Cutting insert, cutting tool, and method of manufacturing machined product

A cutting insert according to an embodiment has a lower surface, an upper surface, a side surface disposed between the lower surface and the upper surface, a pair of corner cutting edges located along an intersection of the upper surface and the side surface, and a major cutting edge located between the pair of corner cutting edges. The major cutting edge has a downwardly dented curvilinear part and a pair of straight parts respectively extending from the curvilinear part toward the pair of corner cutting edges in a side view. A portion of the curvilinear part located lowermost is close to one corner cutting edge in the side view.

TECHNICAL FIELD

The present embodiment relates to a cutting insert, a cutting tool, and a method of manufacturing a machined product.

BACKGROUND ART

As a cutting insert for use in a cutting process of a workpiece, for example, cutting inserts disclosed in Japanese Unexamined Patent Publication No. 9-216113 (Patent Document 1) and Japanese Unexamined Patent Publication No. 11-347826 (Patent Document 2) have conventionally been known. The cutting inserts respectively described in Patent Documents 1 and 2 are specifically used in a milling process, such as a face milling process or an end milling process. In the cutting inserts respectively described in Patent Documents 1 and 2, a cutting edge is curved so as to be dented downward in a side view.

In the cutting inserts respectively described in Patent Documents 1 and 2, setting is made so that a cutting edge angle of a major cutting edge with respect to a workpiece is 45° or 90°. Therefore, when cutting the workpiece, a chip thickness increases, thus leading to large impact exerted on the major cutting edge. Furthermore, there occurs a large amount of heat generated when the major cutting edge cuts the workpiece, and there is a large risk that a fracture occurs in the major cutting edge.

SUMMARY OF THE INVENTION

A cutting insert according to an aspect of the embodiment has a polygonal shaped upper surface has a pair of corner parts and a side part located between the pair of corner parts, a polygonal shaped lower surface corresponding to the upper surface, a side surface disposed between the lower surface and the upper surface, a pair of corner cutting edges located along an intersection of the pair of corner parts of the upper surface and the side surface, and a major cutting edge located between the pair of corner cutting edges. The major cutting edge has a downwardly dented concave shape as a whole, and has a first section having a downwardly dented concave curvilinear shape in a side view, and a pair of second sections being in the shape of a straight-like line. The pair of second sections respectively extend from the first section toward the pair of corner cutting edges, and have a larger height as approaching the pair of corner cutting edges. A portion of the first section which is located lowermost is close to one of the corner cutting edges in the side view.

EMBODIMENTS FOR CARRYING OUT THE INVENTION

A cutting insert1(hereinafter also referred to simply as the insert1) according to an embodiment is described below with reference toFIGS. 1 to 3. A chain double-dashed line inFIG. 1indicates a central axis X of the cutting insert1.

As shown inFIGS. 1 to 3, the insert1of the present embodiment has a lower surface2, an upper surface3, a side surface4disposed between the lower surface2and the upper surface3, a pair of corner cutting edges5(5a,5b) located along an intersection of the upper surface3and the side surface4, and a major cutting edge6located between the pair of corner cutting edges5(5a,5b). The upper surface3has a polygonal shape, and has a pair of corner parts and a side part located between the pair of corner parts. The lower surface2has a polygonal shape corresponding to the upper surface3. The pair of corner cutting edges5is located along an intersection of the pair of corner parts of the upper surface3and the side surface4. The major cutting edge6is located along an intersection of the side part of the upper surface3and the side surface4.

The major cutting edge6has a concave shape that is dented downward as a whole, and has a first section (curvilinear section) and a pair of second sections (straight parts). The first section has a concave curvilinear shape dented downward in a side view. The pair of second sections, each being in the shape of a straight-like line, respectively extend from the first section toward the pair of corner cutting edges5(5a,5b), and have a larger height as approaching the pair of corner cutting edges (5a,5b). A portion (bottom portion)6pof the first section which is located lowermost is closer to the corner cutting edge5b.

One of the corner cutting edges5aand5bwhich is close to a processing surface of a workpiece when cutting the workpiece is taken as a first corner cutting edge5a, and the other located away from the processing surface of the workpiece when cutting the workpiece is taken as a second corner cutting edge5b.

The upper surface3has the polygonal shape, and has a pair of corner parts and a side part located between the pair of corner parts. The lower surface2has the polygonal shape corresponding to the upper surface3. The lower surface2and the upper surface3of the insert1in the present embodiment respectively have a square shape having a plurality of corner parts. The corner parts in the present embodiment are not corners in the strict sense of the word, but have a curved arc shape in the top view.

Therefore, in the insert1of the present embodiment, arc shaped portions respectively located at the corner parts of the upper surface3serve as the corner cutting edges5, and a portion of a circumferential edge of the upper surface3which is located between the arc shaped corner parts is the side part and serves as the major cutting edge6.

A through hole H that penetrates vertically is formed in the insert1. The through hole H extends between a middle portion of the upper surface3and a middle portion of the lower surface2. The through hole H is a hole that permits passage of a screw, and is used for fixing the insert1to a holder by screwing the screw into the holder. An opening of the through hole H has a circular shape in the top view, and has a diameter of, for example, 2-12 mm. The through hole H extends between a center of the upper surface3and a center of the lower surface2. Accordingly, a central axis X of the through hole H extends vertically.

For example, cemented carbide or cermet is usable as a material of the insert1. Examples of compositions of cemented carbide include WC—Co produced by adding cobalt (Co) powder to tungsten carbide (WC), followed by sintering, WC—TiC—Co produced by adding titanium carbide (TiC) to WC—Co, and WC—TiC—TaC—Co produced by adding tantalum carbide (TaC) to WC—TiC—Co. The cermet is a sintered composite material obtained by compositing metal with a ceramic ingredient, and is specifically a titanium compound composed mainly of titanium carbide (TiC) or titanium nitride (TiN).

A surface of the insert1may be coated with a film by chemical vapor deposition (CVD) method or physical vapor deposition (PVD) method. Examples of compositions of the film include titanium carbide (TiC), titanium nitride (TiN), titanium carbonitride (TiCN), and alumina (Al2O3).

The lower surface2or the upper surface3in the insert1has a maximum width of 5-20 mm. A height from the lower surface2to the upper surface3is 2-8 mm. The shapes of the upper surface3and the lower surface2are not limited to the foregoing ones. For example, the shape of the upper surface3in the top view may be a polygonal shape, such as a triangular shape, a pentagonal shape, a hexagonal shape, and an octagonal shape.

As shown inFIGS. 1 and 2, the upper surface3has a land surface31and a rake surface32. The land surface31is continuous with the corner cutting edges5and the major cutting edge6. The corner cutting edges5and the major cutting edge6correspond to an outer edge of the upper surface3. The rake surface32is disposed in a region closer to the through hole H than the land surface31. The rake surface32is an inclined surface whose height decreases as approaching the through hole H. The lower surface2in the present embodiment is disposed on a plane orthogonal to the central axis X.

The land surface31is continuous with the corner cutting edges5and the major cutting edge6, and is disposed in a region closer to the central axis X than the corner cutting edges5and the major cutting edge6. The land surface31is a narrow band shaped surface disposed along the corner cutting edges5and the major cutting edge6. An interior angle formed with the side surface4is larger than with the rake surface32. Specifically, the land surface31is an inclined surface that is approximately parallel to the lower surface2, or an inclined surface whose height increases as approaching the center. A part of a region of the land surface31which is close to the corner cutting edges5may have a smaller height as approaching the center.

The corner cutting edges5and the major cutting edge6are disposed along an intersection of the land surface31and the side surface4. The land surface31is disposed for enhancing strength of the corner cutting edges5and the major cutting edge6. The rake surface32located inside the land surface31is an inclined surface whose height decreases as approaching the center. Therefore, the rake surface32and the side surface4form a small interior angle.

However, the interior angle formed by the land surface31and the side surface4is larger than an interior angle formed by the rake surface32and the side surface4. Therefore, the strength of the corner cutting edges5and the major cutting edge6can be enhanced by having the land surface31. A width of the land surface31located between the outer edge of the upper surface3and an outer edge of the rake surface32is suitably set according to cutting conditions, and is set, for example, in a range of 0.05-0.5 mm.

The rake surface32is continuous with the land surface31and disposed at a region closer to the central axis X than the land surface31. The rake surface32is a surface along which chips cut by the major cutting edge6graze. Therefore, the chips of the workpiece200flow along a surface of the rake surface32. The rake surface32is an inclined surface whose height decreases as approaching the center of the upper surface3in order to achieve a satisfactory disposal of the chips.

Although not particularly illustrated, an inclination angle indicated by an angle formed by the lower surface2in a cross section perpendicular to the rake surface32and the rake surface32needs to be set, for example, in a range of 5-30°. The rake surface32needs to have a height that decreases as approaching the center in order that the rake surface32is capable of scooping out the chips. Therefore, the rake surface32may be made up of a plurality of regions that are different in inclination angle.

To be specific, the rake surface32in the insert1of the present embodiment has a first rake surface321located along a curvilinear part61(first section61) of the major cutting edge6, a second rake surface322located along a straight part62(second section62) of the major cutting edge6, and a third rake surface323located along the corner cutting edge5. In the present embodiment, a rake angle of the second rake surface322is larger than a rake angle of each of the first rake surface321and the third rake surface323. In other words, as compared with the rake angle of the second rake surface322, each of the first rake surface321and the third rake surface323is smaller than the rake angle of the second rake surface322.

A chip flow direction changes in each of regions of the rake surface extending along the corner cutting edges5and the curvilinear part62, which are curved regions in the cutting edge. These regions of the rake surface are therefore apt to receive a relatively large load. It is however possible to enhance strength of these regions because the first rake surface321and the third rake surface323have a relatively large rake angle. This contributes to improving durability of the insert1.

In the present embodiment, the rake angle of the first rake surface321is also larger than the rake angle of the third rake surface323. Owing to the fact that the corner cutting edges5have a larger curvature than the curvilinear part61, a change in flow direction of chips flowing along the third rake surface323is larger than a change in flow direction of chips flowing along the first rake surface321. On this occasion, strength of the third rake surface323can be enhanced owing to the relatively small rake angle of the third rake surface323, thereby improving the durability of the insert1.

Each of the first rake angle321, the second rake angle322, and the third rake angle333needs to be evaluated by a rake angle in a cross section that passes through a center of a region of their respective corresponding cutting edges and is orthogonal to the cutting edge. For example, a rake angle in a cross section that passes through a center of the curvilinear part61and is orthogonal to the curvilinear part61at the center serves as the first rake surface321.

The side surface4is disposed between the lower surface2and the upper surface3. The side surface4functions as a flank surface, and is connected to the outer edge of the upper surface3. The side surface4has a plane part41located at a portion corresponding to the major cutting edge6, and a curved surface42located at a portion corresponding to the corner cutting edges5. Thus, the side surface4has the plane part41being continuous with the major cutting edge6. A length of the plane part41along a direction parallel to the lower surface2in a side view is set, for example, in a range of 5-20 mm. A vertical length of the plane part41in the side view is set in a range of 2-8 mm. The curved surface42is located at a portion where the plane parts41respectively located on different side surfaces are connected to each other.

Owing to the fact that the plane part41is disposed on the side surface4, measurement of a wear condition of the flank surface only needs to observe a degree of wear of a surface of the plane part41. It is therefore easy to measure the wear by an actual measurement from a photograph or the like. In the present embodiment, an entirety extending from an upper end to a lower end in the portion of the side surface4corresponding to the major cutting edge6is taken as the plane part41, but not limited to this. For example, a partial region being continuous with the major cutting edge6may be taken as the plane part41, and a step or the like may be disposed below the plane part41. The major cutting edge6is disposed along the side part that is the intersection of the upper surface3and the side surface4. As shown inFIG. 3, the major cutting edge6has an upwardly concaved shape as a whole in the side view.

Owing to the fact that the plane part41is disposed on the side surface4, a plurality of kinds of inserts1are attachable to the holder without changing the shape of the holder, as long as the side surface4has the same shape as the plane part41. It is consequently possible to machine the workpiece200into a desired shape only by selecting and attaching a necessary insert1to the holder101according to the material of the workpiece200and the size of the workpiece200. That is, it is unnecessary to replace the holder101with one corresponding to the insert1. This simplifies a method of manufacturing a machined product, thereby improving producibility of the machined product.

The major cutting edge6is disposed along the intersection of the upper surface3and the side surface4. As shown inFIG. 3, the major cutting edge6has the first section61(curvilinear part61) having the downwardly dented concave curvilinear shape, and the pair of second sections62(straight parts62) disposed continuously with the curvilinear part61in a side view.

The curvilinear part61is disposed at a portion whose height position is relatively low in the major cutting edge6as shown inFIG. 3. The corner cutting edges5are respectively disposed at portions whose height position is relatively high. Setting is made so that the curvilinear part61is located below the corner cutting edges5so as to be located lower in a range of 0.2-2 mm in a vertical direction. The curvilinear part61is curved in the side view, and has the bottom portion6plocated lowermost in the major cutting edge6in the vertical direction.

With the configuration that the curvilinear part61and the pair of straight parts62interposing therebetween the curvilinear part61are disposed on the major cutting edge6, it is possible to eliminate the possibility that the major cutting edge6comes into contact with the workpiece200over a full length of the major cutting edge6at the same time when cutting the workpiece200, and it is also possible to reduce a portion of the full length of the major cutting edge6which comes into contact with the workpiece200at the same time. Specifically, one of the pair of first corner cutting edges5acomes into contact with the workpiece200, and thereafter the straight part62and the curvilinear part61come into contact with the workpiece200. It is consequently possible to prevent occurrence of chatter vibration in the cutting tool100by preventing a rapid increase in cut resistance of the major cutting edge6of the insert1so as to relax impact transmitted from the workpiece200to the insert1.

As shown inFIG. 6, the bottom portion6pof the curvilinear part61(first section61) is disposed close to the second corner cutting edge5bof the pair of corner cutting edges5(5a,5b) which is located above, in a state in which the insert1is attached to the holder101. In other words, when cutting the workpiece200located below, the bottom portion6pis close to the second corner cutting edge5bof the pair of corner cutting edges5(5a,5b) which is located away from the processing surface of the workpiece.

By locating the bottom portion6pclose to the second corner cutting edge5bwhen cutting the workpiece, the insert1is capable of ensuring a region of a small cutting edge angle in the major cutting edge6with respect to the workpiece while ensuring an amount of depth of cut of the major cutting edge6as a whole, in the state in which the insert1is attached to the holder101. Specifically, it is possible to decrease a cutting edge angle of a second straight part62bconnected to the second corner cutting edge5b.

When the amount of depth of cut is large as in the case of using a region of the major cutting edge6which also covers a portion close to the second corner cutting edge5b, a cut resistance against the major cutting edge6also becomes extremely large. It is however possible to reduce the cut resistance applied to the straight part62owing to the small cutting edge angle of the straight part62bconnected to the second corner cutting edge5bthat is apt to receive the relatively large load. It is therefore possible to reduce cut resistance applied to the entirety of the major cutting edge6.

It is consequently possible to thin chips and reduce heat generated in the major cutting edge6particularly in a high-feed-rate processing in which a cutting edge angle is 30° or less. Specifically, even when a depth of cut is increased and the insert1is subjected to large cut resistance during an engraving process or the like, the cutting edge located at a position at which the depth of cut is large has a small cutting edge angle. This makes it possible to decrease a chip thickness and reduce load applied to the cutting edge, thereby reducing the occurrence of fracture of the major cutting edge6. The occurrence of fracture of the major cutting edge6is thus reducible.

The insert1of the present embodiment has the square shape in the top view, and has four side parts and four corer parts. A pair of two corner parts is adjacent to each of the side parts. Therefore, the insert1of the present embodiment has four major cutting edges6. The corner cutting edges5are disposed between the major cutting edges6located along the outer edge of the upper surface3. Accordingly, there are four corner cutting edges5.

The insert1of the present embodiment has the square shape in the top view. Accordingly, there are the four major cutting edges6and the four corner cutting edges5, but not limited to this. The number of each of the major cutting edges6and the corner cutting edges5may be, for example, three, five, or six or more according to the polygonal shape of the insert1in the top view.

One of the four major cutting edges6is used in the cutting process of the workpiece in the cutting tool100that uses the insert1of the present embodiment and is shown inFIG. 4. When the major cutting edge6being used is deteriorated due to the cutting process over a long period of time, the insert1needs to be temporarily removed from the holder101, and thereafter attached again to the holder101by rotating the insert190° with respect to the central axis X. Thus, other major cutting edge6that is not yet used is usable in the cutting process of the workpiece200.

The intersection of the upper surface3and the side surface4is not a strict line form made by intersection of the two surfaces. When the intersection of the upper surface3and the side surface4is sharpened at an acute angle, the durability of the major cutting edge6may deteriorate. Hence, an intersecting portion of the upper surface3and the side surface4may have a slightly curvilinear shape, that is, may be subjected to a so-called honing process.

The major cutting edge6does not have the straight-like line as a whole in a side view, but has a downwardly concaved shape in a state in which the lower surface2is placed below and the upper surface3is placed above. Specifically, the major cutting edge6has the curvilinear part61(first section61) having the downwardly dented concave curvilinear shape and the pair of straight line parts62(second sections62) disposed continuously with the curvilinear part61. The pair of straight line parts62respectively extend from the curvilinear part61toward the pair of corner cutting edges5. When the major cutting edge6has this shape, it is easier to cause the major cutting edge6to be obliquely contacted with the workpiece than when the major cutting edge6has a straight-like line parallel to the upper surface3. It is therefore possible to reduce cut resistance when the major cutting edge6bites into the workpiece, thus leading to a satisfactory cutting process of the workpiece.

One of the pair of straight parts62(second sections62) which extends toward the first corner cutting edge5ais taken as a first straight part62a, and the other extending toward the second corner cutting edge5bis taken as a second straight part62b.

The description that the straight part62extends toward the corner cutting edges5is not intended to limit to the meaning that a virtual extension line of the straight part62intersects the corner cutting edges5, but implies that the straight part62merely extends toward the side on which the pair of corner cutting edges5aand5bare located. For example, inFIG. 5, the first corner cutting edge5ais located at a left end, and therefore, one that extends from the curvilinear part61toward a left side is taken as the first straight part62a. InFIG. 5, the second corner cutting edge5bis located at a right end, and therefore, one that extends from the curvilinear part61toward a right side is taken as the second straight part62b.

The shape of the curvilinear part61is not particularly limited as long as having the downwardly dented concave curvilinear shape. It is possible to employ, for example, an arc shape, an elliptical arc shape, or a parabolic shape. In the present embodiment, the curvilinear part61has the downwardly dented arc shape. In this case, it is less liable to receive influence of an axial rake when the insert1is attached to the holder101, thereby allowing the insert1to stably bite into the workpiece.

Here, the major cutting edge6is described below assuming that the entirety of the major cutting edge6has the straight-like line. Strong chatter vibration occurs in the insert1when the major cutting edge6of the insert1starts to bite into an end surface of the workpiece200. When the entirety of the major cutting edge6has a mere straight-like line, the entirety of the major cutting edge6may start to simultaneously come into contact with the workpiece200depending on an angle at which the major cutting edge6starts to come into contact with the workpiece200. Consequently, large impact may be applied to the insert1, and vibration may occur, causing chatter vibration. Furthermore, the occurrence of chatter vibration makes it difficult to improve cutting conditions, failing to improve machining efficiency.

If the entirety of the major cutting edge6has the downwardly concave curvilinear shape, the major cutting edge6may start to make a point contact with the workpiece. However, when started to bite into the workpiece, the full length of the major cutting edge6becomes longer than one in which the entirety of the major cutting edge6has the straight-like line. This may lead to a longer period of time during which strong impact is continuously applied to the insert1.

In the insert1of the present embodiment, the major cutting edge6has the first section61having the downwardly dented concave curvilinear shape, and the pair of second sections62disposed continuously with the first section61. Therefore, the entirety of the major cutting edge6does not come into contact with the workpiece200when started to bite into the workpiece200. It is also possible to decrease the full length of the major cutting edge6than the case where the entirety of the major cutting edge6has the downwardly dented concaved curvilinear shape over the full length of the major cutting edge6. Therefore, the insert1of the present embodiment is capable of reducing cut resistance, relaxing impact, and preventing an increase in cut resistance when the insert1starts to bite into the workpiece.

When a surface of the workpiece has significant unevenness, a depth of cut is considerably varied all the time. On this occasion, if the entirety of the major cutting edge6has the concave curvilinear shape, a cutting edge angle is not constant, failing to carry out a stable cutting process. However, with the present embodiment, the major cutting edge6has the straight part62, and a region where the cutting edge angle is constant is divided into two stages, thereby reducing variations in cut resistance due to a change in depth of cut.

As shown inFIG. 6 or 7, the bottom portion6pthat is the portion located lowermost in the curvilinear part61of the major cutting edge6is disposed close to the second corner cutting edge5bof the pair of corner cutting edges5(5a,5b) which is located away from the processing surface of the workpiece. The bottom portion6pis disposed at a position in a downward direction which is, for example, 0.2-1.2 mm lower than a height position of the corner cutting edge5b. As shown inFIG. 7, the major cutting edge6has a length of, for example, 5-25 mm in a plane direction along the lower surface2, and the bottom portion6pis disposed with deviation of, for example, 0.5-1.5 mm toward the second corner cutting edge5bwith respect to a central position P of the length of the major cutting edge6in the plane direction.

Of the pair of straight parts62(62a,62b), the second straight part62bclose to the second corner cutting edge5bis made shorter than the first straight part62aclose to the first corner cutting edge5a. This makes it possible to ensure a large amount of depth of cut of the major cutting edge6as a whole. In the state in which the insert1is attached to the holder101, an inclination angle of the major cutting edge6with respect to a parallel line L along the surface of the workpiece is as follows. That is, setting is made so that an inclination angle a1of the first straight part62aextending toward the corner cutting edge5ais, for example, 5-15°, and an inclination angle a2of the second straight part62bextending toward the corner cutting edge5bis, for example, 3-13°. The setting is also made so that the inclination angle a2is smaller than the inclination angle a1.

Furthermore, owing to the fact that, of the pair of straight parts62(62a,62b), the second straight part62bclose to the second corner cutting edge5bis shorter than the first straight part62aclose to the first corner cutting edge5a, it is possible to effectively decrease a contact length that the second straight part62bcomes into contact with the workpiece200. It is therefore possible to reduce an increase in cut resistance when the second straight part62bstarts to bite into the workpiece200. Specifically, owing to the fact that the inclination angle a2of the second straight part62bwith respect to the parallel line L is smaller than the inclination angle a1of the first straight part62a, and the length of the second straight part62bis smaller than the length of the first straight part62a, it is possible to decrease a chip thickness obtainable by the second straight part62bto be used when the amount of depth of cut is large. It is therefore possible to improve fracture resistance and improve strength of the insert1.

As described above, the major cutting edge6has the curvilinear part61having the downwardly dented concave curvilinear shape, and the pair of straight parts62disposed continuously with the curvilinear part61. Hence, there are advantages of both in the case where the entirety of the major cutting edge6has the straight-like line, and the case where the entirety of the major cutting edge6has the concave curvilinear shape. Furthermore, owing to the fact that the bottom portion6pof the curvilinear part61is close to the second corner cutting edge5b, it is possible to effectively reduce the disadvantage that the contact length during contact with the workpiece200becomes long when the entirety of the major cutting edge6has the straight-like line. With the insert1of the present embodiment, the major cutting edge6has the downwardly concaved shape as a whole. It is therefore avoidable that the entirety of the major cutting edge6comes into contact with the workpiece at the same time when the major cutting edge6comes into contact with the workpiece. This makes it possible to carry out a satisfactory cutting.

In the insert1according to the present embodiment, the major cutting edge6has the concaved curvilinear part61and the pair of straight parts62(62a,62b) that respectively extend from the curvilinear part61toward the pair of corner cutting edges5(5a,5b) in the side view. The bottom portion6pin the curvilinear part61is close to the second corner cutting edge5bof the pair of corner cutting edges5(5a,5b) which is located above when cutting the workpiece200located below. This contributes to relaxing impact and preventing an increase in cut resistance when the insert1starts to bite into the workpiece200.

Additionally, the major cutting edge6in the present embodiment has the concave shape that is dented toward the inside of the upper surface3in the top view. In other words, the major cutting edge6in the present embodiment has the concave shape that is dented toward the center of the upper surface3. Here, being dented toward the center of the upper surface3implies being located closer to the center of the upper surface3than a tangent line that contacts both of the pair of corner cutting edges5(5a,5b). A distance between a portion closest to the center of the upper surface3and the tangent line is set in a range of 0.02-0.2 mm.

The major cutting edge6in the present embodiment has the concave shape in the top view as described above. Therefore, when cutting the workpiece by attaching the insert1to the holder101, it is possible to decrease a cutting edge angle on the outer peripheral side of the major cutting edge6. This contributes to decreasing a chip thickness in the vicinity of the corner cutting edges5during a shoulder milling process, thereby relaxing impact during cutting. It is therefore possible to improve fracture resistance of the corner cutting edges5and the major cutting edge6.

The present invention is not limited to the foregoing embodiment, and various changes, improvements, or the like can be made therein without departing from the spirit and scope of the present invention.

A cutting tool100of an embodiment is described below with reference toFIGS. 4 to 7.FIGS. 4 to 6show a state in which the insert1is attached via a screw103to an insert pocket102(hereinafter also referred to simply as the pocket102) of the holder101. A chain double-dashed line inFIG. 4indicates a rotation central axis Y of the cutting tool100.

As shown inFIGS. 4 to 6, the cutting tool100of the present embodiment includes the holder101having the rotation central axis Y and having a plurality of pockets102on an outer peripheral surface on a front end side of the holder101, and the insert1to be attached to each of the pockets102.

The holder101has an approximately columnar shape around the rotation central axis Y. The pockets102are disposed on the outer peripheral surface on the front end side of the holder101. The pockets102are portions to which the insert1is attached, and open into the outer peripheral surface and a front end surface of the holder101. The pockets102may be disposed at equal intervals or unequal intervals. The holder101is provided with the pockets102, and therefore does not have a strict columnar shape.

The inserts1are respectively attached to the pockets102disposed on the holder101. The inserts1are attached so that the major cutting edge6protrudes forward beyond the front end surface of the holder101, namely, further toward the workpiece beyond the front end surface of the holder101. Specifically, the inserts1are attached to the holder101so that the first corner cutting edge5aand a part of the major cutting edge6protrude beyond the front end surface of the holder101.

On this occasion, the first corner cutting edge5ais secured to a position that protrudes most beyond the front end surface of the holder101during cutting. As shown inFIG. 5, the inserts1are respectively attached to the pockets102of the holder101so that the corner cutting edge5aprotrudes forward beyond the front end surface of the holder101. Thereby, the inserts1are fixed to the holder101so that the bottom portion6pof the curvilinear part61is close to the second corner cutting edge5blocated above and away from the processing surface of the workpiece.

Each of the inserts1is attached via the screw103to the pocket102in the present embodiment. That is, each of the inserts1is attached to the holder101by inserting the screw103into the through hole H of the insert1, and then inserting a front end of the screw103into a screw hole (not shown) formed in the pocket102, and thereafter fixing the screw103to the screw hole. For example, steel and cast iron are usable as the holder101. Of these materials, it is particularly preferable to use high-rigidity steel.

<Method of Manufacturing Machined Product>

A method of manufacturing a machined product according to an embodiment is described below with reference toFIGS. 8 to 10.FIGS. 8 to 10show the method of manufacturing the machined product. The machined product is manufacturable by subjecting a workpiece to a cutting process. A cutting method in the present embodiment includes the following steps:

(1) rotating the cutting tool100as typified by the foregoing embodiment;

(2) bringing the major cutting edge6in the cutting tool100being rotated into contact with the workpiece200; and

(3) separating the cutting tool100from the workpiece200.

More specifically, a first step is to bring the cutting tool100relatively near the workpiece200while rotating the cutting tool100around the rotation central axis Y. A subsequent step is to cut the workpiece200by bringing the major cutting edge6of the cutting tool100into contact with the workpiece200as shown inFIG. 9. A final step is to keep the cutting tool100relatively away from the workpiece200.

In the present embodiment, the workpiece200is fixed and the cutting tool100is brought near. InFIGS. 8 and 9, the workpiece200is fixed and the cutting tool100is rotated around the rotation central axis Y. InFIG. 10, the workpiece200is fixed and the cutting tool100is kept away. Although the workpiece200is fixed and the cutting tool100is moved in each of the steps in the cutting process in the manufacturing method of the present embodiment, it is, of course, not intended to limit to this embodiment.

For example, in the step (1), the workpiece200may be brought near the cutting tool100. Similarly, in the step (3), the workpiece200may be kept away from the cutting tool100. When the cutting process is continued, it is necessary to repeat the step of bringing the major cutting edge6of the insert1into contact with different portions of the workpiece200, while the cutting tool100is kept rotating. When the major cutting edge6being used is worn away, the major cutting edge6not yet used needs to be used by rotating the insert190 degrees with respect to the central axis X of the through hole H. Representative examples of the material of the workpiece200include carbon steel, alloy steel, stainless steel, cast iron, and nonferrous metals.

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