JP2016005860A - Scanline processing method using ball end mill - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for applying precise scanline-processing to high-hardness steel like finish processing even if an axial cut-in amount is larger like rough processing.SOLUTION: A method applies scanline-processing to high-hardness steel whose HRC is not lower than 40 by using a ball end mill having four pieces or more of blades. Each cutting edge of the ball end mill is constituted of a ball blade whose curved angle is 35 to 45°, and an external peripheral blade which is smoothly connected to the ball blade and whose torsion angle is 35 to 45°. The method performs the scanline-processing at a feed speed Vf which is not lower than 500 mm/min with a rake angle of the ball blade in a radial direction set as a negative angle, a rake angle of the external peripheral blade in the radial direction set as a positive angle, and a cut-in amount ap in an axial direction set as ten times or larger of a cut-in amount ae in the radial direction.

Description

  The present invention relates to a method for scanning line processing using a ball end mill capable of high-precision scanning line processing into a three-dimensional shape as in finishing processing even with a large axial depth of cut, such as roughing, for high hardness steel materials. .

  A mold for molding a material at a high temperature changes in shape due to heat cracking or softening as it is used. Therefore, an operation (resync) of cutting the molding surface of the mold to regenerate the molding cavity is performed. Particularly in the case of a die for hot forging or cold forging, a hard nitrided layer is often formed on the surface, and the hard nitrided layer is removed during resynchronization, so the tool requires high durability. Is done.

  A scanning line processing method using a ball end mill is known per se. For example, Japanese Patent Application Laid-Open No. 2005-096044 (Patent Document 1) includes a substantially hemispherical ball portion on which a ball blade is formed and an outer peripheral blade following the ball blade. It is disclosed that scanning line finishing is performed using a ball end mill that has a step between the flank face of the ball blade and the flank face of the outer peripheral blade. Patent Document 1 describes that after this scanning line finishing process, a manual polishing step for final finishing is not required or can be alleviated. However, as described in the example of scanning line machining using a 2-flute ball end mill with an axial cutting depth of 0.15 mm, the scanning line machining described in Patent Document 1 has very small axial cutting. Limited to finishing.

  Japanese Patent Laid-Open No. 5-337718 (Patent Document 2) discloses a ball end mill having a plurality of ball blades and an outer peripheral blade, in which the core thickness of the outer peripheral blade portion is set in the range of 70 to 90% of the tool blade diameter, and the outer peripheral blade. Discloses a ball end mill having a rake angle of −30 to 0 °. Patent Document 2 describes an example of cutting with an axial cutting depth of 10 mm using this ball end mill. However, since the outer helix angle is as small as 25 °, the rigidity of one blade is low and it is not suitable for high-efficiency cutting.

  Japanese Patent No. 4407975 (Patent Document 3) is a ball end mill in which a hemispherical ball blade is provided at the tip of a tool body, wherein the ball blade includes a first blade portion having a rotation axis as a starting end, and a first blade portion. A first blade having a second blade connected to the end and a third blade connected to the end of the second blade, wherein the first blade is convex in the rotational direction when viewed from the distal end in the rotational axis direction; It has an arc shape (circumferential angle 60 to 120 °) having a radius (0.025 to 0.10 times the outer diameter D), and the second blade portion has a second curvature radius (greater than the first curvature radius) convex in the rotational direction. It discloses a three-blade ball end mill that has an arc shape or a linear shape, and the third blade portion has an arc shape having a convex third curvature radius (smaller than the second curvature radius) in the rotation direction. Patent Document 3 describes that since the ball blade can be lengthened, the contact area between the work material and the ball blade can be expanded, and the machinability can be improved, and as a result, the feed speed and the cutting depth can be increased. doing. However, since the ball end mill of Patent Document 3 is not smoothly connected to the ball blade and the outer peripheral blade, it is not only suitable for processing using the outer peripheral blade, and the ball blade has a small helix angle and requires high rigidity. Not suitable for high-efficiency machining.

  Japanese Patent Laid-Open No. 2001-179519 (Patent Document 4) is a method of contouring a work material using a ball end mill, in which the ball end mill is cut in a predetermined amount in a first direction parallel to the rotation axis. A method is disclosed in which the ball end mill is moved in a second direction orthogonal to the first direction along a predetermined tool path in each cutting step, and the cutting amount in the first direction in each cutting step is sequentially reduced. Patent Document 4 describes that the wear (boundary wear) generated at the boundary between the cutting portion and the non-cutting portion of the ball end mill is reduced by sequentially reducing the cutting amount in the first direction, thereby extending the tool life. ing. However, since the method of Patent Document 4 is contour processing, a large number of multidirectional cutting streaks remain on the cutting surface. Such a cutting streak is difficult to remove even by scanning line finishing, and there is a problem that a polishing step is required.

Japanese Unexamined Patent Publication No. 2005-096044 JP-A-5-337718 Japanese Patent No. 4407975 JP 2001-179519 JP

  Therefore, the object of the present invention is to form a three-dimensional shape with a high degree of accuracy, such as finishing, even in the case of resynchronization processing or direct engraving processing on a hard steel material, even in the case of a large axial cut amount as in roughing. To provide a method of scanning line processing using a ball end mill capable of scanning line processing.

  As a result of diligent research in view of the above object, the present inventor has found that even a high-hardness steel material has a ball blade that is greatly curved and smoothly connected to the outer peripheral blade, and the radial rake angle of the ball blade is a negative angle. And, using a ball end mill with a rake angle in the radial direction of the outer peripheral blade as a positive angle, it was discovered that high-precision scanning line machining can be performed with a large axial cutting amount and a high feed rate, and the present invention has been conceived. .

The method of the present invention for scanning line machining a high hardness steel material of HRC 40 or more using a ball end mill of 4 blades or more,
Each cutting edge is constituted by a ball blade having a bending angle of 35 to 45 ° and an outer peripheral blade having a twist angle of 35 to 45 ° smoothly connected thereto, and the radial rake angle of the ball blade is a negative angle, Using a ball end mill with the rake angle in the radial direction of the outer peripheral blade as a regular angle,
The scanning line machining is characterized in that the axial cutting amount ap is 10 times or more the radial cutting amount ae and the scanning line machining is performed at a feed speed Vf of 500 mm / min or more.

  The axial cut amount ap is preferably 0.5 to 3.0 times the diameter D of the cutting edge portion. Moreover, it is preferable that the ratio of the axial cut amount ap and the radial cut amount ae is 10 to 200.

  The cutting speed Vc is preferably 40 to 300 m / min, and the tool feed speed Vf is preferably 500 to 4500 mm / min.

  The rake face of the ball blade of the ball end mill used for the scanning line processing is a curved surface convex in the rotation direction, and the degree of curvature of the convex curved surface (falling down to the line segment connecting the vertices of the convex curved surface to both ends of the convex curved surface) The ratio of the length of the vertical line and the length of the line segment connecting both ends of the convex curved surface is preferably 1 to 10%.

  It is preferable that the radial rake angle of the ball blade is −37 to −11 °, and the radial rake angle of the outer peripheral blade is +2 to + 12 °.

  The ball blades are preferably arranged in an unevenly divided manner in the circumferential direction around the rotation axis of the ball end mill. The unequal division angle of the ball blade is preferably 2 to 5 °.

  The scanning line processing method of the present invention is preferably used to resink a used mold made of a high hardness steel material of HRC 40 or more and having a hardened layer on the surface.

  The maximum surface roughness Rz of the steel material after the scanning line roughing is preferably 6.5 or less.

  The method of the present invention has a cutting edge constituted by a ball blade having a bending angle of 35 to 45 ° and an outer peripheral blade having a twist angle of 35 to 45 ° smoothly connected thereto, and the radial rake of the ball blade is obtained. Because a ball end mill with a negative angle and a positive rake angle in the radial direction of the outer peripheral edge is used, high-hardness steel with HRC 40 or more can be finished with a large axial depth of cut as in roughing. Such scanning line processing with high processing accuracy can be performed efficiently. For this reason, resynchronization of a mold having a hard surface layer can be performed with a finishing accuracy by one scanning line processing. In addition, scanning line processing can be performed with high efficiency even by direct engraving of a rectangular parallelepiped work material.

It is a side view which shows an example of the 4-flute ball end mill used for the scanning line processing method of this invention. FIG. 2 is a front view showing a ball blade of the four-blade ball end mill of FIG. FIG. 2 is an enlarged view showing a trajectory of a ball blade of the four-blade ball end mill of FIG. FIG. 2 is an enlarged front view showing an example of a medium-low gradient blade of the four-blade ball end mill of FIG. FIG. 2 is a cross-sectional view taken along the line II of the four-blade ball end mill of FIG. FIG. 2 is a sectional view of the four-blade ball end mill of FIG. 1 taken along the line II-II. FIG. 3 is a III-III cross-sectional view of the four-blade ball end mill of FIG. FIG. 4 is a cross-sectional view taken along the line IV-IV of the four-blade ball end mill of FIG. It is a side view which shows an example of the 5-flute ball end mill used for the scanning line processing method of this invention. FIG. 7 is a partially enlarged front view showing a ball blade of the five-blade ball end mill of FIG. FIG. 7 is a cross-sectional view taken along the line II of the five-blade ball end mill of FIG. FIG. 7 is a II-II sectional view of the five-blade ball end mill of FIG. FIG. 7 is a III-III cross-sectional view of the five-blade ball end mill of FIG. FIG. 7 is a IV-IV cross-sectional view of the five-blade ball end mill of FIG. It is a side view which shows an example of the 6-flute ball end mill used for the scanning line processing method of this invention. FIG. 10 is an enlarged front view showing a cutting edge in a ball portion of the six-blade ball end mill of FIG. FIG. 10 is a cross-sectional view taken along the line II of the six-blade ball end mill of FIG. FIG. 10 is a sectional view of the six-blade ball end mill of FIG. 9 taken along the line II-II. FIG. 10 is a sectional view of the six-blade ball end mill of FIG. 9 taken along the line III-III. FIG. 10 is a cross-sectional view of the six-blade ball end mill of FIG. 9 taken along the line IV-IV. It is the schematic which shows the process of the scanning line processing method of this invention. It is the schematic which shows the processing path of the scanning line processing method of this invention. It is the schematic which shows the process of the contour line processing method. It is the schematic which shows the processing path of contour line processing. It is a schematic perspective view which shows the process path | route of the conventional scanning line finishing process. It is a perspective view which shows an example of the metal mold | die processed by the scanning line processing method of this invention.

  Embodiments of the present invention will be described below in detail with reference to the accompanying drawings, but the present invention is of course not limited thereto. The description regarding each embodiment is applicable also to other embodiment unless there is particular notice.

  The scanning line processing method of the present invention is suitable for processing a high hardness steel material having a Rockwell hardness of HRC 40 or more. The upper limit of the HRC of the work material is not particularly limited, but is practically about 65. For example, in the case of a mold to be resynced, even if it has a hardened layer (nitrided layer) with an HRC of 65 to 75 on the surface, it can be processed with high efficiency and high accuracy by the scanning line processing method of the present invention. As will be described later, the scanning line machining method of the present invention has a large depth of cut and feed amount and high cutting efficiency, so it can be referred to as “rough machining”. No finishing process is required. Therefore, the method of the present invention is not limited to roughing.

[1] Ball End Mill The number of blades of the ball end mill used in the present invention is 4 or more, preferably 4 to 6. Within this range, the number of blades of the ball end mill may be appropriately selected according to the scanning line machining conditions and the work material. If the number of blades is 3 or less, the machining efficiency is low, so it is not suitable for high efficiency machining. In addition, it is not only difficult to increase the number of blades to 7 or more with an outer diameter of a ball end mill that is suitable for scanning line machining with finishing machining accuracy. May cause clogging and cause chipping.

  In order to perform scanning line machining with a finishing depth with a large depth of cut and feed amount, it is preferable to set the diameter D of the ball end mill to 0.5 to 20 mm. When the diameter of the ball end mill is less than 0.5 mm, chipping tends to occur because the space for discharging chips is small. On the other hand, if the diameter of the ball end mill exceeds 20 mm, precise machining becomes difficult.

  The blade length L of the ball end mill is preferably 0.5D to 3.0D. If the blade length L is less than 0.5D, the outer peripheral blade cannot be formed. If the blade length L exceeds 3D, the rigidity of the ball end mill decreases.

(1) Four-Flute Ball End Mill FIGS. 1 to 4 show an example of a ball end mill 40 suitable for the scanning line processing method of the present invention. This ball end mill includes a cylindrical shank portion 2 and a cutting edge portion 3. The cutting edge portion 3 includes a ball portion 3a at the tip, and an outer peripheral blade portion 3b between the ball portion 3a and the shank portion 2. The cutting blade portion 3 is formed with four cutting blades 5a, 5b, 5c, 5d having a predetermined twist angle, and each cutting blade 5a-5d is an arc-shaped ball blade 6a formed on the ball portion 3a. , 6b, 6c, 6d and spiral outer peripheral blades 7a, 7b, 7c, 7d formed on the outer peripheral blade portion 3b. Each ball blade 6a-6d and each outer peripheral blade 7a-7d are smooth (bending points). Without connection). As shown in FIG. 2, four ball blades 6a to 6d are arranged around the rotation center point O via the gashes 17a to 17d in the ball portion 3a, respectively.

  In order to increase the rigidity of the ball blades 6a to 6d and suppress chipping during cutting, the bending angle γ3 of each of the ball blades 6a to 6d is preferably 35 to 45 °, and more preferably 37 to 43 °. The bending angle λ3 is an angle formed by a tangent L1 at the start point P (P1, P2, P3, P4) of each of the ball blades 6a to 6d and a straight line L2 passing through the start point P and the end point T3 of the ball blade. If the bending angle λ3 is less than 35 °, the resistance applied to each of the ball blades 6a to 6d is large, so that there is a high possibility that chipping will occur. On the other hand, when the bending angle λ3 is greater than 45 °, the load applied to the work material is large, and chatter vibration is generated, resulting in deterioration of the machined surface quality. In this specification, a point U (U1, U2) approximately 0.01D from the start point P (P1, P2, P3, P4) of each ball blade 6a to 6d is used as the tangent L1 at the start point P of the ball blade. , U3, U4).

  The bending angle λ1 of each ball blade at a position T1 of 0.5D from the rotation center axis O is preferably 6 to 13 °, and the bending angle λ2 of each ball blade at a position T2 of 0.75D from the rotation center axis O is 14 to 22 ° is preferred. The bending angle λ1 is an angle formed between a tangent L1 at the starting point P of each ball blade and a straight line L3 passing through a point T1 located at a position 0.5D from the rotation center axis O of each ball blade. The bending angle λ2 is an angle formed by a tangent L1 at the starting point P of each ball blade and a straight line L3 passing through a point T2 at a position 0.75D from the rotation center axis O of each ball blade.

  In order to increase the rigidity of the outer peripheral blades 7a to 7d and suppress chipping during side cutting, the twist angle η of each outer peripheral blade 7a to 7d is preferably 35 to 45 °, and more preferably 37 to 43 °. When the twist angle η is less than 35 °, the resistance applied to each outer peripheral blade is large, so that there is a high possibility that chipping will occur. On the other hand, when the torsion angle η is greater than 45 °, chatter vibration due to an increase in the load applied to the work material occurs, resulting in a deterioration of the machined surface quality.

  As described above, since the ball blade has a large curvature angle λ1 and a large torsion angle η of the outer peripheral blade, the rigidity of the cutting edge can be increased, and thus the load applied when removing the surface hard layer of the work material in resynchronization or the like can be increased. Can withstand.

  In the ball end mill, in order to reduce chatter vibration, it is preferable to dispose the ball blades 6a to 6d in an irregular manner in the circumferential direction around the rotation axis. The division angle in unequal division is desirably 2 to 5 °. When the division angle is smaller than 2 °, the effect of suppressing chatter vibration is insufficient. On the other hand, if the split angle is larger than 5 °, the load applied to each ball blade increases, and there is a concern that chipping and breakage increase.

  As shown in FIGS. 2 and 3, scoop surfaces 11a to 11d (only 11a is visible in FIG. 3) are formed in the front of the ball blades 6a to 6d in the rotational direction, and the flank (land) is rearward in the rotational direction. 9a, 9b, 9c, 9d are formed. Further, gashes 17a to 17d are formed in front of the rake faces 11a to 11d in the rotation direction, and the gashes 17a to 17d constitute a part of each chip discharge groove 4.

  3 and 4 show the vicinity of the rotation center point O of the ball portion 3a. Ball blades 6a to 6d (only 6a and 6c are visible in FIG. 3) are points P1, P2, P3, and P4 near the rotation center point O from the outer periphery of the cutting edge 3 (only P1 and P3 are visible in FIG. 6). It extends to. Middle and low gradient blades 8a, 8b, 8c, and 8d extend between the points P1 to P4 and the rotation center point O. Therefore, the points P1 to P4 can be called the tips of the ball blades 6a to 6d, the outer ends of the medium / low gradient blades 8a to 8d, or the connection points between the ball blades 6a to 6d and the medium / low gradient blades 8a to 8d. Relief surfaces 10a, 10b, 10c, and 10d are formed at the rear in the rotational direction of the medium and low gradient blades 8a to 8d. Each flank 10a-10d is connected to the corresponding ball blade flank 9a-9d via boundary lines 15a, 15b, 15c, 15d.

  As is apparent from FIG. 4, each of the medium and low gradient blades 8a to 8d extends from the rotation center point O to the respective points K1 to K4 and is curved backward from the rotation direction, and from each of the points K1 to K4. It consists of a ball blade extension extending to points P1 to P4.

  As shown in FIG. 3, each of the medium and low gradient blades 8a to 8d is inclined at a minute inclination angle α with respect to the plane orthogonal to the rotation axis Ax so that the rotation center point O is the last point in the rotation axis direction. Yes. As a result, the medium and low gradient blades 8a to 8d located inside the tips P1 to P4 of the ball blades 6a to 6d form a very shallow recess 13 having a minute width T. As shown in FIG. 4, the recess 13 is represented by a circle C centered on the rotation center point O and passing through connection points P1 to P4 between the medium and low gradient blades 8a to 8d and the ball blades 6a to 6d.

  The inclination angle α of each of the medium and low gradient blades 8a to 8d is preferably 0.5 to 3 °. When the inclination angle α exceeds 3 °, the cutting edges near the points P1 to P4 (ball blades 6a to 6d and medium to low gradient blades 8a to 8d Early wear and chipping of the end portion are likely to occur. In addition, when the inclination angle α is smaller than 0.5 °, the medium and low gradient blades 8a to 8d near the rotation center point O are likely to come into contact with the work material, and the effect of the medium and low gradient blades 8a to 8d that reduce cutting resistance is achieved. Disappear. A more preferable inclination angle α is 1 to 2 °. As described above, since each of the medium and low gradient blades 8a to 8d is inclined rearward in the rotation axis direction with a minute inclination angle, chatter vibration can be suppressed in high feed cutting.

  The ball portion 3a and the outer peripheral blade portion 3b of the four-blade ball end mill 40 (FIG. 1) have different cross-sectional shapes (perpendicular to the rotation axis) along the rotation axis. Fig. 5 (a) shows the II cross section at a position separated by 0.10D in the rotational axis direction from the connection points P1 to P4 between the medium and low gradient blades 8a to 8d and the ball blades 6a to 6d, and Fig. 5 (b) shows the connection. Fig. 5 (c) shows the II-II cross section at a position 0.25D away from the points P1 to P4 in the rotation axis direction, and Fig. 5 (c) shows the III-III cross section at a position 0.40D away from the connection points P1 to P4 in the rotation axis direction. FIG. 5 (d) shows an IV-IV cross section at a position separated from the connection points P1 to P4 by 0.70D in the rotation axis direction.

  As shown in FIG. 5 (a), at the tip side position (II cross section) of the ball blades 6a to 6d adjacent to the connection points P1 to P4 of the medium and low gradient blades 8a to 8d and the ball blades 6a to 6d, each chip The discharge groove 4 includes a groove bottom surface 4a and a relatively small groove wall surface 4b. In the II cross section, the radial rake angle δ1 of each of the ball blades 6a to 6d is preferably −37 to −11 °, and more preferably −32 to −16 °. When the rake angle δ1 in the radial direction of each of the ball blades 6a to 6d is less than −37 ° or more than −11 °, the rigidity and the edge strength are low, and stable cutting of a high-hardness material cannot be performed.

  As shown in FIG. 5 (b), the intermediate point between the connection points P1 to P4 of the medium and low gradient blades 8a to 8d and the ball blades 6a to 6d, and the connection point T3 of the ball blades 6a to 6d and the outer peripheral blades 7a to 7d. At the point (II-II cross section), each chip discharge groove 4 is composed of a groove bottom surface 4a and a groove wall surface 4b enlarged from the II cross section. Also in the II-II cross section, the radial rake angle δ2 of each of the ball blades 6a to 6d is preferably −37 to −11 °, more preferably −32 to −16 °.

  As shown in FIG. 5 (c), at the connection point T3 (III-III cross section) of the ball blades 6a to 6d and the outer peripheral blades 7a to 7d, the short first rake faces 11a to 11d of the ball blades 6a to 6d are The concave second rake faces 71a to 71d are connected via a boundary (bending point) 47. The second rake surfaces 71a to 71d constitute a chip discharge groove 4 composed of a groove wall surface 4b and a groove bottom surface 4a extending from the clearance surface of the ball blade forward in the rotation direction. Also in the III-III cross section, the radial rake angle δ3 of each of the ball blades 6a to 6d is preferably −37 to −11 °, more preferably −32 to −16 °.

  The second radial rake angle γ1 shown in FIG. 5 (c) is preferably 0 to 12 °, and more preferably 2 to 10 °. When the second radial rake angle γ1 is less than 0 ° or more than 12 °, the rigidity of the cutting edge and the strength of the cutting edge decrease, and stable cutting of a hard material cannot be performed.

  In order to increase the rigidity and cutting edge strength of the cutting edge, the rotational axis distance from the connection points P1 to P4 between the medium and low gradient blades 8a to 8d and the ball blades 6a to 6d is from 0.10D (II section) to 0.40D (III- It is preferable to gradually increase the rake angle in the radial direction of the ball blades 6a to 6d within a range of −37 to −11 ° until the (III section).

  As shown in FIG. 5 (d), the second rake faces 71a to 71d reach the outer peripheral blades 7a to 7d at a position (IV-IV cross section) separated from the connecting points P1 to P4 by 0.70D in the rotation axis direction. ing. The second rake faces 71a to 71d are smoothly connected to the flank faces 70a to 70d of the outer peripheral blades forward in the rotational direction via the groove bottom face 4a to constitute the chip discharge groove 4. In the IV-IV cross section, the radial rake angle β1 of the outer peripheral blades 7a to 7d is preferably +2 to + 12 °, more preferably +4 to + 10 °. When the rake angle β1 in the radial direction of the outer peripheral blades 7a to 7d is less than + 2 ° or more than + 12 °, the rigidity of the cutting edge and the strength of the cutting edge are lowered, and stable cutting of a high-hardness material cannot be performed.

  As shown in FIGS. 5 (a) and 5 (b) showing a cross section perpendicular to the rotation axis, the rake surfaces 11a to 11d of the ball blades 6a to 6d are preferably curved surfaces convex in the rotation direction. The degree of curvature of the convex curved surface of each rake face 11a to 11d is expressed by the ratio h / g of the length h of the perpendicular line dropped from the vertex of the convex curved surface to the length g of the line segment connecting both ends of the convex curved surface. Is done. The curvature h / g of the convex curved surface of each rake face 11a to 11d is preferably 1 to 10% (for example, 3%). If the curvature h / g of the convex surfaces of the rake surfaces 11a to 11d of each ball blade 6a to 6d is less than 1%, the rigidity and cutting edge strength of the ball part 3a are insufficient, and if it exceeds 10%, the machinability deteriorates. It becomes easy to generate chipping. A more preferable range of the curvature h / g of the convex curved surfaces of the rake surfaces 11a to 11d of the ball blades 6a to 6d is 1 to 8%.

(2) Five-Flute Ball End Mill FIG. 6 shows an example of a five-flute ball end mill 50 used in the scanning line machining method of the present invention, and FIG. In FIG. 6, the same reference numerals are assigned to the same portions as the above-described four-blade ball end mill 40. The five-blade ball end mill 50 is integrated with five ball blades 6a, 6b, 6c, 6d, 6e and the ends P1, P2, P3, P4, P5 of each ball blade 6a, 6b, 6c, 6d, 6e. Middle and low gradient blades 8a, 8b, 8c, 8d, 8e extending to the rotation center point O. Gashes 17a, 17b, 17c, 17d, and 17e are formed in front of the ball blades 6a, 6b, 6c, 6d, and 6e in the rotation direction.

  The ball portion 3a and the outer peripheral blade portion 3b of the five-blade ball end mill 50 (FIG. 6) have different cross-sectional shapes (perpendicular to the rotation axis) along the rotation axis. Fig. 8 (a) shows the II cross section at a position separated by 0.10D in the rotation axis direction from the connection point P1-P5 between the medium and low gradient blades 8a-8e and the ball blades 6a-6e, and Fig. 8 (b) is the connection Fig. 8 (c) shows the II-II cross section at a position separated by 0.25D from the points P1 to P5 in the rotation axis direction, and Fig. 8 (c) shows the III-III cross section at a position separated by 0.40D from the connection points P1 to P5 in the rotation axis direction. FIG. 8 (d) shows an IV-IV cross section at a position separated from the connecting points P1 to P5 by 0.70D in the rotation axis direction.

  As shown in FIG. 8 (a) and FIG. 8 (b), the tip side position (II cross section) of the ball blades 6a to 6e adjacent to the connection points P1 to P5, and the connection points P1 to P5 and the ball blades 6a to 6e. At a substantially intermediate point (II-II cross section) between the connecting point of the outer peripheral blades 7a to 7e and the cutting edge 4 to the rotation direction front, the chip discharge groove 4 is connected to the groove bottom surface 4a connected to the rake surfaces 11a to 11e of the ball blades 6a to 6e. And a groove wall surface 4b extending from the flank face of each of the ball blades 6a to 6e.

  The radial rake angles δ4 and δ5 of the ball blades 6a to 6e shown in FIGS. 8 (a) and 8 (b) are each preferably −37 to −11 °, more preferably −32 to −16 °. When the radial rake angles δ4 and δ5 of the ball blades 6a to 6e are less than −37 ° or more than −11 °, the rigidity of the cutting edge and the strength of the cutting edge are lowered, and stable cutting of a hard material cannot be performed.

  As shown in FIG. 8 (c), at the connection point (III-III cross section) of the ball blades 6a to 6e and the outer peripheral blades 7a to 7e separated by 0.40D in the rotation axis direction from the connection points P1 to P5, the ball blade 6a The short first rake surfaces 11a to 11e of ˜6e are connected to the concave second rake surfaces 71a to 71e via the boundary (bending point) 47. The second rake face surfaces 71a to 71e constitute the groove wall face 4b and the chip discharge groove 4 via the groove bottom face 4a. Even in the III-III cross section, the rake angle δ6 in the 6a to 6e radial direction of the ball blade is preferably −37 to −11 °, more preferably −32 to −16 °.

  In the III-III cross section, the second radial rake angle γ2 is preferably 0 to + 12 °, more preferably +2 to + 10 °. When the second radial rake angle γ2 is less than 0 ° or more than + 12 °, the rigidity and cutting edge strength of the cutting edge decrease, and stable cutting of a hard material cannot be performed.

  As shown in FIG. 8 (d), at the position 0.74D away from the connection points P1 to P5 in the rotation axis direction (IV-IV cross section), the concave second rake faces 71a to 71e are the outer peripheral blades 7a to 7e. Has reached. The second rake surfaces 71a to 71e are smoothly connected to the groove wall surface 4b extending from the outer peripheral blade at the front in the rotational direction via the groove bottom surface 4a to constitute the chip discharge groove 4. In the IV-IV cross section, the radial rake angle β2 of the outer peripheral blades 7a to 7e is preferably +2 to + 12 °, more preferably +4 to + 10 °. When the rake angle β2 in the radial direction of the outer peripheral blades 7a to 7e is less than + 2 ° or more than + 12 °, the rigidity of the cutting edge and the strength of the cutting edge are lowered, and stable cutting of a high-hardness material cannot be performed.

  As shown in FIG. 8 (a) and FIG. 8 (b), the rake surfaces 11a to 11e of the ball blades 6a to 6e are preferably curved surfaces convex in the rotational direction. The curvature h / g of the convex curved surface of each rake face 11a to 11e is preferably 1 to 10%, and more preferably 1 to 8%.

(3) Six-Flute Ball End Mill FIG. 9 shows a six-flute ball end mill 60 used in the scanning line processing method of the present invention, and FIG. 9 to 10, the same reference numerals are assigned to the same parts as the four-blade ball end mill 40 described above. The six-blade ball end mill 60 is integrally formed from six ball blades 6a, 6b, 6c, 6d, 6e, 6f and ends P1, P2, P3, P4, P5, P6 of each ball blade 6a-6f. It has medium and low gradient blades 8a, 8b, 8c, 8d, 8e, 8f extending to the rotation center point O. Gashes 17a, 17b, 17c, 17d, 17e, and 17f are formed in front of the ball blades 6a to 6f in the rotation direction.

  Although not shown, the medium and low gradient blades 8a to 8f are orthogonal to the rotation axis so that the rotation center point O is located rearward in the rotation axis direction from the connecting portions P1 to P6 with the ball blades 6a to 6f. It is inclined with respect to the surface at an inclination angle α of 0.5 to 3 °.

  The ball portion 3a and the outer peripheral blade portion 3b of the six-blade ball end mill 1 (FIG. 9) have different cross-sectional shapes (perpendicular to the rotation axis) along the rotation axis. Fig. 11 (a) shows the II cross section at a position separated by 0.10D in the rotational axis direction from the connection points P1 to P6 of the medium and low gradient blades 8a to 8f and the ball blades 6a to 6f, and Fig. 11 (b) is the connection Fig. 11 (c) shows the II-II cross section at a position separated from the points P1 to P6 by 0.25D in the rotational axis direction, and Fig. 11 (c) shows the III-III cross section at a position separated by 0.40D from the connection points P1 to P6 in the rotational axis direction. FIG. 11 (d) shows an IV-IV cross section at a position separated from the connection points P1 to P6 by 0.70D in the rotation axis direction.

  As shown in FIG. 11 (a) and FIG. 11 (b), the tip side position (II cross section) of the ball blade adjacent to the connection points P1 to P6, and the connection points P1 to P6, the ball blades 6a to 6f, and the outer peripheral blade At a substantially intermediate point (II-II cross section) with the connection point with 7a to 7f, the chip discharge groove 4 is a groove bottom surface 4a connected to the rake faces 11a to 11f of the ball blades 6a to 6f and a ball blade forward in the rotation direction. The groove wall surface 4b extends from the flank surfaces 6a to 6f.

  The radial rake angles δ7 and δ8 of the ball blades 6a to 6f shown in FIGS. 11 (a) and 11 (b) are each preferably −37 to −11 °, and more preferably −32 to −16 °. When the radial rake angles δ7 and δ8 of the ball blades 6a to 6f are less than −37 ° or greater than −11 °, the rigidity of the cutting edge and the strength of the cutting edge are lowered, and stable cutting of a hard material cannot be performed.

  As shown in FIG. 11 (c), at the connection point (III-III cross section) of the ball blades 6a to 6f and the outer peripheral blades 7a to 7f separated by 0.40D in the rotation axis direction from the connection points P1 to P6, the ball blade 6a The short first rake face 11b of ˜6f is connected to the concave second rake face 71a to 71f via a boundary (bending point) 47. The second rake surfaces 71a to 71f constitute the groove wall surface 4b and the chip discharge groove 4 via the groove bottom surface 4a. Even in the III-III cross section, the rake angle δ9 in the 6a to 6f radial direction of the ball blade is preferably −37 to −11 °, more preferably −32 to −16 °.

  In the III-III cross section, the second radial rake angle γ3 is preferably +0 to + 12 °, more preferably +2 to + 10 °. When the second radial rake angle γ3 is less than 0 ° or more than 12 °, the rigidity of the cutting edge and the strength of the cutting edge are lowered, and stable cutting of a hard material cannot be performed.

  In the six-blade ball end mill 60, in order to increase the rigidity and cutting edge strength of the cutting edge, the rotational axis distance from the connection points P1 to P6 between the medium and low gradient blades 8a to 8f and the ball blades 6a to 6f is 0.10D (II It is preferable to gradually increase the rake angle in the radial direction of the ball blades 6a to 6f within a range of −37 to −11 ° from the cross section) to 0.40D (III-III cross section).

  As shown in FIG. 11 (d), at the position 0.74D away from the connection points P1 to P6 in the rotation axis direction (IV-IV cross section), the concave second rake faces 71a to 71f are the outer peripheral blades 7a to 7f. Has reached. The second rake surfaces 71a to 71f are smoothly connected to the groove wall surface 4b extending from the outer peripheral blade at the front in the rotational direction via the groove bottom surface 4a to constitute the chip discharge groove 4. In the IV-IV cross section, the radial rake angle β3 of the outer peripheral blades 7a to 7e is preferably +2 to + 12 °, and more preferably +4 to + 10 °. When the rake angle β3 in the radial direction of the outer peripheral blades 7a to 7f is less than + 2 ° or more than + 12 °, the rigidity of the cutting edge and the strength of the cutting edge are lowered, and stable cutting of a hard material cannot be performed.

  As shown in FIG. 11 (a) and FIG. 11 (b), the rake surfaces 11a to 11f of the ball blades 6a to 6f are preferably curved surfaces convex in the rotational direction. The curvature h / g of the convex curved surface of each rake face 11a to 11f is preferably 1 to 10%, and more preferably 1 to 8%.

[2] Scan line processing method
(1) Overview FIG. 12 shows the procedure of the scanning line processing method of the present invention, and FIG. 13 shows the processing path of the scanning line rough processing of the present invention. The scanning line machining method is a method of cutting in one direction while following the surface shape of the work material. As described above, in the scanning line processing method of the present invention, each of the cutting edges is constituted by a ball blade having a curved angle of 35 to 45 ° and an outer peripheral blade having a twist angle of 35 to 45 ° smoothly connected thereto. Since a ball end mill with a negative rake angle and a positive rake angle on the outer peripheral blade is used, a high-hardness steel material of HRC 40 or higher without chipping even with a large axial cutting depth ap using the outer peripheral blade It is possible to cut a workpiece 101 made of As a work material made of such a high hardness steel material, for example, DAC (HRC: 48), which is hot forged steel manufactured by Hitachi Metals, Ltd., can be mentioned. The work material may be a rectangular parallelepiped die material or a resync die. The method of the present invention is particularly effective for resync processing of a mold that has been subjected to surface hardening treatment such as nitriding treatment (hardness of the hardened layer: HRC 65 to 75).

  FIG. 14 shows an example of a contour line machining method performed on the same workpiece as shown in FIG. 12, and FIG. 15 shows a contour machining path. In contour processing, a substantially spiral multidirectional cutting streak remains on the processed surface. Since this cutting streak is not completely removed even if the scanning line finishing shown in FIG. 16 is performed, a separate polishing step is required.

(2) Processing conditions In the scanning line processing method of the present invention, (a) the axial cutting depth ap is 10 times or more the radial cutting depth ae, and (b) the feed speed Vf is 500 mm / min or more. It is characterized by.

  When ap / ae is 10 or more, not only ball blades but also outer peripheral blades are used as needed, and deep machining is performed with a large axial cutting depth ap as in roughing, and the radial cutting depth ae is reduced. This means that a finished surface such as finishing is obtained. For example, in the case of mold resynchronization, if the scanning line processing method of the present invention is used, processing can be performed with a finishing processing accuracy to a depth required for one scanning line processing. ap / ae is preferably 10 to 200, more preferably 30 to 170.

  By setting the feed speed Vf to 500 mm / min or more, it is possible to perform scanning line processing efficiently with a large cutting depth as in roughing and high processing accuracy as in finishing. The feed speed Vf is preferably 500 to 4500 mm / min, and more preferably 1000 to 3500 mm / min. When the feed speed Vf exceeds 4500 mm / min, the amount of generated chips becomes excessive, and chip clogging is likely to occur.

  The axial cut ap is preferably set to 0.5D to 3.0D. In the case of 0.5D axial incision ap, the connection part of the ball blade and the outer peripheral edge hits the surface of the work material. In addition, it is important that the outer peripheral blade is smoothly connected to the ball blade as large as 35 to 45 °. When ap is less than 0.5D, only the ball blade is involved in scanning line processing, so high-efficiency scanning line processing cannot be achieved. On the other hand, if ap is over 3.0D, the load increases and the risk of chipping and breakage increases. A preferred axial cut ap is between 0.7D and 2.5D.

  The radial cut ae is preferably set in the range of 0.005D to 0.03D. If ae is less than 0.005D, the efficiency of scanning line processing is too low. On the other hand, if ae exceeds 0.03D, the processing pitch becomes rough, so a good finished surface cannot be obtained. If it is ae within this range, the maximum surface roughness Rz of the scanning line processed surface is 6.5 or less. The quality (surface roughness) of the scanning line processed surface becomes better as ae becomes smaller. For example, when ae is 0.015D, Rz is 4.0 or less, and when ae is 0.005D, Rz is 2.0 or less.

  The cutting speed Vc is preferably 40 to 300 m / min, and more preferably 80 to 150 m / min. If the cutting speed Vc is less than 40 m / min, the cutting resistance is rather excessive. On the other hand, when the cutting speed Vc exceeds 300 m / min, early wear of the cutting edge and welding of chips to the cutting edge occur.

  The present invention will be described in more detail with reference to the following examples, but the present invention is not limited thereto.

Example 1 and Conventional Example 1
A four-blade ball end mill 40 is mounted on an NC-controlled three-axis machining center, and an HRC 50 SKD61 with a surface hardened layer (Rockwell hardness HRC 70) with a thickness of 0.2 mm is formed according to the cutting conditions shown in Table 1. A work material having an uneven shape made of alloy tool steel) was resync processed. The tool protrusion amount OH was 30 mm, and the tool protrusion amount OH / blade diameter D was 3.

  By using the scanning line processing method of the present invention, the processing time and the actual processing distance can be shortened compared to the contour line processing method. In the contour line processing method, multidirectional cutting streaks are generated on the surface, and finishing (polishing) is required. On the other hand, in the scanning line processing method of the present invention, a good processed surface that does not require finishing is obtained.

Example 2
A four-flute ball end mill 40 with a tool diameter smaller than that of Example 1 is mounted on an NC-controlled three-axis machining center, and a surface hardened layer (Rockwell hardness HRC 70) with a thickness of 0.2 mm is formed according to the cutting conditions shown in Table 2. The formed work material having an uneven shape made of SKD61 (alloy tool steel) of HRC 50 was resynced. The tool protrusion amount OH was 18 mm, and the tool protrusion amount OH / blade diameter D was 3.

  In the resynchronization of Example 2, ap / D was 0.83, and the ball blade and the outer peripheral blade were used at the same time, but it was more efficient than when only the ball blade was used, and a good machined surface that did not require finishing could be obtained. did it.

Example 3 and Comparative Examples 1 and 2
Three types with different blade length L in the rotation axis direction, ball blade circumferential angle, ball blade bending angle λ3, outer blade twist angle, ball blade radial rake angle, and outer blade radial rake angle Using a 4-flute ball end mill, a rectangular parallelepiped work piece made of HRC 50 SKD61 (alloy tool steel) according to the cutting conditions shown in Table 3 (width 100 mm, length 250 mm, height 40 mm) was directly carved into a three-dimensional shape (see Fig. 17) with a maximum depth of 12 mm by the scanning line processing method.

注：(1) 切れ刃にチッピングが発生したため、走査線加工を中断した。

Notes: (1) Since the chipping occurred at the cutting edge, the scanning line processing was interrupted.

  In Example 3, it was possible to directly carve a work material made of a steel material with high finishing accuracy without causing chipping at the cutting edge. This is because the four-blade ball end mill of Example 2 has a large ball blade bending angle and a peripheral blade twist angle, the ball blade radial rake angle is negative, and the peripheral blade radial rake angle is positive. Therefore, the rigidity and cutting performance of the outer peripheral blade are high, and it is considered that the scanning line processing can be performed with finishing accuracy while suppressing chipping even in the highly efficient bottom processing.

  On the other hand, in Comparative Examples 1 and 2, even if the scanning line processing method is performed under the same conditions as in Example 2, the processing time is 30 minutes (Comparative Example 1) and 50 minutes (Comparative Example 2), respectively. Chipping occurred in the ball end mill and the test was interrupted. In the four-flute ball end mills of Comparative Examples 1 and 2, the rake angles of the ball blade and the outer peripheral blade are both negative, so that the cutting resistance is large, and the cutting blade is equally divided, and chatter vibration is likely to occur. Therefore, it can be inferred that chipping occurred in the cutting edge when cutting the pocket-shaped region B (FIG. 17) where the entire ball blade is in contact with the work material.

2: Shank
3: Cutting edge
3a: Ball part
3b: Peripheral blade
4: Chip discharge groove
4a: Bottom of groove
4b: Groove wall surface
5a, 5b, 5c, 5d: Cutting edge
6a, 6b, 6c, 6d, 6e, 6f: Ball blade
7a, 7b, 7c, 7d, 7e, 7f: Peripheral blade
8a, 8b, 8c, 8d, 8e, 8f: Medium-low gradient blade
9a, 9b, 9c, 9d, 9e, 9f: Ball blade flank
10a, 10b, 10c, 10d, 10e, 10f: Flank face of medium / low gradient blade
11a, 11b, 11c, 11d: Rake face of the ball blade
13: depression
15a, 15b, 15c, 15d: Boundary lines between the flank face of the medium / low gradient blade and the flank face of the ball blade
17a, 17b, 17c, 17d: Gash
47: Boundary between the first and second rake face of the ball blade
40: Four-flute ball end mill
50: 5-flute ball end mill
60: 6-flute ball end mill
70a, 70b, 70c, 70d: Flank of outer peripheral edge
71a, 71b, 71c, 71d: second rake face
72a, 72b, 72c, 72d: Rake face of outer peripheral edge
101: Work material
103: Machining path
ap: Axial cutting depth
ae: Radial depth of cut
Ax: Center axis of rotation
B: Pocket-shaped machining area
D: Diameter of the cutting edge
g: Length of convex surface
h: Height of convex surface
O: Center of rotation
P1, P2, P3, P4, P5, P6: Connection point between medium and low gradient blade and ball blade
R: Direction of rotation of multi-blade ball end mill
S: Tool traveling direction
T1 to T3: Points on the edge of the cutting edge α: Inclination angle of medium and low gradient blades δ1 to δ9: Radial rake angle of ball blade γ1 to γ3: Second radial rake angle β1 to β3: Radial rake of outer peripheral blade Angle η: Twist angle of outer peripheral blade λ1 to λ3: Curved angle of ball blade

Claims (11)

Using a ball end mill of 4 blades or more, a method of scanning line machining of high hardness steel material of HRC 40 or more,
Each cutting edge of the ball end mill is constituted by a ball blade having a bending angle of 35 to 45 ° and an outer peripheral blade having a twist angle of 35 to 45 ° smoothly connected thereto,
The rake angle in the radial direction of the ball blade is a negative angle, the rake angle in the radial direction of the outer peripheral blade is a positive angle,
A method characterized in that the scanning line machining is performed at a feed rate Vf of 500 mm / min or more with an axial cut depth ap of 10 times or more of the radial cut amount ae.   2. The scanning line machining method according to claim 1, wherein the axial cut amount ap is 0.5 to 3.0 times the diameter D of the cutting edge portion, and a ratio between the axial cut amount ap and the radial cut amount ae. 10 to 200.   3. The scanning line machining method according to claim 1, wherein the cutting speed Vc is 40 to 300 m / min and the tool feed speed Vf is 500 to 4500 mm / min.   4. The scanning line processing method according to claim 1, wherein the rake face of the ball blade is a curved surface convex in the rotation direction.   5. The scanning line processing method according to claim 4, wherein the degree of curvature of the convex curved surface (the length of a perpendicular line dropped from a vertex of the convex curved surface to a line connecting both ends of the convex curved surface and a line segment connecting both ends of the convex curved surface. The ratio of the length to the length is 1 to 10%.   6. The scanning line machining method according to claim 1, wherein a radial rake angle of the ball blade is −37 to −11 °, and a radial rake angle of the outer peripheral blade is +2 to + 12 °. A method characterized by.   7. The scanning line processing method according to claim 1, wherein a used mold made of a high-hardness steel material of HRC 40 or more and having a hardened layer on the surface is resinked.   8. The scanning line machining method according to claim 1, wherein the ball blades are arranged in an unequal division in a circumferential direction around a rotation axis of the ball end mill.   9. The scanning line processing method according to claim 8, wherein the unequal division angle of the ball blade is 2 to 5 degrees.   10. The scanning line processing method according to claim 1, wherein the ball end mill has 4 to 6 cutting edges.   The scanning line processing method according to any one of claims 1 to 10, wherein the maximum surface roughness Rz of the steel material subjected to the scanning line processing is 6.5 or less.

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