JP2006224254A - Ball end mill - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an excellent finishing surface by securely suppressing a chattering vibration in a cutting machining using an end cutting edge of a ball end mill. <P>SOLUTION: In the ball end mill, a plurality of end cutting edges 7 where a rotating trajectory around an axis line O is in a projective semi-spherical shape of an end mill body 1 are formed at the tip of the end mill body 1 rotating around the axis line O. The plurality of end cutting edges 7 is made to be a convex curve which is convex to the rotating direction T side of the end mill body 1 as seen from the tip in the axis line O direction. The curvature radius of the convex curve where at least the end cutting edge 7a of the end mill body 1 among these end cutting edges 7 is made as seen from the tip in the axis line O direction is made as a different curvature radius of the convex curve where the other end cutting edge 7b are made as seen from the tip in the axis line O direction. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a ball end mill in which a bottom blade whose rotation locus is a convex hemisphere is formed at the tip of an end mill body.

As a rolling tool including this type of ball end mill, the inventors of the present invention disclosed in Patent Document 1 that a plurality of cutting blades having a twist are formed on the outer periphery of an end mill body, and at least one of the plurality of cutting blades. Various proposals have been made in which the twist angle of the other blade is set to be different from the twist angle of other blades. Of these, in the ball end mill, the tip of the blade portion is formed in a hemispherical shape, and the bottom blade extending from the outer peripheral cutting blade tip toward the center of rotation forms a convex hemisphere in the rotation trajectory. The bottom blade has a convex curve that is convex in the rotational direction when viewed from the front end in the axial direction of the end mill body. Therefore, according to such a ball end mill, since the twist angle of the outer peripheral cutting edge is different, the distance between one outer peripheral cutting edge and the adjacent outer peripheral cutting edge is continuously directed in the axial direction. Therefore, since the frequencies generated in the end mill main body are changed by rotation and cancel each other, it is possible to prevent the occurrence of resonance (batter vibration) that deteriorates the finished surface.
Japanese Patent Laid-Open No. 62-203710

  However, the ball end mill as described above is often used to form a curved surface on, for example, a mold by the bottom blade whose rotation locus is a convex hemispherical shape. Even if the torsion angles are set to different angles, it is difficult to suppress the occurrence of chatter vibration as described above. For this reason, in the case of machining such molds, it is not possible to obtain a good cutting surface, and finishing work is required after cutting work. There was a risk of being lost.

  The present invention has been made under such a background, and even in the cutting processing of a die or the like using the bottom edge by the ball end mill as described above, generation of chatter vibration is surely suppressed and a good finished surface is obtained. It is an object of the present invention to provide a ball end mill that can achieve an efficient cutting process that can eliminate the subsequent finishing process.

  In order to solve the above problems and achieve such an object, the present invention provides a plurality of convex hemispheres having a rotational locus around the axis of 1 at the tip of the end mill body rotated around the axis. A ball end mill in which a bottom blade is formed, wherein the plurality of bottom blades form a convex curve that is convex toward the rotation direction of the end mill body in the axial front end view, and at least of these bottom blades The curvature radius of the convex curve formed by one bottom blade in the axial front end view is different from the curvature radius of the convex curve formed by the other bottom blade in the axial front end view.

  Therefore, in such a ball end mill, since the curvature radii of the plurality of bottom blades are different in size, the bottom blade can be machined even if it has a single convex spherical shape with a common rotation locus around the axis. The impact and cutting resistance when biting on the material, or the biting cycle will be different, and the vibrations caused by the bottom blades on the end mill body will be different from each other and will cancel each other. The Rukoto. For this reason, according to the ball end mill having the above-described configuration, chatter vibration due to resonance is not excited even in curved surface cutting of a mold or the like in which this bottom blade is used, and as a result, finishing processing in a subsequent process Thus, it is possible to form an excellent cutting surface that does not need to be achieved, and it is possible to achieve both high finished surface accuracy and improved processing efficiency.

  Here, the curvature of the bottom blade having the smallest curvature radius and the bottom blade having the largest curvature radius among the plurality of bottom blades having different curvature radii of the convex curve formed in the axial front end view. The difference in radius is preferably set in a range of 20% to 50% of the curvature radius of the bottom blade having the largest curvature radius. That is, if the difference in radius of curvature is so small that it is less than 20% of the radius of curvature of the bottom blade having the largest radius of curvature, the impact and cutting resistance acting on each bottom blade will not change so much, and the above-described effect of suppressing chatter vibration will be achieved. May not be successful enough. On the other hand, if the difference in the radius of curvature is so large that it exceeds 50% of the radius of curvature of the bottom blade having the largest radius of curvature, the bottom blade having a large radius of curvature and the bottom blade having a small radius of curvature are particularly separated from each other in the circumferential direction. In such a case, there is an extreme gap in the circumferential interval between these bottom blades, and there is a risk that the chip discharge performance may be impaired at the portion where the bottom blades are close to each other in the circumferential direction. However, in the part spaced apart in the circumferential direction, the cutting amount of the bottom blade on the rear side in the rotational direction becomes large, and wear is remarkably promoted, and the end mill life may be shortened.

  1 and 2 show a first embodiment when the present invention is applied to a two-blade solid ball end mill. In the present embodiment, the end mill body 1 is formed of a hard material used as a cutting tool material such as cemented carbide or high speed steel and has a substantially cylindrical shape centering on the axis O, and the rear end side (FIG. 1). 1) is a cylindrical shank portion 2 and a tip side (right side in FIG. 1) portion is a blade portion 4 provided with a cutting blade 3. The shank portion 2 is a spindle of a machine tool. By being held by the end and rotated in the rotation direction T around the axis O, the workpiece is cut by the cutting blade 3 formed on the blade portion 4.

  In this embodiment, in the blade portion 4, the two chip discharge grooves 5 sandwich the axis O on the outer periphery of the end mill body 1 in the present embodiment, which is twisted in the rotation direction T around the axis O as it goes from the front end side to the rear end side. The rotation trajectory around the axis O forms a single cylindrical surface around the axis O at the outer peripheral side ridge of the wall surface facing the rotation direction T of the chip discharge grooves 5. Thus, the outer peripheral cutting edge 6 of the cutting edges 3 is formed. In the present embodiment, the positions of the tips of the peripheral cutting edges 6 in the circumferential direction are symmetrical positions opposite to each other with respect to the axis O, and are equally spaced in the circumferential direction.

  On the other hand, from the front ends of these outer peripheral cutting edges 6, the outer peripheral cutting edges 6 are smoothly and continuously connected to the inner peripheral axis O toward the front end side of the end mill body 1 as if they are continuous. The bottom blades 7 are formed so as to be curved toward each other, and the bottom blades 7 have a hemispherical shape in which the rotation locus around the axis O has a center on the axis O and protrudes toward the tip side. Has been. Accordingly, in the present embodiment, the cutting edge 3 composed of two outer peripheral cutting edges 6 and a bottom cutting edge 7 is formed on the cutting edge 4 at the tip of the end mill body 1, respectively. Are arranged at equal intervals in the circumferential direction, and the inner peripheral ends thereof are connected to each other on an axis O serving as a rotation center of the distal end portion of the blade portion 4. A gash 8 is formed at the tip of the blade 4 so that a portion in the rotation direction T of the chip discharge groove 5 is cut out.

  Further, these bottom blades 7 are formed to have a smooth convex curve shape that is convex toward the rotation direction T as shown in FIG. 2 when viewed from the front in the axis O direction. When viewed, an S-shape is exhibited in the front view of the axis O direction. In these bottom blades 7, the radius of curvature of the convex curve formed by at least one bottom blade 7 as viewed from the front end in the axis O direction is different from the radius of curvature of the convex curve formed by the other bottom blade 7 as viewed from the front in the axis O direction. In this embodiment, the curvature radii of the convex curves formed by the plurality of bottom blades 7 when viewed from the front in the direction of the axis O are different from each other. The radius of curvature of the convex curve formed by the bottom blade 7a is made smaller than the radius of curvature of the convex curve formed by the other bottom blade 7b located on the lower side in FIG. Accordingly, the curvature of these convex curves is, conversely, that the other bottom blade 7b is smaller than the one bottom blade 7a, that is, the other bottom blade 7b is gentler than the one bottom blade 7a when viewed from the front end of the axis O. It is designed to bend.

  Here, the difference in the radius of curvature of the one bottom blade 7a having a small curvature radius of the convex curve with respect to the other bottom blade 7b having a large curvature radius of the convex curve is the curvature of the other bottom blade 7b. It is made to become the range of 20%-50% of a radius. Further, as described above, the positions of the tips of the outer peripheral cutting edges 6, that is, the positions of the outer peripheral ends of the bottom cutting edge 7 are symmetrical with respect to the axis O in the circumferential direction in the present embodiment, and the inner peripheral ends of the bottom cutting edge 7 are Since this corresponds to the axis O, in this embodiment, the amount of protrusion of the bottom blade 7 that forms a convex curve in the direction of the tip in the direction of the axis O toward the rotation direction T is one bottom blade 7a having a small curvature radius. Is made larger than the other bottom blade 7b having a large curvature radius.

  If the ball end mill configured as described above is used to perform curved surface cutting of a die that uses this bottom blade 7 exclusively, the impact of each bottom blade 7 when it bites into the work material as the end mill body 1 rotates, The resistance is such that one bottom blade 7a having a smaller curvature radius formed by the convex curve gradually bites from the tip toward the rotation direction T side than the bottom blade 7b having a larger curvature radius. Becomes smaller. In addition, in the present embodiment, since the protruding amounts of the convex curves formed by the bottom blades 7a and 7b are different as described above, until one bottom blade 7a bites and the other bottom blade 7b bites. And the period from when the other bottom blade 7b bites to when the one bottom blade 7a bites are different from each other.

  Accordingly, even when cutting is performed while the bottom blades 7a and 7b bite the work material alternately, the vibrations acting on the end mill body 1 from the bottom blades 7a and 7b are different in magnitude. In addition, since the periods are different from each other in the present embodiment, it is possible to reliably prevent the resonance caused by the repetitive action of the vibration having a constant magnitude, that is, chatter vibration from occurring in the end mill body 1. It becomes possible. Then, by appropriately setting the difference between these radii of curvature within the above range, for example, the vibrations acting from these bottom blades 7a and 7b can be canceled and canceled out. Therefore, it is possible to prevent deterioration of the finished surface accuracy due to chatter vibrations, and further to improve the finished surface accuracy, thereby eliminating the trouble of finishing the work material again in a later process. It is possible to promote efficient cutting.

  Further, in this embodiment, the difference in curvature radius of the convex curve formed by the bottom blades 7a and 7b having different curvature radii in this way is 20% to 50% with respect to the curvature radius of the other bottom blade 7b having a larger curvature radius. Thus, it is possible to maintain smooth chip discharge performance and end mill life while more reliably suppressing chatter vibration as described above. That is, if the difference in curvature radius is so small that it is less than 20% of the curvature radius of the bottom blade 7b having a large curvature radius, that is, if the difference in curvature radius between the convex curves formed by the bottom blades 7a and 7b is small, the bottom blade The magnitude and period of the vibration acting on the end mill body 1 from 7a and 7b are not so changed, and there is a possibility that resonance cannot be reliably prevented.

  On the other hand, if the difference between the radii of curvature is too large, the bottom blade 7a having a small curvature radius particularly when the outer peripheral end of the bottom blade 7 is in a symmetric position with respect to the axis O as in this embodiment. , The circumferential interval from the rotation direction T side to the bottom blade 7b having a large curvature radius is reduced, and accordingly, the size of the chip discharge groove 5 and the gash 8 at the tip of the blade portion 4 must be reduced. In some cases, chip clogging may occur. On the other hand, the distance in the circumferential direction from the bottom blade 7b having a large radius of curvature to the bottom blade 7a having a small radius of curvature on the rotation direction T side is large, so that the amount of cutting by the other bottom blade 7b is one. Thus, there is a possibility that the wear of the other bottom blade 7b is promoted more than the one bottom blade 7a, and the life as a ball end mill may be shortened. Therefore, the difference in the radius of curvature is desirably in the range of 20% to 50% as in the present embodiment.

  In this embodiment, the positions of the outer peripheral ends of the bottom blades 7a and 7b and the tips of the outer peripheral cutting blades 6 are arranged at equal intervals in the circumferential direction and symmetrical with respect to the axis O. They may be arranged at equal intervals and asymmetrical with respect to the axis O.

  Next, FIG. 3 and FIG. 4 show a second embodiment when the present invention is applied to a four-blade ball end mill, and the same reference numerals are used for parts common to the first embodiment. Will be omitted. That is, in the ball end mill of the second embodiment, the cutting edge 3 composed of four outer peripheral cutting edges 6 and a bottom cutting edge 7 is provided in the circumferential direction as shown in FIG. The curvature radius of the convex curve which is formed at intervals and is convex in the rotational direction T formed by at least one bottom blade 7 of these cutting blades 4 as viewed from the front in the direction of the axis O is other than The bottom blade 7 has a size different from the radius of curvature of the convex curve formed when viewed from the front in the direction of the axis O, and specifically, a pair of one of the pair of ones positioned on opposite sides with respect to every other axis O around the circumference. The curvature radius of the convex curve of the bottom blade (bottom blade extending in the left-right direction in FIG. 2) 7a is the same as that of the convex curve of the other pair of other bottom blades (bottom blade extending in the vertical direction in FIG. 2) 7b. It is smaller than the radius of curvature.

  Here, in this embodiment, the curvature radius of a pair of said one bottom blade 7a and the curvature radius of the other pair of said other bottom blades 7b are mutually equal. Similarly to the first embodiment, the difference between the curvature radii of the convex curve formed by the other bottom blade 7b having the larger radius of curvature and the one bottom blade 7a having the smaller curvature is the same as the convexity formed by the other bottom blade 7b. The curvature radius of the curve is in the range of 20% to 50%.

  Further, in the present embodiment, as shown in FIG. 4, the other bottom blade 7b has the axis line on the inner peripheral side of the tip end of the blade portion 4 like the bottom blade 7 (bottom blades 7a, 7b) of the first embodiment. The bottom edge 7a of the one bottom blade 7a is positioned slightly away from the axis O toward the outer peripheral side so as not to be continuous with each other. Has been. Furthermore, in the present embodiment, these four bottom blades 7 (7a, 7b) are spaced from the other bottom blade 7b having a large radius of curvature of the convex curve in the rotational direction T side. The distance to one bottom blade 7a having a small curvature radius is larger than the distance from one bottom blade 7a having a small curvature radius of the convex curve to the other bottom blade 7b having a large curvature radius on the rotation direction T side. It is made to become small.

  Therefore, even in the ball end mill of the second embodiment as described above, it is possible to prevent the vibration caused by the plurality of bottom blades 7 from acting periodically with a constant magnitude as in the first embodiment. Generation of chatter vibration can be prevented, and excellent machining accuracy can be achieved with excellent finished surface accuracy. Moreover, since the difference in the radius of curvature of the convex curve formed by these bottom blades 7a and 7b is in the range of 20% to 50% of the large radius of curvature of the other bottom blade 7b, this effect can be reliably achieved. However, it is possible to prevent the chip discharge performance and the end mill life from being impaired.

  Moreover, in this embodiment, the position of the outer peripheral end of the bottom blade 7 is slightly rearward in the rotational direction T in one bottom blade 7a having a larger curvature radius of the convex curve than the positions arranged at equal intervals in the circumferential direction. Recessed portions are unequally spaced in the circumferential direction, whereby the bottom blades 7a and 7b are the most protruding portions in the rotational direction T that form a convex curve that is convex when viewed from the front in the axis O direction. 2 can be arranged so as to be positioned at substantially equal intervals in the circumferential direction as shown in FIG. 2, and therefore, the gap between the bottom blades 7a and 7b is widened. Thus, it is possible to more effectively prevent the end mill life from being shortened due to chip clogging or wear of the other bottom blade 7b. However, instead of setting the positions of the outer peripheral ends of the bottom blades 7 at unequal intervals in the circumferential direction in this way, the outer peripheral ends of the respective bottom blades 7 are substantially in the circumferential direction as shown by two-dot chain lines in FIG. Arranged at equal intervals, or conversely to the above, the outer peripheral end of one bottom blade 7a having a larger radius of curvature than the positions arranged at equal intervals in the circumferential direction is positioned on the rotational direction T side. It may be made.

  Further, in the present embodiment, although the four bottom blades 7 are formed, each of the pair of one bottom blade 7a and the other bottom blade 7b located on the opposite sides of the axis O is respectively Since the radii of curvature are equal, the advantage that the molding is relatively easy is also obtained. However, in this embodiment, the radii of curvature formed by the convex curves of the bottom blade 7 located on the opposite side across the axis O are made equal to each other, but they may be different from each other. The curvature radii of all the bottom blades 7 are different as in the first embodiment, the curvature radii of the two bottom blades 7 are the same, the curvature radii of the remaining two bottom blades 7 are different from each other, and both It may be made different.

  In the first and second embodiments, the bottom blade 7 has two and four even blades, but the present invention is applied to a ball end mill with three or five or more odd or even blades. Of course it is possible. Further, as indicated by the chain line in the first embodiment or the second embodiment, the bottom blades 7 may be equally spaced in the circumferential direction at the outer peripheral end, and the inner peripheral axis is more than this. The bottom blades 7 may be equally spaced on at least one circumference centered on the axis O when viewed from the front in the O direction, or the bottom blades 7 may be unequally spaced on any circumference. It may be made to become. Furthermore, even when the outer peripheral ends of the bottom blades 7 are arranged at equal intervals in the circumferential direction on any of the circumferences or at irregular intervals on any of the circumferences, The twist angles of the cutting blades 6 may be equal to each other, or may be different from each other as in the rolling tool described in the above-mentioned Patent Document 1, and the circumferential interval such as the tip of the outer peripheral cutting blade 6 may be It may be set as an interval or may be set as an unequal interval. On the other hand, the present invention may be applied to a ball end mill in which only the bottom blade 7 is formed at the distal end portion of the end mill body 1 without including the outer peripheral cutting blade 6.

It is a side view which shows the 1st Embodiment of this invention. It is a front view of the axis line O direction front view of embodiment shown in FIG. It is a side view which shows the 2nd Embodiment of this invention. FIG. 4 is a front view of the embodiment shown in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 End mill main body 3 Cutting blade 4 Blade part 6 Peripheral cutting blade 7 Bottom blade 7a One bottom blade 7b in which the curvature radius of the convex curve formed in the axial O direction front view is reduced 7b The curvature radius of the convex curve formed in the axial O direction front view The other bottom blade with an increased O O End mill body 1 axis T Rotation direction of end mill body 1

Claims (2)

  A ball end mill in which a plurality of bottom blades having a convex hemisphere having a rotation locus around the axis is formed at a tip portion of an end mill body rotated around an axis, wherein the plurality of bottom blades are A convex curve that is convex toward the rotational direction of the end mill body is formed in the axial front end view, and at least one of the bottom blades has a curvature radius of the convex curve that is formed in the axial front end view. A ball end mill characterized in that a bottom blade has a size different from a radius of curvature of a convex curve formed in the axial front end view. Among the plurality of bottom blades, the difference in curvature radius between the bottom blade having the smallest curvature radius and the bottom blade having the largest curvature radius is 20% to 50% of the curvature radius of the bottom blade having the largest curvature radius. The ball end mill according to claim 1, wherein the ball end mill is in the range.

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