Patent Application
20230105814
The present invention relates to a method for manufacturing a cutting tool, and more particularly to a post-treatment method for improving the fracture resistance of a cutting edge of a cutting tool.
In a cutting tool in which a tool body made of cemented carbide is coated with a hard coating, a technique is known in which tensile residual stress of the hard coating or the tool body is released by a post-treatment, or compressive residual stress is applied to improve the fracture resistance of a cutting edge. For example, Japanese Unexamined Patent Application, First Publication No. H06-108258 discloses a method of controlling residual stress by an impact force generated by allowing submillimeter-order steel balls to collide with a tool surface in shot peening. Japanese Unexamined Patent Application, First Publication No. 2012-223808 discloses a surface treatment method of irradiating a nanosecond laser to reduce the tensile stress of a TiCN hard coating or to apply compressive stress. As in Japanese Unexamined Patent Application, First Publication No. 2018-183862, a technique is also known in which the propagation of minute cracks can be suppressed by causing the residual stress value in a direction parallel to the ridge portion of a cutting edge to be larger than the residual stress value in a direction orthogonal to the ridge portion of the cutting edge, and as a result, the fracture resistance of the cutting edge is improved. Published Japanese Translation No. 2020-525301 of the PCT International Publication discloses a method of applying compressive residual stress to a base material made of cemented carbide by performing so-called nanosecond laser peening using a high-energy nanosecond laser having a pulse width of about several ns and a pulse energy of several hundred mJ.
Japanese Unexamined Patent Application, First Publication No. H06-108258
Japanese Unexamined Patent Application, First Publication No. 2012-223808
Japanese Unexamined Patent Application, First Publication No. 2018-183862
Published Japanese Translation No. 2020-525301 of the PCT International Publication
In the method of Japanese Unexamined Patent Application, First Publication No. H06-108258, the compressive residual stress of a hard phase of a hard coating or the surface layer of the tool body can be increased by adjusting the material and size of the media, or by increasing the projecting pressure and projecting time of shot peening. However, when too high compressive residual stress is applied, peeling of the hard coating and the generation vertical cracks that become the origin of defects during the use of the tool become significant, and local compressive stress around the vertical cracks is released. Therefore, there is a problem that the residual stress varies greatly for each product lot and it becomes difficult to apply compressive residual stress higher than a certain value. Here, the vertical crack is a crack that divides the hard coating or the surface layer of the tool body, and a gap having a width of about several hundred nm is generated. Vertical cracks release compressive residual stress in a direction perpendicular to the film thickness (surface direction), which is not preferable. According to Japanese Unexamined Patent Application, First Publication No. H06-108258, the maximum value at which compressive residual stress can be stably applied by shot peening is described as about −200 MPa for the hard coating (TiC) and about −800 MPa for the tool body (WC) (compression is considered negative).
In the method of Japanese Unexamined Patent Application, First Publication No. 2012-223808, an oxide layer (Al2O3) which is an upper layer of the hard coating is removed by using the nanosecond laser, and a compressive residual stress of up to about 1 GPa is applied to a non-oxide layer (TiCN) which is a lower layer of the hard coating. This mechanism is not mentioned in the specification of Japanese Unexamined Patent Application, First Publication No. 2012-223808, but is considered to be a kind of so-called laser peening because the lower layer is impacted by the mechanical reaction that occurs when the oxide layer is instantaneously removed in a time on the order of nanoseconds and the oxide layer is scattered by fine particles, plasma, or the like. According to examples of Japanese Unexamined Patent Application, First Publication No. 2012-223808, a compressive residual stress of about 1 GPa can be applied to the lower layer (TiCN) at a peak power density (0.02 GW/cm2) close to the lower limit at which the oxide layer can be removed. However, when a higher peak power density is applied, the compressive residual stress of the lower layer is conversely decreased. It is considered that the reason for this is that the compressive residual stress is released by the effect of heat due to the excessive laser beam hitting the lower layer. However, at a low peak power density of about 0.02 GW/cm2 as in Japanese Unexamined Patent Application, First Publication No. 2012-223808, the effect of applying compressive residual stress to the surface layer of the tool body immediately under the hard coating can hardly be obtained. That is, the fracture resistance of the tool body cannot be improved.
In Japanese Unexamined Patent Application, First Publication No. 2018-183862, although a difference is provided between the residual stress value in the direction orthogonal to the ridge portion of the cutting edge made of α-Al2O3 and the residual stress value in the direction parallel to the ridge portion of the cutting edge by the shot peening, the media are uniformly projected against the rake face during the shot peening, so that it is difficult to stably apply a large residual stress difference.
In the nanosecond laser peening of Published Japanese Translation No. 2020-525301 of the PCT International Publication, it is generally necessary to perform the treatment in a state in which the tool is installed in water in order to increase an impact force. However, in this case, the beam is scattered due to fluctuations in the water surface and bubbles generated in the laser-irradiated portion, and the residual stress of an edge tip varies for each tool, so that there is a problem that the stability of the tool performance as a product is lowered. Another problem is that the process is complicated due to the treatment in water, the need to apply a heat protective layer, and the like.
In view of the above circumstances, an object of the present invention is to provide a method for manufacturing a cutting tool in which a high compressive residual stress can be stably applied to a hard coating and a tool body, thereby improving the fracture resistance of a cutting edge.
According to an aspect of the present invention, there is provided a method for manufacturing a cutting tool, in which the cutting tool includes a tool body made of a sintered alloy, a hard coating which is disposed on an outer surface of the tool body and has at least a layer formed of any of a carbide, a nitride, and a carbonitride, or a composite compound thereof, and a cutting edge which is formed at a ridge portion of the tool body and includes a portion of the hard coating located at the ridge portion, the method including: a laser peening step of directly irradiating the hard coating with a pulsed laser having a pulse width of 100 ps or less to apply compressive residual stress to the hard coating and a surface region of the tool body.
In the method for manufacturing a cutting tool according to the above aspect, the cutting tool in which the hard coating is formed on the outer surface of the tool body is irradiated with a short pulsed laser having a pulse width of 100 ps (picosecond) or less at a peak power density of desirably 1 TW (terawatt)/cm2 or more, for example, in the air from above the hard coating. This treatment is so-called ultrashort pulsed laser peening, and is a technique of applying compressive residual stress to the surface of a workpiece (cutting tool) by generating a shock wave in the workpiece by the mechanical reaction that occurs when a plasma generated by slightly processing the surface of the workpiece subjected to laser irradiation is explosively diffused, and thus applying plastic deformation and crystal defects such as dislocations. In the above aspect of the present invention, by performing the laser peening under the above laser conditions, it is possible to stably apply compressive residual stress while suppressing the occurrence of vertical cracks in the hard coating and the tool body. In addition, by setting the pulse width to 100 ps or less, the effect of heat due to the laser irradiation is significantly suppressed, so that the peak power density, that is, the energy of the shock wave can be increased. Accordingly, for example, a residual stress of 0 or less to the layer (the layer formed of any of a carbide, a nitride, and a carbonitride, or a composite compound thereof) contributing to the fracture resistance of the hard coating, and −1000 MPa or less to WC particles of the surface region of the tool body, that is, a compressive residual stress can be applied.
As described above, according to the method for manufacturing a cutting tool in the above aspect, a high compressive residual stress can be applied to both the hard coating and the tool body while suppressing the occurrence of vertical cracks by the laser peening step under the special laser conditions. Accordingly, the fracture resistance of the cutting edge can be improved. Good cutting accuracy is maintained and the tool life is extended.
Furthermore, since the compressive residual stress can be stably applied, variation in the quality of the cutting tool can be suppressed. In addition, since the laser irradiation can be performed in the air and pre- and post-treatment steps are not particularly required, compared to a generally known stress control technique such as wet blasting, in the present invention, the treatment can be performed easily and at high speed, and the productivity is improved.
In the method for manufacturing a cutting tool, it is preferable that in the laser peening step, the hard coating is irradiated with a pulsed laser having a pulse width of 10 ps or less.
In this case, for example, it is possible to apply a residual stress of −1000 MPa or less to the hard coating and −1500 MPa or less to the surface region of the tool body, that is, a higher compressive residual stress.
In the method for manufacturing a cutting tool, it is preferable that in the laser peening step, the hard coating is irradiated with a pulsed laser having a pulse width of 10 fs or more.
In this case, since the hard coating is irradiated with a short pulsed laser having a pulse width of 10 fs (femtosecond) or more from above, an excessive decrease in the pulse width is suppressed, and the time for applying an impact to the workpiece is secured. Therefore, the impact due to the laser irradiation stably reaches the deep part of the workpiece. High compressive residual stress can be stably applied not only to the hard coating but also the surface region of the tool body.
In the method for manufacturing a cutting tool, it is preferable that in the laser peening step, anisotropy is applied to the compressive residual stress of the hard coating and the tool body in a direction parallel to the cutting edge and in a direction orthogonal to the cutting edge.
In the method for manufacturing a cutting tool, it is preferable that in the laser peening step, a pulsed laser irradiation point interval in the direction parallel to the cutting edge and a pulsed laser irradiation point interval in the direction orthogonal to the cutting edge are caused to be different from each other.
In this case, anisotropy can be applied to the compressive residual stress of the hard coating and the tool body. That is, a difference of a predetermined value or more can be provided between the compressive residual stress value in the direction parallel to the cutting edge and the compressive residual stress value in the direction orthogonal to the cutting edge. For example, unlike the above configuration, compared to a case where the compressive residual stress value is increased as a whole by causing the pulsed laser irradiation point interval in the direction parallel to the cutting edge and the pulsed laser irradiation point interval in the direction orthogonal to the cutting edge to be the same value and a narrow pitch (a case where isotropy is applied), according to the above configuration of the present invention, damage to the hard coating can be suppressed, and the fracture resistance required for the cutting edge can be efficiently applied depending on the kind of cutting, the work material, and the like.
Specifically, by causing the pulsed laser irradiation point interval in the direction parallel to the cutting edge to be smaller than the pulsed laser irradiation point interval in the direction orthogonal to the cutting edge, the compressive residual stress in the direction parallel to the cutting edge can be higher than the compressive residual stress in the direction orthogonal to the cutting edge (the absolute value of the residual stress can be increased). In this case, for example, it is possible to suppress the propagation of so-called thermal cracks in the direction orthogonal to the cutting edge.
Alternatively, by causing the pulsed laser irradiation point interval in the direction orthogonal to the cutting edge to be smaller than the pulsed laser irradiation point interval in the direction parallel to the cutting edge, the compressive residual stress in the direction orthogonal to the cutting edge can be higher than the compressive residual stress in the direction parallel to the cutting edge. In this case, for example, it is possible to suppress the propagation of so-called intermittent cracks in the direction parallel to the cutting edge.
In the method for manufacturing a cutting tool, it is preferable that in the laser peening step, the spot diameter of the pulsed laser irradiating the hard coating is set to 10 μm or more and 200 μm or less.
When the spot diameter is 10 μm or more, local damage or peeling of the hard coating is less likely to occur during laser irradiation. When the spot diameter is 200 m or less, it is possible to suppress a decrease in the value of the compressive residual stress applied to the hard coating and the surface of the tool body. By setting the spot diameter to 20 μm or more and 100 μm or less, the above-mentioned effect can be made more remarkable, which is more desirable.
In the method for manufacturing a cutting tool, in the laser peening step, there are two methods, one is to scan the pulsed laser in the direction parallel to the cutting edge, and the other is to scan the pulsed laser in the direction orthogonal to the cutting edge. However, from the viewpoint of quality, it is preferable to perform scanning with the pulsed laser in the direction orthogonal to the cutting edge.
For example, compared to the case where the pulsed laser is scanned in the direction parallel to the cutting edge, according to the above configuration of the present invention, there are cases where damage to the hard coating is suppressed, and a higher compressive residual stress can be applied. In order to further suppress the damage to the hard coating, it is preferable that the pulsed laser is scanned in a direction that approaches the cutting edge from the position away from the cutting edge, that is, from the rake face side toward the cutting edge in the direction orthogonal to the cutting edge.
According to the method for manufacturing a cutting tool according to one aspect of the present invention, a high compressive residual stress can be stably applied to a hard coating and a tool body, thereby improving the fracture resistance of a cutting edge.
A cutting tool 10 according to an embodiment of the present invention and a method for manufacturing the cutting tool 10 will be described with reference to the drawings. The cutting tool 10 of the present embodiment is a cutting insert. The cutting tool 10 of the present embodiment is used, for example, for an edge tip replaceable insert holder for turning a work material.
As shown in
In the present embodiment, the direction in which a center axis C of the cutting tool 10 extends, that is, the direction parallel to the center axis C is referred to as an axial direction. In a plan view of the cutting tool 10, the center axis C is located at the center of the cutting tool 10. The center axis C extends along the thickness direction of the cutting tool 10.
The direction orthogonal to the center axis C is called a radial direction. In the radial direction, the direction approaching the center axis C is called a radially inward side, and the direction away from the center axis C is called a radially outward side.
The direction about the center axis C is called a peripheral direction.
As shown in
The pair of plate surfaces 10a and 10b have a polygonal shape and face the axial direction of the center axis C. In the present embodiment, the pair of plate surfaces 10a and 10b each have a quadrangular shape. The pair of plate surfaces 10a and 10b has one plate surface (front surface) 10a and the other plate surface (back surface) 10b. The one plate surface 10a and the other plate surface 10b are disposed apart from each other in the axial direction and face opposite to each other in the axial direction.
In the present embodiment, in the axial direction, the direction from the other plate surface 10b toward the one plate surface 10a is called one side in the axial direction, and the direction from the one plate surface 10a toward the other plate surface 10b is called the other side in the axial direction.
Of the pair of plate surfaces 10a and 10b, in at least one plate surface 10a, a part (corner portion or the like) of the plate surface 10a faces a work material (not shown) during cutting.
Of the pair of plate surfaces 10a and 10b, at least one plate surface 10a has a rake face 5. The rake face 5 forms at least a part of the plate surface 10a. In the present embodiment, the rake face 5 is disposed at least each of two corner portions of the four corner portions located on the peripheral edge portion of the plate surface 10a. The two corner portions are disposed at positions with 180-degree rotational symmetry about the center axis C.
As shown in
The land portion 5a is a portion of the rake face 5 connected to the cutting edge 3. The land portion 5a is disposed on the radially inward side of the cutting edge 3. In the present embodiment, the land portion 5a is an inclined surface that inclines toward the other side in the axial direction as it goes toward the radially inward side from the cutting edge 3. The land portion 5a may have a flat plate shape extending in a direction perpendicular to the center axis C.
The inclined portion 5b is a portion of the rake face 5 located on the radially inward side 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 that inclines toward the other side in the axial direction as it goes toward the radially inward side from the land portion 5a. The amount of displacement in the axial direction of the inclined portion 5b per unit length along the radial direction is larger than the amount of displacement in the axial direction of the land portion 5a per unit length along the radial direction. That is, the inclination of the inclined portion 5b with respect to a virtual plane (not shown) perpendicular to the center axis C is larger than the inclination of the land portion 5a with respect to the virtual plane.
As shown in
The outer peripheral surface 10c has a flank face 6. The flank face 6 forms at least a part of the outer peripheral surface 10c. The flank face 6 is disposed in a portion of the outer peripheral surface 10c adjacent to each rake face 5.
The through-hole 10d passes through the cutting tool 10 in the axial direction. The through-hole 10d opens to the pair of plate surfaces 10a and 10b and extends in the axial direction. The center axis of the through-hole 10d is disposed coaxially with the center axis C. In the shown example, the through-hole 10d has a circular hole shape. For example, a clamp screw (not shown) or the like is inserted into the through-hole 10d.
The cutting edge 3 is formed at a ridge portion where the rake face 5 and the flank face 6 are connected to each other, that is, an intersecting ridge portion between the rake face 5 and the flank face 6. In the present embodiment, the cutting edge 3 is disposed at least each of two corner portions of the four corner portions located on the peripheral edge portion of the plate surface 10a. As shown in
As shown in
The cutting edge 3 is formed of the ridge portion (the intersecting ridge portion) of the tool body 1 and a portion of the hard coating 2 coating the ridge portion.
As shown in
Through a laser peening step, which will be described later, the residual stress in a surface region of the tool body 1 is, for example, −1000 MPa or less, and preferably −1500 MPa or less. The surface region (surface layer) of the tool body 1 may be a region from the surface of the tool body 1 to a depth of at least 1 μm.
As shown in
The film thickness of the hard coating 2 is, for example, 1 μm or more and 30 μm or less as a whole. The hard coating 2 is formed of a single layer or a plurality of layers. In the present embodiment, the hard coating 2 is formed of a plurality of layers laminated on the outer surface of the tool body 1. The hard coating 2 has the first layer 2a located on the outer surface of the tool body 1 and a second layer 2b located on the first layer 2a. The hard coating 2 may have a third layer (not shown) located on the second layer 2b. Furthermore, the hard coating 2 may be formed of four or more layers. Of the plurality of layers of the hard coating 2, the thickest layer is the first layer 2a. In a case where the hard coating 2 is a single layer, the hard coating 2 has the first layer 2a. That is, the hard coating 2 has at least the first layer (layer) 2a. The film thickness of the first layer 2a is, for example, 1 μm or more and 20 μm or less.
Through the laser peening step described later, the residual stress of the hard coating 2, specifically, the residual stress of the first layer 2a is 0 MPa or less (that is, the compressive residual stress is applied), and preferably −1000 MPa or less.
The first layer 2a is disposed on the outer surface of the tool body 1 directly or indirectly with an intermediate layer (not shown) interposed therebetween. The first layer 2a is formed of any of a carbide, a nitride, and a carbonitride, or a composite compound thereof. The first layer 2a is, for example, a TiCN layer or the like. The TiCN layer subjected to the laser peening step described later improves the fracture resistance of the cutting edge 3.
The second layer 2b is disposed on the outer surface of the first layer 2a directly or indirectly with an intermediate layer (not shown) interposed therebetween. The second layer 2b is formed of a carbide, a nitride, a carbonitride, an oxide, or a boride of Group 4a, 5a, and 6a metals of the periodic table, a carbide, a nitride, or a carbonitride of Si, an oxide or a nitride of Al, a mutual solid solution thereof, diamond, cubic boron nitride, or the like. Since the second layer 2b is not limited by the film type of the first layer 2a of the hard coating 2, those generally used as a hard coating for a cutting tool are listed here. The second layer 2b is, for example, an Al2O3 layer or a TiN layer. Alternatively, the second layer 2b may be an Al2O3 layer, and the third layer (not shown) may be a TiN layer. By providing the Al2O3 layer, the heat resistance and wear resistance of the rake face 5 and the cutting edge 3 are improved. By providing the TiN layer, the external appearance of the cutting tool 10 is enhanced, and whether or not the cutting tool 10 has been used, that is, whether the cutting tool 10 has been used or not can be easily identified.
In the example shown in
Next, a method for manufacturing the cutting tool 10 will be described.
The method for manufacturing the cutting tool 10 of the present embodiment includes a sintering step, a film forming step, and the laser peening step.
In the sintering step, a green compact in the shape of the tool body 1, that is, an intermediate formed body formed by compacting in the manufacturing process of the tool body 1 is sintered. In the present embodiment, the green compact has a plate shape, specifically, a polygonal plate shape.
In the film forming step, the hard coating 2 having a layer formed of any of a carbide, a nitride, and a carbonitride, or a composite compound thereof is formed on the outer surface of the sintered tool body 1. That is, in the film forming step, the hard coating 2 having at least the first layer 2a is formed on the outer surface of the tool body 1. In the present embodiment, the first layer 2a is formed on the outer surface of the tool body 1 directly or indirectly with an intermediate layer (not shown) interposed therebetween, and the second layer 2b is formed on the first layer 2a directly or indirectly with an intermediate layer (not shown) interposed therebetween. Although not particularly shown, the third layer may be formed on the second layer 2b directly or indirectly with an intermediate layer interposed therebetween. Alternatively, the hard coating 2 formed of four or more layers including the first layer 2a, the second layer 2b, and the third layer may be formed.
As shown in
More preferably, in the laser peening step, the hard coating 2 is irradiated with a pulsed laser L having a pulse width of 10 fs (femtosecond) or more. More desirably, in the laser peening step, the hard coating 2 is irradiated with a pulsed laser L having a pulse width of 500 fs or more.
The peak power density of the pulsed laser L is preferably 1 TW (terawatt)/cm2 or more, more preferably 5 TW/cm2 or more, and even more desirably 20 TW/cm2 or more. As described above, by applying an impact at 1 TW (terawatt)/cm2 or more, high compressive residual stress can be stably applied to the tool body 1 and the hard coating 2. More preferably, the peak power density is 10 PW (petawatt)/cm2 or less. The reason is that plasma due to air breakdown is generated from around 10 PW (petawatt)/cm2, and shields the laser beam.
As shown in
Specifically, the range A is hatched by laser beam scanning using a galvano scanner and an fθ lens (not shown). The treatment atmosphere at this time is the air or a gas. The gas is, for example, an inert gas that suppresses oxidation. The laser beam is a pulsed laser L having a pulse width of 100 ps or less, and desirably, a laser beam adjusted by appropriately changing the pulse width and pulse energy so that the peak power density is 1 TW/cm2 or more is used. The peak power density is a value calculated by pulse energy/(pulse width×spot area). It is appropriate that the spot diameter on the surface of the workpiece (the cutting tool 10) for the pulsed laser L is 10 m or more and 200 μm or less. That is, in the laser peening step, it is preferable that the spot diameter of the pulsed laser L irradiating the hard coating 2 is 10 μm or more and 200 μm or less. When the spot diameter is 10 μm or more, local peeling of the hard coating 2 is less likely to occur during laser irradiation. When local peeling of the hard coating 2 occurs, the strength of the edge tip is significantly reduced. Therefore, it is necessary to suppress the occurrence of local peeling. When the spot diameter is 200 m or less, it is possible to suppress a decrease in the value of the compressive residual stress applied to the hard coating 2 and the surface of the tool body 1. It is more desirable that the spot diameter is set to 20 μm or more and 100 μm or less.
In the present embodiment, in the laser peening step, anisotropy is applied to the compressive residual stress of the hard coating 2 and the tool body 1 in the direction parallel to the cutting edge 3 and the direction orthogonal to the cutting edge 3. Specifically, as shown in
In the laser peening step, the pulsed laser L is scanned in the direction orthogonal to the cutting edge 3. Specifically, as shown in
Specifically, the scanning direction S is a direction that approaches the cutting edge 3 in the direction orthogonal to the cutting edge 3. In the present embodiment, the radially outer end portion of the inclined portion 5b, the land portion 5a, and the cutting edge 3 are scanned with the pulsed laser L in this order along the direction orthogonal to the cutting edge 3. That is, the pulsed laser L is scanned in a direction from the rake face 5 toward the cutting edge 3 in the direction orthogonal to the cutting edge 3.
A plurality of circles shown by the two-dot chain lines in
In the method for manufacturing the cutting tool 10 of the present embodiment described above, the cutting tool 10 in which the hard coating 2 is formed on the outer surface of the tool body 1 is irradiated with a short pulsed laser having a pulse width of 100 ps or less, for example, in the air from above the hard coating 2. This treatment is so-called ultrashort pulsed laser peening, and is a technique of applying compressive residual stress to the surface of a workpiece by generating a shock wave in the workpiece by the mechanical reaction that occurs when a plasma generated by slightly processing the surface of the workpiece (cutting tool 10) subjected to laser irradiation is explosively diffused, and thus applying plastic deformation and crystal defects such as dislocations. In the present embodiment, by performing the laser peening under the above laser conditions, it is possible to stably apply compressive residual stress while suppressing the occurrence of vertical cracks in the hard coating 2 and the tool body 1. In addition, by setting the pulse width to 100 ps or less, the effect of heat due to the laser irradiation is significantly suppressed, so that the peak power density, that is, the energy of the shock wave can be increased. Accordingly, for example, a residual stress of 0 or less to the first layer 2a, which is a layer contributing to the fracture resistance of the hard coating 2, and −1000 MPa or less to WC particles of the surface region of the tool body 1, that is, a compressive residual stress can be applied.
As described above, according to the present embodiment, a high compressive residual stress can be applied to both the hard coating 2 and the tool body 1 while suppressing the occurrence of vertical cracks by the laser peening step under the special laser conditions. Accordingly, the fracture resistance of the cutting edge 3 can be improved. Good cutting accuracy is maintained and the tool life is extended.
Furthermore, since the compressive residual stress can be stably applied, variation in the quality of the cutting tool 10 can be suppressed. In addition, since the laser irradiation can be performed in the air and pre- and post-treatment steps are not particularly required, compared to a generally known stress control technique such as wet blasting, in the present embodiment, the treatment can be performed easily and at high speed, and the productivity is improved.
In the present embodiment, it is preferable that in the laser peening step, the hard coating 2 is irradiated with a pulsed laser L having a pulse width of 10 ps or less.
In this case, for example, it is possible to apply a residual stress of −1000 MPa or less to the hard coating 2 and −1500 MPa or less to the surface region of the tool body 1, that is, a higher compressive residual stress.
More preferably, in the laser peening step, the hard coating 2 is irradiated with a pulsed laser L having a pulse width of 2 ps or less. In this case, for example, it is possible to apply a residual stress of −1500 MPa or less to the hard coating 2 and −2000 MPa or less to the surface region of the tool body 1, that is, a higher compressive residual stress.
In the present embodiment, it is preferable that in the laser peening step, the hard coating 2 is irradiated with a pulsed laser L having a pulse width of 10 fs or more.
In this case, an excessive decrease in the pulse width of the pulsed laser L is suppressed, and the time for applying an impact to the workpiece is secured. Therefore, the impact due to the laser irradiation stably reaches the deep part of the workpiece, that is, the surface region of the tool body 1 immediately under the hard coating 2. High compressive residual stress can be stably applied to both the hard coating 2 and the tool body 1. More preferably, in the laser peening step, the hard coating 2 is irradiated with a pulsed laser L having a pulse width of 500 fs or more. Accordingly, the above-mentioned effect becomes more remarkable.
In the present embodiment, in the laser peening step, anisotropy is applied to the compressive residual stress of the hard coating 2 and the tool body 1 in the direction parallel to the cutting edge 3 and in the direction orthogonal to the cutting edge 3. Specifically, in the laser peening step in the present embodiment, the pulsed laser irradiation point interval Dy in the direction parallel to the cutting edge 3 and the pulsed laser irradiation point interval Dx in the direction orthogonal to the cutting edge 3 are caused to be different from each other.
In this case, anisotropy can be applied to the compressive residual stress of the hard coating 2 and the tool body 1. That is, a difference of a predetermined value or more can be provided between the compressive residual stress value in the direction parallel to the cutting edge 3 and the compressive residual stress value in the direction orthogonal to the cutting edge 3. For example, unlike the above configuration, compared to a case where the compressive residual stress value is increased as a whole by causing the pulsed laser irradiation point interval Dy in the direction parallel to the cutting edge 3 and the pulsed laser irradiation point interval Dx in the direction orthogonal to the cutting edge 3 to be the same value and a narrow pitch (a case where isotropy is applied), according to the above configuration of the present embodiment, damage to the hard coating 2 can be suppressed, and the fracture resistance required for the cutting edge 3 can be efficiently applied depending on the kind of cutting, the work material, and the like.
Specifically, by causing the pulsed laser irradiation point interval Dy in the direction parallel to the cutting edge 3 to be smaller than the pulsed laser irradiation point interval Dx in the direction orthogonal to the cutting edge 3, the compressive residual stress in the direction parallel to the cutting edge 3 can be higher than the compressive residual stress in the direction orthogonal to the cutting edge 3 (the absolute value of the residual stress can be increased). In this case, for example, it is possible to suppress the propagation of so-called thermal cracks in the direction orthogonal to the cutting edge 3.
Alternatively, by causing the pulsed laser irradiation point interval Dx in the direction orthogonal to the cutting edge 3 to be smaller than the pulsed laser irradiation point interval Dy in the direction parallel to the cutting edge 3, the compressive residual stress in the direction orthogonal to the cutting edge 3 can be higher than the compressive residual stress in the direction parallel to the cutting edge 3. In this case, for example, it is possible to suppress the propagation of so-called intermittent cracks in the direction parallel to the cutting edge 3.
In the present embodiment, it is preferable that in the laser peening step, the spot diameter of the pulsed laser L irradiating the hard coating 2 is set to 10 μm or more and 200 μm or less.
When the spot diameter is 10 μm or more, local damage or peeling of the hard coating 2 is less likely to occur during laser irradiation. When the spot diameter is 200 m or less, it is possible to suppress a decrease in the value of the compressive residual stress applied to the hard coating 2 and the surface of the tool body 1. By setting the spot diameter to 20 μm or more and 100 μm or less, the above-mentioned effect can be made more remarkable, which is more desirable.
In the present embodiment, in the laser peening step, the pulsed laser L is scanned in the scanning direction S, that is, in the direction orthogonal to the cutting edge 3.
For example, compared to a case where the pulsed laser L is scanned in the direction parallel to the cutting edge 3, according to the above configuration of the present embodiment, damage to the hard coating 2 is suppressed. In order to further suppress the damage to the hard coating 2, it is preferable that the pulsed laser L is scanned in a direction that approaches the cutting edge 3 from the position away from the cutting edge 3, that is, from the rake face 5 side toward the cutting edge 3 in the direction orthogonal to the cutting edge 3.
The present invention is not limited to the above-described embodiment, and changes and the like in the configuration can be made without departing from the gist of the present invention, for example, as described below.
In the above-described embodiment, in the laser peening step, anisotropy is applied to the compressive residual stress by causing the pulsed laser irradiation point interval Dy in the direction parallel to the cutting edge 3 and the pulsed laser irradiation point interval Dx in the direction orthogonal to the cutting edge 3 to be different from each other. However, the present invention is not limited thereto, and for example, anisotropy may be applied to the compressive residual stress by changing the peak power density in the direction orthogonal to the cutting edge 3, that is, in the scanning direction S of the pulsed laser L, or in the direction parallel to the cutting edge 3, that is, in a direction orthogonal to the scanning direction S of the pulsed laser L (for example, for each predetermined scanning unit) while setting the pulsed laser irradiation point intervals Dy and Dx to the same value (constant).
In the case of this modification example, since the scanning is performed along the cutting edge 3, the laser peening treatment can be performed at high speed, and the production efficiency of the cutting tool 10 is high. In addition, as shown in
In the above-described embodiment, the cutting tool 10 used for the edge tip replaceable insert holder is taken as an example, but the cutting tool 10 is not limited thereto. The cutting tool 10 may be used, for example, in an edge tip replaceable drill, an edge tip replaceable end mill, or the like for milling a work material.
In addition, the cutting tool 10 which is a cutting insert is taken as an example, but the cutting tool 10 is not limited thereto. The cutting tool 10 may be, for example, a solid type drill, an end mill, a reamer, or other cutting tools.
In addition, configurations (constituent elements) described in the above embodiment, the modification examples, and supplements may be combined, and additions, omissions, substitutions, and other changes can be made without departing from the gist of the present invention. Furthermore, the present invention is not limited to the above-described embodiment, but is limited only to the scope of claims.
Hereinafter, the present invention will be specifically described with reference to examples. However, the present invention is not limited to the examples.
As the examples and comparative examples of the present invention, a plurality of laser-untreated cutting tools 10, that is, cutting inserts described in the above-described embodiment were prepared. Specifically, these cutting tools 10 were cutting inserts having a JIS standard CNMG120408 shape. The tool body 1 was made of a WC cemented carbide having a composition of 7.5 mass % of Co and an average WC particle size of 1.5 μm. As the hard coating 2, 4 μm of a TiCN layer as the first layer 2a, 1 μm of an Al2O3 layer as the second layer 2b, and 0.3 μm of a TiN layer as the third layer were formed on the outer surface of the tool body 1 in this order by a chemical vapor deposition (CVD) method.
In a post-step of this film formation, each cutting tool 10 was subjected to a laser treatment, that is, a laser peening step. Specifically, in the air, the rake face 5 of the cutting tool 10 was irradiated and scanned with a laser beam vertically, that is, in the axial direction such that the rake face 5 and the cutting edge 3 were subjected to the laser treatment. In all of the examples and comparative examples, no sacrificial film was formed on the hard coating 2, and the laser treatment was directly performed on the hard coating 2. The wavelength of the laser used was 1030 nm, the repetition rate was 10 kHz, the beam profile was Gaussian, and the spot diameter on the surface of the workpiece was φ30 μm.
Specifically, in order to investigate the relationship between the laser peak power density and the residual stress of each of the first layer 2a of the hard coating 2 and the surface region of and the tool body 1, the laser peening step was performed on each of the cutting tools 10 under different laser conditions. As for the laser conditions, the pulsed laser irradiation point intervals Dx and Dy were both set to 20 μm, the pulse width was adjusted in a range of 10 fs (femtosecond) to 10 ns (nanosecond), and the pulse energy was adjusted in a range of 0.4 mJ to 2 mJ, and the peak power density was changed in a range of 41 GW (gigawatt)/cm2 to 5.66 PW (petawatt)/cm2.
Among the above laser conditions, the cutting tools 10 irradiated with a pulsed laser having a pulse width of 100 ps or less (and a peak power density of 1 TW/cm2 or more) were Examples 1 to 10 of the present invention, and the cutting tools subjected to laser irradiation under other laser conditions were Comparative Examples 1 to 4. The untreated cutting tool that was not subjected to laser irradiation was Comparative Example 5.
The residual stress of each cutting tool 10 was measured as follows. The residual stresses of the tool body 1 and the hard coating 2 (first layer 2a) were measured by using an X-ray residual stress measuring device manufactured by Pulstec Industrial Co., Ltd. and using a cosa method. A Cu tube was used as an X-ray source, and a WC (113) diffraction peak near 2θ=154° and a TiCN (431) diffraction peak near 2θ=133° were used to measure each residual stress. Using an X-ray shielding plate, only a width of 0.3 mm was exposed from the tip end of the edge tip of the cutting edge 3, and measurement was performed so that the stress value was obtained only in the laser-treated portion.
The relationship between the laser conditions and the measured residual stress values is shown in Tables 1 and
The criteria for determination in Table 1 are as follows.
A: The residual stress of TiCN (hard coating) is −1500 MPa or less, and the residual stress of WC (tool body) is −2000 MPa or less, so that the effect of increasing the compressive residual stress is particularly significantly obtained.
B: The residual stress of TiCN (hard coating) is −1000 MPa or less, and the residual stress of WC (tool body) is −1500 MPa or less, so that the effect of increasing the compressive residual stress is significantly obtained.
C: The residual stress of TiCN (hard coating) is 0 MPa or less, and the residual stress of WC (tool body) is −1000 MPa or less, so that the effect of increasing the compressive residual stress is significantly obtained.
D: The criteria of C are not satisfied, so that the effect of increasing the compressive residual stress is not significantly obtained. Specifically, the residual stress of TiCN (hard coating) exceeds 0 MPa, and the residual stress of WC (tool body) exceeds −1000 MPa.
As shown in Table 1, Examples 1 to 10 were determined as A, B, or C, so that the compressive residual stress was significantly increased. Specifically, it was confirmed that Examples 1 to 8 were determined as A or B, and a more significant effect was obtained. Particularly, it could be seen that Examples 4 to 6 were determined as A, and the compressive residual stress was particularly significantly increased. In Examples 1 to 3, the residual stress of TiCN (hard coating) reached −2000 MPa, but the residual stress of WC (tool body) did not reach −2000 MPa. It is considered that the reason for this is that when the pulse width becomes smaller than a predetermined value, the time for which an impact is applied to the workpiece is shortened, and the impact does not sufficiently reach the deep part of the workpiece.
On the other hand, Comparative Examples 1 to 4 were determined as D. Under the laser conditions of Comparative Examples 3 and 4 in which the pulse width was 1 ns or more, it was not possible to apply the compressive residual stress to WC (tool body). It is considered that the reason for this is the effect of heat.
Next, in order to investigate the relationship between the pulsed laser irradiation point intervals Dx and Dy and the anisotropy of the compressive residual stress, the laser peening step was performed on each of the cutting tools 10 under different laser conditions. As for the laser conditions, all the pulsed laser irradiation point intervals Dy in the direction parallel to the cutting edge 3 were set to 15 μm, and the pulsed laser irradiation point intervals Dx in the direction orthogonal to the cutting edge 3 were changed to 25 μm, 35 μm, and 50 μm for each of the cutting tools 10 such that Examples 11 to 13 were set. The laser conditions other than the above were set to the same as those in Example 5 described above.
The residual stress of each of the cutting tools 10 was measured in the same manner as in the measurement method described above. Then, the residual stress values Gx and Gy were measured by changing the X-ray incident direction in the x direction (the direction orthogonal to the cutting edge 3) and the y direction (the direction parallel to the cutting edge 3). The results are shown in Table 2 below.
As shown in Table 2, in each of Examples 11 to 13, there was a difference between the residual stress in the x direction and the residual stress in the y direction of TiCN (hard coating), and there was a difference between the residual stress in the x direction and the residual stress in the y direction of WC (tool body). That is, it was confirmed that in Examples 11 to 13, anisotropy was applied to the compressive residual stress. In addition, there was a trend that the anisotropy became more significant as the difference between the pulsed laser irradiation point intervals Dx and Dy increased. For example, in Example 13, a difference of more than 1000 MPa could be provided between the residual stress in the x direction and the residual stress in the y direction of the WC (tool body).
According to the method for manufacturing a cutting tool of the present invention, a high compressive residual stress can be stably applied to a hard coating and a tool body, thereby improving the fracture resistance of a cutting edge. Therefore, industrial applicability is achieved.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2020-017887 | Feb 2020 | JP | national |
| 2021-015304 | Feb 2021 | JP | national |
This application is a U.S. National Phase Application under 35 U.S.C. § 371 of International Patent Application No. PCT/JP2021/004403 filed on Feb. 5, 2021 and claims the benefit of priority to Japanese Patent Applications No. 2020-017887 filed on Feb. 5, 2020, and No. 2021-015304 filed on Feb. 2, 2021, the contents of all of which are incorporated herein by reference in their entireties. The International Application was published in Japanese on Aug. 12, 2021 as International Publication No. WO/2021/157716 under PCT Article 21(2).
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2021/004403 | 2/5/2021 | WO |
