Patent Description:
There conventionally is known a cutting insert that has a generally triangular outline shape in top view and in bottom view, as disclosed in <CIT>, for example. The cutting insert disclosed in <CIT> is arranged so that the shape is the same even if the upper and lower faces are flipped, and the cutting edges can be replaced and used for a total of six times. Such a cutting insert is used in shoulder milling, for example, where orthogonal wall surfaces are machined, or the like, and is provided with a major cutting edge that primarily machines a wall surface, a wiper edge that machines a bottom face, and a corner edge that connects the major cutting edge and wiper edge. A cutting insert configured thus is referred to as a negative type, and has a flank clearance angle of <NUM>°. Accordingly, the wedge angle is great and the level of strength of the cutting edge is high.

<CIT> discloses a double-sided milling cutting insert and to a milling tool having a first cutting edge arranged at an intersection of a top side and a side surface, a second cutting edge arranged at an intersection of a bottom side and the side surface.

Generally, the radial rake angle is set to a negative value when installing a negative-type cutting insert, to prevent the edge portion of the lower face from overlapping the rotational trajectory of the cutting edge when installed to the body. Installing the cutting insert in this way secures a large gap between the flank and rotational trajectory. However, in this case, the space above the rake face of the cutting insert is narrowed proportionately to the increase in space between the flank and rotational trajectory, and produced chips are discharged less readily.

When installing the cutting insert to the body with the top and bottom having been reversed so that this rake face is the face in contact with the body, the cutting insert may be attached to the body at a posture deviated from the initially intended posture if the rake face has been damaged due to abrasion by chips. If the posture of the cutting insert attached to the body changes, cutting performance, state of the machining surface, and so forth, also change in a corresponding manner. With the foregoing in view, it is an object of the present invention to provide a cutting insert where there is little damage to the rake face.

A cutting insert according to the present invention is provided in claim <NUM>.

According to this aspect, the first minor cutting edge flank that connects to the minor cutting edge is recessed further toward the center side of the cutting insert as compared to the second minor cutting edge flank. A sufficient gap can be secured between the first minor cutting edge flank and the rotational trajectory of the cutting edge even without setting the radial rake angle to a negative value. The radial rake angle can be set to around <NUM>° as to the body, so a space known as a pocket where produced chips extend can be formed larger. Accordingly, a cutting insert can be provided where chips can be prevented from abrading and damaging the rake face of the cutting insert according to the present invention.

In the cutting insert according to the above aspect, the connecting cutting edge flank preferably further includes a third connecting cutting edge flank that connects to the second connecting cutting edge flank. Preferably, the clearance angle of the first connecting cutting edge flank is <NUM>°, the clearance angle of the second connecting cutting edge flank is a positive value, and the clearance angle of the third connecting cutting edge flank is <NUM>°. The minor cutting edge flank preferably further includes a third minor cutting edge flank that connects to the second minor cutting edge flank and that has a clearance angle of <NUM>°.

According to this aspect, when the top and bottom of the cutting insert is reversed and cutting edges at the lower face are used, parts that had been functioning as the first, second and third connecting cutting edge flanks of the cutting edges at the upper face function as third, second, and first minor cutting edge flanks at the cutting edges at the lower face. In the same way, parts that had been functioning as the first, second and third minor cutting edge flanks of the cutting edges at the upper face function as third, second, and first connecting cutting edge flanks at the cutting edges at the lower face. Accordingly, the cutting insert can be reversed top and bottom and still be used in the same way as before reversing.

In the cutting insert according to the above aspect, the third minor cutting edge flank preferably is situated outward from the first minor cutting edge flank in top view, and the third connecting cutting edge flank preferably is situated inward from the first connecting cutting edge flank in top view.

According to this aspect, the third minor cutting edge flank protrudes outward (toward the outer circumferential side) as compared to the first minor cutting edge flank, so the third minor cutting edge flank of the minor cutting edge (lower portion of the wiper edge) is thick, and the minor cutting edge is not readily fractured. The first minor cutting edge flank (upper portion of the wiper edge) can be retracted inward (toward the center side) while maintaining strength of the minor cutting edge, thereby enabling a large gap to be secured between the first minor cutting edge flank and the rotational trajectory of the cutting edge.

In the cutting insert according to the above aspect, an angle a formed by the major cutting edge and the minor cutting edge preferably is <NUM>° < a < <NUM>°.

According to this aspect, the cutting insert can be suitably used for shoulder milling.

According to the above aspect, the connecting cutting edge preferably curves outward in top view.

According to this aspect, the connecting cutting edge is not fractured as readily as a straight connecting cutting edge (corner edge) intersecting at an acute angle.

In the cutting insert according to the above aspect, the outline shape in top view and an outline shape in bottom view preferably are the same.

According to this aspect, the top and bottom can be reversed and the cutting edges at the lower face of the cutting insert can be used when the cutting edges at the upper face are worn or damaged.

In the cutting insert according to the above aspect, the upper face preferably has a general regular polygonal shape, and even more preferably, the connecting cutting edge of the upper face and the connecting cutting edge of the lower face do not overlap in top view.

According to this aspect, the minor cutting edge on the upper face side and the connecting cutting edge on the lower face side are at offset positions in top view, and accordingly even if the minor cutting edge at the upper face side is greatly damaged due to fracturing or the like, for example, the connecting cutting edge at the lower face side is not readily affected. In the same way, even if the connecting cutting edge at the upper face side is damaged, the minor cutting edge at the lower face side is not readily affected.

In the cutting insert according to the above aspect, the connecting cutting edge flank of the upper face preferably connects to the wiper edge of the lower face, and the wiper edge flank of the upper face preferably connects to the corner edge of the lower face.

According to the present invention, a cutting insert can be provided where chips can be prevented from abrading and damaging the rake face of the cutting insert according to the present invention.

An embodiment of the present invention will be described below with reference to the Figures. Note that in the Figures, items denoted by the same reference symbols have the same or equivalent configurations. Two axes, an X axis and Z axis that are orthogonal to each other, are set such as illustrated in <FIG> and <FIG>, to facilitate description. Also, when describing the positional relation between two objects, a case where an object B is situated at a position further in the direction of the arrowhead side of the Z axis in relation to another object A may be described as "object B is above object A". Further, a case where the object B is situated at a position on the opposite side in the direction of the arrowhead side of the Z axis in relation to the other object A may be described as "object B is below object A".

<FIG> is a perspective view illustrating a cutting insert <NUM> according to an embodiment of the present invention. The cutting insert <NUM> according to the present embodiment is configured including an upper face <NUM>, a lower face <NUM> on the opposite side from the upper face <NUM>, and a side face <NUM> connecting between the upper face <NUM> and lower face <NUM>, as illustrated in <FIG>. A through hole <NUM> that passes through from the upper face <NUM> to the lower face <NUM> is formed. A fastener such as a screw or the like is inserted into the through hole <NUM>, and the cutting insert <NUM> is fixed to a body <NUM>, which is the main body portion of the cutting tool. The body <NUM> will be described in detail later with reference to <FIG> and <FIG>.

<FIG> is a plan diagram (top diagram) illustrating the upper face <NUM> of the cutting insert <NUM> illustrated in <FIG>. In the following description, viewing the cutting insert <NUM> from the upper face <NUM> toward the lower face <NUM> may be referred to as a "top view" (plan view), and viewing the cutting insert <NUM> from the lower face <NUM> toward the upper face <NUM> may be referred to as a "bottom view" (underside view). The cutting insert <NUM> has the same shape when rotated <NUM>° on the X axis shown in <FIG>. In other words, the outline shape in top view and the outline shape in bottom view are the same. Accordingly, the configuration of the upper face <NUM> will be described in detail representatively, and repetitive description regarding the configuration of the lower face <NUM> will be omitted.

The upper face <NUM> has a <NUM>° rotationally-symmetrical shape on a center axial line of the through hole <NUM>, which corresponds to the center of the cutting insert <NUM>, as illustrated in <FIG>. A ridge line where the upper face <NUM> and side face <NUM> intersect will be referred to as "side ridge portion" of the upper face <NUM>. In the same way, a ridge line where the lower face <NUM> and side face <NUM> illustrated in <FIG> intersect will be referred to as "side ridge portion" of the lower face <NUM>. The side ridge portions of the upper face <NUM> and lower face <NUM> act as cutting edges that contribute to cutting.

In the example illustrated in <FIG> and <FIG>, a configuration is made where there are three sets of cutting edges connected, each set made up of a straight minor cutting edge <NUM> (hereinafter referred to as "wiper edge"), a connecting cutting edge <NUM> that connects to the wiper edge <NUM> and curves toward the outward direction of the cutting insert <NUM> (hereinafter referred to as "corner edge"), and major cutting edges <NUM>, <NUM>, and <NUM> connecting to the corner edge <NUM>. Note that the wiper edge <NUM> is not restricted to being straight, and may have a gradual curving form.

In the example illustrated in <FIG> and <FIG>, each major cutting edge <NUM>, <NUM>, and <NUM> includes a first major cutting edge straight portion <NUM> which is straight and connects to the corner edge <NUM>, a major cutting edge curved portion <NUM> that connects to the first major cutting edge straight portion <NUM> and which is curved with a relatively small curvature, and a second major cutting edge straight portion <NUM> which is straight and connects to the major cutting edge curved portion <NUM>.

That is to say, the second major cutting edge straight portion <NUM> of a certain set A connects to the wiper edge <NUM> of another set B, and the wiper edge <NUM> of the certain set A further connects to the second major cutting edge straight portion <NUM> of yet another set C. The wiper edge <NUM> functions to reduce the surface coarseness of the machined surface of the work. The first major cutting edge straight portion <NUM>, the major cutting edge curved portion <NUM>, and the second major cutting edge straight portion <NUM> undertake a greater part of cutting as a so-called major cutting edge.

The angle formed between a line extending from the wiper edge <NUM> and a line extending from the first major cutting edge straight portion <NUM> is greater than <NUM>° and smaller than <NUM>°. In the example illustrated in <FIG>, a line extending from the wiper edge <NUM> and a line extending from the first major cutting edge straight portion <NUM> intersect at an angle of <NUM>°. The cutting insert <NUM> shaped thus is well-suited to shoulder milling. The upper face <NUM> has a land <NUM>, a rake face <NUM>, and an insert seat contact face <NUM> in the example illustrated in <FIG>. The land <NUM> connects to each of the cutting edges <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> and descends the farther away from these cutting edges. The rake face <NUM> connects to the land <NUM> and descends the farther away from the cutting edges, at an angle greater than that of the land <NUM>.

The insert seat contact face <NUM> connects to the rake face <NUM>, and comes into contact with a bottom face of an insert seat <NUM> formed on the body <NUM>, which will be described later. The insert seat contact face <NUM> is a part serving as a reference for the angles of the parts of the cutting insert <NUM>. In other words, the degrees of inclination of the parts such as the cutting edges and so forth are defined with the insert seat contact face <NUM>, which is deemed to be a level surface, as a reference.

<FIG> is a side view, viewing the cutting insert <NUM> from a direction facing the side face <NUM> corresponding to the major cutting edges <NUM>, <NUM>, and <NUM>. In further detail, <FIG> is a side view, viewing the cutting insert <NUM> from the front of the side face <NUM> connecting to the major cutting edge curved portion <NUM>. In the same way, <FIG> is a side view, viewing the cutting insert <NUM> illustrated in <FIG> from a direction facing the side face <NUM> corresponding to the corner edge <NUM>. It can be seen from <FIG> that the cutting edges configured including the wiper edge <NUM>, corner edge <NUM>, major cutting edges <NUM>, <NUM>, and <NUM>, and so forth, first descend from a certain corner edge 22a toward another adjacent corner edge 22b, and thereafter rise.

<FIG> is a cross-sectional view taken along line V-V in <FIG>, and is a cross-sectional view taken at the middle of the corner edge <NUM>, i.e., at a position corresponding to the middle point of the length of the corner edge <NUM>. The side face <NUM> (so-called flank) corresponding to the corner edge <NUM> has a first corner edge flank (first connecting cutting edge flank) <NUM> that directly connects to the corner edge <NUM> and has a clearance angle of <NUM>°, a second corner edge flank (second connecting cutting edge flank) <NUM> that connects to the first corner edge flank <NUM> and has a positive value for the clearance angle, and a third corner edge flank (third connecting cutting edge flank) <NUM> that connects to the second corner edge flank <NUM> and has a clearance angle of <NUM>°, as illustrated in <FIG>.

The flanks <NUM>, <NUM>, and <NUM> of the corner edge <NUM> configured thus are arranged such that the third corner edge flank <NUM> is situated inward from the first corner edge flank <NUM> in top view. In other words, the distance from the center axis of the through hole <NUM> is shorter for the third corner edge flank <NUM> as compared to the first corner edge flank <NUM>.

<FIG> is a cross-sectional view taken along line VI-VI in <FIG>, and is a cross-sectional view taken at the middle of the wiper edge <NUM>, i.e., at a position corresponding to the middle point of the length of the wiper edge <NUM>. Flanks <NUM>, <NUM>, and <NUM> that are part of the side face <NUM> and correspond to the wiper edge <NUM> have a first wiper edge flank (first minor cutting edge flank) <NUM> that directly connects to the wiper edge <NUM> and has a clearance angle of <NUM>°, a second wiper edge flank (second minor cutting edge flank) <NUM> that connects to the first wiper edge flank <NUM> and has a negative value for the clearance angle, and a third wiper edge flank (third minor cutting edge flank) <NUM> that connects to the second wiper edge flank <NUM> and has a clearance angle of <NUM>°, as illustrated in <FIG>.

The flanks of the wiper edge <NUM> configured thus are arranged such that the third wiper edge flank <NUM> is situated outward from the first wiper edge flank <NUM> in top view. In other words, the distance from the center axis of the through hole <NUM> is longer for the third wiper edge flank <NUM> as compared to the first wiper edge flank <NUM>.

When reversing the top and bottom of the cutting insert <NUM> according to the present embodiment to use the cutting edges of the lower face <NUM>, the third corner edge flank <NUM> becomes the first wiper edge flank <NUM> of the wiper edge <NUM> at the lower face <NUM>. In the same way, when reversing the top and bottom to use the cutting edges of the lower face <NUM>, the third wiper edge flank <NUM> becomes the first corner edge flank <NUM> of the lower face <NUM>. Due to such a shape, the corner edge <NUM> of the upper face <NUM> and a corner edge <NUM> of the lower face <NUM> do not overlap in top view, and are at positions offset from each other in the circumferential direction on the center axis of the through hole <NUM>.

Next, a state where the cutting insert <NUM> has been attached to the body will be described. <FIG> is a perspective view illustrating a cutting tool that has been provided with the cutting insert <NUM>. <FIG> is a frontal view illustrating the tip end of the cutting tool. The cutting insert <NUM> is attached to the generally-cylindrical body <NUM> with the insert seat contact face <NUM> (see <FIG>) of the lower face <NUM> abutting the body <NUM>, as illustrated in <FIG> and <FIG>. The body <NUM> to which the cutting insert <NUM> has been attached is configured to be capable of cutting by rotating in the direction that the upper face <NUM> is facing.

The body <NUM> has four insert seats <NUM> for loading cutting inserts <NUM> at the tip end thereof, the four insert seats <NUM> having been formed equidistantly. The normal of the bottom face of each insert seat <NUM> is inclined as to the rotational axis of the body <NUM>, and faces the machining surface of the work. Accordingly, when the cutting insert <NUM> is attached to the body <NUM>, the cutting insert <NUM> appears to be tilted forward when viewed from a perpendicular direction as to the rotational axis of the body <NUM>.

An open space <NUM> (hereinafter referred to as "pocket") is formed above the upper face <NUM>. Chips being produced are curled into an appropriate size at the pocket <NUM>. A spray port <NUM> that sprays air and/or coolant is formed in an inner wall of the pocket <NUM>.

Next, advantages of the above embodiment will be described. <FIG> is a Figure for describing the positional relation between the rotational trajectory and flanks <NUM>, <NUM>, and <NUM> corresponding to the corner edge <NUM> in the cutting insert <NUM> according to the present embodiment, schematically illustrating a gap s1 between the flanks <NUM>, <NUM>, and <NUM> and the rotational trajectory of the cutting tip of the corner edge <NUM> in the cutting insert <NUM>, in a state of having been installed to the body <NUM>. <FIG> is a Figure for describing the positional relation between the rotational trajectory and a flank corresponding to a corner edge in a common cutting insert that has a clearance angle of <NUM>°, schematically illustrating a gap s2 between a flank (side face) <NUM> and rotational trajectory of a cutting tip of a corner edge <NUM> of a cutting insert <NUM>, in a state of having been installed to a body <NUM>.

The second corner edge flank <NUM> having a clearance angle of a positive value is formed on the cutting insert <NUM>, so the size of the gap s1 created between the surface of the flank and the rotational trajectory is greater than the size of the gap s2 created between the surface of the flank and the rotational trajectory in a common cutting insert that has a clearance angle of <NUM>°, which has been attached to the body <NUM> so as to assume the same posture, as illustrated in <FIG>. There is no need to attach a cutting insert <NUM> to the body <NUM> with a radial rake angle having a great negative value in an attempt to secure a gap. A large pocket <NUM> can be secured, so produced chips can be prevented from abrading and damaging the upper face <NUM> of the cutting insert <NUM>.

The upper and lower faces of the cutting insert <NUM> have a <NUM>° rotationally-symmetrical shape, and further the cutting insert <NUM> has the same shape when rotated <NUM>° on the X axis. Accordingly, the cutting edges can be replaced for a total of six times when worn or damaged.

The wiper edge <NUM> on the upper face side and the corner edge <NUM> on the lower face side are at offset positions in the cutting insert <NUM> in top view, and accordingly even if the wiper edge <NUM> at the upper face side is greatly damaged due to fracturing or the like, the corner edge <NUM> at the lower face side is not readily affected. In the same way, even if the corner edge <NUM> at the upper face side is damaged, the wiper edge at the lower face side is not readily affected.

The third corner edge flank <NUM> that connects to the second corner edge flank <NUM> having a positive clearance angle value is provided, and moreover the clearance angle of the third corner edge flank <NUM> is <NUM>°. Accordingly, there is no need to secure a sufficiently great size for the gap s1 and excessively reduce the size of the lower face <NUM>. Securing a large size for the lower face <NUM> also secures a large size for an insert seat contact face formed on the lower face <NUM>, so the cutting insert <NUM> is fixed to the body <NUM> more solidly.

The presence of the second wiper edge flank <NUM> with a clearance angle of a negative value that connects to the first wiper edge flank <NUM> with a clearance angle of <NUM>°, and the third wiper edge flank <NUM> with a clearance angle of <NUM>° that connects thereto, make for a thicker lower portion of the wiper edge <NUM>, so fracturing and so forth of the wiper edge <NUM> occurs less readily. That is to say, in a case where the first wiper edge flank <NUM> extends to the lower face <NUM>, the length from the center of the cutting insert <NUM> (the above-described center axial line of the through hole <NUM>) to the side face is constant at s3 (illustrated in <FIG>), but the cutting insert <NUM> has the second wiper edge flank <NUM> and third wiper edge flank <NUM>, so the length from the center of the cutting insert <NUM> to the side face <NUM> is s4 (illustrated in <FIG>) that is longer than s3, near the lower face <NUM>. Accordingly, the strength of the wiper edge <NUM> is greater.

Description has been made regarding the present invention by way of an embodiment as an example thereof, but the present invention is not restricted to the above embodiment.

Although description has been made in the above embodiment that the entire side ridge portion of the upper face <NUM> is a cutting edge, an embodiment may be made where only part of the side ridge portion is a cutting edge. In this case, the upper face <NUM> needs to have at least one minor cutting edge, a connecting cutting edge connecting to the minor cutting edge, and a major cutting edge connecting to the connecting cutting edge.

Also, although description has been made in the above embodiment that the connecting cutting edge (corner edge) <NUM> is a curved cutting edge, an embodiment may be made where the connecting cutting edge <NUM> is a straight cutting edge. It should be noted, however, that the connecting cutting edge <NUM> is fractured less readily if curved.

Also, although description has been made in the above embodiment that the clearance angle of the first corner edge flank <NUM> is <NUM>°, an embodiment may be made having a clearance angle of a positive value. In this case, the clearance angle of the second corner edge flank <NUM> will have a clearance angle of an even greater positive value.

Also, although description has been made in the above embodiment that the major cutting edge curved portion <NUM> is situated between the first major cutting edge straight portion <NUM> and the second major cutting edge straight portion <NUM>, an embodiment may be made where a straight cutting edge is provided instead of the major cutting edge curved portion <NUM>. That is to say, the major cutting edge may be a straight cutting edge that connects between one corner edge and another corner edge.

Also, although description has been made in the above embodiment that a line extending from the wiper edge <NUM> and a line extending from the first major cutting edge straight portion <NUM> intersect at an angle of <NUM>°, the cutting insert according to the present invention is not restricted to this value. It should be noted, however, that the cutting insert can be suitably used for shoulder milling if the intersecting angle a of these two lines is in a range of <NUM>° < a < <NUM>°.

Also, although description has been made in the above embodiment that the clearance angle of the third corner edge flank <NUM> is <NUM>° and the clearance angle of the third wiper edge flank <NUM> is <NUM>°, and that the third corner edge flank <NUM> is situated inward from the first corner edge flank <NUM> in top view and similarly the third wiper edge flank <NUM> is situated outward from the first wiper edge flank <NUM> in top view, the third corner edge flank <NUM> and third wiper edge flank <NUM> are not restricted to this. That is to say, the clearance angles of the third corner edge flank <NUM> and third wiper edge flank <NUM> may be set as appropriate in accordance with mode of use. The third corner edge flank <NUM> may be situated outward from the first corner edge flank <NUM>, and the third wiper edge flank <NUM> may also be situated inward from the first wiper edge flank <NUM>.

Also, although description has been made in the above embodiment that the upper face <NUM> and lower face <NUM> have a generally triangular shape that is <NUM>° rotationally symmetrical, an embodiment may be made where the shape is another generally polygonal shape, such as a generally quadrangular or generally hexagonal shape, for example.

Also, although description has been made in the above embodiment that the third corner edge flank <NUM> of the upper face <NUM> is the first wiper edge flank <NUM> of the wiper edge of the lower face <NUM>, and the third wiper edge flank <NUM> of the upper face <NUM> is the first corner edge flank <NUM> of the lower face <NUM>, an embodiment may be made where the positions of the corner edges and wiper edges are not offset between the upper and lower faces.

Claim 1:
A cutting insert (<NUM>), comprising:
an upper face (<NUM>);
a lower face (<NUM>); and
a side face (<NUM>) connecting the upper face and the lower face;
wherein cutting edge sets (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>) are formed on at least part of an intersecting ridge line portion of the upper face and the side face,
wherein each of the cutting edge sets includes
a major cutting edge (<NUM>, <NUM>, <NUM>),
a minor cutting edge (<NUM>), and
a connecting cutting edge (<NUM>) that connects the major cutting edge and the minor cutting edge,
wherein the major cutting edge (<NUM>) of one of the cutting edge sets connects to the minor cutting edge (<NUM>) of another one of the cutting edge sets,
wherein, in a side view, viewing the cutting insert (<NUM>) from a direction facing the side face (<NUM>) corresponding to the major cutting edges (<NUM>, <NUM>, <NUM>), the cutting edges (<NUM>, <NUM>, <NUM>) first descend from a certain corner edge (22a) toward another adjacent corner edge (22b), and thereafter rise,
wherein a minor cutting edge flank (<NUM>, <NUM>) that is part of the side face and that corresponds to the minor cutting edge includes
a first minor cutting edge flank (<NUM>) that connects to the minor cutting edge and that has a clearance angle of <NUM>°, and
a second minor cutting edge flank (<NUM>) that connects to the first minor cutting edge flank and that has a clearance angle of a negative value,
wherein a connecting cutting edge flank (<NUM>, <NUM>) that is part of the side face and that corresponds to the connecting cutting edge includes
a first connecting cutting edge flank (<NUM>) that connects to the connecting cutting edge and that has a clearance angle of <NUM>° or greater, and
a second connecting cutting edge flank (<NUM>) that connects to the first connecting cutting edge flank and has a clearance angle that is greater than the clearance angle of the first connecting cutting edge flank.