JP2013107154A - Cutting insert - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cutting insert which can sufficiently suppress deterioration in the roughness of a finished surface of a workpiece which is caused by crater wear in a rake face even if turning a high-hardness material.SOLUTION: A cutting blade 7 with an arc-shaped corner blade 7A formed at a corner of the rake face 2 is formed at a side ridge of the rake face 2 that forms a polygonal shape of an insert body 1. A stepped part 2B where the rake face 2 is lowered in height in the middle of proceeding to an inner side of the rake face 2 from a protruded end P of the corner blade 7A is formed in the rake face 2 so as to cross the corner blade 7A.

Description

  The present invention relates to a cutting insert capable of suppressing deterioration of finished surface roughness of a work material due to crater wear, particularly in turning of a hard material.

  For example, when turning a hard material such as alloy steel or hardened steel, when using a cutting insert in which a cutting edge is formed on a cutting edge tip made of a sintered material of high hardness cBN (cubic boron nitride) In order to suppress crater wear and flank wear on the rake face in such a cutting insert, or boundary wear generated at the boundary between the work material and the cutting edge, Patent Document 1 discloses sintering that constitutes the rake face. It has been proposed that the volume content of cBN be different between the body layer and the sintered body layer mainly constituting the flank. Patent Document 2 proposes forming a plurality of coating layers made of titanium nitride, titanium aluminum nitride, or the like on the surface of a cBN sintered body.

Japanese Patent No. 2861486 JP-A-10-245287

  However, even with these cutting inserts as described in Patent Documents 1 and 2, it is possible to sufficiently suppress crater wear on the rake face as long as the chips of the high hardness material rub out on the rake face and flow out. This crater wear cannot be achieved from the cutting boundary, which is the boundary where the cutting edge is cut into the workpiece, to the feed boundary, which is the boundary where the cutting edge forms the finished surface of the workpiece. In other words, chipping and chipping occur, resulting in deterioration of the finished surface roughness and abnormal wear on the flank.

  The present invention has been made under such a background, and even when turning a high-hardness material as described above, the finished surface roughness of the work material is sufficiently deteriorated due to crater wear on the rake face. It aims at providing the cutting insert which can be controlled.

  In order to solve the above-mentioned problems and achieve such an object, the present invention has an arcuate corner blade at the corner of the rake face at the side ridge of the rake face forming the polygonal shape of the insert body. A cutting edge is formed, and on the rake face, a step portion where the rake face is lowered in the middle from the tip of the corner blade toward the inside of the rake face is formed so as to intersect the corner blade. It is characterized by that.

  In the cutting insert configured as described above, the rake face of the insert body has a height higher than the rake face of the arc-shaped corner blade cut into the work material on the way to the inside of the rake face. A stepped portion is formed so as to be lowered, and this stepped portion is formed so as to intersect the corner blade, so that the intersection of the corner blade and the stepped portion is directed toward the finished surface side of the work material. The chips generated on the side where the cutting edge is cut into the work material are less likely to be rubbed against the rake face that is lowered by one step beyond the stepped portion.

  Therefore, if the intersection of the corner blade and the stepped portion is positioned on the protruding end side (feed direction side) of the corner blade with respect to the feed boundary which is the boundary on the side where the cutting blade forms the finished surface of the work material, Chips can be prevented from rubbing on the rake face of the cutting edge that forms this finished surface, and chipping and chipping due to crater wear can lead to deterioration of the finished surface roughness and abnormal flank wear. Can be sufficiently suppressed.

  Here, the cutting blade includes a pair of linear blades that are in contact with the corner blades at both ends of the corner blade, the crossing angle formed by these linear blades is 80 °, and the corner blade is honed. In the formed cutting insert, the intersection between the edge of the corner edge, which is the boundary between the honing and the flank of the corner blade, and the stepped portion is defined as the intersection between the corner blade and the stepped portion. A straight line extending in a direction intersecting the outside of the rake face at an angle of 5 ° on the corner blade side with respect to the straight blade on the side where the intersection is located when viewed from the direction facing the rake face, and the corner blade The distance between the intersection and the contact point is in the range of 0.01 mm to 0.1 mm in the direction along the straight line, It is desirable that the step amount between the intersection ridgeline between the rake face lowered by the stepped portion and the flank and the intersection is in the range of 0 mm to 0.05 mm in the direction facing the rake face. .

  That is, in the cutting insert having a crossing angle of 80 ° formed by such a pair of straight blades, the contact points of the work material as the straight blade on the side that forms the finished surface of the work material moves toward the rear side in the feed direction. This is the contact between the cutting edge and the work material when arranged so as to be separated from the finished surface at an angle of 5 °, that is, the feed boundary. As described above, the corner blade and the stepped portion are more than the feed boundary. Even if the point of intersection with the corner blade is located on the tip side of the corner blade, the distance between the point of intersection and the contact point is smaller than the above range, or the step amount of the rake face lowered by the step portion is smaller than the above range. Then, even on the rake face thus lowered, it may not be possible to sufficiently prevent scraping of the chips, and crater wear may not be suppressed.

  On the other hand, if the distance between the intersection and the contact point is larger than the above range or the step amount is larger than the above range, a finished surface of the work material is formed on the feed boundary side. The cutting edge moves away from the machining surface formed on the cutting boundary side, so that it is impossible to reliably finish the finished surface and the required finished surface roughness cannot be obtained, or the finished surface is roughened by biting of chips, etc. There is a risk of variations.

  Further, as a cutting insert for turning the high hardness material as described above, the corner blade, at least a portion of the linear blade in contact with the corner blade, and at least a portion of the stepped portion intersecting the corner blade. Is a cutting insert formed on a cutting edge tip made of a cubic boron nitride sintered body disposed on the rake face.

  As described above, according to the present invention, it is possible to prevent the crater wear of the rake face due to the scraping of the chips from reaching the cutting boundary of the cutting edge to cause chipping, chipping, abnormal wear of the flank, and the like. Even when turning a hard material such as alloy steel or hardened steel, the deterioration of the finished surface roughness of the work material can be sufficiently suppressed.

It is a top view which shows one Embodiment of the cutting insert of this invention. It is ZZ sectional drawing in FIG. FIG. 2 is an enlarged plan view around a corner blade in the embodiment shown in FIG. 1. FIG. 2 is an enlarged side view around a corner blade in the embodiment shown in FIG. 1. It is a top view in the case of turning with the embodiment shown in FIG. 1 attached to a holder. It is a figure which shows the Example of this invention.

  1 to 4 show an embodiment of the present invention. In the present embodiment, the insert body 1 has a polygonal flat plate shape, in particular, a rhomboid flat plate shape with an acute angle portion of 80 °, and one of the both side surfaces forming the rhombus is a rake face 2, The other is a seating surface 3 on an insert mounting seat of a holder, which will be described later, and four peripheral surfaces arranged around the rake surface 2 and the seating surface 3 are flank surfaces 4.

  Further, a mounting hole 5 through which a clamp screw for fixing the insert body 1 to the insert mounting seat is inserted in the center portion of the rake face 2 penetrates in the thickness direction of the insert body 1 and the seating surface 3 is inserted. It is formed so as to open at the center. In the cutting insert of the present embodiment, a rake face 2 and a seating face 3 excluding honing and a step surface, which will be described later, are perpendicular to the insert center line O that is the center line of the mounting hole 5 and the flank 4 Is a negative insert extending parallel to the insert center line O, and is formed to be 180 ° rotationally symmetrical around the insert center line O.

  Here, the insert body 1 has a direction perpendicular to the rake face 2 (the thickness direction or the insert center line O) at the acute angle portion of the rake face 2 of the base body 1A formed of cemented carbide. A notch 1B is formed in a substantially isosceles triangle shape when viewed from the direction) and an L-shape when viewed from the flank 4 side, and a cutting edge tip 6 is attached to the notch portion 1B. This cutting edge tip 6 is a layered sintered body obtained by integrally sintering an upper layer 6A made of a cubic boron nitride sintered body and a lower layer 6B made of a cemented carbide, with the upper layer 6A facing the rake face 2 side. It is joined and attached by brazing to the notch 1B.

  By attaching the cutting edge tip 6 in this way, the acute angle corner of the rhombus formed by the rake face 2 to be disposed on the upper layer 6A made of the cubic boron nitride sintered body of the cutting edge tip 6 is formed. A corner edge 7A having an arc shape is formed by forming a crossed ridge line portion of the pair of relief surfaces 4 intersecting the acute angle corner portion in a cylindrical surface shape. Further, from both ends of the corner blade 7A, a pair of linear blades 7B and 7C extending in a tangential direction in contact with the corner blade 7A at the both ends when viewed from the direction facing the rake face 2 are intersected by the rake face 2 and the flank face 4. The cutting edge 7 of the cutting insert of this embodiment is comprised by these corner blades 7A and the linear blades 7B and 7C. Therefore, the crossing angle θ formed by these straight blades 7B and 7C is 80 °.

  Further, a honing 8 is formed on the cutting edge 7 in a range of the pair of straight cutting edges 7B and 7C from the one straight cutting edge 7B to the corner cutting edge 7A and exceeding the protruding end P of the corner cutting edge 7A. The honing 8 is a chamfer honing in the present embodiment, and intersects the flank 4 with an obtuse angle, and the intersecting ridge line that is the boundary between the honing 8 and the flank 4 intersected in this way is one straight line. The edge edge ridgeline L of the cutting edge 7 that is substantially involved in the cutting from the blade 7B to the corner edge 7A.

  On the other hand, of the pair of straight blades 7B and 7C, the rake face 2 connected to the other straight blade 7C is a step surface 2A that is one step lower than the rake face 2 connected to the one straight blade 7B and the corner blade 7A. The rake face 2 has a rake face from the intersection of the corner blade 7A and the bisector of the pair of straight blades 7B and 7C when viewed from the direction facing the rake face 2, that is, from the tip P of the corner blade 7A. On the way to the inner side of 2, a stepped portion 2 </ b> B is formed in which the rake face height decreases discontinuously at the stepped surface 2 </ b> A. And this level | step-difference part 2B cross | intersects the edge edge ridgeline L of this corner blade 7A in the intersection R located in the protrusion P side of the corner blade 7A rather than the contact Q of said other straight blade 7C and the corner blade 7A. Has been.

  Here, if the stepped surface 2A is formed with the stepped portion 2B intersecting the corner blade 7A on the rake face 2 as described above, the stepped surface 2A is one step parallel to the rake face 2 connected to the protruding end P of the corner blade 7A. The cutting edge 7 may be lowered by one step on the other straight blade 7C side, and the height of the rake face 2 increases as the distance from the lowered cutting edge 7 along the step portion 2B increases. An inclined surface that gradually increases may be used, and the inclined surface thus inclined may be cut off in the middle of the rake face 2.

  In this embodiment, as shown in FIG. 2, the U-shaped concave groove flattened in the direction of the insert center line O and having a certain width from the intersection R along the other straight blade 7C is the one straight line. Extending in a direction oblique to the blade 7B, the bottom surface of the groove is the step surface 2A, and the wall surface rising from the bottom surface toward the inside of the rake surface 2 is the step portion 2B. 2B is formed so as to be orthogonal to the rake face 2 connected to the tip P of the corner blade 7A.

  Furthermore, in the present embodiment, the intersection R between the edge edge ridge line L of the corner blade 7A and the stepped portion 2B is located in the direction perpendicular to the rake face 2 as shown in FIG. The corner blade 7A is located more than the contact point S between the straight line M and the corner blade 7A extending in a direction intersecting the outside of the rake face 2 on the corner blade 7A side at an angle α of 5 ° with respect to the other straight blade 7C on the side. The distance A between the intersecting point R and the contact point S is located on the protruding end P side, and is in the range of 0.01 mm to 0.1 mm in the direction along the straight line M.

  Further, in the present embodiment, the step amount B between the intersection ridge line N of the step surface 2A of the rake face 2 and the flank 4 lowered by the step portion 2B and the intersection R is as shown in FIG. In the direction facing the rake face 2 (vertical direction in FIG. 4), the range is 0 mm to 0.05 mm. That is, the contact point Q between the other straight blade 7C of the cutting blade 7 and the other straight blade 7C among the corner blades 7A formed on the intersecting ridge line N where the step surface 2A and the flank 4 intersect. The side portion is formed so as to extend on the extension line of the edge edge ridge line L on the protruding edge P side of the corner blade 7A or on the lower side of the seating surface 3, and in FIG. Is formed at a position lower than the blade edge ridge line L so as to extend in parallel with the blade edge ridge line L.

  However, the step surface 2A, which is lowered by one step with respect to the rake face 2 connected to the tip P of the corner blade 7A, is positioned on the upper layer 6A made of the cubic boron nitride sintered body of the cutting edge tip 6. That is, the step amount B does not exceed the thickness of the upper layer 6A. Further, not only the corner blade 7A but also the pair of linear blades 7B and 7C are formed so as to extend on the upper layer 6A to some extent from the contact point with the corner blade 7A.

  Further, in the present embodiment, the concave grooves forming the stepped surface 2A and the stepped portion 2B are formed between the base 1A of the insert body 1 and the cutting edge tip 6 on the other straight blade 7C side as shown in FIGS. It straddles the boundary and reaches the obtuse corner of the rhombus formed by the rake face 2. Further, the step B extends perpendicularly to the straight line M when viewed from the direction facing the rake face 2 and crosses the boundary between the base 1A and the cutting edge tip 6 and then obliquely crosses the one straight edge 7B. Have been to.

  The cutting insert configured as described above has one of the rhombuses formed by the rake face 2 on the insert mounting seat 11 whose insert body 1 is formed at the tip of the holder 10 of the blade-tip-exchangeable tool as shown in FIG. It is seated so that the acute angle portion protrudes, and is fixed by a clamp screw 12 inserted through the mounting hole 5 and is detachably attached.

  Further, when the cutting insert thus attached to the holder 10 is used for the outer diameter turning of the work material W made of alloy steel, hardened steel, or the like, as shown in FIG. 3, it intersects with the one acute angle portion. Of the pair of straight blades 7B and 7C, one straight blade 7B is directed to the front side (left side in FIG. 5) in the feed direction F parallel to the rotation axis of the work material W, and has a step on the corner blade 7A. The other straight blade 7 </ b> C on the side where the portion 2 </ b> B is crossed is directed and held toward the outer peripheral surface H of the work material W.

  Further, at this time, in the cutting insert having the crossing angle θ formed by the pair of linear blades 7B and 7C of 80 ° as in the present embodiment, as shown in FIG. The straight blade 7C is generally given an angle α (front cutting edge angle) α of 5 ° with respect to the rotation axis of the work material W, and the outer periphery of the straight blade 7C moves toward the rear side (right side in FIG. 5) in the feed direction F. It is arranged so as to be separated from the surface H. Accordingly, the straight line M extends in parallel with the rotation axis of the work material W when the cutting insert thus disposed is viewed from the direction facing the rake face 2.

  As shown in FIG. 3, the cutting insert arranged in this way cuts the corner blade 7A formed at the one acute angle portion into the outer peripheral surface H of the work material W rotated around the rotation axis. The outer peripheral surface H is turned by being fed and fed forward in the feed direction F. Accordingly, a portion of the corner blade 7A located on the front side in the feed direction F and cut into the work material W serves as a cutting boundary, and located on the rear side in the feed direction F to define the outer peripheral surface H of the work material W. A portion finished to a predetermined outer diameter becomes a feed boundary, which is the position of the contact S in contact with the straight line M, and an intersection R between the step portion 2B and the corner blade 7A is a contact S serving as the feed boundary. Rather than the feed direction F side.

  In the cutting insert having the above-described configuration, the rake face 2 of the insert main body 1 on which the corner blade 7A is formed is moved to the inside of the rake face 2 through the honing 8 from the tip P of the corner blade 7A. As described above, the step 2B that lowers the height of the surface 2 is formed so as to intersect the corner blade 7A at the intersection R. For this reason, the chips generated on the cutting boundary side of the corner blade 7A are sent so as to be spaced from the step surface 2A of the rake face 2 inside the step portion 2B beyond the step portion 2B. It flows out to the rear side in the direction F, and it is difficult to be abraded by the step surface 2A.

  Therefore, according to the cutting insert having the above-described configuration, the crater wear due to the scraping of the chips is prevented from reaching the position of the contact S that is the feeding boundary from the cutting boundary side of the rake face 2 beyond the stepped portion 2B. be able to. For this reason, it is possible to prevent chipping and chipping due to crater wear at the feed boundary that finishes the outer peripheral surface H of the work material W to a predetermined outer diameter, and thereby high hardness materials such as alloy steel and hardened steel. In this turning process, the finished surface roughness can be improved, and the occurrence of abnormal wear on the flank 4 can be suppressed.

  However, the distance A in the feed direction F between the stepped portion 2B where the height of the rake face 2 is lowered by one step from the rake face 2 connected to the tip P of the corner blade 7A to the stepped face 2A and the contact S serving as the feed boundary is short. If the step amount B between the cutting edge edge ridge line L and the step surface 2A, which is an intersection ridge line between the flank 4 of the corner blade 7A and the honing 8 which is substantially involved in cutting, is too small, the cutting will occur. It may not be possible to reliably prevent crater wear on the boundary side from reaching the feed boundary side, and there is a risk that the roughness of the finished surface will be deteriorated.

  On the other hand, the distance A is too long so that the stepped portion 2B and the contact point S serving as the feed boundary are too far apart in the feed direction F, or the step amount B is too large and cutting is performed at the feed boundary. If the intersecting ridge line N between the stepped surface 2A and the flank 4 involved and the edge edge ridge line L of the corner blade 7A are too far away in the direction facing the rake face 2, the cutting edge 7 on the cutting boundary side cuts the workpiece. The cutting edge 7 that finishes the processed surface on the feed boundary side with respect to the processed surface formed on the material W is too far away, so that it is impossible to reliably finish to the desired finished surface roughness, There is a possibility that the roughness of the finished surface may vary due to biting.

  Here, as in the present embodiment, in the cutting insert in which the crossing angle θ formed by the pair of straight blades 7B and 7C at the acute angle portion on the rake face 2 of the insert body 1 is 80 °, the work material is as described above. The other straight blade 7C directed to the outer peripheral surface H of W is inclined so as to move away from the rotation axis of the work material W at an angle α of usually 5 ° toward the rear side in the feed direction F. A relief is given to the other straight blade 7C. Accordingly, the feed boundary at which the corner blade 7A contacts the workpiece W on the rear side in the feed direction F is inclined with respect to the other straight blade 7C at an angle α of 5 ° and the straight line M in contact with the corner blade 7A. It becomes the said contact S with the corner blade 7A.

  Then, the distance A from the contact S to the front side of the corner 7A along the straight line M from the contact S in the feed direction F, that is, the distance A to the contact S as in this embodiment is in the range of 0.01 mm to 0.1 mm. If the intersection R of the stepped portion 2B and the edge edge ridge line L of the corner blade 7A is positioned so that the crater wear at the feed boundary can be reliably suppressed, as demonstrated in the examples described later, It is also possible to prevent the finished surface roughness from being deteriorated and uneven. Similarly, the step amount B is similarly set to a range of 0 mm to 0.05 mm in the direction facing the rake face 2 as in this embodiment, so that the crater wear at the feed boundary, the degradation of the finished surface accuracy, and the variation are caused. Can be prevented.

  In addition, as a cutting insert as in this embodiment for turning a high-hardness material such as alloy steel or hardened steel, in order to more reliably prevent deterioration of the finished surface roughness due to crater wear and abnormal wear of the flank 4. Of the cutting blade 7, the corner blade 7A, the portion of the pair of linear blades 7B and 7C that contact at least the corner blade 7A, and the portion of the stepped portion 2B that intersects at least the corner blade 7A are arranged on the rake face 2. It is desirable to form on the upper layer 6A which consists of the hard cubic boron nitride sintered compact of the provided cutting blade chip | tip 6. FIG.

  Moreover, although this embodiment demonstrated the case where the outer diameter turning of the workpiece W was performed as mentioned above, it can also be used for the inner diameter turning of the prepared hole formed in the workpiece W, Of course, it is also possible to use the cutting insert having the above-described configuration for the end face turning of the material W. In the case of end face turning, the other straight blade 7C on the side where the intersection R between the stepped portion 2B and the corner blade 7A is located is fed in the feed direction at the angle α with respect to the plane perpendicular to the rotation axis of the work material W. It arrange | positions so that it may space apart as it goes to the back side of F, and a cutting insert is sent out to the feed direction F along the plane perpendicular | vertical to this rotating shaft, and end surface turning is performed.

  Furthermore, in the present embodiment, a so-called cutting insert with a right hand is described in which the straight blade directed to the processing surface side of the work material W among the pair of straight blades 7B and 7C is the other straight blade 7C. However, it is also possible to apply the present invention to a so-called unintentional cutting insert in which both of the pair of straight blades 7B and 7C can be used toward the work surface of the work material. In this case, the stepped portion 2B in the above embodiment may be formed symmetrically with respect to the bisector of the pair of straight blades 7B and 7C and intersect with both end sides of the corner blade 7A.

  Furthermore, in the present embodiment, the stepped portion 2B is perpendicular to the rake face 2 connected to the tip P of the corner blade 7A via the honing 8, but as the rake face 2 moves toward the stepped face 2A. It may be an inclined surface that is inclined inward of the rake face 2, and has a concave curved surface that is smoothly connected to the step surface 2A at a position away from the intersection R with the cutting edge ridge line L of the corner blade 7A. Or you may.

  Examples of the present invention will be described below to explain the effect of limiting the numerical values of the distance A and the step amount B in the embodiment. In this example, based on the above embodiment, three types of cutting inserts were manufactured in which the distance A and the step amount B were variously changed within the above range. Table 1 shows the distance A (mm) and the step amount B (mm) as Examples 1 to 3.

  The cutting inserts of Examples 1 to 3 are of the CNGA120408GA type in basic shape and dimensions, and the honing width of the honing 8 is 0.13 mm, the honing angle is 25 °, and is a boundary with the flank 4. The cutting edge edge ridge line L is rounded with a radius of 0.03 mm. In addition, the acute angle portion of the rake face 2 is a range connecting points on the straight blades 7B and 7C that are 2.5 mm away from the intersection of the extension lines of the pair of straight blades 7B and 7C toward the corner blade 7A. The cutting edge tip 6 was joined so that an upper layer 6A made of a cubic boron nitride sintered body was disposed therein.

  On the other hand, as a comparative example with respect to Examples 1 to 3, the basic shape, dimensions, and joining range of the cutting edge tip 6 are the same as those of Examples 1 to 3, and at least one of the distance A and the step amount B is out of the above range. The following three types of cutting inserts were manufactured. These are referred to as Comparative Examples 1 to 3, and the distance A (mm) and the step amount B (mm) are also shown in Table 1. Further, as Comparative Example 4, the basic shape, dimensions, and joining range of the cutting edge tip 6 are the same as those in Examples 1 to 3, and the normal cubic boron nitride sintered body CNGA120408GA type with no stepped portion is formed. A cutting insert was also prepared.

  And the outer diameter turning process is performed on the work material W made of alloy steel by the cutting inserts of Examples 1 to 3 and Comparative Examples 1 to 4, and the transition of the finished surface roughness for each processing time, that is, constant Of Finished Surface Roughness (Maximum Height of Roughness Curve in JIS B 0601 2001: Rz) in Rotational Axis Direction of Workpiece W Finished by Feeding Cutting Insert at Feed Rate It was measured. The result is shown in FIG. The work material W is an SCM415 material (hardness 60HRC) having a diameter of 100 mm and a length of 300 mm in the rotation axis direction. Using a CNC lathe NL2500 manufactured by Mori Seiki Co., Ltd., cutting speed is 200 m / min, feed Turning was performed by dry cutting at a speed of 0.20 mm / rev and a cutting depth of 0.15 mm.

  From the results shown in FIG. 6, the theoretical surface roughness is 6.2 μm, whereas in the cutting inserts of Examples 1 to 3 according to the above embodiment of the present invention, the finished surface roughness is lower than this. Even when the cutting edge 7 at the end of turning 270 seconds after the start of turning is confirmed, crater wear is suppressed from the cutting boundary to the step 2B, and does not reach the feeding boundary. It was.

  However, in the second and third embodiments in which the step amount B is 0 mm, that is, the intersecting ridge line N that becomes the cutting edge 7 of the feed boundary extends on the extension line of the cutting edge ridge line L of the corner blade 7A, the above-described steps In addition, it was confirmed that when turning was continued, crater wear was more likely to proceed toward the feed boundary as compared with Example 1. For this reason, it is considered that the step amount B is preferably larger than 0 mm and within a range of about 0.005 mm to 0.045 mm even within the above range.

  On the other hand, compared with Examples 1 to 3, in Comparative Example 1 in which both the distance A and the step amount B slightly exceed the above ranges, the finished surface roughness suddenly becomes unstable immediately before the end of the turning process, which is not preferable. No results. Further, in Comparative Example 2 where the step amount B is significantly larger than 0.05 mm even if the distance A is 0.1 mm or less, the intersecting ridge line N between the step surface 2A and the flank 4 is the edge edge ridge line L of the corner blade 7A. However, the point which becomes the feed boundary substantially is not determined and the desired finished surface roughness cannot be obtained from the initial stage of turning.

  Further, in Comparative Example 3 where the distance A is greater than 0.1 mm even if the step amount B is 0.05 mm or less, crater wear occurs between the contact S as the feed boundary and chipping occurs at the cutting edge. As a result, the finished surface roughness deteriorates and varies. Further, in Comparative Example 4, which is an ISO standard ordinary cutting insert in which the stepped portion 2B is not formed, the honing 8 is continuous, so that the crater wear extends and a chipping occurs at the end of the turning process.

DESCRIPTION OF SYMBOLS 1 Insert body 2 Rake face 2A Step surface 2B Step part 3 Seating surface 4 Relief surface 5 Mounting hole 6 Cutting edge tip 6A Upper layer 6B Lower layer 7 Cutting edge 7A Corner blade 7B, 7C Straight blade 8 Honing O Insert center line P Corner blade 7A Projection tip Q Contact point between corner blade 7A and other straight blade 7C L Cutting edge edge ridge line of corner blade 7A R Crossing point of cutting edge ridge line L and stepped portion 2B M The other straight line when viewed from the direction facing rake face 2 A straight line extending in a direction intersecting the outside of the rake face 2 on the corner blade 7A side at an angle α of 5 ° with respect to the blade 7C. A contact point between the straight line M and the corner blade 7A. Distance B Step height of step 2B α Angle formed by the other straight blade 7C with respect to the straight line M when viewed from the direction facing the rake face 2 (5 °)
θ Tolerance angle of a pair of straight blades 7B and 7C (80 °)
W Work material H Outer surface of work material W

Claims (3)

  A cutting edge having an arcuate corner blade at the corner of the rake face is formed at the edge of the rake face forming the polygonal shape of the insert body, and the rake face is formed from the tip of the corner blade. A cutting insert, characterized in that a stepped portion having a lower rake face in the middle of the rake face is formed so as to intersect the corner blade.   The cutting blade includes a pair of straight blades that are in contact with the corner blades at both ends of the corner blade, the crossing angle formed by these straight blades is 80 °, and the corner blade is formed with a honing, The intersection of the edge of the corner blade, which is the boundary between the honing and the flank of the corner blade, and the stepped portion is the straight blade on the side where the intersection is located when viewed from the direction facing the rake face. On the other hand, on the corner blade side, the corner blade is located on the projecting end side of the corner blade from the contact point between the corner blade and a straight line extending in a direction intersecting at an angle of 5 ° to the outside of the rake face. And the distance between the intersection ridgeline of the rake face and the flank face lowered by the stepped portion and the intersection point in the direction along the straight line. Step The cutting insert according to claim 1, wherein the amount is in a range of 0 mm to 0.05 mm in a direction facing the rake face.   The corner blade, a portion of the linear blade that is in contact with at least the corner blade, and a portion of the step portion that intersects at least the corner blade is a cubic boron nitride sintered body disposed on the rake face. The cutting insert according to claim 1, wherein the cutting insert is formed on a cutting edge chip made of the same.

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