface 7e is constant. Therefore, it is possible to prevent the strength of the bottom blade 8 from being unnecessarily impaired on the rear end side in the O-direction of the axis.

Further, in the present embodiment, the radial width H of the chamfer surface 7e on the rear end side of the bottom blade 8 with respect to the center P of the bottom blade 8 is the radius of the hemisphere formed by the rotation locus around the axis O of the bottom blade 8. Since it is in the range of 0.03 × R to 0.25 × R with respect to R, it is possible to avoid an increase in cutting resistance while maintaining the strength of the bottom blade 8.

That is, if the width H of the chamfer surface 7e on the rear end side of the bottom blade 8 in the radial direction with respect to the center P of the bottom blade 8 is small enough to be less than 0.03 × R, the chamfer surface 7e becomes too small and the bottom. The strength of the blade 8 may be impaired. On the other hand, on the contrary, if the width H is larger than 0.25 × R, the chamfer surface 7e may become too large, which may lead to an increase in cutting resistance.

Furthermore, in the present embodiment, the groove bottom portion 7c and the second gash 9 pass through the intersection Q and face the first wall surface 7a of the first gash 7 along a straight line orthogonal to the first wall surface 7a. The tangent line M1 tangent to the crossed ridge line L1 forming a convex curve that is convex toward the tip end side of the first wall surface 7a and the bottom surface 9a of the second gash 9 on the tip end side of the end mill main body 1 is the bottom. It is designed to intersect the axis O extending from the center P of the blade 8 toward the tip side at an angle θ1 within the range of 35 ° to 75 °, whereby good chips are maintained while maintaining the sharpness of the bottom blade 8. It is possible to move away.

That is, when the angle θ1 formed by the tangent M1 with respect to the axis O extending from the center P of the bottom blade 8 toward the tip side is less than 35 °, the chamfer surface 7e extends close to the end mill rotation center C and the bottom blade 8 There is a risk that the sharpness of the eggplant will decrease. On the other hand, conversely, when the angle θ1 formed by the tangent M1 with respect to the axis O extending from the center P of the bottom blade 8 toward the tip side exceeds 75 °, the chamfer surface 7e is formed from the rear end side in the axis O direction. It may be too much, and it may not be possible to improve chip separation on the tip side.

1 End mill body 2 Shank part 3 Cutting edge part 4 Tip flank 5 Chip discharge groove 6 Outer blade 7 First gash 7a First gash 7 First wall surface 7b First gash 7 bottom surface 7c First gash Groove bottom of 7 7d 2nd wall surface of 1st gash 7e Chanfer surface 7f Groove bottom position of 1st gash 7 8 Bottom blade 8a Long bottom blade 8b Short bottom blade 9 2nd gash 9a 2nd gash Bottom surface of 9 9b Groove bottom position of the second gash 9 O End mill body 1 axis T End mill rotation direction C End mill rotation center P Bottom blade 8 axis O The center of the hemisphere formed by the rotation locus around the O The intersection of the groove bottom 7c and the second gash 9 R The radius of the hemisphere formed by the rotation locus around the axis O of the bottom blade 8 R1 The minimum curvature in the cross section orthogonal to the axis O of the groove bottom 7c of the first gash 7. Radius R2 Minimum radius of curvature in a cross section orthogonal to the axis O of the bottom surface 9a of the second gash 9. Radial width with respect to the center P of the bottom blade 8 of the chamfer surface 7e. Crossing ridge line between wall surface 7a and bottom surface 7b and second gash 9 M1 A tangent line θ1 tangent line M1 tangent to the convex curve formed by the crossing ridge line L1 between the first wall surface 7a and the second gash 9 from the center P of the bottom blade 8. Angle formed from the center P of the bottom blade 8 with respect to the axis O on the tip side of the center P of the bottom blade 8 Angle formed with respect to the axis O on the tip side of the center P of N1 N1 first gash twist line N2 second gash twist line α Twist angle with respect to the axis O of N2 F1 A straight line O connecting the axis O in a cross section intersecting the second gash 9 and orthogonal to the axis O and the groove bottom position 7f of the first gash 7 F2 Straight line O in the same cross section as the straight line F1 The crossing angle of the straight line γ straight line F1 and F2 connecting the second gash 9 and the groove bottom position 9b of the second gash 9.

Claims (5)

A chip discharge groove that opens to the tip flank of the end mill body and extends toward the rear end side in the axis direction is formed on the outer periphery of the tip end portion of the end mill body that is rotated around the axis in the end mill rotation direction, and the chip discharge groove is formed. At the tip of the groove, a concave groove-shaped first gash is formed so as to cut out the bottom surface of the chip discharge groove toward the inner peripheral side of the end mill body, and the first gash faces the end mill rotation direction of the first gash. A ball end mill in which a hemispherical bottom blade is formed on the peripheral edge of the wall surface on the outer peripheral side of the tip of the wall surface so that the rotation locus around the axis has a center on the axis and is convex toward the tip. There,
The first gash has a first wall surface, a bottom surface facing the outer peripheral side of the tip of the end mill main body, and a groove bottom portion extending between the bottom surface and the first wall surface.
At least on the first wall surface of the first gash, a groove-shaped second gash is formed so as to further cut out the first wall surface at a distance from the bottom blade.
The first gash and the second gash are formed so as to twist toward the rear end side in the axial direction and in the direction opposite to the rotation direction of the end mill.
With respect to the axis of the second gash twist line connecting the groove bottom position where the distance from the axis of the arc having the minimum radius of curvature in the cross section orthogonal to the axis of the second gasch is the shortest in the axial direction. The twist angle is
A first gash twist line connecting the groove bottom positions where the distance from the axis of the arc having the minimum radius of curvature in the cross section orthogonal to the axis of the groove bottom of the first gasch is the shortest in the axial direction. A ball end mill characterized in that it is larger than the twist angle with respect to the above axis. The second gash is formed from the first wall surface of the first gash to the bottom surface beyond the groove bottom portion.
A rotation locus around the axis of the bottom blade when viewed from a direction facing the first wall surface along a straight line orthogonal to the first wall surface through the intersection of the groove bottom portion and the second gash. The angle formed by the straight line passing from the center of the hemisphere formed by the center to the intersection of the groove bottom and the second gash with respect to the axis extending from the center of the bottom blade toward the tip side is 40 ° to 85 °. The ball end mill according to claim 1, wherein the ball end mill is within the range. The difference between the twist angle of the second gash twist wire with respect to the axis and the twist angle of the first gash twist wire with respect to the axis is within the range of 2 ° to 15 °. The ball end mill according to claim 1 or 2. The axis and the first in a cross section orthogonal to the second gash when the first gash twist line is extended to the rear end side in the axis direction while maintaining the twist angle with respect to the axis. For the straight line connecting the groove bottom position of the gosh,
Any one of claims 1 to 3, wherein the straight line connecting the axis and the groove bottom position of the second gash in the same cross section is deviated in the end mill rotation direction about the axis. The ball end mill described in the section. The intersection angle between the straight line connecting the axis and the groove bottom position of the first gash in the cross section and the straight line connecting the axis and the groove bottom position of the second gash is in the range of 5 ° to 30 °. The ball end mill according to claim 4, wherein the ball end mill is provided inside.

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