JP4711638B2 - Throwaway tip - Google Patents

Description

  The present invention relates to a throw-away tip whose surface is coated with a coating layer.

  In the metal cutting field, the processing conditions are becoming stricter year by year, and as a cutting tool used therefor, a throw-away tip in which a coating layer is coated on the surface of a hard sintered base material such as cemented carbide or cermet has become widespread. In such a throw-away tip, it is well known that when the coating layer is thickened, the wear resistance is improved, but the toughness of the cutting edge is deteriorated.

As a method for solving this problem, a method of partially thinning or removing the coating layer of the cutting edge portion by honing as in Patent Document 1 has been proposed. Further, according to Patent Document 2, it is described that local damage of the coating layer in the cutting edge portion can be prevented by smoothly honing the surface roughness of this coating layer to 0.2 μm or less at Rmax. .
JP-A-2-48103 Japanese Patent Laid-Open No. 1-16302

  However, recently, the machining conditions tend to be severe, and the requirement to extend the tool life for the throw-away inserts has become stricter, and the coating layer on the conventional cutting blade is simply thinned by honing. Even with smooth throw-away inserts, cutting forces with a particularly high load due to severe cutting conditions such as the machining of difficult-to-cut materials such as stainless steel, Ti alloys and Pb-free free-cutting steel In the rake face side cutting edge area on the rake face side from the center, the coating layer is strongly impacted and the coating layer is peeled off, chipping generated in the cutting edge part cannot be suppressed, or chipping resistance In the specification where the coating layer thickness is thin for emphasis, the coating layer wear progresses quickly and coating There will be worn at an early stage, there is a limit to the tool life in any case.

  The present invention has been made in order to solve the above-mentioned problems, and an object of the present invention is to provide a throw-away tip having a coating layer that has excellent wear resistance and can improve the chipping resistance of the cutting edge portion. It is to provide.

  In the present invention, the surface roughness in the flank side cutting edge region from the cutting edge central portion toward the flank face while reducing the surface roughness of the coating layer in the cutting edge portion as a whole, It is characterized by adjusting and polishing so as to be smaller than the surface roughness in the rake face side cutting edge region from the center of the cutting edge toward the rake face.

  As a result, the temperature of the contacted work material can be increased by increasing the cutting edge temperature at the time of cutting, and the deformation of the work material can be promoted to reduce the cutting resistance. However, the cutting resistance does not become excessively large, and the chipping resistance can be improved. In addition, the flank face cutting edge region that has the greatest effect on the finished surface roughness of the work material has good welding resistance. Since the finished surface roughness of the work material can be increased, chipping generated at the cutting edge can be suppressed while maintaining high wear resistance, resulting in a long-lasting throw-away tip. .

  In addition, since the polishing amount in the rake face side cutting edge region in the above configuration is smaller than the polishing amount in the flank face cutting edge region, the thickness of the coating layer in the rake face side cutting edge region where wear is most likely to proceed during cutting. Thus, the life of the rake face side cutting edge region due to wear can be prevented.

That is, the throw-away tip of the present invention is a throw-away tip in which the surface of a base material made of a hard sintered body is coated with a coating layer harder than the base material, and the polishing end position of the flank side cutting edge region The base material before coating the coating layer is honed so that the adhesion strength of the coating layer is higher than the adhesion strength at the center portion of the flank, and the average arithmetic mean at the center portion of the rake face Polishing is performed so that the roughness (Ra) is smaller than the average arithmetic average roughness (Ra) at the center portion of the flank face, and includes a cross ridge from the rake face side on the surface of the coating layer. The cutting edge region extending over the flank side is polished and the flank side cutting edge region located on the flank side of the cutting edge region. Surface roughness in the outermost surface is TiN of the is polished so as to be smaller than the surface roughness on the rake face side cutting edge region located rake face side, and the coating layer of the cutting edge region, TiC , TiCN, TiCO, TiNO and TiCNO are selected from the group consisting of TiCNO, and the Ti-based surface layer is the most in the flank side cutting edge region from the center of the cutting edge to the flank side. It is polished .

  Here, the presence of polishing scratches on the polishing surface of the coating layer can release residual stress generated in the coating layer and prevent the coating layer from peeling off from the base material. It is desirable in terms of the effect that it can be improved.

  Moreover, the average arithmetic mean roughness (Ra) in the flank side cutting edge area | region which goes to the said flank from the said cutting edge center part is 0.05-0.35 micrometer, The rake face side which goes to the rake face from the said cutting edge center part The average arithmetic average roughness (Ra) in the cutting edge region is preferably 0.10 to 0.45 μm from the viewpoints of improving wear resistance, reducing cutting resistance, welding resistance, and fracture resistance.

Further, the distance L _A from flank to the polishing end position P _A of the rake face side cutting edge _region, the flank side switching from the rake face as viewed from the flank when viewed from the rake face when the distance L _B to the polishing end position P _B of the blade area, the ratio (L a _{/ L B)} is to be 0.8 to 3, improvement and high fracture resistance by improving the impact resistance This is desirable in terms of achieving both wear resistance and maintenance.

Furthermore, the outermost surface of the coating layer is made of a Ti-based surface layer, and the Ti-based surface layer is most polished in the flank face side cutting edge region on the flank face side from the cutting blade center part, In order to reduce the residual stress in the coating layer and improve the fracture resistance of the coating layer, and to solve the problem of welding and coating layer oxidation due to rising cutting edge temperature without increasing the cutting resistance during processing Is important .

Furthermore, the Al ₂ O ₃ layer existing under the Ti-based surface layer is exposed at the most polished portion of the Ti-based surface layer, which indicates that the coating layer has welding resistance and oxidation resistance. It is desirable in terms of improving the finished surface roughness of the work material by improving the plastic deformation resistance.

Further, the average arithmetic average roughness (Ra) at the center portion of the rake face following the rake face side cutting edge region is larger than the average arithmetic average roughness (Ra) at the center portion of the flank face following the flank side cutting edge region. Polishing to be small is important in terms of improving chip discharge. In addition, in a double-sided chip in which both surfaces become rake surfaces in order, there is an effect that it is possible to prevent back chipping when arranged on the seat surface.

  Furthermore, the presence of the polished Ti-based surface layer at the center portion of the rake face following the rake face side cutting edge region results in a beautiful appearance with a shiny gold color, and the use / unused state of the cutting edge is visually observed. This is desirable because it can be easily confirmed.

  According to the throw-away tip of the present invention, the surface roughness in the flank side cutting edge region toward the flank from the center of the cutting edge while reducing the overall surface roughness of the coating layer in the cutting edge, By adjusting and polishing so as to be smaller than the surface roughness in the rake face side cutting edge region from the central portion of the cutting edge toward the rake face, the cutting edge temperature of the cutting material is increased and contacted. The temperature can be increased, the deformation of the work material can be promoted, and the cutting resistance can be reduced. As a result, the cutting resistance is not increased excessively even under severe cutting conditions, and the fracture resistance is increased. In the flank face cutting edge region that has the greatest influence on the finished surface roughness of the work material, it is possible to show good welding resistance and increase the finished surface roughness of the work material. Abrasion resistance It is possible to suppress the chipping that occurs in the cutting edge portion while maintaining the sex is of a long life cutting insert.

  In addition, since the polishing amount in the rake face side cutting edge region in the above configuration is smaller than the polishing amount in the flank face cutting edge region, the thickness of the coating layer in the rake face side cutting edge region where wear is most likely to proceed during cutting. Thus, the life of the rake face side cutting edge region due to wear can be prevented.

  An example of the throw-away tip (hereinafter simply referred to as a tip) of the present invention will be described with reference to FIG.

  According to FIG. 1, a chip 1 has a cutting edge 5 formed at a crossing ridge portion between a main surface forming a rake surface 3 and a side surface forming a flank 4 of a base material 2 having a substantially flat plate shape, and the base material 2. A coating layer 6 is coated on the surface. Further, according to FIG. 1, a honing portion 8 is provided from the rake face 3 to the flank face 4 of the cutting edge 5.

  According to the present invention, with respect to the cutting edge 5 region extending from the rake face 3 to the flank face 4 including the intersecting ridges on the surface of the coating layer 6, in the flank face edge area 10 on the flank face 4 side from the cutting edge central portion 8. A major feature is that the surface roughness is smaller than the surface roughness in the rake face side cutting edge region 9 on the rake face 3 side from the cutting edge central portion 8, whereby the cutting resistance is excessive even under severe cutting conditions. Therefore, the chipping generated in the cutting edge portion can be suppressed while maintaining high wear resistance without lowering the welding resistance of the cutting edge portion. In the present invention, when the total thickness of the coating layer 6 is 15 μm or less, particularly when the coating layer 6 is 10 to 15 μm, the coating layer 6 is not particularly peeled off, and the balance between fracture resistance and wear resistance is good and effective. In addition, the tool life can be extended.

  In addition, the cutting blade center part 8 in this invention points out the ridgeline part which protrudes most when the cutting blade 5 is observed in the state which inclined the seating surface of the chip | tip 1 by 45 degrees.

Here, the presence of polishing flaws on the polishing surface of the coating layer 6 can release the residual stress generated in the coating layer 6 and prevent the coating layer 6 from peeling from the base material 2, This is desirable in terms of the effect of improving the fracture resistance. Incidentally, the above polishing scratches refers to one of the streaks, it by machining abrasive as lapping or brushing is polished while rubbing the coating layer surface. Further, it is desirable in terms of stress relaxation that the polishing scratches are in random directions.

  Further, the average arithmetic average roughness (Ra) in the flank face cutting edge region 10 on the flank face 4 side from the cutting edge central portion 8 is 0.05 to 0.35 μm, and rake is directed from the cutting edge central portion 8 toward the rake face 3. When the average arithmetic average roughness (Ra) in the surface-side cutting edge region 9 is 0.10 to 0.45 μm, the wear resistance is improved, the cutting resistance is reduced, the welding resistance and the fracture resistance are improved. Is desirable.

  In addition, regarding the measurement of the surface roughness of the coating layer 6 surface in the present invention, a contact type surface roughness meter is used or a non-contact type laser microscope is used so that the measurement surface is perpendicular to the laser microscope. Measure while moving the tip. When the cutting edge shape itself has waviness, the surface roughness is calculated after subtracting this waviness and approximating a straight line.

Furthermore, the rake face 3 when viewed flank 4 when viewed from the rake face 3 (the side surface of the chip 1) the distance L _A to the polishing end position P _A of the rake face side cutting edge region _9, the flank 4 when the distance _{L B} to the polishing end position _{P B} of the flank side cutting edge region 10 from (the side surface of the chip 1), the ratio _(L a / _{L B)} is 0.8 to 3, especially 1 to 2, Further, 1.1 to 1.5 is desirable from the viewpoint of achieving both improvement in fracture resistance due to improvement in impact resistance and maintenance of high wear resistance.

Furthermore, the outermost surface of the coating layer 6 is made of a Ti-based surface layer, and the Ti-based surface layer is most polished in the flank face-side cutting edge region 10 on the flank face 4 side from the cutting edge central portion 8. It is important for reducing the residual stress in the coating layer 6 and improving the fracture resistance of the coating layer 6 and smoothing the finished surface roughness of the work material without increasing the cutting resistance during processing. There is .

Furthermore, the Al ₂ O ₃ layer existing under the Ti-based surface layer is exposed in the most polished portion of the Ti-based surface layer, which indicates that the coating layer 6 has welding resistance and oxidation resistance. It is desirable in terms of improving the finished surface roughness of the work material by improving the workability and plastic deformation resistance.

Here, above the exposed the Al ₂ O ₃ layer that can maintain a stable cutting characteristics that the crystal structure is α-type the Al ₂ O ₃ layer is to enhance the stability of the Al ₂ O ₃ layer during cutting Is desirable. In general, the α-type Al ₂ O ₃ layer tends to be coarsened during the film formation process and the surface roughness tends to be low. However, according to the present invention, when the α-type Al ₂ O ₃ layer is formed, However, it is possible to exhibit excellent cutting performance as a cutting blade 4 that is smooth and has a surface state constituted by the specific surface roughness.

The crystal structure of the Al ₂ O ₃ layer can be confirmed by XRD measurement on the surface. In addition, this effect is lost even in a layer in which the peak of the κ-type Al ₂ O ₃ layer is mixed at a peak intensity ratio of 1/5 or less with respect to the main peak of the α-type Al ₂ O ₃ layer in XRD measurement. Absent.

  Further, the average arithmetic average roughness (Ra) in the rake face central portion 12 following the rake face side cutting edge region 9 is the average arithmetic average roughness (Ra) in the flank face central portion 13 following the flank face cutting edge region 10. Polishing to be smaller than that is desirable in terms of improving chip discharge. In addition, in a double-sided chip in which both surfaces sequentially become the rake face 3, there is also an effect that it is possible to prevent back chipping when arranged on the seat surface.

  Further, the remaining Ti-based surface layer in the rake face central portion 12 following the rake face side cutting edge region 9 results in a beautiful appearance with a glossy yellowish color and the use / unuse of the cutting edge. It is desirable in that the use state can be easily confirmed visually.

Further, according to the present invention, it is important that the base material 2 is subjected to a honing process (hereinafter abbreviated as a base material honing portion 15) on the cutting edge (crossing ridge) 5 before forming the coating layer 6. It is . At this time, it is desirable that the adhesion strength of the coating layer 6 at the polishing end position of the flank side cutting edge region 10 is higher than the adhesion strength at the central portion 13 of the flank surface 4, and thereby, particularly at the time of cutting, the work material The coating layer 6 on the cutting edge 5 is improved by improving the adhesion of the coating layer 6 near the end 16 of the base material honing portion 15 that becomes a cutting edge ridge line that is likely to generate microchipping due to peeling of the coating layer 6 due to friction. Therefore, chipping resistance and wear resistance of the chip 1 can be remarkably improved, and the life of the chip 1 can be extended.

  The adhesion strength in the present invention refers to the adhesion strength of the coating layer 6 measured by a so-called scratch test in which the surface of the coating layer 6 is rubbed with a load cell and the strength at which the coating layer 6 is peeled off is measured.

  Here, the improvement of the adhesion strength of the coating layer 6 is effective when performed on the vicinity 17 of the end of the base material honing part 15 that is the cutting edge ridge line, but from the side end position (rake face 3) of the chip. It is sufficient to improve the adhesion strength in the region where the height H is up to 1 mm, and the conditions where the adhesion strength is improved in the range where the height H exceeds 1 mm may increase costs and honing time. It is not practical for manufacturing.

  Further, according to FIG. 1, the base material honing unit 15 is R honing, but it may be chamfer honing as in the point of increasing the sharpness of the cutting edge 5.

  Further, the arithmetic average roughness (Ra) of the interface between the honing portion 8 and the coating layer 6 in the vicinity 16 of the end portion of the base material honing portion is to increase the adhesion strength of the coating layer 6 in the vicinity of the end portion 16 of the base material honing portion. Further, it is desirable that the thickness is 1 μm or less, particularly 0.1 to 0.5 μm. In addition, the above-mentioned unevenness | corrugation is arithmetic surface roughness (except for the unevenness | corrugation except the waviness | corrugation based on the basic shape of the cutting blade 5 in the said interface in the cross-sectional SEM photograph of the arbitrary parts containing the interface of the honing part 8 and the coating layer 6 ( Ra) A value obtained in light of the calculation method. In addition, it is desirable that the surface roughness of the central portion of the flank 4 is 0.5 to 2 [mu] m, particularly 0.6 to 1.5 [mu] m in terms of arithmetic average roughness (Ra). This surface roughness (Ra) is quantified by observation with a scanning electron microscope (SEM) in the cross section of the chip 1.

  On the other hand, in the present invention, the base material 2 can be any of cemented carbide, cermet, or ceramic. However, the base material 2 is particularly superfluous in terms of adhesion strength with the coating layer 6 and easy shape adjustment during honing. It can be most suitably applied to a hard alloy.

On the other hand, for the coating layer 6, TiC, TiCN, TiN, (TiM) N (wherein M is at least one selected from the group of Al, Si, Zr and Cr) formed by CVD or PVD, Al _At least one layer selected from the group consisting of ₂ O ₃ , diamond (including PCD and DLC), and cBN or a multilayer of these can be applied, but the coating layer formed by the CVD method is the most preferable in terms of adhesion strength. It is valid.

  Next, a method for manufacturing the above-described chip 1 of the present invention will be described.

  First, a substantially flat base material 2 is produced, and honing is performed on the portion of the base material 2 forming the cutting edge 5.

  Here, in order to perform R honing, as shown in FIG. 2 (a), first, the rake face 3 of the base material 2 is arranged as a machining surface, and the flank 4 side of the base material 2 is fixed to the fixing jig. Fix at 21. At this time, the protruding amount h for protruding the base material 2 from the fixed jig is not only directly under the conventional cutting blade, but also protruded from the rake face to 1.1 mm or more to a height of about 1/3 of the chip flank face.

And as a method of performing R honing, while placing a grindstone 22 of grade G200 or higher in which abrasive grains are dispersed in a rubber member on the rake face side of the chip and applying a pressure of ² to 4 kg / cm ² , The lapping method in which the grindstone is rotated for 10 seconds can be machined so that the cutting edge 5 is scraped into an R shape, and at the same time, the flank portion directly below the cutting blade 5 is not scraped but is boiled. As a result, the portion processed to be boiled is slightly polished to improve the surface roughness to the extent that the adhesion of the coating is improved, and the fresh surface of the base material is exposed. The adhesion force of such a portion of the coated layer can be improved, and the adhesion strength of the coating layer and the chip resistance of the tip can be improved in the vicinity 16 of the end of the base material honing portion.

  Here, the amount of polishing by R honing is, for example, a = 0.01 to 0.2 mm on the rake face side and flank face side in order to achieve both wear resistance and fracture resistance of the cutting edge 5. It is desirable that b = 0.005 to 0.08 mm. That is, when the polishing amount of R honing exceeds the above range, the cutting edge end portion is excessively polished and the adhesion of the coating layer is reduced.

  On the other hand, in order to perform C honing (changing ho honing) on the cutting blade, first, as shown in FIG. 2B, honing is performed in a state where the tip 1 is arranged at a specific angle θ by the fixing jig 25. The cutting blade 5 is protruded, and the cutting blade 5 is applied to a rotating grindstone 26 for polishing. The polishing amount of the cutting blade 5 may be controlled while observing the polishing state of the cutting blade 5 with a microscope.

  The amount of polishing by chamfer honing is, for example, a = 0.05 to 0.2 mm on the rake face side and b = 0.02 to 0 on the flank face side in order to achieve both the sharpness of the cutting edge 5 and the prevention of chipping. .1 mm and honing angle θ = 15-30 ° are desirable.

  In order to increase the adhesion strength of the coating layer 6 at the terminal position of the flank side cutting edge region 9, it is desirable to include an R honing process as a honing method. In particular, even when performing C honing, R honing is performed in advance. It is desirable to give it.

  Then, a coating layer is deposited on the honed chip by a vapor phase synthesis method such as a CVD method or a PVD method.

  Then, the coating layer of the cutting blade 5 portion is lightly polished again from the rake face side in the same manner as the R honing, and the uppermost layer thickness of the coating is made thinner or removed than the other portions.

  At this time, according to the present invention, the tip 1 is formed as shown in FIG. 3 using a brush that is easily bent, such as a pig hair brush, and a polishing liquid in which a diamond powder having a particle size of 3 μm or less and a lubricating oil are mixed. The brush surface is polished so that the rake face 3 is pushed deeply into the inside from the surface of the brush 28, so that the brush is polished while being bent from the end face (cross ridge portion) of the rake face 3 of the chip 1 to the flank face side. Therefore, it is possible to polish the coating layer 6 to the above-described surface roughness by adjusting the elastic force of the brush and the pressing pressure.

  Further, by this method, the surface roughness of the coating layer 6 on the entire rake face 3 can be smoothed, and the polishing state can be adjusted to make the rake face have a glossy yellowish color.

  Grade 400 (with abrasive grains dispersed in a rubber member on the rake face side of the chip on the surface of a CNMG-shaped chip base material made of a cemented carbide obtained by bonding WC particles with an average particle diameter of 1.5 μm with Co. TKX) is mounted and subjected to R honing, and then the cutting blade 5 to be honed is protruded in a state where the chip 1 is arranged at a specific angle, and the cutting blade 5 is applied to the rotating grinding wheel. The chamfer honing was performed so that the rake face side a = 0.1 mm, the flank face b = 0.04 mm, and the honing angle θ = 20 °. The amount of honing was confirmed by observing with a microscope.

Then, a multilayer coating layer of TiCN by a CVD method _{(8μm) -Al 2 O 3 (} 2.5μm) -TiN (0.5μm) was formed with respect to the chip base material, the cutting edge of the coating film A chip was prepared by polishing the coating layer of the above by the processing method shown in the table. Sample No. About 1-5, it grind | polished for 120 second in the state which pushed the chip | tip to the depth shown in Table 1 using the polishing liquid which mixed 0.1-3 micrometers diamond powder and lubricating oil to the brush shown in Table 1.

  For the obtained chip, the arithmetic average surface roughness (Ra) at the rake face side cutting edge region, the flank face side cutting edge region, the rake face center portion, and the flank face center portion of the coating layer was measured at three locations, and the average value was calculated. Calculated. For measurement, a contact type surface roughness meter was used or a non-contact type laser microscope was used, and measurement was performed while moving the tip so that the measurement surface was perpendicular to the laser microscope. When the cutting edge shape itself has waviness, the surface roughness was calculated after subtracting this waviness and approximating a straight line.

Further, using a metal microscope, escape from the rake face when viewed from a distance L _A, flank from the flank face to the polishing end position P _A of the rake face side cutting edge region when viewed from the rake face of the chip The distance L _B to the polishing end position P _{B in} the surface side cutting edge region was measured, and the ratio (L _A / L _B ) was calculated. Furthermore, it was confirmed whether or not the Al ₂ O ₃ layer was exposed at the cutting edge. The results are shown in Table 1. Sample No. About 1-4, it confirmed that the part with the smallest surface roughness (Ra) was grind | polished most by microscopic observation. Also, as a result of the scratch test, the flank honing end of the coating layer had higher adhesion than the flank center.

  Further, a cutting test was performed under the following conditions, and the total cutting time until the cutting edge was lost was measured. The results are shown in Table 1.

Cutting conditions Cutting speed: 150 m / min
Cutting depth: 3mm
Feeding: 0.4mm / rev
Work material: SCM440 with 4 grooves Cutting condition: Dry

As shown in Table 1, depending on the polishing conditions, the surface roughness in the flank side cutting edge region from the flank center side to the flank side depends on the polishing conditions, and the surface in the rake face side cutting edge region from the cutting edge center portion to the rake face side Sample No. with the same roughness. In 5-7, all had a low fracture resistance. Sample No. For No. 7, the Ti-based surface layer on the entire rake face was removed and the Al ₂ O ₃ layer was exposed, and the rake face was black, making it difficult to identify whether the cutting edge was used or not. It was.

It is a schematic sectional drawing which shows an example of the throw away tip of this invention. It is a conceptual diagram for demonstrating the grinding | polishing process ((a) R honing, (b) chamfer honing) of the base material of the throw away tip of this invention. It is a conceptual diagram for demonstrating the grinding | polishing process of the coating layer of the throw away tip of this invention.

Explanation of symbols

1: Throw away tip (chip)
2: base material 3: rake face 4: flank face 5: cutting edge 6: coating layer
8 : Cutting edge central part 9: Rake face side cutting edge area 10: Relief face side cutting edge area 12: Rake face central part 13: Relief face central part 15: Base material honing part 16: Honing part end 17 of coating layer: Base metal honing end

Claims (6)

A throw-away tip in which the surface of a base material made of a hard sintered body is coated with a coating layer harder than the base material, and the adhesion strength of the coating layer at the polishing end position of the flank side cutting edge region is a flank surface The base material before coating the coating layer is honed so as to be higher than the adhesion strength at the center of the rake face, and the average arithmetic average roughness (Ra) at the center of the rake face is the center of the flank. A cutting edge region that is polished so as to be smaller than the average arithmetic average roughness (Ra) in the portion and extends from the rake face side to the flank face side from the rake face side on the surface of the coating layer The surface roughness of the flank side cutting edge region positioned on the flank side of the cutting edge region is polished, and the surface roughness of the cutting edge region is Polished and and the outermost surface of the coating layer is selected TiN, TiC, TiCN, TiCO, from a group of TiNO and TiCNO to be smaller than the surface roughness on the rake face side cutting edge region located on the side A throw-away tip comprising at least one Ti-based surface layer, wherein the Ti-based surface layer is most polished in a flank side cutting edge region on the flank side from the center of the cutting edge .   The throw-away tip according to claim 1, wherein a polishing flaw exists on the polishing surface of the coating layer.   The average arithmetic mean roughness (Ra) in the flank side cutting edge region from the cutting edge central part toward the flank is 0.05 to 0.35 μm, and the rake face side cutting edge area from the cutting edge central part toward the rake face The throw-away tip according to claim 1 or 2, wherein the average arithmetic average roughness (Ra) in 0.10 is 0.10 to 0.45 µm. The distance L _A from flank to the polishing end position P _A of the rake face side cutting edge _region, the flank side cutting edge region from the rake face as viewed from the flank when viewed from the rake face polishing end position when the distance _{L B} to _{P B,} the ratio _(L a / _{L B)} is indexable insert according to any one of claims 1 to 3, characterized in that a 0.8 to 3 of the . Wherein in the portion where a Ti-based surface layer is most polished, throw-away tip of claim 1, wherein the Al ₂ O ₃ layer existing in the lower layer of the Ti-based surface layer is exposed. The throw-away tip according to any one of claims 1 to 5 , wherein the Ti-based surface layer remains while being polished at a central portion of the rake face.

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