VEINED TOOL BLANK AND DRILL

Abstract

A tool blank is substantially cylindrical and includes a front end, a rear end and a central longitudinal axis extending therebetween. At least one vein of a superhard material is formed in the blank at the front end. The vein has a depth in the axial direction and a bottom surface, a first side surface and a second side surface. Each vein has an extension in an inward direction from the periphery of the blank. For each vein, the first side surface forms an inclination angle with respect to the longitudinal axis that varies with the radial distance to the longitudinal axis of the blank over at least a major part of the extension. The inclination angle corresponds to a desired axial rake angle of a drill to be manufactured from the tool blank. A drill manufactured from such tool blank and a method for manufacturing a drill is provided.

Claims

1. A tool blank for a drill, the tool blank being substantially cylindrical and comprising: a front end, a rear end and a central longitudinal axis extending therebetween; and at least one vein of a superhard material formed at the front end, wherein the vein has a depth in an axial direction and includes a bottom surface, a first side surface and a second side surface, and wherein the vein has an extension in an inward direction from a periphery of the tool blank, wherein the first side surface of the vein forms an inclination angle with respect to the longitudinal axis that varies with a radial distance to the longitudinal axis over at least a major part of the extension of the vein, such that the inclination angle substantially corresponds to a desired axial rake angle of a drill to be manufactured from the tool blank.

2. The tool blank according to claim 1, wherein the vein is located such that a cutting edge of the drill to be manufactured can be formed of the superhard material.

3. The tool blank according to claim 1, wherein the second side surface has an inclination angle with respect to the longitudinal axis that is the same as the inclination angle of the first side surface.

4. The tool blank according to claim 1, wherein a width of the vein is constant over at least a major part of the depth and extension of the vein.

5. The tool blank according to claim 1, wherein the inclination angle decreases continuously along the extension of the vein from the periphery of the tool blank.

6. The tool blank according to claim 1, wherein at least a part of the bottom surface of the vein is inclined with respect to the longitudinal axis of the tool blank such that the depth of the vein decreases along the extension of the vein from the periphery of the tool blank, wherein the inclination of the bottom surface corresponds to a profile of the cutting edge of a drill to be manufactured from the tool blank.

7. The tool blank according to claim 1, comprising at least two veins of the superhard material formed at the front end.

8. The tool blank according to claim 7, wherein the veins meet and connect at the longitudinal axis of the tool blank.

9. The tool blank according to claim 7, wherein the veins do not extend all the way to the longitudinal axis of the tool blank, such that there is a region at the front end of the tool blank, around the longitudinal axis, that does not include any vein.

10. The tool blank according to claim 1, wherein at least a part of the tool blank is made by additive manufacturing.

11. The tool blank according to claim 1, wherein the superhard material is poly-crystalline diamond or cubic boron nitride.

12. A drill manufactured from a tool blank according to claim 1, wherein the drill includes at least one cutting edge formed at least partly from the superhard material.

13. The drill according to claim 12, comprising at least two cutting edges and two flutes.

14. A method for manufacturing a drill, comprising the steps of: forming a substantially cylindrical nib pre-blank with at least one vein slot at a front end thereof, wherein forming the vein slot includes the steps of forming a bottom surface at a depth and forming a first and a second side surface in an extension inwards from a periphery of the nib pre-blank, wherein the step of forming the first side surface includes forming the first side surface at an inclination angle to a longitudinal axis of the nib pre-blank that varies with a radial distance to the longitudinal axis over at least a major part of the extension of the vein slot, such that the inclination angle substantially corresponds to a desired axial rake angle of the drill; filling the vein slot at least partially with powder or slurry including particles of a superhard material; applying high pressure and high temperature to the nib pre-blank to fuse the superhard material in the vein slot with the nib pre-blank to form a sintered nib having at least one vein of the superhard material; forming a complete tool blank by connecting the sintered nib to a substantially cylindrical tool blank base body; and forming at least one cutting edge and at least one flute in the tool blank by removing material of the tool blank, wherein the cutting edge is formed at least partly from the superhard material.

15. The method according to claim 14, wherein the sintered nib is connected to the tool blank base body by brazing or sinter fusing.

16. A method according to claim 14, wherein the nib pre-blank is formed by additive manufacturing.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0036] FIG. 1 shows a tool blank according to the invention.

[0037] FIG. 2A-2B show a drill manufactured from the tool blank in FIG. 1.

[0038] FIGS. 3A-3F show a tool pre-blank, wherein FIG. 3A is an isometric view, FIG. 3B is a side view, FIG. 3C is a top view, and FIGS. 3D-3F are cross-sectional views.

[0039] FIG. 4 is an isometric view of another embodiment of a tool pre-blank.

[0040] FIG. 5 is an isometric view of yet another embodiment of a tool pre-blank.

[0041] FIGS. 6A and 6B are an isometric view and a side view, respectively, of yet another embodiment of a tool pre-blank.

[0042] FIG. 7 is a flowchart illustrating a method for manufacturing a drill.

DETAILED DESCRIPTION OF EMBODIMENTS

[0043] FIG. 1 is a side view of a tool blank 1 according to the invention. The tool blank has a front end 2, a rear end 3 and a central longitudinal axis L extending therebetween. The tool blank is comprised of a nib 15, in which two veins 4 (of which one is visible in FIG. 1) are formed, and a tool blank base body 16. The nib 15 and the base body 16 is connected at an interface 17. Even though indicated with solid lines in the drawings herein, the interface 17 is not necessarily visible to the eye. The veins 4 have a depth D in the axial direction and each vein 4 extends over the front end 2 of the tool blank 1 in an inward direction from the periphery of the tool blank.

[0044] FIGS. 2A and 2B show a drill 5 manufactured from the tool blank in FIG. 1. The drill comprises cutting edges 7 formed from the veins of superhard material. The drill according to this example embodiment comprises other features as well, for example flutes 7 and coolant channels 8 for conveying coolant through the drill to the cutting edges. Each cutting edge 7 is formed at an intersection between a rake surface (face) and a relief surface (flank). The axial rake angle is the angle between the face and a line parallel to the central longitudinal axis. At the periphery of the drill, the rake angle is equivalent to the helix angle but decreases when approaching the central longitudinal axis of the drill. As seen in FIGS. 2A-2B, the superhard material in the veins 4 of the tool blank 1 is partly exposed in the drill 5 after manufacturing thereof, such that the cutting edges, and at least parts of the rake- and clearance surfaces, are formed of superhard material.

[0045] FIGS. 3A-3F show a tool pre-blank 10, i.e. a tool blank in a state in which veins of superhard material have not yet been formed. In this example embodiment, the tool pre-blank 10 is a nib pre-blank (e.g. with a geometry corresponding to a nib 15 as shown in FIG. 1), having a central longitudinal axis L, and made of cemented carbide. The tool pre-blank 10 comprises two vein slots 4 formed at a front side 2 of the tool pre-blank 10. The two vein slots 4 are symmetrically arranged, circumferentially spaced by 180, and extend inwards, substantially radially, towards each other from opposite sides of the periphery of the tool pre-blank, and meet and connect at the longitudinal axis L. Each vein slot 4 has a depth D in the axial direction and has a bottom surface 12, a first side surface 13, and a second side surface 14. The first side surface 13 forms an inclination angle with respect to the longitudinal axis L that varies with the radial distance to the longitudinal axis L. The varying inclination angle substantially corresponds to the desired axial rake angle of a drill to be manufactured from the tool pre-blank.

[0046] In this embodiment, the second side surface 14 has an inclination angle that varies in the same way as the first side surface, such that the width of each vein slot 4 is constant. As best seen in FIGS. 3D-3F, being cross-sectional views at different sections (B, C, A, respectively, as indicated in FIG. 3C), the inclination angle is greatest close to the periphery (FIG. 3Fsection B-B). At the periphery, the inclination angle correspond to the helix angle of a drill to be manufactured from the tool pre-blank 10. When approaching the axial longitudinal axis L, the inclination angle of the first side surface decreases (FIG. 3Esection C-C). At the longitudinal axis, the inclination angle of the first side surface is close to zero (FIG. 3Dsection A-A, wherein the first surface extends in the axial direction nearly parallel to the longitudinal axis L).

[0047] FIG. 4 shows another embodiment of a tool pre-blank comprising three vein slots 4 that meet and connect at the longitudinal axis of the tool pre-blank. The veins are symmetrically arranged, circumferentially spaced around the tool pre-blank by 120.

[0048] FIG. 5 shows another embodiment of a cemented carbide tool pre-blank, wherein the two vein slots 4 do not extend all the way to the longitudinal axis of the tool pre-blank. Hence, after forming the veins, there will be a region at the front end of the tool blank, around the longitudinal axis, that does not comprise any vein. A drill manufactured from such tool blank will have cutting edges of which some parts located close to the longitudinal axis, e.g. the chisel, is formed from cemented carbide and not the superhard material of the veins. Cemented carbide is tougher than the superhard material and a configuration wherein the chisel is made of cemented carbide may be advantageous in certain applications.

[0049] FIGS. 6A-6B shows another embodiment of a cemented carbide tool pre-blank comprising two vein slots 4. Contrary to the embodiment shown in FIGS. 3A-3F, the bottom surface 12 is arranged non-perpendicularly to the longitudinal axis. The bottom surface is inclined with respect to the longitudinal axis such that the depth of the vein slot decreases when approaching the longitudinal axis of the tool pre-blank. The inclination of the bottom surface corresponds to the profile of the cutting edge of a drill to be manufactured from the tool pre-blank. Thus, in the embodiment shown in FIGS. 6A-6B, the parts of the bottom surface close to the longitudinal axis has an inclination that corresponds to the desired drill point angle, whereas a peripheral part of the bottom surfaces is curved, i.e. with a varying inclination, corresponding to a desired corner modification of the drill, in this case a corner radius.

[0050] FIG. 7 is a flowchart illustrating a method for producing a cutting tool body according to the invention.

[0051] In step 701, a substantially cylindrical nib pre-blank is formed with at least one vein slot at a front end thereof. Forming each vein slot comprises the steps of forming a bottom surface at a depth, and forming a first and a second side surface in an extension inwards from the periphery of the nib pre-blank. The step of forming the first side surface comprises forming the surface at an inclination angle to a longitudinal axis of the nib pre-blank that varies with the radial distance to the longitudinal axis over at least a major part of the extension of the vein slot, such that the inclination angle substantially corresponds to a desired axial rake angle of the drill. Preferably, the nib pre-blank is made by additive manufacturing. Various kinds of additive manufacturing methods could be used, such as, for example, selective laser sintering or electron beam melting. Such techniques are well known in the art and are not further described herein.

[0052] In step 702, the vein slots are at least partly filled with powder or a slurry comprising particles of a superhard material. Thus, a mass of particles, i.e. powder, comprising particles of the superhard material, e.g. poly-crystalline diamond (PCD) or polycrystalline cubic boron nitride (PCBD) may be used to fill the vein slots. Optionally, binder materials such as alcohols, or any other binder material that may be used in the art may be added to the particles to form a slurry. The powder/slurry is packed into the vein slots so as to at least partially fill the vein slots of the blank. The vein slots may be completely filled or even overfilled with powder/slurry.

[0053] In step 703, a high pressure and high temperature is applied to the nib pre-blank such as to fuse the superhard material in the vein slots with the nib pre-blank, forming a sintered nib having veins of the superhard material. The nib pre-blank may be subjected to pressures of about 45 Kbar to about 90 Kbar and temperatures of about 1200 to about 1600 C. for approximately about 1 to about 50 minutes. When the particles of superhard material have been bonded directly to each other and to the carbide by the sintering process, the nib is removed from the press. Apparatuses and techniques for such sintering are disclosed in U.S. Pat. Nos. 2,941,248, 3,141,746, 3,745,623 and 3,743,489.

[0054] In step 704, the sintered nib is connected to a tool blank base body, such as a conventional tool blank, e.g. a cemented carbide rod. This can be achieved by brazing or sinter fusing or by any other technique known in the art suitable for connecting two pieces of cemented carbide.

[0055] In step 705, flutes and cutting edges are formed by removing material of the tool blank, wherein the cutting edges are formed at least partly from the veins of superhard material. This step usually involves grinding. Other techniques for forming flutes and/or cutting edges, or other geometrical features of the drill, includes laser machining and electro erosion.