Cutting insert

A cutting insert which is excellent in both cutting edge strength and chip evacuation is provided. A corner edge of the cutting insert is formed in an arc shape. In a direction perpendicular to a rotation axis of a body, a width of the corner edge is 40% or more and 50% or less of a width of the cutting insert. An upper surface has a negative land which is formed along a cutting edge and has a negative angle. The angle of the negative land increases from one end, which is connected to an inner cutting edge, of both ends of the corner edge toward the other end.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application relates to and claims priority from Japanese Patent Application No. 2020-039878, filed on Mar. 9, 2020 and Japanese Patent Application No. 2019-079331, filed on Apr. 18, 2019, the entire disclosure of which is incorporated herein by reference.

BACKGROUND

Field

The present invention relates to a cutting insert used for cutting, and more particularly to a cutting insert attached to an indexable cutting tool used for milling.

Description of Related Art

There is a desire to design a cutting edge having high strength with which a work material having high hardness can be machined.

SUMMARY

When an axial rake angle (axial rake) is set to be a negative angle (negative), the rake angle reduces at both a tip and an outer circumference of a milling tool, and cutting edge strength can increase. On the other hand, when the axial rake angle is set to be a negative angle, chips are easily discharged toward a lower side (the tip side) of the milling tool, and clogging of chips, rubbing of the chips on a work surface, and the like easily occur. On the other hand, when a rake surface of a cutting insert is formed into a flat surface and the axial rake angle is set to be a positive angle, a true rake angle increases as a distance from the tip of the milling tool increases, and the cutting edge strength decreases.

An object of the present invention is to provide a cutting insert which is excellent in both cutting edge strength and chip evacuation.

A cutting insert according to an aspect of the present invention is a cutting insert which is mounted on a body rotating about a rotation axis and constitutes an indexable cutting tool together with the body. The cutting insert includes a lower surface mounted on a seat surface of the body, an upper surface opposite to the lower surface, and a circumferential surface connecting the lower surface to the upper surface. A cutting edge is formed at a ridge line at which the upper surface and the circumferential surface intersect. The cutting edge has an inner cutting edge and a corner edge. The corner edge is formed at a position farther from the rotation axis than the inner cutting edge and is connected to the inner cutting edge. The corner edge is formed in an arc shape in a plan view seen from a direction facing the upper surface. In a direction perpendicular to the rotation axis, a width of the corner edge is 40% or more and 50% or less of a width of the cutting insert. The upper surface has a negative land which is formed along the cutting edge and has a negative angle, and a flat surface which is connected to the negative land and parallel to the lower surface. The angle of the negative land increases from one end, which is connected to the inner cutting edge, of ends of the corner edge toward the other end.

According to this aspect, the angle of the negative land formed adjacent to the corner edge has a smaller value at a portion located closer to the tip of the milling tool. By providing the negative land of which a land angle gradually changes to a positive side toward a side away from the tip of the milling tool, the cutting edge strength can be enhanced while the chip evacuation is be improved.

In the above aspect, the cutting edge of the cutting insert further has a linear wiper edge which is connected to the corner edge and parallel to the rotation axis. In the ridge line in the wiper edge, the linear ridge line of the upper surface preferably intersects the wiper edge at an obtuse angle.

According to this aspect, since the wiper edge wipes a machined surface of the corner edge, roughness of the machined surface is improved. In the linear ridge line, since the linear ridge line of the upper surface and the wiper edge intersect at an obtuse angle, the linear ridge line coming into contact with a work surface and deteriorating roughness of the machined surface can be prevented in advance.

In the above aspect, it is preferable that the cutting insert further include a through hole penetrating from the upper surface to the lower surface, and when the upper surface is viewed from above, a proportion of the flat surface in an area excluding the through hole from the upper surface is preferably 90% or more.

When there is unevenness on the upper surface, restrictions on how to move a grindstone when grinding the cutting insert occur. According to this aspect, since most of the upper surface is formed of a flat surface, grinding is easily performed. It can be manufactured with higher precision than a cutting insert having a chip breaker or the like formed on the upper surface.

According to the present invention, it is possible to provide a cutting insert which is excellent in both cutting edge strength and chip evacuation.

DETAILED DESCRIPTION

A preferred embodiment of the present invention will be described with reference to the accompanying drawings. Also, in each of the drawings, components denoted by the same reference numerals have the same or similar configurations. In a cutting insert10of the present invention, whole parts of cutting edges10f,10g, and10mare disposed at a substantially constant height from a lower surface10b(seeFIGS. 4 and 5). A negative land10qprovided along a corner edge10fis formed such that an angle thereof increases from θ1to θ2from one end12, which is connected to an inner cutting edge10g, to the other end13(seeFIGS. 6 and 7). By providing the negative land of which a land angle gradually changes to a positive side toward a side away from a tip of a milling tool, cutting edge strength can be enhanced while chip evacuation can be improved. Hereinafter, each configuration will be described in detail with reference toFIGS. 1 to 10.

FIGS. 1 and 2are perspective views showing an example of the cutting insert10according to one embodiment of the present invention. As shown inFIGS. 1 and 2, the cutting insert10includes an upper surface10a, the lower surface10bopposite to the upper surface10a, and circumferential surfaces10d,10d′,10e, and10e′ connecting the upper surface10ato the lower surface10b.

The circumferential surfaces include a pair of substantially flat side surfaces10dand10d′ and a pair of front surfaces10eand10e′ providing connection between the pair of side surfaces. In the following description, one of the pair of side surfaces may be referred to as a first side surface10d, and the other may be referred to as a second side surface10d′. Similarly, one of the pair of front surfaces may be referred to as a first front surface10e, and the other may be referred to as a second front surface10e′.

FIG. 3is a top view of the cutting insert10from the upper surface10a. As shown inFIG. 3, a ridge line at which the upper surface10aand the first side surface10dintersect is formed in a straight line shape. Similarly, a ridge line at which the upper surface10aand the second side surface10d′ intersect is formed in a straight line shape parallel to the ridge line of the first side surface10d. As shown inFIG. 3, an interval between the ridge lines, formed in the straight line shapes, of the first and second side surfaces10dand10d′ is defined as a width W of the cutting insert10. The width W of the cutting insert10is, for example, 4 to 4.5 mm.

In the illustrated example, the lower surface10bof the cutting insert10is formed in a planar shape. A through hole H to penetrate the upper surface10aand the lower surface10bis formed in a central part of the cutting insert10. The cutting insert10is fixed to a body B by screwing a clamp screw penetrating the through hole H with a female screw provided on a seat surface of the body B of an indexable cutting tool. In this case, the cutting insert10is fixed to the body B such that the side surface10dside is close to a rotation axis AX of the body B and the side surface10d′ side is far from the rotation axis AX of the body B (seeFIG. 9). The body B will be described later in detail with reference toFIGS. 8 to 10.

FIG. 4is a side view of the cutting insert10from the second side surface10d′ of the circumferential surfaces.FIG. 5is a side view of the cutting insert10from the second front surface10eof the circumferential surfaces. As shown inFIGS. 4 and 5, the circumferential surfaces10d,10d′,10e, and10e′ of the cutting insert10include a vertical part10hwhich is connected to the lower surface10band perpendicular to the lower surface10b, a connection part10jwhich is connected to the vertical part10hand expands such that a cross-sectional area thereof parallel to the lower surface10bincreases toward a side away from the lower surface10b, and an inclined part10kwhich is connected to the connection part10jand expands such that a cross-sectional area thereof parallel to the lower surface10bincreases toward a side away from the lower surface10b.

In the following description, an angle at which the circumferential surfaces are inclined with respect to a central axis of the through hole H is referred to as an inclination angle. In addition, the angle formed between the central axis of the through hole H and the circumferential surfaces is obtained as a complementary angle of the angle formed by a direction vector of the central axis and a normal vector of the circumferential surfaces. As shown inFIG. 5, the circumferential surfaces10d,10d′,10e, and10e′ of the connection part10jhave a larger inclination angle (a first inclination angle α) than the circumferential surfaces of the vertical part10h. Therefore, an increase rate of the cross-sectional area is large. On the other hand, the circumferential surfaces of the inclined part10khave a smaller inclination angle (a second inclination angle1) than the circumferential surfaces of the vertical part10h. Therefore, the increase rate of the cross-sectional area is small.

Further, heights in a direction perpendicular to the lower surface10bincrease in the order of the vertical part10h, the connection part10j, and the inclined part10k. In addition, a height h3of the inclined part10kis larger than a sum h1+h2of a height h1of the vertical part10hand a height h2of the connection part10j.

In other words, the cutting insert10has a constricted shape from the upper surface10ato the lower surface10b, and has a structure in which the inclined part10kcontracts such that the cross-sectional area gradually decreases from the upper surface10atoward the lower surface10b, the connection part10jthen contracts such that the cross-sectional area decreases greatly toward the lower surface10b, and the vertical part10his connected to the lower surface10bwhile a constant cross-sectional area is maintained. Also, the inclination angles of the connection part10jand the inclined part10kneed not be constant. However, an average value of the inclination angle of the connection part10jand an average value or a representative value of the inclination angle of the inclined part10khave a magnitude correlation therebetween.

As shown inFIGS. 1 and 2, a cutting edge is formed on at least a part of the ridge line at which the upper surface10aand the first front surface10eintersect. The cutting edge includes a corner edge10fand an inner cutting edge10g. Similarly, the corner edge10fand the inner cutting edge10gare formed as a cutting edge at the ridge line at which the upper surface10aand the second front surface10e′ intersect. The cutting insert10has a structure that is 180° axially symmetric with respect to the center axis of the through hole H. That is, the first front surface10eand the second front surface10e′ have substantially the same shape and function. For that reason, the first front surface10ewill be described in detail as a representative, and repeated descriptions of the second front surface10e′ will be omitted.

The corner edge10fis provided at a corner part of the cutting insert10and is formed to have a predetermined curvature when viewed from a direction facing the upper surface10a. In other words, the corner edge10fis formed in an arc shape. The curvature of the corner edge10fcan be selected in accordance with a specification of a corner R to be machined. For example, when the specification of the corner R is 2 mm, the cutting insert10in which the corner edge10fhas a predetermined radius of curvature (for example, slightly less than 2 mm) may be selected such that the corner R after machining in consideration of a rotation locus of the corner edge is 2 mm.

In the present embodiment, as shown inFIG. 3, the corner edge10fwhich is larger and has a larger curvature than usual is formed. In the illustrated example, a width Wf of the corner edge10fis 40% or more and 50% or less of the width W of the cutting insert10in the direction perpendicular to the rotation axis AX of the body B. More specifically, when viewed from the direction facing the upper surface10a, the corner edge10fis formed from the side surface10d′ to a position of 40% to 50% in a direction of the width W (a direction connecting the first side surface10dand the second side surface10d′), and the radius of curvature is formed, for example, to be 50% or less of the width W.

In addition, in the example shown inFIGS. 3 and 5, the inner cutting edge10gis formed continuously with the corner edge10f. The inner cutting edge10gincludes the other end12connected to the corner edge10f, and one end11connected to the first side surface10dformed substantially linearly when viewed from the direction facing the upper surface10a.

As shown inFIGS. 4 and 5, the upper surface10ais formed to be flat and parallel to the lower surface10b. In other words, a ridge line of the upper surface10aincluding the corner edge10fand the inner cutting edge10gis positioned at substantially the same height from the lower surface10bover the entire circumference thereof. More specifically, the upper surface10ahas a flat surface10pwhose height (distance) from the lower surface10bis constant, and the negative land10qsurrounding the flat surface10p.

Ridge lines at which the negative land10qand the circumferential surfaces10d,10d′,10e, and10e′ intersect have a height from the lower surface10bwhich is substantially equal to that of the flat surface10pand are slightly lower than the flat surface10p. That is, distances from the lower surface10bbetween all parts of the cutting edges10f,10g, and10mformed on the ridge lines and the upper surface10aare substantially constant. A difference in height between the cutting edge at the highest position from the lower surface10band the cutting edge at the lowest position from the lower surface10bis, for example, 1 mm or less.

In the example shown inFIG. 4, a wiper edge10mis formed on a side opposite to the inner cutting edge10gwith the corner edge10finterposed therebetween. The wiper edge10mis formed to be much shorter than the corner edge10fand the inner cutting edge10g. The other end of the wiper edge10mis connected to a linear ridge line of the upper surface10a. The ridge line and the wiper edge10mintersect at an obtuse angle γ of almost 180° at an inner angle, as shown inFIG. 5.

As shown inFIGS. 6 and 7, the negative land10qhaving a negative angle (01to02) is formed adjacent to the cutting edge on the upper surface10a.FIG. 6is a cross-sectional view along line VI-VI inFIG. 3.FIG. 7is a cross-sectional view along line VII-VII inFIG. 3. As shown inFIGS. 6 and 7, the angle of the negative land10qadjacent to the corner edge10fgradually increases to approach a positive value from one end12connected to the inner cutting edge10gtoward the other end13connected to the wiper edge10m.

In the illustrated example, an angle θ1of the negative land10qat the end12on the inner cutting edge10gside shown inFIG. 6is −20°. The angle of the negative land10qgradually increases from θ1toward the end13connected to the wiper edge10m. An angle θ2of the negative land10qat the end13on the wiper edge10mside shown inFIG. 7is −8°.

In addition, the upper surface10ais configured of the flat surface10p, in which a chip breaker or the like is not formed, in most of the portion excluding the through hole H and the negative land10q. A proportion of the flat surface10pto the upper surface10ais 90% or more.

FIG. 8is a perspective view showing an example of an end mill E on which two cutting inserts10are mounted,FIG. 9is a diagram of a tip part of the end mill E, including the tip and the vicinity thereof, when viewed from a direction perpendicular to the rotation axis AX, andFIG. 10is a diagram of the tip part of the end mill E when viewed from the direction of the rotation axis AX. The end mill E is an example of the indexable cutting tool. The end mill E shown inFIGS. 8 to 10is a small-diameter end mill E having a tool diameter of 8 mm to 20 mm and can be used, for example, for machining a mold.

As shown inFIGS. 8 to 10, two seat surfaces F and F′ for mounting the cutting inserts10are formed on a cylindrical body B at the tip part of the end mill E. Female screws are formed in the seat surfaces F and F′. By screwing a clamp screw CS penetrating the through hole H of the cutting insert10with the female screw, the lower surface10bof the cutting insert10is pressed against each of the seat surfaces F and F′, and each cutting insert10is fixed to the body B. A base end of the end mill E opposite to the tip part is fixed to a machine tool (not shown).

In this case, the front surface10efaces in the same direction as the rotation axis AX. As described above, the cutting insert10is mounted on the body B such that the side surface10dis close to the rotation axis AX and the side surface10d′ is far from the rotation axis AX. Therefore, the corner edge10fand the inner cutting edge10gare present from an outer circumferential side toward a center of the end mill E.

Hereinafter, a structure for increasing rigidity of the body B will be described. The cutting insert10according to the present embodiment contributes to increasing the rigidity of the body B. Since the width W of the cutting insert10is extremely thin, that is, 4 to 4.5 mm, the body B on which the cutting insert10is mounted is also thin. As a volume of the body B decreases, the rigidity of the body B also decreases.

In addition, in order to securely bring the side surface of the cutting insert into contact with a wall surface of a tip seat of the body when the cutting insert is mounted on the body, a relief (a recessed part) is formed around a corner part connecting the seat surface and the wall surface of the tip seat. The inventors of the present application have focused on the point that removing the corner part of the tip seat to form the relief has an effect on the rigidity of the body.

Since the cutting insert10according to the present embodiment is provided with the inclined part10kand the connection part10j, an edge of the lower surface10bis moved toward a center side of the lower surface10bas compared with a typical cutting insert in which the inclined part10kand the connection part10jare not provided. For this reason, as shown inFIG. 10, it is possible to reduce the relief formed at each of corner parts C and C′ of the tip seat of the body B on which the cutting insert10is mounted, that is, to increase a cross-sectional area of the body B. Therefore, the rigidity of the body B can be increased.

Further, since the width W of the cutting insert10is very narrow, that is, 4 to 4.5 mm, each contact area of the seat surface F and the seat surface F′ of the tip seat is also restricted. When the contact area is too small, the cutting insert cannot be stably mounted on the body B. Since the cutting insert10is provided with the vertical part10hfollowing the inclined part10k, an area of the lower surface10bcan be increased as compared with a case in which there is no vertical part10h. Therefore, a large contact area of the cutting insert with each of the seat surface F and the seat surface F′ of the chip seat can be secured.

Also, since a circumferential surface of the inclined part10khaving a relatively small inclination angle can be brought into contact with the wall surface of the tip seat, the cutting insert10can be supported more stably as compared with a case in which a circumferential surface having a large inclination angle is brought into contact with the wall surface of the tip seat. Therefore, the cutting insert10according to the present embodiment can achieve both improvement in rigidity of the body B and stable mounting.

Next, effects of the present embodiment will be described. The angle (θ1to θ2) of the negative land10qformed adjacent to the corner edge10fhas a smaller value (for example, θ1) at a portion located closer to the tip of the milling tool. By providing the negative land of which the land angle gradually changes to a positive side toward a side away from the tip of the milling tool, cutting edge strength can be enhanced while chip evacuation can be improved.

As a second (secondary) effect of the present embodiment, the cutting insert10is disposed on the tool body B to form a positive axial rake angle, and accordingly, in the case of cutting a work material that is not a hard material, if the cutting insert10is replaced such that the rake angle becomes a positive angle, the tool body B can be shared in cutting of a high-hardness material and cutting of other work materials.

In addition, since the wiper edge10mis connected to the corner edge10f, roughness of a machined surface of a standing wall is improved. Since the linear ridge line connected to the wiper edge10mand the wiper edge10mintersect at an obtuse angle, contact of the linear ridge line with a workpiece is avoided. Therefore, it is possible to prevent a situation in which the linear ridge line comes into contact with a work surface and deteriorates roughness of the machined surface.

Further, grooves and irregularities such as a chip breaker are not formed on the upper surface10a, and most of the upper surface10ais formed of the flat surface10p. Accordingly, when the negative land10qis formed by grinding, a degree of freedom in moving a grindstone increases, and manufacturing costs decrease. That is, the cutting insert10can be manufactured with higher precision than a cutting insert having a complicated shape on which a chip breaker or the like is formed.

The present invention can be variously modified without departing from the gist thereof. For example, some components of one embodiment may be combined with other embodiments within a range of an ordinary creativity of those skilled in the art.