JP7409244B2 - ball end mill - Google Patents

Description

The present invention provides a chip discharge groove that is formed on the outer periphery of the tip of an end mill body that is rotated in the rotational direction of the end mill around an axis, and that is opened at the tip flank of the end mill body and extends toward the rear end side in the axial direction. A groove-shaped gash is formed at the tip of the chip discharge groove so that the bottom surface of the chip discharge groove is cut out toward the inner circumference of the end mill body. The present invention relates to a ball end mill in which a hemispherical bottom blade is formed on the ridge portion, and the rotation trajectory around the axis has its center on the axis and is convex toward the tip side.

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

Japanese Patent Application Publication No. 5-042410

However, as in the ball end mill described in Patent Document 1, the radius (R) of the bottom roundness of the bottom blade located at 45 degrees from the ball center of the ball blade part to the end mill rotation axis is the end mill diameter (D ), the chip pocket is enlarged by setting R = (0.15 to 0.3) × D, and the rake angle is set to 5° or more to improve cutting performance. There is a risk that the bottom blade may be chipped or damaged.

In addition, if the gash extends to the vicinity of the end mill rotation center where the axis passes through the tip flank of the end mill body due to the radius of the rounded bottom of the blade and the rake angle of the bottom blade, the circumferential speed is close to 0, resulting in large cutting. Even in the vicinity of the rotation center of the end mill where a load is applied, the strength of the bottom blade decreases, making chipping and breakage more likely to occur.

Moreover, in Patent Document 1, whereas normally the chip pocket of the ball cutting edge is smoothly continuous with the peripheral cutting edge, as mentioned above, the chip pocket of the ball cutting edge is 45 degrees from the center of the ball of the ball cutting edge to the end mill rotation axis. Even if the chip pocket is enlarged by setting the radius (R) of the roundness of the bottom blade of the bottom blade located at the end mill diameter (D) to R = (0.15 to 0.3) It is stated that the joints do not pose any problems when forming the cutting edge, but when using the bottom blade on the rear end side in the axial direction from this 45° angle, the joints will allow for good chip evacuation. There is a risk that sex may be inhibited.

On the other hand, when the rake angle is made smaller and the chip pocket is also made smaller to increase the cutting edge angle of the bottom cutting edge, it is especially important to rotate the end mill body at high speed to perform cutting, or to perform cutting with a large depth of cut. In this case, chip evacuation performance is impaired and chip clogging occurs, leading to an increase in cutting resistance.

The present invention was made against this background, and while ensuring good chip evacuation and suppressing the increase in cutting resistance due to chip clogging, it also prevents the strength of the bottom edge from decreasing and prevents chipping and breakage on the bottom edge. The purpose of the present invention is to provide a ball end mill that has a long end mill life and does not cause such problems.

In order to solve the above-mentioned problems and achieve such objects, the present invention has an opening in the tip flank of the end mill body on the outer periphery of the tip of the end mill body that is rotated in the rotational direction of the end mill about the axis. A chip discharge groove extending toward the rear end in the axial direction is formed, and the tip of the chip discharge groove has a concave groove shape so that the bottom surface of the chip discharge groove is cut out toward the inner peripheral side of the end mill body. A first gash is formed, and a rotation locus about the axis has a center on the axis at the edge portion on the outer peripheral side of the tip of the first wall surface of the first gash facing the rotation direction of the end mill. A ball end mill is provided with a hemispherical bottom blade that is convex toward the tip side, and the first gash includes the first wall surface, a bottom surface facing the outer peripheral side of the tip end of the end mill body, A groove bottom extending between the bottom surface and the first wall surface, and at least the first wall surface of the first gash is provided with a groove bottom portion extending between the bottom blade and the first wall surface. A second gash in the shape of a concave groove is formed so as to further cut out the wall surface, and the first gash and the second gash are arranged in a direction different from each other in the rotational direction of the end mill as they move toward the rear end side in the axial direction. The groove bottom position, which is formed so as to be twisted toward the opposite side, and where the distance from the axis of the circular arc having the minimum radius of curvature in the cross section perpendicular to the axis of the second gash is the shortest, is defined as the axis. The distance from the axis of the circular arc such that the torsion angle of the second gash torsion line connected in the direction with respect to the axis is the minimum radius of curvature in a cross section perpendicular to the axis of the groove bottom of the first gash is the shortest. The torsion angle of the first gash torsion line connecting the groove bottom positions in the axial direction is larger than the torsion angle with respect to the axis.

In the ball end mill configured in this way, at least the first wall surface facing the end mill rotation direction of the concave first gash formed at the tip of the chip discharge groove is further cut. A second gash is formed in the shape of a concave groove, and this second gash is formed on the edge of the first gash on the outer peripheral side of the tip of the first wall facing the end mill rotation direction. It is spaced apart from the bottom blade.

Therefore, the cutting edge angle of the bottom blade can be largely secured by the first wall surface of the first gash near the rotation center of the end mill and on the outer periphery of the end mill body, and the size of the chip pocket can also be maintained by the first gash. A large amount of space can be secured by the second gash formed by cutting out at least the first wall surface of the. For this reason, it is possible to prevent chipping, breakage, etc. due to a decrease in the strength of the bottom blade due to a decrease in the blade angle of the bottom blade, while improving chip evacuation performance and suppressing an increase in cutting resistance due to chip clogging. becomes possible.

Furthermore, 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 toward the opposite side to the end mill rotation direction. The second gash torsion line connects in the axial direction the groove bottom position where the distance from the axis of the circular arc having the minimum radius of curvature in the cross section orthogonal to the axis of the second gash is the shortest. The groove bottom position where the distance from the axis of the circular arc where the torsion angle with respect to the axis is the minimum radius of curvature in the cross section perpendicular to the axis of the groove bottom of the first gash is the shortest is connected in the axial direction. It is larger than the twist angle of the first gash twist line with respect to the axis.

As a result, the second gash is formed to be twisted more toward the rear end side of the end mill in the axial direction than the first gash, so that On the end side, the second gash can be formed deeper relative to the first wall of the first gash. For this reason, it is possible to further improve the chip discharging performance, and it is also possible to improve the chip separation performance by increasing the height from the bottom blade to the second gash. Moreover, since the torsion angle of the second gash can be made close to the torsion angle of the chip discharge groove, it is possible to prevent the chip discharge performance from being inhibited 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, the groove bottom and the second gash from the center of the hemisphere formed by the rotation locus of the bottom blade about the axis when viewed from the direction facing the first wall along a straight line passing through the intersection and perpendicular to the first wall. It is desirable that the angle that a straight line passing through the intersection of the bottom and the second gash makes with the axis extending from the center of the bottom blade to the tip side is within the range of 40° to 85°.

In such a case, the intersection between the groove bottom and the second gash is one of the boundaries between the first and second gashes on the tip side in the axial direction. If the angle that the straight line passing through the bottom blade makes with the axis extending from the center of the bottom blade to the tip side is smaller than 40°, the second gash will come too close to the center of rotation of the end mill, causing chipping or damage to the bottom blade. It may become easier.

On the other hand, if the angle between the straight line passing through this intersection from the center of the bottom cutter and the axis extending from the center of the bottom cutter to the tip side is greater than 85°, most of the rake face of the bottom cutter is This will be occupied by the first wall surface of the gash, and there is a possibility that it will be difficult to improve chip evacuation performance.

Note that the difference between the torsion angle of the second gash torsion line with respect to the axis and the torsion angle of the first gash torsion line with respect to the axis is preferably within a range of 2° to 15°. . If the difference in 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 chip evacuation and chip separation properties cannot be sufficiently improved. If the angle exceeds 15°, the second gash becomes too deep on the rear end side, which may reduce the strength of the bottom blade and the end mill body.

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

In this way, with respect to the straight line connecting the axis and the groove bottom position of the first gash in the same cross section perpendicular to the axis, a straight line connecting the axis and the groove bottom position of the second gash is connected to the end mill with the axis as the center. By shifting in the rotational direction and providing a phase difference between the groove bottom positions of the first and second gashes, when cutting with a particularly large depth of cut, the gap generated by the bottom blade on the rear end side in the axial direction The groove bottom position of the second gash where thick chips curve can be moved away from the bottom blade.

Therefore, thick chips can be guided into the large chip pocket formed by the second gash, curved by the groove bottom portion, and efficiently divided. Therefore, with this configuration, the chip pocket formed by the second gash can be effectively utilized, and even when the depth of cut is large, chips can be stably disposed of.

In this case, the intersection angle between the straight line connecting the axis in the cross section and the groove bottom position of the first gash and the straight line connecting the axis and the groove bottom position of the second gash is 5°. It is desirable that the angle be within the range of ~30°. If this intersection angle is less than 5°, the bottom position of the groove of the second gash may not be sufficiently far away from the bottom blade, and the chip pocket may not be able to be used effectively; if it exceeds 30°, Conversely, the groove bottom position of the second gash may be too far away from the bottom blade, leading to an increase in cutting resistance.

As explained above, according to the present invention, by forming the second gash at a distance from the bottom blade, it is possible to improve chip evacuation even when cutting with a large depth of cut. It is possible to suppress an increase in cutting resistance due to chip clogging, and it is also possible to secure the blade angle of the bottom blade to prevent a decrease in strength of the bottom blade, and to prevent chipping, breakage, etc. from occurring.

FIG. 1 is a perspective view of the tip of an end mill main body showing an embodiment of the present invention. FIG. 2 is a front view of the embodiment shown in FIG. 1 when viewed from the distal end side in the axial direction. FIG. 3 is a side view as viewed in the direction of arrow X in FIG. 2. FIG. 4 is an enlarged side view of the tip of the end mill main body in FIG. 3. FIG. It is a VV sectional view in FIG. 4. FIG. 5 is a WW sectional view in FIG. 4. FIG. It is a XX sectional view in FIG. 4. It is a YY sectional view in FIG. 4. It is a ZZ sectional view in FIG. 4.

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

In such a ball end mill, the shank part 2 is gripped by the main shaft of a machine tool, and the end mill body 1 is rotated around the axis O in the end mill rotation direction T, and in a direction perpendicular to the axis O, or between the axis O and the axis O. By feeding out diagonally in a direction perpendicular to the direction, the cutting edge formed in the cutting edge part 3 performs groove processing or shoulder cutting on the workpiece material.

The outer periphery of the cutting blade 3 has an opening in the tip flank 4 which is the tip surface of the cutting blade 3, and is twisted around the axis O in the opposite direction to the rotational direction T of the end mill. A chip discharge groove 5 is formed that extends to. In this embodiment, four chip discharge grooves 5 are formed at intervals in the circumferential direction, and these chip discharge grooves 5 are cut upward toward the outer circumference at the tip of the shank portion 2.

On the outer peripheral edge of the wall surface of these chip discharge grooves 5 facing the end mill rotational direction T, an outer peripheral edge 6 of the cutting blades is formed, which uses this wall surface as a rake surface. The outer circumferential cutter 6 in this embodiment is formed so that its rotation locus around the axis O forms a cylindrical shape centered on the axis O, and, like the chip evacuation groove 5, the axis changes toward the rear end side in the direction of the axis O. It is twisted around O in the opposite direction to the rotation direction T of the end mill.

On the other hand, at the tip of each chip discharge groove 5, a wall surface facing the end mill rotation direction T and a wall surface facing the opposite side to the end mill rotation direction T of each chip discharge groove 5 are arranged so that the wall surface facing the end mill rotation direction T is directed toward the inner peripheral side of the end mill main body 1. A groove-shaped first gash 7 is formed in a cutout manner. The first gash 7 includes 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 body 1, and a groove bottom 7c extending between the first wall surface 7a and the bottom surface 7b. and a second wall surface 7d facing opposite to the end mill rotation direction T in this embodiment, and the width between the first and second wall surfaces 7a and 7d increases toward the outer circumferential side of the end mill body 1. It is formed to gradually become wider.

Furthermore, a rotation locus around the axis O is formed on the edge of the outer peripheral side of the tip of the first wall surface 7a where the first wall surface 7a of the first gash 7 intersects with the tip flank surface 4 of the end mill body 1. 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 edge of the chip discharge groove 5, respectively.

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

In this embodiment, the first gash 7 is constructed such that the first and second wall surfaces 7a and 7d and the bottom surface 7b extend substantially linearly as shown in FIG. 6 in a cross section perpendicular to the axis O. The groove bottom 7c is formed in a concave curved shape such as a concave arc with a very small radius of curvature that contacts the first wall surface 7a and the bottom surface 7b. The minimum radius of curvature R1 in the cross section perpendicular to the axis O of the groove bottom 7c is 0.005×R to 0.15×R with respect to the radius R of the hemisphere formed by the rotation locus of the bottom blade 8 around the axis O. considered to be within the range.

Furthermore, a groove-shaped second gash 9 is formed on at least the first wall surface 7a of the first gash 7, spaced apart from the bottom blade 8, so as to further cut out the first wall surface 7a. ing. In this embodiment, this second gash 9 has a first gash extending 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 perpendicular to the axis O. The gash 7 extends across the bottom surface 7b beyond the groove bottom 7c, and further reaches the second wall surface 7d to be connected 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 main body 1 is formed so that its entirety has a concave curved shape in a cross section perpendicular to the axis O, as shown in FIGS. 6 to 9. There is. The concave curve formed by the bottom surface 9a of the second gash 9 in a cross section perpendicular to the axis O has a minimum radius of curvature R2 at a position where the bottom surface 9a is approximately in contact with a circle inscribed in the bottom surface 9a with the axis O as the center. This minimum radius of curvature R2 is within the range of 0.03×R to 0.2×R with respect to the radius R of the hemisphere formed by the rotation locus of the bottom blade 8 around the axis O. has been done.

Furthermore, in this embodiment, the minimum radius of curvature R2 of the second gash 9 in a cross section perpendicular to the axis O is the minimum radius of curvature R2 of the groove bottom 7c of the first gash 7 in a cross section perpendicular to the axis O. larger than R1.

Further, a second gash 9 having a concave curve shape in a cross section perpendicular 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 7c. As shown in FIGS. 3 and 4, the first wall surface 7a and the bottom surface 7b, which are linear, intersect with each other. The intersecting ridge line L1 between the wall surface 7a and the second gash 9 and the intersecting ridge line between the bottom surface 7b and the second gash 9 form a convex curved mountain shape convex toward the tip side in the direction of the axis O, and the groove bottom The intersection Q between the gash 7c and the second gash 9 is formed in a valley shape sandwiched between a mountain shape formed by the intersection ridge line L1 between the first wall surface 7a and the bottom surface 7b.

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

On the other hand, a mountain-shaped intersecting ridge line L1 between the first wall surface 7a of the first gash 7 and the second gash 9 extends from the protruding end on the front end side in the direction of the axis O to the outer peripheral side of the end mill body 1 toward the rear end side. The first wall surface 7a portion remaining between the intersecting ridgeline and the bottom blade 8 with the second gash 9 spaced therefrom extends the second gash 9 and the tip flank 4 as they are in the end mill rotation direction T. The chamfered surface 7e is formed by chamfering the ridgeline portion which becomes the bottom edge 8 when the blades are crossed. Therefore, a portion closer to the rear end in the direction of the axis O than the tangent M1 is the chamfer surface 7e.

The width H of the chamfer surface 7e in the radial direction with respect to the center P of the bottom blade 8 is made larger on the front end side in the axis O direction than on the rear end side, and in this embodiment, it is widest on the tangent line M1. , the width gradually becomes narrower toward the rear end side, and the width remains narrow and constant at the rear end side in the axis O direction.

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

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 in accordance with the twisting of the chip discharge groove 5 and toward the opposite side to the end mill rotation direction T. ing. Therefore, the first and second wall surfaces 7a, 7d and bottom surface 7b of the first gash 7, which are substantially straight in a cross section perpendicular to the axis O, are twisted in the direction of the axis O.

Then, as shown in FIG. 6, the groove bottom position 7f where the distance from the axis O of the circular arc having the minimum radius of curvature R1 in the cross section perpendicular to the axis O of the groove bottom 7c of the first gash 7 is the shortest is determined in FIG. The minimum radius of curvature in the cross section perpendicular to the axis O of the second gash 9 as shown in FIG. The groove bottom position 9b where the distance from the axis O of the circular arc R2 is the shortest is connected in the direction of the axis O as shown in FIG. 3, so that the twist angle β of the second gash torsion line N2 with respect to the axis O becomes large. It is formed.

Here, in this embodiment, the difference β-α between the torsion angle β of the second gash torsion line N2 with respect to the axis O and the torsion angle α of the first gash torsion line N1 with respect to the axis O is 2° to 15 It is said to be within the range of °.

Furthermore, in this embodiment, the second gash 9 as shown in FIG. With respect to the straight line F1 connecting the axis O in a cross section perpendicular to the axis O and the groove bottom position 7f of the first gash 7, the axis O and the groove bottom position 9b of the second gash 9 in the same cross section A straight line F2 connecting these lines is deviated from the axis O in the end mill rotation direction T.

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

In the ball end mill configured in this way, at least the first wall surface 7a facing the end mill rotation direction T of the first gash 7 in the shape of a concave groove formed at the tip of the chip discharge groove 5 has this first gash. The first wall surface 7a of the first gash 7 is further cut out at a distance from the bottom blade 8 formed on the edge of the outer peripheral side of the tip of the wall surface 7a to form a groove-shaped second gash. 9 is formed.

Therefore, the size of the chip pocket for accommodating chips can be ensured largely by the second gash 9 formed by cutting 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 ensured largely by the first wall surface 7a of the first gash 7 near the end mill rotation center C and on the outer peripheral side of the end mill main body 1. Therefore, it is possible to prevent a decrease in the strength of the bottom blade 8 due to a reduction in the blade angle of the bottom blade 8, while improving chip evacuation performance and suppressing an increase in cutting resistance due to chip clogging.

Moreover, in this embodiment, the second gash 9 is located at the groove bottom 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. 7c to the bottom surface 7b, and further reaches a second wall surface 7d facing opposite to the end mill rotation direction T. Therefore, the capacity of the chip pocket by the second gash 9 can be secured even larger, so that good chip discharge performance 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 opposite side to the end mill rotation direction T, similarly to the chip discharge groove 5. It is designed so that it can be Therefore, as the end mill main body 1 rotates during cutting, chips generated by the bottom blade 8 are fed into the chip discharge groove 5 on the rear end side and discharged, so that good chip discharge performance can be obtained. I can do it.

In this case, in the ball end mill having the above-mentioned configuration, the groove bottom position 9b is determined such that the distance from the axis O of the arc having the minimum radius of curvature R2 in the cross section perpendicular to the axis O of the second gash 9 is the shortest. The axis O of the arc where the torsion angle β of the second gash torsion line N2 connected in the direction of the axis O with respect to the axis O is the minimum radius of curvature R1 in the cross section perpendicular to the axis O of the groove bottom 7c of the first gash 7. The first gash torsion line N1 connecting the groove bottom position 7f with the shortest distance from the groove bottom position in the axis O direction is formed to have a different torsion angle so as to be larger than the torsion angle α with respect to the axis O.

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

Therefore, according to the ball end mill configured in this way, the capacity of the chip pocket by the second gash 9 can be further increased to further improve chip evacuation performance, and the second gash 9 can be By increasing the height of the gash 9 to the bottom surface 9a, it is possible to improve chip separation performance.

In addition, since the torsion angle β of the second gash 9 can be made closer to the torsion angle of the chip discharge groove 5, the center P Even in cutting operations that use the bottom blade 8 on the rear end side in the axis O direction with the center at , there is no risk that good chip evacuation performance will be hindered by the joint between the second gash 9 and the chip evacuation groove 5. .

Moreover, in the present embodiment, the difference β-α between the torsion angle β of the second gash torsion line N2 with respect to the axis O and the torsion angle α of the first gash torsion line N1 with respect to the axis O is 2° to 15 Since it is within the range of 100 °C, it is possible to prevent the strength of the bottom blade 8 and the end mill body 1 from decreasing while improving the chip discharging performance and chip breaking performance more reliably.

That is, if the difference β-α between the torsion angles β and α is so small as to be 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 chip discharge performance and chip separation performance cannot be sufficiently improved. On the other hand, if the difference β-α between the torsion angles β and α is so large as to exceed 15°, the second gash 9 will be carved too deeply on the rear end side in the axis O direction, causing the bottom blade 8 and the end mill body 1 to be cut. There is a risk that the strength of the blade portion 3 will decrease.

Furthermore, in this 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 body 1, beyond the groove bottom 7c. In this case, the straight line M2 passing from the center P of the bottom blade 8 through the intersection Q between the groove bottom 7c and the second gash 9 is relative to the axis O extending from the center P of the bottom blade 8 toward the tip side. The angle θ2 formed is within the range of 40° to 85°. Therefore, chipping, breakage, etc. of the bottom blade 8 can be reliably prevented while ensuring better chip evacuation performance.

That is, if the angle θ2 made by the straight line M2 passing through the intersection Q from the center C of the bottom blade 8 with 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 If the end mill rotation center C is too close to the end mill rotation center C, there is a possibility that the bottom blade 8 is likely to be chipped or damaged.

Conversely, if the angle θ2 made by the straight line M2 passing through this intersection Q from the center P of the bottom blade 8 with the axis O extending from the center P of the bottom blade 8 toward the tip side is larger than 85°, the angle θ2 of the bottom blade 8 Most of the rake face will be occupied by the first wall surface 7a of the first gash 7, which may make it difficult to improve chip evacuation performance.

In addition, in this embodiment, when the first gash torsion line N1 is extended toward the rear end side in the axis O direction with the twist angle α with respect to the axis O, it intersects the second gash 9 and is orthogonal to the axis O. In contrast to the straight line F1 connecting the axis O in the cross section and the groove bottom position 7f of the first gash 7, the straight line F2 connecting the axis O in the same cross section and the groove bottom position 9b of the second gash 9 connects the axis O. The center is shifted in the end mill rotation direction T.

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 is connected to the axis O and the groove bottom position of the first gash 7 with the axis O as the center. 7f in the end mill rotational direction T from the straight line F1 connecting the gashes 7f, 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, it becomes possible to move the groove bottom position 9b of the second gash 9, where the thick chips generated by the bottom blade 8 on the rear end side in the direction of the axis O are curved, away from the bottom blade 8.

Therefore, by guiding the thick chips generated by the large cut into the large chip pocket formed by the second gash 9 and curving them by the groove bottom position 9b, the chips can be efficiently separated. I can do it. Therefore, in this embodiment, the chip pocket formed by the second gash 9 can be effectively used, and even when the depth of cut is large as described above, stable processing of thick chips is facilitated. becomes possible.

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

That is, if the intersection angle γ is less than 5°, the groove bottom position 9b of the second gash 9 cannot be moved sufficiently away from the bottom blade 8, and the chip pocket by the second gash 9 cannot be used effectively. There is a risk that you will not be able to do so. On the other hand, if this intersection angle γ exceeds 30°, the groove bottom position 9b of the second gash 9 will be too far away from the bottom blade 8, and the chips will be long and will scrape the bottom surface 9a of the second gash 9. This may cause chip clogging, etc., which may lead to an increase in cutting resistance.

On the other hand, in this embodiment, the minimum radius of curvature R2 in the cross section perpendicular to the axis O of the second gash 9 is the minimum radius of curvature R2 in the cross section perpendicular 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, by forming the second gash 9, it is possible to prevent stress from concentrating on the bottom blade 8, so that the rigidity of the bottom blade 8 can be ensured and the life of the end mill can be extended. Become.

In addition, in this embodiment, the minimum radius of curvature R2 in the cross section perpendicular 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 of the bottom blade 8 around the axis O. It is set to be within the range of R to 0.2×R, which makes it possible to ensure even better chip evacuation, and also to reliably prevent chipping, breakage, etc. 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 chip evacuation performance. On the other hand, if the minimum radius of curvature R2 of the second gash 9 is larger than the above range, the first gash 7 will be cut out too much and the strength of the bottom blade 8 will not be ensured. There is a risk that it will disappear.

Furthermore, in this embodiment, the minimum radius of curvature R1 in the cross section perpendicular to the axis O of the groove bottom 7c of the first gash 7 is relative to the radius R of the hemisphere formed by the rotation locus of the bottom blade 8 around the axis O. Since it is within the range of 0.005×R to 0.15×R, it is possible to ensure good chip evacuation performance and also to reliably prevent chipping and breakage of the bottom blade 8. It becomes possible.

That is, if the minimum radius R1 of the groove bottom 7c of the first gash 7 is smaller than the above range, there is a risk that chips will be caught in the groove bottom 7c and cause clogging. On the other hand, if the minimum radius R1 of the groove bottom 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 direction of the axis O than the second gash 9 will be impaired, leading to chipping. There is a risk that damage or defects may occur.

Furthermore, a first wall surface 7a remaining between the bottom blade 8 and the intersection ridgeline of the first wall surface 7a of the first gash 7 and the bottom surface 9a of the second gash 9 on the outer peripheral side of the tip of the end mill main body 1 As mentioned above, when the second gash 9 and the tip flank 4 are extended in the end mill rotation direction T and intersect, the chamfer surface 7e is a chamfered surface 7e that is obtained by chamfering the ridgeline portion that is the bottom blade 8. However, in this embodiment, the width H of the chamfer surface 7e in the radial direction with respect to the center P of the bottom blade 8 is larger on the front end side in the axis O direction than on the rear end side.

Therefore, according to this embodiment, the strength of the bottom blade 8 can be maintained on the tip side in the direction of the axis O where a large cutting load is applied, and the radius of rotation around the axis O is increased, so that chips are not generated. On the rear end side of the bottom blade 8, which is generated in large quantities, it is possible to promote good chip separation.

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

Furthermore, in this embodiment, the width H in the radial direction 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 R is within the range of 0.03×R to 0.25×R, it is possible to avoid an increase in cutting resistance while maintaining the strength of the bottom blade 8.

That is, if 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 so small as to be less than 0.03×R, the chamfer surface 7e becomes too small and the bottom There is a possibility that the strength of the blade 8 may be impaired. On the other hand, if the width H is so large as to exceed 0.25×R, the chamfer surface 7e becomes too large, which may lead to an increase in cutting resistance.

Furthermore, in the present embodiment, the first gash 7 faces the first wall surface 7a of the first gash 7 along a straight line passing through the intersection Q between the groove bottom 7c and the second gash 9 and perpendicular to the first wall surface 7a. When viewed from the direction of It intersects the axis O extending from the center P of the blade 8 toward the tip end at an angle θ1 within the range of 35° to 75°, thereby maintaining the sharpness of the bottom blade 8 and producing good chipping. It becomes possible to try to separate.

That is, if the angle θ1 that this tangent line M1 makes with 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 will extend close to the end mill rotation center C, and the bottom blade 8 The sharpness of the blade may deteriorate. On the other hand, if the angle θ1 that this tangent line M1 makes with 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 direction of the axis O. As a result, it may become impossible to improve chip separation on the tip side.

1 End mill body 2 Shank portion 3 Cutting blade portion 4 Tip flank 5 Chip discharge groove 6 Peripheral blade 7 First gash 7a First wall surface of first gash 7 7b Bottom surface of first gash 7 7c First gash 7 groove bottom 7d second wall surface of first gash 7 7e chamfer surface 7f groove bottom position of first gash 7 8 bottom blade 8a long bottom blade 8b short bottom blade 9 second gash 9a second gash 9 bottom surface 9b Groove bottom position of the second gash 9 O Axis of the end mill body 1 T End mill rotation direction C End mill rotation center P Center of the hemisphere formed by the rotation locus of the bottom blade 8 around the axis O Q The first gash 7 Intersection between the groove bottom 7c and the second gash 9 R Radius of the hemisphere formed by the rotation locus of the bottom blade 8 around the axis O R1 Minimum curvature of the groove bottom 7c of the first gash 7 in a cross section perpendicular to the axis O Radius R2 Minimum radius of curvature in the cross section perpendicular to the axis O of the bottom surface 9a of the second gash 9 H Width in the radial direction of the chamfer surface 7e with respect to the center P of the bottom blade 8 L1 The first radius on the tip side of the end mill body 1 An intersecting ridgeline between the wall surface 7a and the bottom surface 7b and the second gash 9 M1 A tangent that touches the convex curve formed by an intersecting ridgeline L1 between the first wall surface 7a and the second gash 9 from the center P of the bottom blade 8 θ1 The tangent M1 is Angle made from the center P of the bottom blade 8 to the axis O on the tip side M2 A straight line passing from the center P of the bottom blade 8 to the intersection Q between the groove bottom 7C and the second gash 9 θ2 The straight line M2 is the bottom blade 8 N1 First gash twist line N2 Second gash twist line α Twist angle of first gash twist line N1 with respect to axis O β Second gash twist line Twisting angle of N2 with respect to the axis O F1 Straight line 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 Axis O in the same cross section as the straight line F1 A straight line connecting the groove bottom position 9b of the second gash 9 γ Intersection angle of straight lines F1 and F2

Claims (5)

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

Images