Cutting tool

Abstract

Cutting tool that features: a drill body (1) which is rotated about a central axis (P); four or more cutting edges (3, 5) which are formed on an end section (10) of the drill body (1) such that they point towards a front side of a direction of rotation; a flute (2) which is formed between the cutting edges (3, 5) which are adjacent to each other in a circumferential direction and which extends essentially in a spiral shape along the central axis (P), wherein one end section (10) has a first tip section (11) which contains the central axis (P) and forms a first tip angle (θ11), and a second tip section (12) which extends from the first tip section (11) to an outer circumferential edge of the drill body (1) and forms a second tip angle (θ12) which is larger than the first tip angle (θ11), and the drill body (1) has a first core thickness section (13) which is designed in such a way that its core thickness gradually decreases from one end section (10) to the other end section (20), and a second core thickness section (14) which is designed in such a way that its core thickness is constant from the first core thickness section (10) to the other end section (20), and a thinning section (6) formed at a tip of the flute (2) and comprising a first thinning (61) arranged on a flank surface side of the cutting edges (3, 5) and a second thinning (62) arranged from the first thinning (61) to the flute (2), wherein the first thinning (61) has an ingress angle (θ21) and an opening angle (θ31) which are greater than an ingress angle (θ22) and an opening angle (θ32) of the second thinning (62).

Description

Background area

[0001] The present invention relates to a cutting (drilling) tool having four or more cutting edges, which is excellent in both its biting property into a work material and its chip removal property. Description of the state of the art

[0002] As a means for improving the machining efficiency of a work material with a drill, a 4-flute drill has been conventionally proposed, which has twice as many cutting edges as a conventional 2-flute drill (see Patent Publication JP 2019-048347 A). The prior art 4-flute drill is intended to improve the biting property into the work material and prevent the formation of burrs on the back of the work material and has the following configuration. In other words, on the tip surface of such a 4-flute drill, the four cutting edges consist of two main cutting edges extending from a radially outer peripheral end portion to the center, and two sub-cutting edges arranged circumferentially between the main cutting edges and extending from the radially outer peripheral end portion to the center point.In addition, when viewing the tip surface in the direction along the length of the sub-cutting edges, the burr lines and the like of the main cutting edges are formed in a convex shape protruding toward the tip surface from the radial outer peripheral side to the center, and when viewing the tip surface in the direction along the length of the main cutting edges, the burr lines and the like of the sub-cutting edges are formed in a concave shape depressed toward the tip surface from the radial outer peripheral side to the center.

[0003] DE 10 2009 003 287 A1 discloses a drill with a hard metal head and a steel shaft. The head has cutting edges on one front side.

[0004] From DE 103 31 328 A1, a drill with a cylindrical main body and a shank is known. The cylindrical main body has grooves providing cutting edges at an axially distal end of the cylindrical main body, lands each provided by a circumferential portion of the cylindrical main body and located between the grooves, and a ridge provided by a central portion of the cylindrical main body, connecting the lands and extending in an axial direction of the cylindrical main body. The ridge has a rearwardly inclined portion provided by at least one axially distal end portion of the ridge such that the thickness of the ridge gradually or continuously decreases at the rearwardly inclined portion when viewed in the direction away from the axially distal end of the cylindrical main body and toward the shank.In addition, the back may have a non-rearwardly sloping portion provided by an axially proximate end portion and an intermediate portion of the back.

[0005] DE 10 2011 016 209 A1 discloses a rotary cutting tool with an elongated body arranged around a longitudinal axis. The elongated body contains a spiral groove and a cutting tip made of polycrystalline diamond. The cutting tip comprises an inner section with an inner tip angle and an outer section with an outer tip angle different from the inner tip angle. The drill is preferably formed by thinning at the cutting end of the drill. Summary

[0006] The invention is defined by the features of the independent claim. Preferred embodiments are specified in the dependent claims.

[0007] However, although the prior art 4-flute drill is capable of drilling holes in the work material with high machining efficiency, the bit size becomes larger (the chisel edge becomes thicker) than that of a 2-flute drill to ensure the strength of the drill tip and because the thinnings easily interfere with each other due to the large number of edges. As a result, the biting performance on the work material is still insufficient. Furthermore, in the prior art 4-flute drill, since the width of a chip flute is inevitably narrower than that of a conventional 2-flute drill, the chip flute volume is relatively small, resulting in poor chip evacuation performance.

[0008] Therefore, the present disclosure has been developed in view of such circumstances, and its object is to provide a cutting tool capable of improving both biting property into a work material and chip evacuation.

[0009] To achieve the above object, the present invention has the following configurations.

[0010] [1] An example of a cutting tool according to the present disclosure includes a drill body rotated about a central axis, four or more (main) cutting edges formed at an end portion of the drill body to face a front side of a rotation direction, and a chip flute formed between the cutting edges adjacent to each other in a circumferential direction and extending substantially spirally along the central axis.In addition, (1) the one end portion has a first tip portion containing the central axis and forming (having) a first tip angle, and a second tip portion extending from the first tip portion to an outer peripheral edge of the drill body and forming (having) a second tip angle greater than the first tip angle, and (2) the drill body has a first core thickness portion formed in such a manner that its core thickness gradually decreases from the one end portion to the other end portion, and a second core thickness portion formed in such a manner that its core thickness is constant from the first core thickness portion to the other end portion.

[0011] In this configuration, one end portion of the drill body, where the cutting edges are formed, rests on a work material and rotates to perform hole cutting on the work material. The resulting chips generated by the cutting edges flow through a rake face (chip flute) formed between the circumferentially adjacent cutting edges and are discharged from the machined hole. In this hole cutting, the first tip portion (having a chisel edge) forming the relatively small (sharp) first point angle at the one end portion comes into contact with the work material first. Therefore, even if the chisel edge of the cutting tool becomes generally large compared to that of a 2-flute drill, the biting property on the work material can be sufficiently improved.Furthermore, at one end portion, since the second tip angle of the second tip portion extending from the first tip portion to the outer peripheral edge of the drill body is larger than the first tip angle of the first tip portion, the distance in the central axis direction from the first tip portion biting into the work material to the cutting edge at the outermost periphery becomes relatively short. This reduces the time it takes for the rotation of the drill body to become unstable when the first tip portion bites into the work material and cutting continues by the second tip portion, and improves the guiding function of the drill body because a shoulder of the second tip portion easily fits into the machined hole.

[0012] Furthermore, the core thickness of the first core thickness portion gradually decreases in a portion from one end portion to the other end portion, and the core thickness of the second core thickness portion is made constantly thin in a portion to the other end portion. Therefore, by appropriately adjusting the degree of reduction of the core thickness from the portion near one end portion, the core thickness can be reduced to increase the volume of the chip flute. As a result, chip removal can be further improved.

[0013] [2] Specifically, in the above-described configuration, the first tip portion may be formed as a part extending from the central axis to approximately 20% of a radius of the drill body, the first tip angle may be approximately 120°, and the second tip angle may be approximately 140°. According to the knowledge of the inventors of the present invention, by adopting such a configuration, the excellent biting property into the work material and the excellent guiding function of the drill body described above can be more easily achieved while effectively preventing loss or damage of the first tip portion.

[0014] [3] Specifically, in the above-described configuration, the first core thickness portion may be configured to have a core thickness of approximately 35% of a diameter of the drill body at an outer circumferential seam position of the one end portion and a core thickness taper formed in such a manner that the core thickness decreases by approximately -2% (approximately -2 mm / 100 mm) from the outer circumferential seam position of the one end portion to a position at a distance of approximately twice the diameter of the drill body from the other end portion. According to the knowledge of the inventors of the present invention, with such a configuration, the volume of the chip flute can be increased at an early stage by reducing the core thickness from the part closer to the one end portion while maintaining the rigidity of the drill body. Therefore, the above-mentioned excellent chip removal property can be more easily achieved.

[0015] [4] Furthermore, the above configuration may further include a thinning portion formed at a tip of the chip flute, and including a first thinning portion located on a flank surface side of the cutting edges and a second thinning portion located from the first thinning portion to the chip flute. In such a configuration, an original chisel edge is removed by the thinning portion, thereby forming a thinning cutting edge. In addition, since the thinning portion has a two-stage configuration, the volume of the thinning pocket for discharging chips generated during hole cutting of the work material can be made larger than that of a thinning portion having a single-stage configuration.Since the intersection lines of the thinning cutting edge and the (main) cutting edges can form a more obtuse angle compared to the case where the thinning section has a single-stage configuration, the loss of the intersection lines and the surrounding parts can be suppressed.

[0016] [5] Furthermore, in the above configuration, a penetration angle and an opening angle of the first thinning may be larger than a penetration angle and an opening angle of the second thinning, respectively. In such a configuration, since the volume of the thinning pocket is further increased by the first thinning, the chip removal property can be further improved. In addition, the second thinning can reduce the curl (twisting state) of the generated chips. As a result, the shape of the chips is reduced, and the chips can move more densely and quickly through the flute easily, thereby further improving the chip removal property.

[0017] [6] Moreover, particularly in the above configuration, the penetration angle and opening angle of the first thinning pocket may be approximately 40° and approximately 60°, respectively, and the penetration angle and opening angle of the second thinning pocket may be approximately 30° and approximately 55°, respectively. According to the knowledge of the present inventors, with such a configuration, both the effect of increasing the volume of the thinning pocket and the effect of reducing the chip shape can be efficiently improved and optimized.

[0018] Furthermore, in the present disclosure, the term "approximately" associated with a numerical value refers to the range of the numerical value ±5%. For example, if the numerical value is "10%," "approximately 10%" indicates 9.5% to 10.5%. If the numerical value is "100°," "approximately 100°" indicates 95° to 105°. If the numerical value is "10 times," "approximately 10 times" indicates 9.5 times to 10.5 times.

[0019] According to the present disclosure, the one end portion of the drill body is configured to have the first tip portion and the second tip portion, and the drill body is configured to have the first core thickness portion and the second core thickness portion. Therefore, even with four or more cutting edges, the improvement of both the biting property into a work material and the chip removal property can be achieved. Brief description of the drawings Fig. 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; Fig. 2 is a plan view schematically showing an end portion of an example of a cutting tool according to an embodiment of the present disclosure; Fig. 3 is a schematic front view schematically illustrating the one end portion and its vicinity of an example of the cutting tool according to an embodiment of the present disclosure and explaining a tip angle of the one end portion; Fig. 4 is a schematic front view for explaining a state of a core thickness of a drill body in an example of a cutting tool according to an embodiment of the present disclosure; Fig. Fig. 5A is a schematic cross-sectional view schematically illustrating the one end portion and its vicinity of the cutting tool taken along the line VV of the Fig. 1 and illustrating an angle of penetration of a first dilution; Fig. Fig. 5B is a schematic cross-sectional view schematically illustrating the one end portion and its vicinity of the cutting tool taken along the line VV of the Fig. 1 and illustrates the angle of penetration of a second dilution; Fig. 6 is a perspective view schematically illustrating one end portion of an example of the cutting tool according to an embodiment of the present disclosure and explaining an opening angle of the first thinning; Fig. 7 is a perspective view schematically illustrating one end portion of an example of the cutting tool according to an embodiment of the present disclosure and explaining an opening angle of the second thinning; Fig. 8 is a schematic plan view illustrating the magnification of a peripheral part of a cutting line between a main cutting edge and a thinning cutting edge in an example of the cutting tool according to an embodiment of the present disclosure, and explaining a state of the cutting line; and Fig. 9 is a schematic plan view showing the magnification of a peripheral part of an intersection line between a main cutting edge and a thinning cutting edge in another example of the cutting tool according to an embodiment of the present disclosure, and explaining a state of the intersection line. Detailed description

[0020] An embodiment according to an example of the present disclosure will be described below with reference to the drawings. However, the embodiment described below is merely an example, and an example of the present disclosure can be variously modified and implemented without departing from the spirit of the present disclosure. In addition, in the description of the drawings, the same or similar parts are denoted by the same or similar reference numerals, and the drawings are schematic and do not necessarily correspond to the actual dimensions, ratios, and the like. Moreover, a part in which the dimensions and ratios of the drawings differ from each other is included in the drawings.Also, the embodiment described below is only a part of the present disclosure, and other embodiments achieved by those skilled in the art based on the embodiment of the present disclosure without the need for creative acts fall within the scope of the present disclosure. Configurations of the embodiment

[0021] Fig. 1 is a perspective view schematically illustrating a schematic structure of an example of a cutting tool (4-flute drill) according to an embodiment of the present disclosure. Fig. 2 is a plan view schematically illustrating an end portion of an example of a cutting tool (4-flute drill) according to an embodiment of the present disclosure, the plan view showing the shape of the 4-flute drill in an axial tip view (x-axis and y-axis are each a rough indication).

[0022] A 4-flute drill 100 (cutting tool) is a solid spiral carbide drill having four curved main cutting edges 3 formed at one end portion 10 of a drill body 1 at intervals of, for example, approximately 90° in a circumferential direction in such a manner as to face a front side of a rotational direction. In the drill body 1, four flutes 2 are formed between the circumferentially adjacent main cutting edges 3, which twist and extend substantially spirally along a central axis P. A ridge line at which a wall of a flute 2 facing in the rotational direction intersects with a tip surface of one end portion 10 of the drill body 1 defines a main cutting edge 3, and the main cutting edge 3 forms a gentle concave curve in the rotational direction of the 4-flute drill 100 in the axial tip view.Furthermore, a rim 8 is formed on an outer peripheral surface of the drill body 1 at a position corresponding to each main cutting edge 3.

[0023] The tip surface of one end portion 10 is formed, for example, from a twisted or curved surface and defines a tip flank surface 4 of the main cutting edge 3. A clearance angle of the tip flank surface 4 can be appropriately adjusted according to the type of work material or cutting conditions. That is, the clearance angle is set to a constant angle or, if necessary, increased with increasing distance from the main cutting edge 3 to prevent adhesion of the work material or suppress wear to increase tool life.

[0024] Furthermore, a thinning portion 6 is provided to remove a part of an original chisel edge formed in a central portion of the one end portion 10 of the drill body 1, and after the removal, a chisel edge 7 remains in a central portion of the tip surface of the one end portion 10 in the drill body 1. Four thinning cutting edges 5 formed by the thinning portion 6 form a substantially linear shape in the axial tip view, and the thinning cutting edges 5 and the main cutting edges 3 have intersection lines (intersection lines CP described below) connected to have a predetermined obtuse angle. These four thinning cutting edges 5 are also formed on the one end portion 10 of the drill body 1 to face the front of the rotation direction.In this way, the term “cutting edge” used in the present disclosure is formed by the main cutting edges 3 and the thinning cutting edges 5.

[0025] Furthermore, the thinning portion 6 is a thinning portion having a two-stage configuration including a first thinning portion 61 formed at the tip of the chip flute 2 and disposed on the tip flank surface 4 on the main cutting edge 3 side, and a second thinning portion 62 disposed from the first thinning portion 61 to the chip flute 2.

[0026] Fig. 3 is a schematic front view schematically illustrating the one end portion and its vicinity of an example of the cutting tool (4-flute drill) according to an embodiment of the present disclosure, and explaining a tip angle of the one end portion (the z-axis is a rough indication).

[0027] The one end portion 10 of the drill body 1 has a first tip portion 11 having a region containing the central axis P and forming a sharp head, and a second tip portion 12 extending from a peripheral edge of the first tip portion 11 to an outer peripheral edge of the drill body 1. As shown in Fig. 3, the first tip portion 11 and the second tip portion 12 also have a tip angle θ11 (first tip angle) and a tip angle θ12 (second tip angle), respectively, which have a relationship expressed by the following equation (1). Fig. 3, the dashed lines defining the tip angles θ11 and θ12 are virtual lines parallel to the surface defined by a substantially linear rotation locus obtained when the 4-flute drill continuously rotates around the central axis P. θ11<θ12

[0028] In particular, it is preferable that the first tip portion 11 is formed in such a manner that the first tip portion 11 is a part extending from the central axis P (tool center) to approximately 20% of a radius R of the drill body 1, that is, the diameter of a virtual bottom surface of the first tip portion 11 is 2R × approximately 20% (see Fig. 3). For example, assuming that the diameter φ of the four-flute drill 100 is 10 mm (radius R = 5 mm), the first tip portion 11 is a part where the diameter of its virtual bottom surface is 10 mm × approximately 20% = approximately 2 mm. Furthermore, it is preferable that the tip angle θ11 of the first tip portion 11 is approximately 120°, and the tip angle θ12 of the second tip portion 12 is approximately 140°.

[0029] Fig. Fig. 4 is a schematic front view for explaining a state of a core thickness of the drill body in an example of the cutting tool (4-flute drill) according to an embodiment of the present disclosure. To facilitate understanding of this configuration, Fig. 4 the scale of the drill body 1 is shown by only its radial dimension in comparison to Fig. 1 is suitably enlarged.

[0030] As in Fig. 4, with respect to the core thickness, the drill body 1 of the 4-flute drill 100 has a two-stage configuration. That is, the drill body 1 has a first core thickness portion 13 configured such that the core thickness gradually decreases from d1 to d2 from one end portion 10 to the other end portion 20, and a second core thickness portion 14 configured such that the core thickness is constant at d2 from the first core thickness portion 13 to the other end portion 20.

[0031] In particular, the first core thickness portion 13 has a core thickness d1 of approximately 35% of the diameter φ of the drill body 1 at an outer seam circumferential position 10g of the one end portion 10 and a core thickness taper ST formed in such a manner that the core thickness decreases by approximately -2% (approximately -2 mm / 100 mm) from the outer seam circumferential position 10g of the one end portion 10 to the position at a distance (= 2φ) approximately twice as large as the diameter φ of the drill body 1 to the other end portion 20.For example, assuming that the diameter φ of the 4-flute drill 100 is 10 mm, the maximum core thickness d1 at one end portion 10 on the side of the first core thickness portion 13 is 10 mm × approximately 35% = approximately 3.5 mm, an axial length 2φ of the core thickness cone ST is 20 mm, and the minimum core thickness d2 on the other side of the end portion 20 of the first core thickness portion 13 (which is also the core thickness of the second core thickness portion 14) is d1-(approximately -2% × 20 mm) = approximately 3.5 mm - approximately 0.4 mm = approximately 3.1 mm.

[0032] Next are Fig. 5A and Fig. 5B are cross-sectional views schematically illustrating one end portion and its surroundings of the cutting tool taken along the lines VA-VA and VB-VB of the Fig. 2 (the z-axis is a rough indication). Furthermore, Fig. 5A also shows a diagram for explaining a penetration angle of the first thinning 61, and Fig. 5B is also a diagram for explaining a penetration angle of the second dilution 62. As in Fig. 2, the line VA-VA runs in Fig. 2 parallel to a crossing ridge line between the rake face of the first thinning 61 and the tip flank surface 4 in the fourth quadrant of the xy coordinates of the Fig. 2 (ie a part of the thinning cutting edge 5 formed by the first thinning 61) and is located closer to the thinning section 6 by a predetermined short distance from the thinning cutting edge 5, as shown in Fig. 5A. Accordingly, as shown in Fig. 2, the line VB-VB in Fig. 2 parallel to a crossing ridge line (ie a part of the thinning cutting edge 5 formed by the second thinning 62) between the rake face of the second thinning 62 and the tip flank surface 4 in the fourth quadrant of the xy coordinates of the Fig. 2 and is located closer to the thinning section 6 by a predetermined short distance (the same distance as in the line VA-VA) from the thinning cutting edge, as in Fig. 5B.

[0033] As in Fig. 5A, a penetration angle θ21 of the first thinning 61 is an angle defined by a virtual straight line (dashed straight line in Fig. 5A) passing through both endpoints of a cross-section of the first dilution 61 (the one marked by the dashed round frame C1 in Fig. 5A) in cross-section along the line VA-VA of the Fig. 2, and the central axis P is formed. Accordingly, as in Fig. 5B, a penetration angle θ22 of the second thinning 62 is an angle defined by a virtual straight line (dashed straight line in Fig. 5B), which passes through both endpoints of the cross section of the second dilution 62 in the cross section along the line VB-VB of the Fig. 2 (enclosed by the dashed line around frame C2 of the Fig. 5B) and the central axis P. In particular, it is preferable that the penetration angle θ21 of the first thinning 61 and the penetration angle θ22 of the second thinning 62 have a relationship expressed by the following equation (2). In particular, it is particularly preferable that the penetration angle θ21 of the first thinning 61 is approximately 40° and the penetration angle θ22 of the second thinning 62 is approximately 30°. θ12>θ22

[0034] Next are Fig. 6 and Fig. 7 are perspective views in which one end portion of an example of the cutting tool (4-flute drill) according to an embodiment of the present disclosure is visually recognized from an oblique direction of the tip (x-axis and y-axis are rough indications). As can be seen particularly from the comparison with Fig. 2, Fig. 6 is a perspective view in which the 4-flute drill 100 is viewed from the tip side in the direction orthogonal to the line VA-VA of the Fig. 2 and along the penetration angle θ21 of the first dilution 61 ( Fig. 5A). The example in Fig. 6 is a perspective view in which a concave space of the dilution part 6 is shown in the third quadrant of the xy coordinates of the Fig. 2 is viewed from the side of the first quadrant in the direction of the penetration angle of the first thinning 61. An opening angle θ31 of the first thinning 61 indicates the opening angle formed by opposite surfaces of the first thinning 61 in Fig. 6 (except for an R-shaped portion of a concave lower portion of the first dilution 61). As can be seen from the comparison with Fig. 2, Fig. 7 is a perspective view in which the 4-flute drill 100 is viewed from the tip side in the direction orthogonal to the line VB-VB of the Fig. 2 and along the penetration angle θ22 of the second dilution 62 ( Fig. 5B). The example in Fig. Fig. 7 is a perspective view in which the concave space of the thinning section 6 is located in the third quadrant of the xy coordinates of the Fig. 2 is viewed from the side of the first quadrant in the direction of the penetration angle of the second thinning 62. An opening angle θ32 of the second thinning 62 indicates the opening angle formed by opposite surfaces of the second thinning 62 in Fig. 7 (except for an R-shaped portion of a concave bottom portion of the second thinning 62). Specifically, it is preferable that the opening angle θ31 of the first thinning 61 and the opening angle θ32 of the second thinning 62 have a relationship expressed by the following equation (3). In particular, it is particularly preferable that the opening angle θ31 of the first thinning 61 is approximately 60°, and the opening angle θ32 of the second thinning 62 is approximately 55°. θ31>θ32 Effects and effects of the embodiment

[0035] According to the 4-flute drill 100 configured in this way, the thinning cutting edge 5 formed by the thinning portion 6 has a larger rake angle than the original chisel edge and has a larger thinning pocket volume for discharging chips generated during hole cutting of the work material. Consequently, the cutting resistance and biting force on the work material, as well as chip evacuation, can be improved. Furthermore, in the hole cutting process, since the first tip portion 11 located at the one end portion 10 of the drill body 1 and having a relatively small (sharp) tip angle θ11 comes into contact with the work material first, the biting property on the work material can be sufficiently improved even if the chisel edge 7 tends to be larger than that of a 2-flute drill.In addition, since the position corresponding to each main cutting edge 3 on the outer peripheral surface of the drill body 1 is provided with the rim 8 in the vertical direction of each main cutting edge 3, the force applied to the main cutting edge 3 is easily absorbed by the rim 8, thereby protecting the main cutting edge 3. Since the main cutting edge 3 always has the rim 8 at the opposite position, the diameter (outer diameter, tool diameter) of the drill body 1 can also be easily measured.

[0036] Furthermore, at one end portion 10, since 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, the distance in the direction of the central axis P from the first tip portion 11 biting into the work material to the main cutting edge 3 at the outermost periphery becomes relatively short. This reduces the time it takes for the rotation of the drill body 1 to become unstable when the first tip portion 11 bites into the work material and cutting by the second tip portion 12 progresses, and improves the guiding function of the drill body 1 because the shoulder of the second tip portion 12 easily fits into the machined hole.Particularly, in a case where the first tip portion 11 is formed to become a part extending from the central axis P to approximately 20% of the radius R of the drill body 1, the tip angle θ11 of the first tip portion 11 being approximately 120° and the tip angle θ12 of the second tip portion 12 being approximately 140°, loss or damage of the first tip portion 11 is effectively prevented, and the excellent biting property into the work material and the excellent guiding function of the drill body 1 can be achieved more reliably.

[0037] Furthermore, the first core thickness portion 13 extending from one end portion 10 to the other end portion 20 has the core thickness taper ST so that its core thickness gradually reduces, and the core thickness d2 of the second core thickness portion 14 extending further to the other end portion 20 is set to be constantly thin. Therefore, by appropriately adjusting the degree of core thickness reduction, the core thickness of the part near the one end portion 10 can be reduced to drastically increase the volume of the chip flute 2 at an early stage. As a result, chip removal can be further improved.Particularly, in a case where the core thickness d1 at the outer circumferential seam position 10g of the first core thickness portion 13 is approximately 35% of the diameter φ of the drill body 1, and the core thickness taper ST is formed in such a manner that the core thickness d2 decreases by approximately -2% (approximately -2 mm / 100 mm) of the core thickness d1 from the outer circumferential seam position 10g to the position at a distance approximately twice the diameter φ of the drill body 1 to the other end portion 20, the excellent chip removal property can be achieved more reliably while maintaining the rigidity of the drill body 1.

[0038] Since the thinning portion 6 is provided with a two-stage configuration including the first thinning 61 arranged on the tip flank surface 4 on the main cutting edge 3 side and the second thinning 62 arranged from the first thinning 61 to the chip groove 2, the volume of the thinning pocket can be made larger than that of the thinning portion of the one-stage configuration (only the first thinning 61 or the second thinning 62), whereby the chip removal property can be further improved.

[0039] Fig. 8 is a schematic plan view illustrating the enlargement of a peripheral part of a cutting line CP between the main cutting edge 3 and the thinning cutting edge 5 in an example of the 4-flute drill according to an embodiment of the present disclosure, and explaining a state of the cutting line CP. Fig. 9 is a schematic plan view showing the enlargement of a part corresponding to the Fig. 8, in another example of the 4-flute drill according to an embodiment of the present disclosure and as shown in Fig. 8 explains the state of the cutting line CP between the main cutting edge 3 and the thinning cutting edge 5. The xc-axis and the yc-axis in both diagrams are each a rough indication of the cutting line CP.

[0040] As shown in these diagrams, when the two-stage thinning section 6 is provided, an internal angle θ41 of the intersection line CP between the main cutting edge 3 and the thinning cutting edge 5 can be more obtuse than an internal angle θ42 of the intersection line CP between the main cutting edge 3 and the thinning cutting edge 5 when the single-stage thinning section 6 is provided (ie, a relationship expressed by the following equation (4)). This brings about the advantage of suppressing the loss of the intersection line CP and a surrounding part. θ41>θ42

[0041] Furthermore, by configuring the penetration angle θ21 and the opening angle θ31 of the first thinning 61 to be larger than the penetration angle θ22 and the opening angle θ32 of the second thinning 62, respectively, the volume of the thinning pocket is further increased by the first thinning 61. As a result, the chip evacuation property can be further improved. In addition, the curls of the generated chips (winding state) can also be reduced by the second thinning 62. As a result, the shape of the chips is reduced, allowing the chips to move easily through the chip flute 2 more densely and quickly. As a result, the chip evacuation can be further improved. By setting the penetration angle θ21 and the opening angle θ31 of the first thinning 61 to approximately 40° and approximately 60°, respectively, and by setting the penetration angle θ22 and the opening angle θ32 of the second thinning 62 to approximately 30° and approximately 40°, respectively.approximately 55°, both the effect of increasing the volume of the thinning pocket and the effect of reducing the chip shape can be efficiently improved and optimized.

[0042] Furthermore, the present disclosure can be expressed as follows.

[0043] [1] Cutting tool comprising: a drill body rotated about a central axis; four or more cutting edges formed on an end portion of the drill body so as to face a front side of a rotation direction; a chip groove formed between the cutting edges adjacent to each other in a circumferential direction and extending substantially spirally along the central axis; and a thinning portion formed at a tip of the chip groove and having a first thinning disposed on a flank surface side of the cutting edges and a second thinning disposed from the first thinning toward the chip groove, where the one end portion has a first tip portion containing the central axis and forming a first tip angle, and a second tip portion extending from the first tip portion to an outer peripheral edge of the drill body and forming a second tip angle that is greater than the first tip angle, the drill body has a first core thickness portion formed in such a manner that its core thickness gradually decreases from one end portion to the other end portion, and a second core thickness portion formed in such a manner that its core thickness is constant from the first core thickness portion to the other end portion, and the first thinning has a penetration angle and an opening angle that are greater than a penetration angle and an opening angle of the second thinning.

[0044] [2] The cutting tool described in [1] above, wherein the first tip portion is formed to be a part extending from the central axis to approximately 20% of a radius of the drill body, the first apex angle is approximately 120°, and the second apex angle is approximately 140°.

[0045] [3] The cutting tool described in [1] or [2] above, wherein the first core thickness portion has a core thickness of approximately 35% of a diameter of the drill body at an outer circumferential seam position of the one end portion and a core thickness taper formed in such a manner that the core thickness decreases by approximately -2% from the outer circumferential seam position of the one end portion to a position at a distance approximately twice as large as the diameter of the drill body to the other end portion.

[0046] [4] The cutting tool described in [1] or [2], wherein the penetration angle and the opening angle of the first thinning are approximately 40° and approximately 60°, respectively, and the penetration angle and the opening angle of the second dilution are approximately 30° and approximately 55°, respectively.

Claims

[1] Cutting tool comprising: a drilling body (1) which is rotated about a central axis (P); four or more cutting edges (3, 5) formed on an end portion (10) of the drill body (1) so as to face a front side of a rotation direction; a chip groove (2) formed between the cutting edges (3, 5) adjacent to one another in a circumferential direction and extending substantially spirally along the central axis (P), wherein the one end portion (10) has a first tip portion (11) containing the central axis (P) and forming a first tip angle (θ11), and a second tip portion (12) extending from the first tip portion (11) to an outer peripheral edge of the drill body (1) and forming a second tip angle (θ12) which is greater than the first tip angle (θ11), and the drill body (1) has a first core thickness portion (13) which is formed in such a way that its core thickness gradually decreases from one end portion (10) to the other end portion (20), and a second core thickness portion (14) which is formed in such a way that its core thickness is constant from the first core thickness portion (10) to the other end portion (20), and a thinning portion (6) formed at a tip of the chip flute (2) and having a first thinning (61) arranged on a flank surface side of the cutting edges (3, 5) and a second thinning (62) arranged from the first thinning (61) to the chip flute (2), wherein the first thinning (61) has a penetration angle (θ21) and an opening angle (θ31) that are larger than a penetration angle (θ22) and an opening angle (θ32) of the second thinning (62). [2] Cutting tool according to claim 1, wherein the first tip portion is formed in (11) in such a way that it is a part extending from the central axis (P) to approximately 20% of a radius (R) of the drill body (1), the first apex angle (θ11) is approximately 120°, and the second tip angle (θ12) is approximately 140°. [3] Cutting tool according to claim 1 or 2, wherein the first core thickness portion (13) has a core thickness of approximately 35% of a diameter (φ) of the drill body (1) at an outer circumferential seam position (10g) of the one end portion (10) and a core thickness taper (ST) formed in such a manner that the core thickness decreases by approximately -2% from the outer circumferential seam position (10g) of the one end portion (10) to a position at a distance approximately twice the diameter (φ) of the drill body (1) to the other end portion (20). [4] Cutting tool according to claim 1, wherein the penetration angle (θ21) and the opening angle (θ31) of the first dilution (61) are approximately 40° and approximately 60°, respectively, and the penetration angle (θ22) and the opening angle (θ32) of the second dilution (62) are approximately 30° and approximately 55°, respectively.

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