Drill

Abstract

[Problem] To make it possible, in a drill in which a honed surface is formed on a cutting edge, to suppress flank wear while improving the chipping resistance of the cutting edge by forming said honed surface with a radius. [Solution] In a cross section orthogonal to the extension direction of a main cutting edge 41, a honed surface 41a of the main cutting edge 41 is provided with a rake face–side honed surface 41a1 that describes a curve having a radius of curvature R1 near a rake face 41b formed on the rotation-direction front side of the main cutting edge 41 and a flank-side honed surface 41a2 that describes a curve having a radius of curvature R2 near a flank 7 formed on the rotation-direction rear side of the main cutting edge 41, and an angle θ is provided, toward the rake face 41b side, between the flank 7 and a tangent L1 at the flank 7-side end point of the curve forming the flank-side honed surface 41a2.

Description

drill

[0001] The present invention relates to a drill that is used mainly for metal processing and has a honing surface formed on the cutting edge to prevent breakage.

[0002] The cutting edges of drills, such as small-diameter long drills used for metalworking, are sometimes formed with a honed surface to prevent breakage during cutting (see Patent Documents 1 to 4). In particular, when the honed surface is formed with R-honing, which creates a convex curved surface, the cutting edge strength of the cutting edge is increased, which has the advantage of improving chipping resistance (see Patent Documents 5 to 7).

[0003] In Patent Documents 5 to 7, as shown in Figure 8-(b), in a cross section perpendicular to the extension direction of the main cutting edge 41, a rake face-side honing surface 41a1 with a curvature radius R1 is formed on the honing surface near the rake face on the front side in the direction of rotation of the cutting edge, and a flank face-side honing surface 41a2 with a curvature radius R2 is formed on the flank face 7 (second surface 71) on the rear side in the direction of rotation of the cutting edge. Flank face 7 (71) is inclined toward the rake face 41b from the surface of the workpiece shown by the two-dot chain line.

[0004] Japanese Utility Model Application Publication No. 60-175513 (Claim 1, Specification, page 6, line 11 to page 9, line 5, Figures 3, 6, and 7) Japanese Patent Application Publication No. 2009-18360 (Claim 1, paragraphs 0016 to 0025, Figures 4 and 5) Japanese Patent Application Publication No. 2021-88007 (paragraphs 0022 to 0049, Figures 4, 6, and 7) Japanese Patent Application Publication No. 2015-93351 (paragraphs 0032 to 0048, Figures 5 and 6) Japanese Patent Application Publication No. 60-221208 (Specification, page 6, lines 4 to 17, and Figure 7) Japanese Patent Application Publication No. 2014-8549 (Claim 1, paragraphs 0020 to 0024, and Figure 4) International Publication No. 2024 / 004075 (Claim 1, paragraph 0032, and Figure 6)

[0005] As in Patent Documents 5 to 7, it is believed that by making the radius of curvature R1 of the rake face side honing surface larger than the radius of curvature R2 of the flank face side honing surface, it is possible to increase the chipping resistance of the cutting edge while also improving the cutting sharpness.

[0006] On the other hand, the inventors have found that even when R honing having curved surfaces with different radii of curvature is provided, there is still room for improvement in terms of wear on the flank face.

[0007] In light of the above background, the present invention proposes a drill that satisfies the requirements of forming an R honing to increase the chipping resistance of the cutting edge while suppressing flank wear.

[0008] The drill of the invention described in claim 1 comprises a cutting portion having a plurality of cutting edges on the axial tip side of a shank portion and chip discharge grooves between the cutting edges adjacent in the circumferential direction, wherein the cutting edges include a main cutting edge on the radially outer periphery and a thinning cutting edge that is continuous with the main cutting edge and is located on the radially central side of the main cutting edge, and the main cutting edge and the thinning cutting edge each have a honing surface with a convex curved surface, and in a cross section perpendicular to the direction of extension of the main cutting edge, the honing surface of the main cutting edge has a rake face-side honing surface that is formed on the front side in the direction of rotation of the main cutting edge and describes a curve with a radius of curvature R1 near the rake face, and a flank-side honing surface that is formed on the rear side in the direction of rotation of the main cutting edge and describes a curve with a radius of curvature R2 near the flank, and a tangent L1 at the end point on the flank side of the curve that forms the flank-side honing surface and the flank form an angle θ with respect to the rake face.

[0009] "A honing surface having a convex curved surface" means that in a cross section perpendicular to the extension direction of the major cutting edge 41 and the thinning cutting edge 42 as shown in Figure 1, the honing surface 41a of the major cutting edge 41 and the honing surface 42a of the thinning cutting edge 42 both form a convex curve toward the surface as shown in Figures 2 and 4. "The extension direction of the major cutting edges 41, etc." refers to the direction in which the major cutting edges 41, etc. continue. "In a cross section perpendicular to the extension direction of the major cutting edges 41, etc." means "when the major cutting edges 41, etc. are viewed in a cross section that passes through the major cutting edges 41, etc. and is perpendicular to the major cutting edges 41, etc. themselves," as shown in Figure 4.

[0010] When viewing the main cutting edge 41 in a cross section perpendicular to the direction in which it extends, the cross section (honing surface 41a) of the main cutting edge 41 has at least two curved surfaces: a rake face-side honing surface 41a1 with a curvature radius R1 that forms a convex curve on the surface side (the side facing the workpiece 9), and a flank-side honing surface 41a2 with a curvature radius R2 that forms a convex curve on the surface side, as shown in Figure 1. The "flank" refers to the second flank 71 when two or more flanks 7 are formed.

[0011] The "rake face side honing surface 41a1" is formed on the honing surface 41a closer to the rake face 41b formed on the front side of the main cutting edge 41 in the direction of rotation, and the "flank face side honing surface 41a2" is formed on the rear side of the cutting edge 41 in the direction of rotation closer to the flank face 7.

[0012] The phrase "at least two curved surfaces" means that two or more curved surfaces are formed when viewing the cross section of the main cutting edge 41. Specifically, this means that in addition to the rake face-side honing surface 41a1 with a constant radius of curvature R1 and the flank-side honing surface 41a2 with a constant radius of curvature R2, there may be cases where a honing surface with a different radius of curvature is formed, or there may be a curved surface (curve) where the radius of curvature changes (gradually decreases) from the rake face-side honing surface 41a1 to the flank-side honing surface 41a2, or there may be cases where a flat surface (straight line) is included in part of the circumferential direction of the honing surface 41a (claim 6).

[0013] "The flank-side end point of the curve that forms the flank-side honing surface" refers to the end of the flank-side honing surface (curve) 41a2 on the flank 7 side when viewing the main cutting edge 41 in a longitudinal cross section, and "the tangent line L1 at the end point" refers to the tangent line at the end on the flank 7 side. A more precise definition of "the flank-side end point of the curve that forms the flank-side honing surface" will be described later. "The tangent line L1 and the flank 7 form an angle θ toward the rake face 41b" means that, as shown in Figures 1 and 8-(a), the angle between the tangent line L1 and the flank 7 is θ, and the flank 7 passes closer to the rake face 41b than the tangent line L1 (it is inclined toward the rake face 41b than the surface of the workpiece 9).

[0014] While there are various methods for forming a honed surface, the inventors adopted brushing as a means for forming the honed surface 41a, and then attempted to apply a brush to the honed surface 41a from the rake face 41b side. As a result, they confirmed that by differentiating the radius of curvature R1 of the rake face-side honing 41a1 and the radius of curvature R2 of the flank-side honing 41a2, it was possible to reliably form an angle θ on the rake face 41b side between the flank-side honing surface 41a2 and the flank 7. In conclusion, it was confirmed that it was possible to suppress flank wear while improving the fracture resistance of the main cutting edge 41, thereby improving the tool life during cutting.

[0015] The mechanism by which the effect of suppressing flank wear of the present invention is obtained will be specifically explained below with reference to Figures 8 and 9, which show the relationship between a cross section perpendicular to the extension direction of the major cutting edge 41 and the workpiece. Figure 8 shows the shape of the major cutting edge 41 before cutting the workpiece 9, assuming that the workpiece 9 has been cut, and Figure 9 shows the wear state of the major cutting edge 41 after cutting the workpiece 9. Here, the workpiece 9 is shown hatched.

[0016] In each figure, (a) shows an example of the present invention, and (b) shows comparative examples (1 and 2) shown in Figure 10, which are compared under the same machining conditions as the present invention. In the example of the present invention, as shown in Figure 8-(a), the tangent line L1 at the end point of the curve forming the flank side honing 41a2 on the flank 7 side and the flank 7 (71) form an angle θ toward the rake face 41b, while in the comparative example, the flank side honing 41a2 and the flank 7 (71) are smoothly connected (continuous), and the flank 7 (71) is inclined toward the rake face 41b from the surface of the workpiece 9 shown by the two-dot chain line. In both (a) and (b), the radius of curvature R1, radius of curvature R2, and clearance angle are the same.

[0017] 8-(b), "smooth connection" in the comparative example means that "the flank 7 overlaps the tangent to the circle of radius of curvature R2 indicated by the two-dot chain line drawn by the flank-side honing surface 41a2." This can also be said to mean that "in cross section, the flank 7 (71) is inclined toward the rake face 41b from the surface of the workpiece 9, and the circle drawing the curve of radius of curvature R2 is completely contained within the area on the cutting edge 3 side that is partitioned by the honing surface 41a and the flank 7, which completely includes the flank-side honing 41a2 of the main cutting edge 41."

[0018] "The flank 7 (71) is inclined toward the rake face 41b from the surface of the workpiece 9, while the circle with radius of curvature R2 is completely contained within the area defined by the honing surface 41a and the flank 7" also means "the circle with radius of curvature R2 constituting the flank-side honing surface 41a2 is not discontinuously connected to the line of the flank 7 so that the circle with radius of curvature R2 is completely contained within the area." This includes cases where the flank 7 (71) is inclined toward the rake face 41b from the surface of the workpiece 9, while the line (straight line) of the flank 7 (71) is tangent to the circle with radius of curvature R2, and cases where the curvature changes continuously. When these requirements are met, the flank 7 (71) is located closer to the rake face 41b than the tangent line at the end point of the circle on the flank 7 side, as shown in Figure 8-(b).

[0019] In the example shown in FIG. 8-(b), if it is assumed that "the cutting surface (lower horizontal plane (two-dot chain line)) assumed after cutting, which is parallel to the surface of the workpiece 9 before cutting begins (upper horizontal plane (two-dot chain line)), overlaps with the tangent at the end point on the flank 7 side of a circle (the curve forming the flank-side honing surface 41a2) with a curvature radius R2," then the lowest point of the circle (a point dropped vertically from the center of the circle) in the figure is the end point (starting point of the tangent) on the flank 7 side of the circle. However, assuming that the flank 7 (71) is inclined toward the rake face 41b from the surface of the workpiece 9, if it is assumed that "the flank 7 overlaps with the tangent at the end point on the flank 7 side of the circle (the curve forming the flank-side honing surface 41a2)," then the starting point (tangency point) of the tangent is shifted to the right of the lowest point of the circle in the figure, and the tangent is a straight line sloping upward to the right from the starting point (tangency point).

[0020] Strictly speaking, in comparison with Figure 8-(b), the above-mentioned "end point (end point) on the flank 7 side of the flank-side honing surface 41a2 in the present invention" refers to "a position that is not (completely) contained in the area on the cutting edge 3 side that is partitioned by the honing surface 41a of the main cutting edge 41 and the flank 7" as shown in Figure 8-(a) (Claim 3). The starting point (tangency point) of the tangent line L1 in Figure 8-(a) is shifted to the left of the lowest point of the circle, and the tangent line L1 is a straight line sloping downward to the right from the starting point (tangency point).

[0021] In the present invention, the "tangent line L1 at the end point on the flank 7 side" refers to a tangent line at a position that does not completely encompass the "circle with radius of curvature R2." This means that, in a cross section perpendicular to the extension direction of the major cutting edge 41, the circle with radius of curvature R2 that constitutes the flank-side honing surface 41a2 and the line (straight line) of the flank 7 are discontinuously connected (claim 2). "Discontinuously connected" means that the line (straight line) of the flank 7 is not a tangent line to the circle with radius of curvature R2 that constitutes the flank-side honing surface 41a2, or that the line of the flank 7 and the circle with radius of curvature R2 are curves whose curvature does not change continuously, etc.

[0022] Using the above expression, this can also be rephrased as "the end point on the flank 7 side of the curve forming the flank side honing surface 41a2 is a position that is not included in a circle that draws a curve with a radius of curvature R2 within the area on the cutting edge 3 side that is partitioned by the honing surface 41a of the main cutting edge 41 and the flank 7" (Claim 3).

[0023] In the comparative example shown in FIG. 8-(b), the flank 7 (71) is inclined toward the rake face 41b from the surface of the workpiece 9, while the flank side honing 41a2 and the flank 7 are smoothly connected (continuous) (the circle describing the curve with radius of curvature R2 is completely contained within the area on the cutting edge 3 side), and therefore the distance L22 from the tip of the cutting edge to the boundary P2 between the flank side honing 41a2 and the flank 7 corresponds to the distance to the end (end point) of the circle with radius of curvature R2.

[0024] In contrast, in the example of the present invention shown in Figure 8-(a), the flank side honing 41a2 and the flank 7 form an angle θ, the circle describing the curve with radius of curvature R2 is not completely contained within the area on the cutting portion 3 side, and the circle and the line of the flank 7 are discontinuous (claims 2 and 3), and it can be seen that the distance L21 from the tip of the cutting edge to the boundary P1 between the flank side honing 41a2 and the flank 7 when viewed in the rotation direction of the drill (tool body) is shorter than the distance L22 in the case where there is no angle θ ((b)).

[0025] Comparing Figures 8-(a) and (b), it can be said that in the example of the present invention, boundary P1 is located closer to the tip of the cutting edge than boundary P2 in the comparative example, and therefore when cutting workpiece 9 under the same machining conditions, the example of the present invention has a shape that makes it easier to suppress flank wear width than the comparative example.

[0026] Thus, in the comparative example, the boundary P2 between the flank side honing 41a2 and the flank 7 is located farther from the tip of the cutting edge than the boundary P1 in the invention example (distance L21 < distance L22), and therefore penetrates deeper into the workpiece 9 in the depth direction. As a result, the flank wear width increases as shown in Figure 9-(b) because it is located deeper in the depth direction. This is also because the circumferential length on the cross section of the flank side honing 41a2 in the comparative example is greater than that of the invention example.

[0027] In contrast to this, in the example of the present invention, the boundary P1 between the flank side honing 41a2 and the flank 7 is located near the cutting edge, and as a result, as shown in Figure 9-(a), it is located closer to the surface of the workpiece 9 in the depth direction than in the comparative example (Figure 9-(b)), and as a result, it can be seen that the flank wear width is suppressed.

[0028] The difference in the wear suppression effect of the invention example compared to the comparative example described above becomes more pronounced as the radius of curvature R2 (circle) of the flank-side honing 41a2 increases, assuming that the rake-side honing 41a1 is continuous with the flank-side honing 41a2. This is because the larger the radius of curvature R2, the greater the difference in distance L2 from the boundary P between the flank-side honing 41a2 and the flank 7 shown in Figure 1 to the cutting edge tip.

[0029] In other words, in the comparative example, when the radius of curvature R2 is increased to improve fracture resistance, the range of the flank 7 that comes into contact with the workpiece 9 is expanded, and as a result, flank wear is likely to progress. In contrast, in the example of the present invention, even if the radius of curvature R2 is increased to improve fracture resistance, the range of the flank 7 that comes into contact with the workpiece 9 is suppressed from expanding, and therefore flank wear is suppressed. As a result, according to the example of the present invention, it is possible to obtain the effect of suppressing flank wear while improving fracture resistance by providing R honing.

[0030] In claim 1, the angle θ between the tangent L1 of the curve forming the flank side honing surface 41a2 and the flank 7 satisfies the relationship 10°≦θ≦60° in order to simultaneously ensure the fracture resistance of the main cutting edge 41 and suppress flank wear resistance (claim 5). By setting θ≦60°, the width of the flank side honing 41a2 can be sufficiently secured, resulting in sufficient fracture resistance. On the other hand, if θ is 10°≦θ, the flank 7 is less likely to come into contact with the workpiece, thereby suppressing flank wear. A more preferable angle θ is 15°≦θ≦50°.

[0031] Furthermore, if the tangent line at the end point of the curve forming the rake face-side honing surface 41a1 on the rake face 41b side is made continuous with the rake face 41b in a cross section perpendicular to the extension direction of the main cutting edge 41 (claim 4), the transition section from the rake face 41b to the rake face-side honing surface 41a1 will have a smooth shape with no corners. As a result, there is no risk of chips generated by cutting colliding with the corners, improving the safety of the main cutting edge 41 (cutting edge 4).

[0032] In this case, "the tangent to the curve forming the rake face side honing surface 41a1 at the end point on the rake face 41b side is continuous with the rake face 41b" means that in a cross section perpendicular to the extension direction of the main cutting edge 41, the rake face 41b and the tangent to the curve forming the rake face side honing surface 41a1 at the end point on the rake face 41b side are located on the same line.

[0033] In claim 4, particularly if the radius of curvature of the curve from the rake face side honing surface 41a1 to the flank side honing surface 41a2 is continuously changed, there are no discontinuous parts or corners in the curved surface (curve) from the rake face side honing surface 41a1 to the flank side honing surface 41a2, so even if chips produced by cutting work collide with it, partial damage is less likely to occur and the safety of the main cutting edge 41 (cutting edge 4) is improved.

[0034] It is appropriate that the radii of curvature R1 and R2 satisfy the relationship 1.0<R1 / R2≦5.0 (claim 7). If R1 / R2≦5.0 (R1 is 5 times or less than R2), the change in curvature of the curve transitioning from the rake face-side honing surface 41a1 to the flank face-side honing surface 41a2 is prevented from becoming too large, ensuring sufficient rigidity of the cutting edge of the main cutting edge 41. On the other hand, if 1.0<R1 / R2 (R1<R2), it is possible to improve both chipping resistance and sharpness.

[0035] In a cross section perpendicular to the direction of extension of the main cutting edge, the honing surface of the main cutting edge has a rake face-side honing surface that describes a curve with radius of curvature R1, and a flank face-side honing surface that describes a curve with radius of curvature R2, and a tangent line L1 at the end point on the flank side of the flank face honing surface and the flank form an angle θ toward the rake face, so even if the radius of curvature R2 is large, the boundary P between the flank face-side honing 41a2 and the flank face 7 can be brought closer to the tip of the cutting edge. As a result, it is possible to suppress flank wear while improving the fracture resistance of the main cutting edge 41.

[0036] 4A and 4B are cross-sectional views taken along line a-a in FIG. 4, showing an example of the relationship between the honing surface, rake face, and flank face formed on the main cutting edge of a drill. This is a perspective view of the upper main cutting edge in FIG. 3, as seen from the front side in the rotational direction. This is an end view of the cutting edge of the drill as seen from the tip face side in the axial direction. This is a view as seen in the x direction of FIG. 3. This is a view as seen in the y direction of FIG. 3. This is an enlarged view of a portion including the main cutting edge and thinning cutting edge in FIG. 4. This is an elevation view of the entire drill. This is a schematic cross-sectional view showing the relationship between the main cutting edge and the workpiece in a direction perpendicular to the extending direction of the main cutting edge before cutting, where (a) is an example of the present invention and (b) is a comparative example. This is a schematic cross-sectional view showing the wear state of the main cutting edge of the example of the present invention shown in FIG. 8A after actually cutting the workpiece, and (b) is a schematic cross-sectional view showing the wear state of the main cutting edge of the comparative example shown in FIG. 8B after actually cutting the workpiece under the same machining conditions as (a). 1 is a graph showing the results of wear when a workpiece is cut (a hole (blind hole) is formed) for a certain period of time using a drill of the present invention under the conditions shown in Table 1, together with a comparative example.

[0037] 1 and 2 show an example of a drill 1 manufactured as shown in Figures 3 to 7, which has a cutting portion 3 with multiple cutting edges 4 and chip discharge grooves 5 between circumferentially adjacent cutting edges 4, 4, at the axial tip end of the shank portion 2, and the cutting edges 4 have a main cutting edge 41 on the radially outer periphery and a thinning cutting edge 42 that is continuous with the main cutting edge 41 and is located radially toward the center of the main cutting edge 41, and the main cutting edge 41 and the thinning cutting edge 42 are each formed with convexly curved honing surfaces 41a and 42a. The axis of the shank portion 2 corresponds to the rotation axis O of the drill body (drill 1).

[0038] 7, the drill 1 is divided axially into a shank portion 2 located axially rearward of the drill body and a cutting portion 3 formed axially further toward the tip end thereof, and a pair (two) cutting edges 4, 4 are mainly formed on a tip end surface 30 at the axial tip of the cutting portion 3. The drawing shows an example of a solid-type drill 1 in which the cutting portion 3 is integrated with the drill body, but there is also the case of an indexable drill 1 in which the cutting portion 3 is detachably fixed and held in the drill body.

[0039] As shown in Figure 4, a thinning portion 6 facing the chip discharge groove 5 is formed on the rear side in the rotational direction of the flank 7 of each cutting edge 4. The thinning portion 6 is composed of a rake face 42b (described later) of the thinning cutting edge 42 and, on the front side in the rotational direction, a thinning surface 61 that is a curved surface that continues to the second chamfering surface 8 shown in Figure 4, or a continuous curved surface. As shown in Figure 6, which is an enlarged view of Figure 4, and Figure 2, which is a detailed view thereof, honing surfaces 41a and 42a are formed on the main cutting edge 41 and the thinning cutting edge 42, respectively.

[0040] The "tip surface 30" refers to the area (portion) excluding the chip flute 5 and thinning surface 61 when the tip surface 30 of the drill body is viewed in the direction of the rotation axis O, and refers to the area of ​​the flank 7. Figures 1 to 3 show an example in which the second surface 71 as the flank 7 is formed on the rear side of the cutting edge 4 in the rotational direction, and the third surface 72 is formed continuously on the rear side of the second surface 71 in the rotational direction, but there is also a case in which the third surface 72 is not formed. In the example of Figures 1 to 3, the flank 7 is the area combining the second surface 71 and the third surface 72. Figure 2 shows the tip surface 30 when the main cutting edge 41 and the thinning cutting edge 42 are viewed from the radially outer side toward the center in the rotational direction.

[0041] As shown in Figure 3, the cutting edge 4 is formed from the end of the chisel edge 43 toward the radially outer periphery of the tip face 30, and in the radial direction, it consists of a main cutting edge 41 on the radially outer periphery side, and a thinning cutting edge 42 that is continuous with the main cutting edge 41, is located on the radially central side of the main cutting edge 41, and is connected to the end of the chisel edge 43.

[0042] 1, the rake face-side honing surface 41a1 is located closer to the rake face 41b formed on the front side in the direction of rotation of the main cutting edge 41, and the flank face-side honing surface 41a2 is located closer to the flank 7 (second surface 71) formed on the rear side in the direction of rotation of the main cutting edge 41. To ensure sufficient rigidity and sharpness of the cutting edge of the main cutting edge 41, it is appropriate for the radii of curvature R1 and R2 to satisfy the relationship 1.0<R1 / R2≦5.0 (claim 7).

[0043] The example in Figure 1 is characterized in that a tangent line L1 at the end point of the curve forming the flank-side honing surface 41a2 on the flank 7 (second surface 71) side and the flank 7 (second surface 71) form an angle θ toward the rake face 41b (claim 1). The fact that the flank 7 forms an angle θ toward the rake face 41b means that the boundary P between the flank-side honing surface 41a2 and the flank 7 in Figure 1 can be brought closer to the cutting edge.

[0044] In the example of Figure 1, the angle θ between the tangent L1 at the end point on the flank 7 (second surface 71) side of the curve forming the flank-side honing surface 41a2 and the flank 7 (second surface 71) satisfies the relationship 10°≦θ≦60° in order to enhance the chipping resistance of the main cutting edge 41 while suppressing flank wear (Claim 5).

[0045] 1, in a cross section perpendicular to the direction of extension of the main cutting edge 41, the tangent line at the end point on the rake face 41b side of the curve that forms the rake face-side honing surface 41a1 is continuous with the rake face 41b (claim 4). As a requirement of the present invention, the tangent line at the end point on the rake face 41b side does not necessarily have to be continuous with the rake face 41b, but if it is continuous, there are no discontinuous parts or corners in the curve (curved surface) that transitions from the rake face 41b to the rake face-side honing surface 41a1, so there is a high level of safety against partial breakage even if chips generated by cutting collide with it.

[0046] 1, the radius of curvature of the curve extending from the rake face-side honing surface 41a1 to the flank-side honing surface 41a2 changes continuously (claim 6). As a result, the change in the curve (curved surface) in the transition portion from the rake face-side honing surface 41a1 to the flank-side honing surface 41a2 is continuous, providing a high level of safety against breakage due to discontinuity in rigidity.

[0047] 1 also satisfies the relationship 1.0<R1 / R2≦5.0 (claim 7). If R1 and R2 are within this range, the change in curvature of the curve transitioning from the rake face-side honing surface 41a1 to the flank face-side honing surface 41a2 will not be too large, ensuring sufficient rigidity of the cutting edge of the main cutting edge 41. At the same time, chipping resistance and sharpness can be improved.

[0048] 10 shows the results of a cutting test evaluating the condition of a workpiece 9 after cutting using drills 1 (invention example and comparative examples 1 and 2) with different honing shapes. Specifically, the graph shows the maximum wear width of the flank 7 (vertical axis) versus the number of holes (horizontal axis) when each drill 1 was used to cut (form blind holes) a certain number of times in a workpiece (DAC HRC45) under the conditions shown in Table 1 below. The hole depth H was 10 mm, and the L / D (total length / diameter) ratio shown in FIG. 7 was 5.

[0049] In the example of the present invention used in this experiment, the flank side honing 41a2 and the flank 7 form an angle θ toward the rake face 41b, as shown in Figure 8-(a). In Comparative Example 1, the flank side honing 41a2 and the flank 7 do not form an angle θ toward the rake face 41b, as shown in Figure 8-(b). In Comparative Example 2, the honing surface 41a has a constant radius of curvature overall. In both cases, the clearance angle is 10°, and the shapes other than the honing surface 41a are identical.

[0050] As shown in Figures 9-(a) and 9-(b), in all examples, no breakage occurred on the cutting edge that would make it difficult to continue cutting up to the number of drilled holes reached 120, but differences in flank wear (width) were confirmed. Figure 10 shows that in all examples, the wear width increased at a nearly constant rate up to the number of drilled holes reached 60 and from 60 to 120, and the rate of increase in wear width slowed down once the number of drilled holes exceeded 60. However, compared to Comparative Examples 1 and 2, the rate of increase in wear width for Drill 1 of the present invention was the lowest, making it difficult for wear to progress.

[0051] Furthermore, when the number of drilled holes reached 120, the maximum wear width was reduced to approximately 42% (0.022 / 0.053) compared to Comparative Example 1 shown in Figure 11-(b), and to approximately 69% (0.022 / 0.032) compared to Comparative Example 2 shown in Figure 11-(c). From the above, it was confirmed that the present invention makes it possible to suppress flank wear while improving fracture resistance.

[0052] ​1...Drill (drill body), O...Rotation axis, 2...Shank portion, 3...Cutting portion, 30...Tip surface, 4...Cutting edge, 41...Main cutting edge, 41a...Honing surface, 41a1...Rake side honing surface, 41a2...Flank side honing surface, 41b...Rake face, 42...Thinning cutting edge, 42a...Honing surface, 42b...Rake face, 43...Chisel edge, 5...Chip discharge groove, 6...Thinning portion, 61...Thinning surface, 7...Flank face, 71...Second surface, 72...Third surface, 8...Second chamfering surface, 9...Workpiece material, R1...Radius of curvature of rake side honing surface, R2...Radius of curvature of flank side honing surface, L1...Tangent at the end point on the flank side of the curve forming the flank side honing surface, θ...angle formed by tangent L1 and the flank (second surface) toward the rake face, P...boundary between the flank side honing and the flank when the flank side honing and the flank form an angle θ, L2...distance from the tip of the cutting edge to the boundary P between the flank side honing and the flank when the flank side honing and the flank form an angle θ, P1...boundary between the flank side honing and the flank in an example of the present invention when the flank side honing and the flank form an angle θ, L21...distance from the tip of the cutting edge to boundary P1 between the flank side honing and the flank when the flank side honing and the flank form an angle θ in an example of the present invention, P2...boundary between the flank side honing and the flank when the flank side honing and the flank are smoothly connected in a comparative example, L22...distance from the tip of the cutting edge to boundary P2 between the flank side honing and the flank when the flank side honing and the flank are smoothly connected in a comparative example.

Claims

1. A drill having a cutting section on the axial tip side of a shank portion having a plurality of cutting edges and chip discharge grooves between adjacent cutting edges in the circumferential direction, wherein the cutting edges include a main cutting edge on the radially outer periphery and a thinning cutting edge that is continuous with the main cutting edge and is located on the radially central side of the main cutting edge, and wherein a honing surface with a convex curved surface is formed on each of the main cutting edge and the thinning cutting edge, and wherein, in a cross section perpendicular to the direction of extension of the main cutting edge, the honing surface of the main cutting edge has a rake face-side honing surface that is formed on the front side in the direction of rotation of the main cutting edge and that describes a curve with a radius of curvature R1 near the rake face, and a flank-side honing surface that is formed on the rear side in the direction of rotation of the main cutting edge and that describes a curve with a radius of curvature R2 near the flank, and wherein a tangent line L1 at the end point on the flank side of the curve that forms the flank-side honing surface forms an angle θ with the flank side.

2. A drill having a cutting section on the axial tip side of the shank portion, the cutting edges of which have multiple cutting edges and chip discharge grooves between adjacent cutting edges in the circumferential direction, the cutting edges having a main cutting edge on the radially outer periphery and a thinning cutting edge that is continuous with the main cutting edge and is located on the radially central side of the main cutting edge, the main cutting edge and the thinning cutting edge each having a convexly curved honing surface, and in a cross section perpendicular to the direction of extension of the main cutting edge, the honing surface of the main cutting edge has a rake face-side honing surface that is formed on the front side in the direction of rotation of the main cutting edge and describes a curve with a radius of curvature R1 near the rake face, and a flank face-side honing surface that is formed on the rear side in the direction of rotation of the main cutting edge and describes a curve with a radius of curvature R2 near the flank, and in a cross section perpendicular to the direction of extension of the main cutting edge, the circle with radius of curvature R2 that constitutes the flank face-side honing surface is discontinuously connected to the line of the flank.

3. A drill having a cutting portion on the axial tip side of the shank portion, the cutting edges of which have a plurality of cutting edges and chip discharge grooves between adjacent cutting edges in the circumferential direction, the cutting edges having a main cutting edge on the radially outer periphery and a thinning cutting edge continuous with the main cutting edge and located on the radially central side of the main cutting edge, the main cutting edge and the thinning cutting edge each having a convexly curved honing surface formed thereon, in a cross section perpendicular to the extending direction of the main cutting edge, the honing surface of the main cutting edge has a rake face side honing surface formed on the front side of the main cutting edge in the rotation direction, which is close to the rake face, and which describes a curve with a radius of curvature R1, and a flank side honing surface formed on the rear side of the main cutting edge in the rotation direction, which is close to the flank, and which describes a curve with a radius of curvature R2, a flank-side end point of the curve that forms the flank-side honing surface, the flank-side end point being at a position that does not include a circle that describes the curve with the radius of curvature R2 within an area on the cutting edge side that is partitioned by the honing surface and the flank of the main cutting edge.

4. A drill as described in any one of claims 1 to 3, characterized in that in a cross section perpendicular to the extension direction of the main cutting edge, a tangent to the curve forming the rake face side honing surface at the end point on the rake face side is continuous with the rake face.

5. The drill according to claim 1, characterized in that the angle θ formed between the tangent L1 at the end point on the flank side of the curve forming the flank side honing surface and the flank is 10°≦θ≦60°.

6. A drill according to any one of claims 1 to 3, characterized in that the radius of curvature of the curve extending from the rake side honing surface to the flank side honing surface changes continuously.

7. A drill according to any one of claims 1 to 3, characterized in that the radius of curvature R1 and the radius of curvature R2 satisfy the relationship 1.0<R1 / R2≦5.0.

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