Cutting insert, cutting tool and cutting method for workpiece using the same

A cutting insert has a main body which is provided with an upper surface, a side surface, at least one groove which is formed in the side surface and which extends to the upper surface at one end, and a plurality of split cutting blades which are split by the at least one groove. The upper surface is provided with inclined portions corresponding to the split cutting blades. The distance of respective lower ends of the inclined portions from the corresponding split cutting blades increases toward the centers of the corresponding cutting blades in a plan view. A cutting tool having the cutting insert and a method for cutting a workpiece using the cutting tool are also provided.

TECHNICAL FIELD

The present invention relates to a cutting insert, a cutting tool to which the cutting insert is attached and a cutting method for workpiece using the cutting tool.

BACKGROUND ART

Conventionally, through-away type cutting tools having excellent economical efficiency have been heavily used as cutting tools (for example, rotating tools) such as face mills and end mills. The cutting tool is formed by attaching a cutting insert to a holder.

The cutting insert having a long cutting edge is subjected to a large load at cutting. In order to reduce this load, for example, Unexamined Patent Publication No. 9-57519 discloses a cutting insert including a cutting edge located at an intersection between an upper surface and a side surface, and a groove formed on the side surface so as to divide the cutting edge. When the cutting insert is used for the cutting tool, a chip finely divided in the width direction is generated, so that cutting resistance applied to the cutting insert at cutting can be reduced. As the number of the grooves is increased, the length of each of the divided cutting edges becomes smaller and thus, the width of the chip also becomes smaller, thereby reducing the cutting resistance.

Since the narrow chips are easy to curl and discharged in an extended state, the chip tends to be clogged between the workpiece and the cutting edge. This configuration may disadvantageously cause damage of a worked surface of the workpiece and the cutting insert. Therefore, there has been a demand for a cutting insert that reduces the cutting resistance at cutting and has excellent chip discharging efficiency.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a cutting insert that reduces the cutting resistance at cutting and has excellent chip discharging efficiency. Another object of the present invention is to provide a highly durable cutting tool to which the cutting insert is attached and a cutting method for a workpiece using the cutting tool.

A cutting insert in accordance with an embodiment of the present invention includes a main body having an upper surface, a side surface, a groove that is formed on the side surface and extends to the upper surface at one end and a plurality of divided cutting edges that are located at an intersection line of the upper surface and the side surface and divided by the groove. The upper surface includes inclined parts located corresponding to the divided cutting edges, the inclined parts being in higher positions as being away from the intersection line. A distance of lower ends of the inclined parts from the corresponding divided cutting edges increases toward centers of the corresponding divided cutting edges from ends thereof in a top plan view.

A cutting tool in accordance with an embodiment of the present invention includes a holder and the cutting insert attached to an outer part of the holder at a front end, and at least a part of the plurality of divided cutting edges protrudes outwards from the outer part of the holder at the front end.

A cutting method for workpiece in accordance with an embodiment of the present invention is a method of cutting the workpiece by use of the cutting tool includes steps of rotating the cutting tool, bringing at least a part of the plurality of divided cutting edges of the rotating cutting tool into contact with a surface of the workpiece and separating the workpiece from the cutting tool.

According to the cutting insert, the cutting resistance at cutting can be reduced and even with a narrow chip having no sufficient rigidity to curl can be given appropriate rigidity by compression in the width direction and thus, can be curled. Therefore, according to the cutting insert, the cutting resistance at cutting can be reduced and excellent chip discharging efficiency can be achieved even with chips of small width. The cutting tool can have excellent durability. According to the cutting method for workpiece, cutting with high working accuracy can be stably performed over a long time.

DETAILED DESCRIPTION

An embodiment of a cutting insert according to the present invention will be described in detail with reference toFIGS. 1 to 4. As shown inFIG. 1andFIG. 2, the cutting insert in accordance with this embodiment (hereinafter refereed to as “insert”)1is formed of a main body having an upper surface2, side surfaces3and a lower surface9. A through hole8that penetrates the upper surface2and the lower surface9is substantially vertically formed at the center of the upper surface2. The through hole8serves to insert a screw member21for fixing the insert1to a holder11described later thereinto.

A cutting edge4is formed along an intersection line between the upper surface2and each side surface3. A plurality of grooves5that extend to the upper surface2and divide the cutting edge4are formed on each of the side surfaces3. The cutting edge4includes a plurality of divided cutting edges41divided by the grooves5. Further, inclined parts6corresponding to the divided cutting edge41are formed on the upper surface2so as to be located in higher positions as they move inwards from the cutting edge4, that is, away from the intersection line. The “inwards” means the inner side of the insert1relative to the cutting edge4, that is, the side of the through hole8.

The main body of the insert1is shaped like a substantially polygonal plate. Specifically, the main body is shaped like a substantially rectangular plate in a top plan view. Thus, the insert1has four cutting edges4. The shape of the polygon is not specifically limited and may be the shape that those skilled in the art normally employ for the insert, such as triangle, tetragon, pentagon, hexagon and octagon.

A region of the upper surface2, which conforms to the cutting edges4, functions as a cutting face. A region of the side surfaces3, which conforms to the cutting edges4, functions as a relief. The lower surface9functions as a seating face attached to the holder11. In this embodiment, the side surfaces3inclines so as to be located inwards toward the lower surface9. That is, the insert1is a positive insert in which a positive relief angle α is given to the side surface3functioning as the relief. The relief angle α is appropriately selected from the range of 5 to 30 degrees.

Each of the cutting edges4includes the plurality of divided cutting edges41divided by the plurality of grooves5placed on the side surface3side by side. In this embodiment, the cutting edge4includes five divided cutting edges41. A corner cutting edge42connected to the cutting edge4is formed on the intersection line between the upper surface2and the side surface3at each corner of the insert1.

As described above, the grooves5are formed so as to divide the cutting edges4. Thus, since chips generated by the divided cutting edges4become small, the cutting resistance at cutting can be reduced. Such insert1having the plurality of divided cutting edges41is especially suitable for heavy cutting.

The shape of the grooves5is not specifically limited as long as they are formed so as to extend to the upper surface2. For example, in a top plan view, the grooves may be linear or as shown inFIG. 2(b), a part of the grooves5may be made wide. The width and depth of the grooves5are not also specifically limited. For example, in consideration of the load applied at cutting, the width of an intermediate part of each groove may be made largest.

The number of the grooves5may be set depending on the type of the used workpiece. Generally speaking, as the number of grooves5is larger, the cutting resistance is decreased, but the width of the resulting chip becomes smaller. For this reason, in the conventional insert, when the number of the grooves is increased, enough rigidity to curl the chip cannot be obtained, lowering the chip discharging efficiency. Therefore, when considering the chip discharging efficiency, the number of the grooves on one side surface is practically limited.

In this embodiment, as described later, the insert is provided with the inclined parts6each having a rising part (that is, a lower end of the inclined part6)6a, a distance from the corresponding divided cutting edge41of which increases toward the center of the divided cutting edge41from the end of the divided cutting edge41. The lower ends6aare curved in a top plan view. For this reason, by compression in the width direction, even a narrow chip can have appropriate rigidity to be curled. Therefore, even when more grooves5are provided than a conventional insert, the excellent chip discharging efficiency can be achieved.

In this embodiment, four grooves5are formed on one side surface3. Two to five grooves5are generally formed on one side surface3. Although the same number of grooves5is formed on each side surface3, different side surfaces3may have different number of grooves.

For example, the grooves5are preferably disposed on each side surface3so as to be rotationally symmetric about a center line vertically extending in the thickness direction of the main body.

The inclined parts6are formed inward of the cutting face along the divided cutting edges41on the upper surface2. As shown inFIGS. 4(a),4(b), each inclined part6is formed so as to have a larger height from the lower surface9(seating face) as inclined part6moves away from the divided cutting edge41.

The inclined parts6are formed to curl the chips generated by the divided cutting edges41. Therefore, as shown inFIG. 1andFIG. 2, the plurality of inclined parts6corresponding to the respective divided cutting edges41are formed along the divided cutting edges41.

As shown inFIG. 3, in a top plan view, each inclined parts6is formed so that the lower end6ais away from the corresponding divided cutting edge41toward the center of the divided cutting edge41from both ends of the divided cutting edge41. That is, the distance from the corresponding divided cutting edge41increases toward the center of the divided cutting edge41from the both ends of the divided cutting edge41. For example, given that the distance between the lower end6aand the divided cutting edge41inFIG. 4(a) is X1and the distance between the lower end6aand the divided cutting edge41inFIG. 4(b) is X2, X1is larger than X2. As shown inFIG. 3, the lower end6ais formed to be concave in a top plan view. With such configuration, the chips generated by the divided cutting edges41firstly come into contact with the lower ends6aof the inclined parts6from ends thereof in the width direction, thereby being squeezed (compressed in the width direction), resulting in that enough rigidity to curl the chips to be narrower is imparted to the chips.

For example, as shown inFIGS. 4(c) and4(d), each inclined part6preferably has a recessed first concave part in a cross section taken along a line parallel to the divided cutting edge41in a top plan view, for example, a vertical cross section parallel to the divided cutting edge41(hereinafter referred to as “parallel cross section”). That is, each inclined part6has a concave surface extending perpendicular to the intersection line. Thereby, the chip compressed by the lower end6ain the width direction is curled while holding its compressed state.

As shown inFIGS. 4(c) and4(d), the first concave part of the concave inclined part6may partially have a flat part6bin the parallel cross section. Specifically, each inclined part6has the flat surface6bhaving substantially uniform height toward ends of the corresponding divided cutting edge41from the center of the divided cutting edge41. InFIGS. 4(c) and4(d), the width of the flat part6bis larger as the flat part6bis away from the divided cutting edge41. That is, as shown inFIG. 3, the flat part6bis substantially triangular. Thereby, suitable discharge to the outside (chip discharging efficiency) can be achieved without retention of the curled chip in the inclined part.

In the above-mentioned case, the curvature of a curved surface adjacent to the flat part6bis appropriately set according to the shape of the inclined parts6. For example, the flat part6bshown inFIGS. 4(c) and4(d) is located at the center of the inclined parts6. The cross section shown inFIG. 4(d) is further from the divided cutting edge41than the cross section inFIG. 4(c). The curvature of the curved surface adjacent to the flat part6binFIG. 4(c) is set to be smaller than the curvature of the curved surface adjacent to the flat part6binFIG. 4(d).

Further, as shown inFIG. 3andFIG. 4, it is preferred that each inclined part6has a first inclined part61including the lower end6aand a second inclined parts62that is in a higher position than the first inclined parts61and has a large inclination angle relative to a horizontal surface (lower surface9). The term “higher position” means a higher position in the thickness direction of the insert1. More specifically, when the insert1is set on the lower surface9as the seating face, the second inclined part62is located in a higher position using the cutting edge4as a reference.

In the case where the inclined part6has at least two inclined surfaces having different inclination angles relative to the horizontal surface, it is possible to curl chips of various thicknesses. For example, chips of different thicknesses are generated according to the feed rate of the cutting tool. In this embodiment, the chip of large thickness can be curled by the first inclined parts62having a smaller inclination angle, while the chip of small thickness can be curled by the second inclined parts61having a larger inclination angle. In addition, curl radius and chip discharge can be also controlled. The above-mentioned effects can be also obtained, for example, by making the inclined parts6to be a curved part having many continuous inclined surfaces having different inclination angles relative to the horizontal surface, that is, a recessed second concave part when viewed from a cross section perpendicular to the divided cutting edge41.

Protruded parts7alternately placed with the inclined parts6are formed on the upper surface of the insert1. The protruded parts7serve to stabilize the chip discharging direction so as to prevent the chips generated by the divided cutting edges41from contacting each other, and to guide the chips to the inclined parts6. Thereby, the chips can be reliably curled. InFIG. 2, the plurality of protruded part7are formed so as to extend inwards from the respective grooves5.

Each of the protruded parts7has a pair of inclined side surfaces. The pair of inclined side surfaces are inclined from the top of the protruded part7toward the cutting faces of the upper surface2, which correspond to two divided cutting edges41located at the both ends of the grooves5. The protruded parts7each have such pair of side surfaces, thereby preventing the discharging direction of the chips generated by the divided cutting edges41from swinging to the left and to the right.

Next, with reference toFIG. 5, an embodiment of the cutting tool according to the present invention will be described. As shown inFIG. 5, the cutting tool10is formed by attaching the above-mentioned insert1to an outer part of the holder11at a front end.

In this embodiment, although the holder11is shaped like a disc, the holder may be rod-like, cylinder-like, etc. The holder11has eight insert pockets12to which the insert1is attached. Thus, the cutting tool10includes eight inserts1.

Each insert1is attached so that the divided cutting edges41protrude from the outer circumferential surface of the holder11. Each insert1is screwed into the insert pocket12by the screw member21.

The cutting tool10is provided with the insert1, thereby preventing a plurality of chips finely divided in the width direction from striking against each other. As a result, it is possible to improve the chip discharging efficiency and increase the life of the tool.

In this embodiment, the insert1is attached to the insert pocket12through a sheet member13. Thus, even when a defect occurs in the cutting edge4of the insert1or the like, since the holder11located at the defect of the cutting edge4is protected with the sheet member13, damage of the holder11can be suppressed. Therefore, the life of the holder11can be increased.

In the insert1in this embodiment, each of the divided cutting edges41is inclined so as to get away from its front end toward its rear end with respect to an axis line S of the holder11. That is, the insert1is formed by attaching the divided cutting edges41with a positive axial rake angle to the holder11. Thereby, the cutting resistance can be further reduced. For this reason, even under more harsh cutting conditions such as heavy cutting with a large cutting amount, excellent cutting performances can be achieved.

In this embodiment, when attaching the insert1to the insert pockets12, the sheet member13is placed between the insert1and the insert pocket12, but the insert1may be in direct contact with the insert pocket12. Further, although the cutting tool in this embodiment is a face mill, the cutting tool is not limited to the face mill and may be an end mill.

<Cutting Method for Workpiece>

With reference toFIG. 6, a cutting method for workpiece in accordance with an embodiment of the present invention will be described using a case where the cutting tool10is used as an example. The cutting method for workpiece in accordance with this embodiment includes following steps (i) to (iii):

as shown inFIG. 6(a), the step of rotating the cutting tool10about the axis line S of the holder11in a direction of an arrow A and moving the cutting tool10in a direction of an arrow B so as to bring the cutting edges of the cutting tool10closer to a workpiece100;

as shown inFIG. 6(b), the step of bringing the cutting edges4of the insert1into contact with a surface of the workpiece100and moving the cutting tool10in a direction of an arrow C to cut the surface of the workpiece100; and

as shown inFIG. 6(c), the step of moving the cutting tool10in a direction of an arrow D to separate the cutting tool10from the workpiece100.

As described above, in this embodiment, since the steps (i) to (iii) are performed using the cutting tool10having the excellent chip discharging efficiency and long life, working efficiency and finished surface accuracy can be improved. That is, the chips generated by the divided cutting edges41can be prevented from being clogged between the workpiece100and the cutting edges4, and defects of the cutting edges4and the grooves5can be suppressed. As a result, cutting with high working accuracy can be stably performed over a long time.

The cutting tool10only needs to be relatively closer to the workpiece100, and for example, the workpiece100may be moved to be closer to the cutting tool10. Similarly, in the step (iii), the workpiece100only needs to be relatively further from the cutting tool10, and for example, the workpiece100may be moved to be further from the cutting tool10. When cutting is continued, the step of bringing the cutting edge4of the insert1into contact with a different place of the workpiece100may be repeated while keeping the cutting tool10to be rotated. When a cutting edge4that is using is worn, the insert1may be rotated by 90 degrees relative to the center axis of the through hole8to use an unused cutting edge4.

Although some embodiments of the present invention have been described above, as a matter of course, embodiments of the present invention are not limited to the above-mentioned embodiments and may be any embodiment as long as it does not deviate from the object of the invention. For example, although a plurality of grooves are formed in the above-mentioned embodiments, according to the present invention, at least one groove may be needed.