JP2009028861A - Cutting insert, and cutting tool and cutting method using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cutting insert, a cutting tool with the cutting insert attached to a tool holder, and a cutting method using the cutting tool, capable of performing polishing processing in a short period of time, suppressing fouling of a display part caused by chips and easily reading a display, in the cutting insert displaying information on a tool on the relief surface of the cutting insert. <P>SOLUTION: The side surface of a plurality of side surfaces, provided with the relief surface includes a first flat part applied with the polishing processing and also continued to a cutting edge, a second flat part applied with the polishing processing and also separated from the first flat part, and a rough surface part not applied with the polishing processing and also positioned between the first flat part and the second flat part. The information on the cutting insert is displayed on the second flat part. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a cutting insert provided with a coating layer on the surface of a substrate, a cutting tool in which the cutting insert is attached to a tool holder, and a cutting method using the cutting tool.

  Conventionally, for cutting inserts used for cutting of steel, cast iron, etc., Ti nitride, carbide, carbonitride, Al2O3, or Ti and Al on the surface of a substrate such as a WC-based cemented carbide or TiCN-based cermet A technique for improving the tool life by forming a coating layer of a solid solution of nitride, carbide, carbonitride, carbonate, or the like is known.

  In addition, a method is known in which the cutting edge portion of the cutting insert is subjected to cutting edge processing such as honing and chamfering to improve the cutting edge strength and increase the tool life.

The present applicant improved the grinding method of the flank and formed a sharp edge cutting edge part, and the surface roughness (Ra) of the area from the cutting edge part to the middle of the flank face on the flank face was 0.1 μm. The following technique is proposed, and the surface roughness (Ra) in the region B from the middle to the other end of the flank is larger than that in the region A. Thereby, while being able to form a sharp edge easily in a cutting-blade part, the surface roughness only of the cutting-blade vicinity area which affects chip discharge | emission property can be improved. As a result, the sharpness is improved and the finished surface of the work material can be smoothed (see, for example, Patent Document 1).
In addition, the cutting insert as described above, specifically, a cutting insert used for cutting a metal part or the like, is stipulated in an industrial standard such as a JIS standard for its shape and size. Moreover, in order to improve the working efficiency when actually using the cutting insert, a symbol is attached to the surface of the cutting insert so that the type of the cutting insert can be easily recognized on the appearance (for example, Patent Document 2), A technique for adding a symbol in the vicinity of a corner so that the used corner can be identified is disclosed (for example, Patent Document 3).
JP 2005-7531 A JP-A-8-66805 Registered Utility Model No. 3004884

  However, when displaying the identification information of the tool on the flank of the cutting insert, if displayed on an unpolished part, that is, an unpolished part with a large surface roughness, the displayed external shape is caused by the surface roughness. There is a problem that it is blurred or difficult to read due to the relationship between the background color and the display color. Further, in the cutting process, there is a problem that dirt due to cutting (caused by chips, cutting oil, etc.) is easily attached to a portion having a large surface roughness, and the reading of the display becomes difficult.

  Further, it is conceivable to polish the entire flank so as not to cause such a problem. However, since the coating layer formed on the surface of the substrate is made of a very hard material, the polishing process takes a long time, resulting in a problem that the production efficiency is lowered.

  In addition, it is conceivable to provide a display on the top surface of the cutting insert where the rake face is formed, but the rake face is easy for chips to pass through, and if the surface shape is processed by a breaker groove etc., the display location is limited. It is not preferable because it is done.

  Therefore, in view of the above problems, the present invention can perform a polishing process in a short time in a cutting insert that displays tool information on the flank of the cutting insert, and stains on a display portion caused by chips. And a cutting tool with which the cutting insert is attached to a tool holder, and a cutting method using the cutting tool.

  The cutting insert according to the present invention includes a base and a coating layer formed on the surface of the base, and includes a top surface having a rake surface, a plurality of side surfaces including a side surface having a flank, and the rake surface. And a cutting edge formed on at least a part of an intersecting ridge line with the flank, of the plurality of side surfaces, the side surface provided with the flank surface is subjected to a polishing process and the cutting edge is provided. A first smooth part formed continuously with the blade, a second smooth part formed by polishing and spaced apart from the first smooth part, and the first smooth part not polished A rough surface portion positioned between the smoothing portion and the second smoothing portion is provided, and the second smoothing portion displays identification information.

  In the above invention, the rake face is preferably formed with a breaker. Furthermore, it is preferable that the rake face is polished.

  The base has a lower surface having a second rake face, has a second cutting edge at least at a part of an intersecting ridge line between the second rake face and the flank face, and has the flank face. The side surface includes a third smooth portion that is polished and continuously formed with the second cutting edge, and a second rough surface portion between the second smooth portion and the third smooth portion. It is preferable to provide.

  Moreover, it is preferable that the base | substrate is provided with the rough surface part on the side surface of every other surface on the basis of the side surface provided with the said flank.

  Further, the coating layer includes at least one layer made of aluminum oxide, and nitride, carbide, carbonitride, oxide, carbonate, nitride oxide of an element selected from titanium, zirconium, and hafnium on the outermost surface It is preferable to have a layer made of carbonitride.

  Moreover, it is preferable that a 1st smooth part is for cutting resistance reduction at the time of cutting.

  Moreover, it is preferable that the cutting insert is for cast iron processing.

  The cutting tool of the present invention is characterized in that the cutting insert according to the present invention is attached to a tool holder.

  Further, the cutting method of the present invention is a cutting method of cutting a work material using the cutting tool according to the present invention, wherein a proximity step of relatively bringing the cutting tool closer to the work material, and the work A cutting step of rotating the material or the cutting tool, bringing the cutting tool into contact with the surface of the work material, and cutting the work material; and a separation step of relatively moving the work material and the cutting tool away from each other These are provided.

  In the first aspect of the present invention, the first smoothing part formed continuously with the cutting edge suppresses the adhesion of chips near the cutting edge and is positioned between the first smoothing part and the second smoothing part. By promoting the adhesion of chips on the rough surface portion, it is possible to suppress the adhesion of chips to the displayed second smooth portion. That is, the display reading can be maintained while improving the performance of the cutting edge. In addition, since it is not necessary to perform the polishing process on the entire flank, the polishing time is shortened and the production efficiency can be improved.

  The present invention relates to a cutting insert provided with a coating layer on the surface of a substrate, and the cutting insert is attached to an insert pocket of a tool holder or used as a cutting tool. The cutting tool is used for cutting a work material such as steel or cast iron.

A first embodiment of the present invention will be described with reference to FIGS. 1 and 2. FIG. 1 is a perspective view of a cutting insert according to the first embodiment of the present invention, and FIG. 2 is a side view of a side surface provided with a flank of the cutting insert according to the first embodiment of the present invention. . In the cutting insert 1 according to the first embodiment of the present invention, a coating layer of TiC, TiN, Al ₂ O ₃ or the like is formed on the surface of a substrate such as a WC-based cemented carbide or a TiCN-based cermet. This cutting insert 1 has a plurality of side surfaces 3 including a top surface 2 provided with a rake face through which chips are rubbed and a side surface provided with at least one flank. A cutting edge 5 is formed on at least a part of the intersecting ridge line between the rake face and the flank face. In other words, a rake face is formed on the upper surface side and a flank face is formed on the side surface side continuously with the cutting edge 5.

  As a feature of the present invention, in the side surface 3 provided with the flank, the first smoothing portion 31 that is polished and continuously formed with the cutting edge, and the height of the side surface 3 is polished and processed. The second smoothing portion 32 formed away from the first smoothing portion 31 in the vertical direction and the polishing process is not performed, and the side surface is located between the first smoothing portion 31 and the second smoothing portion 32. A rough surface portion is provided. Moreover, the display 5 which is the identification information of the cutting insert 1 is attached | subjected to the 2nd smooth part 32. FIG.

  The first smooth portion 31 formed continuously with the cutting edge suppresses the progress of flank wear (flank wear) caused by chip adhesion near the cutting edge 5 and the work material directly rubbing the flank face. Can do. Moreover, the rough surface part 35 located between the 1st smooth part 31 and the 2nd smooth part 32 can accelerate | stimulate adhesion of a chip resulting from the roughness of a surface. As a result, dirt due to chips is less likely to adhere to the second smooth portion where the display 4 is made. Further, since the second smooth portion 32 itself is also polished, it is difficult for chips to adhere. These synergistic effects can maintain the reading of the display 5 while improving the performance of the cutting edge. In addition, since the display portion is provided in the second smooth portion subjected to the polishing process, the outer shape of the display 5 becomes clearer than the case where the display 5 is formed in a place where the polishing process is not performed. Becomes easier.

  Moreover, when the 2nd smooth part 32 is formed by mirror surface processing, since an external shape becomes clearer like the character was written on the beautiful campus, display information can be confirmed easily. Further, since it is not necessary to perform polishing on the entire flank, the polishing time is shortened and the production efficiency can be improved.

  The first smoothing unit 31 preferably has a maximum height Rz in the range of 0.05 to 0.6 μm and a surface roughness skewness Rsk in the range of −0.6 to −0.2. Within this range, it is difficult for dirt to adhere to the vicinity of the cutting edge, and long-time cutting can be performed without reducing cutting performance.

  Further, the rough surface portion 35 preferably has a maximum height Rz in the range of 1 to 5 μm and a surface roughness skewness Rsk in the range of −0.2 to 0.5. Within this range, dirt caused by chips tends to adhere. By attaching dirt at the location, it is possible to suppress the dirt from attaching to the second smooth portion.

  In addition, about the measuring method of the maximum height Rz and the surface roughness skewness Rsk, the maximum height Rz and the surface roughness skewness Rsk in the measurement region are measured using a stylus type surface roughness measuring device for the cutting insert to be measured. Was measured under the conditions of a cut-off value of 0.25 mm, a reference length of 0.8 mm, and a scanning speed of 0.1 mm / second in accordance with JIS B0601'01. The measured values were measured at arbitrary three locations in each region.

  In addition, as information of the cutting insert 1 to display, what is prescribed | regulated by industrial standards, such as a JIS standard, for example is mentioned. Specifically, grades relating to various dimensions such as inscribed circle dimensions, corner heights, chip thicknesses, and the like are applicable. This is properly used according to the finished surface roughness, finish dimensional accuracy, etc. required for a product manufactured by cutting.

  As the first embodiment, the top view is a quadrangle (square). However, the shape of the cutting insert is not limited to this, and includes a side surface including at least one flank. Any one having a plurality of side surfaces 3 may be used, and conventionally used polygons such as triangles and rhombuses, circles and other special shapes can be used.

  Moreover, the chipping surface may be provided with a breaker made up of protrusions and grooves for processing chips, and the scooping surface may be polished.

  Although it is possible to provide an indication on the rake face of the cutting tool, since the rake face is rubbed through, the temperature becomes the highest during cutting. Therefore, when a display is provided on the rake face, the display is likely to be shaved due to the friction of chips. Moreover, when providing a breaker on a rake face, it is necessary to attach a display location to the part except a breaker, and a design will be restrict | limited to a cutting insert. On the other hand, in the present invention, since the display portion is provided on the flank, these problems can be prevented.

  About the display 5 in this invention, there is no limitation in particular as description contents, such as a character, a symbol, a figure, and display methods, such as an inkjet and a laser processing, The thing used conventionally can be used.

  Further, the coating layer includes at least one layer made of aluminum oxide, and nitride, carbide, carbonitride, oxide, carbonate, nitrogen oxide of an element selected from titanium, zirconium, and hafnium on the outermost surface. It is preferable that it consists of a thing and a carbonitrous oxide. In the case where an aluminum oxide layer is included as the coating layer, the surface and the surface are particularly rough and dirt is likely to adhere, so that the effects of the present invention appear more remarkably. Further, by forming a bright color coating layer such as titanium nitride on the outermost surface, the outer shape of the display becomes clearer and the reading of the display becomes easier.

  In addition, the cutting insert 1 in this invention is especially effective when it is used for the cast iron process in which dirt is easy to adhere due to chips.

  Further, by effectively using the rough surface portion 35 formed on the side surface provided with the flank surface, and having the rough surface portion on every other side surface with respect to the rough surface portion 35, it is possible to slip when the cutting insert is replaced. Acting as a stop, the efficiency of the replacement work can be improved. That is, there is a problem that the flank surface that has been polished has a tendency to slip off when the cutting insert is manually attached and removed. On the other hand, by forming a rough surface portion on at least two sides of every other surface, it is effective as an anti-slip when an operator holds the cutting insert by manually sandwiching it.

  Next, a second embodiment will be described. FIG. 3 is a side view of a side surface provided with a flank face of a cutting insert according to the second embodiment. This cutting insert 1 has a cutting edge in at least a part of an intersecting ridge line between an upper surface 2 having a rake surface and a side surface 3 having a flank, and a lower surface 6 having a second rake surface and the same side surface as described above. 3 has a second cutting edge in at least a part of the ridge line intersecting with the third ridge line.

  In addition, in the side surface 3 having the flank as in the first embodiment, the first smooth portion 31 that is polished and continuously formed with the cutting edge is subjected to the polishing process and the polishing process. A second smoothing portion 32 that is formed apart from the first smoothing portion 31 in the height direction of the side surface, and between the first smoothing portion 31 and the second smoothing portion 32 on the side surface that has not been polished. The rough surface portion located in Further, the second smoothing portion 32 has a display 4 portion to which information on the cutting insert 1 is attached.

  Further, the side surface 2 provided with the flank is positioned between the second smoothing portion 32 and the third smoothing portion, which is subjected to polishing and is formed continuously with the second cutting edge. A second rough surface portion 36 is formed.

  This enables so-called double-sided use in which the upper and lower surfaces of the cutting insert are used interchangeably, and the second smoothness can be obtained even when cutting is performed using either the cutting edge or the second cutting edge. The adhesion of dirt caused by chips on the portion 32 can be suppressed. Therefore, it is possible to obtain both the effects of improving the life of the cutting insert by using both sides and improving the period until the display 5 becomes difficult to read.

  Moreover, in 2nd Embodiment, although the rough surface part 35 and the 2nd rough surface part 36 are connected on the right and left of the 2nd smooth part of the said side surface, as shown in FIG. 4, the rough surface part 35 and the 2nd smooth part 32 are shown. The second rough surface portion 36 may be formed up to the short portion in the longitudinal direction of the side surface, and may be formed continuously in the thickness direction of the cutting insert.

  The cutting insert of this invention is attached to a tool holder as shown, for example in FIG. 5, and is used as a cutting tool. FIG. 5 illustrates a rolling tool that is used as a cutting tool by fixing the work material and rotating the tool. However, the present invention is not limited to this, and the work material is rotated by fixing the tool. It is also possible to use it for a turning tool.

[Production method]
The production method of the present invention will be described below. The above-mentioned substrate has a hard phase composed of at least one selected from the group consisting of tungsten carbide (WC) and, if desired, carbides, nitrides, and carbonitrides of Group 4, 5, and 6 metals of the periodic table, cobalt (Co). And / or made of cemented carbide bonded with a binder phase composed of an iron group metal of nickel (Ni), Ti-based cermet, or ceramics such as silicon nitride, aluminum oxide, diamond, cubic boron nitride. .

  For example, in the case of using a cemented carbide as the substrate, the method for producing such a substrate is 5 to 10% by mass of metal cobalt (Co) powder with respect to tungsten carbide (WC) powder, Group 4, 5, 6 metals of the periodic table. Cutting tool shape by press molding, adding and mixing at least one compound selected from the group of carbides (excluding tungsten carbide), nitrides, and carbonitrides at a ratio of 0.1 to 8.0% by mass To form. And after performing a binder removal process with respect to this molded object, it baking at 1350-1550 degreeC for 0.5 to 3 hours in a vacuum, and the base | substrate which consists of a cemented carbide alloy is produced.

  Next, the entire surface of the substrate is blasted for the purpose of improving the adhesion between the coating layer and the substrate and reflecting the surface properties of the coated coating layer with respect to the substrate surface before the coating layer is formed. . As the processing conditions, abrasive grains of alumina # 200 to 1000 are used, and the maximum height (Rz) is adjusted to a uniform roughness of about 0.3 μm to 1.5 μm at an ejection pressure of 2 to 10 MPa. At this time, a round honing may be formed on the cutting edge by intensively blasting toward the cutting edge, and it is also possible to remove burrs on the cutting edge that occur during molding.

Further, the honing amount is set such that the radius of curvature is R = 0.02 to 0.06 mm, so that processing such as brushing and blasting is performed so as to obtain a cutting edge shape in which both sharpness and fracture resistance are balanced.
For example, a TiN layer having a thickness of 0.1 to 1.0 μm is formed as the first layer on the surface of the substrate, and a TiCN layer having a columnar crystal structure having excellent wear resistance and fracture resistance is formed as the second layer. The film is formed with a thickness of ˜15 μm. A granular TiCN layer is formed to a thickness of 0.05 to 1.0 μm as the third layer, and a TiCNO layer is formed to a thickness of 0 to 0.2 μm as the fourth layer. Then, the _{the Al} 2 _{O 3} layer having excellent oxidation resistance as the fifth layer to 0.5~8.0μm coating. Further, a TiN layer or a TiC layer is formed as a sixth layer with a thickness of 0.5 to 1.5 μm. These coating layers 3 are more excellent in wear resistance as the film thickness is thicker, but their fracture resistance is lowered by residual stress due to a difference in thermal expansion between the substrate and the coating layer. Therefore, the layer thickness needs to be set to an optimum value according to the cutting application of the tool such as the work material and cutting conditions.

As a specific film forming condition of the coating layer, in order to form a titanium nitride (TiN) layer which is the first lowermost layer, titanium chloride (TiCl ₄ ) gas is used as a reactive gas composition in an amount of 0.1 to 0.1. 10% by volume, 5% to 60% by volume of nitrogen (N ₂ ) gas, and the remaining mixed gas consisting of hydrogen (H ₂ ) gas are sequentially adjusted, and the temperature in the chamber is set to 800 to 1100 ° C. and the pressure is set to 5 to 85 kPa. Adjust so that Next, in order to form a titanium carbonitride (TiCN) layer as the second layer, the reaction gas composition is 0.1 to 10% by volume of titanium chloride (TiCl ₄ ) gas and 0 to nitrogen (N ₂ ) gas. 40% by volume, acetonitrile (CH ₃ CN) gas is 0.3 to 2.0%, and the remaining gas mixture is hydrogen (H ₂ ) gas, and the inside of the chamber is 750 to 900 ° C., pressure Adjust to 5 to 85 kPa. In order to form a granular TiCN layer as the third layer, the reaction gas composition is 3 to 10% by volume of titanium chloride (TiCl ₄ ) gas, 5 to 40% by volume of nitrogen (N ₂ ) gas, and methane. A mixed gas composed of (CH ₄ ) gas in an amount of 1 to 15% by volume and the remainder consisting of hydrogen (H ₂ ) gas is sequentially adjusted so that the temperature in the chamber is 950 to 1100 ° C. and the pressure is 5 to 85 kPa. . Further, to form a TiCNO layer as the fourth layer, titanium chloride (TiCl ₄ ) gas is 0.1 to 3% by volume, methane (CH ₄ ) gas is 0.1 to 10% by volume, carbon dioxide ( A mixed gas consisting of 0.01 to 5% by volume of CO ₂ ) gas, 5 to 60% by volume of nitrogen (N ₂ ) gas, and the remaining hydrogen (H ₂ ) gas is prepared and introduced into the reaction chamber, The inside is adjusted to 800 to 1100 ° C. and 5 to 30 kPa. In order to form the Al ₂ O ₃ layer as the fifth layer, aluminum chloride (AlCl ₃ ) gas is 3 to 20% by volume, hydrogen chloride (HCl) gas is 0.5 to 3.5% by volume, Using a mixed gas composed of 0.01 to 5.0% by volume of carbon dioxide (CO ₂ ) gas, 0 to 0.1% by volume of hydrogen sulfide (H ₂ S) gas, and the remainder consisting of hydrogen (H ₂ ) gas, It adjusts so that it may become 900-1100 degreeC and 5-10 kPa. Finally, in order to form a sixth layer of titanium nitride (TiN) or titanium carbide (TiC), the reaction gas composition is 0.1 to 10% by volume of titanium chloride (TiCl ₄ ) gas, and titanium nitride (TiN). In the case of (5), nitrogen (N ₂ ) gas is 5 to 60% by volume, and in the case of titanium carbide (TiC), methane (CH ₄ ) gas is 5 to 60% by volume, and the balance is hydrogen (H ₂ ) gas. It adjusts and the inside of a chamber is adjusted so that it may become the furnace temperature 800-1100 degreeC and the pressure 5-85 kPa.

And among the surface of the formed coating layer, diamond abrasive grains of # 1000 or more and # 300 with respect to the first smooth part and the second smooth part (in the second embodiment, the third smooth part). Polishing is performed using the above SiC abrasive grains, or # 300 or more Al ₂ O ₃ abrasive grains, using a relatively soft brush made of pig hair or nylon and having a bristle length of 100 mm or more. In order not to remove too much the surface reflecting the surface property of the substrate, the processing time can be adjusted between 20 seconds and 100 seconds, so that the surface property can be optimized. Further, it is possible to perform desired processing by performing centrifugal projection blast processing using abrasive grains in which an elastic material and a hard material are mixed, or blast processing using a medium such as air.

  Further, at this time, the rough surface portion that is not subjected to the polishing process (in the second embodiment, the second rough surface portion) is masked so that the polishing process is not performed. The masking material may be any metal or ceramic that is difficult to polish.

  In addition, it is preferable to process the 2nd smooth part so that surface roughness may become small compared with a 1st smooth part and a 3rd smooth part. That is, the first smoothing part and the third smoothing part aim to reduce the cutting resistance during the cutting process, whereas the second smoothing part aims to maintain a clear reading of the display. . For this reason, the value of the surface roughness required for clarification of the outer shape of the display is smaller than the value of the surface roughness required for reducing the cutting resistance at the time of cutting.

[Cutting method]
Below, the cutting method which processes the work material 15 using the cutting tool 10 which attached the cutting insert 1 of this invention is demonstrated with reference to drawings.

  First, as shown in FIG. 5, the cutting insert 1 according to the present invention is attached to a tool holder. Next, as shown in FIG. 6, the cutting tool 10 is brought close to the rectangular parallelepiped work material 15 and the cutting blade of the cutting insert is brought into contact with the surface of the work material 15. Thereby, the surface of the work material 15 is cut. Thereafter, the cutting tool 10 is separated from the work material 15 as shown in FIG. By repeating the process, the work material is processed into a target shape.

  In the cutting method of the present invention, since it is possible to suppress the adhesion of dirt due to chips on the display portion attached to the side surface provided with the flank during cutting, long-term cutting is possible, Even after machining, information on the cutting insert can be easily determined.

Moreover, although the cutting method according to the present invention has been described with reference to the rolling tool in FIGS. 5 to 7, the present invention is not limited to this, and a turning tool is used as long as the same process is performed. However, the same effect can be obtained.

It is a perspective view of the cutting insert which concerns on the 1st Embodiment of this invention. It is a side view of the side provided with the flank of the cutting insert which concerns on the 1st Embodiment of this invention. It is a side view of the side surface provided with the flank of the cutting insert which concerns on the 2nd Embodiment of this invention. It is a side view of the side surface provided with the flank of the cutting insert which concerns on other embodiment of this invention. It is a perspective view which shows the proximity | contact process in the cutting method of this invention. It is a perspective view which shows the cutting process in the cutting method of this invention. It is a perspective view which shows the separation | spacing process in the cutting method of this invention.

Explanation of symbols

1: Cutting insert 2: Upper surface 3: Side surface 31: First smooth portion 32: Second smooth portion 33: Third smooth portion 35: Rough surface portion 36: Second rough surface portion 5: Display 6: Lower surface 10: Cutting tool 15: Work material

Claims (11)

A substrate and a coating layer formed on the surface of the substrate;
In a cutting insert having a top surface with a rake surface, a plurality of side surfaces including a side surface with a flank surface, and a cutting blade formed on at least a part of an intersecting ridge line of the rake surface and the flank surface,
Of the plurality of side surfaces, a side surface provided with a flank is subjected to a polishing process and a first smooth part formed continuously with the cutting edge, and a polishing process is performed and the first smooth part And a second smooth part that is formed apart from the first and second smooth parts that are not polished and positioned between the first smooth part and the second smooth part,
The said 2nd smooth part displays the identification information, The cutting insert characterized by the above-mentioned.   The cutting insert according to claim 1, wherein a breaker is formed on the rake face.   The cutting insert according to claim 1 or 2, wherein the rake face is polished. The base body has a lower surface having a second rake face, and has a second cutting edge on at least a part of an intersecting ridge line between the second rake face and the flank face,
The side surface provided with the flank is polished between the third smoothing portion formed continuously with the second cutting edge and between the second smoothing portion and the third smoothing portion. The cutting insert according to claim 1, further comprising two rough surface portions.   The cutting insert according to any one of claims 1 to 4, wherein the base body includes a rough surface portion on every other side surface with respect to the side surface including the flank surface. The first smooth portion has a maximum height Rz of 0.05 to 0.6 μm and a surface roughness skewness Rsk of −0.6 to −0.2,
The cutting insert according to any one of claims 1 to 5, wherein the rough surface portion has a maximum height Rz of 1 to 5 µm and a surface roughness skewness Rsk of -0.2 to 0.5.   The coating layer includes at least one layer made of aluminum oxide, and nitride, carbide, carbonitride, oxide, carbonate, nitride oxide of an element selected from titanium, zirconium, and hafnium on the outermost surface, The cutting insert according to any one of claims 1 to 6, further comprising a layer made of carbonitride oxide.   The cutting insert according to any one of claims 1 to 7, wherein the first smooth portion is used for reducing cutting resistance during cutting.   The cutting insert according to any one of claims 1 to 8, wherein the cutting insert is for machining cast iron.   A cutting tool comprising the cutting insert according to claim 1 attached to a tool holder. A cutting method for cutting a work material using the cutting tool according to claim 10,
A proximity step of relatively bringing a cutting tool closer to the work material;
A cutting step of rotating the work material or the cutting tool, bringing the cutting tool into contact with the surface of the work material, and cutting the work material;
A cutting method comprising: a separation step of relatively separating the work material and the cutting tool.

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