Cutting insert, cutting tool and method for manufacturing cut product

A cutting insert includes an end cutting edge, a first major cutting edge, and a second major cutting edge. The height of the end cutting edge relative to an imaginary plane orthogonal to a central axis of a through-hole is fixed. The height of the first major cutting edge relative to the imaginary plane increases, when viewed from a side, moving away from the end cutting edge. The height of the second major cutting edge relative to the imaginary plane decreases, when viewed from a side, moving away from the first major cutting edge. When viewed from a side, the angle of inclination, relative to the imaginary plane, of an imaginary line connecting both ends of the second major cutting edge is greater than an angle of inclination, relative to the imaginary plane, of an imaginary line connecting both ends of the first major cutting edge.

TECHNICAL FIELD

The present invention relates to a cutting insert, a cutting tool, and a method for manufacturing a cut product.

BACKGROUND

Japanese Unexamined Patent Application Publication No. H9-225724 (Patent Document 1) discloses an example of a conventional tip that can be used as a cutting insert in a process for machining a workpiece. The tip disclosed in Patent Document 1 includes a plurality of cutting edges that have a circular arc shape when viewed from the side and have a curved shape that protrudes outwards when viewed from directly above. With this cutting edge configuration, when the cutting edge is brought into contact with the workpiece, the portion of the cutting edge that has the greatest height contacts the workpiece first, and shorter portions of the cutting edge contact the workpiece gradually. This makes it possible to reduce the impact force on the tip.

As illustrated inFIGS. 16 and 17, when a cutting edge309has a curved shape that protrudes outwards when viewed from directly above like the circular arc-shaped cutting edge disclosed in Patent Document 1, the thickness R1of chips cut from a workpiece201by a region of the cutting edge near an end portion that contacts the bottom machining surface201aof the workpiece201(hereinafter, referred to as a first region309a) is less than the thickness R2of chips cut from the workpiece201by a region of the cutting edge farther away from the end portion (hereinafter, referred to as a second region309b). Therefore, a relatively large force is applied to the second region309b.

Meanwhile, in the tip disclosed in Patent Document 1, the cutting edge309has a circular arc shape and is therefore bilaterally symmetric about the center of the cutting edge, which has the greatest height. As a result, even if the first region309acuts the workpiece201in a satisfactory manner, the inclination of the cutting edge309is insufficient in the second region309b. This makes it more difficult for the second region309bto cut the workpiece201in a satisfactory manner.

The present invention was made in view of the above-mentioned problems and aims to provide a cutting insert having satisfactory cutting ability even when the cutting edge has a curved shaped that protrudes outwards when viewed from directly above, as well as a cutting tool and a method for manufacturing a cut product.

SUMMARY OF THE INVENTION

One aspect of the present invention is a cutting insert, including: a top surface; a bottom surface; a side surface disposed between the top surface and the bottom surface; a cutting edge formed along an edge where the top surface and the side surface meet; and a through-hole formed from a center portion of the top surface through a center portion of the bottom surface. The cutting edge includes, in order, an end cutting edge, a first major cutting edge and a second major cutting edge.

The height of the end cutting edge relative to an imaginary plane orthogonal to a central axis of the through-hole is fixed. The first major cutting edge has a curved shape that protrudes outwards when viewed from directly above, and the height of the first major cutting edge relative to the imaginary plane increases, when viewed from a side, moving away from the end of the first major cutting edge connected to the end cutting edge. The second major cutting edge has a curved shape that protrudes outwards when viewed from directly above, and the height of the second major cutting edge relative to the imaginary plane decreases, when viewed from a side, moving away from the end of the second major cutting edge connected to the first major cutting edge. When viewed from the side, the angle of inclination of the second major cutting edge relative to the imaginary plane is greater at the center of the second major cutting edge than at either end thereof. Moreover, when viewed from a side, the angle of inclination, relative to the imaginary plane, of an imaginary line connecting both ends of the second major cutting edge is greater than the angle of inclination, relative to the imaginary plane, of an imaginary line connecting both ends of the first major cutting edge.

DETAILED DESCRIPTION OF THE INVENTION

A cutting insert according to an embodiment of the present invention will be described in detail below with reference to figures. Note that for the sake of simplicity, the figures referenced below are simplified drawings illustrating only the primary components of the embodiment needed to fully describe the present invention. Therefore, the present cutting insert may also include various other components not depicted in the figures in the present specification. Furthermore, the dimensions of the components as depicted in the figures do not necessarily represent the actual dimensions of those components or the actual dimensional proportions between those components.

As illustrated inFIGS. 1 to 10, a cutting insert1according to the present embodiment includes a top surface3, a bottom surface5, and a side surface7. The bottom surface5is disposed opposite to the top surface3. The side surface7is disposed between the top surface3and the bottom surface5so as to connect the top surface3and the bottom surface5. A cutting edge9is formed along the edge where the top surface3and the side surface7meet. In the cutting insert1according to the present embodiment, a central axis X passes through the center of the bottom surface5and the center of the top surface3.

The cutting insert1also has a through-hole11that is formed going from the center portion of the top surface3to the center portion of the bottom surface5and that creates openings in the centers of the top surface3and the bottom surface5. The through-hole11surrounds the central axis X, and the through direction of the through-hole11is parallel to the central axis X. The through-hole11is formed so that a fixing screw can be inserted therethrough in order to fix the cutting insert1to the holder of a cutting tool.

The top surface3and the bottom surface5are both substantially circular when viewed from directly above, and both have approximately the same shape. The bottom surface5is smaller than the top surface3. As a result, when viewed from the side, the side surface7slopes inwards towards the central axis X going from the portion that connects to the top surface3to the portion that connects to the bottom surface5.

The maximum width for the top surface3and the bottom surface5in the cutting insert1of the present embodiment is from 5 to 20 mm. Moreover, the height from the bottom surface5to the top surface3is from 2 to 8 mm. Here, the maximum width of the top surface3refers to the maximum value of the width of the top surface3when viewed from directly above. Similarly, the maximum width of the bottom surface5refers to the maximum value of the width of the bottom surface5when viewed from directly below. Moreover, the height from the bottom surface5to the top surface3refers to the magnitude of the dimension that runs parallel to the central axis X between the top end of the top surface3and the bottom end of the bottom surface5.

Note that the shapes used for the top surface3and the bottom surface5are not limited to the shapes described above. Although the top surface3is substantially circular, the curved portions that run around the periphery of the top surface3are not limited to smooth circular arcs, for example. These curved portions may be parabola-shaped or elliptic curve-shaped, for example, and protrude outwards.

Examples of materials for the cutting insert1include cemented carbide alloys and cermets, for example. Examples of cemented carbide alloys include, WC—Co alloys in which cobalt (Co) powder is added to tungsten carbide (WC) and the resulting mixture is sintered; WC—TiC—Co alloys in which titanium carbide (TiC) is added to WC—Co; and WC—TiC—TaC—Co alloys in which tantalum carbide (TaC) is added to WC—TiC—Co. Moreover, specific examples of cermet (sintered composite materials composed of ceramic and metal materials) include titanium compounds in which titanium carbide (TiC) or titanium nitride (TiN) is the main ingredient.

The surface of the cutting insert1may be coated with a film using a chemical vapor deposition (CVD) or physical vapor deposition (PVD) method. Examples of compositions for this film include titanium carbide (TiC), titanium nitride (TiN), titanium carbonitride (TiCN), and alumina (Al2O3).

As illustrated inFIG. 2andFIGS. 7 to 10, the top surface3includes a land face13, a rake face15, and a bottom face17. The land face13is formed along the cutting edge9. In other words, the land face13runs around the periphery of the top surface3and is connected to the cutting edge9. The land face13is substantially parallel to the bottom surface or sloped downwards moving towards the center of the cutting insert1. The land face13may also be sloped upwards moving towards the center of the cutting insert1.

Here, “substantially parallel” does not mean that the two surfaces must be exactly parallel and includes cases in which the surfaces are misaligned by about ±1°. If the bottom surface is not planar and it is difficult to evaluate whether the land face13is parallel thereto, the inclination of the land face13may be compared to the central axis X instead of to the bottom surface. In other words, whether the land face13is orthogonal to the central axis X may be evaluated.

The cutting edge9is formed along the edge where the land face13and the side surface7meet. The land face13is formed to increase the strength of the cutting edge9. If no land face13is included, the cutting edge9is formed along the edge where the rake face15and the side surface7meet. The rake face15is positioned on the inner side of the land face13and is surrounded thereby. The rake face15is sloped downwards towards the bottom surface5moving towards the center of the cutting insert1. The angle of inclination of the rake face15is larger than the angle of inclination of the land face13.

In other words, the strength of the cutting edge9can be increased by including the land face13and making the angle of inclination of the land face13smaller than the angle of inclination of the rake face15. Note that the “angle of inclination” of the rake face15and the land face13refers to the angle between each face and a line orthogonal to the central axis X in the cross section including the central axis X. The width of the land face13that is disposed between the outer periphery of the top surface3and the outer periphery of the rake face15may be set as appropriate on the basis of the cutting conditions. The width of the land face13may be set to a value in the range of 0.01 to 1 mm, for example.

The edge where the top surface3and the side surface7meet and along which the cutting edge9is formed is not a perfectly straight line of the type that would be formed where two perfectly flat planes intersect. If the edge where the top surface3and the side surface7meet includes any acute angles, the durability of the cutting edge9decreases. Therefore, a so-called honing process may be performed around the portion where the top surface3and the side surface7meet in order to form a slight curved surface.

The rake face15is positioned on the inner side of the land face13. The rake face15rakes away cut chips from the cutting edge9. As a result, chips cut from the workpiece slide over the surface of the rake face15. The rake face15is sloped downwards towards the bottom surface5moving away from the land face13so that the rake face15can satisfactorily rake away chips. In other words, in the cutting insert1of the present embodiment, the rake face15is sloped downwards moving towards the center of the top surface3.

Grooves19are formed in the rake face15. When the cutting process is performed using a coolant, these grooves19provide locations where the coolant can easily pool. This enhances cooling of the cutting edge9.

The bottom face17is positioned on the inner side of the rake face15. In the cutting insert1of the present embodiment, the bottom face17is a planar face perpendicular to the central axis X. An opening of the through-hole11is located at the center of the bottom face17. In the present embodiment, the top surface3includes the land face13, the rake face15, and the bottom face17. However, the top surface3is not limited to these configurations. For example, the top surface3may also include a breaker face that slopes upwards away from the bottom surface5moving away from the land face13and that is arranged on the inner side of the bottom face17.

The cutting edge9is formed along the edge where the top surface3and the side surface7meet. The cutting edge9includes, in order, an end cutting edge21, a first major cutting edge23, a second major cutting edge25, and a minor cutting edge27. The cutting insert1of the present embodiment includes six cutting edge groups, each including an end cutting edge21, a first major cutting edge23, a second major cutting edge25, and a minor cutting edge27. In adjacent cutting edge groups, the minor cutting edge27of one cutting edge group is adjacent to the end cutting edge21of the next cutting edge group. Therefore, when viewed from directly above, the cutting edge groups are rotationally symmetric about the central axis X, each spanning 60°. Each end cutting edge21, first major cutting edge23, second major cutting edge25, and minor cutting edge27is smoothly connected to the adjacent cutting edge.

A cutting process can be performed using a single one of these cutting edge groups. When one of the cutting edge groups wears out after a long cutting process, another one of the plurality of cutting edge groups may be used. In other words, the cutting insert1can be temporarily removed from the holder, rotated 60°, for example, around the central axis X, and reattached to the holder. In this way, one of the adjacent cutting edge groups can be used to start a new cutting process on the workpiece.

The rake angles of the rake face15are set such that the rake angles θ1to θ4are equal. As illustrated inFIG. 7, the rake angle θ1is the rake angle of the region corresponding to the end cutting edge21. As illustrated inFIG. 8, the rake angle θ2is the rake angle of the region corresponding to the first major cutting edge23. As illustrated inFIG. 9, the rake angle θ3is the rake angle of the region corresponding to the second major cutting edge25. As illustrated inFIG. 10, the rake angle θ4is the rake angle of the region corresponding to the minor cutting edge27.

Note thatFIG. 7is a cross-sectional view of a cross section that includes the central axis X and intersects with the end cutting edge21.FIG. 8is a cross-sectional view of a cross section that includes the central axis X and intersects with the first major cutting edge23.FIG. 9is a cross-sectional view of a cross section that includes the central axis X and intersects with the second major cutting edge25.FIG. 10is a cross-sectional view of a cross section that includes the central axis X and intersects with the minor cutting edge27.

The cutting insert1of the present embodiment includes six cutting edge groups; however, the present embodiment is not limited only to such configurations. For example, the cutting insert1may include four cutting edge groups, which when viewed from directly above are rotationally symmetric about the central axis X, each spanning 90°. Moreover, the cutting insert1may include eight cutting edge groups, which when viewed from directly above are rotationally symmetric about the central axis X, each spanning 45°.

The end cutting edge21contacts the bottom machining surface of the workpiece and cuts therealong. During the cutting process, the end cutting edge21is the lowermost portion of the cutting tool. Therefore, the end cutting edge21is positioned furthest away from the end of the holder when the cutting insert1is attached thereto. The end cutting edge21is used so as to contact the bottom machining surface of the workpiece, and therefore the height of the end cutting edge21relative to an imaginary plane L orthogonal to the central axis X running through the through-hole11is fixed. The end cutting edge21is positioned so as to contact the bottom machining surface of the workpiece and can therefore also be used as a flat cutting edge.

The first major cutting edge23is adjacent to the end cutting edge21and has a curved shape that protrudes outwards when viewed from directly above. When viewed from the side, the height of the first major cutting edge23relative to the imaginary plane L increases moving away from the end of the first major cutting edge23that is connected to the end cutting edge21. The chips cut from the workpiece are thicker in the regions cut by the first major cutting edge23than in the regions cut by the end cutting edge21.

When the cutting insert1of the present embodiment is viewed from the side, the height of the end cutting edge21relative to the imaginary plane L is fixed, while the height of the first major cutting edge23relative to the imaginary plane L increases moving away from the end of the first major cutting edge23that is connected to the end cutting edge21. The chips produced during the cutting process are relatively thin in the regions thereof cut by the first major cutting edge23, and the gentle slope of the first major cutting edge23reduces rapid increases in cutting resistance.

Like the first major cutting edge23, the second major cutting edge25has a curved shape that protrudes outwards when viewed from directly above. The second major cutting edge25is adjacent to the first major cutting edge23and is separated thereby from the end cutting edge21. Furthermore, when viewed from the side, the height of the second major cutting edge25relative to the imaginary plane L decreases moving away from the end of the second major cutting edge25that is connected to the first major cutting edge23.

As with the first major cutting edge23, the chips cut from the workpiece are thicker in the regions cut by the second major cutting edge25than in the regions cut by the end cutting edge21. Therefore, a greater force is easy to apply to the second major cutting edge25than to the end cutting edge21. However, the height of the second major cutting edge25relative to the imaginary plane L is not fixed, and the second major cutting edge25is sloped. Therefore, the cutting resistance on the second major cutting edge25during the cutting process can be reduced.

The chips cut from workpiece are even thicker in regions cut by the second major cutting edge25than in regions cut by the first major cutting edge23. However, in the cutting insert1of the present embodiment, when viewed from the side, the angle of inclination of the second major cutting edge25relative to the imaginary plane L is larger at the center of the second major cutting edge25than at either end thereof. Moreover, the angle of inclination θ5of an imaginary line connecting both ends of the second major cutting edge25relative to the imaginary plane L is larger than the angle of inclination θ6of an imaginary line connecting both ends of the first major cutting edge23relative to the imaginary plane L.

The first major cutting edge23slopes gently upwards away from the imaginary plane L moving away from the end cutting edge21. The second major cutting edge25slopes rapidly downwards towards the imaginary plane L moving away from the first major cutting edge23. Therefore, the cutting resistance on the second major cutting edge25may be even smaller than the cutting resistance on the first major cutting edge23during the cutting process. The angle of inclination θ5of the second major cutting edge25(which is positioned in the region where the chips become relatively thick) relative to the imaginary plane L is relatively large, and therefore the workpiece can be cut in a stable manner.

Note that the angle of inclination of the second major cutting edge25relative to the imaginary plane L is larger at the center of the second major cutting edge25than at either end thereof because the second major cutting edge25is smoothly connected to the first major cutting edge23and the minor cutting edge27. Here, the “center” of the second major cutting edge25refers to the portion positioned between the ends of the second major cutting edge25. However, the manner in which the angle of inclination of the second major cutting edge25is configured relative to the imaginary plane L is not particularly limited.

For example, as illustrated inFIG. 11A, when viewed from the side, the center of the second major cutting edge25in a direction perpendicular to the central axis X may have a large angle of inclination relative to the imaginary plane L. Alternatively, as illustrated inFIG. 11B, a portion of the second major cutting edge25that is closer, when viewed from the side, to the first major cutting edge23than is the center of the second major cutting edge25in the direction perpendicular to the central axis X may have a large angle of inclination relative to the imaginary plane L. Or, as illustrated inFIG. 11C, a portion of the second major cutting edge25that is closer, when viewed from the side, to the minor cutting edge27than is the center of the second major cutting edge25in the direction perpendicular to the central axis X may have a large angle of inclination relative to the imaginary plane L. Note that in each drawing inFIGS. 11A to 11C, the dimensions of the second major cutting edge25in the direction parallel to the central axis X are exaggerated in order to make the inclination of the second major cutting edge25easier to see.

The height of the first major cutting edge23relative to the imaginary plane L increases moving away from one end of the first major cutting edge23. The height of the second major cutting edge25relative to the imaginary plane L decreases moving away from one end of the second major cutting edge25. If the height of the second major cutting edge25relative to the imaginary plane L instead increases moving away from that same end of the second major cutting edge25, the durability of the cutting edge9may decrease. This is because this configuration results in too large a difference between the height of the other end of the second major cutting edge25relative to the imaginary plane L and the height of the end cutting edge21relative to the imaginary plane L.

The height of the other end of the second major cutting edge25is smaller than the height of the end cutting edge21relative to the imaginary plane L. This makes it possible to maintain a sufficiently large difference in height between the ends of the second major cutting edge25, and therefore the length of the second major cutting edge25can be increased while still maintaining a relatively large angle of inclination. As a result, the second major cutting edge25can cut wide, relatively thick chips from the workpiece.

In the cutting insert1of the present embodiment, the top surface3and the bottom surface5are both substantially circular. Therefore, the side surface7has a curved, substantially cylindrical shape. The entire surface of the side surface7is not curved; the side surface7also includes planar regions7a. These planar regions7aare separated from the cutting edge9and positioned around the bottom surface5side of the side surface7. Each planar region7ais positioned below one of the second major cutting edges25. The present embodiment has six second major cutting edges25and therefore has six planar regions7aas well.

The planar regions7afunction as binding faces for fixing the cutting insert1to the holder. If the side surface7is perfectly cylindrical, the cutting insert1is prone to rotation about the central axis X when attached to the holder. This may make it difficult to stably fix the cutting insert1to the holder. However, the planar regions7acontact the holder and make it difficult for the cutting insert1to rotate about the central axis X. This makes it possible to stably fix the cutting insert1to the holder.

The planar regions7aare formed by removing portions of the originally cylindrical side surface7to form flat faces. Therefore, the durability of the portions of the cutting edge9above the planar regions7amay be decreased.

However, in the cutting insert1of the present embodiment, the planar regions7aare positioned primarily below the second major cutting edges25. More specifically, when the cutting insert1is viewed directly from the side from the planar region7aside, each planar region7ais positioned such that an imaginary line that runs through the center of that planar region7aand is parallel to the central axis X intersects with the respective second major cutting edge25. As described above, the cutting resistance on the second major cutting edge25is smaller than the cutting resistance on the other portions of the cutting edge9. Positioning the planar regions7abelow the second major cutting edges25, where the cutting resistance is relatively small, reduces the possibility of damage to the cutting edge9.

When the cutting insert1of the present embodiment is viewed from the side, the width of each planar region7ain a direction orthogonal to the central axis X is larger than the width of each second major cutting edge25in the direction orthogonal to the central axis X. Furthermore, the entire second major cutting edge25is positioned above the respective planar region7a. Therefore, any effects applied to one of the planar regions7aduring the cutting process can be reduced across the entire corresponding second major cutting edge25.

Note that inFIG. 4, hatching is added to the planar regions7ato make the positions of those planar regions7amore apparent.

Moreover, when the side surface7is slanted, as in the cutting insert1of the present embodiment, the difference between the distance of the end cutting edge21from the central axis X and the distance of the other end of the second major cutting edge25from the central axis X tends to be large. This large difference in distances makes the R-shape of the machining surface of the workpiece more prone to distortion. However, because the second major cutting edge25slopes downwards towards the bottom surface5moving away from one end of that second major cutting edge25, large differences between the height of the second major cutting edge25at each end thereof relative to the imaginary plane L and the height of the end cutting edge21relative to the imaginary plane L can be prevented.

The cutting edge9includes, in order, the end cutting edge21, the first major cutting edge23, and the second major cutting edge25, each configured as described above. Due to the presence of the end cutting edge21(which has a fixed height relative to the imaginary plane L), the angles of inclination of the first major cutting edge23and the second major cutting edge25can be made larger than in a configuration in which the cutting edge9includes only the first major cutting edge23and the second major cutting edge25.

Moreover, due to the presence of the end cutting edge21(which is positioned to contact the bottom machining surface of the workpiece), the first major cutting edge23and the second major cutting edge25can be positioned farther away from the bottom machining surface of the workpiece than in the configuration in which the cutting edge9includes only the first major cutting edge23and the second major cutting edge25. This facilitates moving the positions of the first major cutting edge23and the second major cutting edge25, by an amount equal to the region where the end cutting edge21is positioned, to regions in which the workpiece is thicker and in which more cutting force is applied during the cutting process.

The chips cut from the workpiece are thinner in the regions cut by the end cutting edge21and the first major cutting edge23than in the regions cut by the second major cutting edge25. Therefore, when the end cutting edge21and the first major cutting edge23first contact the workpiece, the resulting impact force on the cutting insert1is small. As a result, the effects of such impact forces on the cutting insert1of the present embodiment are minor, and the cutting insert1can stably cut the workpiece even in regions where the resulting chips are relatively thick.

In the description above, the term “angle of inclination” of each portion of the cutting edge9refers to the angle between an imaginary line that connects both ends of the portion of the cutting edge9in question and the imaginary plane L that is orthogonal to the central axis X of the through-hole11when that portion of the cutting edge9is viewed from the side from a direction orthogonal to a line tangent to that portion of the cutting edge9when viewed from directly above. More generally, the angle of inclination is the inclination of the portion of the cutting edge9in question when viewed from the side from a direction normal to that portion.

For example,FIGS. 5 and 6are side views from a direction orthogonal to a line tangent to the end cutting edge21. Here, the angle between an imaginary line that runs parallel to the center portion of the cutting edge9(that is, the end cutting edge21) and the imaginary plane L that is orthogonal to the central axis of the through-hole is the angle of inclination of the end cutting edge21. However, the end cutting edge21has a fixed height relative to the imaginary plane L, and therefore the angle of inclination of the end cutting edge21is 0°.

Moreover, under the definition provided above for angle of inclination, the angle of inclination θ6of the first major cutting edge23, the angle of inclination θ5of the second major cutting edge25, and the angle of inclination θ7of the minor cutting edge27as illustrated inFIG. 4, for example, refer to angles of inclination θ5, θ6, and θ7. Note, however, that the actual values for each angle of inclination may be different than the angles depicted inFIG. 4. The values for the angle of inclination θ6of the first major cutting edge23and the angle of inclination θ5of the second major cutting edge25are not particularly limited. However, the angle of inclination θ6of the first major cutting edge23may be set to a value in the range of 2.5 to 3.5°, and the angle of inclination θ5of the second major cutting edge23may be set to a value in the range of 4 to 6°, for example.

The minor cutting edge27is connected to the second major cutting edge25and is disposed on the opposite side to the first major cutting edge23. In other words, the minor cutting edge27is adjacent to the second major cutting edge25and is separated thereby from the first major cutting edge23. Moreover, each minor cutting edge27is connected to the end cutting edge21of the adjacent cutting edge group. In other words, each minor cutting edge27connects the second major cutting edge25of one cutting edge group to the end cutting edge21of the adjacent cutting edge group.

Therefore, the height of the minor cutting edge27relative to the imaginary plane L increases moving away from the end connected to the second major cutting edge25, and the other end of the minor cutting edge27is connected to the end cutting edge21of the adjacent cutting edge group and equal thereto in height relative to the imaginary plane L.

Furthermore, when viewed from the side, the angle of inclination θ7(relative to the imaginary plane L) of an imaginary line that connects both ends of the minor cutting edge27is larger than the angle of inclination θ5(relative to the imaginary plane L) of an imaginary line that connects both ends of the second major cutting edge25. The value for the angle of inclination θ7of the minor cutting edge27is not particularly limited but may be set to a value in the range of 7 to 15°, for example.

In the cutting insert1of the present embodiment, the second major cutting edge25is longer than the minor cutting edge27. This makes it possible to further enhance the durability of the cutting insert1.

The height of the second major cutting edge25relative to the imaginary plane L decreases moving towards the minor cutting edge27. Likewise, the height of the minor cutting edge27relative to the imaginary plane L decreases moving towards the second major cutting edge25. Therefore, when viewed from the side, a recess is formed at the boundary between the second major cutting edge25and the minor cutting edge27. In cutting processes that employ the minor cutting edge27to achieve a greater cut depth, cutting stress may become concentrated at the boundary between the second major cutting edge25and the minor cutting edge27. However, because the second major cutting edge25is longer than the minor cutting edge27, a large range of cut depths can still be achieved in cutting processes that employ only the end cutting edge21, the first major cutting edge23, and the second major cutting edge25and do not employ the minor cutting edge27.

Moreover, as illustrated inFIG. 4, when viewed from the side from a direction parallel to the end cutting edge21, the first major cutting edge23and the second major cutting edge25each include a straight portion. Therefore, when the cutting insert1contacts the workpiece from a direction perpendicular to the end cutting edge21such as when the axial rake angle is 0°, the angles of inclination of the first major cutting edge23and the second major cutting edge25relative to the workpiece can remain constant when those cutting edges start cutting into the workpiece.

When using a circular arc-shaped cutting edge such as the one disclosed in Patent Document 1, the cutting ability of the cutting edge changes according to the orientation of the cutting edges relative to the workpiece and is therefore not uniform. As a result, the cutting process is prone to destabilization. Moreover, because the cutting ability of the cutting edge changes, the impact force applied to the cutting edge may also change according to the cutting conditions, such as when the cut depth is increased, for example. This may result in a decrease in the durability of the cutting insert. However, when the first major cutting edge23and the second major cutting edge25each include a straight portion, as described above, changes in cutting ability due to the orientation of each cutting edge relative to the workpiece can be kept small. This makes it possible to enhance the durability of the cutting insert1.

Moreover, variations in the angles of inclination of the first major cutting edge23and the second major cutting edge25relative to the workpiece when those cutting edges start cutting into the workpiece can be kept small regardless of whether the axial rake angle is positive or negative. The cutting insert1therefore has good versatility across a wide variety of axial rake angles.

In the cutting insert1of the present embodiment, the cutting edge9is only formed along the edge where the top surface3and the side surface7meet, and the side surface7is slanted relative to the top surface3and the bottom surface5. However, the present embodiment is not limited to such a configuration. The side surface7may be perpendicular to the top surface3and the bottom surface5, and cutting edges9may be formed both along the edge where the top surface3and the side surface7meet and along the edge where the bottom surface5and the side surface7meet, for example. When the cutting insert1is configured such that a cutting edge9is also formed along the edge where the bottom surface5and the side surface7meet, the bottom surface5may also include a land face13, a rake face15, and a bottom face17like those of the top surface3.

Next, a cutting tool101according to an embodiment of the present invention will be described with reference to figures.

As illustrated inFIG. 12, the cutting tool101of the present embodiment includes a holder103having an insert pocket107formed in the end thereof and the above-described cutting insert1, which is mounted within the insert pocket107such that the cutting edge9protrudes out from the end of the holder103. The cutting insert1is mounted in the insert pocket107such that the end cutting edge is positioned at the endmost point.

The holder103has a long, thin rod shape. Furthermore, only a single insert pocket107is formed in the end of the holder103. The insert pocket107provides a space in which the cutting insert1can be mounted and forms an opening in the end face and the side surface of the holder103. Because the insert pocket107also forms an opening in the side surface of the holder103, the cutting insert1can be mounted easily.

More specifically, the insert pocket107includes a seating face109parallel to the lengthwise direction of the holder103and a binding side face111that intersects with the seating face109. The cutting insert1is mounted within the insert pocket107. The cutting insert1is mounted such that one of the cutting edge groups thereof protrudes out from both the end and outer periphery of the holder103.

The cutting tool101of the present embodiment includes only a single insert pocket107but may also be configured to include a plurality of insert pockets107.

In the present embodiment, the cutting insert1is mounted to the holder103using a fixing screw105. In other words, the fixing screw105is inserted through the through-hole of the cutting insert1. The end of the fixing screw105is inserted into a screw hole formed in the insert pocket107and rotated such that the screw threads lock together, thereby fixing the cutting insert1to the holder103.

A material such as steel or cast iron may be used for the holder103. It is particularly preferable that high-toughness steel be used as the material for the holder103.

<Method for Manufacturing Cut Product>

Next, a method for manufacturing a cut product according to an embodiment of the present invention will be described with reference to figures.

The cut product is manufactured by machining a workpiece201. The method for manufacturing the cut product of the present embodiment includes the following steps:

(1) Rotating a cutting tool101representative of the embodiment described above.

(2) Bringing the cutting edge9of the rotating cutting tool101into contact with the workpiece201.

(3) Moving the cutting tool101away from the workpiece201.

More specifically, as illustrated inFIG. 13, first the cutting tool101is rotated around the Y axis thereof and brought relatively close to the workpiece201. Next, as illustrated inFIG. 14, the cutting edge9of the cutting tool101is brought into contact with the workpiece201, thereby starting the cut on the workpiece201. Then, as illustrated inFIG. 15, the cutting tool101is moved relatively far away from the workpiece201.

In the present embodiment, the cutting tool101is brought near the workpiece201while the workpiece201is fixed and while the rotating cutting tool101is fixed in the Y axis direction. Moreover, inFIG. 14, the cutting edge9of the rotating cutting insert1contacts the workpiece201, thereby cutting the workpiece201. Furthermore, inFIG. 15, the still rotating cutting tool101is moved away from the workpiece201.

During each step in the cutting process of the manufacturing method of the present embodiment, the cutting tool101is moved to either bring the cutting tool101into contact with the workpiece201or to move the cutting tool101through and out of the workpiece201. However, the method for manufacturing a cut product of the present embodiment is not limited strictly to these actions.

For example, in step (1), the workpiece201can be brought near the cutting tool101. Similarly, in step (3), the workpiece201can be moved away from the cutting tool101. To continue the cutting process, the cutting tool101is kept in the rotating state, and the cutting edge9of the cutting insert1is brought into contact with another location on the workpiece201. This process may be repeated as many times as necessary.

Moreover, representative examples of materials for the workpiece201include carbon steel, steel alloys, stainless steel, cast iron, and non-ferrous metals.

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