Cutting tip, cutting method, pipe joint manufacturing method, and pipe joint

Abstract

To provide a cutting chip which can smoothly perform cutting of a complex shape with a recess part at high speed.SOLUTION: A cutting chip includes a cutting part. Corners forming the cutting part of the cutting chip are constituted with a plurality of curve surfaces whose curvatures are different from each other. The curve surfaces adjacent to each other share a tangent line at the connecting point. The cutting chip can accurately cut a recessed shape and can cut a flat surface or a gentle curve surface relatively close to a flat surface at high speed. Therefore, the cutting chip can smoothly perform cutting of a complex shape with the recess shape at high speed.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a cutting tip, a cutting method, a pipe joint manufacturing method, and a pipe joint that are capable of realizing precise and high-speed machining.

[0002] For example, cutting of the inner surface of a steel pipe end is performed by setting several types of cutting tools (chips) (hereinafter referred to as cutting chips or chips) on an NC (numerical control) lathe. In this processing, a tool (chip) is set according to the shape to be processed. Specifically, when the processing does not involve the formation of a screw groove on the inner surface of the steel pipe and a high degree of finishing precision is required, a diamond-shaped tool (chip) is often used.

[0003] The diamond-shaped cutting tool (tip) has a curved surface formed on the tip side. In such cutting processes, the curvature of the tip of the diamond-shaped cutting tool (tip) is selected depending on the purpose of the process, the required finishing precision, etc.

[0004] For example, when a steel pipe (workpiece) is machined using an NC lathe, minute irregularities with a regular wave pattern known as cutting marks are formed on the cut surface. These irregularities become the surface roughness, which is one way of evaluating the accuracy of the finished cutting process. Surface roughness is measured using an index such as the arithmetic mean roughness (Ra), and is often required to be below a certain value.

[0005] It is known that surface roughness is affected by the radius of curvature of the cutting tool (tip) and the feed rate. That is, when the feed rate is constant, the larger the radius of curvature of the tip of the cutting tool (tip), the lower the surface roughness tends to be. Therefore, a cutting tool (tip) with a large radius of curvature can be fed more efficiently during cutting than a cutting tool (tip) with a small radius of curvature, thereby shortening the processing time.

[0006] On the other hand, the radius of curvature of the curved surface formed on the tip side of the cutting tool (tip) is selected depending on the cutting shape of the cutting process. For example, if the cutting shape includes a recess (hereinafter also referred to as a recessed shape), the cutting tool (tip) cannot cut into that shape unless the radius of curvature is smaller than that of the recessed shape.

[0007] From the viewpoint of the required surface roughness and cutting shape, a diamond-shaped cutting tool (tip) having an appropriate radius of curvature according to these conditions is selected.

[0008] Patent Document 1 discloses such a cutting tip as a steel pipe cutting tool having three cutting surfaces 1, 2, and 3 with different radii of curvature at the tip, where the relationship between the tip radius of curvature R1, the radius of curvature R2 adjacent to the radius of curvature R1, and the radius of curvature R3 adjacent to the radius of curvature R2 is expressed by the formulas (1), (2), and (3). 11R1≦R2≦17R1 …………(1) 11R1≦R3≦17R1 …………(2) R3 <R2…………(3) [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Japanese Patent Application Publication No. 10-006108 Summary of the Invention [Problem to be solved by the invention]

[0010] However, as the machining area in cutting increases, the time required for machining also increases. As mentioned above, the surface roughness of the workpiece is affected by the radius of curvature of the cutting tool (chip) and the feed rate. In other words, increasing the feed rate in cutting is effective for improving productivity, but the surface roughness of the cutting marks also increases as the feed rate increases. In order to achieve both smooth cutting marks with low surface roughness and high productivity, it is necessary to increase the radius of curvature of the tip of the cutting tool (chip).

[0011] As described above, when the cutting shape includes a concave shape, the radius of curvature of the tip of the cutting tool (chip) is selected depending on the radius of curvature of the concave shape. In particular, when the concave shape is narrow, or when the radius of curvature is small, for example, 0.5 mm or less, the constraints on the radius of curvature of the tip of the cutting tool (chip) become strict. As a result, the radius of curvature of the tip of the cutting tool (chip) must be small, which makes it difficult to cut areas other than the concave shape smoothly and at high speed.

[0012] The present invention has been made in consideration of the above problems, and aims to provide a cutting tip, a cutting method, a pipe fitting manufacturing method, and a pipe fitting that are capable of cutting complex cutting shapes, including concave shapes, precisely and at high speed. [Means for solving the problem]

[0013] [1] A cutting tip having a cutting portion, characterized in that the corners forming the cutting portion are composed of multiple curved surfaces with different curvatures, and each of the adjacent curved surfaces shares a tangent at their connection point. [2] The cutting tip according to [1], characterized in that it has an attachment part for attachment to a lathe device. [3] A cutting tip according to [1] or [2], characterized in that the angle of the curved surface having the smallest radius of curvature among the plurality of curved surfaces is 30° or more and 90° or less. [4] The cutting tip according to any one of [1] to [3], wherein the curved surface having the smallest radius of curvature among the plurality of curved surfaces has a radius of curvature of 0.10 mm or more. [5] The cutting tip according to any one of [1] to [4], wherein the curvature radii of the curved surfaces are all 0.80 mm or less. [6] A cutting method for cutting a workpiece by cutting, comprising a cutting step of cutting the workpiece using the cutting tip according to any one of [1] to [5]. [7] The cutting method according to [6], characterized in that in the cutting step, the cutting is performed at a feed rate of 0.05 mm / rev or more and 0.20 mm / rev or less. [8] A method for manufacturing a pipe fitting by cutting the inner surface of a steel pipe by cutting processing, comprising a cutting step of cutting the steel pipe using a cutting tip according to any one of [1] to [5]. [9] A pipe joint characterized by being machined using the cutting tip according to any one of [1] to [5]. [Effects of the Invention]

[0014] The cutting tip of the present invention can accurately cut concave shapes and can cut flat surfaces or gently curved surfaces that are relatively close to flat surfaces at high speed. In other words, it is possible to smoothly and quickly cut complex cutting shapes, including concave shapes. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 2 is a conceptual diagram showing the configuration of a cutting tip. [Figure 2] FIG. 2 is an explanatory view illustrating a cutting portion of a cutting tip. [Figure 3] FIG. 2 is an explanatory view illustrating a cutting portion of a cutting tip. [Figure 4] FIG. 2 is an explanatory view illustrating a cutting portion of a cutting tip. [Figure 5] FIG. 10 is a cross-sectional view showing a cross section of a pipe joint using a cutting tip. [Figure 6] 10A and 10B are explanatory views illustrating a cutting portion of a cutting tip according to a modified example. [Figure 7] FIG. 2 is an explanatory diagram illustrating the cutting mode of a steel pipe by a cutting tip in an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0016] An embodiment of the present invention will be described with reference to the drawings. As shown in FIG. 1, the cutting tip 100 is formed in a plate shape. The cutting tip 100 is formed, for example, in a diamond shape when viewed from a direction perpendicular to one surface 11. The cutting tip 100 is not limited to this shape, and may be any shape that has a curved cutting portion that cuts the cutting object. The shape of the cutting tip 100 may be any of various known shapes, such as a triangular shape or a circular shape.

[0017] The cutting tip 100 has an attachment portion 12 that is attached to a lathe (not shown). The attachment portion 12 is a so-called round hole that penetrates from one surface 11 to the other surface. A pin or the like is inserted into the attachment portion 12, and the cutting tip 100 is fixed to the lathe by being fixed with a known fixing member (not shown).

[0018] When viewed from a direction perpendicular to one surface 11, the cutting tip 100 has a minor axis AX1 connecting apexes P1 and P2 of the diamond shape, and a major axis AX2 (perpendicular to the minor axis AX1) connecting apexes P3 and P4 of the diamond shape.

[0019] The cutting tip 100 has a cutting portion 20 at the tip end side of the long axis AX2. In this embodiment, the cutting portion 20 is formed from one end Pa located on the vertex P1 side to the other end Pd located on the vertex P2 side. The cutting portion 20 is formed in a U-shape when viewed from a direction perpendicular to one surface 11.

[0020] The cutting portion 20 has a first curved surface C1, a second curved surface C2, and a third curved surface C3 that are continuously formed (arranged adjacent to each other) from one end Pa to the other end Pd. Specifically, the first curved surface C1 is formed between one end Pa of the cutting portion 20 and point Pb. The second curved surface C2 is formed between point Pb and point Pc. The third curved surface C3 is formed between point Pc and point Pd. In other words, point Pb is a connection point connecting the first curved surface C1 and the second curved surface C2. Point Pc is a connection point connecting the second curved surface C2 and the third curved surface C3.

[0021] In this embodiment, the second curved surface C2 is formed between points Pb and Pc, sandwiching (including) the major axis AX2. The tip P, which is the farthest from the center of the attachment portion 12 in the direction of the major axis AX2, is located on the second curved surface C2. More specifically, the tip P is located closer to the connection point Pb than the major axis AX2.

[0022] Here, the tip P is used to form a concave shape in the workpiece, which will be described later. Therefore, by positioning the tip P closer to the connection point Pb than the major axis AX2, it is possible to easily form a concave shape when cutting the inner surface of a steel pipe, for example.

[0023] Fig. 2 shows the first curved surface C1 and the second curved surface C2 of the cutting portion 20. As shown in Fig. 2, the first curved surface C1 is a fan-shaped curved surface having a central angle θ1. The first curved surface C1 has a radius of curvature R1.

[0024] The second curved surface C2 is a fan-shaped curved surface having a central angle θ2. In this embodiment, the central angle θ2 of the second curved surface C2 is larger than the central angle θ1 of the first curved surface C1. The second curved surface C2 also has a radius of curvature R2. The radius of curvature R2 of the second curved surface C2 is shorter than the radius of curvature R1 of the first curved surface C1. Therefore, the first curved surface C1 and the second curved surface C2 have different curvatures.

[0025] At the connection point Pb, the adjacent first curved surface C1 and second curved surface C2 share a tangent line L1. That is, a line perpendicular to a line L2 extending from the center CP1 of the first curved surface C1 to the connection point Pb (the tangent line to the first curved surface C1) and a line perpendicular to a line L3 extending from the center CP2 of the second curved surface C2 to the connection point Pb (the tangent line to the second curved surface C2) are positioned to overlap each other.

[0026] 2, the lines L2 and L3 overlap each other. Also, in this figure, the center CP2 of the second curved surface C2 is located on the line L2 that extends from the center CP1 of the first curved surface C1 to the connection point Pb.

[0027] Fig. 3 shows the second curved surface C2 and the third curved surface C3 of the cutting portion 20. As shown in Fig. 3, the third curved surface C3 is a fan-shaped curved surface having a central angle θ3. The third curved surface C3 has a radius of curvature R3.

[0028] In this embodiment, the central angle θ3 of the third curved surface C3 is larger than the central angle θ2 of the second curved surface C2. The radius of curvature R3 of the third curved surface C3 is longer than the radius of curvature R2 of the second curved surface C3. Therefore, the second curved surface C2 and the third curved surface C3 have different curvatures.

[0029] At the connection point Pc, the adjacent second curved surface C2 and third curved surface C3 share a tangent line L4. That is, a line (tangent line to the second curved surface C2) perpendicular to a line L5 extending from the center CP2 of the second curved surface C2 to the connection point Pc overlaps with a line (tangent line to the second curved surface C2) perpendicular to a line L6 extending from the center CP3 of the third curved surface C3 to the connection point Pc. In this figure, the center CP2 of the second curved surface C2 is located on the line L6 extending from the center CP3 of the third curved surface C3 to the connection point Pc.

[0030] In other words, the first curved surface C1, the second curved surface C2, and the third curved surface C3 form a continuous curve (corner) from one end Pa toward the other end Pd, and are formed without a so-called pin angle.

[0031] That is, the multiple curved surfaces C1, C2, and C3 of the cutting portion 20 share tangents L1 and L4 at connection points Pb and Pc between adjacent curved surfaces (curved surfaces C1, C2 and curved surfaces C2, C3). If the connection points Pb and Pc do not share a tangent, the connection points Pb and Pc become so-called pin angles, which may cause streaky scratches on the cutting surface of the workpiece.

[0032] In this embodiment, "sharing a tangent" may mean that the corners of the cutting portion 20 have minute corners that are acceptable for manufacturing purposes. Such corners may be any corners that do not cause visible scratches (for example, streak-like scratches formed in the feed direction) when cutting is performed using the cutting tip 100. For example, the angle formed by the connection points may be less than 5°. Whether or not a pin angle is formed in the cutting portion 20 can be determined, for example, by palpation.

[0033] The first curved surface C1, the second curved surface C2, and the third curved surface C3 have different curvatures. In other words, the corner that forms the cutting portion 20 is made up of a plurality of curved surfaces with different curvatures. In this embodiment, the curvature increases in the order of the second curved surface C2 > the third curved surface C3 > the first curved surface C1.

[0034] Of the multiple curved surfaces, the curved surface C2 having the smallest radius of curvature should have a radius of curvature of 0.10 mm or more, preferably 0.20 mm or more and 0.50 mm or less, and more preferably 0.30 mm or more and 0.40 mm or less.

[0035] If the radius of curvature of the smallest curved surface C2 of the cutting portion 20 is too small, cutting resistance will be concentrated at the tip during cutting, making the tip more susceptible to breakage. As a result of research by the inventors, it was found that this problem can be reduced if the radius of curvature of the curved surface constituting the corner of the cutting portion 20 of the cutting tip 100 is 0.10 mm or more.

[0036] The radii of curvature of the multiple curved surfaces C1, C2, and C3 at the corners of the cutting portion 20 are preferably all 0.80 mm or less, and in particular, the largest radius of curvature among the curved surfaces C1, C2, and C3 is preferably 0.40 mm or more and 0.75 mm or less, and more preferably 0.50 mm or more and 0.70 mm or less.

[0037] If the radii of curvature of the multiple curved surfaces C1, C2, and C3 are too large, the gap between the area cut on the previous circumference and the cutting tip 100 will be narrow, and chips may get caught in that gap, causing scratches on the cut surface. As a result of research by the inventors, it was found that this problem can be reduced if the radii of curvature of the curved surfaces constituting the corners of the cutting portion 20 of the cutting tip 100 are 0.80 mm or less.

[0038] The curvature of the second curved surface C2 only needs to be greater than the curvatures of the first curved surface C1 and the third curved surface C3. Therefore, the first curved surface C1 and the third curved surface C3 may have the same curvature or may have different curvatures.

[0039] Of the multiple curved surfaces C1, C2, and C3 at the corners of the cutting portion 20, the angle θ2 of the curved surface C2 having the smallest radius of curvature is preferably 30° or more and 90° or less, more preferably 35° or more and 80° or less, and even more preferably 40° or more and 60° or less.

[0040] Among the multiple curved surfaces with different curvatures, the curved surface C2 with the smallest radius of curvature is necessary for cutting the concave shape with precision. Therefore, if the angle range is too small, the tip will not fit into the desired concave shape, making it difficult to cut the concave shape with precision. The required angle range depends on the concave shape to be cut, but the inventors' research has shown that an angle range of 30° or more will almost never result in the tip not being able to fit into a narrow concave shape.

[0041] On the other hand, if the angle range of the curved surface C2 with the smallest curvature radius is too large, it becomes difficult to secure the adjacent curved surfaces C1 and C2 with larger curvature radii. As a result, many areas other than the concave shape will be cut with the curved surface C2 with the smallest curvature radius, which will increase the cutting time. In order to secure a sufficient angle range for the curved surfaces C1 and C2 with large curvature radii, it is recommended that the angle range of the curved surface C2 with the smallest curvature radius be 90° or less.

[0042] The tip P may be located between the first curved surface C1 to the third curved surface C3, but is preferably located on the second curved surface C2. The tip P is preferably located closer to the connection point Pb than the major axis AX2. By positioning the tip P in this way, precise and rapid processing can be achieved, for example, when forming a recess (concave shape) that functions as a seal on the inner surface of a steel pipe.

[0043] 4 shows the cutting portion 20 of the cutting tip 100. As shown in FIG. 4, the angle at which an extension line RL1 of the ridgeline from vertex P1 to one end point Pa intersects with an extension line RL2 of the ridgeline from vertex P2 to the other end point Pd, i.e., the angle θ formed by the corner of the cutting portion 20, is preferably less than 90°, and is preferably 20° to 75°, and more preferably 40° to 60°. By setting the angle θ formed by the corner of the cutting portion 20 to be less than 90°, complex shapes including the above-mentioned concave shape can be easily cut.

[0044] An example will be described in which the cutting tip 100 described above is used to cut a steel pipe's inner surface to form a recess (concave shape) to produce a pipe joint. Figure 5 shows a cross section of a pipe joint 40 formed by lathing a steel pipe using the cutting tip 100. As shown in Figure 5, the pipe joint 40 is used, for example, as an oil well pipe joint, and has a thread groove 41 formed from one end to the other end, and a seal portion 42 formed on the other end of the thread groove 41.

[0045] The sealing portion 42 has a straight portion 43 formed in a tapered shape so that the diameter narrows from one end to the other end, a recessed portion 44 formed in a concave shape that is recessed toward the outside of the pipe diameter at the other end of the straight portion 43, and an extension portion 45 extending from the recessed portion 44 toward the inside of the pipe diameter.

[0046] The sealing portion 42 can be formed, for example, by cutting the steel pipe by lathe processing using the cutting tip 100. Specifically, first, the first curved surface C1 to the second curved surface C2 of the cutting portion 20 are pressed against the steel pipe rotating around its axis, and cutting is performed up to a predetermined position where the recessed portion 44 is to be formed. In this way, the straight portion 43 can be formed.

[0047] Next, after forming the recess 44 on the second curved surface C2, the second curved surface C2 to the third curved surface C3 are pressed against the cutting object, and cutting is performed up to a predetermined position where the extension portion 45 is to be formed. In this way, the recess 44 and the extension portion 45 can be formed.

[0048] When forming the seal portion 42, the machining time can be shortened by increasing the peripheral speed of the workpiece and the feed rate of the cutting tip. If the peripheral speed of the workpiece is too high, seizure occurs. Therefore, the upper limit of the peripheral speed of the workpiece is determined by the material of both the workpiece and the cutting tip. For example, if the workpiece is a ferrous material, the upper limit of the peripheral speed should be set to 200 m / min. Furthermore, if the feed rate of the cutting tip is too high, it becomes difficult to meet the required surface roughness. The upper limit of the feed rate should be increased in proportion to the radius of curvature of the curved surface at the corner of the cutting tip. Furthermore, in the cutting process for cutting steel pipes, the feed rate is preferably 0.05 mm / rev or more and 0.20 mm / rev or less. By using the cutting tip 100 of the present invention and performing the cutting process at a feed rate of 0.05 mm / rev or more and 0.20 mm / rev or less, concave shapes can be cut with precision, and flat or gently curved surfaces that are relatively close to flat can be cut at high speed.

[0049] In this way, by performing the above cutting process using the cutting tip 100, it is possible to perform lathe processing precisely and quickly, even if the required surface roughness is satisfied and the processed shape has the recessed portion 44. As a result, when the pipe fitting 40 is used as an oil well pipe fitting, it is possible to realize a highly airtight seal portion 42.

[0050] The pipe joint is not limited to an oil well pipe joint, and is not particularly limited as long as it can be produced by cutting a steel pipe. However, it is preferable that the cutting is performed by lathe cutting. In particular, it is particularly preferable that the lathe cutting has a processed portion formed in the shape of the object to be processed along the feed direction of the lathe cutting, and a recess formed at the tip of the processed portion. Examples of such pipe joints include joints for steel pipe piles, thermal tubes, casing steel pipes, strainer steel pipes (screen pipes), etc. The cutting tip and cutting method of the present invention can also be used for cutting bolts, etc. Modified Examples

[0051] In the above-described embodiment, the cutting portion 20 has three curved surfaces C1 to C3. However, the curved surfaces of the cutting portion 20 may have two or more curved surfaces with different curvatures. FIG. 6 shows a cutting portion 20 having four curved surfaces. As shown in FIG. 6, the cutting portion 20 has a first curved surface C1, a second curved surface C2, a third curved surface C3, and a fourth curved surface C4 that are continuously formed from one end Pa to the other end Pe.

[0052] Specifically, the first curved surface C1 is formed between one end Pa of the cutting portion 20 and point Pb. The second curved surface C2 is formed between point Pb and point Pc. The third curved surface C3 is formed between point Pc and point Pd. The fourth curved surface C4 is formed between point Pd and point Pe.

[0053] That is, point Pb is a connection point connecting the first curved surface C1 and the second curved surface C2, point Pc is a connection point connecting the second curved surface C2 and the third curved surface C3, and point Pd is a connection point connecting the third curved surface C3 and the fourth curved surface C4.

[0054] As described above, the third curved surface C3 and the fourth curved surface C4 also share a tangent (not shown) at the connection point Pd. That is, at the connection point Pd, the tangent to the third curved surface C3 and the tangent to the fourth curved surface C4 are positioned to overlap each other.

[0055] Even when the fourth curved surface C4 is formed in this manner, it is preferable that the radius of curvature of the fourth curved surface C4 is 0.8 mm or less.

[0056] The cutting tip 100 described above can be used not only for processing the inner surface of a steel pipe, but also for processing the outer surface of a steel pipe, a cylindrical or conical steel material, etc. In particular, the cutting tip 100 is preferably used for processing on an NC (numerical control) lathe, as it is capable of processing complex shapes compared to other cutting processes.

[0057] As described above, according to the cutting tip 100 of the present invention, the corners of the cutting portion 20 are composed of multiple curved surfaces with different curvatures, so that the curved surface C2 with a small radius of curvature contributes to highly accurate cutting of a narrow concave shape (recess 44), while the curved surfaces C1, C3, C4, etc. with a large radius of curvature can cut flat surfaces or gently curved surfaces relatively close to flat surfaces (straight portion 43, extension portion 45) at high speed to produce a smooth cutting surface.

[0058] Furthermore, adjacent curved surfaces C1 to C4 share tangent lines L1, L4, and L7 at their connection points Pb, Pc, and Pd, which enables cutting to be performed without leaving streaky scratches on the cutting surface of the workpiece. Therefore, the cutting tip 100 of the present invention can smoothly and quickly cut complex shapes including recesses 44. As a result, it becomes possible to improve the production efficiency of pipe joints such as oil well pipe joints.

[0059] In the above-described embodiment, cutting was performed by attaching the cutting tip 100 to a lathe and bringing the cutting tip 100 into contact with a steel pipe rotated about its axis. However, the cutting method of the present invention is not limited to this embodiment. For example, the steel pipe may be fixed and cut by moving the cutting tip 100 about the axis of the steel pipe. Furthermore, cutting may be performed by attaching the cutting tip 100 to a device or tool other than a lathe. [Example]

[0060] Using the cutting tips of Examples 1 to 9, Comparative Example, and Conventional Examples 1 and 2, a pipe (steel pipe) having an outer diameter of 180 mm and an inner diameter of 120 mm was cut into a machined shape including recess 44 shown in Fig. 7, and the machining time and the radius of curvature of recess 44 (the radius of curvature at point P') were measured. An NC (numerical control) lathe was used as the lathe, and the peripheral speed of the machined surface of the workpiece was 130 m / min.

[0061] The shapes of the cutting tips of Examples 1 to 9, Comparative Example, and Conventional Examples 1 and 2 are shown in Table 1. As shown in Table 1, the feed rate was changed for each tip shape, i.e., each curved surface (C1 to C4) of Examples 1 to 9, Comparative Example, and Conventional Examples 1 and 2.

[0062] The machining time was evaluated as the time required to achieve a surface roughness Ra of 1.5 μm on the cut surface. The surface roughness Ra was measured using a contact surface roughness meter.

[0063] The radius of curvature of the recess 44 (the radius of curvature at point P') was measured based on the shape of the molding material, which was used to mold the shape of the recess 44. Specifically, the shape of the molding material was evaluated by enlarging the contour shape using a projector. The results are shown in Table 1. For each cutting tip, whether a pin angle was formed in the cutting portion 20 was evaluated by palpation.

[0064] [Table 1]

[0065] As shown in Table 1, in Examples 1 to 9, the radius of curvature of the recess 44 (the radius of curvature of point P') was able to be made shorter than in Conventional Example 1. Furthermore, in Examples 1 to 9, the cutting time was able to be made shorter than in Conventional Example 2. Therefore, in Examples 1 to 9, the required machining accuracy of the recess 44 was met, while achieving rapid machining processing.

[0066] The comparative example is a cutting tip having a so-called pin angle in the cutting portion 20. When cutting was performed using the cutting tip of the comparative example, streaky scratches occurred on the cutting surface. Therefore, the required specified value of the surface roughness Ra of the cutting surface could not be met, and it was evaluated as "uncuttable."

[0067] As described above, by performing cutting using the cutting tip 100 according to the present invention, it is possible to process narrow concave shapes with a curvature radius of less than 0.700 with a smaller curvature radius, and it is also possible to cut other flat surfaces and cutting surfaces close to flat surfaces quickly and smoothly. Furthermore, it was shown that Examples 1 to 9 can prevent defects such as scratches on the cutting surface and tool breakage. [Explanation of symbols]

[0068] 100 Cutting Tips 12 Mounting part 20 Cutting part C1 First surface C2 Second surface C3 Third surface C4 Fourth surface Pb, Pc connection points

Claims

1. In a cutting tip having a cutting portion, The corner forming the cutting portion is composed of a plurality of curved surfaces having different curvatures, each of the adjacent curved surfaces shares a tangent at a connection point; a mounting portion formed in a hole shape for mounting to a lathe device; The cutting tip is characterized in that the corner is formed asymmetrically with respect to an axis connecting the center of the attachment portion and the apex of the corner.

2. 2. The cutting tip according to claim 1, wherein the central angle of the curved surface having the smallest radius of curvature among the plurality of curved surfaces is 30 degrees or more and 90 degrees or less.

3. 2. The cutting tip according to claim 1, wherein the curved surface having the smallest radius of curvature among the plurality of curved surfaces has a radius of curvature of 0.10 mm or more.

4. 3. The cutting tip according to claim 2, wherein the curved surface having the smallest radius of curvature among the plurality of curved surfaces has a radius of curvature of 0.10 mm or more.

5. 5. The cutting tip according to claim 1, wherein the plurality of curved surfaces all have a radius of curvature of 0.80 mm or less.

6. A cutting method for cutting a workpiece by cutting, comprising: A cutting method comprising a cutting step of cutting the workpiece using the cutting tip according to any one of claims 1 to 4.

7. A cutting method for cutting a workpiece by cutting, comprising: A cutting method comprising the step of cutting the workpiece using the cutting tip according to claim 5.

8. The cutting method according to claim 6, wherein in the cutting step, the cutting is performed at a feed rate of 0.05 mm / rev or more and 0.20 mm / rev or less.

9. The cutting method according to claim 7, wherein in the cutting step, the cutting is performed at a feed rate of 0.05 mm / rev or more and 0.20 mm / rev or less.

10. A method for manufacturing a pipe joint by cutting the inner surface of a steel pipe by cutting work, A method for manufacturing a pipe joint, comprising a cutting step of cutting the steel pipe using the cutting tip according to any one of claims 1 to 4.

11. A method for manufacturing a pipe joint by cutting the inner surface of a steel pipe by cutting work, A method for manufacturing a pipe joint, comprising a cutting step of cutting the steel pipe using the cutting tip according to claim 5.

12. A pipe fitting characterized by being machined using a cutting tip described in any one of claims 1 to 4.

13. A pipe fitting characterized by being machined using the cutting tip described in claim 5.

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