a rotatable cutting head having a distal portion with radially extending cutting edges and defining a cutting profile having concave and convex cutting subportions;

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] FIELD OF THE DISCLOSURE The present invention relates to a rotatable cutting head having a distal end with radially extending cutting edges for use in metal cutting processes generally, and for drilling operations in particular. [Background technology]

[0002] In the field of cutting tools used in drilling operations, there are several examples of rotatable cutting heads whose leading portion has radially extending cutting edges and defines a cutting profile having a stepped sub-portion.

[0003] US2011 / 0116884A1 discloses a helical bit tool including a bit head having a plurality of helical parts. Each helical part has a side cutting edge facing in the direction of the cutting motion. The surface of the side cutting edge facing in the direction of the cutting motion forms the cutting surface. The back surface of the cutting surface forms the trailing cutting surface. A step region is formed on the top surface of the bit head, where one or more steps are formed whose height decreases from the center of the top surface to the outer surface. The periphery of all the steps is inclined relative to the periphery of the bit head. In some embodiments, there may also be an arcuate groove associated with each step. Due to such steps and grooves, the profile of each side cutting edge is discontinuous and therefore not smoothly curved. A chamfer surface is formed on where the trailing cutting surface connects with the step region and the top surface of the bit head. An upright cutting surface is formed on the side of the chamfer surface near the center of the top surface. The intersection of the chamfer surface, the step region and the top surface of the bit head forms the trailing cutting edge. The intersection of the upright cutting surface and the step area forms a chisel on the backside.

[0004] WO2013 / 143348A1 discloses a twist drill for drilling fine holes on high strength and hardness alloy materials, the twist drill comprising a blade back surface, a twist drill body, a main cutting edge and a side cutting edge. The main cutting edge is mainly composed of a multi-stepped bevel edge, a multi-stepped flat edge, a multi-stepped guiding edge, a boring edge, a boring and finishing edge, an inner edge formed after chisel edge thinning, and a chisel edge, which are connected to each other. Again, due to these steps, the profile of each side cutting edge is discontinuous and therefore not smoothly curved. Summary of the Invention [Problem to be solved by the invention]

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

[0006] It is also an object of the present invention to provide an improved rotatable cutting head having a tip portion configured to perform drilling operations with reduced cutting edge stresses.

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

[0008] In accordance with the present invention, there is provided a cutting head rotatable in a rotational direction about a central axis, the central axis defining a front-rear axial direction; The cutting head includes a tip portion and a middle portion; the tip portion has an axially forward-most 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 a tip point; At least one chisel edge has at least two radially outermost chisel end points; Each front surface has a cutting edge extending radially outward from one of the radially outermost chisel end points; the intermediate portion having at least two chip discharge passages and at least two head lands that are circumferentially alternating; Each head land has a leading edge extending axially rearward from the tip portion, Each chip discharge passage has a head groove; The head groove extends axially rearward from the tip portion and intersects one of the leading edges; Each leading edge has an axially forwardmost end point, The at least two axially forwardmost end points define an imaginary cutting circle; The imaginary cutting circle has a cutting diameter and a center that is coincident with the central axis; At least two cutting edges are included within an imaginary annular ring surface that is circularly symmetric about the central axis; in a cross section taken at a first imaginary radial plane including the central axis and intersecting the imaginary annular ring surface, the imaginary annular ring surface defines two imaginary radial cutting profiles, each imaginary radial cutting profile including a first cutting profile portion, a second cutting profile portion and a third cutting profile portion extending successively radially outward; Each first cutting profile has a first radially innermost end point and a first radially outermost end point and extends radially outward and axially aft away from the central axis; each second cutting profile portion has a second radially innermost end point and a second radially outermost end point and includes a first concave subportion and a second concave subportion spaced apart by a first convex subportion; the entire second concave sub-portion is located radially outward and axially rearward of the entire first concave sub-portion; the first imaginary line is tangent to any point along one of the second cutting contour portions; The first imaginary line is perpendicular to the central axis or inclined radially outward and axially rearward away from the central axis.

[0009] For a better understanding, the invention will now be described, purely by way of example, with reference to the accompanying drawings, in which dashed lines represent cut boundaries of partial views of elements, in which: [Brief description of the drawings]

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

[0011] Attention is directed initially to Figures 1-3, which show a cutting head 20 having a distal portion 22 and an intermediate portion 24, rotatable about a central axis A1 in a rotational direction RD.

[0012] The central axis A1 defines front-rear axial directions DF, DR.

[0013] In some embodiments of the present invention, the cutting head 20 may be manufactured by molding, pressing and sintering a hard metal such as tungsten carbide, and may be coated or uncoated.

[0014] As shown in Figures 1-3, tip portion 22 has an axially forward-most tip point NT contained within central axis A1, and at least two axially forward facing front faces 26 forming at least one chisel edge 28 extending from or including tip point NT.

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

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

[0017] Also, in some embodiments of the present invention, as shown in Figures 1-3, tip portion 22 may have a single chisel edge 28 perpendicular to central axis A1 and including a tip point NT, and single chisel edge 28 may have two radially outermost chisel termination points NRC.

[0018] In other embodiments of the invention (not shown), the tip portion 22 may have at least two chisel edges extending axially aft away from the tip point NT, each chisel edge having a single radially outermost chisel termination point.

[0019] As shown in Figures 1-3, each front face 26 has a cutting edge 30 that extends radially outward from one of the radially outermost chisel end points NRC.

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

[0021] Additionally, 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 extending radially outward from the secondary cutting edge portion 32 either directly or via a transition cutting edge portion 36.

[0022] As shown in FIG. 2, in an embodiment of the present invention in which the primary cutting edge portion 32 and the primary cutting edge portion 34 of each cutting edge 30 are separated by a transition cutting edge portion 36, in a front end view of the cutting head 20, each transition cutting edge portion 36 may be convex, i.e., each transition cutting edge portion 36 may be convex in shape.

[0023] As shown in FIGS. 1-3, each front surface 26 may include a primary clearance surface 38 and a secondary clearance surface 40 adjacent the associated primary cutting edge portion 34 and secondary cutting edge portion 32, respectively.

[0024] Also, as shown in Figures 1-3, the intermediate portion 24 has at least two head lands 42 circumferentially alternating with at least two chip discharge passages 44, each head land 42 having a leading edge 46 extending 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 clearance faces 38 .

[0026] As shown in FIGS. 1-3, each chip discharge passage 44 may have a gutter 50 that extends axially rearward from the tip portion 22 and intersects 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 clearance faces 40 .

[0028] As shown in FIGS. 1-3, each leading edge 46 has an axially forwardmost end point NFA, and the at least two axially forwardmost end points NFA define an imaginary cutting circle CC, the imaginary cutting circle CC having a cutting diameter DC and a center coincident with the central axis A1.

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

[0030] As shown in FIGS. 1 to 3, at least two cutting edges 30 are included within an imaginary annular ring surface SA that is circularly symmetric about a central axis A1.

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

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

[0033] As shown in FIG. 4, in a cross section taken at a first imaginary radial plane PR1 that includes the central axis A1 and intersects the imaginary annular ring surface SA, the imaginary annular ring surface SA forms two imaginary radial cutting contour portions PRC, each of which includes a first cutting contour portion PCP1, a second cutting contour portion PCP2, and a third cutting contour portion PCP3 that extend continuously radially outward.

[0034] In this case, it should be understood that each imaginary radial cutting profile PRC is a circumferential projection of one of the cutting edges 30 on the first imaginary radial plane PR1. It should also be noted that the cutting profile portions PCP1, PCP2, PCP3 constituting a given radial cutting profile PRC do not necessarily correspond to the respective primary cutting edge portion 34, secondary cutting edge portion 32 and transition cutting edge portion 36 of the associated cutting edge 30.

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

[0036] As shown in FIG. 4, in a cross section taken on a first imaginary radial plane PR1, the two imaginary radially cut contour portions PRC exhibit mirror symmetry about the central axis A1.

[0037] As shown in Figures 4 and 5, each first cutting contour portion PCP1 has a first radially innermost end point NRI1 and a first radially outermost end point NROL, and each first cutting contour portion PCP1 extends radially outward and axially rearward away from the central axis A1.

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

[0039] As shown in FIG. 5, each first cutting contour portion PCP1 may form a first inclined acute angle α1 with the central axis A1.

[0040] In some embodiments of the present invention, the first tilt angle α1 may have a minimum value of 45 degrees and a maximum value of 70 degrees, ie, 45°≦α1≦70°.

[0041] Also, in some embodiments of the present invention, the two first radially innermost end points NRI1 may be on the first imaginary circle C1.

[0042] As shown in Figures 4 and 5, each second cutting contour portion PCP2 has a second radially innermost end point NRI2 and a second radially outermost end point NRO2, and includes a first concave sub-portion CCV1 and a second concave sub-portion CCV2 spaced apart by a first convex sub-portion CVX1.

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

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

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

[0046] It will be appreciated that configuring each first cutting contour portion PCP1 to extend radially outward and axially rearward away from the central axis A1, and configuring each second cutting contour portion PCP2 to include the first concave sub-portion CCV1 and the second concave sub-portion CCV2 spaced apart by the first convex sub-portion CVX1, advantageously promotes smooth penetration of the tip portion 22 into the workpiece.

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

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

[0049] As shown in FIGS. 1-5, the second concave sub-portion CCV2 of each imaginary radial cutting contour PRC may 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 be rotated and extend rearward such that each primary cutting edge portion 34 extends radially outward.

[0051] It should be appreciated that the primary clearance surface 38 and the secondary clearance surface 40 may be produced by a fairly precise manufacturing method to achieve the desired configuration of the second cutting profile portion PCP2.

[0052] In some embodiments of the present invention, the primary clearance 38 and the secondary clearance 40 may be produced by a complex grinding process.

[0053] In some embodiments of the present invention, each first radially outermost end point NRO1 may coincide with a second radially innermost end point NRI2 of an adjacent second cutting profile portion.

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

[0055] In some embodiments of the present invention, the second diameter D2 can be between 10% and 30% 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 the third virtual circle C3, and the third virtual circle C3 has a center that coincides with the third diameter D3 and the central axis A1.

[0057] In some embodiments of the present invention, the third diameter D3 can be between 40% and 60% 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% 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% 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 straight line L1 is tangent to any point along one of the second cutting profile portions PCP2, and the first virtual straight 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 straight line L1 does not incline radially outward and axially forward away from the central axis A1.

[0062] It should be appreciated that by configuring each second cutting contour portion PCP2 so that the first imaginary straight line L1 is not inclined radially outward and axially forward away from the central axis A1, each second cutting contour portion PCP2 advantageously has no axial "depression" and therefore no high cutting edge stresses associated with this during the drilling operation.

[0063] It should be appreciated that configuring each second cutting profile portion PCP2 so that there are no axial “depressions” along its length advantageously improves the manufacturability of the primary clearance surface 38 and the secondary clearance surface 40.

[0064] In some embodiments of the present invention, as shown in FIG. 4, a second imaginary straight line L2 that is perpendicular to the central axis A1 and intersects any one point of the second cutting outline portion PCP2 crosses the second cutting outline portion PCP2 only once.

[0065] As shown in FIG. 5, the third imaginary straight line L3 may simultaneously be tangent to the first tangent point NT1 and the second tangent point NT2 along each of the first concave sub-portion CCV1 and the second concave sub-portion CCV2 of one of the imaginary radially cutting contour portions PRC, and the third imaginary straight line L3 may form a second inclined acute angle α2 with the central axis A1.

[0066] In some embodiments of the invention, the second tilt angle α2 may have a minimum value of 55 degrees and a maximum value of 80 degrees, ie, 55°≦α2≦80°.

[0067] Also, in some embodiments of the present invention, the first tilt angle α1 may be less than the second tilt angle α2, ie, α1<α2.

[0068] It should be appreciated that configuring the first inclination angle α1 to be less than the second inclination angle α2 advantageously 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 related virtual radial cutting 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 a smooth penetration of the tip portion 22 into the workpiece.

[0087] 4, the fourth imaginary straight line L4 is tangent to any point along one of the imaginary radially cut contours PRC, and the fourth imaginary straight line L4 may be perpendicular to the central axis A1 or may be inclined radially outward and axially rearward away from the central axis A1, or in other words, the fourth imaginary straight line L4 does not incline radially outward and axially forward away from the central axis A1.

[0088] It should be appreciated that by configuring each imaginary radial cutting contour PRC such that the fourth imaginary straight line L4 is not inclined radially outward and axially forward away from the central axis A1, each imaginary radial cutting contour PRC advantageously has no axial “depression” and the high cutting edge stresses associated with such a depression during the drilling operation.

[0089] It should also be appreciated that configuring each imaginary radially cut contour PRC to have no axial “depressions” along its length advantageously improves the manufacturability of the primary clearance 38 and secondary clearance 40.

[0090] It should further be appreciated that the fourth imaginary straight line L4 may correspond to the first imaginary straight line L1 if it is tangent to the same point of the associated second cutting contour portion PCP2.

[0091] In some embodiments of the present invention, the fifth imaginary straight line L5 is perpendicular to the central axis A1 and intersects any point along one of the imaginary radially cutting contours PRC, and the fifth imaginary straight line L5 may intersect the imaginary radially cutting contour PRC only once.

[0092] It should be understood that the fifth imaginary straight line L5 may correspond to the second imaginary straight line L2 if they intersect at the same point of the associated second cutting contour portion PCP2.

[0093] As shown in Figures 4 and 5, each third cutting contour portion PCP3 has a third radially innermost end point NRI3 and a third radially outermost end point NRO3.

[0094] In some embodiments of the invention, each third radially innermost end point NRI3 may coincide with a second radially outermost end point NRO2 of an adjacent second cutting profile portion.

[0095] Also, in some embodiments of the present invention, the two third radially outermost end points NRO3 may be on the imaginary cutting circle CC.

[0096] The first radially innermost end point NRI1 of each first cutting contour portion PCP1 may coincide with the radially innermost point NRI1 of the associated radial cutting contour portion PRC. Meanwhile, the third radially outermost end point NRO3 of each third cutting contour portion PCP3 may coincide with the radially outermost point NRO3 of the associated radial cutting contour portion PRC. As shown in FIG. 1-FIG. 5, in a cross section taken on a first imaginary radial plane PR1 including the central axis A1, each imaginary radial cutting contour portion PRC extends monotonically in the axial rear direction DR between the radially innermost end point NRI1 and the radially outermost end point NRO3. In other words, in the radially outward direction, each imaginary radial cutting contour portion PRC always extends perpendicular to the central axis A1 or in the axial rear direction.

[0097] In addition to extending monotonically in the axially rearward direction DR, each imaginary radially cutting profile PRC may be smoothly curved between its radially innermost end point NRI1 and its radially outermost end point NRO3. In other words, each imaginary radially cutting profile PRC may be free of discontinuities such as those caused by steps of the kind found in US2011 / 0116884A1 and WO2013 / 143348A1 discussed above. Thus, the angle of the tangent along the length of a given imaginary radially cutting profile PRC changes gradually, rather than undergoing discrete discontinuities due to such steps.

[0098] 4 and 5, the circumferential projection of each cutting edge 30 on the first imaginary radial plane PR1 forms an imaginary radial cutting contour PRC, which may have a radially innermost end point NRI1 on the first imaginary circle C1 and a radially outermost end point NRO3 on the cutting circle CC. Furthermore, between the radially innermost end point NRI1 and the radially outermost end point NRO3, each imaginary radial cutting contour PRC includes two concave sub-portions CCV1, CCV2 spaced apart by a first convex sub-portion CVX1.

[0099] As shown in FIGS. 4 and 5, each third cutting profile portion PCP3 may extend continuously radially outward and axially rearward away from the central axis A1.

[0100] In some embodiments of the present invention, each third cutting profile portion PCP3 may be convex.

[0101] As shown in FIG. 5, the sixth imaginary straight line L6 may be tangent to a third tangent point NT3 along one of the third cutting contour portions PCP3 adjacent to the third radially outermost end point NRO3, and the sixth imaginary straight line L6 may form a third inclined acute angle α3 with the central axis A1.

[0102] In some embodiments of the invention, the third tilt angle α3 may have a minimum value of 60 degrees and a maximum value of 80 degrees, ie, 60°≦α3≦80°.

[0103] It should be appreciated that configuring each third cutting profile portion PCP3 such that the third inclination angle α3 is greater than 60 degrees may enable the drilling of a blind hole into a workpiece having a wide entry angle of greater than 120 degrees, which may be advantageous for the subsequent drilling of a smaller diameter hole along the same hole axis.

[0104] Also, in some embodiments of the present invention, the third tilt angle α3 may be greater than the first tilt angle α1, ie, α3>α1.

[0105] As shown in FIGS. 1-3, a primary rake face 52 may be disposed on each head groove 48 adjacent to the primary cutting edge portion 38 .

[0106] As shown in FIG. 6, in a cross section taken at any point along the length of 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 at a first axial rake angle β1 relative to a first imaginary 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 may be positive.

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

[0109] It should also be appreciated that the primary cutting edge portion 34 is subject to more wear than the secondary cutting edge portion 32 due to the relatively higher cutting speeds, and that the positive primary rake face 52 configuration reduces wear on the primary cutting edge portion 34 and therefore extends the operational life of the primary cutting edge portion 34.

[0110] As shown in FIG. 6, in a cross section taken at a first transverse plane PT1, the primary clearance surface 38 may be inclined at a first clearance angle λ1 relative to a first imaginary horizontal reference line HL1 perpendicular to the central axis A1.

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

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

[0113] In some embodiments of the present invention, the first clearance angle λ 1 may be constant along the length of the primary cutting edge portion 42 .

[0114] As shown in FIGS. 1-3, a secondary rake face 54 is disposed on each gutter 50 adjacent an associated secondary cutting edge portion 32 .

[0115] As shown in FIG. 7, in a cross section taken at any point along the length of 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 at a second axial rake angle β2 relative to a second imaginary 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] It should be understood throughout this specification and the claims that in a configuration in which the secondary rake surface 54 is rotated and extends rearward such that the secondary rake surface 54 extends away from the secondary cutting edge portion 32, the second axial rake angle β2 is negative.

[0118] It should also be appreciated that the secondary cutting edge portion 32 is more susceptible to impact forces than the primary cutting edge portion 34 due to the relatively slower cutting speeds, especially at high feed rates, and that a configuration in which the secondary axial rake angle β2 is negative increases stability and robustness to the secondary cutting edge portion 32, thus extending the operational life of the secondary cutting edge portion 32.

[0119] As shown in FIG. 7, in a cross section taken at a second transverse plane PT2, the secondary clearance surface 40 may be inclined at a second clearance angle λ2 relative to a second imaginary horizontal reference line HL2 perpendicular to the central axis A1.

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

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

[0122] In some embodiments of the present invention, the second clearance angle λ 2 may be constant along the length of the secondary cutting edge portion 32 .

[0123] Also, in some embodiments of the present invention, the second clearance angle λ2 may be equal to the first clearance angle λ1, ie, λ2=λ1.

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

[0125] Attention is now directed to Figures 8 and 9, which illustrate a rotary cutting tool 56 in accordance with 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 grooves 60 that are circumferentially alternating with two shank lands 62, 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 transverse to the longitudinal axis AL, and the cutting head 20 may be removably assembled to the shank 58 with the bottom surface 64 in contact with the support surface 66.

[0127] The arrangement in which the cutting head 20 is removably assembled to the shank 58 allows the cutting head 20 to be manufactured from a suitably hard material, such as tungsten carbide, and the shank 58 to be manufactured from a less hard and expensive material, such as high speed steel. The shank 58 may be reusable after disposal of a worn or damaged cutting head 20.

[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] Also, 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 sides of the direction of rotation RD, the shank 58 may include at least two drive lugs 70, each drive lug 70 having a drive surface 72 facing the direction of rotation RD, and each torque transmission surface 68 may contact 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 FIGS. 8 and 9 , the cutting head 20 may include an assembly projection 74 extending axially rearward from the bottom surface 64 .

[0133] In another embodiment of the invention (not shown), the cutting head 20 and shank 58 may be a single, unitary, integral part, such as a solid drill, and each head flute 38 may merge with one of the shank flutes 60.

[0134] Although the invention has been described in some detail, it should be understood that various changes and modifications can be made without departing from the spirit or scope of the invention as hereinafter claimed.

Claims

1. A cutting head (20) rotatable about a central axis (A1) in a rotation direction (RD), The central axis (A1) defines a front-rear axial direction (DF, DR), The cutting head (20) comprises a tip portion (22) and an intermediate portion (24); said tip portion (22) having an axially forward-most tip point (NT) contained within said central axis (A1), at least two axially forward facing front faces (26) defining at least one chisel edge (28); said at least one chisel edge (28) extending from or including said tip point (NT); the at least one chisel edge (28) has at least two radially outermost chisel termination points (NRC); Each of the front faces (26) has a cutting edge (30) extending radially outward from one of the radially outermost chisel end points (NRC); The intermediate portion (24) has at least two head lands (42) circumferentially alternating with at least two tip discharge passages (44); Each of the head lands (42) has a leading edge (46) extending 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 one of the leading edges (46); Each of said leading edges (46) has a forward most axial end point (NFA); the at least two forwardmost axial end points (NFA) define a virtual cutting circle (CC); said imaginary cutting circle (CC) having a center coincident with the cutting diameter (DC) and said central axis (A1); At least two of the cutting edges (30) are included within an imaginary three-dimensional annular ring surface (SA) that exhibits circular symmetry around the central axis (A1); In a cross section taken in a first imaginary radial plane (PR1) containing said central axis (A1) and intersecting said imaginary annular ring surface (SA), said imaginary annular ring surface (SA) forms two imaginary radial cutting contours (PRC), each of said imaginary radial cutting contours (PRC) including a first cutting contour portion (PCP1), a second cutting contour portion (PCP2) and a third cutting contour portion (PCP3) extending successively radially outward; each said first cutting profile portion (PCP1) has a first radially innermost end point (NRI1) and a first radially outermost end point (NROL) and extends radially outward and axially aft away from said central axis (A1); Each of said second cutting contour portions (PCP2) has a second radially innermost end point (NRI2) and a second radially outermost end point (NRO2) and includes a first curved concave sub-portion (CCV1) and a second curved concave sub-portion (CCV2) spaced apart by a first curved convex sub-portion (CVX1); the second concave sub-portion (CCV2) as a whole is located radially outward and axially rearward of the first concave sub-portion (CCV1) as a whole; A cutting head (20), wherein a first imaginary straight line (L1) tangent to any point along one of the second cutting contour portions (PCP2) is perpendicular to the central axis (A1) or inclined radially outward and axially rearward away from the central axis (A1).

2. a third imaginary straight line (L3) is simultaneously tangent to a first tangent point (NT1) and a second tangent point (NT2) along each of the first concave subportion (CCV1) and the second concave subportion (CCV2) of one of the imaginary radially cut contours (PRC); The third virtual straight line (L3) forms a second acute angle (α2) with the central axis (A1); The cutting head (20) of claim 1, wherein the second inclination angle (α2) has a minimum value of 55 degrees and a maximum value of 80 degrees.

3. 3. The cutting head (20) of claim 2, wherein the entire associated imaginary radial cutting contour (PRC) lies on one side of the third imaginary straight line (L3) apart from the first tangency point (NT1) and the second tangency point (NT2).

4. the first concave sub-portion (CCV1) and the second concave sub-portion (CCV2) have a first concave radius (RCV1) and a second concave radius (RCV2), respectively; The cutting head (20) of 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. said first convex sub-portion (CVX1) has a first convex radius (RCX1); The cutting head (20) of claim 4, wherein the first convex radius (RCX1) exceeds each of the first concave radius (RCX1) and the second concave radius (RCV2).

6. the first convex radius (RCX1) has a third angular extent (EA3); The cutting head (20) of claim 5, wherein the third angular range (EA3) is greater than 30 degrees.

7. The two second radially innermost end points (NRI2) are on a second imaginary circle (C2); the second imaginary circle (C2) has a second diameter (D2) and a center that coincides with the central axis (A1); The cutting head (20) of claim 1, wherein the second diameter (D2) is between 10 and 30 percent of the cutting diameter (DC).

8. The two second radially outermost end points (NRO2) are on a third imaginary circle (C3); the third imaginary circle (C3) has a third diameter (D3) and a center that coincides with the central axis (A1); The cutting head (20) of claim 7, wherein a difference between the third diameter (D3) and the second diameter (D2) is greater than 25 percent of the cutting diameter (DC).

9. each said first cutting profile portion (PCP1) extends linearly radially outwardly and axially rearwardly away from said central axis (A1) and forms a first inclined acute angle (α1) with said central axis (A1); The cutting head (20) of claim 1, wherein the first tilt angle (α1) has a minimum value of 45 degrees and a maximum value of 70 degrees.

10. The cutting head (20) of claim 1, wherein the first radially outermost end point (NRO1) coincides with the second radially innermost end point (NRI2) of the second cutting profile portion.

11. At least two of said radially outermost chisel end points (NRC) define a first imaginary circle (C1); the first imaginary circle (C1) has a first cutting diameter (D1) and a center that coincides with the central axis (A1); The cutting head (20) according to claim 1, wherein the two first radially innermost end points (NRI1) are on the first imaginary circle (C1).

12. The cutting head (20) of claim 1, wherein each said third cutting profile portion (PCP3) is convex.

13. 2. The cutting head (20) of claim 1, wherein each said third cutting contour portion (PCP3) has a third radially innermost end point (NRI3) and a third radially outermost end point (NRO3) and extends continuously radially outward and axially rearward away from said central axis (A1).

14. The cutting head (20) of claim 13, wherein the third radially innermost end point (NRI3) coincides with the second radially outermost end point (NRO2) of the second cutting profile portion.

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

16. The cutting head (20) of claim 13, wherein the third radially outermost end point (NRO3) is on the imaginary cutting circle (CC).

17. Each cutting edge (30) has a radially inner secondary cutting edge portion (32) and a primary cutting edge portion (34); the primary cutting edge portion (34) extends radially outward from the secondary cutting edge portion (32) either directly or via a transition cutting edge portion (36); 2. The cutting head (20) of claim 1, wherein each said forward surface (26) includes a primary clearance surface (38) and a secondary clearance surface (40) adjacent associated said primary cutting edge portion (34) and said secondary cutting edge portion (32), respectively.

18. the second concave sub-portion (CCV2) of each of the imaginary radial cutting contours (PRC) is at least partially defined by the primary cutting edge portion (34); 18. The cutting head (20) of claim 17, wherein each said primary cutting edge portion (34) rotates and extends rearward such that each said primary cutting edge portion (34) extends radially outward.

19. the first concave sub-portion (CCV1) of each of the imaginary radial cutting contours (PRC) is completely defined by the secondary cutting edge portion (32); the first convex sub-portion (CVX1) of each of the imaginary radial cutting contours (PRC) is at least partially defined by the secondary cutting edge portion (32); 18. The cutting head (20) of claim 17, wherein in a front end view of the cutting head (20), each of the secondary cutting edge portions (32) is straight.

20. 18. The cutting head (20) of claim 17, wherein in a front end view of the cutting head (20), each of the transition edge portions (36) is convex.

21. Each of the primary cutting edge portions (34) is formed at an intersection line between one of the head grooves (48) and one of the primary clearance surfaces (38); a primary rake surface (52) disposed on each of the head grooves (48) adjacent an associated primary cutting edge portion (34); In a first transverse plane (PT1) parallel to the central axis (A1) and intersecting one of the primary cutting edge portions (34), in a cross section taken at any point along the length of the first transverse plane (PT1), the primary rake face (52) is inclined at a first axial rake angle (β1) relative to a first imaginary vertical reference line (VL1) parallel to the central axis (A1); The cutting head (20) of claim 17, wherein the first axial rake angle (β1) is positive.

22. Each of the chip discharge passages (44) has a gutter (50); The cutting groove (50) extends axially rearward from the tip portion (22) and intersects one of the head grooves (48); Each of the secondary cutting edge portions (32) is formed at an intersection line between one of the cutting grooves (50) and one of the secondary clearance surfaces (40); a secondary rake surface (54) is disposed on each of the head grooves (50) adjacent an associated secondary cutting edge portion (32); In a second transverse plane (PT2) that is parallel to the central axis (A1) and intersects one of the secondary cutting edge portions (32), in a cross section taken at any point along the length of the second transverse plane (PT2), the secondary rake face (54) is inclined at a second axial rake angle (β2) relative to a second imaginary vertical reference line (VL2) that is parallel to the central axis (A1); The cutting head (20) of claim 17, wherein the second axial rake angle (β2) is negative.

23. A cutting head (20) rotatable about a central axis (A1) in a rotation direction (RD), The central axis (A1) defines a front-rear axial direction (DF, DR), The cutting head (20) comprises a tip portion (22) and an intermediate portion (24); said tip portion (22) having an axially forward-most tip point (NT) contained within said central axis (A1), at least two axially forward facing front faces (26) defining at least one chisel edge (28); said at least one chisel edge (28) extending from or including said tip point (NT); the at least one chisel edge (28) has at least two radially outermost chisel end points (NRC) that define a first imaginary circle (C1); Each of the front faces (26) has a cutting edge (30) extending radially outward from one of the radially outermost chisel end points (NRC); The intermediate portion (24) has at least two head lands (42) circumferentially alternating with at least two tip discharge passages (44); Each of the head lands (42) has a leading edge (46) extending 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 one of the leading edges (46); Each of said leading edges (46) has a forward most axial end point (NFA); the at least two forwardmost axial end points (NFA) define a virtual cutting circle (CC); said imaginary cutting circle (CC) having a center coincident with the cutting diameter (DC) and said central axis (A1); The at least two cutting edges (30) are included within an imaginary three-dimensional annular ring surface (SA) that exhibits circular symmetry around the central axis (A1); A circumferential projection of each of the cutting edges (30) on a first imaginary radial plane (PR1) including the central axis (A1) forms an imaginary radial cutting contour (PRC); the imaginary radially cut contour (PRC) has a radially innermost end point (NRI1) on the first imaginary circle (C1) and a radially outermost end point (NRO3) on the cutting circle (CC); Between the radially innermost end point (NRI1) and the radially outermost end point (NRO3), each of the imaginary radial cutting contours (PRC) is smoothly curved and extends monotonically in the axial rearward direction and includes two concave sub-portions (CCV1, CCV2) spaced apart by a first convex sub-portion (CVX1).

24. Each of the imaginary radial cutting contours (PRC) includes a first cutting contour portion (PCP1), a second cutting contour portion (PCP2) and a third cutting contour portion (PCP3) extending continuously radially outward; each said first cutting profile portion (PCP1) has said first radially innermost end point (NRI1) and said first radially outermost end point (NROL) and extends radially outward and axially aft away from said central axis (A1); each said second cutting contour portion (PCP2) has a second radially innermost end point (NRI2) and a second radially outermost end point (NRO2) and includes said first concave sub-portion (CCV1) and said second concave sub-portion (CCV2) spaced apart by said first convex sub-portion (CVX1); the second concave sub-portion (CCV2) as a whole is located radially outward and axially rearward of the first concave sub-portion (CCV1) as a whole; a first imaginary straight line (L1) is tangent to any point along one of said second cutting contour portions (PCP2); 24. The cutting head (20) of claim 23, wherein the first imaginary straight line (L1) is perpendicular to the central axis (A1) or inclined radially outward and axially rearward away from the central axis (A1).

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