Patent Description:
<CIT> (Patent Literature <NUM>) describes a cutting insert having three fitting portions each protruding in an axial direction and each extending in a radial direction.

<CIT> discloses an interface of a tool system, at which at least two parts of the tool system can be connected to one another, the end face of the one part bearing against the end face of the other part at least in certain places.

A cutting insert according to the present disclosure includes a cylindrical body portion, a cutting portion, a first fitting portion, a second fitting portion, and a third fitting portion. The cylindrical body portion has a first main surface, a second main surface, and an outer circumferential surface, the second main surface being opposite to the first main surface, the outer circumferential surface being continuous to each of the first main surface and the second main surface. The cylindrical body portion is provided with an insertion hole extending between the first main surface and the second main surface. The cutting portion protrudes from the outer circumferential surface in a radial direction. The first fitting portion, the second fitting portion, and the third fitting portion each protrude from the second main surface in an axial direction and each extend in the radial direction. The cutting portion includes a rake face and a flank face continuous to the rake face. A ridgeline between the rake face and the flank face constitutes a cutting edge. When viewed in the axial direction, the cutting portion is provided opposite to the third fitting portion relative to the insertion hole. When viewed in the axial direction, a straight line extending through an outer circumferential end of the cutting edge and a center of the insertion hole overlaps with the third fitting portion and is located between the first fitting portion and the second fitting portion. When viewed in the axial direction, assuming that a central angle between the second fitting portion and the third fitting portion represents a first central angle, a central angle between the third fitting portion and the first fitting portion represents a second central angle, and a central angle between the first fitting portion and the second fitting portion represents a third central angle, the third central angle is smaller than the first central angle and is smaller than the second central angle.

In the cutting insert described in <CIT>, an amount of displacement at a cutting edge becomes large when the cutting insert is attached to a holder, disadvantageously.

The present disclosure has been made in the foregoing problem and has an object to provide a cutting insert and a cutting tool, by each of which an amount of displacement at a cutting edge can be reduced when the cutting insert is attached to a holder.

According to the present disclosure, there can be provided a cutting insert and a cutting tool, by each of which an amount of displacement at a cutting edge can be reduced when the cutting insert is attached to a holder.

A cutting insert is provided in accordance with claim <NUM> and a cutting tool is provided in line with claim <NUM>.

Next, the following describes details of the embodiments of the present disclosure with reference to figures. It should be noted that the same or corresponding portions in the figures are given the same reference characters. Moreover, at least a part of the embodiments described below may be appropriately combined.

First, the following describes a configuration of a cutting tool <NUM> according to the present embodiment. <FIG> is a schematic perspective exploded view showing the configuration of cutting tool <NUM> according to the present embodiment. <FIG> is a schematic perspective view showing a configuration of a cutting insert <NUM> according to a first embodiment.

As shown in <FIG>, cutting tool <NUM> according to the present embodiment mainly has cutting insert <NUM>, a holder <NUM>, and a fastening bolt <NUM>. As shown in <FIG>, cutting insert <NUM> has a cutting portion <NUM> and a cylindrical body portion <NUM>. As shown in <FIG>, cutting portion <NUM> has a cutting edge <NUM>. Cylindrical body portion <NUM> has a first main surface <NUM>, a second main surface <NUM>, an outer circumferential surface <NUM>, and an insertion hole <NUM>. Cutting portion <NUM> is continuous to outer circumferential surface <NUM>. Cutting portion <NUM> protrudes from outer circumferential surface <NUM> in a radial direction. Insertion hole <NUM> extends between first main surface <NUM> and second main surface <NUM>. Second main surface <NUM> is provided with a first fitting portion <NUM>, a second fitting portion <NUM>, and a third fitting portion <NUM>.

As shown in <FIG>, holder <NUM> has a first portion <NUM> and a second portion <NUM>. Second portion <NUM> is continuous to first portion <NUM>. Each of first portion <NUM> and second portion <NUM> is substantially cylindrical. The diameter of first portion <NUM> is smaller than the diameter of second portion <NUM>. First portion <NUM> is provided with a first recess <NUM>, a second recess <NUM>, a third recess <NUM>, and a fastening hole <NUM>. First recess <NUM> is configured to receive first fitting portion <NUM>. Second recess <NUM> is configured to receive second fitting portion <NUM>. Third recess <NUM> is configured to receive third fitting portion <NUM>.

Fastening bolt <NUM> is configured to fix cutting insert <NUM> to holder <NUM>. Fastening bolt <NUM> is disposed in each of insertion hole <NUM> of cutting insert <NUM> and fastening hole <NUM> of holder <NUM>. Fastening bolt <NUM> has a head <NUM> and a screw portion <NUM>. Screw portion <NUM> is continuous to head <NUM>. Head <NUM> has a cylindrical shape or a truncated cone shape, for example. The diameter of head <NUM> is larger than the diameter of screw portion <NUM>. When screw portion <NUM> of fastening bolt <NUM> is fastened into fastening hole <NUM> of holder <NUM>, first fitting portion <NUM>, second fitting portion <NUM>, and third fitting portion <NUM> are pressed against first recess <NUM>, second recess <NUM>, and third recess <NUM>, respectively. Accordingly, cutting insert <NUM> is fixed to holder <NUM>.

Next, the following describes details of the configuration of cutting insert <NUM> according to the first embodiment. <FIG> is a schematic front view showing the configuration of cutting insert <NUM> according to the first embodiment. <FIG> is a schematic bottom view showing the configuration of cutting insert <NUM> according to the first embodiment.

As shown in <FIG>, cutting insert <NUM> according to the first embodiment is a cutting insert <NUM> for fluting process. Second main surface <NUM> is a surface opposite to first main surface <NUM>. Outer circumferential surface <NUM> is continuous to each of first main surface <NUM> and second main surface <NUM>. Outer circumferential surface <NUM> extends in a direction crossing each of first main surface <NUM> and second main surface <NUM>. Insertion hole <NUM> extends along axial direction A of cylindrical body portion <NUM>. Each of first main surface <NUM> and second main surface <NUM> extends along a radial direction B of cylindrical body portion <NUM>. Radial direction B is substantially perpendicular to axial direction A. First main surface <NUM> may be substantially parallel to second main surface <NUM>.

As shown in <FIG>, first fitting portion <NUM>, second fitting portion <NUM>, and third fitting portion <NUM> protrude from second main surface <NUM> in axial direction A. As shown in <FIG>, first fitting portion <NUM>, second fitting portion <NUM>, and third fitting portion <NUM> are located opposite to first main surface <NUM> relative to second main surface <NUM>. As shown in <FIG>, first fitting portion <NUM>, second fitting portion <NUM>, and third fitting portion <NUM> extends in radial direction B. From another point of view, first fitting portion <NUM>, second fitting portion <NUM>, and third fitting portion <NUM> extend along a direction from outer circumferential surface <NUM> toward insertion hole <NUM>.

As shown in <FIG>, cutting portion <NUM> has a rake face <NUM> and a flank face <NUM>. Flank face <NUM> is continuous to rake face <NUM>. A ridgeline between rake face <NUM> and flank face <NUM> constitutes cutting edge <NUM>. Cutting edge <NUM> is in the form of a straight line, for example. As shown in <FIG>, cutting edge <NUM> may be substantially parallel to axial direction A. As shown in <FIG>, when viewed in a direction parallel to first main surface <NUM>, cutting edge <NUM> may cross first main surface <NUM>.

As shown in <FIG>, when viewed in axial direction A, a distance between the outer circumferential end of cutting edge <NUM> and center <NUM> of insertion hole <NUM> is longer than a distance between outer circumferential surface <NUM> of cylindrical body portion <NUM> and center <NUM>. Flank face <NUM> has a first flank face portion <NUM> and a second flank face portion <NUM>. First flank face portion <NUM> is continuous to rake face <NUM>. Second flank face portion <NUM> is continuous to first flank face portion <NUM>. First flank face portion <NUM> is located between rake face <NUM> and second flank face portion <NUM>. Second flank face portion <NUM> is inclined relative to first flank face portion <NUM>. Second flank face portion <NUM> is continuous to outer circumferential surface <NUM>. Second flank face portion <NUM> is located between first flank face portion <NUM> and outer circumferential surface <NUM>. Rake face <NUM> is continuous to outer circumferential surface <NUM>.

As shown in <FIG>, cutting portion <NUM> may further have a first end surface <NUM>. First end surface <NUM> is continuous to rake face <NUM>, first flank face portion <NUM>, second flank face portion <NUM>, and outer circumferential surface <NUM>. In axial direction A, first end surface <NUM> is located between first main surface <NUM> and second main surface <NUM>. As shown in <FIG>, when viewed in axial direction A, cutting portion <NUM> is provided opposite to third fitting portion <NUM> relative to insertion hole <NUM>. From another point of view, insertion hole <NUM> is located between cutting portion <NUM> and third fitting portion <NUM>. When viewed in axial direction A, a straight line (fourth straight line D) extending through the outer circumferential end of cutting edge <NUM> and center <NUM> of insertion hole <NUM> overlaps with third fitting portion <NUM>. Fourth straight line D is located between first fitting portion <NUM> and second fitting portion <NUM>.

First fitting portion <NUM> has a first side surface portion <NUM>, a second side surface portion <NUM>, and a first top surface portion <NUM>. Second side surface portion <NUM> is a surface opposite to first side surface portion <NUM>. First top surface portion <NUM> is continuous to each of first side surface portion <NUM> and second side surface portion <NUM>. Each of first side surface portion <NUM> and second side surface portion <NUM> is inclined relative to second main surface <NUM>. First top surface portion <NUM> may be substantially parallel to second main surface <NUM>. An intermediate line (first intermediate line <NUM>) of first fitting portion <NUM> is located in the middle between a boundary line between first side surface portion <NUM> and first top surface portion <NUM> and a boundary line between second side surface portion <NUM> and first top surface portion <NUM>, for example. A straight line (first straight line C1) along first intermediate line <NUM> extends through center <NUM> of insertion hole <NUM>. A space between first side surface portion <NUM> and second side surface portion <NUM> is narrower as it extends from second main surface <NUM> toward first top surface portion <NUM>.

Second fitting portion <NUM> has a fifth side surface portion <NUM>, a sixth side surface portion <NUM>, and a second top surface portion <NUM>. Sixth side surface portion <NUM> is a surface opposite to fifth side surface portion <NUM>. Second top surface portion <NUM> is continuous to each of fifth side surface portion <NUM> and sixth side surface portion <NUM>. Each of fifth side surface portion <NUM> and sixth side surface portion <NUM> is inclined relative to second main surface <NUM>. Second top surface portion <NUM> may be substantially parallel to second main surface <NUM>. An intermediate line (second intermediate line <NUM>) of second fitting portion <NUM> is located in the middle between a boundary line between fifth side surface portion <NUM> and second top surface portion <NUM> and a boundary line between sixth side surface portion <NUM> and second top surface portion <NUM>, for example. A straight line (second straight line C2) along second intermediate line <NUM> extends through center <NUM> of insertion hole <NUM>. A space between fifth side surface portion <NUM> and sixth side surface portion <NUM> is narrower as it extends from second main surface <NUM> toward second top surface portion <NUM>.

Third fitting portion <NUM> has a ninth side surface portion <NUM>, a tenth side surface portion <NUM>, and a third top surface portion <NUM>. Tenth side surface portion <NUM> is a surface opposite to ninth side surface portion <NUM>. Third top surface portion <NUM> is continuous to each of ninth side surface portion <NUM> and tenth side surface portion <NUM>. Each of ninth side surface portion <NUM> and tenth side surface portion <NUM> is inclined relative to second main surface <NUM>. Third top surface portion <NUM> may be substantially parallel to second main surface <NUM>. An intermediate line (third intermediate line <NUM>) of third fitting portion <NUM> is located in the middle between a boundary line between ninth side surface portion <NUM> and third top surface portion <NUM> and a boundary line between tenth side surface portion <NUM> and third top surface portion <NUM>, for example. A straight line (third straight line C3) along third intermediate line <NUM> extends through center <NUM> of insertion hole <NUM>. A space between ninth side surface portion <NUM> and tenth side surface portion <NUM> is narrower as it extends from second main surface <NUM> toward third top surface portion <NUM>.

As shown in <FIG>, when viewed in axial direction A, assuming that a central angle between second fitting portion <NUM> and third fitting portion <NUM> represents a first central angle θ1, a central angle between third fitting portion <NUM> and first fitting portion <NUM> represents a second central angle θ2, and a central angle between first fitting portion <NUM> and second fitting portion <NUM> represents a third central angle θ3, third central angle θ3 is smaller than first central angle θ1 and is smaller than second central angle θ2. A total of first central angle θ1, second central angle θ2, and third central angle θ3 is <NUM> °. First central angle θ1 is an angle formed between the straight line (second straight line C2) along second intermediate line <NUM> and the straight line (third straight line C3) along third intermediate line <NUM>. Second central angle θ2 is an angle formed between the straight line (first straight line C1) along first intermediate line <NUM> and the straight line (third straight line C3) along third intermediate line <NUM>. Third central angle θ3 is an angle formed between the straight line (first straight line C1) along first intermediate line <NUM> and the straight line (second straight line C2) along second intermediate line <NUM>.

First central angle θ1 is <NUM>°, for example. First central angle θ1 is more than or equal to <NUM>° and less than or equal to <NUM>°, for example. First central angle θ1 may be more than or equal to <NUM>° or may be more than or equal to <NUM>°. First central angle θ1 may be less than or equal to <NUM>° or may be less than or equal to <NUM>°.

Second central angle θ2 is <NUM>°, for example. The second central angle θ2 may be more than or equal to <NUM>° and less than or equal to <NUM>°, for example. Second central angle θ2 may be more than or equal to <NUM>° or may be more than or equal to <NUM>°. Second central angle θ2 may be less than or equal to <NUM>° or may be less than or equal to <NUM>°.

Third central angle θ3 is <NUM>°, for example. Third central angle θ3 may be more than or equal to <NUM>° and less than or equal to <NUM>°. Third central angle θ3 may be more than or equal to <NUM>°, or may be more than or equal to <NUM>°. Third central angle θ3 may be less than or equal to <NUM>° or may be less than or equal to <NUM>°.

As shown in <FIG>, when viewed in axial direction A, the intermediate line (third intermediate line <NUM>) of third fitting portion <NUM> is located on a straight line bisecting third central angle θ3, for example. The straight line bisecting third central angle θ3 may overlap with the straight line (fourth straight line D) extending through the outer circumferential end of cutting edge <NUM> and center <NUM> of insertion hole <NUM>. That is, the straight line (fourth straight line D) extending through the outer circumferential end of cutting edge <NUM> and center <NUM> of insertion hole <NUM> may overlap with third intermediate line <NUM>. From another point of view, when viewed in axial direction A, the straight line (fourth straight line D) extending through the outer circumferential end of cutting edge <NUM> and center <NUM> of insertion hole <NUM> may overlap with third top surface portion <NUM> of third fitting portion <NUM>.

<FIG> is a schematic perspective view showing a configuration of holder <NUM> of cutting tool <NUM> according to the present embodiment. As shown in <FIG>, holder <NUM> has a tip surface <NUM>, a cylindrical surface <NUM>, and a coolant supplying hole <NUM>. Tip surface <NUM> of holder <NUM> is disposed to face second main surface <NUM> of cutting insert <NUM>. Coolant supplying hole <NUM> is opened to cylindrical surface <NUM>. Coolant may be released from coolant supplying hole <NUM> toward cutting edge <NUM>.

As described above, holder <NUM> is provided with first recess <NUM>, second recess <NUM>, and third recess <NUM>. Each of first recess <NUM>, second recess <NUM>, and third recess <NUM> is continuous to each of tip surface <NUM> and cylindrical surface <NUM>. First recess <NUM> has a third side surface portion <NUM>, a fourth side surface portion <NUM>, and a first bottom surface portion <NUM>. Fourth side surface portion <NUM> is a surface opposite to third side surface portion <NUM>. First bottom surface portion <NUM> is continuous to each of third side surface portion <NUM> and fourth side surface portion <NUM>. Each of third side surface portion <NUM> and fourth side surface portion <NUM> is inclined relative to tip surface <NUM>. First bottom surface portion <NUM> may be substantially parallel to tip surface <NUM>. A space between third side surface portion <NUM> and fourth side surface portion <NUM> is wider as it extends from first bottom surface portion <NUM> toward tip surface <NUM>.

Second recess <NUM> has a seventh side surface portion <NUM>, an eighth side surface portion <NUM>, and a second bottom surface portion <NUM>. Eighth side surface portion <NUM> is a surface opposite to seventh side surface portion <NUM>. Second bottom surface portion <NUM> is continuous to each of seventh side surface portion <NUM> and eighth side surface portion <NUM>. Each of seventh side surface portion <NUM> and eighth side surface portion <NUM> is inclined relative to tip surface <NUM>. Second bottom surface portion <NUM> may be substantially parallel to tip surface <NUM>. A space between seventh side surface portion <NUM> and eighth side surface portion <NUM> is wider as it extends from second bottom surface portion <NUM> toward tip surface <NUM>.

Third recess <NUM> has an eleventh side surface portion <NUM>, a twelfth side surface portion <NUM>, and a third bottom surface portion <NUM>. Twelfth side surface portion <NUM> is a surface opposite to eleventh side surface portion <NUM>. Third bottom surface portion <NUM> is continuous to each of eleventh side surface portion <NUM> and twelfth side surface portion <NUM>. Each of eleventh side surface portion <NUM> and twelfth side surface portion <NUM> is inclined relative to tip surface <NUM>. Third bottom surface portion <NUM> may be substantially parallel to tip surface <NUM>. A space between eleventh side surface portion <NUM> and twelfth side surface portion <NUM> is wider as it extends from third bottom surface portion <NUM> toward tip surface <NUM>. A notch <NUM> may be provided between third recess <NUM> and second recess <NUM>. Similarly, notch <NUM> may be provided between third recess <NUM> and first recess <NUM>. Similarly, notch <NUM> may be provided between second recess <NUM> and first recess <NUM>.

<FIG> is a schematic view showing a fitting state between cutting insert <NUM> and holder <NUM>. As shown in <FIG>, when cutting insert <NUM> is fixed to holder <NUM>, first side surface portion <NUM> is in contact with third side surface portion <NUM>. Second side surface portion <NUM> is in contact with fourth side surface portion <NUM>. First top surface portion <NUM> is separated from first bottom surface portion <NUM>. Similarly, fifth side surface portion <NUM> is in contact with seventh side surface portion <NUM>. Sixth side surface portion <NUM> is in contact with eighth side surface portion <NUM>. Second top surface portion <NUM> is separated from second bottom surface portion <NUM>. Similarly, ninth side surface portion <NUM> is in contact with eleventh side surface portion <NUM>. Tenth side surface portion <NUM> is in contact with twelfth side surface portion <NUM>. Third top surface portion <NUM> is separated from third bottom surface portion <NUM>. Since the cutting insert is attached to the holder with the side surface portion of the fitting portion being in contact with the side surface portion of the recess without bringing the bottom surface portion of the fitting portion into contact with the bottom surface portion of the recess in this way, occurrence of positional deviation of the cutting edge in the circumferential direction can be suppressed.

Next, the following describes a configuration of a cutting insert <NUM> according to a second embodiment. <FIG> is a schematic perspective view showing the configuration of cutting insert <NUM> according to the second embodiment.

As shown in <FIG>, cutting insert <NUM> according to the second embodiment is different from cutting insert <NUM> according to the first embodiment in terms of the configuration of cutting portion <NUM>, and the other configuration of cutting insert <NUM> according to the second embodiment is substantially the same as that of cutting insert <NUM> according to the first embodiment. The following mainly describes the configuration different from that of cutting insert <NUM> according to the first embodiment.

As shown in <FIG>, the length of cutting edge <NUM> of cutting insert <NUM> according to the second embodiment is shorter than the length of cutting edge <NUM> of cutting insert <NUM> according to the first embodiment. The area of rake face <NUM> of cutting insert <NUM> according to the second embodiment is smaller than the area of rake face <NUM> of cutting insert <NUM> according to the first embodiment. The area of flank face <NUM> of cutting insert <NUM> according to the second embodiment is smaller than the area of flank face <NUM> of cutting insert <NUM> according to the first embodiment.

Next, the following describes a configuration of a cutting insert <NUM> according to a third embodiment. <FIG> is a schematic perspective view showing the configuration of cutting insert <NUM> according to the third embodiment.

As shown in <FIG>, cutting insert <NUM> according to the third embodiment is different from cutting insert <NUM> according to the first embodiment in terms of the configuration of cutting portion <NUM>, and the other configuration of cutting insert <NUM> according to the third embodiment is substantially the same as that of cutting insert <NUM> according to the first embodiment. The following mainly describes the configuration different from that of cutting insert <NUM> according to the first embodiment.

Cutting insert <NUM> according to the third embodiment is a cutting insert <NUM> for profile process (full radius). As shown in <FIG>, cutting edge <NUM> of cutting insert <NUM> according to the third embodiment has a curved shape. Cutting edge <NUM> may have an arc shape, for example. Flank face <NUM> of cutting insert <NUM> according to the third embodiment has a curved shape.

Next, the following describes a configuration of a cutting insert <NUM> according to a fourth embodiment. <FIG> is a schematic perspective view showing the configuration of cutting insert <NUM> according to the fourth embodiment.

As shown in <FIG>, cutting insert <NUM> according to the fourth embodiment is different from cutting insert <NUM> according to the first embodiment in terms of the configuration of cutting portion <NUM>, and the other configuration of cutting insert <NUM> according to the fourth embodiment is substantially the same as that of cutting insert <NUM> according to the first embodiment. The following mainly describes the configuration different from that of cutting insert <NUM> according to the first embodiment.

Cutting insert <NUM> according to the fourth embodiment is a cutting insert <NUM> for chamfering process. As shown in <FIG>, cutting edge <NUM> of cutting insert <NUM> according to the fourth embodiment may have a first cutting edge portion 44a and a second cutting edge portion 44b. Each of first cutting edge portion 44a and second cutting edge portion 44b is substantially in the form of straight line. First cutting edge portion 44a is inclined relative to second cutting edge portion 44b. Each of first cutting edge portion 44a and second cutting edge portion 44b is inclined relative to the straight line parallel to axial direction A.

Flank face <NUM> of cutting insert <NUM> according to the fourth embodiment has a third flank face portion 42a and a fourth flank face portion 42b. Fourth flank face portion 42b is continuous to third flank face portion 42a. Fourth flank face portion 42b is inclined relative to third flank face portion 42a. Third flank face portion 42a may be continuous to first main surface <NUM>. Fourth flank face portion 42b may be continuous to second main surface <NUM>. A ridgeline between third flank face portion 42a and rake face <NUM> constitutes first cutting edge portion 44a. A ridgeline between fourth flank face portion 42b and rake face <NUM> constitutes second cutting edge portion 44b.

Next, the following describes a configuration of a cutting insert <NUM> according to a fifth embodiment. <FIG> is a schematic perspective view showing the configuration of cutting insert <NUM> according to the fifth embodiment.

As shown in <FIG>, cutting insert <NUM> according to the fifth embodiment is different from cutting insert <NUM> according to the first embodiment in terms of the configuration of cutting portion <NUM>, and the other configuration of cutting insert <NUM> according to the fifth embodiment is substantially the same as that of cutting insert <NUM> according to the first embodiment. The following mainly describes the configuration different from that of cutting insert <NUM> according to the first embodiment.

Cutting insert <NUM> according to the fifth embodiment is a cutting insert <NUM> for end-surface process. As shown in <FIG>, cutting portion <NUM> of cutting insert <NUM> according to the fifth embodiment protrudes from outer circumferential surface <NUM> in radial direction B and also protrudes from first main surface <NUM> in axial direction A. Cutting edge <NUM> extends in a direction substantially parallel to first main surface <NUM>. Cutting edge <NUM> may extend in the direction crossing a straight line along axial direction A. A plane along flank face <NUM> crosses the straight line along axial direction A. Flank face <NUM> may be substantially parallel to first main surface <NUM>. In axial direction A, flank face <NUM> is located opposite to second main surface <NUM> relative to first main surface <NUM>. From another point of view, in axial direction A, first main surface <NUM> is located between flank face <NUM> and second main surface <NUM>.

Next, the following describes a configuration of cutting insert <NUM> according to a sixth embodiment. <FIG> is a schematic perspective view showing the configuration of cutting insert <NUM> according to the sixth embodiment.

As shown in <FIG>, cutting insert <NUM> according to the sixth embodiment is different from cutting insert <NUM> according to the fifth embodiment in terms of the configuration of cutting portion <NUM>, and the other configuration of cutting insert <NUM> according to the sixth embodiment is substantially the same as that of cutting insert <NUM> according to the fifth embodiment. The following mainly describes the configuration different from that of cutting insert <NUM> according to the fifth embodiment.

As shown in <FIG>, the length of cutting edge <NUM> of cutting insert <NUM> according to the sixth embodiment is shorter than the length of cutting edge <NUM> of cutting insert <NUM> according to the fifth embodiment. The area of rake face <NUM> of cutting insert <NUM> according to the sixth embodiment is smaller than the area of rake face <NUM> of cutting insert <NUM> according to the fifth embodiment. The area of flank face <NUM> of cutting insert <NUM> according to the sixth embodiment is smaller than the area of flank face <NUM> of cutting insert <NUM> according to the fifth embodiment. Cutting portion <NUM> of cutting insert <NUM> according to the sixth embodiment may have a second end surface <NUM>. Second end surface <NUM> may be substantially parallel to flank face <NUM>. In axial direction A, second end surface <NUM> is located between flank face <NUM> and first main surface <NUM>.

Next, the following describes function and effect of cutting insert <NUM> and cutting tool <NUM> according to each of the above-described embodiments.

According to cutting insert <NUM> according to each of the above-described embodiments, when viewed in axial direction A, cutting portion <NUM> is provided opposite to third fitting portion <NUM> relative to insertion hole <NUM>. When viewed in axial direction A, the straight line extending through the outer circumferential end of cutting edge <NUM> and center <NUM> of insertion hole <NUM> overlaps with third fitting portion <NUM> and is located between first fitting portion <NUM> and second fitting portion <NUM>. When viewed in axial direction A, assuming that the central angle between second fitting portion <NUM> and third fitting portion <NUM> represents first central angle θ1, the central angle between third fitting portion <NUM> and first fitting portion <NUM> represents second central angle θ2, and the central angle between first fitting portion <NUM> and second fitting portion <NUM> represents third central angle θ3, third central angle θ3 is smaller than first central angle θ1 and is smaller than second central angle θ2. Accordingly, an amount of displacement at the cutting edge can be reduced when cutting insert <NUM> is attached to holder <NUM>. Moreover, with the increased precision of position of the cutting edge, cutting insert <NUM> according to the present embodiment can be applied to a process that requires a particularly high degree of precision. Furthermore, vibrations during cutting can be suppressed, thereby improving precision of processing and tool life.

According to cutting tool <NUM> according to each of the above-described embodiments, first side surface portion <NUM> is in contact with third side surface portion <NUM>. Second side surface portion <NUM> is in contact with fourth side surface portion <NUM>. Top surface portion <NUM> is separated from bottom surface portion <NUM>. Since the cutting insert is attached to the holder with the side surface portion of the fitting portion being in contact with the side surface portion of the recess without bringing the bottom surface portion of the fitting portion into contact with the bottom surface portion of the recess in this way, occurrence of positional deviation of the cutting edge in the circumferential direction can be suppressed.

First, cutting inserts <NUM> according to samples <NUM> to <NUM> were prepared. As cutting insert <NUM> according to each of samples <NUM> to <NUM>, cutting insert <NUM> shown in <FIG> was used. As shown in <FIG>, in cutting insert <NUM> according to each of samples <NUM> to <NUM>, third fitting portion <NUM> is located opposite to cutting portion <NUM> relative to insertion hole <NUM>. The straight line bisecting third central angle <NUM> overlaps with the straight line extending through the outer circumferential end of cutting edge <NUM> and center <NUM> of insertion hole <NUM>. <FIG> is a schematic bottom view, not in accordance with the claimed invention, showing a configuration of cutting insert <NUM> according to sample <NUM>. As shown in <FIG>, in cutting insert <NUM> according to sample <NUM>, third fitting portion <NUM> is located between insertion hole <NUM> and cutting portion <NUM>. The straight line bisecting third central angle <NUM> overlaps with the straight line extending through the outer circumferential end of cutting edge <NUM> and center <NUM> of insertion hole <NUM>. <FIG> is a schematic bottom view, not in accordance with the claimed invention, showing a configuration of cutting insert <NUM> according to sample <NUM>. As shown in <FIG>, in cutting insert <NUM> according to sample <NUM>, third fitting portion <NUM> is located between insertion hole <NUM> and cutting portion <NUM>. The straight line bisecting third central angle <NUM> is inclined relative to the straight line extending through the outer circumferential end of cutting edge <NUM> and center <NUM> of insertion hole <NUM>.

In cutting insert <NUM> according to sample <NUM>, first central angle <NUM> was set to <NUM>°, second central angle <NUM> was set to <NUM>°, and third central angle <NUM> was set to <NUM>°. In cutting insert <NUM> according to sample <NUM>, first central angle <NUM> was set to <NUM>°, second central angle <NUM> was set to <NUM>°, and third central angle <NUM> was set to <NUM>°. In cutting insert <NUM> according to sample <NUM>, first central angle <NUM> was set to <NUM>°, second central angle <NUM> was set to <NUM>°, and third central angle <NUM> was set to <NUM>°. In cutting insert <NUM> according to sample <NUM>, first central angle <NUM> was set to <NUM>°, second central angle <NUM> was set to <NUM>°, and third central angle <NUM> was set to <NUM>°. In cutting insert <NUM> according to sample <NUM>, first central angle <NUM> was set to <NUM>°, second central angle <NUM> was set to <NUM>°, and third central angle <NUM> was set to <NUM>°. In cutting insert <NUM> according to sample <NUM>, first central angle <NUM> was set to <NUM>°, second central angle <NUM> was set to <NUM>°, and third central angle <NUM> was set to <NUM>°. In cutting insert <NUM> according to sample <NUM>, first central angle <NUM> was set to <NUM>°, second central angle <NUM> was set to <NUM>°, and third central angle <NUM> was set to <NUM>°. In cutting insert <NUM> according to sample <NUM>, first central angle <NUM> was set to <NUM>°, second central angle <NUM> was set to <NUM>°, and third central angle <NUM> was set to <NUM>°.

<FIG> is a schematic perspective view showing a state in which cutting insert <NUM> is attached to holder <NUM> using the fastening bolt. Torque along fastening direction <NUM> of fastening bolt <NUM> was set to <NUM> N. Axial force in an insertion direction <NUM> of fastening bolt <NUM> was set to <NUM> N. By performing finite element method (FEM) analysis, maximum amount of displacement among the amounts of displacement at all the positions of cutting insert <NUM> were calculated. Each of the amounts of displacement is the absolute value of an amount of displacement from the original model. It should be noted that in order to stabilize the position of the cutting edge when cutting insert <NUM> is attached to holder <NUM>, it is more important to reduce the amount of displacement at the cutting edge than to reduce the maximum amount of displacement.

The amounts of displacement (mm) at the cutting edges of cutting inserts <NUM> according to samples <NUM> to <NUM> were <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>, respectively. The maximum amounts of displacement (mm) in cutting inserts <NUM> according to samples <NUM> to <NUM> were <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> and <NUM>, respectively.

Each of cutting inserts <NUM> according to samples <NUM> and <NUM> is an equally divided cutting insert <NUM> (in which first central angle θ1 to third central angle θ3 are equal to one another). On the other hand, each of cutting inserts <NUM> according to samples <NUM> to <NUM> is an unequally divided cutting insert <NUM> in which the cutting edge is disposed at the narrow angle side. As shown in Table <NUM>, the amount of displacement at the cutting edge of cutting insert <NUM> according to each of samples <NUM> to <NUM> was smaller than the amount of displacement at the cutting edge of cutting insert <NUM> according to each of samples <NUM> and <NUM>. That is, it was confirmed that the amount of displacement at the cutting edge can be reduced by employing unequally divided cutting insert <NUM>.

Cutting insert <NUM> according to sample <NUM> is a cutting insert <NUM> in which third fitting portion <NUM> is opposite to cutting portion <NUM> relative to insertion hole <NUM> (from another point of view, the cutting edge is located at the narrow angle side). On the other hand, cutting insert <NUM> according to sample <NUM> is a cutting insert <NUM> in which third fitting portion <NUM> is at the same side as cutting portion <NUM> relative to insertion hole <NUM> (from another point of view, the cutting edge is located opposite to the narrow angle side). As shown in Table <NUM>, the amount of displacement at the cutting edge of cutting insert <NUM> according to sample <NUM> was smaller than the amount of displacement at the cutting edge of cutting insert <NUM> according to sample <NUM>. That is, it was confirmed that the amount of displacement at the cutting edge can be reduced by disposing the cutting edge at the narrow angle side.

Among cutting inserts <NUM> according to samples <NUM> to <NUM>, the angles of third central angles θ3 differ from one another. As shown in Table <NUM>, it was confirmed that as third central angle θ3 becomes smaller, the maximum amount of displacement becomes larger but the amount of displacement at the cutting edge becomes smaller. It is difficult to design cutting insert <NUM> in which third central angle θ3 is less than <NUM>°. Hence, third central angle θ3 is desirably more than or equal to <NUM>° and less than or equal to <NUM>°. In consideration of the maximum amount of displacement and the design, third central angle θ3 is more desirably more than or equal to <NUM>° and less than or equal to <NUM>°.

The embodiments and examples disclosed herein are illustrative and non-restrictive in any respect. The scope of the present invention is defined by the terms of the claims, rather than the embodiments described above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

Claim 1:
A cutting insert (<NUM>) comprising:
a cylindrical body portion (<NUM>) having a first main surface (<NUM>), a second main surface (<NUM>), and an outer circumferential surface (<NUM>), the second main surface being opposite to the first main surface, the outer circumferential surface being continuous to each of the first main surface and the second main surface, the cylindrical body portion being provided with an insertion hole (<NUM>) extending between the first main surface and the second main surface;
a cutting portion (<NUM>) protruding from the outer circumferential surface in a radial direction; and
only three fitting portions, namely a first fitting portion (<NUM>), a second fitting portion (<NUM>), and a third fitting portion (<NUM>) each protruding from the second main surface in an axial direction and
each extending in the radial direction, wherein
the cutting portion includes a rake face (<NUM>) and a flank face (<NUM>) continuous to the rake face, and a ridgeline between the rake face and the flank face constitutes a cutting edge (<NUM>),
when viewed in the axial direction, the cutting portion is provided opposite to the third fitting portion relative to the insertion hole, when viewed in the axial direction, a straight line extending through an outer circumferential end of the cutting edge and a center of the insertion hole overlaps with the third fitting portion and is located between the first fitting portion and the second fitting portion, and when viewed in the axial direction, assuming that a central angle between the second fitting portion and the third fitting portion represents a first central angle (θ1), a central angle between the third fitting portion and the first fitting portion represents a second central angle (θ2), and a central angle between the first fitting portion and the second fitting portion represents a third central angle (θ3), the third central angle is smaller than the first central angle and is smaller than the second central angle.