JP2014039994A5 - - Google Patents

Description

Multi-blade ball end mill

The present invention is a solid type multi-blade ball end mill made of cemented carbide that can obtain a long life even when high-feed roughing is performed on hard-hardened hard materials such as hardened steel used in various dies. about the.

In recent years, in the automobile industry, the electronic equipment industry, and the like, needs for manufacturing members such as various parts using a mold are expanding. Along with this, there has been a strong demand for a ball end mill for cutting a die into a three-dimensional curved surface with high efficiency (high feed processing). To fabricate such mold, the ball end mill for high feed machining a high-hardness alloy steel, multi three or more balls blades (the arcuate cutting edge) provided at the tip portion of the tool body from conventional A bladed ball end mill is used. When the workpiece is cut using a ball end mill, the rotation speed of the point on the rotation axis (or rotation axis) of the ball blade is 0, and the rotation speed of the ball blade near the rotation axis is 0. Very close to low speed. For this reason, during machining, a large machining load acts on the rotation axis of the ball blade and its vicinity, so the wear of the cutting edge is accelerated in the vicinity of the rotation axis. Chipping and defects are likely to occur.

For this reason, as a ball end mill for rough machining (high feed machining) of members made of difficult-to-cut materials (for example, dies), the structure around the rotation axis of the ball blade has been improved. Patent Documents 1 to 9 propose multi-blade ball end mills (hereinafter referred to as “multi-blade ball end mills”) having means for preventing the occurrence of chipping and chipping.

In Patent Document 1 (Japanese Patent Laid-Open No. 10-128611), in order to prevent breakage and early wear near the apex (rotation axis) of the bottom blade, the bottom blade land has a convex curved surface, and three or more In a ball end mill having a bottom blade, there has been proposed a ball end mill configured such that the edges of each land are in contact with the center of the apex of the entire bottom blade.

Patent Document 2 (Japanese Patent Laid-Open No. 2002-187011) describes a multi-blade ball end mill provided with three or more ball blades for eliminating chip pockets near the rotation axis and preventing chip clogging. Furthermore, a ball end mill has been proposed in which each ball blade land is thinned so that each ball blade is missing at and near the rotation center of the tool body. The thinning provided in the multi-blade ball end mill has a recess formed in a range from the rear of the ball blade in the rotation direction to beyond the ball blade to the front in the rotation direction, and acts as a chip pocket near the rotation axis. Yes.

Patent Document 3 (Japanese Patent Application Laid-Open No. 2003-225821) describes that in a ball end mill provided with three or more ball blades, minute chipping or chipping occurs at the axial center portion of the ball blade when high-speed feeding is performed. In order to prevent this, all the ball blades reach the vicinity of the shaft center, and the end portions on the shaft center side are substantially in contact with each other, and the cross-section of the gash provided between the ball blades is V-shaped. End mills have been proposed.

Patent Document 4 (Japanese Patent Laid-Open No. 2005-224898) proposes a ball end mill that has a structure that sufficiently secures the strength around the rotation center at the tip of the end mill body with respect to a three-blade ball end mill. In Patent Document 4, the inner peripheral end of the gash and the ball cutting edge formed between the ball cutting edge (arc-shaped cutting edge) is spaced apart from the rotation center to form a chisel portion. In addition, the chisel part has a chisel blade that extends to the center of rotation connected to the inner peripheral edge of the ball blade at the intersecting ridge line between the flank faces adjacent to each other in the circumferential direction so that it substantially follows the hemisphere formed by the rotation trajectory of the ball blade. It is described to form.

Patent Document 5 (JP-2009-56559), a ball end mill was such that better configure discharge of the chip from the tool center be carried out high-efficiency machining is proposed. This ball end mill has two or more ball blades, and is configured to be immersed without providing a ball blade at the tool rotation center. a U-shaped groove formed so as to extend outwardly from the tool center of rotation, further the groove portion has a structure in which each respective one between the ball cutting edge.

Patent Document 6 (JP-A-9-267211), a ball end mill suitable for high-speed cutting, such as mold have been proposed. The ball end mill is more than twice the width of at least the land width along the cutting edge in the nose portion of the ball cutting edge, provided with a substantially V-shaped end cutting edges at a low gradient in the above 4 °, the rake of the ball cutting edge This is a 2-flute ball end mill with a negative angle in the normal direction and a rake angle of the bottom edge of 0 ° or a positive angle.

Patent Document 7 (Japanese Patent No. 3,840,660), suppressing the wear amount of the end mill tip, multi blade ball end mill good processing accuracy can be obtained has been proposed. The multi-blade ball end mill has three or more balls blade has a heart left portion in the axial section, the ball blade was inflection from the vicinity of the axial center portion, extending to the next blade in the rotation direction of the ball end mill It has a cutting edge that is, these cutting edge has a substantially polygonal shape of the ball end mill bottom view. A configuration in which the ball blades are arranged in unequal divisions has also been proposed.

Patent Document 8 (Japanese Patent No. 4412687), a ball end mill for finish machining of the mold and the like have been proposed. In this finishing end mill , two or more cutting edges are arranged at the center, and when viewed from the front, the end on the rotation center side of the two or more cutting edges is the most protruding point in the axial direction. the rotation center side of the point, to extend the only flank of symmetry of the cutting edge in at least the center of rotation, provided with a ridge that crossed the flank in a concave shape from the rotation locus of the end mill, the distance between the axial outermost projecting point 0.3 mm It is set to be greater than or equal. Furthermore, this finishing end mill has a ridge line intersecting the flank face connected to a symmetric cutting edge at the center of rotation and a line segment connecting the center of rotation of the end mill and the most protruding point in the axial direction. It has a continuous structure with an inclination of less than 1 degree.
The ball end mill described in Patent Document 8 is provided with such a configuration, thereby increasing the strength near the rotation center and improving chip discharge performance to prevent chipping of the cutting edge, and It is effective to improve the finished surface roughness by being slightly spaced from the center of rotation.

Patent Document 9 (JP-A-11-216608), solid ball end mill suitable for simultaneously finishing applications with flat and curved machining has been proposed. In this solid ball end mill, the nose portion of the ball blade is provided with a notch in a substantially V shape in an axial cross-sectional view, and at least one bottom blade connected to the ball blade is provided in the notch portion , so that the bottom blade has a medium to low gradient. More than 5 degrees and less than 15 degrees, and the connection part between the bottom blade and the ball blade is connected with a short round cutting edge to suppress the occurrence of chipping and chipping near the rotation center of the ball blade. It is .

Japanese Patent Laid-Open No. 10-128611 (Claim 1, paragraphs 0011 to 0013, FIG. 1) JP 2002-187011 A (Claim 1, paragraphs 0011 to 0016, FIGS. 1 to 3) Japanese Patent Laying-Open No. 2003-225821 (Claim 1, paragraphs 0018 to 0022, FIGS. 1 to 2) JP 2005-224898 A (Claim 1, paragraphs 0012 to 0020, FIGS. 2 to 3 and FIG. 5) JP 2009-56559 A (Claim 1, paragraphs 0028 to 0036, FIGS. 1 to 4) JP-A-9-267211 (Claims 1 to 3, paragraphs 0006 to 0010, FIGS. 2 to 4) Japanese Patent No. 3840660 (Claim 1, Claim 3, Paragraphs 0006 to 0008, FIG. 2, FIG. 3) Japanese Patent No. 4412687 (Claim 1, paragraphs 0006 to 0008, FIGS. 3 and 4) Japanese Patent Laid-Open No. 11-216608 (Claim 1, paragraphs 0006 to 0007, FIGS. 6 to 7)

In the ball end mill described in Patent Document 1, all of the ball cutting edge is tangent to the rotation axis, the width that form flank of the ball cutting edge (lands) of the rotation direction of the ball end mill is constant (ibid (See Figure 1). Although large load to the rotation axis near the cutting in the ball cutting edge acts, when flank of the ball end mill rotating direction width (land) constant, the lack of strength of the cutting edge for the cutting load, the rotational axis ball blade chipping or defect in the vicinity, or a problem that the progress of the wear is fast that occur.

The multi-blade ball end mill described in Patent Document 2 is formed with a thinning that becomes a recess in the vicinity of the rotation axis of the ball blade, and this thinning acts as a chip pocket in the vicinity of the rotation axis. Is to improve. However, in order not formed rotation axis and the cutting edge to the rotation axis near the ball cutting edge, since the ball blade axis of rotation near it acts a large load, the ball blade axis of rotation near Chipping or loss, or a problem that the progress of the wear is fast that occur.

The multi-blade ball end mill described in Patent Document 3 is such that all the ball blades extend to the vicinity of the rotation axis, the end portions on the rotation axis side of the ball blades are substantially in contact with each other, and between the ball blades 1 is a ball end mill having a configuration in which a cross-section of a gasche provided in a V-shape is formed. However, the multi-blade ball end mill described in Patent Document 3 is generated by means for improving the strength (rigidity) of the ball blade formed near the rotation axis and the cutting edge at the end of the ball blade on the rotation axis side. No means are disclosed for improving the discharge of the generated chips.

The multi-blade ball end mill described in Patent Document 4 is formed with a chisel portion arranged at a distal end portion of the end mill main body at a distance from the center of rotation, and the chisel portion intersects flank surfaces adjacent in the circumferential direction. Although it is a ball end mill in which a chisel blade that extends to the center of rotation is formed on the ridge line and continues to the inner peripheral end of the ball blade, the following problems occur .

That is, in the multi-blade ball end mill, as described in Patent Document 4, it is extremely difficult to form a fine chisel blade so as to substantially follow the hemisphere formed by the rotation trajectory of the ball blade. Even if the chisel blade can be formed, when the flank face of the ball blade is connected to the rotation axis, a convex protrusion is formed in the vicinity of the rotation axis. For this reason, if such a multi-blade ball end mill is used to perform high-feed machining in order to increase the efficiency of roughing of the work material, chipping or chipping may occur in the ball blade starting from the convex protrusion Becomes higher. Therefore, it is considered that the multi-blade ball end mill described in Patent Document 4 cannot perform the high-feed machining intended by the present invention.

In the ball end mill described in Patent Document 5, a groove portion extending outward from the rotation axis of the tool in a substantially V shape or a substantially U shape in a sectional view is provided between the ball blades at the tool tip portion. By providing each one, it is a ball end mill that prevents chips from staying near the tip of the ball blade. However, the ball end mill described in Patent Document 5, since the cutting edge to the rotation axis near the ball cutting edge does not exist, due to the large load acting on the rotation axis near during cutting, the ball blade rotation axis generating end to chipping and loss of the neighborhood, or a problem that progression of wear of the ball cutting edge becomes fast that occur.

The ball end mill described in Patent Document 6 is provided with a V-shaped bottom blade with a medium to low gradient in the vicinity of the rotation axis of the ball blade, and mainly for finishing a three-dimensional curved surface such as a mold. The two-blade ball end mill is equipped with three or more multi-blade ball blades for rough machining of dies and the like, and each ball blade and bottom blade (medium low gradient blade) The structure of the rake face and flank face is not disclosed. When a medium / low gradient blade is provided near the rotation axis for high feed roughing of dies, etc., the shape and arrangement of the medium / low gradient blade, the rake face and flank shape, in further improving the configuration of the connecting portion between the low slope blades, it is important to prevent the occurrence of chipping and defects such as low gradients blade and ball cutter in the rotation axis near the time of cutting.

The multi-blade ball end mill described in Patent Document 7 is provided with a center-remaining portion in the shaft center portion, and the ball blade is bent from the vicinity of the shaft center portion and extended to the next blade in the rotation direction of the ball end mill. A blade is provided, and these extended cutting blades are ball end mills having a substantially polygonal shape when viewed from the bottom of the ball end mill. Therefore, this multi-blade ball end mill has an uncentered portion in the shaft center portion, and does not have a cutting edge formed toward the shaft center portion in the vicinity of the shaft center portion. For this reason, during cutting, the cutting resistance in the axial center and the vicinity thereof becomes high and the progress of wear is accelerated, so it is not suitable as a multi-blade ball end mill for performing high-feed roughing of the present invention. .

The ball end mill for finishing described in Patent Document 8 has the end on the rotation center side of two or more cutting edges in the front view as the most protruding point in the axial direction , and closer to the rotation center than the most protruding point in the axial direction. Further, at least the flank face of the symmetrical cutting edge is extended at the center of rotation, and a ridge that intersects the flank face is provided in a concave shape from the rotation locus of the end mill. That is, the flank provided on the rotation center side from the most projecting point in the axial direction has no cutting edge. For this reason, when the ball end mill described in Patent Document 8 is used for high-feed roughing of difficult-to-cut materials with high hardness, early wear near the rotation center and its vicinity proceeds due to a large cutting load acting near the rotation center. This causes chipping and chipping on the ball blade. Thus, the ball end mill described in Patent Document 8 is not suitable for high feed roughing difficult to cut materials of high hardness.

The ball end mill described in Patent Document 9 has a notch portion of the ball blade provided with a notch in a substantially V shape in an axial sectional view, and provided with at least one bottom blade connected to the ball blade in the notch portion. the low slope in the blade 5 degrees or more, be one obtained by less than 15 degrees, a ball Lumpur end mill to be used for finishing purposes. When trying to use this ball end mill for high-feed roughing of difficult-to-cut materials, since the slope of the middle and lower edges of the bottom blade is 5 degrees or more and less than 15 degrees , a large cutting load acts on this bottom blade, There is a high possibility that chipping and chipping will occur in the bottom blade early. Therefore, in order to use a ball end mill with a bottom blade for high-feed roughing of difficult-to-cut materials with high hardness, further improvements in the bottom blade's medium and low gradient angles, the shape of the bottom blade, etc. are required. .

An object of the present invention is a ball end mill of multi-blade having three or more ball blades, by improving the structure of the rotation axis near the ball cutting edge formed at the tip of the cutting edge portion, the rotation Providing a multi-blade ball end mill that improves the strength of the cutting edge near the shaft center and improves chip evacuation, extending the life of high-feed roughing of hard materials with high hardness such as hardened steel It is in.

Multi blade ball end mill of the present invention comprises a shank portion for rotating the rotation axis as the center, and a cutting edge portion having three or more cutting edges having a ball blade tip,
Middle and low gradient blades extend from the tip of each ball blade to the rotation axis in the vicinity of the rotation axis of the tip ,
Each of the medium and low gradient blades is inclined at 0.5 ° or more and 3 ° or less on the side of the shank portion with respect to a plane orthogonal to the rotation axis,
At least part of said rotation axis side of the middle low gradient blade is characterized by a concave curved shape in the direction of rotation behind.

Each of the medium and low gradient blades is composed of a curved medium and low gradient blade recessed in the rearward direction of rotation provided on the rotation axis side, and a linear medium and low gradient blade provided on the ball blade side, and the rotation axis direction It is preferable that the radial width of the concave curved medium / low gradient blade in plan view is larger than the radial width of the linear medium / low gradient blade.

Each medium / low gradient blade preferably comprises only the concave curved medium / low gradient blade.

The radial width X of each medium and low gradient blade is preferably 1.25% or more and 3.75% or less of the diameter D of the cutting edge portion.

The rotational direction end point a1 of the concave curved medium / low gradient blade of the medium / low gradient blade is preferably on the rotational axis side from the position a which is half the radial width X1 of the concave curved medium / low gradient blade. .

The multi-blade ball end mill of the present invention preferably comprises four cutting edges.

The multi-blade ball end mill of the present invention is preferably a solid ball end mill made of cemented carbide . The manufacturing method is to mold a cemented carbide powder in which Co (cobalt) powder is mixed with WC (tungsten carbide) powder, and after firing the obtained molded body, the cutting edge, gash, chip discharge groove, It includes a step of performing finishing (grinding) such as a flank and rake face.

The multi-blade ball end mill of the present invention can achieve the following effects.
(1) Each Medium low gradient blade is inclined with a small angle of inclination α to the side of the shank portion 2 with respect to a plane perpendicular to the rotation axis O from the vicinity of the rotation axis O of the ball cutting edge. Thus, the leading edge portion of the rotation axis O direction of the cutting edge portion 3 has a small width t, and has a chip pocket low gradient blades are arranged (recessed portions) in inclined to the shank portion . As a result, even if a large load is applied in the vicinity of the rotation axis O during the high feed roughing , the medium / low gradient blades 8a, 8b, 8c, 8d can cut the work material. Chips generated by the medium and low gradient blades are discharged from the chip pockets to the chip discharge grooves through the respective gashes. For this reason, even if high-feed cutting is performed, chip clogging can be prevented from occurring near the rotation axis O of each ball blade, and early wear, chipping and chipping of the ball blade can be prevented.

(2) The present invention, in the vicinity of the rotation axis, and in the low order gradients blade is inclined at a small angle to the side of the shank portion, a point on the axis of rotation in the multi-blade ball end mill and the workpiece Can be avoided. For this reason, there is no region where the cutting speed is zero in the cutting edge that comes into contact with the work material, and stable cutting can be performed.

1 is a side view showing a multi-blade ball end mill according to a first embodiment of the present invention. FIG. 2 is an enlarged side view schematically showing a tip portion of a cutting edge portion of the multi-blade ball end mill shown in FIG. FIG. 2 is an enlarged front view of the cutting edge portion of the multi-blade ball end mill shown in FIG. 1 as viewed from the direction of the rotation axis O. FIG. 4 is a partial cross-sectional view taken along line B1-B1 of FIG. FIG. 4 is an enlarged front view showing the vicinity of a rotation axis O of a cutting edge portion of the multi-blade ball end mill of the reference example shown in FIG. FIG. 3 is a partial perspective view showing an example of the configuration in the vicinity of the rotation axis O of the multi-blade ball end mill of the present invention. FIG . 6 is a partial perspective view showing another example of the configuration in the vicinity of the rotation axis O of the multi-blade ball end mill of the present invention. FIG. 7 is a partial perspective view showing the configuration in the vicinity of the rotation axis O in FIG. 6 in a further enlarged manner. FIG. 8 is a partial perspective view further enlarging the configuration in the vicinity of the rotation axis O in FIG. (a) is a sectional view taken along line B2-B2 of FIG. 8 , and (b) is a sectional view taken along line B3-B3 of FIG. FIG. 10 is a partial perspective view showing still another example of the configuration in the vicinity of the rotational axis O of the multi-blade ball end mill of the present invention. FIG. 10 is a partial perspective view showing still another example of the configuration in the vicinity of the rotational axis O of the multi-blade ball end mill of the present invention. FIG. 6 is a partial front view showing another example of the arrangement of medium and low gradient blades in the vicinity of the rotational axis O of the multi-blade ball end mill of the present invention. It is a partial front view which shows the characteristic on the shape of the medium-low-gradient blade of the multiblade ball end mill of this invention. FIG. 15 is an enlarged view of FIG. FIG. 5 is a front view showing a three-blade ball end mill according to a second embodiment of the present invention . It is a photograph showing the wear state of the ball blade after cutting for 30 minutes with a multi-blade ball end mill in Experimental Example 1, (a) shows the wear state of the present invention example, (b) is a comparative example. Indicates the wear state. It is a photograph showing the wear state of the ball blade after cutting for 60 minutes with a multi-blade ball end mill in Experimental Example 1 , (a) shows the wear state of the present invention example, (b) is a comparative example. Indicates the wear state. It is a photograph showing the wear state of the ball blade after cutting for 90 minutes with a multi-blade ball end mill in Experimental Example 1 , (a) shows the wear state of the present invention example, (b) is a comparative example. Indicates the wear state. It is an enlarged photograph showing the wear state of the ball blade after performing the cutting process for 90 minutes on the work material in Experimental Example 2 , the multi-blade ball end mill of the present invention example 1 in the upper stage, and the comparative example 1 in the lower stage A multi-blade ball end mill is shown . It is an enlarged photograph showing the wear state of the ball blade after performing the cutting process for 40 seconds on the work material in Experimental Example 3 , the multi-blade ball end mill of the present invention example 1 in the upper stage, and the comparative example 2 in the middle stage The multi-blade ball end mill is shown below, and the multi-blade ball end mill of Comparative Example 3 is shown in the lower stage. A diagram showing the difference in structure of the cutting edge of the cemented carbide solid type multi blade ball end mill, (a) and (b) shows a conventional example, shows an example of the present invention (c). In Experimental Example 4 , it is a diagram showing the results of measuring the three component forces Fx, Fy, Fz of the cutting force of the multi-blade ball end mill, (a) is a multi-blade ball end mill of the present invention example 1, (b) is a comparison example 1 multi blade ball end mill, shows a multi-blade ball end mill of Comparative example 3 (c). It is a figure which shows the result of having measured the 3 component force Fx, Fy, Fz of cutting resistance when the ball blade is arranged in unequal division in Experimental example 5, (a) is a multi-blade ball of unequal division 2 ° End mill (Invention example 2), (b) is a multi-blade ball end mill with 4 ° unequal division (Invention example 3), (c) is a multi-blade ball end mill of equally divided example 1, and (d) is an equally divided example. 2 shows a multi-blade ball end mill.

The multi-blade ball end mill of the present invention is a solid-type ball end mill made of cemented carbide suitable for performing high-feed roughing, particularly for hard-to-cut materials with high hardness. It has at least 3 ball blades to do.

Here, the “hard hardness difficult-to-cut material” is a high-hardness metal material having a hardness HRC of 40 or more, particularly an HRC of 50 or more, for example, SKD61, SKD11 or SKD11 which is an alloy tool steel subjected to quenching treatment. Powder high speed etc. are shown.
A "roughing" is a process carried out prior to finishing, the machining allowance of the cutting edge are as large as possible the cutting, in general, in order to increase the machining efficiency, depth of cut, or feed This is a process with a large amount. For this reason, the processing load of the cutting tool becomes large.
“High feed machining” is a process in which the feed rate (Vf) is increased to perform high-efficiency machining, or a process in which the axial cut depth (ap) and the radial cut depth (ae) are increased. For example, when cutting a workpiece with HRC 60 using a conventional two-blade ball end mill (blade diameter: 8 mm), the feed rate (Vf) is 1000 mm / min or more and the axial depth of cut (ap) is It is said that the cutting process is 0.2 mm or more and the radial cutting depth (ae) is 0.6 mm or more.

The basic configuration of the multi-blade ball end mill according to the first embodiment of the present invention will be described below with reference to FIGS. The first embodiment will be described by taking a multi-blade ball end mill having four ball blades as an example, but the feature of the present invention is applied to a multi-blade ball end mill having about three to six ball blades. Can

[First embodiment]
As shown in FIG. 1, the multi-blade ball end mill 1 according to the first embodiment includes a shank portion 2 and a cutting edge portion formed at the front end portion (left end portion in FIG. 1) of the shank portion 2. 3 and has a substantially cylindrical shape with an overall length of L. The rear side (right end in FIG. 1) of the shank portion 2 is a portion to be mounted on the machine tool. On the outer peripheral surface of the cutting edge portion 3, four spiral chip discharge grooves 4 having a predetermined twist angle are formed at equal intervals, and the wall surface constituting the chip discharge groove 4 is a multi-blade ball end mill 1 An outer peripheral blade 5 is formed on a ridge line where a surface facing the rotation direction (“A” direction shown in FIG. 3) of the (shank portion 2) and the outer peripheral relief surface of the cutting blade portion 3 intersect.

Cut toward the outer peripheral side of the distal end portion of the blade portion 3 to the rotation axis O of the multi-blade ball end mill 1, four ball cutting 6a, 6b, 6c, 6d and four gash 7a, 7b, 7c, and a 7d They are formed alternately (see Fig. 3). With each ball blade 6a~6d are connected to each peripheral cutting edges 5, each gash 7a, 7b, 7c, 7d are connected to each chip discharge flute 4. In FIG. 1, “D” is the diameter of the cutting edge part 3, “d” is the diameter of the shank part 2, “l” is the length of the cutting edge part 3 (blade length), and “O” is a multi-blade ball end mill 1 The rotation axis (rotation center axis) of (shank part 2) is shown .

FIG. 2 is a side view schematically showing an enlarged configuration of the distal end portion of the cutting edge portion 3 shown in FIG. As shown in FIG. 2, arc-shaped ball blades 6a, 6b, 6c and 6d (6a and 6c are shown in FIG. 2) are located at positions P1, P2, P3 and P4 near the rotation axis O (in FIG. 2). P1 and P3 are shown), and medium and low-gradient blades 8a, 8b, 8c and 8d (only 8a and 8c are shown in FIG. 2) are connected together from positions P1, P2, P3 and P4. , in the low gradient blades 8a, 8b, 8c, the end of the 8d is that Sessu the rotation axis O. As described later, in a low gradient blades 8a, 8b, 8c, 8d is a plan view seen from the direction of the rotation axis O, a linear cutting edge, recessed in the direction of rotation A rear curved cutting edge It is good also as a structure which connected to (refer FIG. 6) .

  In FIG. 2, 11a is a rake face of the ball blade 6a, and 9c is a flank face of the ball blade 6c. As described above, each of the ball blades 6a to 6d includes the corresponding flank surfaces 9a to 9d and the rake surfaces 11a to 11d.

Further, as shown in FIG. 2, each in a low gradient blades 8a, 8b, 8c, 8d (in FIG. 2 8a, shown only 8c) from the rotation axis position near the O P1, P2, P3, P4 extends toward the rotation axis O, is inclined at a minute inclination angle α on the side of the shank portion 2. As a result, the ball blades 6a, 6b, 6c, 6d have a minute amount in a plan view on the side of the rotational axis O, that is, inside the position surrounded by the positions P1, P2, P3, P4 in the vicinity of the rotational axis O. A very shallow depression 13 having a width t is formed.

Among low-gradient edges 8a, 8b, 8c, the tilt angle α of 8d, an angle formed between the plane and the middle low gradient edge perpendicular to the rotation axis O is set to a minute range of 0.5 ° 3 ° or more or less ing. The inclination angle α is preferably to set the range of 2 ° less than 1 °. When the inclination angle α exceeds 5 °, cutting edges (ball blades or medium-low gradients) near the positions P1, P2, P3, P4 due to the cutting load acting on the positions P1, P2, P3, P4 near the rotation axis O Early wear and chipping of the edge of the blade are likely to occur . Therefore, the inclination angle α is 5 ° or less, preferably set to 3 ° or less. Further, when the inclination angle α is smaller than 0.5 °, since the intersection of the rotation axis O and the middle low gradient blade by depth of cut during cutting is likely to contact with the workpiece, a position near the rotation axis O P1, Cutting loads at P2, P3, and P4 increase, and chipping or the like is likely to occur at the ball blades in the vicinity. Therefore, the inclination angle α is to be set to 3 ° less than 0.5 °.

In a first embodiment of the present invention, each middle low gradient blades 8 a to 8 d, by which is inclined at an inclination angle alpha, with a small width t around the rotation axis O in a plan (side) view recess 13 is formed. Recess in the four in the 13 low gradient blades 8a, 8b, 8c, with each end of the 8d contact the rotation axis O, and they are arranged at equal intervals (90 ° intervals) around the rotation axis O Yes. Moreover, the hollow part 13 is connected with the gashes 7a-7d.

In FIG. 2, the width formed by the two midsole gradient blades 8a and 8c facing each other through the rotation axis O (measured in a direction perpendicular to the rotation axis O) , that is, the width t of the recess 13 is cut. When the diameter D is 2.5 to 7.5% of the diameter D of the blade part 3, for example, when the diameter D is 8 mm, it is preferably 0.2 to 0.6 mm. When the width t of the hollow portion 13 is less than 2.5% of the diameter D , the inclination angle α needs to be extremely large in order to provide the intersection of the rotation axis O and the medium / low gradient blade on the shank portion side . production becomes difficult. In addition, when the width t of the hollow portion 13 exceeds 7.5% of the diameter D , the ball blade is shortened according to the length of the insole gradient blade, so that the multi-blade ball end mill targeted by the present invention is highly efficient. Cutting cannot be realized.

As described above, the multi-blade ball end mill of the present invention includes: (a) medium and low gradient blades 8a, 8b, from the tip of each of the ball blades 6a, 6b, 6c, 6d to the rotation axis O in the vicinity of the rotation axis O; 8c and 8d extend, and (b) each of the medium and low gradient blades 8a, 8b, 8c and 8d is 0.5 ° or more and 3 ° or less on the shank portion 2 side with respect to the plane perpendicular to the rotation axis O. It is characterized in that it is inclined by an angle α, and (c) at least a portion of each of the medium and low gradient blades 8a, 8b, 8c, 8d on the side of the rotational axis O is recessed in the rear in the rotational direction. The medium and low gradient blades 8a, 8b, 8c, and 8d are composed of only the curved medium and low gradient blades that are gently depressed in plan view. It may be composed of

Due to the above features, the cutting edge portion 3 (each ball blade) is provided with a hollow portion 13 having a minute width t at the most distal portion in the direction of the rotation axis O, and the hollow portion 13 is formed in the gash 7a to 7d. Since it is connected, it acts as a tip pocket that exists in the vicinity of the rotational axis O at the foremost portion of the cutting edge portion 3. As a result, extremely thin chips generated by the medium and low gradient blades 8a, 8b, 8c and 8d during the cutting process are discharged from the chip pocket to the chip discharge groove 4 through the gashes 7a, 7b, 7c and 7d. Even when high feed cutting is performed, chip clogging can be prevented from occurring in the vicinity of the rotational axis O of each ball blade.

As shown in FIG. 5, “the vicinity of the rotation axis O” means the intervals between the rotation axis O and the intersections P1, P2, P3, and P4 of the medium and low-gradient blades and the ball blades with the rotation axis O as the center. The inside of the circle C with a radius . In other words, “in the vicinity of the rotation axis O” is an inner region (indentation 13) of a circle having a diameter t centered on the rotation axis O.

The portions where the medium and low gradient blades 8a, 8b, 8c and 8d are in contact with the rotation axis O (the end portion of the medium and low gradient blades) are only a minute distance from the substantially hemispherical rotation locus of the ball blades 6a, 6b, 6c and 6d. Because it sinks inward, it does not come into contact with the work material during cutting. Therefore, low-gradient edges 8a, 8b, 8c, the occurrence of chipping or defect in the rotation axis O portion 8d can be prevented therein.

Referring to FIG. 3-12 illustrating the details of the configuration of a distal end portion of the blade 3 off. As shown in FIG. 3, in the multi-blade ball end mill 1 of the first embodiment, four ball cutting 6a at the tip of the rotation axis O direction of the cutting edge portion 3, 6b, 6c, 6d, respectively gash 7a, 7b, 7c, are arranged at equal intervals (90 °) around the rotation axis O through 7d. A groove bottom ( deepest part ) is formed in each of the gashes 7a to 7d. By appropriately setting the gash sectional shape so as to correspond to like rake angle of each ball cutting edge can be arranged a groove bottom of each gash (7b1 shown in FIG. 4, 7C1,7d1 the like shown in FIG. 6) in position .

Each of the ball blades 6a, 6b, 6c, 6d has a gently convex curved shape in the direction of rotation A of the multi-blade ball end mill 1 when viewed from the direction of the rotation axis O as shown in FIG. And rake faces 11a, 11b, 11c, 11d (rake faces 11a, 11b, 11c, 11d are not shown in FIG. 3) on the front side in the rotational direction A of each ball blade 6a, 6b, 6c, 6d. Is formed. Further, on the front side in the rotation direction A of the rake surfaces 11a to 11d of the ball blades, gashes 7a, 7b, 7c, and 7d are formed. Thus, the rake face 11a~11d of the ball cutting edge is the one side of the gash 7a to 7d.

Convex curved respective ball blades 6a, 6b, 6c, the direction of rotation A rearward flank of 6d (land) 9a, 9b, 9c, and 9d are formed, each flank 9a, 9b, 9c, 9d rotation Gash 7a, 7b, 7c and 7d are formed behind the direction A. Each flank 9a, 9b, 9c, 9d and the gash 7a, 7b, 7c, ridge 14a and 7d, 14b, 14c, 14d are gently convex curved in the direction of rotation A. The width W1 in the rotational direction A of each flank 9a, 9b, 9c, 9d gradually increases as the distance from the rotational axis O increases, as shown in FIG .

The cutting load of each ball blade 6a, 6b, 6c, 6d increases as it moves away from the rotation axis O, but the width W1 increases as it moves away from the rotation axis O, so the strength (rigidity) of each ball blade is secured. It can also prevent the occurrence of chipping or loss of each ball cutting edge in high feed roughing.

FIG. 4 shows a main part of a cross section along line B1-B1 of FIG. As shown in FIG. 4, a rake face 11b is formed in front of the rotation direction A of the ball blade 6b, and a flank 9b is formed behind the rotation direction A of the ball blade 6b. Furthermore, a gash 7b having a gash groove bottom 7b1 is formed in front of the rake face 11b of the ball blade 6b in the rotational direction A , and the rake face 11b constitutes one side of the gash 7b. The other side surface (not shown) of the gash 7b connected to the flank 9c of the ball blade 6c is in front of the rotational direction A of the gash groove bottom 7b1. In FIG. 4, the rake angle γ1 of the rake surfaces 11a to 11d of each ball blade including the rake surface of the ball blade 6b is positive, but the rake angle γ1 of each ball blade, that is, the direction orthogonal to the rotation axis O The rake angle (the rake angle of the cross section perpendicular to the axis) is preferably set in the range of −30 ° to 20 °.

By setting the rake angle γ1 of each ball blade within the range of -30 ° or more and 20 ° or less, even when highly efficient cutting is performed, chipping and chipping of the ball blade are prevented and stable cutting is achieved. Processing becomes possible. When the rake angle γ1 of each ball blade is smaller than −30 °, the ball blade rigidity is improved, but the cutting resistance increases. Therefore, when highly efficient cutting is performed, chatter vibration tends to occur. is there. In addition, when the rake angle γ1 of each ball blade is larger than 20 °, the cutting resistance is reduced and the machinability is improved, but the ball blade rigidity is reduced, so that chipping is performed when highly efficient cutting is performed. And tend to be deficient.

Gash 7a, 7b, 7c, 7d formed in front of the rotation direction A of each of the ball blades 6a, 6b, 6c, 6d is a V-shaped or substantially U-shaped cross section like the gash 7b shown in FIG. a groove having a shape, a ball cutting edge 6a during cutting, 6b, discharges 6c, 6d, and medium low gradient blades 8a, 8b, 8c, collects chips generated by 8d in chip discharge groove 4 . These gashes 7 a to 7 d are connected to the recess 13.

The configuration of the medium and low gradient blades 8a, 8b, 8c, and 8d in the vicinity of the rotation axis O will be described with reference to FIG. As shown in FIG. 5, each of the ball blades 6a, 6b, 6c, 6d is formed up to points P1, P2, P3, and P4 in the vicinity of the rotation axis O. From each point P1, P2, P3 , P4 Each of the medium and low gradient blades 8a, 8b, 8c, and 8d is formed so as to contact the rotation axis O, and these medium and low gradient blades 8a, 8b, 8c, and 8d are arranged on a plane orthogonal to the rotation axis O. It is inclined at a minute inclination angle α toward the shank section 2 side against (see Fig. 2). FIG. 5 shows an example in which each of the medium and low gradient blades 8a, 8b, 8c, and 8d is linear .

5 showing a plan view as viewed from the rotation axis O direction, the middle low gradient blades 8a, 8b, 8c, the rotational direction A behind the 8d, flank the low gradient edge in the flat or shaped substantially planar 10a, 10b, 10c, and 10d are formed. Each medium low gradient blade flank 10a, 10b, 10c, 10d also, in so as to follow the inclination angle alpha of the low gradient blade 8 a to 8 d, are inclined to the shank portion 2 with an angle of inclination alpha. Each medium low gradient blade flank 10a, 10b, 10c, 10d, the corresponding ball blade flank 9a, 9b, 9c, 9d and border 15a, 15b, 15c, are connected together via 15d. Between adjacent flank surfaces 10a, 10b, 10c, and 10d are minute groove portions that communicate with gashes 7a, 7b, 7c, and 7d, respectively.

Width W2 in the low gradient blade flank 10a, 10b, 10c, 10d rotational direction A of, as shown in FIG. 5, thus gradually increasing the distance from the rotation axis O.

Among low gradient blade flank 10a, 10b, 10c, 10d, as shown in FIG. 5, including a circle C connecting the positions P1, P2, P3, P4 of at least the rotation axis O vicinity. In the example shown in FIG. 5, the flank faces 10a, 10b, 10c, and 10d of the medium and low gradient blades are rhombic planes having the rotation axis O as a vertex. The flank faces 10a, 10b, 10c, and 10d of the medium and low gradient blades are formed by grinding using a rotating grinding wheel with a minute width, so these flank faces are considered in consideration of ease of grinding. An extremely minute convex shape (spherical shape) or a minute concave surface may be formed slightly upward. If the flank surfaces 10a, 10b, 10c, and 10d are convex, the rigidity is improved, and if they are concave, the chip discharging property is improved .

Although large load in the vicinity of the rotation axis O in the cutting acts, as described above, and gradually according to the width W2 of the rotation direction A of the flank 10a~10b of each medium low gradient blades away from the rotation axis O because increases in low gradient blades 8a, 8b, 8c, stiffness 8d is improved as the distance from the rotation axis O. Since the medium and low gradient blades 8a, 8b, 8c, and 8d are inclined toward the shank, the portions where the ends of the medium and low gradient blades 8a, 8b, 8c, and 8d are in contact with the rotation axis O are the work material. Although the width W2 of the flank face of the medium / low gradient blade gradually increases as it moves away from the rotation axis O, the rigidity of the portion where the medium / low gradient blades 8a, 8b, 8c, 8d contact the work material Is sufficiently secured. As a result, it is possible to prevent the occurrence of chipping or loss of low gradient blade 8a~8d in during cutting.

6, the configuration in the vicinity of the rotation axis O, shown further enlarged from the rotation axis O direction. In Figure 6, the middle low gradient blade 8a~8d consists not straight, the curved cutting edge that gently recessed in the direction of rotation A rear, a straight cutting edge. In the example shown in FIG. 6 , the medium / low gradient blade 8d includes a curved medium / low gradient blade 8d1 recessed in the rearward direction of rotation A and a linear medium / low gradient at the end K of the curved medium / low gradient blade 8d1. The blade 8d2 is integrally formed. In FIG. 6, only the curved medium / low gradient blade 8d1 and the straight medium / low gradient blade 8d2 are illustrated, but the other medium / low gradient blades 8a to 8c are configured similarly to the medium / low gradient blade 8d. It is said. The configuration of this medium / low gradient blade is a feature of the present invention . In FIG. 6, 7c1 indicates the gash groove bottom of the gash 7c, and 7d1 indicates the gash groove bottom of the gash 7d.

Due to the above-described features, the medium / low gradient blades 8a to 8d can be made longer than the medium / low gradient blade composed of only the linear cutting blades shown in FIG. Accordingly, in suppressing the decrease in rigidity of the end K of the low gradient blade 8d1, in so possible to increase the volume of the space of the recess portion 13 for discharging the chips with low gradients blade, in low gradient blade 8a~8d The evacuation performance of the chips generated in step 1 is further improved . Especially off the case of a multi-blade ball end mill is greater diameter D of the blade 3, the discharge of the chips is improved when the roughing high feed went hard-to-cut materials of high hardness.

The relationship between the rake surfaces 11a to 11d of the ball blades 6a to 6d, the rake surfaces 12a to 12d of the medium and low gradient blades 8a to 8d, and the gashes 7a to 7d will be described with reference to FIGS. To do. Figure 7 shows another example of the arrangement of the rake face and the gash low gradient edge in shown in FIG. 6, FIG. 8 shows a further enlarged to 6, FIG. 9 shows a further enlarged to FIG.

As shown in FIG. 6, the rake surfaces 12a to 12d of each medium and low gradient blade and the rake surfaces 11a to 11d (11a and 11b are not shown) of each ball blade are different surfaces . The groove bottoms 7a1 to 7d1 (7a1 and 7b1 are not shown) of each gasche are arranged behind the rotation direction A of the medium and low gradient blades . For example, the gash groove bottom 7d1 shown in FIG. 6 (FIG. 8) is arranged in the rotational direction A behind the low slope edge 8d inside. With this configuration, the rigidity of the low-gradient edge in the vicinity of the rotation axis O is increased.

The above configuration will be described with reference to FIGS. Groove bottom gash 7d shown in FIG. 8 7d1, to the low slope edge 8d in consisting ridgeline formed between rake surface 12d flank 10d of the low-gradient edges 8d in, are arranged in the direction of rotation A rear.

As shown in FIG. 10, one method for realizing the above configuration is to set the rake angle γ2 of the rake surfaces 12a to 12d of the medium and low gradient blades 8a to 8d to the rake surfaces 11a to 11d of the ball blades 6a to 6d. than the rake angle γ1 is to increase the negative side. This large rake angle γ2 of Medium-low gradient blade on the negative side than the rake angle γ1 of the ball cutting edge, rake face 11a~11d of each ball blade, the rake surface of the medium each corresponding low gradients blade 8a~8d It will be located behind rotation direction A from 12a-12d. For this reason, when grinding is performed to form various types of cutting edges in the cutting edge portion 3, the rake face of the medium and low gradient blade connected to the end portions P1 to P4 of the ball blade and the rake face of the ball blade There may be a minute step in the connecting portion.

Another method for realizing the above configuration is to increase the size of the gasches 7a to 7d. The medium-low gradient blade 8d shown in FIG. 6 (FIG. 8) will be described as an example. For example, the width in the rotation direction A of the gash 7d is increased by grinding. This allows placement than Medium low gradient edge 8d in the direction of rotation A rear groove bottom 7d1 gash 7d. Further, as shown in FIG. 7 (FIG. 9), a groove bottom 7d1 of the gash 7d is formed from a boundary point K1 where the scoop surface 12d of the medium / low gradient blade 8d1 and the scoop surface 11d of the ball blade intersect on the gash 7d side. May be.

With the above structure, the rigidity of the low-gradient edge in the vicinity of the rotation axis O is increased. The clearance angles of the flank faces 9a to 9d of the ball blade and the clearance angles of the flank faces 10a to 10d of the medium / low gradient blade are set to substantially the same value. Further, the clearance angle of the flank 9a~9d ball blade, by setting the range clearance angle of 7 ° or 21 ° or less of the flank 10a~10d low gradient blade within, the difficult-to-cut materials of high hardness In order to perform high-feed roughing, high-efficiency cutting with a large depth of cut or feed amount prevents chipping or chipping of ball blades and medium / low-gradient blades. Stable cutting is possible.

If the clearance angle of the flank faces 9a to 9d of the ball blade and the clearance angle of the flank faces 10a to 10d of the medium / low gradient blade are smaller than 7 ° , the rigidity of the ball blade and the medium / low gradient blade will be improved, but the clearance surface Since the cutting resistance due to the progress of wear increases, chatter vibration tends to occur when performing highly efficient cutting. In addition, when the clearance angle of the flank surfaces 9a to 9d of the ball blade and the flank angle of the flank surfaces 10a to 10d of the medium / low gradient blade is larger than 21 °, the cutting resistance is reduced and the machinability is improved. Since the strength (rigidity) of the blade and the medium / low gradient blade is lowered, chipping and chipping tend to occur when performing highly efficient cutting. Therefore, the clearance angle of the flank 10a~10d of the clearance angle of the flank 9a~9d ball blade, in low gradient blade is preferably 7 ° or 21 ° or less, more preferably 19 ° 9 ° or higher.

Details of the above configuration example will be described based on FIG. 8 and FIG. 9 by taking the ball blade 6d and the medium / low gradient blade 8d as an example. In FIG. 8, the medium / low gradient blade 8d having the rake face 12d includes a curved medium / low gradient blade 8d1 that is recessed backward in the rotation direction A from the rotation axis O to the end K, and the rotation axis from the end K. While it formed in a straight line to the vicinity position P4 heart O made of a low slope blade 8d2 Prefecture. In FIG. 8, the straight medium / low gradient blade 8d2 is connected to the ball blade 6d at a position P4 in the vicinity of the rotational axis O, and the concave medium / low gradient blade 8d1 and the straight medium / low gradient blade 8d2 A rake face 11d of the ball blade 6d is formed from the boundary point K. The rake face 11d is used as one side face of the gash 7d, and the ridge line on the rotation direction A side of the rake face 11d is used as a groove bottom 7d1 of the gash 7d. Groove bottom gash 7d 7d1 is positioned in the rotational direction A backward from the low slope edge 8d inside.

Ball blade 6d low and low slope edge 8d shown in FIG. 8 has the following configuration. That is, in the low-gradient edges 8d is in the low gradient edge 8d flank 10d and the middle low gradient edge 8d rake face 12d and recessed rotationally trailing formed by curved first ridge 8d1 (in concave-curved low slope blade 8d1), from the rake face 12d of the first and a second ridge straight leading to the end K of the ridge 8d1, and a flank 10d in the low gradient edge 8d, in low slope edge 8d It is composed of a second ridge line 8d2 ( linear medium / low gradient blade 8d2) formed by the rake face 11d of the ball blade 6d inclined backward in the rotation direction A. Other ball blades 6a to 6c and other medium / low gradient blades 8a to 8c have the same configuration as the ball blade 6d and medium / low gradient blade 8d .

As described above, increase in the negative side than the low gradient edge rake angle a (.gamma.2) rake angle of the ball cutting edge (.gamma.1) in shown in FIG. 10 (a), the width in the rotational direction A of the gash 7a~7d If is increased , there may be a step formed in the gashes between the rake face of each medium and low gradient blade and the rake face of the ball blade. When this step is generated, the reinforcing portion may be formed so as to fill a part of the gasche in which the step portion is generated during grinding of the cutting edge portion 3. This reinforcement part becomes a reinforcement part which gave grinding processing in order to connect both rake faces smoothly, and can improve the rigidity of medium-low gradient blades 8a-8d.

FIG. 10 (a) shows a cross section taken along line B2-B2 of the medium / low gradient blade 8d shown in FIG. 8, and FIG. 10 (b) shows a cross section taken along line B3-B3 of the ball blade 6d shown in FIG. As shown in FIGS. 10 (a) and 10 (b), the rake angle γ1 of the ball blade 6d is preferably set in the range of −30 ° to 20 °, and the rake angle γ2 of the medium / low gradient blade 8d is It is desirable to set in the range of -30 ° to 20 °.

When the rake angle γ2 of the medium / low gradient edge 8d is smaller than −30 °, the rigidity of the medium / low gradient edge 8d is improved, but the cutting resistance increases and the chip discharge performance deteriorates. In this case, chatter vibration tends to occur. In addition, when the rake angle γ1 of the medium / low gradient blade 8d is larger than 20 °, the cutting resistance is reduced and the machinability is improved, but the rigidity of the medium / low gradient blade 8d is reduced, so that highly efficient cutting is performed. In such a case, chipping and defects tend to occur. For this reason, it is more preferable that the rake angle γ2 of the medium / low gradient blade 8d is set in a range of −10 ° to 15 °.
Moreover, it is desirable to set the ball blade 6d to be larger on the negative side than the rake angle γ1. As a result, the rigidity of the medium / low gradient blades 8a to 8d can be improved, so that chipping and chipping of the medium / low gradient blades can be prevented even if a large machining load is applied to each medium / low gradient blade during machining. I can .

FIG. 9 which is an enlarged view of FIG. 7 shows an example in which the groove bottom 7d1 of the gash 7d is formed from the boundary point K1 where the rake surface 12d of the medium / low gradient blade 8d1 and the rake surface 11d of the ball blade intersect on the gash 7d side. Show . As shown in FIG. 9, when the groove bottom 7d1 of the gash 7d is formed from the boundary point K1 , the width of the rake face 11d of the ball blade can be increased, so that the grinding of the rake face 11d is facilitated, and the ball edge 6d and the straight line The rigidity of the medium- and low-gradient blade 8d2 is improved .

FIG. 11 shows another configuration example in the vicinity of the connection point P4 between the medium / low gradient blade 8d and the ball blade 6d in the vicinity of the rotation axis O. The same applies to the other medium / low gradient blades 8a, 8b, and 8c.

In the example shown in FIG. 11, the medium / low gradient blade 8d is shorter than that shown in FIG . Without providing the straight medium / low gradient blade 8d2, the end of the medium / low gradient blade 8d is integrally connected to the ball blade 6d at the position P4 in the vicinity of the rotation axis O, and the groove bottom 7d1 of the gash is formed from the position P4. doing. Further, a rake face 11d of the ball blade 6d is formed from the position P4 . As described above, the configuration shown in FIG. 11 is also applied to the other medium / low gradient blades 8a to 8c and the other ball blades 6a to 6c.

Figure 12 shows a further improved embodiment for the embodiment shown in FIG. 11. FIG. 12 shows an example in which the gash groove bottom 7d1 is formed from the edge portion K2 on the ash line of the ridge line formed by the rake face 12d of the medium / low gradient edge 8d and the rake face 11d of the ball edge 6d. In this configuration example, it is possible to increase the width of the rake face 11d of the ball blade 6d, it is possible to improve the strength of the ball cutting edge 6d. Configuration shown in FIG. 12 are also employed for the low gradient blades 8a~8c and other balls blade 6a~6c among others.

In the present invention, the positions P1, P2, P3, and P4 in the vicinity of the rotation axis O that is a connection point between the medium and low gradient blades 8a, 8b, 8c, and 8d and the ball blades 6a, 6b, 6c, and 6d. Which of the above-described embodiments is adopted for the configuration in the vicinity of the like may be appropriately determined in consideration of the diameter D of the cutting edge portion 3, the ease of grinding in the vicinity of the rotation axis O, and the like.

In the multi-blade ball end mill of the present invention, the flank 9a, 9b, 9c, 9d of the ball blade and the flank 10a, 10b, 10c, 10d of the medium and low gradient blade were formed using an ultra-thin rotating grinding wheel. Although grinding is performed using an NC control grinding device, grinding of the flank faces 9a to 9d of the ball blade and grinding of the flank faces 10a to 10d of the medium and low gradient blades are performed in separate steps . The reason for this is because very grinding flank 10a~10d low gradient edge in the small range (area) that must be accurately grinding wheel having a fine grinding wheel width, for example, grinding wheel width This is because it is necessary to use a grinding wheel of 1 mm or less.

As described above, since the grinding of the flank 9a to 9d of the ball blade and the grinding of the flank 10a to 10d of the medium and low gradient blade are performed in separate steps, the flank 9a to 9d of the ball blade, and Grinding traces (grinding lines) appearing on the surfaces of the flank 9a and flank 10a when the surfaces of the flank 10a to 10d of the medium and low gradient blades are observed with a microscope, for example, 30 to 50 times larger It can be seen that the direction of is different.

FIG. 13 shows another example of the configuration in the vicinity of the rotational axis O of the multi-blade ball end mill of the present invention, which is a curved medium / low gradient blade in which medium / low gradient blades 8a, 8b, 8c, 8d are recessed backward in the rotation direction A. An example consisting only of The structural features in the vicinity of the rotation axis O shown in FIG. 13 are formed between the relief surfaces 10a, 10b, 10c, 10d of the medium and low gradient blades where the concave curved surface portions 16a, 16b, 16c, 16d are adjacent. That is .

The concave curved surface portions 16a, 16b, 16c and 16d are grooves provided to connect the adjacent flank surfaces 10a and 10b, the flank surfaces 10b and 10c, the flank surfaces 10c and 10d, and the flank surfaces 10d and 10a. Etc. These concave curved surface portion 16a, the gash 7a from the rotation axis O, 7b, 7c, are formed toward 7d, each gash 7a from the rotation axis O, 7b, 7c, cross section perpendicular to the direction toward the 7d Slowly such a substantially U-shaped. Further, the concave curved surface portions 16a, 16b, 16c and 16d are gently inclined downward from the vicinity of the rotation axis O toward the respective gashes 7a, 7b, 7c and 7d.

Of the concave curved surface portions 16a, 16b, 16c, 16d, the configuration of the concave curved surface portion 16d formed between the adjacent flank surfaces 10d and 10a will be described as an example. The rake face 12d and a side face behind the flank 10a in the rotational direction A are configured. The concave curved surface portions 16a, 16b, 16c and 16d are formed by machining into a substantially U-shaped cross section using an NC-controlled grinding machine equipped with a thin disc-shaped diamond grindstone.

The concave curved surface portions 16a, 16b, 16c, and 16d are formed of extremely thin and minute chips generated by the medium and low gradient blades 8a, 8b, 8c, and 8d during the cutting of the work material, and the gashes 7a, 7b, 7c, and 7d The action of discharging in the direction is performed. Among low-gradient edges 8a, 8b, 8c, gash 7a of chips generated by 8d, 7b, 7c, emissions to 7d are inclined (a) each flank 10a, 10b, 10c, 10 are on the side of the shank portion Inclination with an angle α and (b) the concave curved surface portions 16a, 16b, 16c, and 16d are further improved.

  Subsequently, other features of the medium / low gradient blade in order to perform high-feed machining of a work material using the multi-blade ball end mill of the present invention will be described. FIG. 14 is a plan view of the distal end portion of the cutting edge portion 3 when viewed from the direction of the rotation axis O, and is a view for explaining the shape characteristics of the medium / low gradient blade.

The width X of the medium / low gradient blade is preferably set in the range of 1.25% to 3.75% of the diameter D of the cutting edge 3. Among the width X of the low-gradient edges, in a plan view of the tip portion of the cutting edge portion 3 from the rotation axis O direction, a distance to the end of the low-gradient edge in the rotation axis O. In the example shown in FIG. 14, in the low gradient edge 8d is composed of recessed curved in low gradient blade 8d1 and linear in the low gradient blade 8d2 Metropolitan in the direction of rotation A rear, the width X is the rotation axis O is the distance to the end of the linear in the low gradient blade 8d2 (end of the ball cutting edge 6d side) from.

The above-mentioned width X of the medium / low gradient blade ensures the length of the ball blade and ensures that the cutting blade (medium / low gradient blade) near the rotation axis O where the cutting speed is 0 is inclined to the shank part 2 side. to, it is possible to high-efficiency cutting.

If in the less than 1.25% of the diameter D of the cutting portion 3 expired width X of the low-gradient edges, inclined middle low gradient edge in contact with the rotation axis O in order to provide the end of the low-gradient edges on the side of the shank portion Since it becomes necessary to make the angle α extremely large, it becomes difficult to machine the medium and low gradient blades and their flank faces. Further, in case where the width X of the low gradient blade exceeds 3.75% of the diameter D of the cutting portion cut, since the ball blade 6a~6d is relatively shorter than the width X of the insole gradient blade purpose the invention and to that cutting using the high-efficiency high-feed by multi blade ball end mill it can not be achieved.

FIG. 15 is an enlarged view of FIG. In the present invention, when the medium and low gradient blades 8a, 8b, 8c, and 8d are constituted by only concave curved medium / low gradient blades or straight medium / low gradient blades and concave curved medium / low gradient blades , the concave curve It is desirable that the shape of the middle and low gradient blade is as follows.

Low Gradient blade 8d1 in concave-curved indicating the desired shape in the concave-curved lower gradient edge in FIG. 15 will be described as an example. In the concave curved medium / low gradient blade 8d1, the point a1 located on the most rear side with respect to the rotation direction A is closer to the rotation axis O side than the point a which is the center position of the concave curved medium / low gradient blade 8d1. It is desirable to provide it. The other concave curved medium / low gradient blades 8a1, 8b1, and 8c1 are the same as described above. Thereby, the rigidity of each concave-curved medium / low gradient blade can be further improved.

Among low-gradient edges 8a, 8b, 8c, low gradient edge in the concave-curved 8d is desirable to extend continuously towards the rotation axis O to the ball cutting edge. Furthermore, when a concave curved medium / low gradient blade and a linear medium / low gradient blade are provided, the concave curved medium / low gradient blade, the linear medium / low gradient blade, and the ball blade are continuous as one cutting blade. Te, it is desirable to constitute the cutting edge led to integrally. In this case, it is preferable to provide a concave curved medium / low gradient blade on the rotation axis O side and a linear medium / low gradient blade on the ball blade side .

Note that a1 point located rearward of the most rotational direction during concave-curved lower gradient blades, when provided at the center in the concave-curved lower gradient blade, or the center of the lower gradient blades in concave-curved When it is provided on the ball blade side from point a, the angle formed by the concave curved medium / low gradient blade and the straight medium / low gradient blade or the angle formed by the concave curved medium / low gradient blade and the ball blade is small. For this reason, stress concentrates on a portion where the angle is reduced due to a load of cutting work, and the rigidity of the concave-curved medium / low gradient blade tends to decrease.

In the present invention, when the medium / low gradient blade is constituted only by the concave curved medium / low gradient blade, the above-mentioned “point a which is the center position of the concave curved medium / low gradient blade” is as follows. Defined in That is, the rotation axis O, the interval between any point M of the curve shape in low gradient on the blade, the rotation axis O, and a connection point between the curved during ball blade is connected to a low gradient blade The point M that is the position of the straight line connecting the two points (corresponding to the width X of the medium and low gradient blade described above) is defined as the above-mentioned “point a”.

Similarly, in the present invention, when the medium / low gradient blade is composed of a straight / medium / low gradient blade and a concave / curved medium / low gradient blade, the rotation axis O and any arbitrary on the concave / curved medium / low gradient blade are arranged . When the distance from the point M is half the width X of the medium / low gradient blade shown in FIG. 14, the point M is defined as the “point a”.

Further, in the present invention, the above-described “point a1 located on the most rear side with respect to the rotation direction A in the concave curved medium / low gradient blade” is defined as follows. That is, the rotation axis O and, connecting the connection point of the in concave-curved lower gradient blade and ball blade linear or rotational axis O and, during concave-curved lower gradient blade and linear low gradient blade A point on the concave curved medium / low-gradient blade that is located closest to the rear side in the rotation direction A is defined as “point a1”.

Further, in the present invention, as shown in FIG. 15, in the medium and low gradient blades including the concave curved medium and low gradient blades 8d1 and the like, the point a1 that is located most rearward in the rotational direction A is based on the rotational axis O. It is desirable to be within a section h of 20% or more and 40% or less of the width X1 of the concave curved medium / low-gradient blade when measured. Thereby, the rigidity of the medium / low gradient blades such as the concave curved medium / low gradient blade 8d1 is further improved.

When the point a1 located on the most rearward side in the rotational direction of the concave curved medium / low gradient blade is measured with reference to the rotation axis O, it is less than 20% of the width x1 of the concave curved medium / low gradient blade. If provided in a position it is, difficult through the concave-curved lower gradient blade is formed by grinding ing. In addition, when the point a1 is provided at a position exceeding 40% of the width x1 of the concave curved medium / low gradient blade when measured from the rotation axis O, the rigidity of the concave curved medium / low gradient blade is provided. However, it tends to decrease slightly.

[Production method]
The multi-blade ball end mill of the present invention is a solid type ball end mill made of a WC-based cemented carbide. Ball end mill made of cemented carbide, as described above, WC cemented carbide powder obtained by mixing Co (cobalt) powder (tungsten carbide) powder was molded into a cylindrical shape by a mold, the obtained molded body 1300 after firing at about ° C., and performs a predetermined finishing the cutting edge or the like, further, if necessary, be produced by coating the wear-resistant hard coating on the surface of the cutting edge portion 3. This hard film is made of , for example, TiSiN, TiAlSiN, CrSiN, AlCrSiN, or the like . Specifically, it consists of any one of nitride, carbonitride, and oxynitride containing one or more elements selected from the elements of periodic table 4a, 5a, 6a group metals, Al, Si, B It is desirable to coat the hard coating to a thickness of 3-5 μm .

Molding and sintering of the solid-type multi-blade ball end mill, can be performed by conventionally general powder molding methods have been employed in and firing method, a detailed description thereof will be omitted.
In order to produce the multi-blade ball end mill of the present invention, finishing processing is performed on the cutting edge portion 3 of the multi-blade ball end mill after firing, in particular, the ball blades 6a, 6b, 6c, 6d at the tip of the cutting edge portion 3. , low gradient blades 8a, 8b, 8c, 8d, gash 7a, 7b, 7c, finishing and 7d into a predetermined shape performed in. Finishing is performed using an NC (CNC) controlled grinding machine equipped with a thin disc-shaped diamond grinding wheel.

[Second Embodiment]
FIG. 16 is a front view of the distal end portion of the cutting edge portion 3 of the multi-blade ball end mill according to the second embodiment of the present invention as viewed from the direction of the rotation axis O. The multi-blade ball end mill 1a according to the second embodiment includes three ball blades 6a, 6b, 6c, and from the end portions P1, P2, P3 of each of the ball blades 6a, 6b, 6c, medium to low gradient blades 8a, 8b, 8c extends to the rotation axis O. Further, the three ball blades 6a, 6b, 6c are arranged at equal intervals around the rotation axis O, and gashes 7a-7c are provided between the ball blades . Since the basic configuration other than this is substantially the same as that of the four-blade multi-blade ball end mill of the first embodiment, a detailed description of the configuration is omitted.

A description will be given of an experimental example in which a multi-blade ball end mill made of cemented carbide according to an example of the present invention is manufactured, the work material is cut, and the wear state of the cutting edge is observed and evaluated.

(Experiment 1)
A four-blade ball end mill made of the WC base of the present invention (hereinafter referred to as Invention Example 1) was prototyped and a surface cutting experiment (Experimental Example 1) was performed on a work material made of SKD61 (alloy tool steel). Then, the wear of the ball blade and the medium / low gradient blade was observed. In Experimental Example 1, for comparison with the present invention Example 1, Comparative Example 1 was carried out similar cutting experiments for the four cutting edges ball end mill which is already commercially available. The multi-blade ball end mill of Comparative Example 1 has a shape in which the tip portion of the cutting edge portion is immersed in the vicinity range C (corresponding to the circle “C” shown in FIG. 5) of the rotation axis O. is a multi-blade ball end mill that does not have a low gradient edge in which is provided (equivalent to a multi-blade ball end mill described in Patent Document 5).

The multi-blade ball end mill of the present invention example 1 used in Experimental Example 1 has four ball blades, the diameter D of the cutting edge portion 3 is 8 mm, the width t of the hollow portion 13 shown in FIG. 2 is 0.55 mm, low slope edge inclination angle α is 2 °, and the width X of the middle low gradient blade is 0.275 mm, in the low gradient blade low gradient low gradient blade and concave-curved in a straight line as shown in FIG. 6 in The end point a1 in the rotational direction of the concave curved medium / low gradient blade is provided at a position that is 30% of the width X1 of the concave curved medium / low gradient blade . The overall length L of the multi-blade ball end mill is 100 mm, and the tool protrusion amount OH when mounted on an NC-controlled 3-axis machining center is 32 mm, that is, “tool protrusion amount OH / diameter D” (OH / D) It was set to 4 .
The clearance angle of the ball blade of the multi-blade ball end mill of Example 1 of the present invention is 10 °, the rake angle of the ball blade is −11 °, the clearance angle of each medium / low gradient blade is 10 ° , and the rake angle of the medium / low gradient blade is It was −11 °. On the other hand, the multi-blade ball end mill of Comparative Example 1 has a medium-to-low-gradient blade provided in Invention Example 1 with a ball blade clearance angle of 17 ° and a ball blade rake angle of −14 °. I didn't .

In Experimental Example 1, the multi-blade ball end mills of Invention Example 1 and Comparative Example 1 were mounted on an NC-controlled three-axis machining center, and cutting was performed under the following cutting condition 1. And after 30 minutes have passed since the start of machining (after 30 minutes machining), 60 minutes have passed (after 60 minutes machining), and 90 minutes have passed (after 90 minutes machining), the cutting edge (ball blade) In order to observe the wear of the flank, the amount of exposure of the base material due to wear was measured as the flank wear width (VBmax).

(Cutting condition 1)
Machining method: Flat cutting by dry cutting (air blow) Cutting speed (Vc): 94 [m / min]
Number of revolutions (n): 3750 [min ^-1 ]
Feed rate (Vf): 1500 [mm / min]
Feed per tooth (fz): 0.1 [mm / tooth]
Axial depth of cut (ap): 0.7 [mm]
Radial depth of cut (ae): 1.75 [mm]
Tool protrusion (OH): 32 [mm]

The results of the carried out in cutting conditions 1 cutting experiment shown in FIGS. 17 to 19. FIGS. 17 to 19 are photographs showing the state of wear of the cutting edge after 30 minutes have elapsed, 60 minutes have elapsed, and 90 minutes have elapsed, respectively, in an enlarged manner from the direction of the rotation axis O. Te, in each figure (a) shows the present invention example 1, (b) shows a comparative example 1. The rotation axis O is located at the center of each photograph shown in FIGS . 17 to 19, and four ridge lines and surfaces extending in an arc shape from the rotation axis O toward the outer peripheral portion are ball blades (6a, 6b, 6c, a 6d) and its flank (9a, 9b, 9c, 9d ). In these photographs, in order to clearly show the position of the ball cutting edge and a flank, the sign of the ball cutting edge in FIG. 17 (a) (6a, 6b , 6c, 6d) and, flank the coding (9a, 9b, 9c , and 9d), it indicates the sign (O) of the rotation axis.

The following matters were found from the results of Experimental Example 1 shown in FIGS.
(1) In the multi-blade ball end mill of Example 1 of the present invention, when the cutting time reached 60 minutes, no chipping, chipping, or wear occurred on the four ball blades and the medium / low gradient blade (FIG. 17). (See (a) and Fig. 18 (a)).

(2) In the multi-blade ball end mill of Invention Example 1, when the cutting time reached 90 minutes, the wear width of the flank face of the ball blade was 0.12 mm. This wear width is uniform wear (see FIG. 19 (a)) generated on the cutting edge in normal cutting, and is considered not to affect the machining accuracy of the work material. The wear width is an average value of the flank wear width (VBmax) of a 4-blade ball blade.

(3) In the multi-blade ball end mill of Comparative Example 1, when the cutting time reaches 30 minutes, a uniform and minute wear width is observed on the flank surface near the rotation center axis of the ball blade (FIG. 17 (b )), It was confirmed that the wear width further expanded after the cutting time reached 60 minutes (see Fig. 18 (b)).

(4) In the multi-blade ball end mill of Comparative Example 1, when the cutting time reached 90 minutes, as shown in FIG. 19 (b), the wear width expanded from the ball blade to the flank to 0.20 mm . The wear width of 0.20 mm is close to the life of a general roughing tool, and is considered to affect the machining accuracy of the work material.

(5) The results of the above (1) to (4), multi-blade ball end mill of the present invention Example 1, can be reduced to half the wear width of the ball cutting edge after machining 90 minutes in Comparative Example 1, It can be judged that it has a long life.

(Experimental example 2)
When the tool protrusion amount OH when the multi-blade ball end mill of the present invention was mounted on an NC-controlled three-axis machining center was made larger than that of Experimental Example 1, the wear of the ball blade and the medium / low gradient blade by cutting was observed .
In Experimental Example 2, OH / D is set to 6, and the standing wall of the work material made of steel type “YXR3 (58 HRC)” (YXR3 is a registered trademark) used for cold forging dies under the following cutting condition 2 The pocket equipped with was cut (length: 25 mm, width: 25 mm, height: 14.7 mm). The specifications of the ball end mills of the present invention and the comparative example used in Experimental Example 2 were the same as those of the multi-blade ball end mill of the present invention Example 1 and Comparative Example 1 used in Experimental Example 1, respectively.

(Cutting condition 2)
Processing method: Dry cutting (air blow), pocket processing of standing wall Cutting speed (Vc): 38 [m / min]
Number of revolutions (n): 1500 [min ^-1 ]
Feed rate (Vf): 225 [mm / min]
Feed per tooth (fz): 0.075 [mm / tooth]
Axial depth of cut (ap): 0.35 [mm]
Radial depth of cut (ae): 1.23 [mm]
Tool overhang (OH): 48 [mm]

Figure 20 shows an enlarged photograph showing the wear of the ball cutting edge when performing cutting of 90 minutes workpiece in Experimental Example 2, the present invention example 1 in the upper row, the Comparative Example 1 in the lower. The “imaging direction A” shown in FIG. 20 indicates that the image was taken from the direction of the extension line of the rotation axis O of the multi-blade ball end mill, and the “imaging direction B” was taken from an oblique upper side on the extension line of the rotation axis O. It shows that .

From the results of Experimental Example 2, the following matters were clarified.
(1) In the present invention example 1 , the wear width of the flank face of the ball blade was 0.07 mm, and the wear was stable. No wear or breakage of the medium or low gradient blade was confirmed.
(2) In Comparative Example 1 , the wear width of the flank face of the ball blade was 0.07 mm, but chipping occurred in the ball blade at the position indicated by a circle in the row in the photographing direction B of FIG. The cause of such chipping in the ball blade of Comparative Example 1 is that there is no cutting edge in the recessed area C near the rotation axis O of the ball blade, so the pocket portion with a standing wall is cut. This is presumably because chattering vibration occurred in the range C and chatter vibration occurred.

(Experiment 3)
The tool protrusion amount OH was further increased compared to Experimental Example 2 (OH / D = 7), and a cutting test was performed on the work material made of SKD11 (60 HRC) under the following cutting condition 3, and the ball blade and The wear of medium and low gradient blades was observed . In Experiment 3, the present invention uses a multi-blade ball end mill of the present invention Example 1 in Experimental Example 1 and Experimental Example 2, Comparative Examples using two kinds of multi-blade ball end mill.

One of the two types of multi-blade ball end mills of the comparative example has a configuration in which all the ball blades are extended to the rotation axis O, and the ends of the ball blades on the rotation axis O side are substantially in contact with each other. A multi-blade ball end mill (hereinafter referred to as Comparative Example 2). Multi blade ball end mill of Comparative Example 2 corresponds to a multi-blade ball end mill described in Patent Document 3.

Another type of the comparative example is a multi-blade ball end mill of the present invention shown in FIG. 5, in which the flank faces 10a, 10b, 10c, 10d of the insole gradient blade are not inclined toward the shank portion. (Hereinafter referred to as Comparative Example 3).

(Cutting condition 3)
Machining method: Flat cutting by dry cutting (air blow) Cutting speed (Vc): 94 [m / min]
Number of revolutions (n): 3750 [min ^-1 ]
Feed rate (Vf): 1500 [mm / min]
Feed per tooth (fz): 0.1 [mm / tooth]
Axial depth of cut (ap): 0.7 [mm]
Radial depth of cut (ae): 1.75 [mm]
Tool protrusion (OH): 56 [mm]

Figure 21 is an enlarged photograph showing the wear of the ball cutting edge when performing cutting for 40 seconds in the workpiece by Experimental Example 3. Cutting distance by cutting for 40 seconds in the experimental example 3 is 1 m, Fig. 21 shows a state of the ball cutting edge in the cutting early (early after the start of cutting). In the upper part of FIG. 21, Example 1 of the present invention, Comparative Example 2 in the middle, and Comparative Example 3 in the lower part are shown . Shown in FIG. 21, "the imaging direction A" and "imaging direction B" is the same as displayed in Figure 20, "the imaging direction A" and "imaging direction B".

The following matters were clarified from the results of Experiment Example 3 in which the tool protrusion amount OH was increased to 56 mm.
(1) In Inventive Example 1, as shown in the upper part of FIG. 21, normal wear occurred at the location of the ball blade indicated by a circle . In addition, no wear or defects were found on the medium and low gradient blades.
(2) In Comparative Example 2, the occurrence of chipping was confirmed at the location of the ball blade indicated by a circle in the middle of FIG.
(3) In Comparative Example 3, occurrence of minute local chipping was confirmed on the ball blade indicated by a circle in the lower part of FIG.

(4) In the multi-blade ball end mills of Comparative Example 2 and Comparative Example 3, it is considered that the cause of chipping and chipping in the ball blade early after the start of cutting is as follows. In the multi-blade ball end mills of Comparative Examples 2 and 3, the tip of each ball blade was extended so as to be in contact with the rotation axis O, and the cutting process was performed with the tool protrusion amount OH increased to 56 mm. In addition, unstable cutting with the processing load concentrated on the tip of the ball blade during flat cutting causes chatter vibration, and the processing load acting on the ball blade is uneven due to chatter, resulting in chipping. Can be guessed. On the other hand, in the present invention example 1, the low-gradient edge in the four as described above with respect to the rotation axis O perpendicular to the plane, because the slightly inclined to the side of the shank portion, these four also equally contribute to cutting in low gradient blade, considered chatter vibration has not occurred.

From the results of Experimental Examples 1 to 3, in the multi-blade ball end mill, the arrangement and configuration of the cutting edge in the vicinity of the tip of the ball blade, that is, in the vicinity of the rotation axis O, are large in generating chatter vibration during cutting. It is considered to have an influence. The reason for this will be described with reference to FIG.

FIG. 22 (a) shows an example of a conventional solid carbide multi-blade ball end mill made of cemented carbide , in which an arc-shaped ball blade 20 is formed at a portion intersecting with the rotation axis O (hereinafter referred to as “conventional”). example 1 "hereinafter) indicating the. Using the multi-blade ball end mill of Conventional Example 1 to perform high-feed roughing on difficult-to-cut materials 21 with high hardness, a large machining load acts on the portion of the ball blade that intersects the rotation axis O, and the ball blade Cuts while contacting the workpiece 21 at a point Q that intersects the rotational axis O. At this time, since the point Q cutting (rotational) speed is 0, the ball cutter 20 will perform cutting in an unstable state while dragging the point Q with respect to the workpiece 21. When cutting is performed in such an unstable state, vibration such as chatter vibration is induced and chipping or the like occurs in the ball blade.

22 (b) is an example of a rotation axis O vicinity of a conventional multi-blade ball end mill provided with a recess 22 so as to remove the ball blade (hereinafter, referred to as "prior art 2") the schematic configuration of a distal end portion of the Show . In Conventional Example 2, the end of the ball blade 20 is disposed at the edge of the recess 22. Conventional Example 2 corresponds to the ball end mill disclosed in Patent Document 5.

When high feed roughing is performed on the hard hard-to-cut material 21 using the multi-blade ball end mill of the conventional example 2 , a large machining load acts on the edge of the recess 22, so it is arranged at the edge of the recess 22. progress of wear at the end near the ball cutting edge 20 there are faster, resulting in cutting in an unstable state is carried out to induce chattering, chipping the ball cutter 20 is generated. Therefore, the configuration of the cutting edge in the vicinity of the rotational axis O provided in the ball end mills of Conventional Example 1 and Conventional Example 2 is not suitable for high-feed machining of the hard-to-cut material 21 with high hardness.

FIG. 22 (c) schematically shows the configuration of the tip of the multi-blade ball end mill of the present invention (hereinafter referred to as “example of the present invention”). In the example of the present invention, a medium / low gradient blade connected to the ball blade in the vicinity of the rotation axis O and in contact with the rotation axis O is provided. It is inclined to the side of the part. That is, the multi-blade ball end mill of the distal end portion in the recess portion 13 (see FIG. 2) are formed, the low gradient blade 8a in contact with the rotation axis O connected to the ball cutting edge 20 in the recess 13, 8b etc. Is arranged . The angle at which the medium / low gradient blade is inclined toward the shank portion 2 (inclination angle with respect to the plane perpendicular to the rotation axis O) is as small as 0.5 ° or more and 3 ° or less.

In this way, using the multi-blade ball end mill of the present invention having the basic configuration shown in FIG. 22 (c), for example, a multi-blade ball end mill having four ball blades, a hard hard-to-cut material 21 When the high feed roughing is performed, the end of the ball blade side such as the four medium and low gradient blades 8a, 8b and the vicinity thereof are four points Q1, Q2, which are 90 ° apart from the work material 21, Q3 and Q4 carries out the cutting (Figure 22 (c) in the illustrated only Q1, Q3), since the main cutting ball blades 21, cutting in a stable condition with respect to the work material 21 is advanced. As a result, the multi-blade ball end mill of the present invention is unlikely to generate chatter vibrations, and therefore, it is considered that no chipping or the like occurs in the ball blade.

As described above, when high-feed roughing is performed on difficult-to-cut materials with high hardness, the arrangement and configuration of cutting edges near the tip of the ball blade, that is, near the rotation axis O, generate chatter vibration. Therefore, an experiment (Experimental Example 4) was conducted to confirm the state of vibration generation by measuring the cutting resistance during cutting.

(Experimental example 4)
In Example 4, a multi-blade ball end mill one invention embodiment, the 3 component force waveform cutting force when performing the cutting of the workpiece using two multi-blade ball end mill of Comparative Example Measurement was made with a cutting dynamometer manufactured by Kistler, and the presence or absence of vibration was determined from the time-series changes in the waveforms of the three component forces Fx, Fy, and Fz . The multi-blade ball end mill of the example of the present invention used in Experimental Example 4 has the same specification as that of Inventive Example 1 used in Experimental Examples 1 to 3. Moreover, multi-blade ball end mill of the two comparative examples were the ball end mill of Comparative Example 1 used in the experiment example 1, the same specification as in Comparative Example 3 was used in Experimental Example 3.

In Experimental Example 4, fitted with a multi-blade ball end mill of the present invention and comparative examples as a tool overhang OH in 3-axis machining center of each NC control is 32 mm (OH / D = 4 ), Experimental Example 1 Under the same cutting condition 1, a workpiece made of YXR3 (58 HRC) (YXR3 is a registered trademark) was subjected to plane cutting .

Figure 23 is a 3 component force Fx of the measured in Experimental Example 4 cutting resistance, Fy, shows the time series change of Fz, the horizontal axis represents the time elapsed after the (second) and the vertical axis represents the cutting resistance (N). FIG. 23 (a) shows the change in cutting resistance of the multi-blade ball end mill of Example 1 of the present invention, FIG. 23 (b) shows the change in cutting resistance of the ball end mill of Comparative Example 1, and FIG. shows a change in cutting resistance of the multi-blade ball end mill of Comparative example 3.

  The following items (1) to (4) were clarified from the results of Experimental Example 4 shown in FIG.

(1) The multi-blade ball end mill of Example 1 of the present invention shown in FIG. 23 (a) has a lower cutting resistance than that of Comparative Example 1 in all of the three component forces Fx, Fy, and Fz, and the time-series change of the waveform is regularly stabilized . This is the vibration is very small that occurred during cutting, irregular changes in vibration, i.e., indicates that chatter vibration is not generated.

(2) The multi-blade ball end mill of Comparative Example 1 shown in FIG. 23 (b) has a higher cutting resistance than the Example 1 of the present invention for all three component forces Fx, Fy, and Fz, and the time-series variation of the cutting resistance waveform is not. It was a rule (unstable). This is thought to be because the time series change of the cutting force waveform became irregular due to the occurrence of chatter vibration.

(3) For cutting waveform change in the resistance of the multi-blade ball end mill of Comparative Example 3 shown in FIG. 23 (c), but Fx is substantially the same as Working Example 1, Fy and Fz are as in the present invention Example 1 It was not a stable and regular change. The reason for this is thought to be that minute chatter vibrations occurred because the ball end mill of Comparative Example 3 did not have the medium and low gradient blades provided in Example 1 of the present invention.

(4) According to the above (1) to (3), the multi-blade ball end mill of the present invention has a recessed portion 13 at the tip , and the medium and low gradient blades 8a, 8b and the like have a small inclination angle α at the recessed portion 13. since the inclined shank portion with, it can be determined that the chatter vibration generating can be effectively suppressed.

(Experimental example 5)
In a rotary cutting tool such as a radius end mill, in order to suppress chatter vibration that occurs when the number of blades is increased in order to perform high-feed machining, a cutting blade (bottom blade) provided at the tip is so-called “unequal”. A means of arranging in “divided” is adopted. Disposing the cutting edges in unequal divisions means that a plurality of cutting edges formed at the tip are not arranged at the same angle (equal intervals) in the circumferential direction of the tool body around the rotation axis O. In other words, the cutting edges adjacent to each other about the rotation axis O are arranged at different angles. Multi blade ball end mill of the present invention used in the experiment example 1-4, four ball cutting a 90 ° interval around the rotation axis O, i.e., which was arranged in equally divided (equal angles or equal intervals) is there.

Therefore, in Experimental Example 5, a multi-blade ball end mill in which four ball blades are unequally divided is used to cut a work material made of YXR3 (58 HRC) (YXR3 is a registered trademark) under the following cutting conditions 5 the 3 component force waveform cutting resistance when processed measured, unequal division of the ball blade was evaluated whether there is effective in suppressing the chatter vibration. In this experiment, 90 ° corner processing was performed after linear planar processing, and linear planar processing was performed again without reducing the cutting speed . In Experimental Example 5, in order to compare with a multi-blade ball end mill arranged in unequal division, a three-component force waveform of cutting resistance was also measured for a multi-blade ball end mill equally divided. Therefore, in Example 5, nonuniform 2 ° (invention example 2) as the next four, nonuniform 4 ° (Invention Example 3), a multi-blade equal division Example 1, and equally dividing Example 2 An experiment was conducted on a ball end mill.

(Unequal division 2 °: Invention Example 2)
The multi-blade ball end mill of Example 2 of the present invention , except that four ball blades are sequentially arranged at angles of 88 °, 92 °, 88 ° and 92 ° (unequally divided 2 °) with the rotation axis O as the center , Other configurations are the same as those of the multi-blade ball end mill of Example 1 of the present invention used in Experimental Examples 1 to 3 .

(Unequal division 4 °: Invention Example 3)
The multi-blade ball end mill of Example 3 of the present invention , except that four ball blades are arranged at an angle of 86 °, 94 °, 86 ° and 94 ° (unequally divided 4 °) around the rotation axis O , Other configurations are the same as those of the multi-blade ball end mill of Example 1 of the present invention used in Experimental Examples 1 to 3 .
For multi-blade ball end mills with unequal division 2 ° and unequal division 4 °, the rake angle of the ball blade is -10 °, the clearance angle of the ball blade is 10 °, and the rake angle of the medium and low gradient blades 8a to 8c. Was set to −10 °, and the clearance angle of the medium and low gradient blade was set to 10 °. Further, the twist angle of the chip discharge groove 4 was set to 30 °.

(Equal division example 1)
It is the same specification as the multi-blade ball end mill of the present invention example 1 used in Experimental Examples 1 to 3, and is a ball end mill in which four ball blades are arranged equally divided at 90 ° around the rotation axis O. . The rake angle and clearance angle of the medium and low-gradient blades 8a to 8c of this multi-blade ball end mill were set to the same values as those of the ball end mill with unequal division 2 ° and 4 °.
(Equal division example 2)
A multi-blade ball end mill having the same specifications as the multi-blade ball end mill of Comparative Example 1 used in Experimental Examples 1 and 2, in which four ball blades are equally divided at 90 ° about the rotation axis O. The rake angle of the ball blade near the rotational axis of this multi-blade ball end mill is -14 °, the clearance angle of the ball blade is 17 °, and the twist angle of the chip discharge groove 4 is 40 °.

(Cutting condition 5)
Processing method: Plane cutting by dry cutting (air blow) Cutting speed (Vc): 100 [m / min]
Number of revolutions (n): 4000 [min ^-1 ]
Feed rate (Vf): 1920 [mm / min]
Feed per tooth (fz): 0.12 [mm / tooth]
Axial depth of cut (ap): 0.3 [mm]
Radial depth of cut (ae): 0.1 [mm]
Tool protrusion (OH): 32 [mm]

FIG. 24 shows a waveform of the three component forces of the cutting force in Experimental Example 5. In FIG. 24, (a) is a multi-blade ball end mill with a non-uniform division of 2 ° (Invention Example 2), (b) is a multi-blade ball end mill with a non-uniform division of 4 ° (Invention Example 3), and (c) is equal division example 1 of the ball end mill, showing (d) is a multi-blade ball end mill of equal division example 2 (Comparative example 1).

From the results of Experimental Example 5 shown in FIG. 24, the matters described in (1) to (4) below were found.
(1) In the multi-blade ball end mill with 2 ° unequal division shown in Fig. 24 (a) (Example 2 of the present invention), the waveform of the three component force is compared with that of Example 1 with equal division shown in Fig. 24 (c). Fx, Fy, and Fz showed no minute amplitude fluctuations. It can be determined that chatter vibration due to resonance did not occur in the multi-blade ball end mill (Example 2 of the present invention) with unequal division.
(2) In the non-uniformly divided 4 ° multi-blade ball end mill (Invention Example 3) shown in FIG. 24 (b), it can be determined that chatter vibration due to resonance has not occurred as in (1) above. it can.

(3) In the multi-blade ball end mill of the equally divided example 2 shown in FIG. 24 (d), as in the equally divided example 1 shown in FIG. 24 (c), the three component force waveforms Fx, Fy, and Fz are very small. A fluctuation in amplitude appeared. Accordingly, it can be determined that chatter vibration due to resonance has occurred in the multi-blade ball end mill of the equally divided example 2.
(4) From the above (1) to (3), it can be determined that if the ball blades formed at the tip of the multi-blade ball end mill of the present invention are arranged in unequal divisions, it is effective in suppressing chatter vibration due to resonance. . Since the chatter vibration is generated fluctuation in the increasing the cutting resistance (difference between the maximum value and the minimum value of the angle) the angle of the difference between the unequal division becomes large due to resonance, the ball end mill of the present invention constructed from four cutting edges In this case, it is desirable that the difference in unequal division angle, that is, the upper limit of the angle difference from 90 ° is about 5 °.

In Experimental Examples 1 to 5, the four-blade ball end mill has been described. However, it is considered that a three-blade or five to six-blade ball end mill exhibits the same effect .

Moreover, the multi-blade ball end mill of the present invention can be put to practical use as a multi-blade ball end mill having a cutting edge portion with a diameter D of about 1 to 30 mm. The clearance angle and rake angle of each ball blade, the clearance angle and rake angle of the medium and low gradient blades are set to appropriate values within the above-mentioned range according to the hardness of the work material, the diameter D of the cutting edge portion, and the like. set to.

According to the present invention, it is possible to provide a multi-blade ball end mill that can obtain a long life even when high-feed roughing is performed on hard-to-cut materials such as hardened steel. In addition, even when cutting general steel materials, by improving the machinability near the rotation axis, which is a particular problem of multi-blade ball end mills, chipping and chipping of ball blades and medium / low gradient blades are suppressed. The cutting using the tip can be performed stably. The present invention is particularly suitable for a roughing process in die cutting.

1, 1a: Multi-blade ball end mill
2: Shank
3: Cutting edge
4: Chip discharge groove
5: Peripheral blade
6a, 6b, 6c, 6d: Ball blade
7a, 7b, 7c, 7d: Gash
7b1, 7c1, 7d1: Gash groove bottom
8a, 8b, 8c, 8d: Medium-low gradient blade
8a1, 8b1, 8c1, 8d1: Convex medium / low gradient blade
8a2, 8b2, 8c2, 8d2: Straight medium and low gradient blades
9a, 9b, 9c, 9d: Ball blade flank
10a, 10b, 10c, 10d: Flank face of medium / low gradient blade
11a, 11b, 11c, 11d: Rake face of the ball blade
12a, 12b, 12c, 12d: Rake face of medium / low gradient blade
13: depression
Ridge flank and the gash of the ball cutting edge: 14a, 14b, 14c, 14d
15a, 15b, 15c, 15d: Boundary lines between the flank face of the ball blade and the flank face of the medium / low gradient blade
16a, 16b, 16c, 16d: concave curved surface
A: Direction of rotation of multi-blade ball end mill
C: Range near the rotation axis
D: Diameter of the cutting edge
K: End of concave curved medium / low gradient blade
L: Overall length
O: Rotation axis of multi-blade ball end mill
P1, P2, P3, P4: Position near the rotation axis
W1: Rotational width of ball blade flank
W2: Rotational width of flank face of medium / low gradient blade l: Blade length
t: Width of hollow part α: Inclination angle of medium / low gradient blade γ1: Rake angle of ball blade γ2: Rake angle of medium / low gradient blade
X: Width of medium / low gradient blade
X1: Width of concave / curved medium / low gradient blade
a: Point located at the center of a concave curved medium / low gradient blade
a1: Point located on the rearmost side in the rotational direction of the concave curved medium / low gradient blade
h: Section that is in the range of 20% to 40% of the width of the concave curved medium / low gradient blade

Claims (6)

A shank portion for rotating the rotation axis as a center, a multi-blade ball end mill comprising a cutting edge portion having three or more cutting edges having a ball blade tip,
Middle and low gradient blades extend from the tip of each ball blade to the rotation axis in the vicinity of the rotation axis of the tip ,
Each of the medium and low gradient blades is inclined at 0.5 ° or more and 3 ° or less on the side of the shank portion with respect to a plane orthogonal to the rotation axis,
A multi-blade ball end mill characterized in that at least the portion on the rotational axis side of each of the medium and low gradient blades has a curved shape recessed backward in the rotational direction . The multi-blade ball end mill according to claim 1, wherein each of the medium and low gradient blades has a curved medium and low gradient blade recessed on the rear side in the rotation direction provided on the rotation axis side, and a linear medium blade provided on the ball blade side. A multi-blade ball end mill comprising a low-gradient blade and having a radial width of the concave-curved medium / low-gradient blade in a plan view in the rotational axis direction larger than a radial width of the linear medium / low-gradient blade . 3. The multi-blade ball end mill according to claim 2, wherein each of the medium and low gradient blades includes only the concave curved medium and low gradient blade . The multi-blade ball end mill according to any one of claims 1 to 3, wherein a radial width X of each of the medium and low gradient blades is 1.25% or more and 3.75% or less of a diameter D of the cutting blade portion. Blade ball end mill. The multi-blade ball end mill according to any one of claims 1 to 4, wherein a rotational end point a1 of the concave curved medium / low gradient blade of the medium / low gradient blade is a radial width of the concave curved medium / low gradient blade. A multi-blade ball end mill characterized by being on the rotational axis side of position a which is half of X1 . The multi-blade ball end mill according to any one of claims 1 to 5, comprising four cutting edges .