JP2022143008A - Cutting tool and cutting tool manufacturing method - Google Patents

Abstract

To provide a cutting tool which can suppress occurrence of sudden chipping of blade tip during cutting and of which life can be stably extended, and a manufacturing method therefor.SOLUTION: A cutting tool 10, which has a rake face 5, a flank 6, and a cutting blade 3 positioned at a ridge line part to which the rake face and the flank are connected, comprises: a sintered alloy tool base body 1; and a hard coating 2 placed on a surface of the tool base body 1. The hard coating 2 is configured from single layer or a plurality of layers overlapping in a film-thickness direction of the hard coating 2, and has an entire film thickness of 1 μm or more and 30 μm or less. The hard coating 2 has a plurality of coating peeling parts 21 with polygonal cross section at least on the rake face 5. The coating peeling part 21 is formed by laser peening treatment.SELECTED DRAWING: Figure 2

Description

TECHNICAL FIELD The present invention relates to a cutting tool and its manufacturing method, and more particularly to a surface-coated cutting tool with excellent chipping resistance and its manufacturing method.

Conventionally, there has been known a cutting tool in which a tool substrate made of cemented carbide is coated with a hard coating, that is, a surface-coated cutting tool. In this type of surface-coated cutting tool, the chipping resistance of the cutting edge is enhanced by imparting compressive residual stress to the surface layer of the hard coating or tool substrate. Specifically, a method of applying compressive residual stress by shot peening is well known, for example, as disclosed in Patent Document 1.

JP-A-6-108258

In the shot peening treatment as in Patent Document 1, if a high compressive residual stress of 1 GPa or more is applied to the cutting tool, sudden chipping of the cutting edge is more likely to occur, and the tool life becomes unstable. The reason for this is that random collisions of the media with the hard coating randomly generate points where stress is locally increased (stress concentration points), which act as starting points for coating peeling and cracking during cutting. It is thought that it will become

An object of the present invention is to provide a cutting tool capable of suppressing the occurrence of sudden cutting edge fracture during cutting and stably prolonging the tool life, and a method of manufacturing the same.

One aspect of the present invention is a cutting tool comprising a rake face, a flank face, and a cutting edge located on a ridge where these are connected, comprising a tool base made of a sintered alloy, and on the surface of the tool base and a hard coating disposed, wherein the hard coating is composed of a single layer or a plurality of layers overlapping in the thickness direction of the hard coating, and the total thickness is 1 μm or more and 30 μm or less, and the The hard coating has a plurality of coating stripped portions with a polygonal cross section at least on the rake face.
In addition, one aspect of the present invention is a method for manufacturing a cutting tool having a rake face, a flank face, and a cutting edge positioned at a ridgeline where they are connected, wherein the surface of a tool substrate made of a sintered alloy a laser peening step of applying a laser peening process from the hard coating disposed on the hard coating, wherein the laser peening step provides compressive residual stress to at least the hard coating on the rake face and the surface layer of the tool base, A plurality of film peeling portions each having a polygonal cross section are formed on the hard film.

In the present invention, compressive residual stress is imparted to the hard coating in the vicinity of the cutting edge (at least the rake face) and the surface layer of the tool substrate by performing laser peening on the hard coating. Thereby, the chipping resistance in the vicinity of the cutting edge is enhanced. "Laser peening" is a process in which a short-pulse laser, etc., is irradiated onto the hard coating, and the mechanical reaction occurs when fine particles or plasma generated on the surface of the hard coating scatter, impacting the hard coating and the tool substrate. It is a technique to give compressive residual stress by giving and inducing plastic deformation.

In the laser peening treatment, a uniform impact can be imparted to the surface layer portion and the hard coating of the tool base by hatching scanning (raster scanning) with a laser beam. This laser impact and its mechanical reaction act to planarize the surface of the hard coating and tool substrate. As a result, points at which stress is locally increased (stress concentration points) are generated on the uneven convex portions on the surface of the tool base. Due to the occurrence of such stress concentration points, the portions of the hard coating located directly above the protrusions are destroyed and removed, and minute coating peeling portions such as cracks with polygonal cross sections and pinholes are formed. be. Although the reason why the film-peeled portion has a polygonal shape is not clear, it is thought to be due to some spontaneous action at the time of stress fracture. The shape of the peeled film portion of the present invention is a special shape that cannot be obtained by conventional shot peening treatment or general film forming treatment.

Then, by forming the film peeling portion, it is possible to selectively release the locally excessively high stress at the stress concentration point without reducing the compressive residual stress increased by the laser peening treatment as a whole. . As a result, peeling of the film and cracking that originate from the stress concentration point during cutting are suppressed, and sudden chipping of the cutting edge is suppressed. That is, the chipping resistance of the cutting tool is stably enhanced.
In addition, the ratio of the size (surface area) of the coating peeling part to the surface area of the hard coating is very small, and the surface area of the hard coating does not change before and after forming the coating peeling part. is well maintained.

As described above, according to the present invention, it is possible to suppress the occurrence of sudden chipping of the cutting edge during cutting, and to stably extend the tool life.

In the above cutting tool, it is preferable that the film-peeled portion has a diameter of 1 μm or more and 30 μm or less.

If the diameter of the film-peeled portion is 1 μm or more, the stress at the stress concentration point can be suitably released by forming the film-peeled portion, and the above effects can be stably obtained.
If the diameter of the film peeling portion is 30 μm or less, the above-described effects of the film peeling portion can be obtained, and the occurrence of large peeling of the film starting from the film peeling portion during cutting can be suppressed. In addition, adhesion to the hard coating due to the peeled portion of the coating can be suppressed.

In the above cutting tool, it is preferable that the ratio of the total area of the plurality of film peeling portions to the unit area of the hard film is 0.5% or more and 10% or less.
In the above cutting tool, the ratio is more preferably 1% or more and 6% or less.

If the above ratio is 0.5% or more, local stress concentration is stably released by the action (function) of the peeled film portion. As a result, it is possible to stably suppress sudden chipping of the cutting edge, thereby suppressing chipping and the like. It should be noted that when the above ratio is 1% or more, the effect of suppressing chipping or the like becomes more pronounced, which is more desirable.
If the above ratio is 10% or less, adhesion to the hard coating and the like can be suppressed while the above-described effects of the coating peeled portion can be obtained. In addition, when the above-mentioned ratio is 6% or less, the effect of suppressing welding or the like becomes more remarkable, which is more desirable.

In the above cutting tool, it is preferable that the tool substrate has a residual stress of −1 GPa or less in a surface layer portion of the tool substrate located on the rake face.

In this case, since a large compressive residual stress is imparted to the tool base, fracture resistance in the vicinity of the cutting edge is more stably enhanced.

In the above cutting tool, it is preferable that the film peeling portion is a pinhole or a crack.

When the film peeling portion is a pinhole, it is easy to confirm that the film peeling portion has been formed by observing, for example, an SEM image (backscattered electron image) of the surface of the hard film after the laser peening treatment.
When the film peeling portion is a crack, it is easy to suppress adhesion to the hard film while obtaining the above-described effects of the film peeling portion.

ADVANTAGE OF THE INVENTION According to the cutting tool of one aspect of this invention, and the manufacturing method of a cutting tool, generation|occurrence|production of sudden cutting edge chipping during cutting can be suppressed, and tool life can be extended stably.

FIG. 1 is a perspective view showing the cutting tool of this embodiment. FIG. 2 is an enlarged cross-sectional view showing the vicinity of the cutting edge of the cutting tool of this embodiment. FIG. 3 is an enlarged SEM image showing the surface of the hard coating after laser peening treatment. FIG. 4 is an SEM image showing an enlarged cross section in the vicinity of the cutting edge after laser peening treatment. FIG. 5 is an SEM image showing an enlarged cross section in the vicinity of the cutting edge after laser peening treatment. FIGS. 6(a) to 6(c) are perspective views schematically explaining the method of manufacturing the cutting tool. FIG. 7(a) is a cross-sectional view near the cutting edge for explaining the laser peening treatment of the cutting tool manufacturing method, and FIG. 7(b) is a schematic diagram showing an enlarged part of FIG. 7(a) is. FIG. 8(a) is a cross-sectional view near the cutting edge for explaining the laser peening treatment of the cutting tool manufacturing method, and FIG. 8(b) is a schematic diagram showing an enlarged part of FIG. 8(a) is.

A cutting tool 10 and a method for manufacturing the same according to one embodiment of the present invention will be described with reference to the drawings. The cutting tool 10 of this embodiment is a cutting insert called a so-called cemented carbide insert or the like. The cutting tool 10 of the present embodiment is used, for example, as an indexable cutting tool for turning a work material.

As shown in FIG. 1, the cutting tool 10 of this embodiment is plate-shaped. Specifically, the cutting tool 10 is in the shape of a polygonal plate, and in the illustrated example is in the shape of a rectangular plate. The cutting tool 10 may have a polygonal plate shape, a disk shape, or the like, other than the rectangular plate shape.

In this embodiment, the direction in which the central axis C of the cutting tool 10 extends, that is, the direction parallel to the central axis C is called the axial direction. The central axis C is located at the center of the cutting tool 10 in plan view of the cutting tool 10 . The central axis C extends along the thickness (board thickness) direction of the cutting tool 10 .
A direction perpendicular to the central axis C is called a radial direction. Of the radial directions, the direction closer to the central axis C is called the radial inner side, and the direction away from the central axis C is called the radial outer side.
The direction of rotation around the central axis C is called the circumferential direction.

As shown in FIG. 2 , the cutting tool 10 of this embodiment includes a sintered alloy tool base 1 and a hard coating 2 disposed on the surface (outer surface) of the tool base 1 . In other words, the cutting tool 10 of this embodiment is a surface-coated cutting tool in which the tool substrate 1 is coated with the hard film 2 .

The tool substrate 1 is mainly composed of at least one hard phase selected from carbides, nitrides, and mutual solid solutions of metals of groups 4a, 5a, and 6a of the periodic table, and Ni, Co, or Ni—Co alloy. It is made of a sintered alloy composed of a binder phase of 2 to 15% by weight. In this embodiment, the tool base 1 is made of a WC-based cemented carbide. The tool base 1 may be made of cermet such as TiC-based or Ti(C,N)-based.

The hard coating 2 is deposited on the surface of the tool base 1 by chemical vapor deposition (CVD) or physical vapor deposition (PVD). The hard coating 2 is composed of carbides, nitrides, oxides, borides, Si carbides, nitrides, Al oxides, and nitrides of group 4a, 5a, and 6a metals of the periodic table, and mutual solid solutions thereof, diamond , cubic boron nitride, or the like. The material of the hard coating 2 is not particularly limited, and a material generally used for so-called cemented carbide tools can be selected.

The hard coating 2 is composed of a single layer or a plurality of layers stacked in the thickness direction of the hard coating 2 . When the hard coating 2 is composed of a plurality of layers, each layer may be made of different materials or may be made of the same material. The hard coating 2 has a total thickness of 1 μm or more and 30 μm or less.

The “film thickness direction” of the hard coating 2 in this embodiment corresponds to the direction perpendicular to the surface of the hard coating 2 . In the present embodiment, the direction from the hard coating 2 toward the tool substrate 1 in the film thickness direction is called the tool substrate 1 side from the hard coating 2 in the film thickness direction, or simply the inside in the film thickness direction. In the film thickness direction, the direction from the tool substrate 1 to the hard film 2 is called the side of the tool substrate 1 to the hard film 2 in the film thickness direction, or simply the outside in the film thickness direction.

The hard coating 2 is arranged on the surface of the tool base 1 at least in a region including a cutting edge 3 described later. In this embodiment, the hard coating 2 is arranged at least on a cutting edge 3, a rake face 5 and a flank face 6, which will be described later. The hard coating 2 may be formed over the entire surface of the tool base 1 .

Further, as shown in FIG. 1, the cutting tool 10 includes a pair of plate surfaces 10a and 10b, an outer peripheral surface 10c, and a through hole 10d.
The pair of plate surfaces 10a and 10b are polygonal and face the axial direction. In this embodiment, each of the pair of plate surfaces 10a and 10b has a rectangular shape. The pair of plate surfaces 10a and 10b has one plate surface 10a and the other plate surface 10b. One plate surface 10a and the other plate surface 10b face opposite sides in the axial direction.

In this embodiment, of the axial directions, the direction from the other plate surface 10b to the one plate surface 10a is referred to as the axial direction one side, and the direction from the one plate surface 10a to the other plate surface 10b is referred to as the axial direction other side. called side.
Of the pair of plate surfaces 10a and 10b, at least one of the plate surfaces 10a is arranged such that a portion of the plate surface 10a (near the corner portion) faces a work material (not shown) during cutting.

The outer peripheral surface 10c is located between the pair of plate surfaces 10a and 10b in the axial direction and faces radially outward. The outer peripheral surface 10c is connected to the pair of plate surfaces 10a and 10b at both ends in the axial direction. The outer peripheral surface 10 c extends in the circumferential direction and is arranged over the entire circumferential area of the cutting tool 10 .

10 d of through-holes penetrate the cutting tool 10 to an axial direction. 10 d of through-holes extend in the inside of the cutting tool 10 at an axial direction, and open to a pair of board|plate surface 10a, 10b. A central axis of the through hole 10d is arranged coaxially with the central axis C of the cutting tool 10 . In the illustrated example, the through hole 10d is circular. For example, a clamp screw, a clamp member, or the like (not shown) is inserted into the through hole 10d.

The cutting tool 10 also includes a rake face 5 , a flank face 6 and a cutting edge 3 .
The rake face 5 is arranged on at least one plate surface 10a of the pair of plate surfaces 10a and 10b. The rake face 5 constitutes at least part of the plate face 10a. The rake face 5 is positioned at a corner portion of one plate face 10a. In the present embodiment, the rake face 5 is arranged at each of at least two of the four corners positioned on the outer periphery of the plate surface 10a. The two corner portions are arranged at positions that are 180° rotationally symmetrical with respect to the central axis C. As shown in FIG.

As shown in FIG. 2, the rake face 5 has a land portion 5a and an inclined portion 5b.
The land portion 5 a is a portion of the rake face 5 that is connected to the cutting edge 3 . The land portion 5 a is arranged radially inside the cutting edge 3 . In this embodiment, the land portion 5a is an inclined surface located on the other side in the axial direction as it extends radially inward from the cutting edge 3 . Note that the land portion 5a may have a planar shape extending in a direction perpendicular to the central axis C. As shown in FIG.

The inclined portion 5b is a portion of the rake face 5 located radially inward of the land portion 5a.
The inclined portion 5b is connected to the radially inner end portion of the land portion 5a. The inclined portion 5b is an inclined surface located on the other side in the axial direction as it goes radially inward from the land portion 5a. The amount of axial displacement per unit length along the radial direction of the inclined portion 5b is greater than the amount of axial displacement per unit length along the radial direction of the land portion 5a. That is, the inclination of the inclined portion 5b with respect to a virtual plane (not shown) perpendicular to the central axis C is greater than the inclination of the land portion 5a with respect to the virtual plane.

As shown in FIG. 1, the flank 6 is arranged on the outer peripheral surface 10c. The flank 6 constitutes at least part of the outer peripheral surface 10c. The flanks 6 are arranged on portions adjacent to the respective rake faces 5 of the outer peripheral surface 10c. In the present embodiment, the flanks 6 are arranged in at least two of the four corners protruding radially outward on the outer peripheral surface 10c. The two corner portions are arranged at positions that are 180° rotationally symmetrical with respect to the central axis C. As shown in FIG.

The cutting edge 3 is located at the ridge line where the rake face 5 and the flank face 6 are connected. In the present embodiment, the cutting edge 3 is arranged at at least two corners among the four corners positioned on the outer periphery of the plate surface 10a. As shown in FIG. 2, the cutting edge 3 has round honing in this embodiment. The cutting edge 3 may have chamfer honing.

As shown in FIG. 1, the cutting edge 3 has a corner edge portion 3a and a straight edge portion 3b. The corner edge portion 3a has a convex curved shape protruding radially outward. The straight blade portion 3b is straight and connected to the corner blade portion 3a. In this embodiment, a pair of straight blade portions 3b are connected to both end portions in the blade length direction in which the corner blade portion 3a extends. That is, a pair of linear blade portions 3b are provided.

In FIG. 2, the tool base 1 has a residual stress of −1 GPa or less in the surface layer portion 1a located on the rake face 5 of the tool base 1 . The tool base 1 has a residual stress of -1 GPa or less in the surface layer portion 1a in a predetermined range A from the cutting edge 3. That is, compressive residual stress is applied to the surface layer portion 1a of the tool base body 1 . In this embodiment, the predetermined range A is a range of at least 200 μm from the cutting edge 3 on the rake face 5 . The predetermined range A is preferably a range of 500 μm or less from the cutting edge 3 on the rake face 5 . That is, the predetermined range A in the present embodiment is at least part of the rake face 5 . Therefore, in the present embodiment, the predetermined range A may be appropriately rephrased as the rake face 5 . In addition, since the predetermined range A is a portion irradiated with a short pulse laser in the laser peening process to be described later, it may be rephrased as a "laser irradiation range".
Further, the "surface layer portion 1a of the tool base 1" in the present embodiment refers to a surface layer portion of the tool base 1 which is at least 1 μm deep from the surface of the tool base 1 (interface with the hard coating 2).

As shown in FIGS. 5 and 7(a), the tool base 1 has unevenness on the surface of at least a predetermined range A. As shown in FIG. That is, the tool base 1 has a plurality of projections 11 and a plurality of recesses 12 arranged on the surface of at least a predetermined range A. As shown in FIG. By making the surface of the tool base 1 uneven, the arithmetic mean roughness Ra of the surface of the predetermined range A of the tool base 1 is suitably 0.2 μm or more and 0.6 μm or less. In other words, by setting the arithmetic mean roughness Ra within the above numerical range, the surface of the tool base 1 is provided with minute unevenness. The arithmetic mean roughness Ra is more preferably 0.3 μm or more and 0.5 μm or less.

The arithmetic mean roughness Ra is measured, for example, as follows.
A vertical section near the cutting edge 3, that is, a section perpendicular to the blade length direction in which the cutting edge 3 extends, is subjected to so-called sectioning by FIB (Focused Ion Beam) processing, and an SEM image of this section (for example, 3000 times magnification) is obtained. The profile of the interface between the hard coating 2 and the tool substrate 1 is randomly (arbitrarily) extracted at a plurality of locations (for example, 5 locations), and the surface roughness is calculated from the average value of the surface roughness at each location with a reference length of 30 μm.

In addition, instead of providing a plurality of protrusions 11 and a plurality of recesses 12 on the surface of the tool base 1 in a predetermined range A, for example, as schematically shown in FIGS. Only a plurality of projections 11 may be provided on a smooth surface extending perpendicularly to the direction.

As shown in FIG. 2, the hard coating 2 has a plurality of coating stripped portions 21 at least in a predetermined range A. As shown in FIG. That is, the hard coating 2 has a plurality of coating stripped portions 21 at least on the rake face 5 . As shown in FIGS. 4, 5 and 8(a) and (b), each film peeling portion 21 is arranged directly above the convex portion 11 in a predetermined range A, or the like. That is, the plurality of film peeling portions 21 include a plurality of film peeling portions 21 overlapping the convex portions 11 when viewed from the film thickness direction. When viewed from the film thickness direction, the film peeling portion 21 overlapping the convex portion 11 is called the first film peeling portion, and the film peeling portion 21 overlapping the portion other than the convex portion 11 (the concave portion 12 and the smooth portion) of the surface layer portion 1a is called the first film peeling portion. It may also be referred to as a two-coating stripping section.

The film peeling portion 21 is, for example, a crack having a U-shaped longitudinal section along the film thickness direction as shown in FIG. 5, or a pinhole as shown in FIG. As shown in FIG. 5 , in the case of cracks, part of the hard coating 2 may remain in the coating stripped portion 21 without being removed. In the example shown in each figure, the film peeling portion 21 has a smaller diameter in the film thickness direction from the hard film 2 toward the tool base 1 side, that is, as it goes inward in the film thickness direction. In FIGS. 4 and 5, a portion (top) of the projection 11 is exposed at the bottom of the film peeling portion 21 .

FIG. 3 is an SEM image (backscattered electron image) showing the surface of the hard coating 2 in a predetermined range A. FIG. As shown in FIG. 3, the pinhole (coating peeling portion) 21 has a triangular shape, a square shape, a pentagonal shape, or the like in plan view in the film thickness direction, that is, a polygonal shape. When the film peeling portion 21 is a crack, the film peeling portion 21 has a polygonal cross section perpendicular to the film thickness direction. That is, in both the form of pinhole and crack, the film peeling portion 21 has a polygonal cross section.

In plan view in the film thickness direction, the ratio of the total area of the plurality of film peeling portions 21 to the unit area of the hard film 2 is preferably 0.5% or more and 10% or less. More preferably, the ratio is 1% or more and 6% or less. Moreover, the film peeling portion 21 has a diameter of 1 μm or more and 30 μm or less. When the film peeling portions 21 are pinholes, for example, 50 or more and 1000 or less film peeling portions 21 are preferably provided per 1 mm ² of the surface of the hard film 2 .

Although not shown, the hard coating 2 may have pinholes other than the coating peeling portion 21 . This pinhole is, for example, a circular hole, and is arranged in a portion other than the predetermined range A in the hard coating 2 . The circular pinholes are not formed by the laser peening treatment described later, but are formed unintentionally, for example, in a film forming process, and have the same configuration and function as the film peeling portion 21. not a thing The number of pinholes as the film peeling portion 21 arranged in the predetermined range A is larger than the number of other pinholes arranged in the portion other than the predetermined range A.

Next, a method for manufacturing the cutting tool 10 will be described.
Although not particularly illustrated, the method for manufacturing the cutting tool 10 of the present embodiment includes a sintering process, a film forming process, and a laser peening process.

In the sintering step, the green compact having the shape of the tool base 1, that is, the intermediate green compact compacted in the manufacturing process of the tool base 1 is sintered. In this embodiment, the powder compact is plate-shaped, specifically, a polygonal plate-shaped.

In the film forming process, a hard coating having a predetermined thickness consisting of a single layer or multiple layers is formed on the surface of the sintered tool base 1 by chemical vapor deposition (CVD) or physical vapor deposition (PVD). 2 is deposited.

In the laser peening process, a pulse laser (short-pulse laser) having a pulse width of 10 ps (picoseconds) or less, for example, is irradiated from the hard coating 2 placed on the surface of the tool base 1 to perform laser peening. In this embodiment, a short-pulse laser having a pulse width of about 1 ps is irradiated from above the hard coating 2 . The term “laser peening” refers to irradiating the hard coating 2 with a short-pulse laser or the like. This is a technique of imparting compressive residual stress by giving an impact to the substrate 1 to induce plastic deformation.
The reason why the pulse width of the pulse laser is set to 10 ps or less is that the peak power density of the laser is increased while eliminating the thermal effect on the workpiece, and a large compressive residual stress is generated in the surface layer 1a of the hard coating 2 and the tool base 1 due to the strong impact. This is for giving

As shown in FIG. 2, in the laser peening step, the short-pulse laser is applied to a predetermined range A (laser irradiation range) covering the radial outer end of the inclined portion 5b, the land portion 5a and the cutting edge 3. That is, in this embodiment, in the laser peening step, compressive residual stress is applied to at least a predetermined range A from the cutting edge 3, that is, the hard coating 2 in the rake face 5, and the surface layer portion 1a of the tool base 1 by laser peening.
Specifically, as shown in FIG. 6B, by hatching scanning (raster scanning) with a pulse laser (laser beam) L from above the hard coating 2, the hard coating 2 and the surface layer portion 1a of the tool base 1 Gives uniform impact. 6A to 6C, illustration of the hard coating 2 on the tool substrate 1 is omitted. A plurality of circles shown in FIG. 6B represent spots B of the pulse laser L on the work surface. In this embodiment, these spots B are made to overlap each other.

In the laser peening step, as shown in FIG. 2, the residual stress of the surface layer portion 1a of the tool base 1 in a predetermined range A from the cutting edge 3 is set to −1 GPa or less, and as shown in FIG. A plurality of the above-described film peeling portions 21 are formed in portions of the film 2 that are located directly above the plurality of protrusions 11 arranged on the surface of at least a predetermined range A of the tool base 1 . That is, in this embodiment, in the laser peening process, a plurality of peeled film portions 21 each having a polygonal cross section are formed in the hard film 2 .

Specifically, by subjecting the hard coating 2 and the surface layer 1a of the tool base 1 to laser peening treatment, as shown in FIG. As shown in 8(a), a force acts to flatten the surfaces of the hard coating 2 and the tool base 1. FIG. As a result, as shown in FIG. 6(c), points (stress concentration points) P at which stress is locally increased are generated on each convex portion 11 on the surface of the tool base 1 and the like. 7(b) and FIG. 8(b), a portion of the hard coating 2 located directly above the protrusion 11 (stress concentration point). S and the like are destroyed and removed, and film peeling portions 21 such as cracks and pinholes having a U-shaped cross section (longitudinal cross section) along the film thickness direction, for example, are formed.

That is, the inventors of the present invention have extensively studied the laser peening treatment method for the surface-coated cutting tool 10, and found that the appropriate surface roughness of the surface of the tool substrate 1 (for example, 0.2 μm≦Ra≦0.2 μm as described above). 6 μm), and furthermore, by optimizing the laser irradiation spot diameter and the overlap ratio between pulses, the portion of the hard coating 2 such as directly above the convex portion 11 that is the stress concentration point P is formed into a pinhole shape. It has been found that the stress concentration point P can be selectively released by removing it or forming it into a crack.

According to the cutting tool 10 and the method for manufacturing the cutting tool 10 of the present embodiment described above, the following effects are obtained.
In this embodiment, a compressive residual stress is applied to the hard coating 2 in the vicinity of the cutting edge 3 (at least the rake face 5) and the surface layer 1a of the tool base 1 by performing laser peening on the hard coating 2. Thereby, chipping resistance in the vicinity of the cutting edge 3 is enhanced.

In the laser peening process, a stress concentration point P is generated on each uneven convex portion 11 on the surface of the tool base 1 due to the laser impact of the laser beam L and the mechanical reaction R thereof. Due to the occurrence of such a stress concentration point P, the part S of the hard coating 2 located directly above the protrusion 11 is destroyed and removed, and minute coating peeling such as a crack with a polygonal cross section and a pinhole is caused. A portion 21 is formed. Although the reason why the peeled film portion 21 has a polygonal shape is not clear, it is considered to be due to some spontaneous action at the time of stress fracture. The shape of the film peeling portion 21 of the present embodiment is a special shape that cannot be obtained by conventional shot peening processing or general film forming processing.

Then, by forming the coating stripped portion 21, the locally excessively high stress at the stress concentration point P can be selectively released without reducing the compressive residual stress increased by the laser peening treatment as a whole. can be done. Therefore, peeling of the film and cracking starting from the stress concentration point P during cutting are suppressed, and sudden chipping of the cutting edge is suppressed. That is, the chipping resistance of the cutting tool 10 is stably enhanced.
The ratio of the size (surface area) of the film peeling portion 21 to the surface area of the hard film 2 is very small, and the surface area of the hard film 2 does not change before and after the film peeling portion 21 is formed. 2 maintains good wear resistance.

As described above, according to the present embodiment, it is possible to suppress the occurrence of sudden chipping of the cutting edge during cutting, and to stably extend the tool life.

Further, in the present embodiment, the film peeling portion 21 has a diameter of 1 μm or more and 30 μm or less.
If the diameter of the peeled film portion 21 is 1 μm or more, the stress at the stress concentration point P can be released favorably by forming the peeled film portion 21, and the above effects can be stably obtained.
If the diameter of the film peeling portion 21 is 30 μm or less, the above-described effects of the film peeling portion 21 can be obtained, and the occurrence of large peeling of the film starting from the film peeling portion 21 during cutting is suppressed. In addition, adhesion to the hard coating 2 caused by the coating peeling portion 21 can be suppressed.

Further, in the present embodiment, the ratio of the total area of the plurality of film peeling portions 21 to the unit area of the hard film 2 is 0.5% or more and 10% or less, preferably 1% or more and 6% or less.
If the above ratio is 0.5% or more, local stress concentration is stably released by the action (function) of the film peeling portion 21 . This makes it possible to stably suppress sudden chipping of the edge of the cutting edge 3, thereby suppressing chipping and the like. It should be noted that when the above ratio is 1% or more, the effect of suppressing chipping and the like becomes more remarkable, which is more desirable.
If the above ratio is 10% or less, adhesion to the hard coating 2 or the like is suppressed while the above-described effects of the coating peeling portion 21 are obtained. It should be noted that when the above ratio is 6% or less, the effect of suppressing welding or the like becomes more pronounced, which is more desirable.

Further, in the present embodiment, the tool base 1 has a residual stress of −1 GPa or less in the surface layer portion 1a of the tool base 1 located on the rake face 5 .
In this case, since a large compressive residual stress is applied to the tool base 1, the chipping resistance in the vicinity of the cutting edge 3 is more stably enhanced.

Moreover, in this embodiment, the film peeling portion 21 is a pinhole or a crack.
When the film peeling portion 21 is a pinhole, it is easy to confirm that the film peeling portion 21 has been formed by observing the surface of the hard film 2 with an SEM image (backscattered electron image) after the laser peening treatment.
When the film peeling portion 21 is a crack, the adhesion to the hard film 2 and the like can be easily suppressed while the above-described effects of the film peeling portion 21 are obtained.

Further, in the present embodiment, when the film peeling portions 21 are arranged in the range of 50 or more and 1000 or less per 1 mm ² of the surface of the hard film 2, the following effects are obtained.
By providing 50 or more film peeling portions 21 per unit area of 1 mm ² of the hard film 2 , local stress concentration is stably released. That is, it is possible to form the peeled coating portion 21 with high accuracy directly above each stress concentration point P in the hard coating 2, stably suppressing sudden chipping of the cutting edge, and suppressing chipping and the like.
In addition, by providing 1000 or less film peeling portions 21 per unit area of 1 mm ² of the hard film 2, the effects of the film peeling portions 21 described above can be obtained, while welding and the like to the hard film 2 are suppressed. .

Further, in the present embodiment, the predetermined range A in which the laser peening treatment is performed is a range of at least 200 μm from the cutting edge 3 on the rake face 5 .
In general, a cutting tool is often judged to have reached the end of its tool life when the rake face is worn to a range of 200 μm from the cutting edge (in the initial unused position) due to cutting. According to the above configuration of the present embodiment, chipping resistance in the vicinity of the cutting edge 3 can be stably enhanced until the tool life expires.

Further, in the present embodiment, the surface of the tool substrate 1 in the predetermined range A, that is, the surface of the tool substrate 1 located on the rake face 5 (the interface with the hard coating 2) has an arithmetic mean roughness Ra of 0.2 μm or more. It is 0.6 μm or less.
When the arithmetic mean roughness Ra is 0.2 μm or more, the surface of the tool base 1 is prevented from becoming too smooth, and the plurality of protrusions 11 that serve as stress concentration points P on the surface of the tool base 1 are stabilized. formed by As a result, the peeled film portion 21 is stably formed in the portion S of the hard film 2 located directly above each convex portion 11, and the above effects become more pronounced.
Further, when the arithmetic mean roughness Ra is 0.6 μm or less, the protrusions 11 on the surface of the tool base 1 are prevented from becoming too large. Therefore, it is possible to suppress the problem that the peeled film portion 21 formed directly above the convex portion 11 becomes too large, that is, the occurrence of large peeling of the hard film 2 . Thereby, the wear resistance of the hard coating 2 is maintained well.
In order to further enhance the above effects, it is more preferable that the arithmetic mean roughness Ra is 0.3 μm or more and 0.5 μm or less.

It should be noted that the present invention is not limited to the above-described embodiments, and, for example, as described below, changes in configuration can be made without departing from the gist of the present invention.

In the above-described embodiment, an example in which the cutting tool 10 is used as an indexable cutting tool was given, but the present invention is not limited to this. The cutting tool 10 may be used, for example, as an indexable drill or an indexable end mill for milling a work material.
Moreover, although the example which the cutting tool 10 is a cutting insert was mentioned, it does not restrict to this. The cutting tool 10 may be, for example, a solid type drill, end mill, reamer and other cutting tools.

The present invention may combine the configurations described in the above-described embodiments and modifications without departing from the gist of the present invention, and addition, omission, replacement, and other modifications of the configuration are possible. . Moreover, the present invention is not limited by the embodiments described above, but only by the claims.

EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples. However, the present invention is not limited to this example.

<Manufacturing example and cutting test>
A cutting insert having a JIS standard CNMG120408 shape was prepared as each of the cutting tools of the examples and comparative examples of the present invention. The tool substrate 1 of each cutting tool is made of WC cemented carbide with a composition of 8.0 mass % Co. On the surface of the tool base 1, the flat portion (land portion 5a) of the rake face 5 positioned within a predetermined range A of 200 μm from the cutting edge 3 has an arithmetic mean roughness Ra of 0.42 μm. As the hard coating 2, a titanium carbonitride layer having a thickness of 5 μm was formed on the surface of the tool base 1 by the CVD method. Thereafter, an α-Al ₂ O ₃ layer with a thickness of 2 μm and a TiN layer with a thickness of 0.2 μm were formed on the titanium carbonitride layer by the CVD method.

Next, a short pulse laser is irradiated to a predetermined area A from above the hard coating 2 by hatching scanning under the following laser conditions, and a laser peening process is performed to form a polygonal pinhole (coating peeling portion) in the hard coating 2 in plan view. Examples 1 to 8 are those in which 21 was formed. The overlap ratio is obtained by [{(beam spot diameter)-(feed amount of one pulse of laser beam)}/(beam spot diameter)]×100.
[Laser conditions]
・Laser wavelength: 1030 nm
・Pulse energy: 0.4mJ
・Repetition frequency: 10kHz
・Pulse width: 1 ps
・Spot diameter on workpiece surface: either φ30 μm or φ60 μm ・Overlap ratio: 12.5%, 25%, 50% or 75%

The residual stress of the surface layer 1a of the tool base 1 ("WC residual stress" in Table 1 below) was measured using an X-ray residual stress measuring device manufactured by Pulstec, using the cos α method. A Cu tube was used as the X-ray source, and the residual stress was measured using the WC (113) diffraction peak near 2θ=154°. Using an X-ray shielding plate, only a width of 0.2 mm was exposed from the cutting edge 3 to the rake face 5 side, and measurement was performed so that the stress value of only the laser peening treated portion was obtained.

As a comparative example other than the above, the following was prepared.
That is, after the formation of the hard coating 2, Comparative Example 1 was untreated, and Comparative Example 2 was subjected to wet blasting treatment (shot peening treatment) under the following wet blasting conditions instead of laser peening treatment. .
[Wet blasting conditions]
・Media: ZrO ₂ (zirconia)
・Media diameter: 200 μm
・Projection pressure: 0.35 MPa
・Projection time: 60 seconds ・Projection angle to the rake face normal: 45 degrees

For each of the cutting tools of Examples 1 to 8 and Comparative Examples 1 and 2, the number of film peeling portions 21 included per unit area of 1 mm ² on the surface of the hard film 2, specifically, the polygonal shape having a diameter of 1 μm or more and 30 μm or less The number of pinholes was measured. The number of film-peeled portions 21 was counted from an image obtained by scanning electron microscope (SEM) observation. In addition, the ratio of the total area of the plurality of film peeling portions 21 to the unit area of the hard film 2 (hereinafter sometimes simply referred to as the total area ratio of the film peeling portions 21) was measured.

Using the cutting tools of Examples 1 to 8 and Comparative Examples 1 and 2, a turning wet cutting test was performed under the following cutting conditions to measure the cutting time until reaching the tool life. The tool life was defined as the cutting time from the start of cutting until the maximum flank wear width (chipping length) reached 0.2 mm. The results are shown in Table 1 below.
[Cutting conditions]
・Work material: SUS304 hexagonal material φ50mm (intermittent cutting)
・Cutting speed: 80m/min
・Incision: 2mm
・Feed: 0.3mm/rev

The criteria for judgment in Table 1 were as follows.
A: The cutting time until reaching the end of the tool life is excellent, specifically 20 minutes or longer.
B: A long cutting time until reaching the tool life, specifically longer than 15 minutes.
C: It cannot be said that the cutting time until reaching the tool life is long, specifically 15 minutes or less.

As shown in Table 1, Examples 1 to 8 were judged as A or B, and it was found that the tool life was increased. Among them, the number of pinholes per unit area of 1 mm ² of the hard coating 2 is in the range of 50 to 1000, and the total area ratio of the coating peeling portion 21 is in the range of 1% to 6%. 7 was confirmed to significantly increase the tool life.

Specific considerations are as follows.
In Examples 2 to 7, compared with Comparative Example 1 in which no laser peening treatment was performed, the cutting time (life time) until the tool life was reached was doubled or more. It is believed that this is because pinholes (coating stripped portions) 21 are randomly scattered in the hard coating 2 by the laser peening treatment, thereby relaxing the local stress concentration. Further, the residual stress of the surface layer portion 1a of the tool base 1 is set to -1.0 GPa or less, resulting in a large effect. In Example 8, since the number of pinholes was too large, the number of exposed portions of the surface of the tool base 1 was increased, leading to increased welding chippings and affecting the service life.
In Comparative Example 2, although the residual stress in the surface layer portion 1a of the tool base 1 was -1 GPa or less due to the wet blasting, the stress concentration easily caused sudden chipping of the coating, so the life time was not greatly improved. rice field.

According to the cutting tool and the method for manufacturing the cutting tool of the present invention, it is possible to suppress the occurrence of sudden chipping of the cutting edge during cutting, and to stably extend the tool life. Therefore, it has industrial applicability.

REFERENCE SIGNS LIST 1 tool substrate 1a surface layer portion 2 hard coating 3 cutting edge 5 rake face 6 flank 10 cutting tool 11 convex portion 21 coating peeling portion A predetermined range , P... stress concentration point, S... part of the hard coating located directly above the protrusion (stress concentration point)

Claims (7)

A cutting tool comprising a rake face, a flank face, and a cutting edge located on a ridge where they are connected,
a tool substrate made of a sintered alloy;
a hard coating disposed on the surface of the tool base,
The hard coating is composed of a single layer or a plurality of layers overlapping in the thickness direction of the hard coating, and the total thickness is 1 μm or more and 30 μm or less,
The hard coating has, at least on the rake face, a plurality of coating peeling portions having a polygonal cross section.
Cutting tools. The film peeling portion has a diameter of 1 μm or more and 30 μm or less,
The cutting tool according to claim 1. The ratio of the total area of the plurality of film peeling portions per unit area of the hard film is 0.5% or more and 10% or less.
The cutting tool according to claim 1 or 2. The ratio is 1% or more and 6% or less,
The cutting tool according to claim 3. The tool base has a residual stress of -1 GPa or less in a surface layer portion of the tool base located on the rake face.
A cutting tool according to any one of claims 1 to 4. The film peeling part is a pinhole or a crack,
A cutting tool according to any one of claims 1 to 5. A method of manufacturing a cutting tool having a rake face, a flank face, and a cutting edge located on a ridge to which they are connected, comprising:
A laser peening step of applying a laser peening treatment from the hard coating disposed on the surface of the sintered alloy tool base,
In the laser peening step, compressive residual stress is applied to at least the hard coating on the rake face and the surface layer portion of the tool base, and a plurality of coating peeling portions having a polygonal cross section are formed on the hard coating.
A method of manufacturing a cutting tool.

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