A rotatable cutting head having a tip portion with three radially extending cutting edges that form a linear rotation profile.

Abstract

A cutting head (20) rotatable about a central axis (A1), the cutting head (20) having a tip portion (22) and an intermediate portion (24). The tip portion (22) has an axially forward-most tip point (NT) contained within the central axis (A1) and three axially forward facing front faces (26) defining three chisel edges (28) extending axially rearward away from the tip point (NT), each front face (26) having a radially extending cutting edge with a second cutting edge portion (32) extending radially outward from one of the chisel edges (28) and a first cutting edge portion (34) extending radially outward therefrom. Each first cutting edge portion (34) is contained within an imaginary annular ring surface having an annular ring width spanning at least its radially inner and outer radial end points. In a front end view of the cutting head, each first cutting edge portion (34) is concave and the radial plane intersects an imaginary annular plane to form imaginary straight lines each having a length equal to the annular ring width.

Description

[Technical field]

[0001] The present invention relates to a rotatable cutting head having a tip portion with three radially extending cutting edges for use in metal cutting processes generally, and for drilling operations in particular. [Background technology]

[0002] Within the field of cutting tools used in drilling operations, there are many examples of rotatable cutting heads having radially extending cutting edges, the cutting edge portions of which form a substantially linear rotation profile.

[0003] US Patent No. 7,832,966 discloses a helical drill configuration capable of machining a substantially flat-bottom hole. The cutting end of the body member has two cutting edges symmetrically oriented on either side of the drill's axis of rotation. In one embodiment, the first and second cutting edge portions form a continuous surface that provides strength and tool stability. The height of the second portion of each of the cutting edges remains relatively constant along the horizontal direction to form a substantially flat-bottom hole. In this embodiment, a center point is defined by two inclined apex faces. A central straight chisel edge is formed by the intersection of the two inclined apex faces. The first cutting edge section extends from the chisel edge to the second cutting edge section. The first cutting edge section for both cutting edges is formed by symmetrically thinning the two apex faces. Stresses in the central portion of the helical cutting tool are limited by the chisel edges and the first section of the cutting edges near the central portion, which has a balanced geometry. The balanced geometry of the helical drill also prevents the drill from wobbling and causing misalignment in the hole being drilled. The chisel edge may be fused to the first curved cutting edge, and the first curved cutting edge may have a positive rake angle to facilitate cutting.

[0004] US Patent Application Publication No. 2019 / 262910 discloses a drill including a plurality of lands extending to a cutting edge, adjacent lands being separated by flutes with a base contour arranged in a generally helical configuration along a central axis of the drill body. The drill also includes a drill tip having a plurality of contours, each having a straight portion extending toward an outer diameter of the drill body and an arc portion extending from the straight portion toward a chisel of the drill body. The drill further includes a plurality of gash contours positioned within the plurality of flutes. The gash contours extend from the chisel of the drill body, the gash contours being oblique to the base contour of the flutes.

[0005] SUMMARY OF THE PRESENT EMBODIMENT It is an object of the present invention to provide an improved rotatable cutting head having three radially extending cutting edges, the cutting edge portions of which are configured to produce a precisely linear rotation profile.

[0006] It is also an object of the present invention to provide an improved rotatable cutting head having three circumferentially spaced chip discharge passages with head grooves configured to maximize chip discharge passage volume.

[0007] It is a further object of the present invention to provide an improved rotatable cutting head capable of machining a substantially flat shoulder surface between two coaxial through holes having different diameters. Summary of the Invention

[0008] According to the present invention there is provided a cutting head rotatable about a rotational centre axis, said centre axis defining a forward axial direction and an aft axial direction, said cutting head comprising: a tip portion having an axially forward-most tip point contained within said central axis and three axially forward facing front faces defining three chisel edges extending axially aft away from said tip point, each front surface has a radially extending cutting edge including a second cutting edge portion extending radially outward from one of the chisel edges and a first cutting edge portion extending radially outward from the second cutting edge portion either directly or through a transition cutting edge portion; each front surface further including a first flank surface adjacent its respective first cutting edge portion; an intermediate portion having three chip discharge passages and three circumferentially alternating head lands, each head land having a leading edge extending axially rearward from the tip portion, and each chip discharge passage having a head groove extending axially rearward from the tip portion and intersecting one of the leading edges; each first cutting edge portion has a radially inner first end point, a radially outer first end point, and a first midpoint between the radially inner first end point and the radially outer first end point, wherein the three radially outer first end points define a first imaginary circle having a first diameter, the three first midpoints define a second imaginary circle having a second diameter, and the three radially inner first end points define a third imaginary circle having a third diameter; the radially outer first end point, the first midpoint, and the radially inner first end point of one of the first cutting edge portions are contained within a first imaginary radial plane, a second imaginary radial plane, and a third imaginary radial plane, each of which contains the central axis line; Each first cutting edge portion is contained within a first imaginary annular ring surface having a first annular ring width spanning at least the radially inner first end point and the radially outer first end point; When viewed from the front end of the cutting head, each first cutting edge portion is concave, The first imaginary radial plane, the second imaginary radial plane, and the third imaginary radial plane intersect the first imaginary annular ring surface to form first imaginary straight lines, second imaginary straight lines, and third imaginary straight lines, respectively, each having a length equal to the first annular ring width.

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

[0010] [Figure 1] FIG. 2 is a perspective view of a cutting head according to the present invention. [Diagram 2] FIG. 2 is a plan view of the cutting head shown in FIG. [Diagram 3] FIG. 2 is a side view of the cutting head shown in FIG. [Figure 4] 4 is a cross-sectional view of the cutting head taken along line IV-IV in FIG. 2. [Diagram 5] 3 is a cross-sectional view of the cutting head taken along line VV in FIG. 2. [Figure 6] 6 is a cross-sectional view of the cutting head taken along line VI-VI in FIG. 2. [Figure 7] 7 is a cross-sectional view of the cutting head taken along line VII-VII in FIG. 2. [Figure 8] 8 is a cross-sectional view of the cutting head taken along line VIII-VIII in FIG. 2. [Figure 9] FIG. 3 is a cross-sectional view of the cutting head taken along line IX-IX in FIG. 2. [Figure 10] 2 is a plan view taken along a virtual inclined plane of the cutting head shown in FIG. 1. [Figure 11] FIG. 11 is a side view of the cutting head shown in FIG. [Figure 12] FIG. 12 is a detailed view of a portion of the cutting head shown in FIG. [Figure 13] 13 is a cross-sectional view of the cutting head taken along line XIII-XIII in FIG. 10 . [Figure 14] FIG. 14 is a detailed view of a portion of the cutting head shown in FIG. [Figure 15] 3 is a cross-sectional view of the cutting head taken along line XV-XV in FIG. 2. [Figure 16] 3 is a cross-sectional view of the cutting head taken along line XVI-XVI in FIG. 2. [Figure 17] 1 is a perspective view of a rotary cutting tool according to the present invention; [Figure 18]FIG. 18 is an exploded view of the rotary cutting tool shown in FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] 1 to 3, a cutting head 20 is shown that is rotatable about a central axis A1 in a rotation direction RD. The cutting head 20 includes a tip portion 22 and a middle portion .

[0012] The central axis A1 defines a forward axial direction DF and an aft axial direction DR.

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

[0014] As shown in Figures 1 to 3, tip portion 22 has an axially forward-most tip point NT contained within central axis A1, and three axially forward-facing front faces 26 that form three chisel edges 28 extending axially rearward away from tip point NT.

[0015] As shown in FIG. 2 , each front surface 26 has a radially extending cutting edge 30 including a second cutting edge portion 32 extending axially rearward and radially outward from one of the chisel edges 28 and a first cutting edge portion 34 extending radially outward from the second cutting edge portion 32 either directly or through a transition cutting edge portion 36.

[0016] For example, it should be appreciated that providing the cutting head 20 with three radially extending cutting edges 30 as compared to two radially extending cutting edges allows the cutting head 20 to perform drilling operations at a higher feed rate.

[0017] In some embodiments of the present invention, the cutting head 20 may exhibit three-fold rotational symmetry about the central axis A1.

[0018] Each front surface 26 includes a first clearance surface 38 adjacent its respective first cutting edge portion 34 and a second clearance surface 40 adjacent its respective second cutting edge portion 32 .

[0019] As shown in Figures 1 to 3, the intermediate portion 24 has three chip discharge passages 44 and three head lands 42 arranged alternately in the circumferential direction, each head land 42 having a leading edge 46 extending axially rearward from the tip portion 22, and each chip discharge passage 44 having a head groove 48 extending axially rearward from the tip portion 22 and intersecting one of the leading edges 46.

[0020] In one embodiment of the present invention, each first cutting edge portion 34 may be formed at the intersection of one of the head grooves 48 and one of the first clearance surfaces 38 .

[0021] As shown in FIG. 2, the three leading edges 46 may define a cutting diameter DC.

[0022] In certain embodiments of the present invention, each leading edge 46 may extend opposite the direction of rotation RD as it extends axially rearward from tip portion 22 .

[0023] Additionally, in some embodiments of the present invention, each leading edge 46 may extend helically along the central axis A1.

[0024] As shown in FIGS. 1-3, each headland 42 may include a radially outwardly facing margin surface 50 intersecting the leading edge 46 thereof.

[0025] In some embodiments of the present invention, each margin surface 50 may extend helically along the central axis A1.

[0026] Additionally, in some embodiments of the present invention, each margin surface 50 may be spaced from one of the front surfaces 26 by a margin chamfer 52 .

[0027] Further, in one embodiment of the present invention, the cutting diameter DC may be measured immediately axially aft of the three margin chamfers 52 .

[0028] It should be understood that throughout this specification and claims, the three leading edges 46 may be slightly axially tapered in the rearward axial direction DR such that the cutting diameter DC decreases by up to 0.01 mm along the length of the three leading edges 46.

[0029] As shown in FIGS. 1 to 3, each first cutting edge portion 34 has a radially inner first end point NIP and a radially outer first end point NOP.

[0030] As shown in FIGS. 1 to 3, each first cutting edge portion 34 has a first midpoint NMP disposed between its radially inner first end point NIP and its radially outer first end point NOP.

[0031] As shown in FIG. 2, the three radially outer first end points NOP define a first imaginary circle C1 having a first diameter D1, the three first midpoints NMP define a second imaginary circle C2 having a second diameter D2, and the three radially inner first end points NMP define a third imaginary circle C3 having a third diameter D3.

[0032] In an embodiment of the present invention, the difference between the first diameter D1 and the third diameter D3 may be greater than 35 percent of the cutting diameter DC, ie, D1-D3>0.35*DC.

[0033] In one embodiment of the present invention, the first diameter D1 may be greater than 90 percent of the cutting diameter DC, ie, D1>0.90×DC.

[0034] Additionally, in some embodiments of the present invention, the first diameter D1 may be smaller than the cutting diameter DC.

[0035] As shown in FIG. 2, in a front end view of the cutting head 20, each of the first cutting edge portions 34 is concave, that is, each of the first cutting edge portions 34 has a concave shape.

[0036] In an embodiment of the invention, each first midpoint NMP may be located rotationally aft of its respective radially inner first end point NIP and radially outer first end point NOP.

[0037] It should be understood that throughout this specification and claims, the location of a point that is "rotationally rear" or "rotationally ahead" of another point along the same cutting edge 30 is considered with respect to the rotational direction RD and within the rotational range of said cutting edge 30.

[0038] As shown in Figure 2, the radially outer first end point NOP, the first midpoint NMP and the radially inner first end point NIP of one of the first cutting edge portions 34 are respectively contained within a first imaginary virtual radial plane PR1, a second imaginary virtual radial plane PR2 and a third imaginary virtual radial plane PR3, and each of the first imaginary radial plane PR1, the second imaginary radial plane PR2 and the third imaginary radial plane PR3 contains the central axis A1.

[0039] In one embodiment of the present invention, the second imaginary radial plane PR2 may be disposed rearward of the first imaginary radial plane PR1 and the third imaginary radial plane PR3 in the rotational direction.

[0040] In addition, in one embodiment of the present invention, the third imaginary radial plane PR3 may be disposed forward in the rotational direction relative to the first imaginary radial plane PR1.

[0041] It should be understood that throughout this specification and the claims, the position of a virtual radial plane that is "rotationally behind" or "rotationally ahead" of another virtual radial plane associated with the same cutting edge 30 is considered with respect to the rotational direction RD and within the rotational range of said cutting edge 30.

[0042] In some embodiments of the present invention, the second imaginary radial plane PR2 and the third imaginary radial plane PR2 may form an acute hook angle θ of at least 10 degrees, i.e., θ≧10°.

[0043] For embodiments of the present invention in which each first cutting edge portion 34 is concave in a front end view of the cutting head 20 and the second imaginary radial plane PR2 and the third imaginary radial plane PR3 form an acute hook angle θ of at least 10°, each head groove 48 is advantageously configured to maximize the volume of its associated chip discharge passage 44 and provide sufficient space for smooth and efficient chip evacuation, although it should be understood that these may be limited due to a cutting head 20 having three or more circumferentially spaced chip discharge passages 44.

[0044] As shown in FIG. 2, when viewed from the front end of the cutting head 20, each of the second cutting edge portions 32 may be straight.

[0045] In some embodiments of the present invention, each second cutting edge portion 32 may extend rotationally rearward as it extends radially outward.

[0046] Additionally, in some embodiments of the present invention, each second cutting edge portion 32 may extend continuously rotationally rearward along its entire length as it extends radially outward.

[0047] In an embodiment of the present invention in which the second cutting edge portion 32 and the first cutting edge portion 34 of each cutting edge 30 are separated by a transition cutting edge portion 36, as shown in FIG. 2, 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 have a convex shape.

[0048] As shown in Figures 1 to 3, each first cutting edge portion 34 is contained within a first imaginary annular ring surface SA1 having a first annular ring width WA1 spanning at least a radially inner first end point NIP and a radially outer first end point NOP.

[0049] According to the present invention, as shown in Figures 4 to 6, the first imaginary radial plane PR1, the second imaginary radial plane PR2 and the third imaginary radial plane PR3 intersect the first imaginary annular ring surface SA1 to form a first imaginary straight line LR1, a second imaginary straight line LR2 and a third imaginary straight line LR3, respectively, each having a length equal to the first annular ring width WA1.

[0050] It should be understood that any imaginary radial plane that contains the central axis A1 may intersect the first imaginary annular ring surface SA1 to form an imaginary straight line having a length equal to the first annular ring width WA1.

[0051] It should also be understood that the first imaginary annular ring surface SA1 exhibits circular symmetry about the central axis A1, i.e. the first imaginary annular ring surface SA1 has an infinite degree of rotational symmetry.

[0052] It should be further understood that each of the first imaginary straight line LR1, the second imaginary straight line LR2 and the third imaginary straight line LR3 has a high degree of straightness, and that the three first cutting edge portions 34 are configured to form a truly straight rotational profile.

[0053] As shown in Figures 7 to 9, in cross sections taken at first transverse planes PT1, PT2 and third transverse planes PT3 which are perpendicular to the first imaginary radial plane PR1, the second imaginary radial plane PR2 and the third imaginary radial plane PR3 and which respectively include the radially outer first end point NOP, the first midpoint NMP and the radially inner first end point NIP of the associated first cutting edge portion 34, adjacent first clearance faces 38 form first acute clearance angles α1, α2 and α3 respectively with respect to the first imaginary horizontal reference line HL1, the second imaginary horizontal reference line HL2 and the third imaginary horizontal reference line HL3 which are perpendicular to the central axis A1.

[0054] In one embodiment of the present invention, the first transverse plane PT1, the second transverse plane PT2 and the third transverse plane PT3 may be perpendicular to the first imaginary straight line LR1, the second imaginary straight line LR2 and the third imaginary straight line LR3, respectively.

[0055] It should be understood that in a particular configuration in which the first imaginary straight line LR1, the second imaginary straight line LR2, and the third imaginary straight line LR3 are perpendicular to the central axis A1 (not shown), the first transverse plane PT1, the second transverse plane PT2, and the third transverse plane PT3 only need to be parallel to the central axis A1, but for convenience, FIG. 2 shows the first transverse plane PT1, the second transverse plane PT2, and the third transverse plane PT3 parallel to the central axis A1.

[0056] It should be understood that throughout this specification and the claims, in any cross section taken at a transverse plane intersecting one of the first cutting edge portions 34, the adjacent first clearance surface 38 extends axially rearward as it moves away from the first cutting edge portion 34.

[0057] In some embodiments of the present invention, the first acute clearance angle α1, the second acute clearance angle α2, and the third acute clearance angle α3 may be equal, ie, α1=α2=α3.

[0058] It should be understood that the first acute relief angle α1, the second acute relief angle α2, and the third acute relief angle α3 may have an accuracy of 1 degree more or less than the nominal value.

[0059] It should also be appreciated that configuring the first acute relief angle α1, the second acute relief angle α2 and the third acute relief angle α3 to be equal can advantageously improve the uniform distribution of wear along the first cutting edge portion 34.

[0060] In one embodiment of the present invention, the first acute clearance angle α1, the second acute clearance angle α2, and the third acute clearance angle α3 may each have a minimum nominal value of 5 degrees and a maximum nominal value of 12 degrees, i.e., 5°≦α1, α2, α3≦12°.

[0061] In this example of the invention, the first acute relief angle α1, the second acute relief angle α2 and the third acute relief angle α3 have a nominal value of 8°.

[0062] As shown in FIG. 8, an imaginary inclined plane PI including the second imaginary straight line LR2 forms an inclination angle π with respect to a second imaginary radial plane PR2 and intersects with the first clearance surface 38 of each of the front faces 26.

[0063] In some embodiments of the present invention, the inclination angle π may be equal to the second acute relief angle α2.

[0064] It should be appreciated that for embodiments of the present invention in which the inclination angle π is equal to the second acute clearance angle α2, as shown in FIG. 8, the imaginary inclined plane PI forms a right angle with the first clearance surface 38 adjacent the first midpoint NMP.

[0065] In some embodiments of the present invention, the imaginary inclined plane PI may intersect the second clearance surface 40 of each front surface 26 .

[0066] FIG. 10 shows a plan view of the cutting head 20 as seen along an imaginary inclined plane PI.

[0067] As shown in Figures 11 and 12, in a view perpendicular to the imaginary inclined plane PI, the radially outer first end point NOP and the radially inner first end point NIP of the associated first cutting edge portion 34 are spaced apart from the second imaginary straight line LR2.

[0068] It should be understood that, as shown in Figures 11 and 12, the first midpoint NMP of the associated first cutting edge portion 34 lies on the second imaginary straight line LR2.

[0069] In one embodiment of the present invention, as shown in Figures 11 and 12, the radially outer first end point NOP and the radially inner first end point NIP of the associated first cutting edge portion 34 may be located on the same side of the second imaginary straight line LR2.

[0070] Also, in one embodiment of the present invention, as shown in Figures 11 and 12, in a view perpendicular to the imaginary inclined plane PI, the radially inner first end point NIP may be spaced apart from the second imaginary straight line LR2 by a correction height HC, which may be greater than 1 percent of the difference between the second diameter D2 and the third diameter D3, i.e., HC > 0.01 × (D2 - D3).

[0071] It should be appreciated that for embodiments of the present invention in which the hook angle θ and / or the second clearance angle α2 are increased, the correction height HC may increase.

[0072] As shown in FIGS. 13 and 14, in a cross section taken along the imaginary inclined plane PI, the first flank 38 may be convex, that is, the first flank 38 may have a convex shape.

[0073] It should be understood that in an embodiment of the present invention in which each first flank 38 is convex in a cross section taken at the imaginary inclined plane PI, and the first imaginary straight line LR1, the second imaginary straight line LR2 and the third imaginary straight line LR3 each have a high degree of straightness, each first flank 38 may be manufactured by a very precise manufacturing method and may have a complex radial range.

[0074] In some embodiments of the present invention, each first flank surface 38 may be manufactured by a grinding process.

[0075] As shown in Figures 4 to 6, in cross sections taken at the first virtual radial plane PR1, the second virtual radial plane PR2 and the third virtual radial plane PR3, the first virtual straight line LR1, the second virtual straight line LR2 and the third virtual straight line LR3 may each form an internal cutting angle Φ that is acute or perpendicular with respect to the central axis A1.

[0076] It should be appreciated that the first imaginary straight line LR1, the second imaginary straight line LR2 and the third imaginary straight line LR3 may each form the same acute or perpendicular internal cutting angle Φ with respect to the central axis A1. It should be appreciated that for embodiments of the invention in which the cutting angle Φ is an acute angle, the first imaginary annular ring surface SA1 may define a three-dimensional frusto-cone shape, and for embodiments of the invention in which the cutting angle Φ is a perpendicular angle, the first imaginary annular ring surface SA1 may define a two-dimensional annular disk shape.

[0077] It should also be understood that throughout this specification and claims, use of the term "internal cutting angle" refers to the angles formed between the first imaginary straight line LR1, the second imaginary straight line LR2, and the third imaginary straight line LR3 and the portion of the central axis A1 extending through the intermediate portion 24 of the cutting head.

[0078] It should be understood that for embodiments of the present invention in which the cutting angle Φ is acute, such that each first cutting edge portion 34 has at least a minimum inclination relative to a first horizontal plane PHI perpendicular to the central axis A1 and intersecting the tip portion 22, the axial cutting forces acting on the at least three first cutting edge portions 34 upon initial contact with the workpiece during a drilling operation are gradually distributed along the at least three first cutting edge portions 34.

[0079] In one embodiment of the present invention, as shown in FIGS. 4 to 6, the cutting angle Φ may be greater than 88 degrees, that is, 88°<Φ≦90°.

[0080] It should be understood that the cutting angle Φ may have an accuracy of 0.5 degrees more or less than the nominal value.

[0081] In this example of the invention, the cutting angle Φ has a nominal value of 89.5°.

[0082] It will be appreciated that for embodiments of the present invention in which the cutting angle Φ is greater than 88 degrees, the at least three first cutting edge portions 34 may be configured to form a substantially flat rotary cutting profile, and the cutting head 20 may be advantageously used in a drilling operation to machine a substantially flat shoulder surface (not shown) between two coaxial through holes having different diameters.

[0083] In another embodiment of the invention (not shown), the cutting angle Φ may be exactly 90 degrees, ie Φ=90°.

[0084] It should be appreciated that for embodiments of the present invention where the cutting angle Φ is exactly 90 degrees, at least three first cutting edge portions 34 may be configured to produce a truly flat rotary cutting profile.

[0085] As shown in Figures 1-3, each second cutting edge portion 32 has a second midpoint NMS located midway along its length.

[0086] As shown in FIG. 2, the three second midpoints NMS define a fourth imaginary circle C4 having a fourth diameter D4.

[0087] In some embodiments of the present invention, the difference between the first diameter D1 and the fourth diameter D4 may be greater than 50 percent of the cutting diameter DC, ie, D1-D4>0.50*DC.

[0088] As shown in FIG. 2, the second midpoint NMS of one of the first cutting edge portions 34 is contained within a fourth imaginary radial plane PR4, and the fourth imaginary radial plane PR4 contains the central axis A1.

[0089] As shown in FIGS. 1-3, a compound cutting edge portion 54 of each cutting edge 30 extending from the radially outer first end point NOP to the second midpoint NMS may be contained within a first imaginary annular ring surface SA1.

[0090] It should be appreciated that for embodiments of the present invention in which each composite cutting edge portion 54 is contained within a first imaginary annular ring surface SA1 and the difference between the first diameter D1 and the fourth diameter D4 is greater than 50 percent of the cutting diameter DC, the first annular ring width WA1 may be greater than 50 percent of half the cutting diameter DC, i.e., WA1 > 0.50 × DC / 2.

[0091] As shown in FIG. 15, the fourth imaginary radial plane PR4 intersects with the first imaginary annular ring surface SA1 to form a fourth imaginary straight line LR4 having a length equal to the first annular ring width WA1.

[0092] As shown in FIG. 15, in a cross section taken at a fourth imaginary radial plane PR4, a fourth imaginary straight line LR4 may form an acute or perpendicular internal cutting angle Φ with respect to the central axis A1.

[0093] It should be understood that in some embodiments of the present invention, the first imaginary straight line LR1, the second imaginary straight line LR2, the third imaginary straight line LR3, and the fourth imaginary straight line LR4 may each form the same acute or perpendicular internal cutting angle Φ with respect to the central axis A1.

[0094] In one embodiment of the invention, the second midpoint NMS may be located rotationally forward of the radially inner first end point NIP of its associated first cutting edge portion 34 .

[0095] As shown in FIG. 2, each second cutting edge portion 32 may extend axially forward as it extends radially inward from its second midpoint NMS.

[0096] In one embodiment of the invention, as shown in Figures 1-3, each second cutting edge portion 32 may include a point cutting edge sub-portion 56 disposed radially inward of its second midpoint NMS, and the point cutting edge sub-portion 56 may form an acute approach angle λ with respect to a second horizontal plane PH2 that is perpendicular to the central axis A1 and intersects the tip portion 22.

[0097] Also, in some embodiments of the present invention, as shown in FIG. 3, the approach angle λ may be at least 15 degrees and at most 30 degrees, ie, 15°≦λ≦30°.

[0098] Furthermore, in some embodiments of the present invention, the first horizontal plane PH1 and the second horizontal plane PH2 may be coplanar.

[0099] It should be understood that the three pointed cutting edge sub-portions 56 may be contained within a second imaginary annular ring surface (not shown) which, in contrast to the first imaginary annular ring surface SA1, does not form an imaginary straight line when intersecting the radial plane.

[0100] It should also be appreciated that the portion of each second flank surface 40 adjacent the associated point cutting edge sub-portion 56 need not have a complex radial extent.

[0101] As shown in FIGS. 1-3, a first rake face 58 may be disposed on each head groove 48 adjacent an associated first cutting edge portion 34 .

[0102] In some embodiments of the present invention, the plurality of first rake faces 58 may face the direction of rotation RD.

[0103] As shown in Figures 7 to 9, in cross sections taken at the first transverse plane PT1, the second transverse plane PT2 and the third transverse plane PT3, the first rake face 58 is inclined at a first axial rake angle β1, a second axial rake angle β2 and a third axial rake angle β3 relative to the first virtual radial plane PR1, the second virtual radial plane PR2 and the third virtual radial plane PR3, respectively.

[0104] In certain embodiments of the present invention, each of the first axial rake angle β1, the second axial rake angle β2, and the third axial rake angle β3 may be positive.

[0105] It should be understood that throughout this specification and the claims, the first axial rake angle β1, the second axial rake angle β2, and the third axial rake angle β3 are positive in a configuration in which the respective portions of the first rake face 58 extend rotationally rearward as they move away from the associated first cutting edge portion 34.

[0106] The first cutting edge portions 34 are subject to greater wear than the second cutting edge portions 32 due to their relatively high cutting speeds, and configuring the first axial rake angle β1, the second axial rake angle β2 and the third axial rake angle β3 to be positive reduces wear of the first cutting edge portions 34, thus extending their operating life.

[0107] As shown in FIG. 16, in a cross section taken at a fourth imaginary transverse plane PT4 perpendicular to the fourth imaginary radial plane PR4 and including the second midpoint NMS of the associated minor cutting edge portion 32, the adjacent second clearance surface 40 forms a fourth acute clearance angle α4 with respect to a fourth imaginary horizontal reference line HL4 perpendicular to the central axis A1.

[0108] In some embodiments of the present invention, the fourth imaginary transverse plane PT4 may be perpendicular to the fourth imaginary straight line LR4, but for convenience, FIG. 2 shows the fourth imaginary transverse plane PT4 parallel to the central axis A1.

[0109] It should be understood that throughout this specification and the claims, in any cross section taken in a transverse plane parallel to the central axis A1 and intersecting one of the second cutting edge portions 32, the second clearance surface 40 extends axially rearward as it moves away from the first cutting edge portion 34.

[0110] In some embodiments of the present invention, the fourth acute clearance angle α4 may be equal to the first acute clearance angle α1, the second acute clearance angle α2, and the third acute clearance angle α3.

[0111] As shown in FIGS. 1-3, each chip discharge passage 44 may have a gash 60 that extends axially rearward from the tip portion 22 and intersects one of the head grooves 48 .

[0112] In some embodiments of the present invention, each second cutting edge portion 32 may be formed at an intersection of one of the gashes 60 and one of the second flank surfaces.

[0113] As shown in FIGS. 1-3, a second rake face 62 may be disposed on each gash 60 adjacent an associated second cutting edge portion 32 .

[0114] In some embodiments of the present invention, the plurality of second rake faces 62 may face the direction of rotation RD.

[0115] As shown in FIG. 16, in a cross section taken at a fourth imaginary transverse plane PT4, the second rake face 62 is inclined at a fourth axial rake angle β4 with respect to a fourth imaginary radial plane PR4.

[0116] In some embodiments of the present invention, the fourth axial rake angle β4 may be negative.

[0117] Also, in some embodiments of the present invention, the negative fourth axial rake angle β4 may have a magnitude greater than 4 degrees.

[0118] It should be understood throughout this specification and the claims that in a configuration in which each portion of the second rake face 62 extends forward in the rotational direction as it moves away from the second cutting edge portion 32, the fourth axial rake angle β4 is negative.

[0119] It should be appreciated that the second cutting edge portions 32 are subject to greater impact forces than the first cutting edge portions 34 due to their relatively low cutting speeds, especially at high feed rates, and that configuring the fourth axial rake angle β4 to be negative improves the stability and robustness of the second cutting edge portions 32, thus extending their operational life.

[0120] In embodiments of the present invention in which the first diameter D1 is smaller than the cutting diameter DC, each cutting edge 30 may include a third cutting edge portion 64 extending radially outward from a radially outer first end point NOP of its first cutting edge portion 34.

[0121] As shown in FIG. 2, in a front end view of the cutting head 20, each of the third cutting edge portions 64 may be convex, that is, each of the third cutting edge portions 64 may have a convex shape.

[0122] In one embodiment of the present invention, each third cutting edge portion 64 may be contained within a first imaginary annular ring surface SA1.

[0123] As shown in FIGS. 1 to 3, each third cutting edge portion 64 has a radially inner third end point NIT and a radially outer third end point NOT.

[0124] In some embodiments of the present invention, the radially inner third end point NIT of each third cutting edge portion 64 may coincide with the radially outer first end point NOP of the associated first cutting edge portion 34 .

[0125] As shown in FIG. 2, in a front end view of the cutting head 20, a first imaginary straight line L1 tangent to one of the third cutting edge portions 64 adjacent to its radially outer third end point NOT may form a negative radial rake angle δ with respect to a second imaginary straight line L2 that includes the radially outer third end point NOT and intersects the central axis A1.

[0126] It should be understood throughout this specification and the claims that in a configuration in which the first imaginary straight line L1 extends rotationally rearward as it extends radially outward from the third cutting edge portion 64, the radial rake angle δ is negative.

[0127] 17 and 18, there is shown a rotary cutting tool 66 in accordance with the present invention, comprising a cutting head 20 and a shank 68 having a longitudinal axis AL.

[0128] The shank 68 has three circumferentially alternating shank grooves 70 with three shank lands 72, and each shank groove 70 may extend helically along the longitudinal axis AL.

[0129] As shown in Figures 17 and 18, the cutting head 20 may have a bottom surface 74 facing axially rearward, the shank 68 may have a support surface 76 transverse to the longitudinal axis AL, and the cutting head 20 may be removably mounted to the shank 68 with the bottom surface 74 in contact with the support surface 76.

[0130] Configuring the cutting head 20 to be removably attached to the shank 68 allows the cutting head 20 to be manufactured from a material of suitable hardness, such as tungsten carbide, and allows the shank 68 to be manufactured from a less hard, less expensive material, such as high speed steel. The shank 68 may be reusable after discarding a worn or damaged cutting head 20.

[0131] In certain embodiments of the present invention, each head groove 48 may intersect the bottom surface 74 and cooperate with one of the shank grooves 70 .

[0132] Also, in one embodiment of the present invention, the bottom surface 74 may be perpendicular to the central axis A1, the support surface 76 may be perpendicular to the longitudinal axis AL, and the central axis A1 may be coaxial with the longitudinal axis AL.

[0133] As shown in Figures 17 and 18, the intermediate portion 24 of the cutting head 20 may include three torque transmission surfaces 78 facing away from the direction of rotation RD, the shank 68 may include three drive lugs 80, each drive lug 80 having a drive surface 82 facing the direction of rotation RD, and each torque transmission surface 78 may contact one of the drive surfaces 82.

[0134] In some embodiments of the present invention, each torque transmission surface 78 may intersect one of the front surfaces 26 .

[0135] As shown in FIGS. 17 and 18, the cutting head 20 may include a mounting projection 84 extending axially rearward from the bottom surface 74.

[0136] In other embodiments of the invention (not shown), the cutting head 20 and shank 68 may be an integral part of a single, unitary structure, such as, for example, a solid drill, and each head groove 48 may merge with one of the shank grooves 70.

[0137] 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 direction of rotation (RD), said central axis (A1) defining a forward axial direction (DF) and a rearward axial direction (DR), said cutting head (20) comprising: a tip portion (22) having an axially forward-most tip point (NT) contained within said central axis (A1) and three axially forward facing front faces (26) defining three chisel edges (28) extending axially aft away from said tip point (NT), Each front surface (26) has a radially extending cutting edge (30) with a second cutting edge portion (32) extending radially outward from one of said chisel edges (28) and a first cutting edge portion (34) extending radially outward from said second cutting edge portion (32) either directly or through a transition cutting edge portion (36); Each front surface (26) further includes a first flank surface (38) adjacent its respective first cutting edge portion (34); an intermediate portion (24) having three chip discharge passages (44) and three circumferentially alternating head lands (42), each head land (42) having a leading edge (46) extending axially rearward from said tip portion (22), each chip discharge passage (44) having a head groove (48) extending axially rearward from said tip portion (22) and intersecting one of the leading edges (46); Each first cutting edge portion (34) has a radially inner first end point (NIP), a radially outer first end point (NOP), and a first midpoint (NMP) between the radially inner first end point (NIP) and the radially outer first end point (NOP), wherein the three radially outer first end points (NOP) define a first imaginary circle (C1) having a first diameter (D1), the three first midpoints (NMP) define a second imaginary circle (C2) having a second diameter (D2), and the three radially inner first end points (NIP) define a third imaginary circle (C3) having a third diameter (D3); the radially outer first end point (NOP), the first midpoint (NMP) and the radially inner first end point (NIP) of one of the first cutting edge portions (34) are contained within a first imaginary radial plane (PR1), a second imaginary radial plane (PR2) and a third imaginary radial plane (PR3), respectively, and each of the first imaginary radial plane (PR1), the second imaginary radial plane (PR2) and the third imaginary radial plane (PR3) contains the central axis line (A1); Each first cutting edge portion (34) is contained within a first imaginary annular ring surface (SA1) having a first annular ring width (WA1) spanning at least said radially inner first end point (NIP) and said radially outer first end point (NOP); When viewed from the front end of the cutting head (20), each first cutting edge portion (34) is concave, the first imaginary radial plane (PR1), the second imaginary radial plane (PR2) and the third imaginary radial plane (PR3) intersect with the first imaginary annular ring surface (SA1) to form first imaginary straight lines (LR1), second imaginary straight lines (LR2) and third imaginary straight lines (LR3), respectively, each having a length equal to the first annular ring width (WA1).

2. In cross sections taken in the first virtual radial plane (PR1), the second virtual radial plane (PR2) and the third virtual radial plane (PR3), the first virtual straight line (LR1), the second virtual straight line (LR2) and the third virtual straight line (LR3) each form an acute or perpendicular internal cutting angle (Φ) with respect to the central axis (A1); The cutting head (20) of claim 1, wherein the cutting angle (Φ) is greater than 88 degrees.

3. 3. The cutting head (20) according to claim 2, wherein in cross sections taken in the first imaginary radial plane (PR1), the second imaginary radial plane (PR2) and the third imaginary radial plane (PR3), the first imaginary straight lines (LR1), the second imaginary straight lines (LR2) and the third imaginary straight lines (LR3) each form the same acute or perpendicular internal cutting angle (Φ) with respect to the central axis (A1).

4. The cutting head (20) according to claim 1, wherein the second imaginary radial plane (PR2) is arranged rotationally rearward of the first imaginary radial plane (PR1) and the third imaginary radial plane (PR3).

5. The cutting head (20) of claim 1, wherein the second imaginary radial plane (PR2) and the third imaginary radial plane (PR3) form an acute hook angle (θ) of at least 10 degrees.

6. 2. The cutting head (20) according to claim 1, wherein in cross sections taken at first (PT1), second (PT2) and third (PT3) transverse planes perpendicular to the first imaginary radial plane (PR1), the second (PR2) and the third imaginary radial plane (PR3) and containing the radially outer first end point (NOP), the first midpoint (NMP) and the radially inner first end point (NIP) of an associated first cutting edge portion (34), adjacent first flank surfaces (38) form first acute relief angles (α1), second acute relief angles (α2) and third acute relief angles (α3) relative to first imaginary horizontal reference lines (HL1), second imaginary horizontal reference lines (HL2) and third imaginary horizontal reference lines (HL3) perpendicular to the central axis (A1), respectively.

7. a virtual inclined surface (PI) including the second virtual straight line (LR2) forms a tilt angle (π) with respect to the second virtual radial plane (PR2) and intersects with the first flank surface (38) of each of the front faces (26); the inclination angle (π) is equal to the second acute relief angle (α2); 7. The cutting head (20) according to claim 6, wherein, in a view perpendicular to the imaginary inclined plane (PI), the radially outer first end point (NOP) and the radially inner first end point (NIP) of the associated first cutting edge portion (34) are spaced apart from the second imaginary straight line (LR2).

8. In a view perpendicular to the imaginary inclined plane (PI), the radially inner first end point (NIP) is spaced from the second imaginary straight line (LR2) by a correction height (HC), The cutting head (20) of claim 7, wherein the compensation height (HC) is greater than one percent of the difference between the second diameter (D2) and the third diameter (D3).

9. The cutting head (20) according to claim 7, wherein, in a view perpendicular to the imaginary inclined plane (PI), the radially outer first end point (NOP) and the radially inner first end point (NIP) of the associated first cutting edge portion (34) are located on the same side of the second imaginary straight line (LR2).

10. The cutting head (20) of claim 7, wherein in a cross section taken at said imaginary inclined plane (PI), said first flank surface (38) is convex.

11. 7. The cutting head (20) of claim 6, wherein the first clearance angle (α1), the second clearance angle (α2), and the third clearance angle (α3) each have a minimum nominal value of 5 degrees and a maximum nominal value of 12 degrees.

12. The cutting head (20) of claim 6, wherein the first clearance angle (α1), the second clearance angle (α2) and the third clearance angle (α3) are equal.

13. Each first cutting edge portion (34) is formed at an intersection line between one of the head grooves (48) and one of the first flank surfaces (38); a first rake surface (58) is disposed in each head groove (48) adjacent an associated first cutting edge portion (34); In cross sections taken at the first transverse plane (PT1), the second transverse plane (PT2), and the third transverse plane (PT3), the first rake face (58) is inclined at a first axial rake angle (β1), a second axial rake angle (β2), and a third axial rake angle (β3) with respect to the first virtual radial plane (PR1), the second virtual radial plane (PR2), and the third virtual radial plane (PR3), respectively; The cutting head (20) of claim 6, wherein each of the first axial rake angle (β1), the second axial rake angle (β2), and the third axial rake angle (β3) is positive.

14. each second cutting edge portion (32) has a second midpoint (NMS) located midway along its length, the three second midpoints (NMS) defining a fourth imaginary circle (C4) having a fourth diameter (D4); The second midpoint (NMS) of one of the second cutting edge portions (32) is contained within a fourth imaginary radial plane (PR4), and the fourth imaginary radial plane (PR4) contains the central axis A1; a compound cutting edge portion (54) of each cutting edge (30) extending from said radially outer first end point (NOP) to said second midpoint (NMS) is contained within said first imaginary annular ring surface (SA1); 13. The cutting head (20) of claim 12, wherein said fourth imaginary radial plane (PR4) intersects said first imaginary annular ring surface (SA1) to form a fourth imaginary straight line (LR4) having a length equal to said first annular ring width (WA1).

15. Each front surface (26) has a second clearance surface (40) adjacent its respective second cutting edge portion (32); In a cross section taken on a fourth transverse plane (PT4) perpendicular to the fourth imaginary radial plane (PR4) and including the second midpoint (NMS) of the associated second cutting edge portion (32), the adjacent second flank surface (40) forms a fourth clearance angle (α4) with respect to a fourth imaginary horizontal reference line (HL4) perpendicular to the central axis (A1); 15. The cutting head (20) of claim 14, wherein the fourth acute clearance angle (α4) is equal to the first acute clearance angle (α1), the second acute clearance angle (α2) and the third acute clearance angle (α3).

16. each chip discharge passage (44) extending axially rearward from said tip portion (22) and having a gash (60) intersecting one of said head grooves (48); Each second cutting edge portion (32) is formed at an intersection line between one of the gashes (60) and one of the second flank surfaces (40); A second rake face (62) is disposed on each gash (60) adjacent the associated second cutting edge portion (32). In a cross section taken at the fourth transverse plane (PT4), the second rake face (62) is inclined at a fourth axial rake angle (β4) with respect to the fourth virtual radial plane (PR4); The cutting head (20) of claim 15, wherein the fourth axial rake angle (β4) is negative.

17. 17. The cutting head (20) of claim 16, wherein the negative fourth axial rake angle (β4) is greater than 4°.

18. The three leading edges (46) define a cutting diameter (DC); 15. The cutting head (20) of claim 14, wherein a difference between said first diameter (D1) and said third diameter (D3) is greater than 35 percent of said cutting diameter (DC).

19. 20. The cutting head (20) of claim 18, wherein the difference between the first diameter (D1) and the fourth diameter (D4) is greater than 50 percent of the cutting diameter (DC).

20. The cutting head (20) of claim 14, wherein each second cutting edge portion (32) extends axially forward as it extends radially inward from its second midpoint (NMS).

21. each second cutting edge portion (32) includes a tip cutting edge sub-portion (56) disposed radially inward of its second midpoint (NMS); The pointed cutting edge sub-portion (56) forms an acute approach angle (λ) with respect to a second horizontal plane (PH2) perpendicular to the central axis (A1); The cutting head (20) of claim 14, wherein the approach angle (λ) is at least 15 degrees and at most 30 degrees.

22. The cutting head (20) of claim 1, wherein, in a front end view of the cutting head (20), each second cutting edge portion (32) is straight.

23. 23. The cutting head (20) of claim 22, wherein each second cutting edge portion (32) extends rotationally rearward as it extends radially outward.

24. The cutting head (20) of claim 1, wherein, in a front end view of the cutting head (20), each transition edge portion (36) is convex.

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