Cutting tool for boring

A cutting tool for boring including a cutting insert fixed at a front end of a bar-shaped holder. The holder includes a cutting surface-sided chip pocket that is concave with respect to the outer circumferential surface of the holder, the cutting edge end of the cutting insert protruding from the outer circumferential surface of the holder, and the cutting surface-sided chip pocket having a bottom surface facing the portion of outer circumferential surface where the cutting edge overhangs. Further, an cutting edge-sided chip pocket is formed at the portion of outer circumferential surface where the cutting edge overhangs such that the edge of the portion of outer circumferential surface where the cutting edge overhangs is concave with respect to the outer circumferential surface of the holder, on the bottom of the cutting surface-sided chip pocket when viewed from the cutting surface.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present disclosure relates to a cutting tool for boring, and more particularly, to a cutting tool for boring (also called a boring bit) which is used for turning the inner circumferential surface of a hole having a circular cross-section, or the inner circumferential surface of a cylindrical pipe, particularly for machining a deep small-diameter hole.

2. Description of the Related Art

Cutting tools for boring are used to machine the inner circumferential surface of a hole of a workpiece (an object to be cut), such that the cutting edge (the front end of a cutting edge for cutting) of a cutting insert (for example, a throw-away type cutting insert) fixed to the front end of a bar-shaped holder overhangs from a side of the outer circumferential surface of the holder. In the cutting tool for boring (hereinafter, also referred to as a cutting tool), when the diameter of the inner circumferential surface of a hole of a workpiece (hereinafter, also referred to as an inner circumferential surface) is small, for example, below φ12 mm, the protrusion amount of the cutting edge from the outer circumferential surface of the holder is about 1.5 mm at most, though it depends on the outer diameter of the holder (normally about 10 mm). Therefore, the gap (space) between the inner circumferential surface of the hole and the outer circumferential surface of the holder becomes too small, such that it is difficult to remove the chips produced in the cutting process from the inlet of the hole of the workpiece at the rear end (base) of the holder (also called a shank) to the outside (rear end side of the holder). Further, the deeper the hole in the cutting conditions, the more serious the problem becomes. As the performance of the chip control (removing) degrades, the chips are easily stuck between the inner circumferential surface of the machined hole and the cutting edge or the holder. Accordingly, the machined surface (inner circumferential surface) is damaged, and the machined surface is roughened. Further, in some cases, machining is inevitably stopped in order to remove the chips. This problem tends to occur in particular in an external oil supply type apparatus in which cutting oil is supplied from the outside, rather than in an internal oil supply type apparatus in which cutting oil is supplied from the front end of the holder.

As a countermeasure considered for controlling the chips, the portion of the holder including the front end in particular which is inserted into the inner circumferential surface of the hole of a workpiece is thinned, in addition to controlling the shape, state, or removing direction of the chips. However, simply thinning the holder causes chatter vibration due to a decrease in stiffness. Therefore, in order to more efficiently remove the chips without causing chatter vibration, a technology has been proposed in which various shapes of chip pockets (concave portions, hereinafter also referred to as pockets) are formed at the head (the portion close to the front end) of the holder where the cutting insert is fixed. This technology intends to effectively remove the chips produced in the inner surface machining to the outside by forming the pockets in the proper places and using them as channels or guides.

For example, a cutting tool for boring (boring bit) has been proposed that has a pocket (front end-sided chip pocket) formed concavely with respect to the outer circumferential surface of a holder above the cutting surface of a cutting insert that is fixed to the front end of a holder; and a chip pocket inclined upward toward the rear end of the head of the holder (shank) and connected to the pocket (space above the cutting surface). According to this cutting tool, a first sub-pocket (cutting surface-sided chip pocket) is formed to extend forward and backward on the outer circumferential surface of the holder where the cutting edge overhangs, in the upper side of the cutting surface of the cutting insert. A second sub-pocket is formed to extend forward and backward on the outer circumferential surface of the holder at the opposite side to the side where the cutting edge overhangs, in the upper side of the cutting surface of the cutting insert. Also, a rib extending forward and backward is formed between the first sub-pocket and the second sub-pocket in the holder, and the front surface (front end surface) of the rib is connected to the inclined pocket. See, for example, Japanese Patent Application Laid-Open No. 2005-279855-A.

In cutting (machining an inner surface) by the cutting tool for boring described above, the following effects (1) and (2) can be achieved on discharging the chips.

(1) Chips produced in machining the inner circumferential surface of a hole and comminuted into in small sizes are received in the first sub-pocket formed on the outer circumferential surface of the holder at the side of the cutting edge from the chip pocket that has received the chips first, and then removed to the outside of the machined hole through the first sub-pocket.

(2) The chips not comminuted are received in the second sub-pocket formed on the outer circumferential surface of the holder at the circumferential opposite side with respect to the cutting edge from the chip pocket, and then removed outside through the second sub-pocket. Therefore, less chips are stuck or come between the machined hole and the holder, such that a very accurate hole can be machined.

3. Problems to be Solved by the Invention

When a sample of a cutting tool having the above configuration (minimum machinable inner diameter: φ10 mm) is used for a cutting test, the following results (1) and (2) are confirmed. The cutting test is performed in two cases where chips are comminuted (sheared) in small sizes (workpiece: stainless steel SUS303) and where chips are relatively continuous (workpiece: stainless steel SUS304), by changing the shape of a breaker of a cutting insert. Here, the test conditions include the diameter (inner diameter) of the hole: 10 mm, hole depth: 20 mm, cut depth: 0.25 mm, cutting feed: 0.05 mm/rev, cutting speed: 80 m/min, and external cutting oil supply.

(1) In the cutting in which chips are comminuted into small sizes, the chips mainly flow only to the first sub-pocket. However, since the chip pocket is small as a concave space, it is difficult to remove the chips to the outside from the chip pocket, such that the chips tend to stick and remain on the inner circumferential surface. Therefore, a quality of the roughness on the machined surface degrades in a finish cutting.

(2) While the continuous chips (relatively long chips) flow to the second sub-pocket as well, the continuous chips tend to flow into the first sub-pocket instead. It appears that this is because chips remain even though removed to the second sub-pocket. Further, since the chip pocket of the first sub-pocket is small in this case as well as a concave space, the chips tend to remain between the first sub-pocket (concaved surface) and the inner circumferential surface of the hole. Therefore, the chips are easily wound and stuck to the cutting edge or the holder, such that a quality of the roughness on the machined inner circumferential surface degrades.

That is, when a relatively small-diameter and deep hole is machined in an external oil supply type apparatus by a cutting tool for boring of the related art, the chips tend to flow into the first sub-pocket and also remain in the hole, regardless of their shape. This phenomenon is seen by observing the removed state of the chips in the cutting process, or by observing the inner circumferential surface of the hole of the workpiece in the process of taking out the cutting tool after cutting is stopped, or in the process of taking out the cutting tool after a deep hole is machined.

SUMMARY OF THE INVENTION

The present invention has been made in consideration of the above problems of the prior art, and an object thereof is to provide a cutting tool for boring which can more smoothly remove chips to the outside (to the rear end side of a holder), regardless of the shape of the chips, even under cutting conditions where a relatively small-diameter and deep hole is machined by a cutting tool for boring.

The present invention, as set forth below, has been achieved by fabricating a plurality of cutting tool samples with various arrangements of pockets close to the front end of a holder, and by continuously developing and improving the samples through repeated cutting tests.

In a first embodiment, the present invention provides a cutting tool for boring, comprising: a bar-shaped holder; and a cutting insert fixed at a front end of the holder, the cutting insert having an cutting edge which overhangs from an outer circumferential surface of the holder, wherein the holder includes: a cutting surface-sided chip pocket that is concave with respect to the outer circumferential surface of the holder on a cutting surface of the cutting insert, the cutting surface-sided cut chip pocked configured to open to a portion of the outer circumferential surface where the cutting edge overhangs, the cutting surface-sided chip pocket having a bottom surface that faces the portion of outer circumferential surface where the cutting edge overhangs at a side opposite the portion of outer circumferential surface where the cutting edge overhangs, and wherein, an cutting edge-sided chip pocket is formed at the portion of the outer circumferential surface where the cutting edge overhangs such that an edge of the portion of the outer circumferential surface where the cutting edge overhangs is concave with respect to the outer circumferential surface of the holder, on a bottom of the cutting surface-sided chip pocket when viewed from the cutting surface.

In a preferred embodiment, a depth of the cutting surface-sided chip pocket from the edge of the portion of the outer circumferential surface where the cutting edge overhangs when viewed from the cutting surface decreases at least at a portion close to the rear end, along a direction toward the rear end of the cutting surface-sided chip pocket.

In another preferred embodiment, the cutting edge-sided chip pocket is formed such that the rear end of the cutting edge-sided chip pocket is behind the rear end of the cutting surface-sided chip pocket, at the rear portion of the holder.

In yet another preferred embodiment, an edge opposite the cutting surface-sided chip pocket in the cutting edge-sided chip pocket forms a protrusion that overhangs, outside of the outer circumferential surface of the holder on a cross-section taken perpendicular to the axial line of the holder.

In yet another preferred embodiment, the cutting edge-sided chip pocket is concaved substantially in parallel with an axial line of the holder.

In yet another preferred embodiment, a chamfered portion is formed where the bottom surface of the cutting surface-sided chip pocket and the bottom surface of the cutting edge-sided chip pocket intersect and where a ridge extending along the frontward and backward of the holder is formed.

In yet another preferred embodiment, the chamfered portion is formed in a convex arc-shaped curve on a cross-section perpendicular to an axial line of the holder.

According to the above embodiments of the present invention, when the inner circumferential surface of a hole of a workpiece is machined by the cutting tool of the present invention, even if the inner circumferential surface comes close to the side of the outer circumferential surface of the holder where the cutting surface-sided chip pocket and the cutting edge-sided chip pocket are formed, a gap (cut chip discharging route) extending in the circumferential direction, corresponding to both pockets, is present between the inner circumferential surface and the outer circumferential surface. Therefore, it is possible to allow the chips flowing to the cutting surface-sided chip pocket (corresponding to the first sub-pocket in the related art described above) of the chips produced to flow or be introduced into the cutting edge-sided chip pocket, even if a small-diameter and deep hole is machined. That is, in the present disclosure, as compared with the related art without such an cutting edge-sided chip pocket, the cutting edge-sided chip pocket connected to the cutting surface-sided chip pocket is further formed, such that the present invention has a configuration in which the cutting surface-sided chip pocket and the cutting edge-sided chip pocket are not separated (not formed at a distance from each other), but rather are formed adjacent to each other. Therefore, it is possible to ensure a large space at the inner circumferential surface of the workpiece (hole), the cutting surface of the holder, and the cutting edge (front flank). Consequently, it is possible to more smoothly remove the cut chip, regardless of the shape of the cut chip.

In the present invention, since the cut chip flowing to the cutting surface-sided chip pocket is allowed to flow to the cutting edge-sided chip pocket, the cut chip is prevented from remaining in the cutting surface-sided chip pocket and can be more efficiently removed to the outside. This effect is remarkable under a cutting condition in which only a small space can be ensured between the outer circumferential surface of the holder in the side of the cutting edge (front flank) and the inner circumferential surface of the workpiece. This is because it is difficult to ensure a large amount of protrusion of the cutting edge from the outer circumferential surface of the holder, as a cutting tool for boring that is used to machine a small-diameter hole. In particular, the effect is remarkable in machining a deep hole. In machining the inner circumferential surface of a hole of a workpiece by the cutting tool of the present invention, since it is possible to more efficiently handle a cut chip in comparison to cutting with a cutting tool of the related art, the roughness of the machined surface of the inner circumferential surface is not decreased. Although a large depth of the cutting edge-sided chip pocket as viewed from the side of the cutting surface is required for ensuring a space for discharging a cut chip, the depth may be set in accordance with machining conditions within a range of ensuring sufficient stiffness, depending on the length or thickness of the holder.

According to the embodiments of the present invention, the chips flowing to the cutting surface-sided chip pocket are guided rearward to the bottom surface by the configuration, such that the chips are actively led to the cutting edge-sided chip pocket of the portion of outer circumferential surface where the cutting edge overhangs. Therefore, the chips are smoothly moved and delivered from the cutting surface-sided chip pocket to the cutting edge-sided chip pocket, so as to prevent the chips from remaining in the cutting surface-sided chip pocket, and to more smoothly remove the chips toward the rear end side of the holder. In the cutting surface-sided chip pocket, the bottom surface facing the portion of outer circumferential surface where the cutting edge overhangs from the front end is determined within a range that does not interfere with the cutting insert. Particularly, the bottom surface is configured such that the removed chips can be efficiently received, in consideration of the removing direction of the chips produced in cutting by the cutting edge (removing angle of the cut chip).

Further, in the present invention, the rear ends of the cutting surface-sided chip pocket and the cutting edge-sided chip pocket may be positioned as close as possible to the rear end (base end) of the holder. This is because the chips can be easily removed to the rear side in this case. Therefore, the position of the rear ends may be determined, corresponding to the depth of the hole to be machined. However, the cutting surface-sided chips are likely to decrease second moment of area against the main component force applied to the front end of the holder in cutting, depending on the forming method. Therefore, when the rear end of the cutting surface-sided chip pocket extends rearward, the stiffness of the holder is easily decreased, which causes chatter vibration. In contrast, since the cutting edge-sided chip pocket is concaved on the portion of outer circumferential surface where the cutting edge overhangs, the second moment of area against the main component force is influenced to a lesser degree. Further, the chips can be easily removed rearward, by positioning the rear end of the cutting edge-sided chip pocket behind the rear end of the cutting surface-sided chip pocket. Therefore, it is possible to increase the discharging performance of the chips while preventing the stiffness from being decreased, by using the configuration described in the exemplary embodiments. Positioning the rear end of the cutting edge-sided chip pocket outside the hole of the workpiece is desirable for more efficiently discharging the chips.

In the embodiment of the present invention described above, the cut chip flowing to the cutting surface-sided chip pocket flows to the cutting edge-sided chip pocket and then is removed to the rear side of the holder. The cut chip flowing into the cutting edge-sided chip pocket is turned into the bottom surface (opposite the cutting surface) of the holder, above the edge of the opposite side to the cutting surface in the cutting edge-sided chip pocket, between the inner circumferential surface of the workpiece and the outer circumferential surface of the holder, by rotation of the workpiece about the cutting edge. In particular, a continuous cutting edge may cause the cut chip to be wound around the holder. Similar to the cutting tool for boring according to the exemplary embodiment of the present invention, when the edge has a protrusion, the protrusion can prevent the cut chip from turning, such that the cut chip is effectively prevented from coming between the inner circumferential surface of the workpiece and the outer circumferential surface of the holder or winding and sticking to the holder. In the cutting tool for boring according to the exemplary embodiment of the present invention, the edge positioned opposite the cutting surface-sided chip pocket in the cutting edge-sided chip pocket implies that the edge is close to the bottom surface (opposite the cutting surface) of the holder in the cutting edge-sided chip pocket. The protrusion may continuously extend along the cutting edge for realizing this function.

Further, as the cutting tool for boring according to the exemplary embodiment of the present invention, since the cutting edge-sided chip pocket is concaved substantially in parallel with the axial line of the holder, it is possible to further prevent a decrease in strength (stiffness) of the holder against the main component force in cutting, as compared with when the cutting edge-sided chip pocket is formed at an angle with respect to the axial line of the holder so as to be spaced apart from the cutting surface toward the rear side. Further, as the cutting tool for boring according to the exemplary embodiment of the present invention, when the cutting edge-sided chip pocket is formed, it is easy to remove the cut chip that has flowed in the cutting edge-sided chip pocket to the rear side of the holder. In this manner, it is possible to prevent the cut chip from turning on the outer circumferential surface of the holder.

In the present invention as described above, the cutting edge-sided chip pocket is formed on the outer circumferential surface such that the edge of the portion of outer circumferential surface where the cutting edge overhangs is concave with respect to the outer circumferential surface of the holder, on the bottom surface of the cutting surface-sided chip pocket when viewed from the side of the cutting surface. As described above, when the inner circumferential surface of a hole of a workpiece is machined, even if the inner circumferential surface comes close to the outer circumferential surface of the holder where the cutting surface-sided chip pocket and the cutting edge-sided chip pocket are formed, a gap (cut chip discharging route) extending in the circumferential direction, corresponding to both pockets is present between the inner circumferential surface and the outer circumferential surface. In the configuration of the present invention described above, the bottom surfaces of both pockets are connected (adjacent to each other) such that the bottom surface of the cutting surface-sided chip pocket intersects with the surface (bottom surface) of the cutting edge-sided chip pocket, thereby forming a ridge extending frontward and backward at the intersecting place, that is, where the bottom surfaces of the two pockets are in contact.

In the present invention, the portion where the ridge extends along the frontward and backward along the holder, that is, where the ridge is formed (the bottom surfaces where the two pockets intersect), may be chamfered. Further, in this case, as the cutting tool for boring according to the exemplary embodiment of the present invention, although the chamfered portion may form a convex arc-shaped curve (convex rounded portion) on the cross-section perpendicular to the axial line of the holder, it may be an inclined chamfered portion that can be easily machined, it may be composed of an arc-shaped curve and a curved surface, or it may have a concave arc shape. That is, chamfering as used herein may be rounded or cut at the portion where the ridge is formed by intersecting the bottom surfaces of the two pockets, so that there is no angle by the ridge.

When the chamfered portion is formed, particularly, the larger the chamfered portion (the radius of the convex rounded portion or the width of the inclined chamfered portion), the larger the gap (cut chip discharging route) extending in the circumferential direction between the inner circumferential surface and the outer circumferential surface, when the inner circumferential surface comes close to the outer circumferential surface where the cutting surface-sided chip pocket and the cutting edge-sided chip pocket are formed, in machining the inner circumferential surface of a hole of the workpiece. Therefore, the cut chip smoothly flows from the cutting surface-sided chip pocket to the cutting edge-sided chip pocket. The size and the cross-sectional shape of the chamfered portion are determined in consideration of the flow of the cut chip or the decrease in stiffness of the holder. As the chamfered portion increases, the boundary between the cutting surface-sided chip pocket and the cutting edge-sided chip pocket becomes unclear and thus both pockets are, so to speak, combined.

DETAILED DESCRIPTION

Next, the present invention is described in detail with reference to the drawings. However, the present invention should not be construed as being limited thereto.

Exemplary embodiments of the present invention are described in detail with reference toFIGS. 1 to 9. Reference numeral101designates a cutting tool for boring (boring bit) according to an exemplary embodiment of the present disclosure. The present exemplary embodiment includes a bar-shaped holder (shank)10and a cutting insert501(positive type of triangular chip, hereafter also referred to as a triangular chip) formed in a triangular plate shape, which is fixed to the front end of the front end-sided portion (head)13of holder10, and its detailed configuration is as follows.

That is, holder10is a cylindrical bar, and has, on its front end, cutting insert501(triangular chip) with a screw hole, and, above a cutting surface503of the chip, a front end-sided chip pocket20that is concave with respect to the outer circumferential surface of holder10(a space above cutting surface503that is concave with respect to the outer circumferential surface of holder10), the cutting insert being fixed by tightening a clamp screw550. However, front end-sided portion13of holder10having a portion fixing triangular chip501has an outer diameter (for example, φ9 mm) that is slightly larger than the outer diameter (for example, φ8 mm) of a rear end-sided portion15(shank) behind portion13, such that holder10is entirely formed in a cylindrical bar composed of two parts having different diameters and a common axis. Although the present exemplary embodiment includes a concave triangular chip seat21to seat and fix triangular chip501at the front end of front end-sided portion13(see, for example,FIG. 2), chip seat21and a cutting surface-sided chip pocket or an cutting edge-sided chip pocket, described below, are formed by cutting as a base, a cylindrical bar made of alloy steel with different diameters and a common axis. Although a front end-sided part before a concave portion14in the circumferential direction at the front end of shank15is referred as front end-sided portion13in the present exemplary embodiment, the lengths of front end-sided portion13and shank15are about 20 mm and 80 mm, respectively.

According to chip seat21of holder10(see, for example,FIG. 2), when triangular chip501is fixed, as shown inFIGS. 1 to 5, one (1) cutting edge505for cutting overhangs from the outer circumferential surface of holder10, such that the cutting surface503is positioned around a plane H (virtual plane) passing through the axial line G of holder10. Further, chip seat21is concave in a notch shape in head13such that cutting edge505is positioned on plane H. The protrusion amount T of cutting edge505from the outer circumferential surface of shank15is set to 1.0 mm, such that cutting tool101according to the present exemplary embodiment is used for machining the inner circumferential surface of a small hole having an inner diameter of at least φ10 mm.

In chip seat21, with cutting insert501fixed, two restricting walls23and24that restrict two sides510(relief sides) of triangular chip501are formed upward from a seat surface22such that the other two (2) cutting edges505not for cutting (hereinafter, referred to as noses in order to discriminate from cutting edge505for cutting) do not overhang from the outer circumferential surface of holder10. Accordingly, the bottom surface (triangular major surface opposite to cutting surface503) of triangular chip501is seated on flat seat surface22of chip seat21, with two (2) sides (relief sides)510and510in contact with restricting walls23and24, and then triangular chip501is clamped by inserting a clamp screw550in a threaded hole25for clamp screw550formed substantially at the center portion of seat surface22. After the clamp screw is inserted, the head (top) of screw550is at substantially the same height as the cutting surface503.

In the present exemplary embodiment, although two restricting walls23and24are formed in a V-shape with 60 degrees, with the front end open, when seen from the side of cutting surface503(see, for example,FIG. 3) such that cutting edge505protruding from the outer circumferential surface of holder10is positioned at the front end, chip seat21is biased to the protrusion side of cutting edge505with respect to the axial line G of holder10. Therefore, when seen from the side of cutting surface503(seeFIG. 3), restricting wall23(protrusion-sided restricting surface) that restricts side510between cutting edge505protruding from the outer circumferential surface and nose505received in a relief portion27(described below) is thinner than restricting wall24that restricts side510between two noses505and505not for cutting. Relief portion27(depression) that receives nose505is formed at the corner where the two restricting walls23and24cross, and is cut inward in a substantially arc shape, when seen from the side of cutting surface503.

Holder10includes a cutting surface-sided chip pocket30that is concave with a substantial flat bottom, with respect to the outer circumferential surface of holder10, and is connected to a front end-sided chip pocket (space)20above the cutting surface503of triangular chip501, in the side of cutting surface503of triangular chip501fixed to head13. Cutting surface-sided chip pocket30is open to the portion18of outer circumferential surface (at the lower portion inFIG. 3) of holder10where cutting edge505of cutting insert501overhangs from the outer circumferential surface of the holder10(front flank of cutting edge505facing the inner circumferential surface of a hole to be machined). Further, cutting surface-sided chip pocket30is made concave to have a bottom surface33facing the portion18of outer circumferential surface where the cutting edge overhangs, in the side opposite the portion18of the outer circumferential surface where the cutting edge overhangs (see S2and S3cross-sections inFIG. 6). Further, in the present exemplary embodiment, cutting surface-sided chip pocket30is formed at the side of cutting edge505(at the lower portion inFIG. 3) from axial line G of holder10, including relief portion27when seen from cutting surface503(see, for example,FIG. 3), in which the width decreases toward the rear end, that is, the depth F1decreases toward the rear end. For reference, the depth F1is about ½ to 0 of the outer diameter of holder10in the present exemplary embodiment. The bottom surface33of cutting surface-sided chip pocket30is in substantially the same plane as the cutting surface503of the triangular chip501, at upper edge26where relatively thin restricting wall23is formed, and at the rear side (the right side inFIGS. 3 and 4) and portion26b, close to triangular chip501, when viewed from the side of the protruding cutting edge505(see, for example,FIG. 4). Further, the bottom surface33rises above cutting surface503toward the rear side from the same plane.

Though a detailed description is provided below, in the present exemplary embodiment, a second cutting surface-sided chip pocket130, which is connected to front end-sided chip pocket20above cutting surface503of triangular chip501, concave with respect to the outer circumferential surface of holder10, with an upper edge29of restricting wall24at substantially the same height as cutting surface503, and extending rearward from the same height portion, is formed opposite the side where cutting edge505overhangs, when seen from the side of cutting surface503. Therefore, a convex portion41that is wide rearward and overhangs upward is formed between two cutting surface-sided chip pockets30and130of the holder10, when viewed from the side of cutting surface503, and a front end43of convex portion41is the front end of bottom surface33which faces the portion18of the outer circumferential surface where the cutting edge overhangs. Front end43of convex portion41forms an inclined front ended surface45that rises (elevates) at an angle rearward from cutting surface503, at the side opposite protruding cutting edge505which is the side of nose505received in relief portion27. Therefore, in the present exemplary embodiment, basically the chips flowing on cutting surface503of triangular chip501are directed toward the bottom surface33of the cutting surface-sided chip pocket30facing the portion18of outer circumferential surface where the cutting edge overhangs, rather than the front ended surface45, when viewed from the side of cutting surface503(see, for example,FIG. 3), thereby enhancing removability. That is, most of the chips in the range of an angle θ, which is seen from the side of cutting surface503, made by axial line G and a line L1constructed from the cutting edge to front end43of convex portion41, are set to be received in the cutting surface-sided chip pocket30. The angle θ may be in the range of 20 to 40 degrees.

Meanwhile, when holder10is seen from the side of cutting surface503, an cutting edge-sided chip pocket50which is cut on the portion18of the outer circumferential surface where the cutting edge overhangs in holder10, that is, the front flank such that an edge35of the portion18of the outer circumferential surface where the cutting edge overhangs of the bottom surface33of the cutting surface-sided chip pocket30, is concave with respect to the outer circumferential surface of holder10. In the present exemplary embodiment, cutting edge-sided chip pocket50is concaved substantially in parallel with axial line G of holder10, along the edge35of the portion18of the outer circumferential surface where the cutting edge overhangs of the cutting surface-sided chip pocket30, that is, along the ridge where the cutting surface-sided chip pocket30and the cutting edge-sided chip pocket50intersect, when viewed from the side of the cutting surface503. Although the depth F2from cutting edge505of cutting edge-sided chip pocket50viewed from the side of cutting surface503is set appropriately in accordance with the protrusion amount T of cutting edge505or thickness of holder10, or in compliance with requirements for ensuring the area of a channel for discharging the chips according to cutting conditions, it may be set within 15 to 30% of the diameter of shank15.

Further, in the present exemplary embodiment, the front end53of the cutting edge-sided chip pocket50starts from the middle portion of the relatively thin restricting wall23, as shown inFIGS. 3 and 4, and the rear end55is positioned behind rear end37of cutting surface-sided chip pocket30and at shank15behind the head13. The cutting edge-sided chip pocket50is formed substantially flat along axial line G of the holder10in the present exemplary embodiment, except for the concave rounded surface around the front and rear ends53and55. Therefore, the cutting edge-sided chip pocket50when holder10is viewed from the side of protruding cutting edge505(see, for example,FIG. 4), that is, as viewed from the front flank of cutting edge505, has a wide flat plane that rises, taking the shape of bottom surface33of the cutting surface-sided chip pocket30, toward the rear side (the right side inFIG. 4), at the middle portion.

Further, in the present exemplary embodiment edge57opposite the cutting surface-sided chip pocket30, in the cutting edge-sided chip pocket50, has a protrusion58that overhangs outward on the cross-section perpendicular to the axial line G of holder10(see, for example,FIG. 6). That is, the edge close to the bottom17of holder10at cutting edge-sided chip pocket50(the ridge where the portion close to bottom17of the outer circumferential surface of the holder10and the cutting edge-sided chip pocket50intersect) forms protrusion58that overhangs outward, along axial line G of the holder10. However, portion59close to protrusion58of the cutting edge-sided chip pocket50(the lower portion inFIG. 4) is provided with a concave rounded portion in a transverse plane (the cross-section perpendicular to axial line G of holder10) (see, for example,FIG. 6).

As described above, since the cutting edge-sided chip pocket50is formed inside the portion18of the outer circumferential surface where the cutting edge overhangs, with respect to the edge35at cutting edge505of the cutting surface-sided chip pocket30, a channel through which the chips flow from the cutting surface-sided chip pocket30to edge the end-sided chip pocket50is ensured, even if the inner circumferential surface of the hole of the workpiece comes close to the side of the outer circumferential surface (front flank) of the side of cutting edge505of the holder10.

In the present exemplary embodiment, although generally described above, the second cutting surface-sided chip pocket130having a width smaller than that of cutting surface-sided chip pocket30and the rear end of second cutting surface-sided chip pocket130positioned ahead of rear end37of pocket30is formed at the side opposite the cutting surface-sided chip pocket30, with axial line G therebetween, when viewed from the side of from cutting surface503. Although a second cutting surface-sided chip pocket130is not necessary in the present invention, if it is included, it is possible to remove chips flowing to the side opposite the protrusion side of cutting edge505, out of second cutting surface-sided chip pocket130. Further, a second cutting surface-sided chip pocket130, when present, contributes to reducing the weight of the front end of holder10, and advantageously prevents chatter vibration when stiffness is sufficient. Similar to cutting surface-sided chip pocket30, second cutting surface-side chip pocket130is connected to front end-sided chip pocket20above the cutting surface503of triangular chip501. Further, the second cutting surface-side chip pocket is concave with respect to the outer circumferential surface of holder10, is open to the outer circumferential surface of holder10opposite the portion where cutting edge505of cutting insert501overhangs, and has a bottom surface133facing the open side.

Next, the operational effects of cutting tool101for boring having the configuration described above, according to the present exemplary embodiment, are described with reference toFIGS. 5 and 7. That is, when an inner circumferential surface603of a hole in a workpiece601is machined by cutting tool101, the inner circumferential surface603is positioned close to the outer circumferential surface of holder10having cutting surface-sided chip pocket30and cutting edge-sided chip pocket50. A gap (cut chip-discharging route) corresponding to both pockets30and50included in this embodiment, in this case, extends between the inner circumferential surface603and the outer circumferential surface of holder10, according to the present cutting tool101(seeFIG. 7). Therefore, cut chip K cut off by cutting edge505and flowing from the front end-sided chip pocket20to the cutting surface-sided chip pocket30is removed to cutting edge-sided chip pocket50at the portion18of the outer circumferential surface where the cutting edge overhangs from holder10. Therefore, as shown inFIGS. 7A and 7B, cut chip K removed to cutting edge-sided chip pocket50is removed outside through opening605of the hole from rear end55. Namely, the cutting edge-sided chip pocket50connected to cutting surface-sided chip pocket30is formed in addition to the pocket30. Consequently, a space between the cutting tool and inner circumferential surface603of the workpiece601increases when the inner circumferential surface603of the hole is machined by cutting tool101according to the present exemplary embodiment. Therefore, compared with the related art not having an cutting edge-sided chip pocket50, cut chip K hardly remains on inner circumferential surface603regardless of its shape. Accordingly, the cut chip can be more efficiently removed outside, thereby preventing the machined surface of inner circumferential surface603from becoming roughened.

In particular, in the present exemplary embodiment, the depth F1of the cutting surface-sided chip pocket30decreases toward the rear side, when viewed from the side of cutting surface503. Therefore, cut chip K flowing to the cutting surface-sided chip pocket30is guided to the bottom surface33and actively guided to the cutting edge-sided chip pocket50at the portion18of the outer circumferential surface where the cutting edge overhangs, as it flows rearward. As such, the cut chip K is more smoothly moved to the cutting edge-sided chip pocket50from the cutting surface-sided chip pocket30. Further, in the present exemplary embodiment, the rear end55of the cutting edge-sided chip pocket50is positioned at rear side of holder10, further behind the rear end37of the cutting surface-sided chip pocket30. Therefore, as shown inFIG. 7, when the machining of the hole, with rear end55of the cutting edge-sided chip pocket50behind opening (inlet)605of the hole is completed, cut chip K can be prevented from remaining in the cutting surface-sided chip pocket30by the cutting edge-sided chip pocket50. Also, cut chip K can be removed more smoothly to the outside from cutting edge-sided chip pocket50. Further, the rear end55of the cutting edge-sided chip pocket50may be positioned as far rearward as possible, unless the stiffness of holder10is adversely affected.

Further, in the present exemplary embodiment edge57opposite the cutting surface503, in the cutting edge-sided chip pocket50, has a protrusion58that overhangs outward on a cross-section perpendicular to the axial line G of the holder10(seeFIGS. 5 and 6). Although understood from the above discussion, the protrusion functions as a stopper that stops cut chip K, even when the cut chip K, having moved from the cutting surface-sided chip pocket30to the cutting edge-sided chip pocket50, may turn to the bottom17of holder10(on a side opposite the cutting surface503) by rotation of the workpiece601between the inner circumferential surface603and the outer circumferential surface of holder10. Accordingly, a remarkable effect is achieved in that it is possible to prevent the cut chip K from sticking and winding on the holder10.

Further, in the present exemplary embodiment, cutting edge-sided chip pocket50extends along axial line G, in parallel with axial line G of the holder10. Therefore, it is possible to achieve the following effect, in addition to the effect described above. The cutting edge-sided chip pocket50is formed toward the rear end from the front end of holder10. Thus, even though parallel with axial line G of holder10, for example, when the cutting edge-sided chip pocket50extends at an angle at a predetermined distance from the cutting surface of the holder10(the cutting edge-sided chip pocket50is not concaved in parallel with axial line G of holder10), the stiffness is decreased in the direction of the main component force applied to the holder10in cutting (namely, the second moment of area decreases), as compared with when it is concaved substantially in parallel with axial line G. On the other hand, in the present exemplary embodiment, since cutting edge-sided chip pocket50is concaved substantially in parallel with axial line G of the holder10, it is easy to prevent the stiffness from decreasing where the cutting edge-sided chip pocket50is formed in the holder10. Namely, it is possible to implement a cross-sectional shape making it easy to prevent a decrease of the second moment of area.

Further, when the cutting edge-sided chip pocket50extends at an angle so as to be spaced apart from the side of the cutting surface of holder10, toward the rear end of holder10, the cutting edge-sided chip pocket50extends not in parallel with axial line G, but in a twisted form, toward the rear end from the front end. Accordingly, the cut chip flowing to the rear end of the cutting edge-sided chip pocket50can easily flow according to the inclination, and therefore the cut chip flowing rearward can easily wind and stick on the outer circumferential surface of holder10. However, it can be also prevented in the present exemplary embodiment.

Next, a cutting tool201for boring according to a second exemplary embodiment of the present disclosure is described with reference toFIGS. 8 to 13. There is a difference in that a rhombus-shaped chip701having two cutting edges505(80 degrees of nose angle) is provided in the second exemplary embodiment, when compared to triangular cutting insert501in the previous exemplary embodiment, but there is essentially no difference in both exemplary embodiments, including operation and effect. Therefore, the shape of the chip seat21and the shape of the cutting surface-sided chip pocket30are only a little different in view of the above difference. The difference will be briefly described. The same parts (or corresponding parts) compared to the previous embodiment are designated by the same reference numerals.

That is, on chip seat21in holder10of cutting tool201according to the present exemplary embodiment, as shown inFIG. 9, rhombus-shaped chip701is fixed. One (1) cutting edge (nose)505for cutting overhangs from the outer circumferential surface of the holder10, as shown inFIGS. 8 to 12, such that the cutting surface503of chip701is positioned around a plane H (virtual plane) passing through axial line G of the holder10and the cutting edge505is positioned on plane H. Further, chip seat21is formed in a concaved shape in a notch shape in head13.

Meanwhile, in the chip seat21, two sides510at both sides of the overhung cutting edge505of rhombus-shaped chip701are positioned at the protrusion side and the front side of the outer circumferential surface of the holder10. On the other hand, two restricting walls23and24restricting two sides (relief sides)510at both sides of the other cutting edge (nose)505not for cutting are raised from the seat surface22at an angle of five degrees in the direction of axial line G and the transverse direction of the holder10, when viewed from the side of cutting surface503. Therefore, the relief portion27receiving nose505is formed at a position corresponding to the position of the nose505. Accordingly, the bottom surface of rhombus-shaped chip701is seated on the flat seat surface22of the chip seat21, with two sides (relief sides)510in contact with the restricting walls23and24, and then, in the same way as the previous embodiment, rhombus-shaped chip701is clamped by inserting clamp screw550in threaded hole25formed at the center portion of the seat surface22. In the present exemplary embodiment, the head (top) of screw550slightly overhangs from cutting surface503.

In the present exemplary embodiment, since the two restricting walls23and24are arranged as described above, when viewed from the side of cutting surface503(seeFIG. 10), the portion of the restricting wall24opposite the side where the cutting edge505overhangs is relatively thin. Further, the cutting surface-sided chip pocket30is concaved rearward from upper edge26of the restricting wall23opposite the restricting wall24. Further, the second cutting surface-sided chip pocket130has a cutting surface29binclined upward toward the rear side and extending rearward, with an upper edge29of restricting wall24, which is opposite the side where the cutting edge505overhangs, at substantially the same height as the cutting surface503.

The present exemplary embodiment is an example having a different cutting insert shape, that is, a modified example of the previous embodiment. As seen above, it is apparent from the present disclosure that the cutting tool can be used for cutting inserts having various chip shapes and can be appropriately modified. In each of the exemplary embodiments, although both pockets are formed such that the ridges rise where the bottom surface of the cutting surface-sided chip pocket and the surface of the cutting edge-sided chip pocket intersect, the cut chip can be easily removed to the cutting edge-sided chip pocket by chamfering the ridges in a predetermined size. In both embodiments, although flat surface19extending in a band shape with a predetermined width along the axial line is concaved on the side of the cutting surface of the shank, this is the fixing portion for fixing the cutting tool to an edge holder with a bolt.

Next, a cutting tool301for boring according to a third exemplary embodiment of the present disclosure is described with reference toFIGS. 14 to 18. However, as described above, although the ridges of holder10are formed where the bottom surface33of the cutting surface-sided chip pocket30and the surface (bottom surface)52of the cutting edge-sided chip pocket50intersect (at the edge35of the portion of the outer circumferential surface where the cutting edge overhangs on the bottom surface33of the cutting surface-sided chip pocket30) in the first and second exemplary embodiments, a chamfered portion36is formed on the ridge in a predetermined size and cross-sectional shape in the present exemplary embodiment (third exemplary embodiment). The present exemplary embodiment is not different from the first exemplary embodiment, except for the chamfered portion36on the ridge (edge35). Therefore, only this difference is described. The same parts are designated by the same reference numerals and the detailed description is omitted.

That is, in cutting tool301for boring of the present exemplary embodiment, chamfered portion36is formed throughout the entire length C2along axial line G, where the bottom surface33of cutting surface-sided chip pocket30and the bottom surface52(surface) of the cutting edge-sided chip pocket50intersects in the holder10, that is, where the ridge (end edge35) extends in the holder10in the first exemplary embodiment. In the present exemplary embodiment, chamfered portion36is formed in a convex arc shape (convex rounded portion), on the cross-section (transverse surface) perpendicular to the axial line G of holder10(seeFIG. 18). In detail, the cutting surface-sided chip pocket30has one (1) bottom surface33, and the cutting edge-sided chip pocket50also has one (1) surface (bottom surface)52, and the bottom surfaces33and52of both pockets30and50intersect in the first exemplary embodiment, such that the ridge is formed at the edge35at the intersection. However, in the present exemplary embodiment, chamfered portion36of the convex rounded portion (arc-shaped curved convex rounded portion) on the cross-section perpendicular to axial line G of holder10is formed throughout the entire length C2, along where the ridge is formed (edge35). As shown in the enlarged view of the cross-section taken along the line S3-S3inFIG. 18, the intersection angle α where the ridge (the edge35is shown by a chain line) is formed in the first exemplary embodiment, that is, where bottom surface33of the cutting surface-sided chip pocket30and the bottom surface52of cutting edge-sided chip pocket50intersect, is larger than 90 degrees. Further, since the convex rounded chamfered portion36will be formed at the ridge (edge35), the bottom surface33of the cutting surface-sided chip pocket30and bottom surface52of cutting edge-sided chip pocket50are smoothly connected by the chamfered portion36.

Further, in the present exemplary embodiment, chamfered portion36is formed in a range C2from the front end53of the cutting edge-sided chip pocket50to the rear end37of the cutting surface-sided chip pocket30. In the present exemplary embodiment, as described above, a ridge is not formed where the bottom surfaces33and52of both pockets30and50intersect, that is, both bottom surfaces33and52are connected by the rounded surface. Therefore, when the inner circumferential surface603of a hole of a workpiece is machined by cutting tool301for boring, since chamfered portion36is formed, even if inner circumferential surface603of the hole of the workpiece is close to the side of the outer circumferential surface where the cutting surface-sided chip pocket30and the cutting edge-sided chip pocket50are formed between the inner circumferential surface and the outer circumferential surface, there is no corner due to the ridge connecting from the cutting surface-sided chip pocket30to the cutting edge-sided chip pocket50, other than the circumferential gap (cut chip discharging route) around the ridge in the first exemplary embodiment, such that the gap is large (wide). Therefore, the cut chip can smoothly flow from cutting surface-sided chip pocket30to the cutting edge-sided chip pocket50.

By forming the chamfered portion36, as described above, as the chamfered portion36(radius of the convex rounded portion) increases, there is no clear boundary between the bottom surface33of cutting surface-sided chip pocket30and the bottom surface52of cutting edge-sided chip pocket50. That is, so to speak, both pockets30and50make one (1) chip pocket. Further, in the present exemplary embodiment, although the chamfered portion36is formed in a convex rounded shape on the cross-section perpendicular to axial line G of holder10, it may be an inclined chamfered portion.

FIG. 19is a view showing an example (fourth exemplary embodiment) of a cutting tool401for boring having an inclined chamfered portion, as shown by the double hatch lines. The present exemplary embodiment is different from the third exemplary embodiment only in the shape and structure of the chamfered portions. Further, the same parts are designated by the same reference numerals, such that the detailed description is omitted. However, when chamfered portion36is an inclined chamfered portion as in the present exemplary embodiment, machining for forming the chamfered portion becomes easy. The inclined chamfered portion may be a 45 degree chamfered portion36formed by cutting the portion close to the end of the cutting surface (end edge35in the first exemplary embodiment) of the bottom surface52of the cutting edge-sided chip pocket50, at an angle of 45 degrees with respect to the bottom surface52. However, it may be formed at less than 45 degrees with respect to the bottom surface52such that both bottom surfaces32and52intersect at a substantially equivalent angle. Alternatively, the inclined chamfered portion may be a multi-stepped chamfered portion, such as a double chamfered portion (chamfered portion composed of two inclinations on the transverse cross-section). A concave rounded portion opposite the convex rounded portion may be provided, if needed. That is, there is no corner due to the ridge of the first exemplary embodiment by the chamfered portion, such that the cut chip is smoothly removed to the cutting edge-sided chip pocket50. Although the size of the chamfered portion36depends on the inner diameter of the workpiece or the depth of the hole, the larger the size, the more the strength of the holder10is decreased. Thus, the size of the chamfered portion should be determined on the basis of the machining conditions or cutting conditions.

From the foregoing, it will be appreciated that various embodiments of the present invention have been described herein for purposes of illustration, and that various modifications may be made without departing from the scope and spirit of the claims appended hereto.

This application is based on and claims priority from Japanese Patent Application No. 2010-083025, filed on Mar. 31, 2010, and Japanese Patent Application No. 2011-027989, filed on Feb. 11, 2011, the disclosures of which are incorporated herein by reference in their entirety.