Cutting tool

Abstract

The present invention provides a cutting tool capable of improving the performance in both the biting property and the chip evacuation property with respect to a workpiece to be cut. The cutting tool includes: a drill body that rotates about a central axis; four or more cutting edges formed at one end of the drill body and facing the front side in the rotation direction; and flute grooves formed between the cutting edges in the circumferential direction and extending in a slightly helical shape along the central axis. Further, (1) the one end has a first tip and a second tip, the first tip includes the central axis and forms a first tip angle, the second tip extends from the first tip to the outer peripheral edge of the drill body and forms a second tip angle greater than the first tip angle, and (2) the drill body has a first core thickness portion and a second core thickness portion, the first core thickness portion is formed such that its core thickness gradually decreases from the one end toward the other end, and the second core thickness portion is formed such that its core thickness is constant from the first core thickness portion toward the other end.

Description

Technical Field

[0001] The present invention relates to a cutting (drilling) tool having more than 4 drill bit cutting edges, which is excellent in both biting property and chip evacuation property with respect to a workpiece to be cut. Background Art

[0002] Conventionally, as a means for improving the machining efficiency of a drill bit with respect to a workpiece to be cut, a four-edge drill bit has been proposed. The number of edges of the four-edge drill bit is twice that of a conventional two-edge drill bit (see Patent Document 1). Such a conventional four-edge drill bit is designed to improve the biting property with respect to the workpiece to be cut and to suppress the generation of burrs on the back side of the workpiece to be cut, and has the following structure. That is, in such a four-edge drill bit, four edges are constituted by two main cutting edges and two sub-cutting edges. Among them, the two main cutting edges are continuous from the outer peripheral side end portion in the radial direction to the vicinity of the center on the front end face of the drill bit, and the two sub-cutting edges are located between the main cutting edges in the circumferential direction and are continuous from the outer peripheral side end portion in the radial direction to the middle of the center side. Further, when observing the front end face along the length direction of the sub-cutting edge, the ridge line of the main cutting edge or the like is formed in a convex shape from the outer peripheral side in the radial direction through the center side toward the front end face side, and when observing the front end face along the length direction of the main cutting edge, the ridge line of the sub-cutting edge or the like is formed in a concave shape from the outer peripheral side in the radial direction through the center side toward the front end face side.

[0003] Prior Art Documents

[0004] Patent Document

[0005] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2019-048347

[0006] Technical Problem

[0007] However, although such a conventional four-edge drill bit can drill a workpiece to be cut with a relatively high machining efficiency, in order to ensure the strength of the front end of the drill bit, and because the number of edges is large and the grinding is easily disturbed, etc., the chisel becomes larger (the web becomes thicker) compared with a two-edge drill bit. As a result, the biting property with respect to the workpiece to be cut is insufficient. In addition, in a conventional four-edge drill bit, the width of one flute is inevitably narrower than that of a conventional two-edge drill bit, so the volume of the flute becomes smaller. As a result, there is a problem of poor chip evacuation property.

[0008] Therefore, the present disclosure has been made in view of such circumstances, and an object thereof is to provide a cutting tool capable of improving both the biting property and the chip evacuation property with respect to a workpiece to be cut. Summary of the Invention

[0009] In order to solve the above problems, the present invention adopts the following structure.

[0010] [1]An example of the cutting tool related to the present disclosure includes: a drill bit body that rotates around a central axis; four or more (main) cutting edges formed at one end of the drill bit body and facing the front side in the rotation direction; and a flute formed between the cutting edges in the circumferential direction and extending in a slightly helical shape along the central axis. Additionally, (1) the one end has a first front end and a second front end, the first front end includes the central axis and forms (has) a first front angle, the second front end extends from the first front end to the outer peripheral edge of the drill bit body, and forms (has) a second front angle greater than the first front angle, (2) the drill bit body has a first core thickness portion and a second core thickness portion, the first core thickness portion is formed such that its core thickness gradually decreases from the one end toward the other end, and the second core thickness portion is formed such that its core thickness is constant from the first core thickness portion toward the other end.

[0011] In this structure, one end of the drill bit body where the cutting edges are formed abuts against the workpiece to be cut and rotates, thereby performing hole cutting of the workpiece to be cut. At this time, the chips generated by the cutting edges flow to the rake face side (flute) formed between the circumferentially adjacent cutting edges and are discharged from the machining hole. In this hole cutting process, since the first front end (including the chisel edge) with a smaller (sharper) first front angle in the one end first contacts the workpiece to be cut, compared with a double-edge drill bit, even if the chisel edge tends to become larger, the biting property into the workpiece to be cut can be sufficiently improved. Additionally, in the one end, the second front angle of the second front end extending from the first front end to the outer peripheral edge of the drill bit body is larger than the first front angle of the first front end, so the distance in the central axis direction from the first front end biting into the workpiece to be cut to the center axis of the outermost cutting edge becomes shorter. As a result, the time when the rotation of the drill bit body becomes unstable when the first front end bites into the workpiece to be cut and the second front end performs cutting is shortened, and the shoulder of the second front end is easily and quickly received in the machining hole, so the guiding function of the drill bit body can be improved.

[0012] Furthermore, since the core thickness of the first core thickness portion of the portion from the one end toward the other end gradually decreases, and the core thickness of the second core thickness portion of the portion further toward the other end from here is thinner and constant, by appropriately setting the degree of reduction of the core thickness, the core thickness can be reduced starting from the portion near the one end to increase the volume of the flute. As a result, the chip evacuation property can be further improved.

[0013] [2]In the above structure, more specifically, the first front end may be a portion from the central axis to about 20% of the radius of the drill bit body, the first front angle is about 120°, and the second front angle is about 140°. According to the insight of the present inventor, by adopting this structure, the defect or breakage of the first front end can be effectively prevented, and it is easier to achieve excellent biting property into the workpiece to be cut and excellent guiding function of the drill bit body.

[0014] [3]In the above structure, more specifically, the first core thickness portion may have a core thickness cone. The first core thickness portion has a core thickness of about 35% of the diameter of the drill bit body at the outer peripheral position of the edge at the one end portion, and from the outer peripheral position of the edge at the one end portion toward the other end portion to a position at a distance of about twice the diameter of the drill bit body, the core thickness is reduced at a ratio of about -2% (about -2 mm / 100 mm). According to the inventor's opinion, by adopting this structure, while maintaining the rigidity of the drill bit body, the core thickness can be reduced starting from a portion closer to the one end portion, so that the volume of the flute can be increased earlier, and thus excellent chip discharge performance of the chips can be more easily achieved.

[0015] [4]In addition, in the above structure, it may further include a grinding portion formed at the front end of the flute and having a first grinding portion and a second grinding portion. The first grinding portion is disposed on the flank side of the cutting edge, and the second grinding portion is disposed from the first grinding portion toward the flute. In this structure, the original chisel edge is removed by the grinding portion to form a ground cutting edge. In addition, since the grinding portion has a two-stage structure, compared with a grinding portion having a one-stage structure, the volume of the grinding pocket for discharging chips generated in the hole cutting of the workpiece can be further increased. In addition, compared with the case where the grinding portion is one-stage, the obtuse angle at the intersection of the ground cutting edge and the (main) cutting edge can be larger, so that chipping at the intersection and the surrounding portions can be suppressed.

[0016] [5]In addition, in the above structure, it may be configured that the plunge angle and the flare angle of the first grinding portion are respectively larger than the plunge angle and the flare angle of the second grinding portion. In this structure, since the first grinding portion further increases the volume of the grinding pocket, the chip discharge performance can be further improved. In addition, the second grinding portion can reduce the curling (winding condition) of the generated chips. As a result, the shape of the chips is reduced, and the chips can move more closely and quickly in the flute, and as a result, the chip discharge performance can be further improved.

[0017] [6]In addition, in the above structure, more specifically, it may be configured that the plunge angle and the flare angle of the first grinding portion are respectively about 40° and about 60°, and the plunge angle and the flare angle of the second grinding portion are respectively about 30° and about 55°. According to the inventor's opinion, by adopting this structure, the effect of expanding the volume of the grinding pocket and the effect of reducing the chip shape can be effectively improved, so as to achieve optimization.

[0018] In addition, in the present disclosure, "about" attached to a numerical value means a range of ±5% of the numerical value. For example, if the numerical value is "10%", then "about 10%" means 9.5% to 10.5%; if the numerical value is "100°", then "about 100°" means 95° to 105°; if the numerical value is "10 times", then "about 10 times" means 9.5 times to 10.5 times.

[0019] According to the present disclosure, one end portion of the drill bit body includes a first front end portion and a second front end portion. In addition, the drill bit body further includes a first core thickness portion and a second core thickness portion. Therefore, even if there are more than 4 cutting edges, the biting property and the chip evacuation property of the workpiece to be cut can be improved simultaneously. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 is a perspective view schematically showing a schematic structure of an example of a cutting tool according to an embodiment of the present disclosure.

[0021] Figure 2 is a top view schematically showing an end portion of an example of a cutting tool according to an embodiment of the present disclosure.

[0022] Figure 3 is a schematic front view schematically showing an end portion of an example of a cutting tool according to an embodiment of the present disclosure and its vicinity, and for explaining a front end angle of the end portion.

[0023] Figure 4 is a schematic front view for explaining a state of a core thickness of a drill bit body in an example of a cutting tool according to an embodiment of the present disclosure.

[0024] Figure 5A is schematically showing along Figure 1 an end portion of the cutting tool and its vicinity in line V-V in, and a schematic cross-sectional view for explaining a cutting angle of a first dressing portion.

[0025] Figure 5B is schematically showing along Figure 1 an end portion of the cutting tool and its vicinity in line V-V in, and a schematic cross-sectional view for explaining a cutting angle of a second dressing portion.

[0026] Figure 6 is a perspective view schematically showing an end portion of an example of a cutting tool according to an embodiment of the present disclosure, and for explaining a spread angle of a first dressing portion.

[0027] Figure 7 is a perspective view schematically showing an end portion of an example of a cutting tool according to an embodiment of the present disclosure, and for explaining a spread angle of a second dressing portion.

[0028] Figure 8 is a schematic top view that magnifies and shows a peripheral portion of an intersection of a main cutting edge and a grinding cutting edge in an example of a cutting tool according to an embodiment of the present disclosure, and is used to illustrate a state of the intersection point.

[0029] Figure 9 is a schematic top view that magnifies and shows a peripheral portion of an intersection of a main cutting edge and a grinding cutting edge in another example of a cutting tool according to an embodiment of the present disclosure, and is used to illustrate a state of the intersection point.

[0030] Description of Main Element Symbols

[0031] Drill Bit Body 1

[0032] Flute 2

[0033] Main Cutting Edge (Cutting Edge) 3

[0034] Front Relief Face 4

[0035] Grinding Cutting Edge (Cutting Edge) 5

[0036] Grinding Portion 6

[0037] Chisel Edge 7

[0038] Land 8

[0039] One End Portion 10

[0040] Edge Outer Peripheral Position 10g

[0041] First Front End Portion 11

[0042] Second Front End Portion 12

[0043] First Core Thickness Portion 13

[0044] Second Core Thickness Portion 14

[0045] The Other End Portion 20

[0046] First Grinding Portion 61

[0047] Second Grinding Portion 62

[0048] Four-Flute Drill Bit (Cutting Tool) 100

[0049] Intersection Point CP

[0050] Edge Lines C1, C2

[0051] Core Thicknesses d1, d2

[0052] Central Axis P

[0053] Radius R

[0054] Core thickness cone ST

[0055] Front end angle (first front end angle) θ11

[0056] Front end angle (second front end angle) θ12

[0057] Cutting-in angle θ21 of the first grinding part

[0058] Cutting-in angle θ22 of the second grinding part

[0059] Spreading angle θ31 of the first grinding part

[0060] Spreading angle θ32 of the second grinding part

[0061] Inner angles θ41, θ42 of the intersection point

[0062] Diameter φ Specific implementation mode

[0063] The implementation mode related to an example of the present disclosure will be described below with reference to the drawings. However, the embodiments described below are merely examples, and an example of the present disclosure can be implemented with various modifications without departing from its gist. In addition, in the description of the drawings, the same or similar parts are labeled with the same or similar symbols. The drawings are schematic and may not be consistent with the actual size or ratio, etc. In addition, there may be parts with different sizes or ratios between the drawings. In addition, the implementation modes described below are only some implementation modes of the present disclosure. Other implementation modes obtained by those of ordinary skill in the art based on the implementation modes of the present disclosure without creative efforts belong to the protection scope of the present disclosure.

[0064] (Structure of the implementation mode)

[0065] Figure 1 is a perspective view schematically showing a schematic structure of an example (four-flute drill bit) of a cutting tool according to an embodiment of the present disclosure. In addition, Figure 2 is a top view of an end portion of an example (four-flute drill bit) of a cutting tool according to an embodiment of the present disclosure, showing the shape of the four-flute drill bit in a front view in the axial direction (with the x-axis and y-axis as the reference).

[0066] The four-edge drill bit 100 (cutting tool) is a twist super-hard solid drill bit having four curved main cutting edges 3. The four main cutting edges 3 face the front side in the rotation direction and are formed, for example, at approximately 90° intervals in the circumferential direction at one end 10 of the drill bit body 1. In the drill bit body 1, four flute grooves 2 extending substantially helically along the center axis P with twist are formed between the main cutting edges 3 adjacent in the circumferential direction. The ridge line where the wall surface of the flute groove 2 in the rotation direction intersects the front end surface of one end 10 of the drill bit body 1 constitutes the main cutting edge 3. In the front end view in the axial direction, the main cutting edge 3 forms a gentle concave curve shape in the rotation direction of the four-edge drill bit 100. In addition, on the outer peripheral surface of the drill bit body 1, margin portions 8 are respectively formed at positions corresponding to the respective main cutting edges 3.

[0067] In addition, the front end surface of one end 10 is formed, for example, by a twisted surface or a curved surface and constitutes the front flank 4 of the main cutting edge 3. The clearance angle of this front flank 4 is set to a predetermined angle, or can be appropriately set to increase as it is farther from the main cutting edge 3 according to the type of the workpiece to be cut or the cutting conditions when necessary, so as to prevent the adhesion of the workpiece to be cut, etc., or to extend the tool life by suppressing wear.

[0068] In addition, in order to remove a part of the original chisel edge formed at the center of one end 10 of the drill bit body 1, a grinding portion 6 is provided, and the drill bit body 1 remains a chisel edge 7 after removal machining at the center of the front end surface of one end 10. The four grinding cutting edges 5 formed by this grinding portion 6 are substantially linear in the front end view in the axial direction. The grinding cutting edges 5 are connected to the main cutting edges 3, and their intersection points (the intersection point CP described later) have a predetermined obtuse angle. At one end 10 of the drill bit body 1, these four grinding cutting edges 5 are also formed to face the front side in the rotation direction. Thus, the main cutting edges 3 and the grinding cutting edges 5 constitute the "cutting edges" in the present disclosure.

[0069] In addition, the grinding portion 6 is formed at the front end of the flute groove 2 and is a two-stage grinding portion having a first grinding portion 61 and a second grinding portion 62. The first grinding portion 61 is disposed on the side of the front flank 4 of the main cutting edge 3, and the second grinding portion 62 is disposed from the first grinding portion 61 toward the flute groove 2.

[0070] Among them, Figure 3 schematically shows an example of one end and its vicinity of a cutting tool (four-edge drill bit) according to an embodiment of the present disclosure, and is a schematic front view (with the z-axis as the reference) for explaining the front angle of this one end.

[0071] One end portion (10) of the drill bit body (1) has: a first front end portion (11), which has a region including the central axis (P) and is pointed; and a second front end portion (12), which extends from the periphery of the first front end portion (11) to the outer periphery of the drill bit body (1). Additionally, as Figure 3 shown, the first front end portion 11 and the second front end portion 12 are respectively formed to have a front end angle θ11 (first front end angle) and a front end angle θ12 (second front end angle), and the front end angle θ11 and the front end angle θ12 have the relationship shown by the following formula (1). Additionally, in Figure 3 , the dashed lines defining the front end angles θ11, θ12 are virtual lines parallel to the surface defined by the substantially linear rotation locus when the four-flute drill bit rotates continuously around the central axis P.

[0072] θ11 < θ12…(1)

[0073] More specifically, the first front end portion 11 is a portion at about 20% of the radius R of the drill bit body 1 from the central axis P (tool center). In other words, the diameter of the virtual bottom surface of the first front end portion 11 is preferably 2R × about 20% (see Figure 3 ). For example, if the diameter (radius R = 5 mm) of the four-flute drill bit 100, then the first front end portion 11 is a portion with a virtual bottom surface diameter of 10 mm × about 20% = about 2 mm. Additionally, it is preferred that the front end angle θ11 of the first front end portion 11 = about 120°, and the front end angle θ12 of the second front end portion 12 = about 140°.

[0074] Furthermore, Figure 4 is a schematic front view showing the state of the core thickness of the drill bit body in an example (four-flute drill bit) of a cutting tool for explaining an embodiment of the present disclosure. Additionally, in Figure 4 , for ease of understanding of this structure, compared with Figure 1 , the scale of the drill bit body 1 is shown only by appropriately magnifying the radial dimension.

[0075] As Figure 4 shown, if focusing on the core thickness, the drill bit body 1 of the four-flute drill bit 100 has a two-stage structure. That is, the drill bit body 1 has a first core thickness portion 13 and a second core thickness portion 14. The first core thickness portion 13 is formed such that the core thickness gradually decreases from d1 to d2 from one end portion 10 to the other end portion 20 of the drill bit body 1, and the second core thickness portion 14 is formed such that the core thickness is constant at d2 from the first core thickness portion 13 to the other end portion 20.

[0076] More specifically, the first core thickness portion 13 has a core thickness cone ST, and the first core thickness portion 13 has the diameter of the drill bit body 1 at the outer peripheral position 10g of one end portion 10 About 35% of the core thickness d1, from the outer peripheral position 10g of one end 10 towards the other end 20 to the diameter of the drill body 1 at a distance about twice that At the position, the core thickness is reduced at a rate of about -2% (about -2 mm / 100 mm). For example, if the diameter of the four-flute drill 100 then the maximum core thickness d1 on the one end 10 side of the first core thickness portion 13 = 10 mm × about 35% = about 3.5 mm, and the axial length of the core thickness cone ST is The minimum core thickness d2 on the other end 20 side of the first core thickness portion 13 (which is also the core thickness of the second core thickness portion 14) = d1 - (about -2% × 20 mm) = about 3.5 mm - about 0.4 mm = about 3.1 mm.

[0077] Next, Figure 5A and Figure 5B respectively schematically show cross-sectional views (with the z-axis as the reference) of one end of the cutting tool and its vicinity along the Figure 2 VA-VA line and VB-VB line in. In addition, Figure 5A is a diagram for explaining the cutting-in angle of the first grinding portion 61, Figure 5B is a diagram for explaining the cutting-in angle of the second grinding portion 62. In addition, as Figure 2 shown, Figure 2 the VA-VA line in is parallel to the intersection edge (i.e., the part of the grinding cutting edge 5 formed by the first grinding portion 61) of the rake face and the front flank 4 of the first grinding portion 61 in the fourth quadrant of the x-y coordinates of Figure 2 , and as Figure 5A shown, it is located near the grinding portion 6 and at a fixed short distance from the grinding cutting edge 5. Similarly, as Figure 2 shown, Figure 2 the VB-VB line in is parallel to the intersection edge (i.e., the part of the grinding cutting edge 5 formed by the second grinding portion 62) of the rake face and the front flank 4 of the second grinding portion 62 in the fourth quadrant of the x-y coordinates of Figure 2 , and as Figure 5B shown, it is located near the grinding portion 6 and at a fixed short distance (the same distance as the distance in the above VA-VA line) from the grinding cutting edge.

[0078] As Figure 5A shown, the cutting-in angle θ21 of the first grinding portion 61 is formed by the virtual straight line ( Figure 2 the dotted straight line in) connecting the two end points of the cross-section of the first grinding portion 61 part in the cross-section along the VA-VA line of Figure 5A (the part enclosed by the dotted circle C1 in) and the central axis P. Similarly, as Figure 5A shown, the cutting-in angle θ22 of the second grinding portion 62 is formed by the virtual straight line ( Figure 5B the dotted straight line in) connecting the two end points of the cross-section of the second grinding portion 62 part in the cross-section along the VA-VA line ofFigure 2 In the cross-section of the VB-VB line, the virtual straight line connecting the two end points of the part of the second grinding part 62 in the cross-section ( Figure 5B the part surrounded by the dashed circle frame C2) and the angle formed by the central axis P. Figure 5B the dashed straight line).

[0079] Specifically, it is preferable that the cutting-in angle θ21 of the first grinding part 61 and the cutting-in angle θ22 of the second grinding part 62 have the relationship shown in the following formula (2). More specifically, it is further preferable that the cutting-in angle θ21 of the first grinding part 61 is about 40° and the cutting-in angle θ22 of the second grinding part 62 is about 30°.

[0080] θ21>θ22…(2)

[0081] Next, Figure 6 and Figure 7 is a perspective view of one end of an example of a cutting tool (four-flute drill) of an embodiment of the present disclosure as viewed obliquely from the front end (with the x-axis and y-axis as the reference). More specifically, from the comparison with Figure 2 , it can be seen that Figure 6 is in the direction orthogonal to the VA-VA line of Figure 2 and along the cutting-in angle θ21 of the first grinding part 61 ( Figure 5A ) when observing the four-flute drill 100 from the front end side. In the example of Figure 6 , it is a perspective view of observing the concave space of the grinding part 6 in the third quadrant of the x-y coordinates of Figure 2 from the first quadrant side in the direction of the cutting-in angle of the first grinding part 61. The opening angle θ31 of the first grinding part 61 represents the opening angle formed by the opposing surfaces of the first grinding part 61 in Figure 6 (however, excluding the R-shaped part at the concave bottom of the first grinding part 61). Similarly, from the comparison with Figure 2 , it can be seen that Figure 7 is in the direction orthogonal to the VB-VB line of Figure 2 and along the cutting-in angle θ22 of the second grinding part 62 ( Figure 5B ) when observing the four-flute drill 100 from the front end side. In the example of Figure 7 , it is a perspective view of observing the concave space of the grinding part 6 in the third quadrant of the x-y coordinates of Figure 2 from the first quadrant side in the direction of the cutting-in angle of the second grinding part 62. The opening angle θ32 of the second grinding part 62 represents the opening angle formed by the opposing surfaces of the second grinding part 62 in Figure 7The opening angle formed by the opposite surface of the second polished portion 62 (however, the R-shaped portion of the concave bottom of the second polished portion 62 is excluded.). Specifically, it is preferred that the opening angle θ31 of the first polished portion 61 and the opening angle θ32 of the second polished portion 62 have a relationship as shown in the following formula (3). More specifically, it is further preferred that the opening angle θ31 of the first polished portion 61 is about 60°, and the opening angle θ32 of the second polished portion 62 is about 55°.

[0082] θ31>θ32…(3)

[0083] (Effects of the Implementation Methods)

[0084] According to the four-edge drill 100 thus constructed, the rake angle of the sharpened cutting edge 5 formed by the sharpening portion 6 is larger than that of the original chisel edge, so that the volume of the sharpening pocket for discharging the chips generated during the hole cutting process of the workpiece is increased, thereby improving the cutting resistance, bite performance, and chip discharge performance of the workpiece. In addition, in the hole cutting process, since the first tip portion 11 having a small (sharp) tip angle θ11 in one end portion 10 of the drill body 1 first contacts the workpiece, the bite performance of the workpiece can be sufficiently improved even if the chisel edge 7 tends to be larger than that of the double-edge drill. In addition, at the positions corresponding to the main cutting edges 3 on the outer peripheral surface of the drill body 1, there are lands 8 in the vertical direction of each main cutting edge 3, so that the lands 8 can easily bear the force applied to the main cutting edge 3, thereby protecting the main cutting edge 3. In addition, there are always lands 8 on the main cutting edge 3 located at the opposite position, so that the diameter (outer diameter, tool diameter) of the drill body 1 can be easily measured.

[0085] In addition, in the one end portion 10, the tip angle θ12 of the second tip portion 12 extending from the first tip portion 11 to the outer peripheral edge of the drill body 1 is larger than the tip angle θ11 of the first tip portion 11, so the distance from the first tip portion 11 to the central axis P direction of the outermost main cutting edge 3 after the first tip portion 11 bites into the workpiece becomes shorter. As a result, the time when the rotation of the drill body 1 becomes unstable when the first tip portion 11 bites into the workpiece and the second tip portion 12 performs cutting is shortened, and the shoulder of the second tip portion 12 is easily and quickly received in the processed hole, so that the guiding function of the drill body 1 can be improved. In particular, when the first front end portion 11 is a portion approximately 20% of the radius R from the center axis P to the drill body 1, the front end angle θ11 of the first front end portion 11 is approximately 120°, and the front end angle θ12 of the second front end portion 12 is approximately 140°, the first front end portion 11 can be effectively prevented from being damaged or broken, and the excellent biting performance of the cut workpiece and the excellent guiding function of the drill body 1 can be more reliably achieved.

[0086] In addition, since the first core thickness portion 13 of the portion from one end portion 10 toward the other end portion 20 has a core thickness cone ST and gradually decreases, and the core thickness d2 of the second core thickness portion 14 of the portion further toward the other end portion 20 from here is thin and constant, by appropriately setting the degree of decrease in the core thickness, it is possible to start reducing the core thickness from a portion closer to the one end portion 10, thereby rapidly increasing the volume of the flute 2 earlier. As a result, the chip evacuation performance can be further improved. In particular, the first core thickness portion 13 has a core thickness d1 of about 35% of the diameter of the drill body 1 at the outer peripheral position 10g of the edge of the one end portion 10, and from the outer peripheral position 10g of the edge of the one end portion 10 toward the other end portion 20 to a distance about twice the diameter of the drill body 1 at the position, when the core thickness decreases at a ratio of about -2% (about -2 mm / 100 mm) of the core thickness d1, the rigidity of the drill body 1 can be maintained, and excellent chip evacuation performance can be more reliably achieved.

[0087] In addition, since the grinding portion 6 having a two-stage structure including the first grinding portion 61 and the second grinding portion 62 is provided, and the first grinding portion 61 is disposed on the side of the flank face 4 at the tip of the main cutting edge 3, and the second grinding portion 62 is disposed from the first grinding portion 61 toward the flute 2, compared with the grinding portion having a one-stage structure (only the first grinding portion 61 or the second grinding portion 62), the volume of the grinding pocket can be further increased, and thus, the chip evacuation performance can be further improved.

[0088] Among them, Figure 8 is a schematic plan view showing an enlarged view of a peripheral portion of the intersection point CP of the main cutting edge 3 and the grinding cutting edge 5 in an example of a four-flute drill according to an embodiment of the present disclosure, and is used to illustrate the state of the intersection point CP. In addition, Figure 9 is an enlarged view showing a portion corresponding to the region shown in Figure 8 in another example of a four-flute drill according to an embodiment of the present disclosure, and is the same as Figure 8 and is a schematic plan view used to illustrate the state of the intersection point CP of the main cutting edge 3 and the grinding cutting edge 5. In addition, the xc axis and the yc axis in the two figures are the reference of the intersection point CP.

[0089] As shown in these drawings, the inner angle θ41 of the intersection point CP of the main cutting edge 3 and the grinding cutting edge 5 when the two-stage structure grinding portion 6 is provided is a larger obtuse angle compared with the inner angle θ42 of the intersection point CP of the main cutting edge 3 and the grinding cutting edge 5 when the one-stage structure grinding portion 6 is provided (that is, has the relationship shown by the following formula (4)). As a result, there is an advantage that damage to the intersection point CP and the peripheral portion can be suppressed.

[0090] θ41 > θ42...(4)

[0091] ​​Further, if the cutting-in angle θ21 and the spreading angle θ31 of the first grinding portion 61 are respectively greater than the cutting-in angle θ22 and the spreading angle θ32 of the second grinding portion 62, the volume of the grinding pocket ground by the first grinding portion 61 is further increased, and thus the chip evacuation performance can be further improved. Further, the curling (winding condition) of the generated chips can be reduced by the second grinding portion 62. Thereby, the shape of the chips is reduced, and the chips can easily move more closely and quickly in the flute 2. As a result, the chip evacuation performance can be further improved. In addition, if the cutting-in angle θ21 and the spreading angle θ31 of the first grinding portion 61 are respectively set to about 40° and about 60°, and the cutting-in angle θ22 and the spreading angle θ32 of the second grinding portion 62 are respectively set to about 30° and about 55°, the effect of expanding the volume of the grinding pocket and the effect of reducing the shape of the chips can be effectively improved, thereby achieving optimization.

[0092] The above has described in detail the above-described embodiment as an example of the present disclosure. However, as described above, the foregoing description only shows an example of the present disclosure in all aspects, and it is obvious that various improvements and modifications can be made without departing from the scope of the present disclosure. In addition, the above-described structural examples can be partially replaced or appropriately combined, and further, the changes appropriately mentioned in each example can be made. In addition, this application is based on a Japanese patent application No. 2021-063934 filed on April 5, 2021, and its description is incorporated herein by reference.

[0093] In addition, the present disclosure can also be described as follows.

[0094] [1] A cutting tool, comprising:

[0095] A drill bit body that rotates about a central axis;

[0096] Four or more cutting edges formed at one end of the drill bit body and facing the front side in the rotation direction;

[0097] Flutes formed between the cutting edges in the circumferential direction and extending in a slightly helical shape along the central axis;

[0098] A grinding portion formed at the front end of the flute and having a first grinding portion and a second grinding portion, the first grinding portion being disposed on the flank side of the cutting edge, and the second grinding portion being disposed from the first grinding portion toward the flute;

[0099] The one end portion has a first front end portion and a second front end portion, the first front end portion includes the central axis and forms a first front end angle, and the second front end portion extends from the first front end portion to the outer peripheral edge of the drill bit body and forms a second front end angle greater than the first front end angle;

[0100] The drill bit body has a first core thickness portion and a second core thickness portion. The first core thickness portion is formed such that its core thickness gradually decreases from the one end portion toward the other end portion. The second core thickness portion is formed such that its core thickness is constant from the first core thickness portion toward the other end portion.

[0101] The cutting-in angle and the opening angle of the first grinding portion are respectively greater than those of the second grinding portion.

[0102] [2] For the cutting tool according to [1] above, the first front end portion is a portion that is about 20% of the radius from the central axis to the drill bit body.

[0103] The first front end angle is about 120°.

[0104] The second front end angle is about 140°.

[0105] [3] For the cutting tool according to [1] or [2] above, the first core thickness portion has a core thickness cone. The first core thickness portion has a core thickness of about 35% of the diameter of the drill bit body at the outer peripheral position of the edge at the one end portion. From the outer peripheral position of the edge at the one end portion to the position at a distance of about twice the diameter of the drill bit body toward the other end portion, the core thickness decreases at a ratio of about -2%.

[0106] [4] For the cutting tool according to [1] or [2] above, the cutting-in angle and the opening angle of the first grinding portion are respectively about 40° and about 60°.

[0107] The cutting-in angle and the opening angle of the second grinding portion are respectively about 30° and about 55°.

Claims

1. A cutting tool, comprising: A drill body that rotates about a central axis; Four or more cutting edges formed at one end of the drill body and facing the front side in the rotation direction; Flute grooves formed circumferentially between the cutting edges and extending in a slightly helical shape along the central axis; The one end has a first tip portion and a second tip portion. The first tip portion includes the central axis and forms a first tip angle. The second tip portion extends from the first tip portion to the outer peripheral edge of the drill body and forms a second tip angle greater than the first tip angle; The drill body has a first core thickness portion and a second core thickness portion. The first core thickness portion is formed such that its core thickness gradually decreases from the one end toward the other end. The second core thickness portion is formed such that its core thickness is constant from the first core thickness portion toward the other end; The cutting tool further includes a grinding portion formed at the front end of the flute groove and having a first grinding portion and a second grinding portion. The first grinding portion is disposed on the flank side of the cutting edge. The second grinding portion is disposed from the first grinding portion toward the flute groove; The plunge angle and the opening angle of the first grinding portion are respectively greater than the plunge angle and the opening angle of the second grinding portion.

2. The cutting tool according to claim 1, characterized in that: The first tip portion is a portion from the central axis to about 20% of the radius of the drill body; The first tip angle is about 120°; The second tip angle is about 140°.

3. The cutting tool according to claim 1 or 2, characterized in that, The first core thickness portion has a core thickness cone. The first core thickness portion has a core thickness of about 35% of the diameter of the drill body at the outer peripheral position of the edge of the one end. From the outer peripheral position of the edge of the one end to the position at a distance of about twice the diameter of the drill body toward the other end, the core thickness decreases at a ratio of about -2%.

4. The cutting tool according to claim 1, characterized in that, The plunge angle and the opening angle of the first grinding portion are respectively about 40° and about 60°; The plunge angle and the opening angle of the second grinding portion are respectively about 30° and about 55°.

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