JP7197809B2 - cutting insert - Google Patents

Description

TECHNICAL FIELD The present invention relates to a cutting insert detachably attached to an insert mounting seat formed at the tip of an end mill body of an indexable ball end mill.

In the cutting insert used in such an indexable ball end mill, two arc-shaped cutting edge portions are formed on opposite sides in the circumferential direction of the rake face. Since the side surface of the cutting insert, which serves as a surface, is convexly curved, the cutting load during cutting causes the curvature of the flank that continues to the arc-shaped cutting edge on the opposite side of the arc-shaped cutting edge used for cutting. The cutting insert tends to shift along the Therefore, for example, in Patent Documents 1 and 2, a protrusion projecting from the bottom surface of the insert mounting seat is formed, and the seating surface of the cutting insert is formed with a groove having a wall surface capable of coming into contact with the protrusion. It is described that such a shearing movement of the cutting insert is prevented by means of such a cutting insert.

Patent Literature 1 describes that only one of the two opposing wall surfaces of the groove is brought into contact with one side surface of the projection. Further, in Patent Document 2, a major cutting edge and a minor cutting edge each having an arcuate cutting edge portion and a linear cutting edge portion are formed, and the major cutting edge and the minor cutting edge are asymmetrical. , cutting from the vicinity of the axis line to the outer circumference of the tip of the end mill body and cutting from a position away from the axis line to the outer circumference by the arc-shaped cutting edge of one type and two cutting inserts of the same shape and size. ing.

JP-A-9-174322 JP-A-11-197933

By the way, in the cutting inserts described in the drawings of these Patent Documents 1 and 2, the two opposing wall surfaces of the groove portion are shown to extend parallel to each other. In addition, if the width of the convex part of the end mill body is increased in order to increase the rigidity of the convex part of the end mill body and secure the strength against the slipping movement of the cutting insert, the width of the groove part of the cutting insert will also be increased, which will reduce the strength of the cutting insert. Inevitably, there is a risk that damage is likely to occur due to the load during cutting. On the other hand, if the width of the groove is reduced to secure the strength of the cutting insert, the width of the protrusion on the end mill body must also be reduced, making it impossible to secure the mounting rigidity of the cutting insert. There is a risk that it will not be possible to reliably prevent the cutting insert from slipping due to this.

The present invention has been made under such a background, and an object of the present invention is to provide a cutting insert capable of reliably preventing displacement during cutting without impairing the strength of the cutting insert. there is

In order to solve the above-mentioned problems and achieve such objects, the cutting insert of the present invention is attached to and detached from an insert mounting seat formed at the tip of the end mill body of an indexable ball end mill that rotates about its axis. A cutting insert that can be mounted, comprising: a rake face directed in the direction of rotation of the end mill body; a seating face facing the opposite side of the rake face and seated on the bottom surface of the insert mounting seat; A flank extending around the surface and the seating surface is provided, and an arcuate cut extending in an arcuate shape in plan view when viewed from the direction facing the rake surface is provided at the intersection ridgeline between the rake surface and the flank surface. Two cutting edges, each having a cutting edge and a linear cutting edge extending in contact with the arcuate cutting edge, are arranged such that the arcuate cutting edge and the linear cutting edge extend in the circumferential direction of the rake face. one of the two cutting edges is a major cutting edge and the other is a minor cutting edge, and the arc-shaped cutting edge portion of the minor cutting edge is the major cutting edge The seating surface has two grooves each having a wall surface capable of coming into contact with a protrusion protruding from the bottom surface of the insert mounting seat. , through-holes that are open to both the flanks that are continuous with the linear cutting edge portions of the minor cutting edge and the major cutting edge, and the flank surfaces that are continuous with the arcuate cutting edge portions of the major cutting edge and the minor cutting edge It is formed in a groove shape, and the groove width of the two groove portions becomes narrower from the linear cutting edge portion side of the cutting edge to the arcuate cutting edge portion side of the cutting edge.

Also, in the indexable ball end mill of the present invention, such a cutting insert is provided on the insert mounting seat formed at the tip of the end mill body that rotates about the axis. It is detachably attached by contacting the wall surface of the groove portion.

The groove portion of the cutting insert according to the cutting insert having such a configuration has a narrow portion in which the groove width narrows from one end side to the other end side in the direction in which the groove portion extends. On the other end side where the groove width is narrow, the thickness of the cutting insert is ensured to disperse the stress and improve the strength. On the other hand, since the groove width becomes wider at one end side of the narrow width portion, in the indexable ball end mill, the convex portion is positioned in the direction in which the groove extends at the portion where the narrow width portion of the groove abuts. By increasing the width from the other end side to the one end side, it is possible to increase the mounting rigidity against the load during cutting work and reliably prevent the cutting insert from slipping.

In such a cutting insert, the arcuate cutting edge portion of the cutting edge is exclusively used for cutting. For each of the two grooves, the linear cutting edge side of the one cutting edge is defined as the one end side, and the arcuate cutting edge side of the other cutting edge is defined as the other end side. When the other cutting edge is used for cutting, the strength of the cutting insert should be ensured at the narrowed other end of the narrow width portion against the cutting load acting on the arcuate cutting edge. In addition, the offset movement of the cutting insert along the arc-shaped cutting edge portion of the cutting edge not used for cutting is ensured at one end of the widened narrow portion away from the arc-shaped cutting edge portion of this cutting edge. can be prevented.

In the cutting insert of the present invention, first, one of the two cutting edges is a major cutting edge and the other is a minor cutting edge. The arcuate cutting edge portion of the minor cutting edge is formed to have a radius equal to that of the arcuate cutting edge portion of the major cutting edge and a shorter peripheral length, and the cutting insert is as described in Patent Document 2. It has an asymmetrical shape. With two cutting inserts of the same shape and size, it is possible to cut from the vicinity of the axis line to the outer circumference of the tip of the end mill body by the arc-shaped cutting edge part of the main cutting edge, and at a position away from this axis line. Cutting from the outer circumference to the outer circumference can be performed by the arc-shaped cutting edge portion of the minor cutting edge, which facilitates management of the cutting insert and is economical.

Therefore, in this case, of the two groove portions, the groove portion having the arc-shaped cutting edge portion side of the minor cutting edge as the other end side is formed on the flank that continues to the arc-shaped cutting edge portion of the minor cutting edge. It may be open.
If the arc-shaped cutting edge portion of the minor cutting edge is formed in a convex curved shape that moves away from the seating surface side and then approaches the seating surface side as it separates from the linear cutting edge portion of the minor cutting edge. Since the arcuate cutting edge portion of the minor cutting edge gradually cuts into the work material from the most convex point with respect to the seating surface, cutting resistance can be reduced.

That is, in cutting inserts used in indexable ball end mills, during cutting, a large cutting load is applied to the tip of the arc-shaped cutting edge, the flank connected thereto, and the side surface of the insert body. Therefore, there is a demand for a cutting edge shape that reduces the cutting load and takes into account chip discharge. In the present invention, attention is also paid to controlling the form of contact between the arc-shaped cutting edge portion and the work material.

For example, when contour line machining is selected as the cutting method, it is desirable to set the tip side of the cutting edge where the chip thickness is thin as the area where the cutting edge bites into the work material. By forming the arc-shaped cutting edge portion in a convex curved shape as described above, the cutting edge has a twisted shape, and the impact acting on the cutting edge can be reduced, resulting in a more preferable cutting edge shape.

On the other hand, when scanning line machining is selected as the cutting method, when cutting in the axial direction of the end mill body, the tip of the arc-shaped cutting edge, where the chip thickness becomes thicker, bites into the work material. , a large cutting load is applied to the tip. Therefore, the strength of the cutting edge can be improved by increasing the thickness of the arc-shaped cutting edge portion by forming a convex curve and providing the most convex point.

When the groove is open on the flank that continues to the arcuate cutting edge of the minor cutting edge, and the arcuate cutting edge of the minor cutting edge is formed in a convex curve, the arcuate cutting edge of the minor cutting edge is formed. The opening of the groove to the flank that continues to the cutting edge is linear cutting of the minor cutting edge from the most convex point where the arcuate cutting edge of the minor cutting edge is most convex with respect to the seating surface. Located on the blade side. As a result, it is possible to prevent the cutting insert from being damaged from the opening of the groove due to the impact when the arc-shaped cutting edge portion of the minor cutting edge bites into the work material from the most convex point.

Specifically, in a bottom view viewed from the direction facing the seating surface, a straight line connecting the most convex point and the center of the arc-shaped cutting edge portion of the minor cutting edge and an arc-shaped cutting edge of the minor cutting edge The end portion of the crossing ridgeline between the flank and the wall surface facing the linear cutting edge portion of the minor cutting edge of the groove that opens to the flank that continues to the cutting edge, toward the seating surface, and the edge of the minor cutting edge. It is desirable that the first crossing angle formed by the straight line connecting the center of the arc-shaped cutting edge is in the range of 5° to 60°.

If the first intersection angle is less than 5°, the opening of the groove connecting to the arc-shaped cutting edge portion of the minor cutting edge to the flank face will be too close to the most convex point, and the arc-shaped cutting edge of the minor cutting edge will be cut off. The cutting insert may be damaged when the part bites. On the other hand, if this first crossing angle is large enough to exceed 60°, when the cutting insert is mounted by inserting the clamp screw into the mounting hole formed in the cutting insert and screwing it into the threaded hole of the insert mounting seat, There is a risk that the grooves and projections will interfere with the mounting holes and screw holes.

Also, as described above, when the groove is opened on the flank that continues to the arc-shaped cutting edge of the minor cutting edge, and the arc-shaped cutting edge of the minor cutting edge is formed in a convex curve, the seating In a bottom view viewed from the direction facing the surface, a straight line connecting the most convex point and the center of the arcuate cutting edge portion of the minor cutting edge and the minor cutting edge toward the arcuate cutting edge portion side It is desirable that the second crossing angle between the cutting edge and the extension of the straight cutting edge is in the range of 10° to 50°.

If the second crossing angle is less than 10°, when the minor cutting edge is used for cutting, the most convex point will be too close to the axis of the end mill body, and the minor cutting edge will be cut from the portion where the rotational speed around the axis is low. The arc-shaped cutting edge portion of the cutting edge cuts into the work material, which may impair the effect of reducing the cutting resistance. On the other hand, if the second crossing angle is greater than 50°, the opening of the groove portion is positioned on the straight line of the minor cutting edge rather than the most convex point on the flank surface connecting to the arcuate cutting edge portion of the minor cutting edge, as described above. When it is attempted to position it on the side of the shaped cutting edge, there is a possibility that the grooves and protrusions will interfere with the mounting hole of the cutting insert and the threaded hole of the insert mounting seat.

Secondly, the cutting insert of the present invention does not have an asymmetrical shape as described above. It may be formed in a 180° rotationally symmetrical shape in the circumferential direction of the rake face with respect to the center line.

In the second case, for example, a cutting insert having two main cutting edges having arc-shaped cutting edge portions with a circumference of 1/4 arc shape and a cutting insert with a radius equal to that of the cutting insert and a circumference length short A cutting insert having two minor cutting edges with arc-shaped cutting edges is prepared, and the arc-shaped cutting edge portion of the major cutting edge cuts from the vicinity of the axis line of the tip of the end mill body to the outer circumference, and from this axis line Cutting from a distant position to the outer circumference can be performed by the arc-shaped cutting edge portion of the minor cutting edge.

Also in this second case, the other end of the groove portion may be open to the flank surface connected to the arcuate cutting edge portion. Further, the cutting edge may be formed in a convex curved shape that moves away from the seating surface side and then approaches the seating surface side as it goes from the arc-shaped cutting edge portion side toward the linear cutting edge portion side. However, in this second case, the opening of the groove portion to the flank surface connected to the arcuate cutting edge portion is located above the most convex point where the cutting edge is most convex with respect to the seating surface. It is desirable to be positioned on the arcuate cutting edge portion side of the cutting edge.

Specifically, in a bottom view viewed from the direction facing the seating surface, a straight line connecting the most convex point of the cutting edge and the center of the arc-shaped cutting edge portion of the cutting edge, and It is desirable that a third intersection angle formed by a straight line connecting the point of contact between the arcuate cutting edge portion and the linear cutting edge portion and the center of the arcuate cutting edge portion be in the range of 40° or less. If the third crossing angle exceeds this range, the opening of the groove to the flank face connected to the arc-shaped cutting edge will be too close to the most convex point, and the cutting edge will move from the most convex point to the work material. Cutting inserts can be damaged when biting.

Also, as in the second case and the above-described first case, the radii of the arcuate cutting edge portions of the two cutting edges formed in one cutting insert are equal to each other. In this case, the groove width at the other end of the narrow portion of the groove is 0.05 times the radius r of the arcuate cutting edge portion of the cutting edge viewed from the direction facing the seating surface. It is desirable to be in the range of r to 0.18×r.

If the groove width at the other end, which is the narrowest in the narrow width portion, is so narrow that it falls below the above range, the width of the projection of the insert mounting seat must also be reduced, making it difficult to ensure rigidity. There is a risk. On the other hand, when the groove width at the other end of the narrow portion is so wide that it exceeds the above range and the wall surfaces of the groove are nearly parallel to each other, it is necessary to secure the wall thickness at the other end side of the narrow portion. It may not be possible to distribute the stress and maintain the strength of the cutting insert.

As described above, according to the present invention, the narrow portion of the groove formed in the seating surface of the cutting insert secures the wall thickness of the cutting insert on the other end side where the groove width is narrow, thereby dispersing the stress. It is possible to improve the strength and prevent the cutting insert from being damaged by the load during cutting. On the other hand, since the groove width of the narrow portion is widened on one end side, it is possible to form the convex portion of the indexable ball nose end mill with a wide width, which increases the mounting rigidity of the cutting insert and reliably prevents slippage. becomes possible.

1 is a perspective view showing a first embodiment of a cutting insert of the present invention; FIG. 2 is a plan view of the embodiment shown in FIG. 1; FIG. 2 is a bottom view of the embodiment shown in FIG. 1; FIG. FIG. 4 is a side view seen in the direction of arrow A in FIGS. 2 and 3; FIG. 4 is a side view seen in the direction of an arrow B in FIGS. 2 and 3; FIG. 4 is a side view seen in the direction of arrow C in FIGS. 2 and 3; FIG. 4 is a side view seen in the direction of an arrow D in FIGS. 2 and 3; Fig. 2 is a perspective view showing the tip of the end mill body in the first embodiment of the indexable ball end mill of the present invention to which the cutting insert of the first embodiment is detachably attached; FIG. 9 is a front view of the tip portion of the end mill body shown in FIG. 8; FIG. 10 is a plan view seen in the direction of an arrow A in FIG. 9; FIG. 10 is a side view seen in the direction of an arrow B in FIG. 9; FIG. 10 is a bottom view as seen in the direction of arrow C in FIG. 9; FIG. 10 is a side view seen in the direction of an arrow D in FIG. 9; 1 is a perspective view showing a tip portion of a first embodiment of an indexable ball end mill of the present invention; FIG. Figure 15 is a front view of the embodiment shown in Figure 14; FIG. 16 is a plan view seen in the direction of arrow A in FIG. 15; 15. It is a side view of the arrow B direction view in FIG. FIG. 16 is a bottom view as seen in the direction of arrow C in FIG. 15; FIG. 16 is a side view seen in the direction of arrow D in FIG. 15; FIG. 10 is a diagram showing stress dispersion states obtained by simulation analysis when the groove width of the other end of the narrow portion of the groove portion is changed, and the groove width is constant. FIG. 10 is a diagram showing stress distribution by simulation analysis when the groove width at the other end of the narrow width portion of the groove portion is changed, the narrow width portion having a narrow width portion with respect to the radius r of the arcuate cutting edge portion; is 0.133×r. FIG. 10 is a diagram showing stress distribution by simulation analysis when the groove width at the other end of the narrow width portion of the groove portion is changed, the narrow width portion having a narrow width portion with respect to the radius r of the arcuate cutting edge portion; is 0.067×r. Fig. 2 is a perspective view showing a second embodiment of the cutting insert of the present invention; Figure 22 is a plan view of the embodiment shown in Figure 21; Figure 22 is a bottom view of the embodiment shown in Figure 21; FIG. 24 is a side view seen in the direction of arrow A in FIGS. 22 and 23; FIG. 24 is a side view seen in the direction of an arrow B in FIGS. 22 and 23; FIG. 6 is a perspective view showing the tip of the end mill body in the second embodiment of the indexable ball end mill of the present invention to which the cutting insert of the second embodiment is detachably attached. 27 is a front view of the tip portion of the end mill body shown in FIG. 26; FIG. FIG. 28 is a plan view seen in the direction of arrow A in FIG. 27; FIG. 28 is a side view of FIG. 27 viewed in the direction of an arrow B; FIG. 28 is a bottom view as seen in the direction of arrow C in FIG. 27; FIG. 28 is a side view seen in the direction of an arrow D in FIG. 27; FIG. 10 is a perspective view showing the tip portion of the second embodiment of the indexable ball end mill of the present invention. Figure 33 is a front view of the embodiment shown in Figure 32; FIG. 34 is a plan view seen in the direction of arrow A in FIG. 33; FIG. 34 is a side view seen in the direction of an arrow B in FIG. 33; FIG. 34 is a bottom view as seen in the direction of arrow C in FIG. 33; FIG. 34 is a side view seen in the direction of an arrow D in FIG. 33;

<<1st Embodiment>>
1 to 7 show a cutting insert 1 according to a first embodiment of the invention. 8 to 13 show the tip of the end mill body 11 in the first embodiment of the indexable ball end mill of the present invention to which the cutting insert 1 of the first embodiment is detachably attached. 14 to 19 show the first embodiment of the indexable ball end mill of the present invention in which the cutting insert 1 of the first embodiment is detachably attached to the insert mounting seat 12 of the end mill body 11. It shows the tip.

The cutting insert 1 of the present embodiment is made of a hard material such as cemented carbide, and has a leaf-like plate shape in plan view as shown in FIG. The upper surface of the cutting insert 1 is the leaf-shaped rake face 2 as described above. The lower surface facing away from the rake surface 2 has a leaf shape substantially similar to the rake surface 2, and is a flat seating surface 3 that is seated on the bottom surface of the insert mounting seat. The side surface extending circumferentially between the rake face 2 and the seating face 3 is a flank face 4 .

At the intersection ridgeline between the rake face 2 and the flank face 4, arcuate cutting edge portions 5a and 6a extending arcuately as shown in FIG. Two cutting edges each having linear cutting edge portions 5b and 6b extending in contact with the arcuate cutting edge portions 5a and 6a are connected to the arcuate cutting edge portions 5a and 6a and the linear cutting edge portions 5b and 6b. They are formed alternately in the circumferential direction of the rake face 2 . One of these two cutting edges is a major cutting edge 5 and the other is a minor cutting edge 6 .

The flank 4 is inclined toward the inner peripheral side of the cutting insert 1 as it goes from the rake face 2 toward the seating surface 3, and the cutting insert 1 of this embodiment is of a positive type. Further, a mounting hole 7 having a circular cross section is formed through the cutting insert 1 at the center of the rake surface 2 and the seating surface 3. The mounting hole 7 on the rake surface 2 side is the seating surface It is formed so as to decrease in diameter toward the three sides.

In the plan view, the arc-shaped cutting edge portion 5a of the major cutting edge 5 has a substantially 1/4 arc shape, whereas the arc-shaped cutting edge portion 6a of the minor cutting edge 6 has a circular shape of the major cutting edge 5. It has the same radius as the arcuate cutting edge 5a, but the circumference is shorter than that of the arcuate cutting edge 5a of the main cutting edge 5. That is, the arc-shaped cutting edge portion 6a is formed in an arc shape shorter than a quarter arc. Along with this, the linear cutting edge portion 5b of the major cutting edge 5 is made shorter than the linear cutting edge portion 6b of the minor cutting edge 6 . That is, the cutting insert 1 of the present embodiment is not 180° rotationally symmetrical about the insert centerline X, which is the centerline of the mounting hole 7, as shown in FIGS. 2 and 3, but is asymmetrical. .

The linear cutting edge portions 5b and 6b of the major cutting edge 5 and the minor cutting edge 6 are formed by the arc-shaped cutting edge portion 5a of the major cutting edge 5 and the linear cutting edge portion 6b of the minor cutting edge 6 in the plan view. From the first end 2a of the intersecting rake face 2 to the second end 2b of the rake face 2 where the linear cutting edge 5b of the major cutting edge 5 and the arcuate cutting edge 6a of the minor cutting edge 6 intersect. , extending toward each other. These first and second end portions 2a and 2b are chamfered so as to intersect the arcuate cutting edge portions 5a and 6a and the linear cutting edge portions 5b and 6b of the major cutting edge 5 and the minor cutting edge 6 at an obtuse angle. formed in the shape of The first end 2a is located closer to the seating surface 3 than the second end 2b.

The arc-shaped cutting edge portions 5a and 6a of the major cutting edge 5 and the minor cutting edge 6 move away from the seating surface 3 side as they separate from the respective linear cutting edge portions 5b and 6b, and then approach the seating surface 3 side. The convex curve formed by the arcuate cutting edge portion 6a of the minor cutting edge 6 is formed in the shape of a convex curve, and the convex curve formed by the arcuate cutting edge portion 6a of the minor cutting edge 6 is the arcuate point of the minor cutting edge 6 at the point where it becomes convex farthest from the seating surface 3. It becomes the most convex point S of the cutting edge portion 6a.
The linear cutting edge portions 5b and 6b of the major cutting edge 5 and the minor cutting edge 6 are, even when viewed from the side facing the flank 4, as shown in FIGS. , 6a, and extends substantially linearly toward the seating surface 3 as it separates from the arcuate cutting edge portions 5a, 6a.

Around the opening of the mounting hole 7 in the central portion of the rake face 2, there is a projection having a substantially elliptical shape in plan view and protruding in a direction away from the seating surface 3 from the major cutting edge 5 and the minor cutting edge 6. 2c is formed. The upper end surface of this protrusion 2c is a flat surface parallel to the seating surface 3, and the mounting hole 7 opens to the upper end surface of this protrusion 2c. The outer peripheral surface of the protrusion 2c is inclined toward the inner side of the rake face 2 toward the upper end surface side. Further, the rake face 2 extends toward the seating surface 3 as it moves away from the major cutting edge 5 and the minor cutting edge 6 and extends toward the inner side of the rake face 2, and then forms a concave curved surface on the outer peripheral surface of the protrusion 2c. are connected.

The flanks 4 connected to the linear cutting edge portions 5b and 6b of the major cutting edge 5 and the minor cutting edge 6 are formed in an inclined planar shape as described above. On the rake face 2 side, the flank 4 connected to the arcuate cutting edge portions 5a and 6a of the major cutting edge 5 and the minor cutting edge 6 extends in the circumferential direction of the cutting insert 1 along these arcuate cutting edge portions 5a and 6a. However, the seating surface 3 side has the plane portion 4a which is inclined and notched into a plane as described above.

On the other hand, as shown in FIG. 3, grooves 8 are formed in the seating surface 3 . In this embodiment, as shown in FIG. 3 in a bottom view viewed from a direction perpendicularly facing the seating surface 3, the first and second two grooves 8A and 8B correspond to the mounting holes 7 in the seating surface 3. They are spaced apart from the opening and formed on opposite sides with the opening therebetween. The first groove 8A is formed closer to the first end 2a of the rake face 2 than the opening of the mounting hole 7, and the second groove 8B is formed closer to the second end 2b of the rake face 2. It is

These grooves 8 are formed in a substantially rectangular cross section perpendicular to the direction in which the grooves 8 extend, which is flattened in the direction of the center line X of the insert along which the mounting hole 7 extends. That is, the groove portion 8 includes two opposed first and second wall surfaces 8a and 8b extending in a direction substantially perpendicular to the seating surface 3, and a seating surface extending between the first and second wall surfaces 8a and 8b. and a bottom surface 8c parallel to the surface 3. The first wall surface 8a of each groove 8 faces the first end 2a of the rake face 2, and the second wall surface 8b faces the second end 2b of the rake face 2. As shown in FIG. The intersection ridges between the first and second wall surfaces 8a and 8b and the seating surface 3 are chamfered with convex curved surfaces, and the corners where the first and second wall surfaces 8a and 8b and the bottom surface 8c intersect are concave curved surfaces. is formed in

These first and second grooves 8A and 8B each have a narrow portion 9 in which the groove width becomes narrower from one end to the other end in the direction in which the first and second grooves 8A and 8B extend. ing. In this embodiment, the side of the flank 4 connected to the linear cutting edge portions 6b, 5b of the minor cutting edge 6 and the major cutting edge 5 is defined as one end side of the first and second groove portions 8A, 8B. The side of the flank 4 connected to the arcuate cutting edge portions 5a and 6a of the cutting edge 5 and the minor cutting edge 6 is the other end side. Further, as shown in FIG. 3, the first and second grooves 8A and 8B are formed as the narrow portion 9 as a whole.

In the present embodiment, the width of the narrow portion 9 is made constant from one end side to the other end side of the first and second groove portions 8A and 8B. That is, the narrow portion 9 is arranged such that the first and second wall surfaces 8a and 8b of the first and second groove portions 8B form a straight line and approach each other from one end side to the other end side in the bottom view. is formed in These first and second grooves 8A and 8B are, in this embodiment, the minor cutting edge 6 and the flank 4, the major cutting edge 5, and the minor cutting edge 6 that are connected to the straight cutting edge portions 6b and 5b of the major cutting edge 5. are formed in the form of through grooves that are open to both the flank faces 4 that continue to the arcuate cutting edge portions 5a and 6a.

The arcuate cutting edge portion 6a of the minor cutting edge 6, which forms a convex curve when viewed from the side, is the opening of the second groove portion 8B to the flank surface 4 connected to the arcuate cutting edge portion 6a of the minor cutting edge 6. It is positioned closer to the linear cutting edge portion 6b of the minor cutting edge 6 than the most convex point S, which is the most convex with respect to the seating surface 3. As shown in FIG. Specifically, as shown in FIG. 3 in the bottom view, a straight line L1 connecting the most convex point S and the center P of the arc formed by the arcuate cutting edge portion 6a of the minor cutting edge 6 and the minor cutting edge 6 The edge Q toward the seating surface 3 of the intersection ridge (excluding the chamfered portion) between the first wall surface 8a of the second groove portion 8B and the flank surface 4 facing the linear cutting edge portion 6b side and the center P A first crossing angle θ1 formed by a straight line L2 connecting the two is in the range of 5° to 60°.

Similarly, in the bottom view, the straight line L1 connecting the most convex point S and the center P of the arcuate cutting edge portion 6a of the minor cutting edge 6 and the minor cutting edge 6 toward the arcuate cutting edge portion 6a side. A second crossing angle θ2 formed by the extension line L3 of the linear cutting edge portion 6b of the cutting edge 6 is in the range of 10° to 50°.
In this embodiment, the groove width W1 of the narrow portion 9 at the other end of the second groove portion 8B that opens to the flank surface 4 of the arc-shaped cutting edge portion 6a of the minor cutting edge 6 is set to the second 0.05×r to 0.18×r with respect to the radius r seen from the seating surface 3 side of the arc-shaped cutting edge portion 6a of the minor cutting edge 6 located on the other end side of the groove portion 8B. . For example, the groove width W1 is in the range of 1 mm to 7 mm. However, in FIG. 3, if the shape of the arc-shaped cutting edge 6a viewed from the seating surface 3 side is deviated from the circular arc, a virtual arc that is closest to the deviated shape is drawn. Therefore, the radius r is obtained from this virtual arc.

On the other hand, the groove width W2 at one end of the narrow portion 9 satisfies W2>W1. The groove width W2 is determined from the seating surface 3 side of the arcuate cutting edge portion (arc-shaped cutting edge portion 6a of the minor cutting edge 6) located on the other end side of the groove portion (second groove portion 8B) having the narrow portion 9. The plane of the linear cutting edge portion 5b of the main cutting edge 5 is within a range of 0.10 × r to 0.30 × r with respect to the radius r in the bottom view seen from the rake face 2 side or in the plan view seen from the rake face 2 side. A range of 0.10×R to 0.32×R is set for the length R in a view or a bottom view. When the first and second wall surfaces 8a and 8b extend linearly in a bottom view viewed from the direction facing the seating surface 3, the groove widths W1 and W2 are equal to those of the first and second wall surfaces 8a and 8b. It is the width in the direction perpendicular to the bisector of the straight line formed by 8a and 8b.

In the bottom view, the straight line L4 formed by the extended surface of the second groove portion 8B toward the other end of the second wall surface 8b is the arc-shaped cutting edge portion 6a side of the minor cutting edge 6. The inclination angle α of the linear cutting edge portion 6b with respect to the extension line L3 is in the range of 45° to 90°. Similarly, in the bottom view, the inclination angle β formed by the straight line L5 formed by the extended surface of the first wall surface 8a of the second groove portion 8B with respect to the linear cutting edge portion 5b of the main cutting edge 5 is 45° to 90°. The inclination angle γ formed by the straight line L4 formed by the extended surface of the second wall surface 8b of the second groove portion 8B with respect to the linear cutting edge portion 5b of the major cutting edge 5 is made smaller than the inclination angle β. ing. In the present embodiment, in the bottom view, the first groove portion 8A extends in a direction intersecting the linear cutting edge portion 6b of the minor cutting edge 6 at an acute angle on the side of the first end portion 2a, and the second groove portion 8B extends. extends in a direction that intersects the linear cutting edge portion 5b of the main cutting edge 5 at an acute angle on the side of the second end portion 2b. These groove widths W1 and W2, the first and second crossing angles θ1 and θ2, and the inclination angles α to γ may be similarly applied to the first groove portion 8A having the narrow portion 9 as well.

The cutting insert 1 of the first embodiment is detachably attached to the insert mounting seat 12 formed at the tip of the end mill main body 11 shown in FIGS. 8 to 13 as described above. 19 constitutes the first embodiment of the indexable ball end mill of the present invention. The end mill main body 11 is formed of a metal material such as steel, and the tip portion thereof has a cylindrical shape centered on the axis line O on the base end side, and has a base end side center on the axis line O. It has a convex hemispherical shape with a radius equal to that of a cylinder. The indexable ball end mill of this embodiment is attached to the insert mounting seat 12 by rotating the end mill main body 11 about the axis O in the end mill rotation direction T and sending it out in a direction intersecting the axis O. A cutting insert 1 is used to cut a material to be cut.

In this embodiment, two tip pockets 13 are formed by notching the outer periphery of the end mill main body 11, and insert mounting seats 12 are provided on the bottom surfaces of these tip pockets 13 facing the end mill rotation direction T, respectively. They are circumferentially spaced apart from each other and formed on opposite sides. The two insert mounting seats 12 are mounted with first and second cutting inserts 1A and 1B of the same shape and size based on the first embodiment, respectively.

These insert mounting seats 12 have a flat bottom surface 12a facing in the end mill rotation direction T, a tip inner peripheral wall surface 12b extending from the bottom surface 12a in the end mill rotation direction T and facing the outer peripheral side of the end mill main body 11, and a tip outer peripheral wall surface. and a wall surface 12c on the outer peripheral side of the rear end facing the .
The wall surfaces 12b and 12c are formed in a planar shape that inclines outwardly of the insert mounting seat 12 as the distance from the bottom surface 12a increases. The planar flank 4 connected to the linear cutting edge portions 5b and 6b of the blade 6 and the flat portion 4a of the flank 4 connected to the arcuate cutting edge portions 5a and 6a on the side of the seating surface 3 can be brought into contact. .

A concave recess 12d is formed between these walls 12b, 12c to avoid contact with the curved flank 4 of the cutting insert 1. As shown in FIG. The bottom surface 12a is formed with a screw hole 12e into which a clamp screw (not shown) inserted through the mounting hole 7 of the cutting insert 1 is screwed. The center line of this threaded hole 12e is formed in a planar shape that continues to the linear cutting edge portions 5b and 6b of the major cutting edge 5 and the minor cutting edge 6 with the seating surface 3 of the cutting insert 1 seated on the bottom surface 12a as described above. With the plane portion 4a on the seating surface 3 side of the flank 4 connected to the flank 4 and the arc-shaped cutting edge portions 5a and 6a in contact with the wall surfaces 12b and 12c, the center line of the mounting hole 7 of the cutting insert 1 It is slightly eccentric toward the concave portion 12d side.

Of these two insert mounting seats 12, the first insert mounting seat 12A is formed by notching the tip of the end mill body 11 to a range including the axis O, as shown in FIGS. ing. In the first insert mounting seat 12A, the first cutting insert 1A is positioned on a convex hemisphere having the arc-shaped cutting edge portion 5a of the main cutting edge 5 extending from the vicinity of the axis O and having the center on the axis O. In addition, the linear cutting edge portion 5b of the main cutting edge 5 is attached so as to be positioned on a cylindrical surface centered on the axis O in contact with the convex hemisphere. Therefore, the planar flank 4 continuous with the linear cutting edge portion 6b of the minor cutting edge 6 of the first cutting insert 1A is brought into contact with the wall surface 12b of the first insert mounting seat 12A, and the wall surface 12c is in contact with the wall surface 12c. The flat portion 4a of the flank 4 of the arc-shaped cutting edge portion 6a of the minor cutting edge 6 of the first cutting insert 1A is brought into contact.

On the bottom surface 12a of the first insert mounting seat 12A, a first convex portion 14A that can abut against the first groove portion 8A formed on the seating surface 3 of the first cutting insert 1A is formed in a screw hole. It is formed so as to protrude further to the tip side than 12e and extend from the outer peripheral surface of the tip portion of the end mill body 11 toward the wall surface 12c. Further, on the bottom surface 12a of the first insert mounting seat 12A, a second convex portion 14B, which can be brought into contact with the second groove portion 8B, protrudes between the screw hole 12e and the wall surface 12c to form the tip of the end mill body 11. It is formed so as to extend from the outer peripheral surface of the portion toward the recess 12d. In this embodiment, the first protrusion 14A is formed in a peninsular shape reaching the wall surface 12c, while the second protrusion 14B is formed in a remote island shape that is spaced apart from the recess 12d and does not reach the recess 12d. It is

These first and second protrusions 14A and 14B have a substantially rectangular cross-section that is flattened in the end mill rotation direction T, perpendicular to the direction in which the first and second protrusions 14A and 14B extend. Of these, the first convex portion 14A extends from the other end side to the one end side (of the end mill main body 11) in the direction in which the first groove portion 8 extends with respect to the first groove portion 8A, which is the narrow portion 9 as a whole. It is formed so that it becomes wider as it goes from the outer peripheral side to the inner peripheral side, except that the connecting portion with the wall surface 12c is constricted. The second convex portion 14B extends from the other end side of the extending direction of the second groove portion 8B to the one end side (inside the end mill main body 11). It is formed so that it becomes wider as a whole as it goes from the peripheral side to the outer peripheral side.

The width of these first and second protrusions 14A and 14B (the width in the direction orthogonal to the direction in which the first and second protrusions 14A and 14B extend) is the same as the width in which the first and second grooves 8A and 8B extend. It is slightly smaller than the width (the width in the direction perpendicular to the direction in which the first and second grooves 8A and 8B extend) at the positions where they abut on the first and second protrusions 14A and 14B in the direction. The projection heights of the first and second projections 14A and 14B from the bottom surface 12a are also slightly smaller than the depths of the first and second grooves 8A and 8B from the seating surface 3 of the first cutting insert 1A.

Of the two insert mounting seats 12, the second insert mounting seat 12B is formed at a position slightly away from the axis O to the outer peripheral side on the tip end side of the end mill body 11, as shown in FIGS. The second cutting insert 1B is mounted on the second insert mounting seat 12B so that the arcuate cutting edge portion 6a of the minor cutting edge 6 of the second cutting insert 1B is mounted on the main cutting edge 5 of the first cutting insert 1A from a position away from the axis O. The linear cutting edge 5b of the major cutting edge 5 of the first cutting insert 1A is aligned with the linear cutting edge 6b of the minor cutting edge 6 while being positioned on the convex hemisphere where the arcuate cutting edge 5a is located. It is attached so as to be positioned on the cylindrical surface where it is located. Therefore, the planar flank 4 continuous with the linear cutting edge portion 5b of the main cutting edge 5 of the second cutting insert 1B is brought into contact with the wall surface 12b of the second insert mounting seat 12B, and the wall surface 12c is in contact with the wall surface 12c. The flat portion 4a of the flank 4 of the arcuate cutting edge portion 5a of the main cutting edge 5 of the second cutting insert 1B is brought into contact.

A third protrusion 14C is formed on the bottom surface 12a of the second insert mounting seat 12B on the tip side of the screw hole 12e, and a fourth protrusion 14C is formed between the screw hole 12e and the wall surface 12c. A convex portion 14D is formed. These third and fourth protrusions 14C and 14D also extend from the outer peripheral surface of the tip of the end mill body 11 toward the inner peripheral side, and the third protrusion 14C extends from the wall surface 12b of the second insert mounting seat 12B. The fourth projection 14D is formed to the front of the recess 12d of the second insert mounting seat 12B with a space to the wall 12b. Therefore, the second groove portion 8B of the second cutting insert 1B contacts the third convex portion 14C, and the first groove portion 8A of the second cutting insert 1B contacts the fourth convex portion 14D.

Further, the third and fourth projections 14C and 14D also have a substantially rectangular cross section perpendicular to the direction in which the third and fourth projections 14C and 14D extend, which is flattened in the end mill rotation direction T, Of these, the third convex portion 14C has a narrow width portion 9 in the entirety of the second groove portion 8B of the second cutting insert 1B with which it abuts, whereas the width of the third convex portion 14C extends in the direction in which the second groove portion 8B extends. The width of the fourth convex portion 14D is formed so as to become wider as it goes from the other end side to the one end side (from the outer peripheral side to the inner peripheral side of the end mill main body 11). It is formed so as to become wider as a whole from the other end side in the extending direction toward the one end side (from the inner peripheral side to the outer peripheral side of the end mill main body 11).

Furthermore, the widths of the third and fourth protrusions 14C and 14D (the widths in the direction orthogonal to the extending direction of the third and fourth protrusions 14C and 14D) are also the same as the second and first grooves 8B and 8A. is slightly smaller than the width at the position contacting the third and fourth protrusions 14C and 14D in the extending direction (the width in the direction perpendicular to the extending direction of the second and first grooves 8B and 8A). ing. Moreover, the protrusion heights of the third and fourth projections 14C and 14D from the bottom surface 12a of the second insert mounting seat 12B are also the same as the second and first groove portions 8B from the seating surface 3 of the second cutting insert 1B. It is slightly smaller than the depth of 8A.

The first and second cutting inserts 1A and 1B are seated on the first and second insert mounting seats 12A and 12B as described above to form a clamp screw having an inverted truncated conical head. As the cutting insert 1 is inserted through the mounting hole 7 and screwed into the screw hole 12e, the center line of the screw hole 12e is slightly eccentric toward the recess 12d from the center line of the mounting hole 7 of the cutting insert 1. 1 is pressed against the side of the recess 12d.

At this time, in the first insert mounting seat 12A, the plane of the flank 4 connecting to the linear cutting edge portion 6b of the minor cutting edge 6 of the first cutting insert 1A and the flank surface 4 connecting to the arcuate cutting edge portion 6a The portion 4a is pressed against the wall surfaces 12b and 12c, respectively. In addition, in the second insert mounting seat 12B, the flank 4 continuous with the linear cutting edge portion 5b of the main cutting edge 5 of the second cutting insert 1B is pressed against the wall surface 12b, thereby The flat portion 4a of the flank 4 that continues to the blade portion 5a is pressed against the wall surface 12c.

Along with this, in the first insert mounting seat 12A, the first and second grooves 8A and 8B of the first cutting insert 1A are formed in the first and second protrusions 14A and 14B so that the tip end of the end mill main body 11 is formed. Abut from the side. Accordingly, these first and second projections 14A and 14B have a side surface 14a facing the tip end side of the end mill body 11, which is the second groove 8A and 8B of the first cutting insert 1A. The wall surface 8b abuts, and a small gap is provided between the first wall surface 8a and the bottom surface 8c of the first and second grooves 8A and 8B and the first protrusion 14A.

In addition, in the second insert mounting seat 12B, the second and first grooves 8B and 8A of the second cutting insert 1B are also formed in the third and fourth projections 14C and 14D from the tip end side of the end mill body 11. abut. Accordingly, the first wall surfaces 8a of the second and first grooves 8B and 8A are in contact with the side surfaces 14a of the end mill body 11 facing the distal end side of the third and fourth projections 14C and 14D, respectively. A slight gap is provided between the second wall surface 8b of the second and first grooves 8B and 8A and the third and fourth projections 14C and 14D. In this manner, the first and second grooves 8A and 8B abut on the first to fourth projections 14A to 14D, thereby preventing the cutting insert 1 from shifting due to load during cutting. .

In the cutting insert 1 and indexable ball end mill configured as described above, the first and second grooves 8A and 8B of the cutting insert 1 are located on one end side in the direction in which the first and second grooves 8A and 8B extend. It has a narrow portion 9 where the groove width narrows toward the other end side, and on the other end side of the first and second groove portions 8A and 8B where the groove width of the narrow portion 9 becomes small, the cutting insert The strength can be improved by securing a large wall thickness of 1. Therefore, even if an excessive load acts on the cutting insert 1 during cutting, it is possible to prevent the cutting insert 1 from being damaged from the first and second grooves 8A and 8B.

On the other hand, since the narrow portion 9 becomes wider on one end side in the direction in which the first and second groove portions 8A and 8B extend, the end mill main body 11 of the indexable ball end mill has the first and second groove portions 8A and 8B. The widths of the first to fourth protrusions 14A to 14D can be formed at the portions where one ends of the grooves 8A and 8B abut. Therefore, it is possible to increase the mounting rigidity of the cutting insert 1 with respect to the load during cutting, thereby more reliably preventing the cutting insert 1 from slipping and performing highly accurate cutting.

In addition, in the cutting insert 1 of this embodiment, the first and second cutting inserts 1A and 1B have the same shape and size, and the arcuate cutting edge portions 5a and 6a of the major cutting edge 5 and the minor cutting edge 6 , and the groove width W1 at the narrowest end of the narrow portion 9 is 0.5 with respect to the radius r viewed from the seating surface 3 side of the arcuate cutting edge portions 5a and 6a. It is in the range of 05×r to 0.18×r, so that the strength of the cutting insert 1 can be improved more reliably and the mounting rigidity can be increased. That is, if the groove width W1 at the other end of the narrow width portion 9 is so narrow that it falls below the above range, the widths of the first to fourth protrusions 14A to 14D on the insert mounting seat 12 must also be narrowed, resulting in cutting. While there is a risk that the mounting rigidity of the insert 1 cannot be increased, the groove width W1 at the other end of the narrow width portion 9 is so wide as to exceed the above range, and the first and second groove portions 8A and 8B have the same width. When the second wall surfaces 8a and 8b are nearly parallel, the strength of the cutting insert 1 can be ensured by ensuring a large wall thickness of the cutting insert 1 on the other end side of the first and second groove portions 8A and 8B. and damage may occur when excessive loads are applied.

FIGS. 20A to 20C are diagrams showing the state of dispersion of stress by simulation analysis when the groove width W1 at the other end of the groove 8 is changed. When the radius r of the arc-shaped cutting edge portion 6a of the minor cutting edge 6 (for example, the arc-shaped cutting edge portion 6a of the minor cutting edge 6) is 15.0 mm, FIG. 9), and FIG. 20B shows a case where there is a narrow portion 9 and the groove width W1 at the other end with respect to the radius r of the arcuate cutting edge portion 6a is 2.0 mm (0.133×r). 20C also has the narrow portion 9 and the groove width W1 at the other end with respect to the radius r of the circular cutting edge portion 6a is 1.0 mm (0.067×r). In the analysis, the rotation speed of the end mill body 11 is 2500 min ^-1 , the rotation speed is 230 m/min, the feed speed is 1500 mm/min (the feed amount per blade is 0.3 mm/1 blade), and the depth of cut and the width of cut are both 15 mm, the work material is S45C (hardness 220 HB), the material of the end mill main body is SKD61 (hardness 45 HRC, tensile strength 1600 MPa, fatigue strength 500 MPa), and evaluation was performed using von Mises stress.

In FIG. 20, the region of the seating surface 3 drawn in white on the side of the groove is the range where the stress is concentrated. 20B and 20C, which have the narrow width portion 9, have a smaller portion drawn in white and the stress is dispersed more than the result of FIG. 20A, which has a constant groove width and does not have the narrow width portion 9. 20C, in which the groove width W1 is particularly small, has the smallest stress concentration range. From this result, it is found that the provision of the narrow width portion 9 can disperse the stress and ensure the strength of the cutting insert 1, and the groove width W1 is in the range of 0.05×r to 0.18×r. is desirable.

The groove width W1 is more preferably in the range of 0.06×r to 0.17×r, more preferably in the range of 0.065×r to 0.16×r. The groove width W1 is preferably in the range of 0.25×W2 to 0.90×W2 with respect to the groove width W2 at one end of the narrow portion 9, and is preferably in the range of 0.30×W2 to 0.85× A range of W2 is more desirable, and a range of 0.32×W2 to 0.80×W2 is even more desirable. On the other hand, the groove width W2 at one end of the narrow portion 9 is preferably in the range of 0.10×r to 0.30×r with respect to the radius r, more preferably in the range of 0.12×r to 0.28×r. is more desirable, and a range of 0.15×r to 0.26×r is even more desirable.

In the cutting insert 1 of this embodiment, the arc-shaped cutting edge portion 6a of the minor cutting edge 6 has the same radius as the arc-shaped cutting edge portion 5a of the major cutting edge 5, but the circumference is shortened, that is, formed asymmetrically. It is Along with this, also in the indexable ball end mill of this embodiment, the first insert mounting seat 12A is formed so as to cut the tip portion of the end mill body 11 to a range including the axis O on the tip side. On the other hand, the second insert mounting seat 12B is formed at a position slightly away from the axis O to the outer peripheral side. Two cutting inserts 1 of the same shape and size are mounted on the first and second insert mounting seats 12A and 12B. The arcuate cutting edge portion 6a of the minor cutting edge 6 of the second cutting insert 1B is positioned on the same convex hemispherical surface so as to extend from the vicinity of the axis O of the tip and to extend from a position away from the axis O. I am letting

Therefore, one type of cutting insert 1 can be used for cutting from the vicinity of the axis O of the tip of the end mill body 11 to the outer circumference, and cutting from a position away from the axis O to the outer circumference, making it easy to manage the cutting insert 1. In addition, only one type of mold is required for manufacturing the cutting insert 1. Also, if the major cutting edge 5 of the first cutting insert 1A and the minor cutting edge 6 of the second cutting insert 1B are worn due to cutting, these cutting inserts 1 may be mounted on the insert mounting seat 12 on the opposite side. , the first cutting insert 1A can be reused as the second cutting insert 1B, and the second cutting insert 1B can be reused as the first cutting insert 1A, which is economical.

Furthermore, in this embodiment, the second groove portion 8B having the narrow portion 9, which is wide on one end side and narrow on the other end side, extends from the arcuate cutting edge portion 6a side of the minor cutting edge 6 to the main cutting edge portion 8B. It extends toward the linear cutting edge portion 5 b side of the blade 5 . The narrow width portion 9 has the linear cutting edge portion 5b side of the major cutting edge 5 as the one end side and the arcuate cutting edge portion 6a side of the minor cutting edge 6 as the other end side. is designed to be Therefore, when the minor cutting edge 6 is used for cutting as the second cutting insert 1B, the second groove portion 8B is a flank surface that continues to the arcuate cutting edge portion 6a of the minor cutting edge 6 as in the present embodiment. 4, the load acting on the minor cutting edge 6 can be received by the other end side of the narrow width portion 9 of the narrow second groove portion 8B, and strength can be ensured. is. The displacement of the second cutting insert 1B along the arc-shaped cutting edge portion 5a of the major cutting edge 5 not used for cutting is caused by the narrow portion 9 of the second groove portion 8B away from the arc-shaped cutting edge portion 5a. This can be reliably prevented by the wide one end side. This is the same even when using the cutting insert 1 as the first cutting insert 1A.

In this embodiment, the arcuate cutting edge portion 5a of the major cutting edge 5 and the arcuate cutting edge portion 6a of the minor cutting edge 6 move away from the seating surface 3 as they separate from the linear cutting edge portions 5b and 6b, and then again. It is formed in a convex curved shape approaching the seating surface 3 side. Therefore, the arcuate cutting edge portions 5a and 6a gradually bite into and cut into the work material from the most convex point S, which is the most convex with respect to the seating surface 3 during cutting. resistance can be reduced. On the other end side where the groove width W1 of the second groove portion 8B formed in the seating surface 3 of the cutting insert 1 becomes narrower, the thickness at the most convex point S can be ensured and the strength can be improved. It is possible to prevent the cutting insert 1 from being damaged by the load during machining. The thickness at the most convex point S is the distance from the seating surface 3 to the most convex point S in the direction perpendicular to the seating surface 3, as indicated by symbol t in FIG. In the narrow width portion 9 on the other end side of the second groove portion 8B, the range in which the thickness of the cutting insert 1 is ensured by the most convex point S is the region indicated by symbol U in FIGS. The value of the insert wall thickness in the region indicated by symbol U is preferably in the range of 0.65×t to 1.00×t with respect to the t value, and preferably in the range of 0.70×t to 1.00×t. More preferably, it is in the range of 0.75×t to 1.00×t.

In this embodiment, the arc-shaped cutting edge portions 5a and 6a are thus formed in a convex curved shape. Although the second groove portion 8B opens to the flank 4 connected to the arc-shaped cutting edge portion 6a of the minor cutting edge 6 as described above, the opening of the second groove portion 8B to the flank 4 is It is located closer to the linear cutting edge portion 6 b side of the minor cutting edge 6 than the most convex point S of the arcuate cutting edge portion 6 a of the minor cutting edge 6 . Therefore, it is possible to prevent the impact from being directly transmitted to the opening of the second groove portion 8B when the arc-shaped cutting edge portion 6a of the minor cutting edge 6 bites into the work material from the most convex point S and cuts into the material. Also, it is possible to prevent the cutting insert 1 from being damaged from the opening of the second groove portion 8B by such an impact.

In order to reliably prevent damage to the cutting insert 1 due to such impact, in the bottom view, the most convex point S and the center P of the arc-shaped cutting edge portion 6a of the minor cutting edge 6 should be aligned as in this embodiment. A connecting straight line L1 and an end portion Q toward the seating surface 3 of the intersection ridge between the first wall surface 8a of the second groove portion 8B facing the linear cutting edge portion 6b side of the minor cutting edge 6 and the flank surface 4. It is desirable that the first crossing angle θ1 between the minor cutting edge 6 and the straight line L2 connecting the center P of the arc-shaped cutting edge portion 6a is in the range of 5° to 60°. Although not shown, the same applies to the arc-shaped cutting edge portion 5a of the main cutting edge 5 and the opening portion of the first groove portion 8A on the other end side.

When the first crossing angle θ1 is smaller than 5°, the opening of the second groove 8B to the flank 4 is the maximum of the arc-shaped cutting edge 6a of the minor cutting edge 6 to which the flank 4 is connected. There is a risk that the cutting insert 1 will be damaged due to the impact when the circular cutting edge 6a bites into the work material from the most convex point S when it comes too close to the convex point S. Conversely, if the first crossing angle θ1 is greater than 60°, the clamp screw inserted through the mounting hole 7 of the cutting insert 1 is screwed into the threaded hole 12e of the insert mounting seat 12 as in the present embodiment to secure the cutting insert. 1, the second groove 8B and the first and second projections 14A and 14B may interfere with the mounting hole 7 and the screw hole 12e. The first crossing angle θ1 is more preferably in the range of 5° to 30°, and even more preferably in the range of 5° to 15°.

In this embodiment, similarly in the bottom view, a straight line L1 connecting the most convex point S of the arcuate cutting edge portion 6a of the minor cutting edge 6 and the center P of the arcuate cutting edge portion 6a and the minor cutting edge 6 The second crossing angle θ2 formed by the extension line L3 of the linear cutting edge portion 6b of the minor cutting edge 6 to the arcuate cutting edge portion 6a side of the secondary cutting edge 6 is in the range of 10° to 50°. While preventing interference between the second groove portion 8B and the first and second convex portions 14A and 14B and the mounting hole 7 and the screw hole 12e, the arcuate cutting edge portion 6a of the minor cutting edge 6 ensures reliable cutting. cutting resistance can be reduced. This also applies to the arcuate cutting edge portion 5a of the main cutting edge 5, although not shown.

That is, when the cutting insert 1 is attached to the second insert mounting seat 12B as the second cutting insert 1B, the extension line L3 is the bottom view facing the seating surface 3 of the second cutting insert 1B, or It is substantially parallel to the axis O of the end mill main body 11 in plan view from the direction facing the rake face 2 along the center line of the mounting hole 7 . Therefore, the second intersection angle θ2 is substantially equal to the intersection angle formed by the axis O and the straight line L1 connecting the center P of the arc-shaped cutting edge portion 6a positioned on the axis O and the most convex point S. Become. However, the linear cutting edge portions 5b and 6b may have a slight back taper angle when the cutting insert 1 is attached to the end mill body 11, so the intersection angle θ2 is strictly the intersection between the straight line L1 and the axis O. Doesn't have to be equal to the angle.

Therefore, if the second intersection angle θ2 is greater than 50°, the second groove portion 8B, the first and second protrusions 14A, 14B may interfere with the mounting hole 7 and the screw hole 12e. If the second intersection angle θ2 is less than 10°, the most convex point S of the arc-shaped cutting edge portion 6a of the second cutting insert 1B is too close to the axis O, and the rotational speed around the axis O is reduced. The arc-shaped cutting edge portion 6a of the minor cutting edge 6 cuts into the work material from a small portion, which may impair the effect of reducing the cutting resistance. This second crossing angle θ2 is more preferably in the range of 20° to 50°, and even more preferably in the range of 35° to 50°.

<<Second Embodiment and Third Embodiment>>
Next, FIGS. 21 to 25 show a second embodiment of the cutting insert of the present invention, and FIGS. 26 to 31 show the cutting insert 21 of this second embodiment and the third embodiment. 32 to 37 show the tip of the end mill body 41 in the second embodiment of the indexable ball end mill of the present invention to which the cutting insert 31 of the present invention is detachably attached. 3. The tip portion of the second embodiment of the indexable ball end mill of the present invention, in which the cutting inserts 21 and 31 of the second and third embodiments are detachably attached to the fourth insert mounting seats 12C and 12D. is shown. In the embodiment shown in FIGS. 21 to 37, elements common to those in the embodiment shown in FIGS. The second crossing angles θ1, θ2, inclination angles α to γ, and the like are also common, so illustration thereof is omitted.

The cutting insert 1 of the first embodiment has arcuate cutting edge portions 5a and 6a with different circumferential lengths on the major cutting edge 5 and the minor cutting edge 6, and is asymmetrical with respect to the insert centerline X passing through the center of the mounting hole 7. On the other hand, the cutting inserts 21 and 31 of the second and third embodiments are characterized by being formed in a 180° rotationally symmetrical shape in the circumferential direction of the rake face 2 with respect to the center line X of the insert.

Further, the cutting insert 21 of the second embodiment has an arcuate cutting edge portion 5a having a substantially 1/4 arc shape and a linear cutting edge in contact with the arcuate cutting edge portion 5a, like the main cutting edge 5 of the cutting insert 1 of the first embodiment. 5 b alternately in the circumferential direction of the rake face 2 . The cutting insert 31 of the third embodiment has an arc-shaped cutting edge portion 6a having a circumferential length shorter than a quarter arc and a linear cutting edge portion 6a in contact with the arc-shaped cutting edge portion 6a, which is the same as the minor cutting edge 6 of the cutting insert 1 of the first embodiment. It has two cutting edges 6b alternately in the circumferential direction of the rake face 2. As shown in FIG. The radii of the arcuate cutting edge portion 5a of the major cutting edge 5 of the second embodiment and the arcuate cutting edge portion 6a of the minor cutting edge 6 of the third embodiment are made equal to each other.

Therefore, the linear cutting edge portions 5b of the two major cutting edges 5 of the cutting insert 21 of the second embodiment and the linear cutting edge portions of the two minor cutting edges 6 of the cutting insert 31 of the third embodiment 6b are parallel to each other. The distance between the linear cutting edge portions 5b of the two major cutting edges 5 of the cutting insert 21 of the second embodiment is the same as that of the linear cutting edge portions 5b of the two minor cutting edges 6 of the cutting insert 31 of the third embodiment. It is larger than the interval between the blade portions 6b.

Also in the cutting inserts 21 and 31 of the second and third embodiments, the seating surface 3 is provided with projections protruding from the bottom surfaces 12a of the third and fourth insert mounting seats 12C and 12D of the end mill body 41. Two groove portions 8 having wall surfaces capable of abutting are formed on the two cutting edges (major cutting edge 5 and minor cutting edge 6) from the linear cutting edge portions 5b and 6b of one cutting edge to the other cutting edge. are formed so as to extend toward the arcuate cutting edge portions 5a and 6a. These two groove portions 8 each have a narrow portion 9 in which the groove width becomes narrower from one end side to the other end side in the extending direction of the groove portion 8 . Also in these second and third embodiments, the linear cutting edge portions 5b and 6b side of the narrow portion 9 is one end side, and the arcuate cutting edge portion 5a and 6a side is the other end side.

Also in these second and third embodiments, the other end of the groove portion 8 is open to the flank 4 connected to the arcuate cutting edge portions 5a and 6a as in the first embodiment, and one end is also a linear cutting edge. It is open on the flank 4 that continues to the blades 5b and 6b. In these second and third embodiments, as shown in FIGS. 21 and 25, the two cutting edges (major cutting edge 5 and minor cutting edge 6) are entirely on the arcuate cutting edge portions 5a and 6a. It is formed in a convex curved shape that moves away from the seating surface 3 side and then approaches the seating surface 3 side as it goes toward the linear cutting edge portions 5b and 6b. The opening of the groove 8 to the flank 4 connected to the arcuate cutting edge portions 5a and 6a is arcuate from the maximum convex point S where the major cutting edge 5 and the minor cutting edge 6 are most convex with respect to the seating surface 3. It is positioned on the side of the cutting edge portions 5a and 6a.

Specifically, as shown in FIG. 23 in a bottom view viewed from the direction facing the seating surface 3, the most convex point S of the cutting edge (major cutting edge 5 in FIG. 3) and the arcuate shape of this major cutting edge 5 A third line formed by a straight line L6 connecting the center P1 of the cutting edge portion 5a and a straight line L7 connecting the point of contact V between the arcuate cutting edge portion 5a and the linear cutting edge portion 5b of the main cutting edge 5 and the center P1. crossing angle θ3 of 40° or less. Of course, the third intersection angle θ3 may be 0°, that is, the straight lines L6 and L7 may overlap.

In the cutting insert 21 of the second embodiment, the arc-shaped cutting edge portion 5a of the main cutting edge 5 is positioned on a convex hemisphere extending from the vicinity of the axis O at the tip of the end mill body 41 and centered on the axis O. In addition, the main cutting edge 5 is attached to the third insert mounting seat 12C so that the linear cutting edge portion 5b of the main cutting edge 5 is positioned on the cylindrical surface centered on the axis O in contact with the convex hemisphere. In the cutting insert 31 of the third embodiment, the arcuate cutting edge portion 6a of the minor cutting edge 6 of the cutting insert 21 of the second embodiment is separated from the axis O from the arcuate cutting edge portion 6a of the major cutting edge 5 of the cutting insert 21 of the second embodiment. The linear cutting edge portion 6b of the minor cutting edge 6 is positioned on the convex hemisphere where the portion 5a is located, and the linear cutting edge portion 5b of the major cutting edge 5 of the cutting insert 21 of the second embodiment is positioned. It is mounted on the fourth insert mounting seat 12D so as to be positioned on the cylindrical surface of the insert.

First to fourth protrusions 14A to 14D are also formed on the bottom surfaces 12a of the third and fourth insert mounting seats 12C and 12D. The groove portion 8 having the narrow portion 9 formed in the seating surface 3 of the cutting inserts 21 and 31 of the second and third embodiments is brought into contact with the first to fourth convex portions 14A to 14D. It is attached. In the indexable ball end mill of the second embodiment, the first protrusion 14A on the tip side of the third insert mounting seat 12C of the end mill main body 41 is peninsula-shaped, unlike the first embodiment. are formed like isolated islands like the second to fourth projections 14B to 14D.

Also in the cutting inserts 21 and 31 of the second and third embodiments and the indexable ball end mill of the second embodiment, the groove portion 8 having the narrow portion 9 is formed on the seating surface 3 of the cutting inserts 21 and 31. is formed. Since this groove portion 8 can abut on the convex portions 14A to 14D formed on the insert mounting seats 12C and 12D, the cutting insert 1 and the indexable ball end mill of the first embodiment can be cut. The strength of the inserts 21 and 31 can be improved to prevent damage, and the cutting inserts 21 and 31 can be prevented from slipping during cutting to perform highly accurate machining.

In the cutting inserts 21 and 31 of these second and third embodiments, the major cutting edge 5 and the minor cutting edge 6 are seated as they move from the arcuate cutting edge portions 5a and 6a toward the linear cutting edge portions 5b and 6b. Since it is formed in a convex curve that approaches the seating surface 3 side after moving away from the surface 3 side, the major cutting edge 5 and the minor cutting edge 6 can gradually bite into the work material from the most convex point S. As a result, the cutting resistance can be reduced, and the strength of the cutting edge can be improved by increasing the thickness.

Moreover, in the cutting inserts 21 and 31 of these second and third embodiments, the other end of the groove 8 is open to the flank 4 connected to the arcuate cutting edge portions 5a and 6a. is positioned closer to the arcuate cutting edge portions 5a and 6a than the most convex point S where the major cutting edge 5 and the minor cutting edge 6 are most convex with respect to the seating surface 3. In the same way as in the above embodiment, it is possible to prevent the impact from being directly transmitted to the opening of the groove 8 in the direction of the center line X of the insert when the most convex point S bites. Damage to the cutting inserts 21, 31 can also be prevented.

When the other end of the groove portion 8 is open to the arc-shaped cutting edge portions 5a and 6a in this way, one end of the groove portion 8 is also linear like the cutting inserts 21 and 31 of the second and third embodiments. When the flank 4 connecting to the cutting edge portions 5b and 6b is open, in a bottom view viewed from the direction facing the seating surface 3, the maximum convex point S of the major cutting edge 5 and the minor cutting edge 6 and the A straight line L6 connecting the center P1 of the arcuate cutting edge portions 5a and 6a, and a point of contact V between the arcuate cutting edge portions 5a and 6a of the major cutting edge 5 and the minor cutting edge 6 and the linear cutting edge portions 5b and 6b. If the third crossing angle θ3 formed by the straight line L7 connecting the center p1 of the arcuate cutting edge portions 5a and 6a is too large, the most convex point S is too close to the opening of the groove portion 8 to the flank surface 4, As described above, damage to the cutting inserts 21 and 31 cannot be reliably prevented. Therefore, the third crossing angle θ3 is desirably 40° or less, more desirably 37° or less, and even more desirably 35° or less.

Further, the cutting inserts 21 and 31 of these second and third embodiments are formed in a shape that is 180° rotationally symmetrical in the circumferential direction of the rake face 2 with respect to the insert centerline X, which is the centerline of the mounting hole 7, as described above. It is As a result, the major cutting edge 5 and the minor cutting edge 6 of each of the cutting inserts 21 and 31 used for cutting while attached to the third and fourth insert mounting seats 12C and 12D are worn. When the life of the cutting inserts 21 and 31 is reached, the cutting inserts 21 and 31 are once removed, rotated 180° around the center line X of the insert, and re-mounted to the third and fourth insert mounting seats 12C and 12D, respectively. Similarly, one cutting insert 21, 31 can be used twice.

According to the present invention, the narrow portion of the groove formed in the seating surface of the cutting insert secures the wall thickness of the cutting insert on the other end side where the groove width is narrow, disperses the stress, and improves the strength. It is possible to prevent the cutting insert from being damaged by the load during cutting. At one end of the groove, the width of the narrow portion is widened, so that the convex portion of the indexable ball nose end mill can be formed with a wide width, which increases the mounting rigidity of the cutting insert and reliably prevents misalignment. It becomes possible.

1 (1A, 1B), 21, 31 cutting insert 2 rake face 3 seating surface 4 flank face 5 major cutting edge 5a arc-shaped cutting edge portion of major cutting edge 5 5b linear cutting edge portion of major cutting edge 5 6 minor cutting edge Blade 6a Arc-shaped cutting edge portion of minor cutting edge 6 6b Linear cutting edge portion of minor cutting edge 6 7 Mounting hole 8, 8A, 8B Groove 9 Narrow portion 11, 41 End mill body 12 (12A to 12D) Insert mounting seat 14A to 14D Protrusions r Radius P of an arc-shaped cutting edge portion (6a) located on the other end side of the narrow portion 9 in the groove (second groove portion 8B) Arc-shaped cutting edge portion of the minor cutting edge 6 in bottom view Center of arc formed by 6a P1 Center of arc formed by arc-shaped cutting edge portion 5a of major cutting edge 5 in bottom view Q Center of arc formed by arc-shaped cutting edge portion 5a of minor cutting edge 6 Edge of the intersection ridge between the wall surface 8a and the flank surface 4 toward the seating surface 3 S Most convex point t Thickness of the cutting insert 1 at the most convex point S U The thickness of the cutting insert 1 is ensured by the most convex point S V Contact point between arc-shaped cutting edge portion 5a and linear cutting edge portion 5b of main cutting edge 5 in bottom view L1 Straight line connecting center P and highest convex point S in bottom view L2 Center P and center P in bottom view A straight line connecting the edge Q L3 An extension line of the linear cutting edge portion 6b of the minor cutting edge 6 toward the arcuate cutting edge portion 6a side of the minor cutting edge 6 in bottom view L6 The most convex of the major cutting edge 5 in bottom view Straight line connecting point S and center P1 L7 Straight line connecting center P1 and point of contact V in bottom view W1 Groove width at the other end of narrow portion 9 W2 Groove width at one end of narrow portion 9 X Insert center line O End mill body Axis of 11 and 41 T Direction of end mill rotation θ1 First intersection angle θ2 Second intersection angle θ3 Third intersection angle

Claims (2)

A cutting insert detachably attached to an insert mounting seat formed at the tip of an end mill body of an indexable ball end mill that rotates around an axis,
A rake face directed in the rotational direction of the end mill body, a seating surface facing the opposite side of the rake face and seated on the bottom surface of the insert mounting seat, and a relief extending around the rake face and the seating face. having a face and
An arcuate cutting edge portion extending in an arcuate shape in a plan view viewed from a direction facing the rake surface and an arcuate cutting edge portion extending in contact with the arcuate cutting edge portion are provided at the intersection ridgeline portion between the rake face and the flank face. Two cutting edges each having a linear cutting edge portion are formed by alternately locating the arcuate cutting edge portion and the linear cutting edge portion in the circumferential direction of the rake face,
One of the two cutting edges is a major cutting edge and the other is a minor cutting edge, and the arcuate cutting edge portion of the minor cutting edge has an equal radius to the arcuate cutting edge portion of the major cutting edge. The circumference is short at
The seating surface is provided with two grooves each having a wall surface capable of abutting against a protrusion protruding from the bottom surface of the insert mounting seat. and the flanks connected to the arc-shaped cutting edge portions of the major cutting edge and the minor cutting edge are formed in the shape of through grooves that are open to both,
The cutting insert, wherein the groove width of the two grooves narrows from the linear cutting edge side of the cutting edge to the arcuate cutting edge side of the cutting edge. The rate at which the groove width narrows is constant,
The groove portion includes a first wall surface and a second wall surface facing each other, a bottom surface parallel to the seating surface between the first wall surface and the second wall surface, and the first wall surface. 2. The cutting insert according to claim 1, wherein said second wall surface extends linearly in a bottom view viewed from a direction facing said seating surface.

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