JP2016117109A - Cutting method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cutting method which can easily and surely suppress the remains of chips and burrs in a penetration hole without using a special tool.SOLUTION: A workpiece 10 is prepared in which a truncated or conical recess 14 which has an opening 14a having the same diameter as that of a penetration hole 15, and whose apex face 14c or an apex 14d is formed in a region which is not larger than a half of a hole diameter φH of the penetration hole 15 is formed at another face 12 in advance, a cutting tool 20 is moved toward the other face 12 from one face 11 of the workpiece 10 along a center axial line LC of the recess 14, and thus, the penetration hole 15 having the same diameter as that of the opening 14a is formed.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a cutting method, for example, a cutting method for forming a through hole for inserting a piston pin or the like into a workpiece such as a connecting rod by rotary cutting.

  In an internal combustion engine such as a reciprocating engine, a connecting rod (also referred to as a connecting rod) that connects the piston and the crankshaft is provided in order to convert a reciprocating motion of the piston into a rotational motion of a crankshaft that is an output shaft. . This connecting rod basically has a large end portion having a through hole (also referred to as a large end hole) for inserting a crank pin of a crankshaft and a through hole (also referred to as a small end hole) for inserting a piston pin of a piston. And a column portion connecting the large end portion and the small end portion.

  By the way, for example, the above-described through hole for the piston pin of the connecting rod is filled with a material powder made of an alloy powder or the like in a mold cavity, and the filled material powder is pressed to form a green compact. After forming the connecting rod coarse material by sintering and forging the green compact, the short cylindrical end portion of the connecting rod coarse material is subjected to drilling processing (also referred to as bore processing) by rotational cutting.

  The drilling process will be described more specifically. As shown in FIG. 6, the connecting rod coarse material A formed by sintering forging has, for example, a small end W of the small end portion W in order to suppress the occurrence of burrs due to the drilling process. A cone having a surface opening Ca having the same diameter as a through hole B (see FIGS. 7F and 7G) formed by drilling on both the front surface Wa side (cutting start surface side) and the back surface Wb side (cutting end surface side). A truncated cone-shaped rear surface depression C having a trapezoidal surface depression C and a rear surface opening Da having the same diameter as the through hole B is formed in advance (see FIG. 7A). The front surface recess C and the back surface recess D are formed coaxially. As shown in FIGS. 7A to 7G, the connecting rod coarse material A (small end W thereof) in which the front surface recess C and the back surface recess D are formed in advance is formed from the inner blade Ea and the outer blade Eb at the tip. A rotary cutting tool F, such as a drill, to which the cutting tool E is mounted is moved while being rotated from the front surface Wa side to the rear surface Wb side along the central axis LC of both recesses. Thereby, the said through-hole B for piston pins which consists of the same hole diameter as the diameter of surface opening Ca and back surface opening Da is formed.

  However, in the conventional drilling process described above, the present inventors may have disc-shaped, coin-shaped, or ring-shaped chips on the back surface Wb side (cutting end surface side) of the small end W. Has been confirmed.

  For such a problem of chips or burrs, for example, in Patent Document 1, a blade portion of a through hole deburring tool is inserted into a through hole (especially a small diameter hole intersecting a surface or a large diameter hole), A method for removing burrs generated in the through holes is disclosed.

Japanese Patent Laid-Open No. 2000-210806

  However, in the conventional method as disclosed in Patent Document 1, since it is necessary to use a separate tool after forming the through hole, there arises a problem that the manufacturing process and the manufacturing man-hour increase.

  This invention is made | formed in view of the subject mentioned above, and provides the cutting method which can suppress the residue of the chip | tip or the burr | flash to a through-hole simply and reliably, without using a separate tool. For the purpose.

  In order to achieve the above-mentioned object, the present inventors have repeatedly conducted numerical analysis and demonstration experiments on the remaining chips on the back surface side (cutting end surface side) of the small end portion as described above. Got.

  That is, as shown in FIGS. 7A to 7G, the rotary cutting tool F is moved from the front surface Wa side toward the back surface Wb side, and the tips thereof (that is, the cutting edges of the inner blade Ea and the outer blade Eb) are the back surface depression D. When approaching the vicinity of the top surface Dc (FIG. 7C), stress in the vicinity of the outer edge of the top surface Dc (in other words, in the vicinity of the corner where the top surface Dc and the side surface Db intersect and in the G region in the figure) When the rotary cutting tool F is fed from the front surface Wa side toward the back surface Wb side, the portion inside the outer edge of the top surface Dc of the back surface recess D (that is, the stress increases G) The portion inside the region) is pushed to the back surface Wb side without being cut by the cutting tool E (FIGS. 7D and 7E). Then, at a certain point in time, a part outside the outer edge of the top surface Dc of the back surface depression D is cut, and an uncut rough material consisting of a portion inside the outer edge of the top surface Dc of the back surface depression D (in this case) Is a disk-shaped or coin-shaped rough material, or a disk-shaped or coin-shaped rough material and a ring-shaped rough material partially connected together) H is connected to a part of the connecting rod rough material. It was thought that it was pushed out to the back surface Wb side by the rotary cutting tool F (FIGS. 7F and 7G).

  In some cases, only the portion near the outer edge of the top surface Dc of the back surface depression D (the portion near the corner where the top surface Dc and the side surface Db intersect and where stress is increased) is the cutting tool E. It is pushed to the rear surface Wb side without being cut, and at a certain point, a part of the outer side of the top surface Dc of the back surface recess D is cut off, and the back surface recess D is composed of a portion near the outer edge of the top surface Dc. It was considered that the cutting rough material (in this case, a ring-shaped rough material) was pushed out to the back surface Wb side by the rotary cutting tool F in a state of being connected to a part of the connecting rod rough material.

  Further, the stress increase near the outer edge of the top surface Dc of the back surface depression D as described above (near the corner where the top surface Dc and the side surface Db intersect) is caused by the position of the outer edge of the top surface Dc of the back surface depression D and the back surface. The position of the outer edge of the opening Da, in particular, the outer diameter of the top surface Dc of the back surface depression D and the diameter of the back surface opening Da (in other words, the diameter of the through hole B to be formed) are related. It was considered that as the position of the outer edge of the top surface Dc approaches the position of the outer edge of the back surface opening Da, stress increases near the outer edge of the top surface Dc of the back surface depression D, and the above-described chips are likely to remain.

  Based on such knowledge, the present inventors have separated the top surface (the outer edge position) of the back surface depression from the back surface opening (the outer edge position), thereby reducing the back surface depression at the time of cutting with the rotary cutting tool. It was found that the stress increase near the outer edge of the top surface can be suppressed, and the remaining (occurrence) of chips or burrs in the through hole can be reliably suppressed.

  That is, the cutting method of the present invention cuts a workpiece to be machined with a cutting tool attached to the tip in the rotational axis direction by moving the cutting tool around the rotational axis while rotating the cutting tool. A cutting method for forming a through hole extending from one surface of the workpiece to the other surface, wherein the workpiece has an opening having the same diameter as the through hole, and the top surface or the top portion thereof is half the hole diameter of the through hole. Prepare a workpiece in which a truncated cone shape or conical recess formed in the following region is formed in advance on the other surface, and move the cutting tool from one surface of the workpiece to the other along the central axis of the recess In this method, the through hole having the same diameter as the opening is formed by moving toward the direction.

  The top surface of the frustoconical recess is formed in a region outside the half of the hole diameter of the through hole. In other words, the outer diameter of the top surface of the recess is larger than half of the hole diameter of the through hole. In this case, as described above, stress increases near the outer edge of the top surface of the depression, and disc-shaped, coin-shaped, or ring-shaped chips may remain on the other side.

  On the other hand, according to the cutting method described above, the depression formed in advance on the other surface of the workpiece has an opening having the same diameter as the through hole, and the top surface or the top portion is less than half the hole diameter of the through hole. By using a truncated cone shape or conical shape formed in the region, the position of the outer edge of the top surface of the recess or the distance between the position of the top portion and the position of the outer edge of the opening can be secured. Since it is possible to reliably suppress an increase in stress in the vicinity of the outer edge of the top surface of the recess during processing, it is possible to easily and reliably suppress the remaining of chips or burrs in the through hole without using a separate tool. .

  Preferably, the depth of the recess is ¼ or more of the hole diameter of the through hole.

  When the depth of the recess is shallower than 1/4 of the hole diameter of the through hole, the distance between the top surface or the top of the recess and the other surface (cutting end surface) of the workpiece is reduced, and cutting is performed as described above. Even if the increase in stress near the outer edge of the top surface of the dent during machining is suppressed, the part where the stress increases near the outer edge of the top surface of the dent during machining due to variations in the physical properties of the workpiece is slightly When pressed to the side, disc-shaped, coin-shaped, or ring-shaped chips may still remain on the other side.

  According to the cutting method described above, by setting the depth of the recess to ¼ or more of the hole diameter of the through hole, the distance between the top surface or the top portion of the recess and the opening (that is, the other surface of the workpiece). Therefore, even if the part where the stress is increased near the outer edge of the top surface of the dent during cutting due to variations in the physical properties of the work, even if the part is pushed to the other side (cutting finish surface) side of the work, The remaining of chips or burrs in the through hole on the other surface side can be more reliably suppressed.

  As can be understood from the above description, according to the present invention, the depression formed in advance on the other surface of the workpiece has an opening having the same diameter as that of the through hole, and the top surface or the top portion has a hole diameter of the through hole. By using a truncated cone shape or conical shape formed in less than half of the area, it is possible to easily and reliably prevent chips or burrs from remaining in the through-holes, and reliably prevent defective products from being produced in the manufacturing process. can do.

It is a longitudinal cross-sectional view which shows an example of the workpiece | work applied to the cutting method of this invention. It is a longitudinal cross-sectional view which shows the other examples of the workpiece | work applied to the cutting method of this invention. It is a longitudinal cross-sectional view which shows the further another example of the workpiece | work applied to the cutting method of this invention. It is an internal block diagram which shows an example of the internal structure of the cutting tool used for the cutting method of this invention. It is the figure explaining the cutting method of this invention in time series, and is the figure explaining the state which has arrange | positioned the workpiece | work with respect to the cutting tool. It is the figure explaining the cutting method of this invention in time series, and is the figure explaining the state cut to about half of the thickness of the workpiece | work with the cutting tool. It is the figure explaining the cutting method of this invention in time series, and is the figure explaining the state cut to the top face vicinity of the back surface hollow of a workpiece | work with a cutting tool. It is the figure explaining the cutting method of this invention in time series, and is the figure explaining the state which the front-end | tip of the cutting tool passed the top face of the back surface depression of a workpiece | work. It is the figure explaining the cutting method of this invention in time series, and is the figure explaining the state where the front-end | tip of the cutting tool approached to the back surface vicinity of the workpiece | work. It is the figure explaining the cutting method of this invention in time series, and is the figure explaining the state where the front-end | tip of the cutting tool reached the back surface of the workpiece | work. It is the figure explaining the cutting method of the present invention in time series, and is the figure explaining the state where the tip of the cutting tool passed the back of the work. It is a perspective view which shows a connecting rod coarse material. It is the figure explaining the conventional cutting method in time series, and is the figure explaining the state which has arrange | positioned the workpiece | work (small end part of a connecting rod rough material) with respect to the cutting tool. It is the figure explaining the conventional cutting method in time series, and is the figure explaining the state cut to about half of the thickness of the workpiece | work with the cutting tool. It is the figure explaining the conventional cutting method in time series, and is the figure explaining the state cut to the top surface vicinity of the back surface depression of a workpiece | work with a cutting tool. It is the figure explaining the conventional cutting method in time series, and is the figure explaining the state which the front-end | tip of the cutting tool passed the position of the top face of the back surface depression of a workpiece | work. It is the figure explaining the conventional cutting method in time series, and is the figure explaining the state where the front-end | tip of the cutting tool approached to the back surface vicinity of the workpiece | work. It is the figure explaining the conventional cutting method in time series, and is the figure explaining the state where the front-end | tip of the cutting tool reached the back surface of the workpiece | work. It is the figure explaining the conventional cutting method in time series, and is the figure explaining the state where the front-end | tip of the cutting tool passed the back surface of the workpiece | work.

  Embodiments of the present invention will be described below with reference to the drawings. In the following description, a description will be given of a drilling process in which a through hole for a piston pin is formed in a small end portion of a steel connecting rod coarse material. Of course, the present invention can be applied to a drilling process in which a through hole having a predetermined hole diameter (for example, a through hole for a crank pin) is formed in a workpiece other than the small end portion of the material. Needless to say, the present invention can also be applied to drilling for forming a through hole in a metal workpiece other than steel (for example, aluminum having a lower hardness than steel) or a resin workpiece.

  1 to 3 are longitudinal sectional views showing a workpiece (small end portion of a connecting rod coarse material) applied to the cutting method of the present invention, and FIG. 4 is a cutting used in the cutting method of the present invention. It is an internal block diagram which shows an example of the internal structure of a tool, and FIG. 5A-FIG. 5G is the figure explaining the cutting method of this invention in time series.

  First, the workpiece 10 applied to the cutting method of the present invention will be described with reference to FIGS. 1 to 3. In the workpiece 10, as described above, in the vicinity of the outer edge of the top surface of the back surface depression at the time of cutting ( In order to suppress the increase in stress at the corner where the top surface and the side surface cross), and to suppress the remaining (occurrence) of chips or burrs in the through hole, the top surface of the back recess (the position of the outer edge) It is separated from the back surface opening (the position of the outer edge) by a predetermined distance.

  That is, as shown in FIG. 1, the workpiece 10 is composed of a substantially parallel surface 11 (cutting start surface, one surface) and a back surface 12 (cutting end surface, the other surface). Both have a frustoconical surface recess 13 having a surface opening 13a having the same diameter as a through hole 15 (see FIGS. 5F and 5G) formed by drilling, and a back surface opening 14a having the same diameter as the through hole 15. A frustoconical back surface recess 14 is formed, and a top surface (surface 13 side surface) 14c of the back surface recess 14 is formed in a region equal to or less than half the hole diameter φH of the through hole 15. In other words, the outer diameter φh of the top surface 14 c of the back surface depression 14 is set to be equal to or less than half the hole diameter φH of the through hole 15. The surface depression 13 and the back depression 14 formed on the front surface 11 and the rear surface 12 of the workpiece 10 are formed on the same axis (common central axis LC).

  The depth (the dimension in the central axis LC direction from the back surface 12 or the back surface opening 14a to the top surface 14c) D is the hole diameter φH of the through hole 15 (that is, the back surface opening 14a). It is preferable that it is set to 1/4 or more of (aperture).

  In addition, an inclination angle (also referred to as a cutting angle) θ of the side surface (conical surface) 14b of the back surface depression 14 with respect to the back surface 12 of the workpiece 10 can be set as appropriate as long as the above conditions are maintained. In addition, it is preferably 45 degrees or more, and desirably 45 degrees.

  In the example shown in FIG. 1, the inclination angle θ of the side surface 14b of the back surface depression 14 is constant from the back surface opening 14a to the top surface 14c. For example, as shown in FIG. θ may be changed stepwise or continuously from the back surface opening 14a to the top surface 14c. In the example shown in FIG. 2, the inclination angle θ changes in two stages from a relatively large inclination angle θ1 to a relatively small inclination angle θ2. When the inclination angle θ is thus changed between the back surface opening 14a and the top surface 14c, as described above, the inclination angle θ of the side surface (conical surface) 14b in contact with the back surface 12 of the workpiece 10 (in FIG. 2, Since it is desirable that the inclination angle θ1) is 45 degrees, it is particularly preferable that the inclination angle θ is changed from 45 degrees toward the top face 14c so as to decrease continuously or stepwise from 45 degrees. it is conceivable that.

  In the example shown in FIG. 1, the back surface depression 14 has a truncated cone shape. For example, as shown in FIG. 3, the top surface 14 d of the back surface depression 14 is disposed on the central axis LC. It is good also as a cone shape (cone shape which does not have a top surface). In this case, the top portion 14 d of the back surface recess 14 is formed in a region that is not more than half of the hole diameter φH of the through hole 15.

  Next, with reference to FIG. 5A to FIG. 5G, an outline of a method (perforation method of the present invention) of performing drilling by rotary cutting on the workpiece 10 shown in FIG. 1 described above will be described.

  In addition, this drilling process is more specifically, for example, as shown in FIG. 4, a cutting tool 20 in which a cutting tool 21 including an inner blade 21 a and an outer blade 21 b is attached to the tip (tip in the rotation axis LR direction). Uses a cutting tool 20 in which an inner blade 21a and an outer blade 21b are mounted in each of two mounting grooves provided at the tip (so that each blade tip protrudes from the tip surface). While rotating around the rotation axis LR, the workpiece 10 is moved along the rotation axis LR, and the workpiece 10 to be processed is cut from the front surface side to the back surface side with the blade 21 attached to the tip. .

  In this drilling process, as shown in FIG. 5A, first, the cutting tool 20 is formed so that the center axis LC of the front surface recess 13 and the back surface recess 14 formed on the workpiece 10 and the rotation axis LR of the cutting tool 20 coincide. On the other hand, the workpiece 10 is arranged.

  Next, the cutting tool 20 is rotated about the rotation axis LR along the rotation axis LR (that is, along the central axis LC of the surface recess 13 and the back recess 14) and from the front surface 11 to the back surface 12 of the workpiece 10. To move at a specified feed rate. Thereby, as shown in FIG. 5B, the workpiece 10 is gradually cut from the front surface 11 side toward the back surface 12 side by the cutting tool 21 (the inner blade 21 a and the outer blade 21 b) provided at the tip of the cutting tool 20. .

  When the cutting tool 20 is further moved from the front surface 11 to the back surface 12 of the workpiece 10 from the state shown in FIG. 5B, the tip of the cutting tool 20 approaches the top surface 14c of the back surface depression 14 as shown in FIG. Since the back surface depression 14 of the workpiece 10 has the shape as described above, even in the state shown in FIG. 5C, the vicinity of the outer edge of the top surface 14c of the back surface depression 14 (the vicinity of the corner where the top surface 14c and the side surface 14b intersect) Thus, an increase in stress in the G region in the figure is suppressed. Therefore, as shown in FIG. 5D, when the tip of the cutting tool 20 passes through the top surface 14 c of the back surface recess 14, the top surface 14 c portion of the back surface recess 14 is formed by the cutting tool 21 provided at the tip of the cutting tool 20. It is cut reliably.

  Next, the tip of the cutting tool 20 (more specifically, the cutting edge of the cutting tool 21 attached to the tip of the cutting tool 20) passes through the top surface 14 c of the back surface recess 14, and the top surface 14 c portion of the back surface recess 14 Is cut, the feed rate of the cutting tool 20 is lowered to suppress the occurrence of burrs on the back surface 12 side due to drilling, and the cutting tool 20 is further moved from the front surface 11 to the back surface 12 of the workpiece 10. Move. As a result, as shown in FIGS. 5E to 5G, a portion outside the back surface recess 14 (portion exhibiting a triangular cross-section) of the workpiece 10 is gradually cut by the cutting tool 21 provided at the tip of the cutting tool 20. When the tip of the cutting tool 20 reaches the back surface 12 of the workpiece 10, a circular cross-sectional through hole 15 extending from the front surface 11 to the back surface 12 is formed in the workpiece 10.

  Thus, according to the cutting method of the present embodiment, the back surface depression 14 formed in advance on the back surface 12 of the workpiece 10 has the back surface opening 14a having the same diameter as the through hole 15 to be formed and the top surface thereof. 14c is a truncated cone formed in a region that is less than half the hole diameter φH of the through hole 15 to ensure an increase in stress near the outer edge of the top surface 14c of the back surface recess 14 during cutting. Therefore, without using a separate tool, it is possible to easily and surely prevent the chips or burrs from remaining in the through-holes 15 and reliably prevent the occurrence of defective products in the manufacturing process.

  Further, by setting the depth D of the back surface recess 14 to ¼ or more of the hole diameter φH of the through hole 15, the top surface 14 c of the back surface recess 14 and the back surface opening 14 a (that is, the back surface 12 of the workpiece 10). Therefore, even if a portion where stress is increased near the outer edge of the top surface 14c of the back surface recess 14 due to variations in physical properties of the work 10 or the like is slightly pushed to the back surface 12 side of the work 10 In addition, it is possible to more reliably prevent chips or burrs from remaining in the through hole 15 on the back surface 12 side of the workpiece 10.

<Experiment and results of verifying generation of chips or burrs in cutting with specimen>
When the inventors made a plurality of test specimens having different shapes of the back surface depressions (Examples 1 to 5 and Comparative Examples 1 to 4) and drilled each specimen using a cutting tool. Generation of chips (disk-shaped, coin-shaped, or ring-shaped chips) and burrs were confirmed.

  Table 1 below shows the shape of the back surface depression of each specimen, the feed rate of the cutting tool, and the results of confirming the presence or absence of chips and burrs after processing in each specimen.

  Each specimen is made of steel, the thickness of each specimen (space between the front surface and the back surface) is 15 mm, and the diameter of the through hole formed in each specimen (that is, the back surface opening of the back surface depression) ) Was 20 mm.

  Moreover, as shown in Table 1, in the test bodies other than Examples 3 and 4, the inclination angle θ of the back surface depression was constant, but in the test bodies of Examples 3 and 4, the inclination angle was near the back surface. θ was changed. Moreover, in the test body other than Example 5, the feed rate of the cutting tool used for the cutting was changed from 0.15 mm / rev to 0.029 mm / rev at a position of 4 mm from the back surface. The body had a constant feed rate of 0.3 mm / rev from the front surface to the back surface.

  As shown in Table 1, drilling is performed by setting the outer diameter of the top surface of the back surface recess to half (1/2) or less of the hole diameter of the through hole to be formed (that is, the diameter of the back surface opening of the back surface recess). It was confirmed that the remaining chips (disc-shaped, coin-shaped, or ring-shaped chips) on the back side of the subsequent workpiece can be reliably suppressed.

  Moreover, it was thought that the residue of the chip | tip on the back surface side of the workpiece | work after drilling can be suppressed more reliably by making the depth of a back surface depression into 1/4 or more of the hole diameter of the said through-hole.

  In addition, if the feed rate of the cutting tool, particularly the feed rate of the cutting tool when the cutting tool portion passes the back side of the specimen (work), is too fast, burrs may occur on the back side (Example 5). However, the cutting tool feed speed is adjusted appropriately. Specifically, the cutting tool after the cutting tool portion at the tip of the cutting tool has passed through the top surface of the back surface recess and before reaching the back surface of the workpiece. It was confirmed that the burr generation on the back side of the workpiece can be surely suppressed by slowing the feed speed of.

  As a result of this experiment, the outer diameter of the top surface of the back surface depression is made less than or equal to half the hole diameter of the through hole to be formed, and after the tip of the cutting tool has passed the top surface of the back surface depression, It has been proved that generation of chips (disk-shaped, coin-shaped, or ring-shaped chips) and burrs on the back side of the workpiece can be reliably suppressed by slowing the feed rate of the cutting tool before reaching.

  The embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration is not limited to this embodiment, and there are design changes and the like without departing from the gist of the present invention. They are also included in the present invention.

  DESCRIPTION OF SYMBOLS 10 ... Work, 11 ... The surface (one side) of a workpiece, 12 ... The back surface (other side) of a workpiece, 13 ... Surface depression, 13a ... Surface opening of a surface depression, 14 ... Back depression, 14a ... Back opening of a back depression, 14b: Side surface of back surface recess, 14c: Top surface of back surface recess, 14d: Top portion of back surface recess, 15 ... Through hole, 20 ... Cutting tool, 21 ... Cutting tool, 21a ... Inner blade, 21b ... Outer blade, LC ... Center axis , LR: rotation axis, φH: diameter of through-hole (diameter of rear surface opening), φh: outer diameter of top surface, D: depth, θ: inclination angle

Claims (5)

By rotating the cutting tool around the rotation axis while moving the tool along the rotation axis, the workpiece to be machined is cut with the cutting tool attached to the tip in the rotation axis direction, and the other side is removed from one side of the workpiece. A cutting method for forming a through hole extending to the direction,
A frustoconical or conical recess having an opening having the same diameter as that of the through hole and having a top surface or a top portion formed in a region equal to or less than half the hole diameter of the through hole is previously formed on the other surface. Prepared work,
The cutting method which forms the said through-hole with the same diameter as the said opening by moving the said cutting tool toward the other side from the one surface of the said workpiece | work along the center axis line of the said hollow.   The cutting method according to claim 1, wherein a depth of the recess is ¼ or more of a diameter of the through hole.   The cutting method according to claim 1 or 2, wherein an angle of inclination of the side surface of the depression with respect to the other surface is 45 degrees or more.   The cutting method according to claim 3, wherein the inclination angle is 45 degrees.   The feed rate of the cutting tool is made slower after the cutting tool has passed the top surface or top of the recess than when the cutting tool passes the top surface or top of the recess. The cutting method described.

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