Tip and cutting tool

Abstract

A tip (30) is attached to a body of a cutting tool (10) and comprises: a leading-end part (330) that is provided with a cutting edge (CE) and a rear-end part (340) that opposes the leading-end part. In the leading-end part (330), the cutting edge (CE) is formed in a step shape including: a center edge (31) disposed at an inner surface (350) side; and an outer peripheral edge (33) disposed at an outer surface (360) side. Further, on a second surface (320), which is a rake face related to the cutting edge (CE), tip breakers (B1, B3) are formed at portions corresponding to the center edge (31) and the outer peripheral edge (33), respectively. Further, the maximum width (W1max) of a tip breaker (B1) at a portion corresponding to the center edge (31) is greater than the maximum width (W3max) of a tip breaker (B3) at a portion corresponding to the outer peripheral edge (33).

Description

Tips and cutting tools

[0001] The present disclosure relates to a tip and a cutting tool including the tip.

[0002] One machining method for forming deep holes in a workpiece is known as "BTA" (Boring and Trepanning Association). Generally, in BTA machining, chips generated during cutting are discharged to the outside through a discharge hole formed inside the cutting tool. For this reason, cutting tools are known that have a mechanism for dividing and segmenting chips between the center cutting edge and the peripheral cutting edge by providing a step shape on the cutting edge of the insert. In this case, chips on the center cutting edge tend to be relatively thick, while chips on the peripheral cutting edge tend to be relatively thin and elongated. Therefore, measures to more appropriately adjust the shape of chips in response to this tendency are needed. As a potential solution to this demand, an insert has been proposed in which the step on the cutting edge is formed as a substantially V-shaped notch (see, for example, Patent Document 1).

[0003] Microfilm of Utility Model Application No. 57-88267 (Utility Model Application No. 58-191913)

[0004] In the above-mentioned conventional inserts, the chip extension direction (extension direction) is controlled to suppress excessive extension of the chips on the peripheral cutting edge side. However, the chip shape control desired from the viewpoint of improving the cutting performance of the workpiece and the chip dischargeability in BTA processing has not yet been satisfactorily resolved. In particular, there is a strong demand for good control of the shape of the chips on the peripheral cutting edge side, which are relatively thin and tend to extend.

[0005] Therefore, an object of the present disclosure is to provide a tip that can suppress excessive elongation of relatively thin, elongate chips that can occur during BTA processing, thereby enabling a cutting edge design and chip disposal that are advantageous for improving the sharpness and chip discharge performance during BTA processing, and a cutting tool equipped with the tip.

[0006] In order to solve the above problems, the present disclosure employs the following configuration.

[0007] [1] An example of a chip according to the present disclosure is a chip used, for example, for drilling a workpiece and attached to the body of a cutting tool. Specifically, the chip includes a tip end portion provided with a cutting edge, a rear end portion opposing the tip end portion, a first side surface connecting the tip end portion and the rear end portion, and a second side surface opposing the first side surface. The tip end portion has a stepped cutting edge including a first cutting edge disposed on the first side surface and a second cutting edge disposed on the second side surface. Furthermore, chip breakers are formed on the rake face associated with the cutting edges at locations corresponding to the first cutting edge and the second cutting edge, respectively. The maximum width of the chip breaker at the location corresponding to the first cutting edge is greater than the maximum width of the chip breaker at the location corresponding to the second cutting edge.

[0008] Here, the "width of the chip breaker" in this disclosure refers to the width along a direction intersecting the extension direction of each cutting edge (for example, a direction perpendicular to the cutting edge, but not limited to this) when viewed in a plane of the chip, or refers to the width of the boundary between the cutting edge and the upper surface of the chip breaker (wall) facing the cutting edge.

[0009] In this configuration, the cutting edges are formed in a stepped shape, defining a step between the first cutting edge and the second cutting edge, thereby breaking up chips into smaller pieces. Furthermore, due to the above-described relationship between the maximum widths of the chip breakers at the portions corresponding to the first cutting edge and the second cutting edge, the distance to the "wall" of the chip breaker for the first cutting edge is greater, thereby weakening the force that curls the chips, making it easier to bend even thick chips. Meanwhile, the distance to the "wall" of the chip breaker for the second cutting edge is shorter, thereby strengthening the force that curls the chips, making it easier to appropriately curl or break thin chips into smaller pieces. In other words, according to the present disclosure, the width of the chip breaker at the portion corresponding to the second cutting edge is narrower relative to the width of the chip breaker at the portion corresponding to the first cutting edge, thereby reducing the curl diameter of thin, easily stretched chips. As a result, it is possible to realize and provide a cutting edge design and chip disposal that are advantageous for improving the sharpness and chip discharge properties in BTA processing.

[0010] [2] In the above configuration, the width of the chip breaker corresponding to the second cutting edge may be increased continuously or intermittently from the first side surface side to the second side surface side. This configuration has the advantage of making it easier to control the shape of the second cutting edge and, ultimately, the cutting edge. More specifically, a characteristic of drilling is that the cutting speed is approximately zero at the center of rotation of the cutting tool and increases toward the outer periphery. Therefore, chips on the outer periphery tend to flow relatively quickly and chips on the central periphery tend to flow relatively slowly. When viewed from the rake face, the chips curl into a fan shape with the center at the inside. If the width of the chip breaker corresponding to the cutting edge is constant (the same), the chips only hit the chip breaker as a "wall" on the outer periphery. However, by increasing the width of the chip breaker toward the outer periphery (i.e., making the chip breaker fan-shaped) as in the above configuration, the chips can hit the entire "wall."

[0011] In this disclosure, the "first side" and "second side" of the insert correspond to the "tool center" and "tool outer periphery" when the insert is attached to a cutting tool. This configuration can also be expressed as the width of the chip breaker at the portion corresponding to the first cutting edge increasing continuously or intermittently from the tool center toward the tool outer periphery.

[0012] [3] In the above configuration, it is also preferable that a chamfered portion is formed at the tip between the second side surface and the peripheral cutting edge. This configuration alleviates stress concentration on the outer surface end of the peripheral cutting edge, preventing damage to that area.

[0013] [4] In the above configuration, it is also preferable that the rake face has a recessed portion formed thereon, which has an inclined surface that slopes downward toward the rear end opposite the front end and connects to a coolant and chip discharge hole provided in the cutting tool body. In such a configuration, when the insert is attached to the cutting tool body, the recessed portion connects to the body's discharge hole, defining a path for discharging coolant and chips from the insert side. Furthermore, because the recessed portion has an inclined surface, pressure loss during the flow of coolant and chips is reduced, improving their dischargeability. This makes it easier to prevent chip clogging during BTA processing.

[0014] [5] An example of a cutting tool according to the present disclosure can be effectively configured with a body and a tip according to the present disclosure attached to the body. That is, the tip has a leading end portion provided with a cutting edge, a trailing end portion opposing the leading end portion, a first side surface connecting the leading end portion and the trailing end portion, and a second side surface opposing the first side surface, and the leading end portion of the tip has a cutting edge formed in a stepped shape including a first cutting edge disposed on the first side surface side and a second cutting edge disposed on the second side surface side. Also, chip breakers are formed on the rake face related to the cutting edges at portions corresponding to the first cutting edge and the second cutting edge, and the maximum width of the chip breaker at the portion corresponding to the first cutting edge is larger than the maximum width of the chip breaker at the portion corresponding to the second cutting edge.

[0015] According to the present disclosure, excessive elongation of relatively thin chips that tend to elongate during BTA processing can be suppressed, resulting in a cutting edge design and chip disposal that are advantageous for improving the sharpness and chip discharge performance during BTA processing.

[0016] Fig. 3 is a perspective view showing an outline of the overall configuration of a cutting tool according to this embodiment. Fig. 4 is a perspective view showing a schematic configuration of a tip provided in the cutting tool according to this embodiment. Fig. 5 is a plan view (top view in Figs. 1 and 2 ), a left side (tip side) side view in Fig. 3A , and a bottom side (outer surface side) side view in Fig. 3A , respectively, showing an outline of a tip provided in the cutting tool according to this embodiment. Fig. 4 is a slightly enlarged plan view of Fig. 3A .

[0017] The present embodiment will be described below with reference to the accompanying drawings. To facilitate understanding of the description, the same components in the drawings will be denoted by the same reference numerals as much as possible, and redundant description will be omitted.

[0018] Fig. 1 is a perspective view showing the overall configuration of a cutting tool according to this embodiment, and Fig. 2 is a perspective view showing the general configuration of a tip included in the cutting tool according to this embodiment. Also, Figs. 3(A) to 3(C) are respectively a plan view (top view in Figs. 1 and 2), a left side (tip side) side view in Fig. 3(A), and a bottom side (outer surface side) side view in Fig. 3(A) that schematically show the tip included in the cutting tool according to this embodiment. Furthermore, Fig. 4 is a slightly enlarged plan view of Fig. 3(A), which is a reprint of Fig. 3(A).

[0019] <Overview of Cutting Tool 10> The cutting tool 10 according to this embodiment is a cutting tool for BTA processing used in drilling. As shown in Fig. 1, the cutting tool 10 includes a body 20, a tip 30, and a guide pad 40. Of these, the body 20 is a member that constitutes substantially the entire cutting tool 10 and is made of, for example, steel.

[0020] As shown in FIG. 1 , the tip portion 21 of the body 20 is generally cylindrical, with a portion of its side cut out, and a seat 210 provided in that portion to mount a tip 30 (described later). The rear end portion 22 of the body 20 is also generally cylindrical, similar to the tip portion 21, and is integrally formed with the tip portion 21. The cutting tool 10 is appropriately held by a machine tool (not shown) at the rear end portion 22 and is driven to rotate about a rotation axis AX during BTA processing of a workpiece. The rotation axis AX coincides with the central axis of the generally cylindrical body 20. In FIGS. 1 and 2 , the rotation direction Y of the cutting tool 10 during BTA processing is indicated by a circular arrow.

[0021] The body 20 is also formed with a discharge hole 23. The discharge hole 23 is a communication hole for guiding and discharging coolant supplied along the outer peripheral surface of the body 20 to the outside together with chips generated during BTA processing. The discharge hole 23 extends along the central axis of rotation AX and is formed to penetrate the entire body 20. The discharge hole 23 is also a through-hole with a substantially circular cross section, and its central axis generally coincides with the central axis of rotation AX. Furthermore, at the connection portion to the tip 30 near the tip 30 described below, the inner surface of the discharge hole 23 is inclined toward the central axis of rotation AX toward the tip 30.

[0022] The tip 30 is a component having a cutting edge CE, which includes a central cutting edge 31 (first cutting edge), an intermediate cutting edge 32, and a peripheral cutting edge 33 (second cutting edge), which are arranged in this order from the inner surface 350 (tool center side Rc) to the outer surface 360 ​​(tool outer peripheral side Rp). The material of the tip 30 is not particularly limited, and it is preferable that the entire tip 30 be formed of, for example, a cemented carbide alloy. Furthermore, at least the portion of the tip 30 including the cutting edge CE may be formed from a hard material such as cermet, ceramic, or a sintered body containing cubic boron nitride, or a hard material having a coating layer formed on the surface of such a hard material by physical vapor deposition or chemical vapor deposition (CVD), or a single crystal diamond or a sintered body containing diamond. Furthermore, the tip 30 is fixed to the seat 210 of the body 20 by, for example, brazing.

[0023] Furthermore, for example, the guide pads 40 are members that abut against the inner surface of a machined hole (a hole formed in a workpiece as the cutting tool 10 rotates) during BTA processing, thereby preventing deformation of the body 20. These guide pads 40 can improve the straightness and roundness of the machined hole.

[0024] When BTA machining is performed with the cutting tool 10, a coolant fluid is supplied from the outside through the gap between the inner circumferential surface of the machining hole and the outer circumferential surface of the body 20. After reaching the vicinity of the tip of the tip 30, the coolant flows into the discharge hole 23 of the body 20 together with the chips generated by the BTA machining. The coolant and the chips then flow through the discharge hole 23 toward the rear end and are discharged to the outside of the cutting tool 10.

[0025] <Specific Configuration of Tip 30> The following describes a more specific configuration of the tip 30. As shown in Fig. 2, the tip 30 includes a first surface 310 (the lower surface in the figure), a second surface 320 (the upper surface, rake surface in the figure), a leading end portion 330, a trailing end portion 340, an inner surface 350 (the left surface, first side surface in the figure), and an outer surface 360 ​​(the right surface, second side surface in the figure).

[0026] The first surface 310 is a surface that faces rearward in the rotation direction Y when the chip 30 is attached to the body 20. On the other hand, the second surface 320 is a surface that faces forward in the rotation direction Y when the chip 30 is attached to the body 20, and is a portion that is exposed by being opened in a notch in the body 20. In other words, the second surface 320 is located on the opposite side facing the first surface 310, and is a surface that faces in the direction of travel when the body 20 rotates around the rotation center axis AX. Also, as shown in FIG. 2 , the second surface 320 has a portion that is parallel to the first surface 310.

[0027] The tip portion 330 is a portion that connects the first surface 310 and the second surface 320, and is the portion that is closest to the tip side Rf when the tip 30 is attached to the body 20. In this tip portion 330, a cutting edge CE for BTA processing is formed on part of the intersection ridge between the tip surface (flank face) and the second surface 320 (rake face).

[0028] The rear end portion 340 also connects the first surface 310 and the second surface 320, and is the portion that is the rearmost side Rb when the tip 30 is attached to the body 20. The rear end portion 340 is located on the opposite side of the tip portion 330 in the direction along the central axis of rotation AX, and is a substantially flat surface that is substantially perpendicular to the first surface 310.

[0029] <Tip Portion 330 of Insert 30> The specific configuration of the tip portion 330 of the insert 30 will be described below. On the rake face (second surface 320) of the cutting edge CE formed on the tip portion 330, chip breakers B1, B2, and B3 are formed at locations corresponding to the center cutting edge 31, intermediate cutting edge 32, and peripheral cutting edge 33, respectively. Furthermore, on the cutting edge CE, the center cutting edge 31, intermediate cutting edge 32, and peripheral cutting edge 33 are formed in a multi-step (stepped) shape. Among the ridgelines, in the planar views shown in FIGS. 3A and 4, a portion C12 of the step C12 between the center cutting edge 31 and intermediate cutting edge 32 and a portion C23 of the step C23 between the intermediate cutting edge 32 and peripheral cutting edge 33 are not considered cutting edges. The cutting edge CE can also be described as being formed in a sawtooth shape in the planar views shown in FIGS. 3A and 4.

[0030] Furthermore, in the plan view shown in FIG. 3A or FIG. 4, the maximum width W1 of the chip breaker B1 at the portion corresponding to the central cutting edge 31 ｍａｘ , the maximum width W2 of the chip breaker B2 at the portion corresponding to the intermediate cutting edge 32 ｍａｘ and the maximum width W3 of the chip breaker B3 at the portion corresponding to the peripheral cutting edge 33 ｍａｘ satisfies the relationship expressed by the following formula (1): ｍａｘ >W2 ｍａｘ ≧W3 ｍａｘ …(1)

[0031] At this time, when designing the shape of the chip 30, the cutting edge CE is determined, and the shapes of the chip breakers B1, B2, and B3 are determined for that cutting edge CE. Based on these, when formulating the "wall" positions in the chip breakers and the shapes connecting each wall, adjustments can be made as appropriate so that the relationship expressed by the above formula (1) is satisfied.

[0032] 2, 3A and 3B, and 4, the central cutting edge 31 is bent in a V-shape (like a dogleg) and functions as a cutting edge up to the vicinity of the rotation center axis AX. Therefore, the chip breaker B1 at the portion corresponding to the central cutting edge 31 is also bent in a V-shape (like a dogleg). Meanwhile, in the same view, the chip breaker B2 at the portion corresponding to the intermediate cutting edge 32 and the chip breaker B3 at the portion corresponding to the peripheral cutting edge 33 each have a substantially trapezoidal shape in a plan view. As a result, the width W2 of the chip breaker B2 and the width W3 of the chip breaker B3 are both configured to increase continuously or intermittently from the inner surface 350 side (tool center side Rc) toward the outer surface 360 ​​side (tool outer peripheral side Rp).

[0033] Furthermore, in this embodiment, in the plan view shown in Figures 3(A) and 4, a step D12 is formed on the rear end 340 side between the chip breaker B1 at the portion corresponding to the central cutting edge 31 and the chip breaker B2 at the portion corresponding to the intermediate cutting edge 32. As a result, the boundary portion T12 connecting the chip breakers B1 and B2 is constricted on both sides. In contrast, the boundary portion T23 connecting the chip breakers B2 and B3 is constricted on one side. Furthermore, in this embodiment, in the plan view shown in Figures 3(A) and 4, a chamfered portion T34 is formed that linearly connects (connects) the outer surface 360 ​​exposed on the tool outer peripheral side Rp and the peripheral cutting edge 33.

[0034] In this embodiment, a recess E321 having an inclined surface 321 that slopes back toward the first surface 310 (decreasing toward the rear end 340 opposite the front end 330) is formed in the portion of the second surface 320 on the rear end 340 side. The recess E321 is smoothly connected, without any steps, to the coolant and chip discharge hole 23 provided in the body 20 on the rear end 340 side. Furthermore, inclined surfaces 322 that slope in the same direction as the inclined surfaces 321 are provided on both sides of the recess E321.

[0035] According to the tip 30 configured as described above and the cutting tool 10 to which it is attached, the cutting edge CE is formed in a stepped shape, and steps C12, C23 are defined at the boundaries T12, T23 between adjacent blades of the central blade 31, intermediate blade 32, and peripheral blade 33. Therefore, chips generated during BTA processing using the cutting tool 10 are broken up into small pieces at the locations of these steps C12, C23. At this time, because multiple steps C12, C23 are defined, the chips can be broken up into smaller pieces compared to when there is a single step.

[0036] In addition, the maximum width W1 of the chip breaker B1 at the portion corresponding to the central cutting edge 31 ｍａｘ The maximum width W2 of the chip breakers B2 and B3 at the portions corresponding to the intermediate cutting edge 32 and the peripheral cutting edge 33, respectively ｍａｘ , W3 ｍａｘ (See the above-mentioned formula (1)). As a result, the distance to the "wall" of the chip breaker B1 for the central cutting edge 31 is increased, weakening the effect of forcibly curling the chips. As a result, even thick chips are easier to bend. On the other hand, the distance to the "wall" of the chip breakers B2 and B3 for the intermediate cutting edge 32 and the peripheral cutting edge 33 is closer than in the case of the chip breaker B1 corresponding to the central cutting edge 31, so the effect of forcibly curling the chips is stronger. As a result, even thin chips are easier to curl appropriately or break into small pieces. From the above, it is possible to realize and provide a cutting edge design and effective chip disposal that are advantageous for improving sharpness and chip discharge in BTA processing.

[0037] Furthermore, the widths W2, W3 of the chip breakers B2, B3 corresponding to the intermediate cutting edge 32 and the peripheral cutting edge 33 are configured to increase continuously or intermittently from the inner surface 350 (tool center side Rc) toward the outer surface 360 ​​(tool outer peripheral side Rp). Generally, in BTA machining, when viewed from the second surface 320 (rake face), the chip curls into a fan shape with its center at the inside. Therefore, if the widths of the chip breakers B1, B2, and B3 corresponding to the cutting edge CE are constant (the same), the chip only hits the chip breaker "wall" on the outer peripheral side. In contrast, by gradually increasing the widths W2, W3 of the chip breakers B2, B3 toward the outer surface 360 ​​(tool outer peripheral side Rp) as in the configuration of this embodiment (i.e., making the chip breaker fan-shaped), the chip can hit the entire "wall." As a result, chip shape control by the intermediate cutting edge 32, the peripheral cutting edge 33, and ultimately the cutting edge CE, is further facilitated.

[0038] Furthermore, the tip 330 is provided with a chamfered portion T34 that connects (connects) the outer surface 360 ​​and the peripheral cutting edge 33 in a straight line, for example, which effectively reduces stress concentration on the side edge of the outer surface 360 ​​of the peripheral cutting edge 33. This makes it possible to prevent breakage of that portion.

[0039] Furthermore, in general, in cutting tools used in BTA machining, similar to the cutting tool 10 according to this embodiment, the entrance of the discharge hole 23 is often positioned as close as possible to the cutting edge CE of the insert 30 to ensure reliable discharge of chips. This narrows the entrance of the discharge hole 23 by the insert 30, making it difficult for coolant containing chips to flow into the discharge hole 23. In this case, chips may clog the entrance of the discharge hole 23. In contrast, according to this embodiment, the recess E321 is provided on the second surface 320 of the insert 30, ensuring a wide discharge path for coolant to flow toward the discharge hole 23. This prevents the entrance of the discharge hole 23 from being narrowed by a portion of the insert 30, reducing pressure loss when coolant and chips flow through the discharge hole 23 and making it easier to prevent chip clogging during BTA machining.

[0040] The present embodiment has been described above with reference to specific examples. However, this is for the purpose of facilitating understanding of the present disclosure and is not intended to limit the present disclosure. In other words, the present disclosure is not limited to these specific examples. Design modifications to these specific examples made by a person skilled in the art are also encompassed within the scope of the present disclosure as long as they comprise the features of the present disclosure. Furthermore, unless otherwise specified, the elements, arrangements, materials, conditions, shapes, dimensions, sizes, scales, etc. of the above-described specific examples are not limited to those exemplified and can be modified as appropriate. Furthermore, the elements of the above-described specific examples can be combined as appropriate as long as no technical contradictions arise.

[0041] That is, for example, as long as the central cutting edge 31 and the peripheral cutting edge 33 are provided, the intermediate cutting edge 32 may not be provided. Furthermore, the shape of the tip 330 and the shapes of the central cutting edge 31, intermediate cutting edge 32, and peripheral cutting edge 33 constituting the cutting edge CE may differ from those shown in the drawings. Furthermore, in the above embodiment, the "chip breaker width" is shown in FIG. 4 as the width along a direction perpendicular to the extension direction of the central cutting edge 31, intermediate cutting edge 32, and peripheral cutting edge 33 in a plan view of the insert. However, as described above, the "chip breaker width" in this disclosure is not limited to the illustrated width, as long as it is in a direction intersecting the extension direction. Furthermore, for example, the width of the boundary between the cutting edge CE and the upper surfaces of the chip breakers B1, B2, and B3 (walls) facing it may also be defined as the "chip breaker width." Furthermore, in the above embodiment, the central cutting edge 31, the first peripheral cutting edge 32, and the second peripheral cutting edge 33 extend in substantially the same direction, but this is also not limited to the illustrated width.

[0042] Furthermore, the chip breakers B1, B2, and B3 may have any functional shape as a "wall," and may be formed as a portion having, for example, a groove or an island. Furthermore, the tip 30 may be removably fastened to the seat 210 of the body 20 with a screw. In this case, the tip 30 is used as a "cutting insert." Furthermore, in the plan view of FIG. 4 , the shape of the boundary T12 connecting the chip breakers B1 and B2 can be adjusted arbitrarily. In the above embodiment, the left and right sides shown are curved and constricted on both sides, as shown by the steps C12 and D12, respectively. However, for example, they may be straight or broken, or the step D12 may not be provided. Similarly, the shape of the boundary 31 connecting the chip breakers B2 and B3 can also be adjusted arbitrarily. In the above embodiment, the left and right sides shown are curved and constricted on both sides, as shown by the step C23, respectively. However, for example, they may be straight, or they may be constricted on both sides with a step like the step D12. In addition, in the planar view of Figure 4, the chamfered portion T34 connecting the outer surface 360 ​​and the peripheral cutting edge 33 is linear, but it may be curved or have some other shape as long as it helps prevent damage to the end of the peripheral cutting edge 33 on the outer surface 360 ​​side.

[0043] DESCRIPTION OF SYMBOLS 10...Cutting tool, 20...Body, 21...Tip portion, 22...Rear end portion, 23...Discharge hole, 30...Tip, 31...Central blade (first cutting blade), 32...Intermediate blade, 33...Peripheral blade (second cutting blade), 40...Guide pad, 210...Seat, 310...First surface, 320...Second surface (rake surface), 321...Inclined surface, 322...Inclined surface, 330...Tip portion, 340...Rear end portion, 350...Inner side surface (first side surface), 360...outer surface (second side surface), AX...rotation center axis, B1, B2, B3...chip breaker, C12, C23...step, CE...cutting edge, D12...step, E321...recess, Rb...rear end side, Rc...tool center side, Rf...tip side, Rp...tool outer periphery side, T12, T23...boundary portion, T34...chamfered portion, W1, W2, W3...width of chip breaker, W1 ｍａｘ , W2 ｍａｘ , W3 ｍａｘ , ...Maximum width of chip breaker, Y...Rotation direction.

Claims

1. A chip used for drilling, comprising a tip provided with a cutting edge, a rear end portion facing the tip, a first side surface connecting the tip and the rear end portion, and a second side surface facing the first side surface; at the tip portion, the cutting edge is formed in a stepped shape including a first cutting edge disposed on the first side surface side and a second cutting edge disposed on the second side surface side; on the rake face related to the cutting edge, chip breakers are formed at portions corresponding to the first cutting edge and the second cutting edge respectively; and the maximum width of the chip breaker at the portion corresponding to the first cutting edge is made larger than the maximum width of the chip breaker at the portion corresponding to the second cutting edge.

2. The chip according to claim 1, wherein the width of the chip breaker at the portion corresponding to the second cutting edge becomes wider continuously or intermittently from the first side surface side toward the second side surface side.

3. The chip according to claim 1, wherein at the tip portion, a chamfered portion is formed between the second side surface and the second cutting edge.

4. The chip according to claim 1, wherein the rake face has an inclined surface descending toward the rear end portion facing the tip portion, and a recess is formed which is connected to a coolant and chip discharge hole provided in the body of the cutting tool.

5. A cutting tool comprising a body and a chip attached to the body; the chip comprises a tip provided with a cutting edge, a rear end portion facing the tip, a first side surface connecting the tip and the rear end portion, and a second side surface facing the first side surface; at the tip portion of the chip, the cutting edge is formed in a stepped shape including a first cutting edge disposed on the first side surface side and a second cutting edge disposed on the second side surface side; on the rake face related to the cutting edge, chip breakers are formed at portions corresponding to the first cutting edge and the second cutting edge respectively; and the maximum width of the chip breaker at the portion corresponding to the first cutting edge is made larger than the maximum width of the chip breaker at the portion corresponding to the second cutting edge.

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