JP6343906B2 - Ball end mill - Google Patents

Description

  The present invention relates to a ball end mill in which a bottom blade having a convex hemispherical shape in which the rotation locus around the axis is centered on the axis is formed at the tip of an end mill main body rotated about the axis.

  As such a ball end mill, for example, in Patent Document 1, each bottom blade land has a convex R-curved surface, and the edges of each land are all in contact with the vertex center of the entire bottom blade. Proposed. Patent Document 2 also has three or more bottom blades, and is bent from the bottom blade (ball blade) in the vicinity of the axial center of the end mill as viewed from the bottom of the end mill, and extends to the next blade in the direction of end mill rotation. The ball end mill is provided with a cutting edge that has a clearance angle smaller than the clearance angle of the bottom edge, the inflection point is a point on the bottom edge, and the position is 0.015 mm or more away from the axis. Has been proposed.

JP-A-10-128611 Japanese Patent No. 3840661

  By the way, in such a ball end mill, normally, the chip discharge groove formed on the outer periphery of the tip end of the end mill body has a V-shaped cross-section or a V-shaped cross-section by a gash grindstone having a trapezoidal outer peripheral surface. A trapezoidal concave groove-shaped gash is formed to extend to the inner periphery, and the rotation trajectory around the axis is at the crossing ridgeline between the wall facing the end mill rotation direction of the gash and the tip flank at the end of the end mill body. The bottom blade is formed in a hemispherical shape having a center on the axis and convex to the tip side.

  However, it is difficult to form a convex V-shaped tip or trapezoidal corner formed by the outer peripheral surface of such a gash grindstone so as to intersect with an angle such as an acute angle, and is actually rounded. It will be. In addition, while the gash is formed by the gash grindstone, the so-called sagging due to wear causes the V-shaped tips and the trapezoidal corners to be rounded. Therefore, as in the ball end mill described in Patent Document 1, even if all the edges of the land, that is, the bottom blade, are in contact with the axis at the vertex center, that is, the end of the end mill main body, the gashes overlap each other and the bottom blade is on the axis. Is not practical because it is no longer formed.

  Therefore, in practice, the gash must be formed to a position slightly away from the axis on the end mill main body tip, and the bottom blade must be formed at the intersecting ridge line portion of the wall surface facing the end mill rotation direction and the tip flank surface. However, in that case, the intersection ridgeline between the rounded part of the inner peripheral edge of the gash and the tip flank is slightly extended in the direction of rotation of the end mill than the bottom blade part having a hemispherical rotation locus. Become.

  However, the clearance angle is given to the tip flank so as to recede from the hemisphere formed by the rotation trajectory as it goes rearward in the end mill rotation direction, and conversely, it projects from the hemisphere toward the end mill rotation direction. Therefore, when a portion extending in the direction of rotation of the end mill is formed at the inner peripheral end of the gasche in this way, a protruding portion that is pointed toward the tip end is formed in the vicinity of the axis at the tip of the end mill body, There is a possibility that the machining surface of the workpiece enters a streak and degrades the machining accuracy, or the sharp protrusion is broken and bites into the bottom blade, leading to a chipping of the bottom blade. Such a problem is also pointed out in Patent Document 2.

  On the other hand, the ball end mill described in Patent Document 2 is supposed to solve the problem of the ball end mill described in Patent Document 1, but the cutting is performed by bending from the bottom blade to the next blade. The flank face of the blade is given a small but flank angle, and such a flank face is formed up to the axial center. Therefore, in the same manner as the ball end mill described in Patent Document 1, the flank face is actually positioned at the axial center position. Pointed protrusions are formed, which may also cause deterioration in processing accuracy and chipping of the bottom blade. In addition, since all the flank surfaces of the cutting blade inflected and stretched from three or more bottom blades are formed up to the axial center, chip discharge performance by the cutting blade in the vicinity of the axis of the end mill body tip is impaired. There is also a risk that

  The present invention has been made under such a background, and it is possible to prevent a sharp protrusion from being formed in the vicinity of the axis at the end of the end mill body, thereby improving processing accuracy and preventing the bottom blade from being damaged. Another object of the present invention is to provide a ball end mill capable of improving the chip discharging performance in the vicinity of the axis of the end mill main body.

In order to solve the above problems and achieve such an object, according to the present invention, a plurality of chip discharge grooves are formed at intervals in the circumferential direction on the outer periphery of the end portion of the end mill body rotated around the axis. In addition, a gash extending toward the inner peripheral side is formed at the tip of these chip discharge grooves, and a wall surface facing the end mill rotation direction of the gash and a tip flank of the tip of the end mill main body intersecting the wall surface. The intersecting ridge portion is formed with hemispherical bottom blades each having a rotational locus around the axis centered on the axis and projecting toward the tip side, and at least two bottom blades of these bottom blades are formed. The blades are extended in the vicinity of the axis at the tip of the end mill body, and two of the above-mentioned gears in which two bottom blades adjacent in the circumferential direction among these at least two bottom blades are formed. The first gash located on the end mill rotation direction side extends beyond the axis on the end mill main body end, and the second gash located on the rear side in the end mill rotation direction extends the axis on the end mill main body end. Of the two bottom blades, the first bottom blade formed on the wall surface facing the end mill rotational direction of the first gash intersects the axis and the first bottom blade is formed so as not to exceed. The first tip flank that intersects the bottom blade of the second tip flank intersects the wall surface of the second gash facing the end mill rotation direction via the second bottom blade of the two bottom blades. The first tip flank extended portion and the second tip flank extended between the first tip flank extended portion and the first tip flank extended portion. Extend to the outer circumference Have concave folding surface is formed, the second bottom cutting edge or an extension thereof, intersecting ridgeline portion between the concave refracting surface or extended surface and the rake face of the second bottom cutting edge thereof, or the concave refracting surface, or by intersection at an obtuse angle to the intersecting edge line region of its extension surface and the tip flank of the second bottom cutting edge, said second bottom blades, continuous extends in a direction intersecting at an obtuse angle to the concave curved folding surface It is characterized by.

  In the ball end mill having such a configuration, first, the first and second bottom blades adjacent to each other in the circumferential direction among the at least two bottom blades extended in the vicinity of the axis at the tip of the end mill body are formed. In the first and second two ashes, the first ghash located on the end mill rotation direction side is formed so as to extend beyond the axis on the end mill main body tip. It is possible to secure a large capacity of the pocket communicating with the groove in the vicinity of the axis, and to improve chip discharge performance by the first bottom blade.

  And the 1st tip flank which intersects the 1st gash via the 1st bottom blade is extended toward the 2nd tip flank which adjoins the end mill rotation direction back side, and this Between the extension portion and the second tip flank, a concave fold surface is formed which is concavely bent to the extension portion of the first tip flank surface and extends to the outer peripheral side. The two bottom blades are connected so as to extend in a direction intersecting the obtuse angle. For this reason, if the second bottom blade is formed as it is on the intersecting ridge line portion between the wall surface facing the end mill rotation direction of the second gash whose inner peripheral end is away from the axis and the second tip flank surface, It is possible to prevent the portion from being formed by extending the first tip flank that recedes from the hemisphere formed by the rotation trajectory of the bottom blade as it goes rearward in the end mill rotation direction and forming a concave bent surface. .

  That is, in the ball end mill having the above-described configuration, the portion where the above-described protrusion is formed is configured to be chamfered by the extended portion of the first tip flank and the concave bent surface. It is possible to improve machining accuracy and extend the end mill life without causing streaking on the machining surface due to the projection or cutting the broken projection into the bottom blade during cutting. It becomes possible. In addition, since the first bottom blade intersects the axis, the rotation locus itself around the axis of the first bottom blade becomes a hemisphere having a center on the axis, thereby further improving the processing accuracy. . Further, the second bottom blade is connected to the concave bent surface extending in the direction of the obtuse angle and extending in the direction intersecting the obtuse angle with the extended portion of the first tip flank. It is also possible to ensure the strength at the inner peripheral edge of the bottom blade of 2 and prevent defects and the like.

  Here, the second bottom blade and the concave bent surface may be configured to directly intersect each other with an obtuse angle, and the second bottom blade and the concave bent surface may be connected to each other through a chamfered portion, a rounded convex curved portion, or the like. The extension line of the bottom blade and the extension surface of the concave curved surface may intersect at an obtuse angle. In either case, the second bottom blade or its extension line and the concave curved surface or its extension may be used. The included angle formed by the straight line connecting the intersection with the surface and the center of the hemisphere formed by the rotation trajectory of the bottom blade and the axis is preferably in the range of 1 ° to 10 °. When it becomes larger, the inner peripheral end of the second bottom blade is too far away from the axis, and cutting is performed with only the first bottom blade in the vicinity of the axis of the end mill main body tip. There is a risk that the burden of the burden will become too large. In addition, if the included angle is smaller than the above range, the extension portion and the concave bent surface of the first tip flank surface may become too small to reliably prevent the formation of the protruding portion. . In order for the second bottom blade to extend in a direction intersecting with the concave bent surface at an obtuse angle, the second bottom blade or an extension line thereof is a rake between the concave bent surface or the extended surface and the second bottom blade. The crossed ridgeline part with a surface, or the crossed ridgeline part of the said concave bending surface or its extension surface, and the front-end | tip flank of a 2nd bottom blade should just cross at an obtuse angle.

  Further, when the three bottom blades are extended in the vicinity of the axis at the tip of the end mill body as in the ball end mills described in Patent Documents 1 and 2, these bottom blades are formed. Of the three gashes, a third gash located on the rear side in the end mill rotation direction of the second gash is formed so as not to exceed the axis on the tip of the endmill body. The surface is extended toward the third tip flank that intersects the wall face of the third gash facing the end mill rotation direction through the third bottom blade of the three bottom blades, and this second A concave bent surface extending to the outer peripheral side is formed between the extended portion of the tip flank and the third tip flank, and is formed in the second bent flank. On the curved surface, the third By connecting the bottom blades so as to extend in a direction crossing the obtuse angle, it is possible to prevent the projection from being formed by the third tip flank while ensuring the strength at the tip of the end mill body more reliably. .

  The concave bent surface is formed by grinding the first tip flank by grinding when the first tip flank is extended toward the second tip flank to form the extension. It can be formed by causing the grindstone to interfere with the second tip flank and scraping the inner periphery of the second tip flank. The same applies to the case where the three bottom blades are extended in the vicinity of the axis at the tip of the end mill body to form the extended portion of the second tip flank and the concave bent surface on the third tip flank.

  In addition to the bottom blade extended in the vicinity of the axis at the tip of the end mill body as described above, that is, the so-called long bottom blade, the tip of the end mill body is far away from the axis, for example, more than the range of the included angle. A so-called short-bottom blade having an inner peripheral edge at a position and having a rotation trajectory forming a convex hemisphere together with the long-bottom blade may be formed.

  As described above, according to the present invention, in the vicinity of the axis at the tip of the end mill body, the first bottom blade is made to intersect the axis so that the rotation trajectory of the bottom blade is surely hemispherical and the first bottom blade In addition, it is possible to improve the chip discharging performance and prevent the projections from being formed in the vicinity of this axis. It is possible to provide a ball end mill having a long life and high processing accuracy by preventing breakage and breakage caused by being bitten by the bottom blade.

It is a perspective view which shows one Embodiment of this invention. It is a side view of embodiment shown in FIG. It is an enlarged front view of embodiment shown in FIG. 5A is a further enlarged front view in the vicinity of the axis at the tip of the end mill body of the embodiment shown in FIG. 1, and FIG. 4B is a side view in the vicinity of the axis in the direction of arrow A in FIG. It is the further enlarged front view of the vicinity of the axis line in the tip end of an end mill main body in the state where the gash at the time of manufacturing the embodiment shown in Drawing 1 was formed. (A) Further enlarged front view in the vicinity of the axis showing the state where the tip flank is formed to the position of the axis at the tip of the end mill body from the state shown in FIG. 5, (b) Arrow line in FIG. 6 (a) FIG. 6 is a schematic side view as viewed in direction A (however, for the sake of explanation, the radius of the hemisphere formed by the rotation trajectory of the bottom blade is smaller than that in FIG. 6A). FIG. 6A is a further enlarged front view in the vicinity of the axis showing a state in which the first and second tip flank surfaces are further extended by a grindstone to form an extension portion and a concave bent surface from the state shown in FIG. FIG. 7A is a schematic side view in the direction of arrow A in FIG. 7A (however, for the sake of explanation, the radius of the hemisphere formed by the rotation trajectory of the bottom blade is made smaller than that in FIG. 7A). ).

  1 to 4 show an embodiment of the present invention. In the present embodiment, the end mill body 1 is formed of a hard material such as cemented carbide and has a columnar shape centered on the axis O, and its rear end (upper right side portion in FIG. 1, upper portion in FIG. 2). ) Is a cylindrical shank portion 2, and a tip portion (lower left portion in FIG. 1, lower portion in FIG. 2) is a cutting edge portion 3. In such a ball end mill, the shank portion 2 is gripped by the main spindle of the machine tool and rotated in the end mill rotation direction T around the axis O, and is fed in a direction crossing the axis O, and the workpiece is moved by the cutting edge portion 3. Cutting.

  A plurality of chip discharge grooves 4 are formed on the outer periphery of the cutting edge 3 at the tip of the end mill body 1 at intervals in the circumferential direction. In the present embodiment, six chip discharge grooves 4 are formed, and each chip discharge groove 4 is spirally twisted toward the rear side in the end mill rotation direction T toward the rear end side in the axis O direction. Is formed. On the intersecting ridge line portion between the wall surface of the chip discharge groove 4 facing the end mill rotation direction T and the outer peripheral flank 5 intersecting the wall surface, the wall surface is raked like the chip discharge groove 4 in a spiral manner. The outer peripheral blades 6 are formed, and the six outer peripheral blades 6 respectively formed in the six chip discharge grooves 4 are positioned on one cylindrical surface with the axis O as the center.

  Further, the tip of the chip discharge groove 4 is further provided with a bottom surface of the chip discharge groove 4 facing the outer peripheral side of the end mill body 1 from the wall surface facing the end mill rotation direction T and a wall surface facing the rear side of the end mill rotation direction T. Gash 7 is formed so as to cut out a portion on the rear side in the end mill rotation direction T. The gash 7 has, for example, a concave groove shape having a V-shaped cross section and includes a wall surface facing the end mill rotation direction T and a wall surface facing the rear side of the end mill rotation direction T. Is extended toward the inner peripheral side of the end mill body 1 as it goes toward the tip side. In addition, this valley bottom part is actually provided with a bottom surface that forms a concave curved section such as a concave arc and is continuous with both wall surfaces of the gash 7 or extends in a direction intersecting with these wall surfaces. The portion where the crossing points is also a concave concave section.

  On the other hand, a tip flank 8 extending to the inner peripheral side of the tip is formed at the tip of the cutting edge 3 so as to continue to the outer flank 5 of the six outer peripheral blades 6. In the present embodiment, each tip flank 8 has a substantially constant width tip first flank (second surface) 8a located on the end mill rotation direction T side, and the end mill rotation direction T rearward of the tip first flank 8a. And a tip second flank 8b provided with a larger clearance angle than the tip first flank 8a. Further, the wall surface facing the rear side in the end mill rotational direction T of the gash 7 adjacent to the rear side in the end mill rotational direction T of each front end flank 8 intersects the rear side in the end mill rotational direction T of the second tip flank 8b. ing.

  Further, an intersection ridge line portion between the wall surface of the gasche 7 facing the end mill rotation direction T and the tip first flank 8a of the tip flank 8 connected to the rear side of the end mill rotation direction T of each gash 7 has an axis O around the axis O. A bottom blade 9 having a hemispherical shape whose rotation locus has a center C on the axis O and protrudes toward the distal end side of the end mill body 1 is formed to be continuous with the distal end of the outer peripheral blade 6. As shown in FIG. 2, these bottom blades 9 are also twisted toward the rear side in the end mill rotation direction T as it goes toward the rear end side of the end mill body 1 in this embodiment.

  In the present embodiment, among these six bottom blades 9 connected to the six outer peripheral blades 6, every other first to third bottom blades 9A to 9C in the circumferential direction are connected to the axis O at the end of the end mill body 1. It is extended to the vicinity and is a so-called long bottom blade. Furthermore, among these first to third bottom blades 9A to 9C, which are long bottom blades, the first bottom blade 9A intersects the axis O at the end of the end mill body 1 as shown in FIG. The bottom blade 9 which is a long bottom blade located adjacent to the rear side in the end mill rotation direction T of the first bottom blade 9A is defined as a second bottom blade 9B. Further, the second bottom blade 9B The bottom blade 9 that is a long bottom blade located adjacent to the rear side in the end mill rotation direction T is the third bottom blade 9C.

  Further, the gash 7 formed on the wall surface in which the first bottom blade 9A faces the end mill rotation direction T is the first gash 7A. Similarly, the second and third bottom blades 9B and 9C change the end mill rotation direction T. The gashs 7 formed on the facing wall surfaces are second and third gashs 7B and 7C, respectively. Furthermore, the tip flank 8 that intersects the wall surface of the first gash 7A via the first bottom blade 9A is the first tip flank 8A, which is also the same as that of the second and third gashes 7B. The tip flank 8 that intersects the wall surface via the second and third bottom blades 9B is the second and third tip flank 8B and 8C, respectively.

  Here, as the first bottom blade 9A intersects the axis O, as shown in FIG. 4A, the first gash 7A has an axis line on the tip end of the end mill body 1 from the outer peripheral side of the cutting blade portion 3. It extends beyond O. On the other hand, the second and third gashes 7B and 7C may cross the axis O at intervals without intersecting the first gash 7A and without intersecting each other in the present embodiment. In such a manner, it is formed up to a position away from the axis O. As shown in FIGS. 4A and 5, the third gash 7C has a larger distance from the axis O than the second gash 7B, and the first to third three gashes 7A. The distance from the axis O of ˜7C, that is, the gash depth, is different from each other.

  Further, the first, second, and third gashes 7A, 7B, and 7C are sequentially arranged at the tip ends of the third, first, and second tip flank surfaces 8C, 8A, and 8B adjacent to the end mill rotation direction T side, respectively. 1 Crosses the flank 8a. Furthermore, since the first gash 7A extends beyond the axis O on the tip of the end mill body 1 as described above, it also intersects the tip first flank 8a of the second tip flank 8B. .

  The first tip flank 8A is extended rearward in the end mill rotation direction T toward the second tip flank 8B, and the first tip flank 8A is extended. Between the portion 8c and the second tip flank 8B, a concave bent surface 10 (first concave bent surface) extending to the outer peripheral side is connected to the extended portion 8c of the first tip flank 8A. 10A) is formed. Further, the second bottom blade 9B intersects the first concave bent surface 10A at an obtuse angle at the inner peripheral end P thereof.

  As shown in FIG. 7B, the intersection of the second bottom blade 9B and the concave bent surface 10, that is, the inner peripheral end P of the second bottom blade 9B and the bottom blade 9 rotate around the axis O. The included angle θ formed by the straight line L connecting the center C of the hemisphere in the locus and the axis O is in the range of 1 ° to 10 °, and the extension 8c and the concave portion of the first tip flank 8A are recessed. The bent surface 10 is formed in a very small range near the axis O at the end of the end mill body 1. However, in FIG. 7B, for the sake of explanation, the radius of the hemisphere formed by the rotation locus of the bottom blade 9 is shown smaller than that in FIG. 7A, and the included angle θ is shown larger.

  Here, in this embodiment, the tip first flank 8a of the first tip flank 8A is the valley bottom portion of the second gash 7B having a concave curved cross section, and the tip first flank of the first tip flank 8A is the first tip flank. The first tip flank is a section having a concave curved cross section where the bottom surface of the valley portion of the second gash 7B intersects with the wall surface facing the end mill rotation direction T up to a position exceeding the concave curve formed by intersecting the surface 8a. It extends so as to recede from the rotation trajectory of the first bottom blade 9A toward the rear side in the end mill rotation direction T at the clearance angle as it is until the position exceeding the concave curve formed by intersecting with the first flank 8a at the front end of 8A. The extension 8c.

  Further, in this embodiment, the extension 8c of the first tip flank 8A intersects the second tip flank 8B via an intersecting ridge line M at an obtuse angle, and the intersecting ridge line M is shown in FIG. ), The end of the end mill body 1 intersects the axis O at the tip. Further, the first concave bent surface 10A is bent and bent at an obtuse angle with respect to the extension portion 8c of the first tip flank 8A, and is connected to the rear side in the end mill rotation direction T and the second bottom blade 9B. Is formed so as to gradually protrude along the extending direction toward the outer peripheral side and intersect the tip first flank 8a and the second bottom blade 9B of the second tip flank 8B at an obtuse angle.

  Furthermore, in the present embodiment, the second tip flank 8B is also extended toward the third tip flank 8C adjacent to the rear side in the end mill rotation direction T. This second tip flank Between the extended portion 8c extended from 8B and the third tip flank 8C, a concave fold surface 10 (extending to the outer peripheral side is connected to the extended portion 8c of the second tip flank 8B. A second concave bent surface 10B) is formed. The third bottom blade 9C intersects the second concave curved surface 10B at an obtuse angle at the inner peripheral end P thereof.

  The extension 8c of the second tip flank 8B also has a first bottom edge 9A as the tip first flank 8a of the second tip flank 8B moves toward the rear side in the end mill rotation direction T at the same flank angle. It is formed so as to extend backward from the rotation locus. However, the extension 8c of the second tip flank 8B does not intersect the third tip flank 8C, and intersects the tip first flank 8a of the second tip flank 8B as described above. The first and third gashes 7A and 7C extend between the first and third gashes 7A and 7C.

  Further, the second concave bent surface 10B is connected to the extended portion 8c of the second tip flank 8B by being bent at an obtuse angle, and gradually rises toward the rear side and the outer peripheral side in the end mill rotation direction T. Then, the front end first flank 8a of the third front flank 8C and the third bottom blade 9C intersect at an obtuse angle. Furthermore, although not shown in the figure, the hemispherical center C formed by the inner peripheral end P of the third bottom blade 9C and the bottom blade 9 in the rotation locus around the axis O, which is an intersection with the second concave bent surface 10B, The angle between the straight line connecting the axis and the axis O is also 1 ° to 10 °, similar to the angle θ formed by the straight line L connecting the inner peripheral end P of the second bottom blade 9B and the center C with respect to the axis O. It is considered as a range.

  As described above, the first to third bottom blades 9A to 9C, which are extended to the vicinity of the axis O at the tip of the end mill main body 1 and are long bottom blades, have a circumferential direction of 1 between them. The remaining three bottom blades 9 are short bottom blades 9D, and the inner peripheral edge P of these short bottom blades 9D is cut away from the center C by cutting out the inner peripheral portion of the tip flank 8D. Is made larger than the above range of the included angle θ formed by the inner peripheral ends P of the second and third bottom blades 9B and 9C. Further, the gash 7D formed on the wall surface in which these short bottom blades 9D face the end mill rotation direction T communicates with the first to third gashs 7A to 7C whose inner peripheral portion is adjacent to the rear side in the end mill rotation direction T. Thus, it does not extend to the vicinity of the axis O.

  In the ball end mill configured as described above, the first tip flank 8A is extended toward the second tip flank 8B to form the extension 8c as described above, and the extension 8c and the first 2 is formed with a concave bent surface 10 (first concave bent surface 10A) that is bent to the extended portion 8c and extends to the outer peripheral side. In addition, as in the case where the second bottom blade 9B is formed as it is on the intersecting ridge line portion between the wall surface of the second gash 7B facing the end mill rotation direction T and the second tip flank 8B, a protruding portion is formed at the inner peripheral end thereof. Can be prevented from being formed. Further, in the present embodiment, the third gash 7C is also formed away from the axis O, whereas the second tip flank 8B is also extended toward the third tip flank 8C to extend the extension portion. Since 8c and the 2nd concave bending surface 10B are formed, it can also prevent that a projection part is formed in the inner peripheral end of the 3rd bottom blade 9C.

  That is, in the vicinity of the axis O at the end of the end mill body 1, the first gash 7A extends beyond the axis O and the second and third gashes 7B, 7C are formed away from the axis O as shown in FIG. In this state, the first to third tip flank surfaces 8A to 8C are ground by feeding the grinding wheel G as shown by the arrow F in FIG. When forming ~ 9C, without extending the first and second tip flank 8A, 8B, the extension line of the portion where the rotation trajectory of the first to third bottom blades 9A-9C forms a hemisphere Since the valley bottom portions of the second and third gashs 7B and 7C have a concave concave section due to the roundness and sagging of the gash grindstone as described above, if they are formed up to the point where they intersect the axis O, these 2nd and 3rd Gash 7 The inner peripheral ends Q of the second and third bottom blades 9B and 9C formed at the intersecting ridge portions of the wall surfaces facing the end mill rotation direction T of 7C and the second and third tip flank surfaces 8B and 8C are: As shown in FIG. 6A, the rotation trajectories of the second and third bottom blades 9B and 9C slightly protrude toward the end mill rotation direction T side from the hemispherical portion.

  However, the second and third tip flank surfaces 8B and 8C formed by the second and third bottom blades 9B and 9C at the intersecting ridge line portions with the wall surfaces of the second and third gashs 7B and 7C are as follows. The clearance angle is given so as to recede from the rotation trajectory toward the end mill rotation direction T, and conversely, the end mill projects in the end mill rotation direction T side with respect to the rotation trajectory. Therefore, as described above, when the inner peripheral ends Q of the second and third bottom blades 9B and 9C protrude toward the end mill rotation direction T, the rotation trajectory around the axis O is also shown in FIG. In addition, protrusions are formed such that these inner peripheral ends Q protrude from the hemisphere formed by the rotation trajectory of the bottom blade 9.

  On the other hand, in the ball end mill having the above configuration, for example, the grinding wheel G is further moved from the state shown in FIG. 6B beyond the axis O as shown by the symbol F in FIG. As shown in FIG. 7 (a), the second tip flank 8A is extended toward the second tip flank 8B to form the extension portion 8c as shown in FIG. It is possible to prevent the inner peripheral end P of the bottom blade 9B from projecting toward the end mill rotation direction T side from the portion of the second bottom blade 9B forming the hemispherical rotation locus.

  As a result, as shown in FIG. 7B, a protrusion projecting from the hemisphere formed by the bottom blade 9 is formed at the inner peripheral end P of the second bottom blade 9B even in the rotation locus around the axis O. Can be prevented. Similarly, the second tip flank 8B is also formed with an extension 8c extending toward the third tip flank 8C, so that a protrusion is formed on the inner peripheral end P of the third bottom blade 9C. It can be prevented from forming.

  7A, for the sake of explanation, the boundary line between the first flank 8a of the first and second tip flank 8A and 8B and its extension 8c (the grinding wheel G is stopped in FIG. 6). The position N) is indicated by a broken line, but the first flank 8a and the extension 8c can be continuously formed by grinding the grinding wheel G. As shown, such a boundary line N can be prevented from appearing on the first and second tip flank surfaces 8A and 8B.

  Therefore, according to the ball end mill having the above-described configuration, it is possible to prevent such a protrusion from causing a streak on the processing surface of the workpiece and causing damage to the processing surface, thereby deteriorating the processing accuracy. Further, it is possible to prevent the protrusion from being broken and biting into the bottom blade 9 during cutting, thereby preventing the bottom blade 9 from being damaged. For this reason, it is possible to promote the extension of the life of the ball end mill while improving the processing accuracy.

  Further, in the ball end mill having the above-described configuration, the first bottom blade 9A intersects the axis O, and the rotation of the first bottom blade 9A as shown by the solid line and the alternate long and short dash line in FIG. The locus itself is a hemisphere having a center C on the axis O. For this reason, for example, even when the groove processing is performed by the ball end mill, the processed groove bottom surface can be accurately formed in a semicircular cross section, and the processing accuracy can be further improved.

  Moreover, the first gash 7A in which the first bottom blade 9A is formed is formed so as to extend beyond the axis O toward the inner peripheral side of the end mill body 1, and communicates with the chip discharge groove 4. A large chip discharge pocket can be secured in the vicinity of the axis O by the first gash 7A. Accordingly, it is possible to improve the discharge performance of the chips generated by the first bottom blade 9A intersecting the axis O in this way, and the first bottom blade 9A may be damaged due to the clogging of chips near the axis O. Can also be prevented.

  Furthermore, in the present embodiment, the first to third gashes 7A to 7C are formed at intervals without crossing each other, so that the strength of the end portion of the end mill body 1 can be ensured. It is possible to more reliably prevent the first to third bottom blades 9A to 9C from being lost. Further, the second and third bottom blades 9B and 9C intersect the first and second concave bent surfaces 10A and 10B at the inner peripheral end P at an obtuse angle. The strength can also be secured, and it is possible to prevent the second and third bottom blades 9B and 9C from being damaged from these inner peripheral ends P. Therefore, according to the ball end mill configured as described above, it is possible to further extend the life.

  However, if the second and third gashs 7B and 7C are formed so as not to cross the axis O, for example, the third gash 7C may be formed so as to intersect the first gash 7A. May be. The concave curved surface 10 may be flat or may be an uneven curved surface. Further, the concave curved surface 10 may intersect the extended portion 8c of the first and second tip flank surfaces 8A and 8B with an angle, or may continue through a concave curved surface.

  Further, in the present embodiment, the included angle θ between the straight line L connecting the inner peripheral end P of the second bottom blade 9B and the center C of the hemisphere formed by the rotation locus of the bottom blade 9 and the axis O is 1 ° to 10 °. The first bottom blade while ensuring the size of the extended portion 8c of the first tip flank 8A and the concave bent surface 10 to a certain extent and reliably preventing the formation of protrusions. It can prevent that the cutting load to 9A becomes large too much, and a defect etc. arise. The same applies to the inner peripheral end P of the third bottom blade 9C.

  That is, when the included angle θ is smaller than the above range, the extension portion 8c of the first tip flank 8A and the concave bent surface 10 also become small, and a protrusion is formed at the inner peripheral end P of the second bottom blade 9B. There is a risk that the formation cannot be reliably prevented. On the other hand, when the included angle θ is larger than the above range, the inner peripheral end P of the second bottom blade 9B is too far from the axis O, and the first bottom blade is located on the inner peripheral side of the inner peripheral end P. The part to be cut by 9A alone becomes too large, and the burden at the time of cutting on the first bottom blade 9A becomes large, so that there is a possibility that chipping occurs or wear is promoted.

  In the present embodiment, the second bottom blade 9B directly intersects the concave bent surface 10 at the inner peripheral end P at an obtuse angle. However, if these extend continuously in a direction intersecting with the obtuse angle, they are continuous. In other words, a chamfered portion, a rounded convex bent portion, or the like may be interposed between the second bottom blade 9B and the concave bent surface 10. In such a case, a straight line L connecting the intersection of the extension line of the second bottom blade 9B and the extension surface of the concave bent surface 10 and the center C of the hemisphere formed by the rotation locus of the bottom blade 9; It is sufficient that the included angle θ formed by is in the range of 1 ° to 10 °. Further, in order for the second bottom blade 9B to be continuous with the concave bent surface 10 so as to extend in an obtuse angle direction, the second bottom blade 9B or the extension line thereof is connected to the concave bent surface 10 or the extension surface thereof. Intersecting ridgeline between the rake face of the second bottom blade 9B, or the ridgeline of the concave bent surface 10 or the extended surface thereof and the tip flank 8B (tip first flank 8a) of the second bottom blade 9B. It suffices if the part intersects an obtuse angle.

  Furthermore, in this embodiment, three short bottom blades 9D are formed every other one in the circumferential direction between the first to third bottom blades 9A to 9C which are long bottom blades as described above. Although the burden of the bottom blade 9 on the outer periphery of the end portion of the end mill body 1 is dispersed, such a short bottom blade 9D may not be formed. Further, in this embodiment, the total three bottom blades 9A to 9C are extended to the vicinity of the axis O in this way, but only the first and second two bottom blades 9A and 9B are of the axis O. It is extended to the vicinity, or four or more bottom blades 9 are extended to the vicinity of the axis O, and one of the bottom blades 9 intersects the axis O as the first bottom blade 9A. It may be done.

DESCRIPTION OF SYMBOLS 1 End mill main body 3 Cutting edge part 4 Chip discharge groove 6 Peripheral blade 7 Gash 7A 1st gash 7B 2nd gash 7C 3rd gash 8 Front end flank 8A First front flank 8B Second front flank 8C Third tip flank 8a Tip first flank 8b Tip second flank 8c Extension 9 Bottom blade 9A First bottom blade 9B Second bottom blade 9C Third bottom blade 9D Short bottom blade 10 Concave bent surface 10A First concave curved surface 10B Second concave curved surface O Axis line of end mill body 1 T End mill rotation direction P Inner peripheral edge C of second and third bottom blades 9B and 9C and short bottom blade 9D C of bottom blade 9 The center L of the hemisphere formed by the rotation trajectory L The straight line connecting the inner peripheral edge P and the center C θ The angle formed by the straight line L and the axis O

Claims (3)

A plurality of chip discharge grooves are formed on the outer periphery of the end portion of the end mill body rotated around the axis at intervals in the circumferential direction, and a gash extending toward the inner peripheral side is formed at the tip of these chip discharge grooves The rotation trajectory around the axis is centered on the axis at the intersection ridgeline between the wall facing the end mill rotation direction of the gasche and the tip flank of the end mill body tip intersecting the wall. A hemispherical bottom blade that is convex on the tip side is formed, and at least two of the bottom blades are extended in the vicinity of the axis at the tip of the end mill body, and at least these Of the two bottom blades, the two above-mentioned gashes in which two bottom blades adjacent to each other in the circumferential direction are formed. A second gash that extends beyond the axis on the front end of the mill body and is positioned rearward in the end mill rotation direction is formed so as not to exceed the axis on the front end of the end mill body. The first bottom blade formed on the wall surface facing the end mill rotation direction of the first gash intersects the axis, and the first tip flank intersecting the first bottom blade is Extending toward the second tip flank that intersects the wall face of the second gash in the end mill rotation direction via the second bottom blade of the two bottom blades. Between the extended portion of the flank and the second tip flank, a concave bent surface extending in the outer peripheral side is formed by continuously bending the extended portion of the first tip flank . 2 bottom blade or its extension line At the intersection ridge line portion of the concave bent surface or its extended surface and the rake face of the second bottom blade, or at the cross ridge line portion of the concave bent surface or its extended surface and the tip flank surface of the second bottom blade by intersecting at an obtuse angle, a ball end mill in which the second end cutting edges, characterized in that are continuous and extend in a direction intersecting at an obtuse angle to the concave curved folding surface.   The angle between the straight line connecting the intersection of the second bottom blade or its extension line and the concave bent surface or its extension surface and the center of the hemisphere formed by the rotation locus of the bottom blade and the axis is 1 °. The ball end mill according to claim 1, wherein the ball end mill is in a range of −10 °.   The three bottom blades are extended in the vicinity of the axis at the end of the end mill body, and among the three gashes formed with these bottom blades, the second gash has a rear end in the rotation direction of the end mill. The third gash located is formed so as not to cross the axis on the tip of the end mill body, and the second tip flank is formed on the wall surface of the third gash facing the end mill rotation direction. It is extended toward the 3rd tip flank which cross | intersects via the 3rd bottom blade of the bottom blades, The extension part of this 2nd tip flank and the said 3rd tip flank In the meantime, a concave bent surface is formed which is continuously bent and extended to the outer peripheral side of the extended portion of the second tip flank, and the third bottom blade intersects the obtuse angle on the concave bent surface. Extending in the direction Ball end mill as claimed in claim 1 or claim 2, characterized in that is.

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