A rotatable cutting head having a radially extending cutting edge at its tip and forming a cutting outer shape with concave and convex cutting sub-parts.

Abstract

The cutting head rotatable about a central axis includes a tip portion and an intermediate portion. The tip portion has an axially forward-most point contained within the central axis and at least two axially forward facing front faces, each front face having a radially extending cutting edge. The intermediate portion has at least two head lands circumferentially alternating with at least two chip discharge passages, each head land having a leading edge extending axially rearward from the tip portion. The cutting edges are contained within an imaginary annular ring surface, and a first imaginary radial plane containing the central axis intersects the imaginary annular ring surface to form two imaginary radial cutting profiles. Each imaginary radial cutting profile has first, second and third cutting profile portions extending continuously radially outward, the second cutting profile portion including first and second concave subportions spaced apart by a first convex subportion.

Description

Technical Field

[0001] The present invention relates to a rotatable cutting head having a radially extending cutting edge at its tip portion for general use in metal cutting operations, and in particular for drilling operations.

Background Art

[0002] In the field of cutting tools used in drilling operations, there are several examples of rotatable cutting heads having a radially extending cutting edge at their tip portion and forming a cutting profile with a stepped sub - portion.

[0003] US2011 / 0116884A1 discloses a spiral bit tool including a bit - head having a plurality of spiral components. Each spiral component has a cross - cutting edge facing the cutting operation direction. The surface of the cross - cutting edge facing the cutting operation direction forms a cutting surface. The back surface of the cutting surface forms a post - cutting surface. A step region is formed on the upper surface of the bit - head, and in the step region, one or more steps are formed whose height gradually decreases from the center of the upper surface to the outer surface. The outer peripheral portion of all steps is inclined with respect to the outer peripheral portion of the bit - head. In some embodiments, an arcuate groove associated with each step may also exist. Due to such steps and grooves, the profile of each cross - cutting edge is discontinuous and thus not smoothly curved. A chamfered surface is formed at the location where the post - cutting surface connects to the step region and the upper surface of the bit - head. A straight cutting surface is formed on the side of the chamfered surface near the center of the upper surface. The intersection of the chamfered surface, the step region and the upper surface of the bit - head forms a post - cutting edge. The intersection line between the straight cutting surface and the step region forms a chisel on its back side.

[0004] WO2013 / 143348A1 discloses a twist drill for drilling micro-holes in high-strength and high-hardness alloy materials, the twist drill comprising a blade back, a twist drill body, a main cutting edge, and a side cutting edge. The main cutting edge mainly consists of a multi-stage beveled edge, a multi-stage flat edge, a multi-stage guide edge, a boring edge, a boring and finishing edge, an inner edge formed after chisel edge thinning, and a chisel edge, all connected to each other. Again, due to these stages, the outer shape of each side cutting edge is discontinuous and therefore not smoothly curved. [Overview of the project] [Problems that the invention aims to solve]

[0005] One objective of the present invention is to provide an improved rotatable cutting head having a tip portion configured to smoothly penetrate a workpiece.

[0006] Another objective of the present invention is to provide an improved rotatable cutting head having a tip portion configured to perform drilling operations while reducing cutting edge stress.

[0007] A further objective of the present invention is to provide an improved rotatable cutting head having a tip that can be manufactured efficiently and accurately. [Means for solving the problem]

[0008] According to the present invention, a cutting head is provided that is rotatable about a central axis in the rotational direction, the central axis defines the front-to-rear axis direction, The cutting head comprises a tip section and an intermediate section. The tip portion has an axially forward tip point contained within the central axis, and at least two axially forward-facing front surfaces forming at least one chisel edge, At least one chisel edge extends from or includes the tip. At least one chisel edge has at least two radially outermost chisel ends, Each front surface has a cutting edge that extends radially outward from one of the final points of the radially outermost chisel, The intermediate portion has at least two chip discharge passages and at least two head lands that are alternating in the circumferential direction. Each headland has a leading edge that extends axially rearward from the tip portion. Each chip discharge passage has a head groove, The head groove extends axially backward from the tip and intersects one of the leading edges. Each leading edge has an axially forward endpoint, At least two axial foremost endpoints define the virtual cutting circle, The virtual cutting circle has a center that coincides with the cutting diameter and the central axis. At least two cutting edges are contained within a virtual annular ring plane that exhibits circular symmetry around the central axis, In a cross-section taken with a first virtual radial plane that includes the central axis and intersects the virtual annular ring surface, the virtual annular ring surface forms two virtual radially cut outer shapes, each virtual radially cut outer shape including a first cut outer shape portion, a second cut outer shape portion, and a third cut outer shape portion that continuously extend radially outward. Each first cut outer shape portion has a first radially innermost endpoint and a first radially outermost endpoint, and extends radially outward and axially backward away from the central axis. Each second cut outer portion has a second radially innermost endpoint and a second radially outermost endpoint, and includes a first concave sub-portion and a second concave sub-portion separated by a first convex sub-portion. The entire second concave sub-part is located radially outward and axially rearward of the entire first concave sub-part. The first virtual line is tangent to any point along one of the second cut outer contours, The first virtual line is either perpendicular to the central axis or inclined radially outward and axially backward away from the central axis.

[0009] For a better understanding, the present invention will now be described merely by way of example with reference to the accompanying drawings. In the drawings, the dashed lines represent the cutting boundary lines of the partial views of the members.

Brief Description of the Drawings

[0010] [Figure 1] It is a perspective view of a cutting head according to the present invention. [Figure 2] It is a top view of the cutting head shown in FIG. 1. [Figure 3] It is a side view of the cutting head shown in FIG. 1. [Figure 4] It is a cross-sectional view of the cutting head shown in FIG. 2 taken along line IV-IV. [Figure 5] It is a detailed cross-sectional view of the cutting head shown in FIG. 4. [Figure 6] It is a cross-sectional view of the cutting head shown in FIG. 2 taken along line VI-VI. [Figure 7] It is a cross-sectional view of the cutting head shown in FIG. 2 taken along line VII-VII. [Figure 8] It is a perspective view of a rotary cutting tool according to the present invention. [Figure 9] It is an exploded view of the rotary cutting tool shown in FIG. 8.

Modes for Carrying Out the Invention

[0011] First, attention is drawn to FIGS. 1 to 3. FIGS. 1 to 3 show a cutting head 20 that is rotatable about a central axis A1 in a rotational direction RD and includes a tip portion 22 and an intermediate portion 24.

[0012] The central axis A1 defines a front-rear axis direction DF, DR.

[0013] In some embodiments of the present invention, the cutting head 20 can be manufactured by shaping and sintering a cemented carbide such as tungsten carbide, and may or may not be coated.

[0014] As shown in FIGS. 1 to 3, the tip portion 22 has an axially foremost tip point NT included within the central axis A1 and at least two axially forward-facing front surfaces 26 that form at least one chisel edge 28, and at least one chisel edge 28 extends from the tip point NT or includes the tip point NT.

[0015] Also, as shown in FIGS. 1 to 3, at least one chisel edge 28 has at least two radially outermost chisel end points NRC.

[0016] In some embodiments of the present invention, at least two radially outermost chisel end points NRC may define a first virtual circle C1, and the first virtual circle C1 has a first cutting diameter D1 and a center that coincides with the central axis A1.

[0017] Also, in some embodiments of the present invention, as shown in FIGS. 1 to 3, the tip portion 22 may have a single chisel edge 28 that is orthogonal to the central axis A1 and includes the tip point NT, and the single chisel edge 28 may have two radially outermost chisel end points NRC.

[0018] In other embodiments of the present invention (not shown), the tip portion 22 may have at least two chisel edges that extend axially rearwardly away from the tip point NT, and each chisel edge has a single radially outermost chisel end point.

[0019] As shown in FIGS. 1 to 3, each front surface 26 has a cutting edge 30 that extends radially outwardly from one of the radially outermost chisel end points NRC.

[0020] In some embodiments of the present invention, the tip portion 22 may have exactly two front surfaces 26 and exactly two cutting edges 30.

[0021] Also, in some embodiments of the present invention, each cutting edge 30 may have a radially inner secondary cutting edge portion 32 and a primary cutting edge portion 34 that extends radially outwardly directly from the secondary cutting edge portion 32 or via a transitional cutting edge portion 36.

[0022] As shown in Figure 2, in the embodiment of the present invention in which the primary cutting edge portion 32 and primary cutting edge portion 34 of each cutting edge 30 are separated by the transition cutting edge portion 36, in the front view of the cutting head 20, each transition cutting edge portion 36 can be convex, that is, each transition cutting edge portion 36 can be convex.

[0023] As shown in Figures 1 to 3, each front surface 26 may include a primary relief surface 38 and a secondary relief surface 40 adjacent to the respective primary cutting edge portion 34 and secondary cutting edge portion 32.

[0024] Furthermore, as shown in Figures 1 to 3, the intermediate portion 24 has at least two chip discharge passages 44 and at least two head lands 42 that are alternating in the circumferential direction, each head land 42 having a leading edge 46 that extends axially rearward from the tip portion 22, and each chip discharge passage 44 has a head groove 48 that extends axially rearward from the tip portion 22 and intersects one of the leading edges 46.

[0025] In some embodiments of the present invention, each primary cutting edge portion 34 may be formed at the intersection of one of the head grooves 48 and one of the primary relief surfaces 38.

[0026] As shown in Figures 1 to 3, each chip discharge passage 44 may have a cutting groove 50, which extends axially rearward from the tip portion 22 and intersects with one of the head grooves 48.

[0027] In some embodiments of the present invention, each secondary cutting edge portion 32 may be formed at the intersection of one of the cutting grooves 50 and one of the secondary relief surfaces 40.

[0028] As shown in Figures 1 to 3, each leading edge 46 has an axial foremost endpoint NFA, and at least two axial foremost endpoint NFAs define a virtual cutting circle CC, the virtual cutting circle CC having a cutting diameter DC and a center that coincides with the central axis A1.

[0029] In some embodiments of the present invention, the cutting head 20 may exhibit twofold rotational symmetry about the central axis A1.

[0030] As shown in Figures 1 to 3, at least two cutting edges 30 are contained within a virtual annular ring surface SA that exhibits circular symmetry around the central axis A1.

[0031] It should be understood that the virtual annular ring surface SA generally defines the three-dimensional shape of a frustum of a cone.

[0032] Therefore, when each cutting edge 30 is rotated 360° around the central axis A1, it traces the same virtual three-dimensional annular ring surface SA.

[0033] As shown in Figure 4, in a cross-section taken at a first virtual radial plane PR1 that includes the central axis A1 and intersects the virtual annular ring surface SA, the virtual annular ring surface SA forms two virtual radial cutting outer shapes PRC, each virtual radial cutting outer shape PRC including a first cutting outer shape portion PCP1, a second cutting outer shape portion PCP2, and a third cutting outer shape portion PCP3 that continuously extend radially outward.

[0034] In this case, it should be understood that each virtual radial cutting outline PRC is a circumferential projection of the cutting edge 30 on the first virtual radial plane PR1. Also, it should be noted that the cutting outline portions PCP1, PCP2, and PCP3 that constitute a given radial cutting outline PRC do not necessarily correspond to the primary cutting edge portion 34, secondary cutting edge portion 32, and transitional cutting edge portion 36 of the associated cutting edge 30.

[0035] The first virtual radial plane PR1 can intersect the virtual annular ring surface SA at any rotational position, but for the sake of understanding Figures 4 and 5, Figure 2 shows the first virtual radial plane PR1 intersecting the front surface 26 of the tip portion.

[0036] As shown in Figure 4, in the cross-section taken along the first virtual radial plane PR1, the two virtual radial cutting outer shapes PRC exhibit mirror symmetry around the central axis A1.

[0037] As shown in Figures 4 and 5, each first cut outer shape portion PCP1 has a first radial innermost endpoint NRI1 and a first radial outermost endpoint NROl, and each first cut outer shape portion PCP1 extends radially outward and axially backward away from the central axis A1.

[0038] In some embodiments of the present invention, each first cut outer shape portion PCP1 may extend linearly radially outward and axially backward away from the central axis A1.

[0039] As shown in Figure 5, each first cut outer shape portion PCP1 can form a first acute inclination angle α1 with respect to the central axis A1.

[0040] In some embodiments of the present invention, the first inclination angle α1 may have a minimum value of 45 degrees and a maximum value of 70 degrees, i.e., 45° ≤ α1 ≤ 70°.

[0041] Furthermore, in some embodiments of the present invention, the two first radial innermost endpoints NRI1 may lie on a first virtual circle C1.

[0042] As shown in Figures 4 and 5, each second cut outer shape portion PCP2 has a second radial innermost endpoint NRI2 and a second radial outermost endpoint NRO2, and includes a first concave sub-part CCV1 and a second concave sub-part CCV2 separated by a first convex sub-part CVX1.

[0043] In some embodiments of the present invention, each of the first concave sub-part CCV1 and the second concave sub-part CCV2 can be curved.

[0044] In some embodiments of the present invention, the first convex sub-part CVX1 may also be curved.

[0045] Furthermore, in some embodiments of the present invention, each first convex sub-part CVX1 may be adjacent to an adjacent first concave sub-part CCV1 and a second concave sub-part CCV2 in a tangent manner.

[0046] It should be understood that configuring each first cutting outer shape portion PCP1 to extend radially outward and axially rearward away from the central axis A1, and configuring each second cutting outer shape portion PCP2 to include the first concave sub-part CCV1 and the second concave sub-part CCV2 separated by the first convex sub-part CVX1, is advantageous in promoting the smooth penetration of the tip portion 22 into the workpiece.

[0047] As shown in Figures 1 to 5, the first concave sub-part CCV1 of each virtual radial cutting outer shape PRC can be completely defined by the secondary cutting edge portion 32, and the first convex sub-part CVX1 of each virtual radial cutting outer shape PRC can be at least partially defined by the secondary cutting edge portion 32.

[0048] In some embodiments of the present invention, as shown in Figure 2, each secondary cutting edge portion 32 in the front view of the cutting head 20 can be a straight line.

[0049] As shown in Figures 1 to 5, the second concave sub-part CCV2 of each virtual radial cutting outer shape PRC can be at least partially defined by the primary cutting edge portion 34.

[0050] In some embodiments of the present invention, each primary cutting edge portion 34 may rotate such that each primary cutting edge portion 34 extends radially outward and backward.

[0051] It should be understood that in order to achieve the desired configuration of the second machined outer shape portion PCP2, the primary flank surface 38 and the secondary flank surface 40 can be produced by a fairly precise manufacturing method.

[0052] In some embodiments of the present invention, the primary flank surface 38 and the secondary flank surface 40 can be generated by complex grinding processes.

[0053] In some embodiments of the present invention, each first radial outermost endpoint NRO1 may coincide with a second radial innermost endpoint NRI2 of an adjacent second cut outer shape portion.

[0054] As shown in FIG. 2, the two second radially innermost end points NRI2 are on a second virtual circle C2, and the second virtual circle C2 has a second diameter D2 and a center that coincides with the central axis A1.

[0055] In some embodiments of the present invention, the second diameter D2 can be between 10 and 30 percent of the cutting diameter DC, that is, DC×0.10 < D2 < DC×0.30.

[0056] As shown in FIG. 2, the two second radially outermost end points NRO2 are on a third virtual circle C3, and the third virtual circle C3 has a third diameter D3 and a center that coincides with the central axis A1.

[0057] In some embodiments of the present invention, the third diameter D3 can be between 40 and 60 percent of the cutting diameter DC, that is, DC×0.40 < D3 < DC×0.60.

[0058] Also, in some embodiments of the present invention, the difference between the third diameter D3 and the second diameter D2 can exceed 25 percent of the cutting diameter DC, that is, D3 - D2 > DC×0.25.

[0059] In the embodiments of the present invention where the difference between the third diameter D3 and the second diameter D2 exceeds 25 percent of the cutting diameter DC, it should be understood that the second cutting profile portion PCP2 significantly contributes to providing a smooth penetration of the tip portion 22 into the workpiece.

[0060] As shown in FIG. 5, the entire second concave sub - portion CCV2 is located radially outside and axially rearward of the first concave sub - portion CCV1.

[0061] Also, as shown in FIG. 4, the first virtual line L1 is tangent to an arbitrary point along one of the second cutting profile portions PCP2, and the first virtual line L1 is perpendicular to the central axis A1 or is inclined radially outward and axially rearward away from the central axis A1. Or, in other words, the first virtual line L1 does not incline radially outward and axially forward away from the central axis A1.

[0062] It should be understood that, by configuring each second cutting outline PCP2 such that the first virtual line L1 is tilted radially outward and axially forward away from the central axis A1, it is advantageous that each second cutting outline PCP2 does not have an axial "recess," and therefore there is no high cutting edge stress associated with this recess during the drilling operation.

[0063] It should be understood that configuring each second machined outer shape portion PCP2 without axial "indentations" along its length is advantageous in improving the manufacturability of the primary flank 38 and the secondary flank 40.

[0064] In some embodiments of the present invention, as shown in Figure 4, a second virtual line L2 perpendicular to the central axis A1 and intersecting at any one point of the second cut shape portion PCP2 crosses the second cut shape portion PCP2 only once.

[0065] As shown in Figure 5, the third virtual line L3 simultaneously tangent to the first positive contact point NT1 and the second positive contact point NT2 along the first concave sub-part CCV1 and the second concave sub-part CCV2 of the virtual radial cutting outer shape PRC, respectively, and the third virtual line L3 can form a second acute inclination angle α2 with respect to the central axis A1.

[0066] In some embodiments of the present invention, the second inclination angle α2 may have a minimum value of 55 degrees and a maximum value of 80 degrees, i.e., 55° ≤ α2 ≤ 80°.

[0067] Furthermore, in some embodiments of the present invention, the first inclination angle α1 may be less than the second inclination angle α2, i.e., α1 < α2.

[0068] It should be understood that configuring the first inclination angle α1 to be less than the second inclination angle α2 is advantageous in that it promotes accurate centering, combined with smooth penetration of the tip portion 22 into the workpiece.

[0069] Furthermore, in some embodiments of the present invention, apart from the first positive contact point NT1 and the second positive contact point NT2, the entire associated virtual radially cutting outer profile PRC may be located on one side of the third virtual straight line L3.

[0070] As shown in FIG. 5, the first concave sub - portion CCV1 and the second concave sub - portion CCV2 each have a first concave radius RCV1 and a second concave radius RCV2.

[0071] In some embodiments of the present invention, each of the first concave radius RCV1 and the second concave radius RCV2 may be less than 50 percent of the cutting diameter DC, that is, RCV1 < DC×0.15, RCV2 < DC×0.15.

[0072] Also, in some embodiments of the present invention, each of the first concave radius RCV1 and the second concave radius RCV2 may be constant.

[0073] Furthermore, in some embodiments of the present invention, each of the first concave radius RCV1 and the second concave radius RCV2 may be less than 3.0 mm.

[0074] As shown in FIG. 5, the first concave sub - portion CCV1 and the second concave sub - portion CCV2 each have a first angular range EA1 and a second angular range EA2.

[0075] In some embodiments of the present invention, the second angular range EA2 may exceed the first angular range EA1.

[0076] Also, in some embodiments of the present invention, the second angular range EA2 may exceed 30 degrees, that is, EA2 > 30°.

[0077] As shown in FIG. 5, the first convex sub - portion CVX1 has a first convex radius RCX1.

[0078] In some embodiments of the present invention, the first convex radius RCX1 may exceed each of the first concave radius RCV1 and the second concave radius RCV2, that is, RCX1 > RCV1, RCX1 > RCV2.

[0079] Also, in some embodiments of the present invention, the first convex radius RCX1 may be less than 30 percent of the cutting diameter DC, that is, RCX1 < DC × 0.30.

[0080] Furthermore, in some embodiments of the present invention, the first convex radius RCX1 may be constant.

[0081] Still further, in some embodiments of the present invention, the first convex radius RCX1 may be less than 6.0 mm.

[0082] As shown in FIG. 5, the first convex sub - portion CVX1 has a third angular range EA3.

[0083] In some embodiments of the present invention, the third angular range EA3 may exceed 30 degrees, that is, EA3 > 30°.

[0084] Also, in some embodiments of the present invention, the third angular range EA3 may exceed the first angular range EA1.

[0085] Furthermore, in some embodiments of the present invention, the third angular range EA3 may be equal to the second angular range EA2.

[0086] It should be understood that in embodiments of the present invention where the first convex radius RCX1 exceeds each of the first concave radius RCV1 and the second concave radius RCV2, and the third angular range EA3 exceeds 30 degrees, the first convex sub - portion CVX1 significantly contributes to providing smooth penetration of the tip portion 22 into the workpiece.

[0087] As shown in Figure 4, the fourth virtual line L4 is tangent to any point along one of the virtual radial cutting outlines PRC, and the fourth virtual line L4 may be perpendicular to the central axis A1, or it may be inclined radially outward and axially backward away from the central axis A1. In other words, the fourth virtual line L4 is not inclined radially outward and axially forward away from the central axis A1.

[0088] It should be understood that if each virtual radial cutting profile PRC is configured such that the fourth virtual straight line L4 is tilted radially outward and axially forward away from the central axis A1, then, advantageously, each virtual radial cutting profile PRC will not have an axial "indentation," and the high cutting edge stress associated with this indentation will be eliminated during the drilling operation.

[0089] It should be understood that configuring each virtual radial cutting outer shape PRC so that there are no axial "indentations" along its length is advantageous in that it improves the manufacturability of the primary relief surface 38 and the secondary relief surface 40.

[0090] It should be further understood that the fourth virtual line L4 can correspond to the first virtual line L1 if it is tangent to the same point on the related second cut-out portion PCP2.

[0091] In some embodiments of the present invention, the fifth virtual line L5 is perpendicular to the central axis A1 and intersects at any point along one of the virtual radial cutting outlines PRC, and the fifth virtual line L5 may traverse the virtual radial cutting outline PRC only once.

[0092] It should be understood that the fifth virtual line L5 can correspond to the second virtual line L2 if it intersects the same point on the related second cutting outline portion PCP2.

[0093] As shown in Figures 4 and 5, each third cut outer shape portion PCP3 has a third radial innermost endpoint NRI3 and a third radial outermost endpoint NRO3.

[0094] In some embodiments of the present invention, each third radial innermost endpoint NRI3 may coincide with the second radial outermost endpoint NRO2 of an adjacent second cut outer shape portion.

[0095] Furthermore, in some embodiments of the present invention, two third radial outermost endpoints NRO3 may lie on a virtual cutting circle CC.

[0096] The first radial innermost endpoint NRI1 of each first cutting profile PCP1 may coincide with the radial innermost point NRI1 of the associated radial cutting profile PRC. On the other hand, the third radial outermost endpoint NRO3 of each third cutting profile PCP3 may coincide with the radial outermost point NRO3 of the associated radial cutting profile PRC. As shown in Figures 1 to 5, in a cross section taken in the first virtual radial plane PR1 containing the central axis A1, each virtual radial cutting profile PRC extends monotonically in the axial rearward direction DR between the radial innermost endpoint NRI1 and the radial outermost endpoint NRO3. In other words, in the radial outward direction, each virtual radial cutting profile PRC is always perpendicular to the central axis A1 or extends in the axial rearward direction.

[0097] Each virtual radial cutting profile PRC extends monotonically in the axial rearward direction DR and can also curve smoothly between the innermost radial endpoint NRI1 and the outermost radial endpoint NRO3. In other words, each virtual radial cutting profile PRC does not need to have discontinuities such as those caused by steps of the type seen in US2011 / 0116884A1 and WO2013 / 143348A1 described above. Therefore, the angle of the tangent along the length of a given virtual radial cutting profile PRC changes gradually rather than through discontinuous discontinuities caused by such steps.

[0098] As shown in Figures 4 and 5, the circumferential projections of each cutting edge 30 on the first virtual radial plane PR1 form a virtual radial cutting outline PRC, which may have a radial innermost endpoint NRI1 on the first virtual circle C1 and a radial outermost endpoint NRO3 on the cutting circle CC. Furthermore, between the radial innermost endpoint NRI1 and the radial outermost endpoint NRO3, each virtual radial cutting outline PRC includes two concave sub-parts CCV1 and CCV2 separated by a first convex sub-part CVX1.

[0099] As shown in Figures 4 and 5, each third cut outer shape portion PCP3 may extend continuously radially outward and axially backward away from the central axis A1.

[0100] In some embodiments of the present invention, each third cut outer shape portion PCP3 may be convex.

[0101] As shown in Figure 5, the sixth virtual line L6 is tangent to the third positive tangency NT3 along one of the third cutting outer shape portions PCP3 adjacent to the third radial outermost endpoint NRO3, and the sixth virtual line L6 can form a third acute inclination angle α3 with the central axis A1.

[0102] In some embodiments of the present invention, the third inclination angle α3 may have a minimum value of 60 degrees and a maximum value of 80 degrees, i.e., 60° ≤ α3 ≤ 80°.

[0103] It should be understood that configuring each third cutting outer shape portion PCP3 such that the third inclination angle α3 exceeds 60 degrees enables drilling blind holes into the workpiece with a wide entry angle exceeding 120 degrees, which may be advantageous for subsequent drilling of smaller diameter holes along the same hole axis.

[0104] Furthermore, in some embodiments of the present invention, the third inclination angle α3 may exceed the first inclination angle α1, i.e., α3 > α1.

[0105] As shown in Figures 1 to 3, the primary rake face 52 is the primary cutting edge portion 3 4 They can be arranged on each adjacent head groove 48.

[0106] As shown in Figure 6, in a first transverse plane PT1 that is parallel to the central axis A1 and intersects one of the primary cutting edge portions 34, the primary rake face 52 may be inclined with a first axial rake angle β1 with respect to a first virtual vertical reference line VL1 that is parallel to the central axis A1.

[0107] In some embodiments of the present invention, the first axial rake angle β1 can be positive.

[0108] Throughout this specification and the claims, it should be understood that in a configuration in which the primary rake face 52 rotates and extends backward so that the primary rake face 52 extends away from the associated primary cutting edge portion 34, the first axial rake angle β1 is positive.

[0109] It should be understood that the primary cutting edge portion 34 is more susceptible to wear than the secondary cutting edge portion 32 due to the relatively higher cutting speed, and that the configuration in which the primary rake face 52 is positive reduces wear on the primary cutting edge portion 34 and therefore extends the operating life of the primary cutting edge portion 34.

[0110] As shown in Figure 6, in a cross-section taken in the first transverse plane PT1, the primary relief surface 38 may be inclined with respect to a first virtual horizontal reference line HL1 perpendicular to the central axis A1 at a first relief angle λ1.

[0111] In some embodiments of the present invention, the first relief angle λ1 may have a nominal value between 5 and 12 degrees, i.e., 5° < λ1 < 12°.

[0112] Throughout this specification and the claims, it should be understood that in any cross-section taken in a transverse plane intersecting one of the primary cutting edge portions 34, the adjacent primary relief surface 38 extends axially backward such that the primary relief surface 38 extends away from the primary cutting edge portion 34.

[0113] In some embodiments of the present invention, the first relief angle λ1 is the primary cutting edge portion. 34 It can be kept constant along its length.

[0114] As shown in Figures 1 to 3, the secondary rake face 54 is positioned on each cutting groove 50 adjacent to the associated secondary cutting edge portion 32.

[0115] As shown in Figure 7, in a second transverse plane PT2 that is parallel to the central axis A1 and intersects one of the secondary cutting edge portions 32, the secondary rake face 54 may be inclined with a second axial rake angle β2 with respect to a second virtual vertical reference line VL2 that is parallel to the central axis A1.

[0116] In some embodiments of the present invention, the second axial rake angle β2 may be negative.

[0117] Throughout this specification and the claims, it should be understood that in a configuration in which the secondary rake face 54 rotates so that it extends away from the secondary cutting edge portion 32 and extends backward, the second axial rake angle β2 is negative.

[0118] It should be understood that the secondary cutting edge portion 32 is more susceptible to impact forces than the primary cutting edge portion 34, especially due to the relatively slower cutting speed at high feed rates, and that the configuration with a negative secondary axial rake angle β2 increases the stability and robustness of the secondary cutting edge portion 32, and therefore extends the operating life of the secondary cutting edge portion 32.

[0119] As shown in Figure 7, in the cross section taken in the second transverse plane PT2, the secondary relief surface 40 may be inclined with a second relief angle λ2 with respect to a second virtual horizontal reference line HL2 perpendicular to the central axis A1.

[0120] In some embodiments of the present invention, the second relief angle λ2 may have a nominal value between 5 and 12 degrees, i.e., 5° < λ2 < 12°.

[0121] Throughout this specification and the claims, it should be understood that in any cross-section taken in a transverse plane intersecting one of the secondary cutting edge portions 32, the adjacent secondary relief surface 40 extends axially backward such that the secondary relief surface 40 extends away from the secondary cutting edge portion 32.

[0122] In some embodiments of the present invention, the second relief angle λ2 can be constant along the length of the secondary cutting edge portion 32.

[0123] Furthermore, in some embodiments of the present invention, the second relief angle λ2 may be equal to the first relief angle λ1, i.e., λ2 = λ1.

[0124] It should be understood that the first relief angle λ1 and the second relief angle λ2 may have an accuracy of either more than 1 degree above the nominal value or less than 1 degree below the nominal value.

[0125] Next, please turn your attention to Figures 8 and 9, which show a rotary cutting tool 56 according to the present invention. The rotary cutting tool 56 comprises a cutting head 20 and a shank 58 having a longitudinal axis AL. The shank 58 has two shank lands 62 and two shank grooves 60 that are alternate in the circumferential direction, and each shank groove 60 may extend helically along the longitudinal axis AL.

[0126] As shown in Figures 8 and 9, the cutting head 20 may have an axially rearward-facing bottom surface 64, the shank 58 may have a support surface 66 that transverses the longitudinal axis AL, and the cutting head 20 may be detachably assembled to the shank 58 with the bottom surface 64 in contact with the support surface 66.

[0127] The configuration in which the cutting head 20 is detachably assembled to the shank 58 allows the cutting head 20 to be manufactured from a sufficiently hard material such as tungsten carbide, and the shank 58 to be manufactured from a less hard and less expensive material such as high-speed steel. The shank 58 can be reused after the worn or damaged cutting head 20 has been disposed of.

[0128] In some embodiments of the present invention, each head groove 48 may intersect the bottom surface 64 and cooperate with one of the shank grooves 60.

[0129] Furthermore, in some embodiments of the present invention, the bottom surface 64 may be perpendicular to the central axis A1, the support surface 66 may be perpendicular to the longitudinal axis AL, and the central axis A1 may be coaxial with the longitudinal axis AL.

[0130] As shown in Figures 8 and 9, the intermediate portion 24 of the cutting head 20 may include at least two torque transmission surfaces 68 facing opposite directions of rotation RD, the shank 58 may include at least two drive projections 70, each drive projection 70 having a drive surface 72 facing the direction of rotation RD, and each torque transmission surface 68 may be in contact with one of the drive surfaces 72.

[0131] In some embodiments of the present invention, each torque transmission surface 68 may intersect one of the front surfaces 26.

[0132] As shown in Figures 8 and 9, the cutting head 20 may include an assembly projection 74 that extends axially rearward from the bottom surface 64.

[0133] In other embodiments of the present invention (not shown), the cutting head 20 and shank 58 may be a single, integrated component, such as a solid drill, with each head groove 4 8 may be merged with one of the shank grooves 60.

[0134] Although the present invention has been described in some detail, please understand that various forms of modification and alteration can be made without departing from the spirit or scope of the invention as claimed below.

Claims

1. A cutting head (20) that is rotatable around a central axis (A1) in the rotational direction (RD), The aforementioned central axis (A1) defines the front-to-rear axis direction (DF, DR), The cutting head (20) comprises a tip portion (22) and an intermediate portion (24), The tip portion (22) has an axially forward tip point (NT) contained within the central axis (A1), and at least two axially forward-facing front surfaces (26) that form at least one chisel edge (28). The at least one chisel edge (28) extends from or includes the axial foremost tip (NT), The at least one chisel edge (28) has at least two radially outermost chisel termination points (NRCs), Each of the aforementioned front surfaces (26) has a cutting edge (30) that extends radially outward from one of the radially outermost chisel termination points (NRC), The intermediate portion (24) has at least two chip discharge passages (44) and at least two head lands (42) that are alternating in the circumferential direction. Each head land (42) has a leading edge (46) that extends axially rearward from the tip portion (22), Each of the chip discharge passages (44) has a head groove (48), The head groove (48) extends axially rearward from the tip portion (22) and intersects with one of the leading edges (46), Each of the leading edges (46) has an axial forward end point (NFA), At least two of the aforementioned axial foremost endpoints (NFAs) define a virtual cutting circle (CC), The virtual cutting circle (CC) has a center that coincides with the cutting diameter (DC) and the central axis (A1), At least two of the cutting edges (30) are contained within a virtual three-dimensional annular ring surface (SA) that exhibits circular symmetry around the central axis (A1), In a cross-section taken at a first virtual radial plane (PR1) that includes the central axis (A1) and intersects the virtual three-dimensional annular ring surface (SA), the virtual three-dimensional annular ring surface (SA) forms two virtual radial cutting outer portions (PRC), and each of the virtual radial cutting outer portions (PRC) includes a first cutting outer portion (PCP1), a second cutting outer portion (PCP2), and a third cutting outer portion (PCP3) that continuously extend radially outward. Each of the first machined outer portions (PCP1) has a first radial innermost endpoint (NRI1) and a first radial outermost endpoint (NROl), and extends radially outward and axially rearward away from the central axis (A1). Each of the second machined outer shape portions (PCP2) has a second radial innermost endpoint (NRI2) and a second radial outermost endpoint (NRO2), and includes a first curved concave sub-part (CCV1) and a second curved concave sub-part (CCV2) separated by a first curved convex sub-part (CVX1). The entire second curved concave sub-part (CCV2) is located radially outward and axially rearward of the entire first curved concave sub-part (CCV1), The first virtual line (L1) tangent to any point along one of the second cut outer portions (PCP2) is either perpendicular to the central axis (A1) or inclined radially outward and axially backward away from the central axis (A1), Each cutting edge (30) has a radially inward secondary cutting edge portion (32) and a primary cutting edge portion (34). The primary cutting edge portion (34) extends radially outward from the radially inward secondary cutting edge portion (32) directly or via the transitional cutting edge portion (36), Each of the aforementioned front surfaces (26) includes a primary relief surface (38) and a secondary relief surface (40) adjacent to the respective primary cutting edge portion (34) and radially inward secondary cutting edge portion (32), The first curved concave sub-part (CCV1) of each virtual radial cutting outer shape (PRC) is completely defined by the radially inner secondary cutting edge portion (32), The first curved convex sub-part (CVX1) of each virtual radial cutting outer shape (PRC) is at least partially defined by the radially inner secondary cutting edge portion (32), In the front end view of the cutting head (20), each of the radially inner secondary cutting edge portions (32) is a straight line.

2. The third virtual straight line (L3) simultaneously tangent to the first positive tangency (NT1) and the second positive tangency (NT2) along one of the first curved concave sub-parts (CCV1) and the second curved concave sub-part (CCV2) of the virtual radial cutting outer shape (PRC), The third virtual line (L3) forms a second acute angle of inclination (α2) with the central axis (A1), The cutting head (20) according to claim 1, wherein the second acute angle of inclination (α2) has a minimum value of 55 degrees and a maximum value of 80 degrees.

3. The cutting head (20) according to claim 2, wherein the entire associated virtual radial cutting outer shape (PRC) is located on one side of the third virtual straight line (L3), separate from the first positive contact point (NT1) and the second positive contact point (NT2).

4. The first curved concave sub-part (CCV1) and the second curved concave sub-part (CCV2) each have a first concave radius (RCV1) and a second concave radius (RCV2), The cutting head (20) according to claim 1, wherein each of the first concave radius (RCV1) and the second concave radius (RCV2) is less than 15 percent of the cutting diameter (DC).

5. The first curved convex sub-part (CVX1) has a first convex radius (RCX1), The cutting head (20) according to claim 4, wherein the first convex radius (RCX1) exceeds the first concave radius (RCX1) and the second concave radius (RCV2), respectively.

6. The first curved convex sub-part (CVX1) has a third angular range (EA3), The cutting head (20) according to claim 5, wherein the third angular range (EA3) exceeds 30 degrees.

7. The two aforementioned second innermost radial endpoints (NRI2) lie on the second virtual circle (C2), The second virtual circle (C2) has a second diameter (D2) and a center that coincides with the central axis (A1), The cutting head (20) according to claim 1, wherein the second diameter (D2) is between 10 and 30 percent of the cutting diameter (DC).

8. The two aforementioned second radial outermost endpoints (NRO2) lie on the third virtual circle (C3), The third virtual circle (C3) has a third diameter (D3) and a center that coincides with the central axis (A1), The cutting head (20) according to claim 7, wherein the difference between the third diameter (D3) and the second diameter (D2) exceeds 25 percent of the cutting diameter (DC).

9. Each of the first machined outer portions (PCP1) extends linearly radially outward and axially backward away from the central axis (A1), forming a first acute inclination angle (α1) with the central axis (A1). The cutting head (20) according to claim 1, wherein the first inclination acute angle (α1) has a minimum value of 45 degrees and a maximum value of 70 degrees.

10. The cutting head (20) according to claim 1, wherein the first radial outermost endpoint (NRO1) coincides with the second radial innermost endpoint (NRI2) of the second cutting outer shape portion.

11. At least two of the radially outermost chisel endpoints (NRCs) define a first virtual circle (C1), The first virtual circle (C1) has a center that coincides with the first cutting diameter (D1) and the central axis (A1), The cutting head (20) according to claim 1, wherein the two first innermost radial ends (NRI1) lie on the first virtual circle (C1).

12. The cutting head (20) according to claim 1, wherein each of the third cutting outer shape portions (PCP3) is convex.

13. The cutting head (20) according to claim 1, wherein each of the third cutting outer shape portions (PCP3) has a third radial innermost endpoint (NRI3) and a third radial outermost endpoint (NRO3), and extends continuously radially outward and axially rearward away from the central axis (A1).

14. The cutting head (20) according to claim 13, wherein the third radial innermost endpoint (NRI3) coincides with the second radial outermost endpoint (NRO2) of the second cutting outer shape portion.

15. The sixth virtual line (L6) is tangent to the third positive tangency (NT3) along one of the third cutting outer shape portions (PCP3) adjacent to the third radial outermost end point (NRO3), The sixth virtual line (L6) forms a third acute angle of inclination (α3) with the central axis (A1), The cutting head (20) according to claim 13, wherein the third acute angle of inclination (α3) has a minimum value of 60 degrees and a maximum value of 80 degrees.

16. The cutting head (20) according to claim 13, wherein the third radial outermost endpoint (NRO3) lies on the virtual cutting circle (CC).

17. The second curved concave sub-part (CCV2) of each virtual radial cutting outer shape (PRC) is at least partially defined by the primary cutting edge portion (34), The cutting head (20) according to claim 1, wherein each primary cutting edge portion (34) extends such that it rotates backward as each primary cutting edge portion (34) moves radially outward.

18. In the front end view of the cutting head (20), each of the transition cutting edge portions (36) is convex, as described in claim 1.

19. Each of the primary cutting edge portions (34) is formed at the intersection of one of the head grooves (48) and one of the primary relief surfaces (38), The primary rake face (52) is arranged on each of the head grooves (48) adjacent to the associated primary cutting edge portion (34), In a first transverse plane (PT1) that is parallel to the central axis (A1) and intersects one of the primary cutting edge portions (34), in a cross-section taken at an arbitrary point along the length of the first transverse plane (PT1), the primary rake face (52) is inclined with respect to a first virtual vertical reference line (VL1) parallel to the central axis (A1) at a first axial rake angle (β1), The cutting head (20) according to claim 1, wherein the first axial rake angle (β1) is positive.

20. Each of the chip discharge passages (44) has a blade groove (50), The blade groove (50) extends axially rearward from the tip portion (22) and intersects with one of the head grooves (48), Each of the radially inner secondary cutting edge portions (32) is formed at the intersection of one of the cutting grooves (50) and one of the secondary relief surfaces (40), The secondary rake face (54) is arranged on each of the head grooves (50) adjacent to the associated radially inward secondary cutting edge portion (32), In a second transverse plane (PT2) that is parallel to the central axis (A1) and intersects one of the radially inner secondary cutting edge portions (32), in a cross-section taken at an arbitrary point along the length of the second transverse plane (PT2), the secondary rake face (54) is inclined with respect to a second virtual vertical reference line (VL2) parallel to the central axis (A1) at a second axial rake angle (β2), The cutting head (20) according to claim 1, wherein the second axial rake angle (β2) is negative.

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