DRILL POINT

Abstract

A drill point for machining of light alloys, such as aluminium alloys, includes a body having a front end with an apex area, a central axis of rotation and at least one cutting structure. Each cutting structure has a primary rake surface, a primary clearance surface, a cutting edge at an intersection between the primary rake surface and the primary clearance surface, and a peripheral cutting corner. The cutting edge extends radially outward from the apex area to the cutting corner. The primary clearance surface, as seen in a front end view, has a breadth that is a distance extending perpendicular to and from the cutting edge to a primary clearance surface edge, which is rotationally trailing the cutting edge. The body further has a nominal cutting radius, which is a radial distance outward from the central axis of rotation to the cutting corner, and which is at least 1 mm.

Claims

1. A drill point for machining of light alloys, such as aluminium alloys, comprising: a body, the body including a front end with an apex area, a central axis of rotation extending rearward from a centre of the apex area, and at least one cutting structure, wherein each cutting structure comprises a primary rake surface, a primary clearance surface, a cutting edge at an intersection between the primary rake surface and the primary clearance surface, and a peripheral cutting corner, wherein the cutting edge extends radially outward from the apex area to the cutting corner, and the primary clearance surface, as seen in a front end view, has a breadth that is a distance extending perpendicular to and from the cutting edge to a primary clearance surface edge, which is rotationally trailing the cutting edge, and a nominal cutting radius, which is a radial distance outward from the central axis of rotation to the cutting corner, and which is at least 1 mm, wherein the cutting edge has a central portion, which extends radially outward from the apex area to a radially outer end, wherein the radially outer end of the cutting edge central portion has a radial distance to the central axis of rotation of at least 10% of the nominal cutting radius, and wherein the primary clearance surface breadth along the cutting edge central portion is at least 0.05 mm and at most 5% of the nominal cutting radius.

2. The drill point according to claim 1, wherein, when the nominal cutting radius is larger than 2 mm, the primary clearance surface breadth along the cutting edge central portion is at most 3% of the nominal cutting radius.

3. The drill point according to claim 1, wherein, when the nominal cutting radius is larger than 5 mm, the primary clearance surface breadth along the cutting edge central portion is at least 1% of the nominal cutting radius.

4. The drill point according to claim 1, wherein the primary clearance surface breadth is 10-30% of the nominal cutting radius along an outer portion of the cutting edge, which extends form the cutting corner and radially inward to at most the outer end of the cutting edge central portion.

5. The drill point according to claim 1, wherein the radially outer end of the cutting edge central portion has a radial distance to the central axis of rotation of at least 35% of the nominal cutting radius.

6. The drill point according to claim 1, wherein the cutting edge comprises a main cutting edge extending radially inward from the cutting corner, and a secondary cutting edge extending radially outward from the apex area to an inner end of the main cutting edge, wherein, as seen in a front end view, the main cutting edge extends with an angle to the secondary cutting edge, and the cutting edge central portion forms the secondary cutting edge.

7. The drill point according to any claim 6, wherein the main cutting edge extends with an angle to the secondary cutting edge such that, as seen in a front end view, an angle between a line through the central axis of rotation and the radially outer end of the secondary cutting edge, and a line through the central axis of rotation and the cutting corner is 20-40°.

8. The drill point according to claim 1, wherein the cutting edge has an edge radius of at most 4 μm.

9. The drill point according to claim 1, wherein each cutting structure includes a forwardly facing front end surface, which front end surface extends radially outward from the apex area to the periphery of the body, and connects to and is rotationally trailing the primary clearance surface edge, wherein the front end surface includes a recess delimited by a recess surface, and the recess surface borders the primary clearance surface edge at least along the cutting edge central portion.

10. The drill point according to claim 9, wherein each cutting structure includes a coolant channel having a coolant opening, which is at least partly located in the recess surface.

11. The drill point according to claim 10, wherein at least a major portion of a radially inner and axially upper quarter of a perimeter of the coolant opening borders the recess surface.

12. The drill point according to claim 10, wherein the recess surface is a concave surface that includes a curved bottom surface extending axially rearward, a radially inner curved part surface extending from the bottom surface to the apex area, and a radially outer curved part surface extending from the bottom surface to the coolant opening.

13. The drill point according to claim 1, wherein the body includes two cutting structures, which are arranged with 180° rotational symmetry around the central axis of rotation, and wherein the body includes a chisel edge connecting the cutting edges of the two cutting structures across the apex area.

14. The drill point according to claim 13, wherein a first thinning surface extends from the chisel edge axially rearward below the rake surface of the cutting edge central portion of a first of the two cutting structures, a second thinning surface extends from the chisel edge axially rearward below the rake surface of the cutting edge central portion of a second of the two cutting structures, wherein the radially inner curved part surface of the recess surface of the first cutting structure borders the second thinning surface via a common edge, and the radially inner curved part surface of the recess surface of the second cutting structure borders the first thinning surface via common edge.

15. A solid drill tool comprising the drill point according to claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In the following, example embodiments will be described in greater detail and with reference to the accompanying drawings, in which:

[0037] FIG. 1 is a perspective front view of an embodiment of a drill point according to the present invention, wherein the drill point is comprised a in front portion of a solid drill tool;

[0038] FIG. 2 is a side view of the entire solid drill tool of FIG. 1;

[0039] FIG. 3 is a font end view of the drill tool with the drill point;

[0040] FIG. 4 is a perspective side view of a front portion of the solid drill tool with the drill point in a first angular position;

[0041] FIGS. 5 and 6 are side views of the front portion of the solid drill tool with the drill point in two different angular positions;

[0042] All the figures are schematic, not necessarily to scale, and generally only show parts which are necessary in order to elucidate the respective embodiments, whereas other parts may be omitted or merely suggested. Unless otherwise indicated, like reference numerals refer to like parts in different figures.

DETAILED DESCRIPTION

[0043] FIGS. 1 and 2 show a solid drill tool in form of a twist drill comprising an embodiment of a drill point 1 according to the present invention. The drill point 1 according to the embodiment constitutes a generally cone shaped front segment 2 of the twist drill. The twist drill further comprises a shank 6 in a rear segment 4 for mounting the twist drill in a machine spindle. A straight segment 3 extends between the front segment 2 and the rear segment 4. Helical chip flutes 5 are arranged in the straight segment 3, which chip flutes 5 continue axially into the drill point 1. The twist drill is configured to rotate around a central axis of rotation 8 in a cutting direction 9 during machining of a work peace, such as for example drilling holes in aluminium alloy. Features of the drill point 1 and the twist drill are leading or trailing relative each other as seen in the cutting direction 9.

[0044] With reference to FIGS. 3-6, the embodiment of the drill point 1 that is comprised in the twist drill will be described.

[0045] The drill point 1 comprises a body having a foremost tip in form of a chisel edge 7. The central axis of rotation 8 extends rearward in the body from the centre of the chisel edge 7.

[0046] The body further comprises two cutting structures 10 that are arranged with 180° rotational symmetry with respect to the central axis of rotation 8. Each cutting structure 10 comprises a cutting edge 11, wherein each cutting edges 11 is connected to a respective end of the chisel edge via a minor transition edge 12. A central area around the central axis of rotation 8, which central area comprises the chisel edge 7 and the minor transition edges 12, forms an apex area 13.

[0047] Each cutting edge 11 extends from a radially outer end of the minor transition edge 12 at the apex area 13 to a peripheral cutting corner 14. A radius from the central axis of rotation 8 to the cutting corner 14 forms a nominal cutting radius 22 of the drill point 1 and also of the example twist drill. The drill point of the embodiment has a nominal cutting radius of 5 mm. As seen in a side view, each cutting edge 11 and minor transition edge 12 are substantially straight and form a point angle β of 140°. Other embodiments may have different cutting edge geometries, for example cutting edges extending substantially in an axial plane.

[0048] Each cutting edge 11 is sharp with an edge radius of at most 4 μm.

[0049] Each cutting edge 11 comprises a main cutting edge 15 extending radially inward from the cutting corner 14, and a central cutting edge portion (32) in form of a secondary cutting edge 16. The secondary cutting edge 16 extends radially outward from the minor transition edge 12 in the apex area and has a radially outer end 23 at a radially inner end of the main cutting edge 15. The main cutting edge 15 comprises a main transition edge 24 closest to the radially outer end 23 of the secondary cutting edge 16. A radial distance from the central axis of rotation 8 to the radially outer end 23 of the secondary cutting edge 16 is 2.07 mm, i.e. at least 35% of the nominal cutting radius 22, i.e. 1.75 mm.

[0050] As seen in the front end view of FIG. 3, the main cutting edge 15 extends with an angle to the secondary cutting edge 16. An angle α between a line through the central axis of rotation 8 and the radially outer end of the secondary cutting edge 16, and a line along the nominal cutting radius 22 through the central axis of rotation 8 and the cutting corner 14 is 20-40°, and in the shown embodiment the angle α is 24°.

[0051] As seen in the front end view of FIG. 3, the secondary cutting edge 16 is substantially straight and the main cutting edge 15 is concave over a major portion, wherein the main transition edge 24 is straight. The minor transition edge 12 is concave. Other embodiments may have different cutting edge geometries.

[0052] Each cutting edge 11 is formed at the intersection of a primary rake surface 17 and a primary clearance surface 18. One of the chip flutes 5 extends rearward from each cutting edge 11. The primary rake surface 17 is a portion of a chip flute surface that is closest to the cutting edge 11.

[0053] As best seen in FIGS. 4 and 6, each secondary cutting edge 16 has a primary rake surface 17 in form of a thinning surface 26. Close to the central axis of rotation 8 at the chisel edge 7 and at the minor transition edge 12, the thinning surface 26 comprises a concave portion. Axially below a major, radially outer length of the secondary cutting edge 16 the thinning surface 26 comprises a planar portion.

[0054] In each cutting structure 10, the primary clearance surface 18 is a forwardly facing surface that is directly rotationally trailing the cutting edge 11.

[0055] Each cutting structure 10 further comprises a forwardly facing front end surface 20. The front end surface 20 extends radially outward from the apex area 13 to the periphery of the body, and connects to and is rotationally trailing the primary clearance surface 18. The primary clearance surface 18 has a trailing edge 19 at the transition to the front end surface 20. The front end surface 20 includes a secondary clearance surface 21, which follows rotationally behind the primary clearance surface 18. A rotationally trailing edge of the secondary clearance surface 21 connects to an axially forward and rotationally leading surface 31 of the chip flute 5. The axially forward and rotationally leading surface 31 and the primary rake surface 17 are part surfaces of the same chip flute 5, but are associated with a respective different one of the cutting structures 10. The front end surface 20 follows a portion of the periphery of the body.

[0056] As seen in the front end view of FIG. 3, the primary clearance surface 18 has a breadth (b), which measured perpendicular to the cutting edge 11. The breadth (b) is a distance from the cutting edge 11 to the primary clearance surface edge 19.

[0057] The breadth (b) of the primary clearance surface along the secondary cutting edge 16 is 0.06 mm, i.e. more than 0.05 mm and 1% of the nominal cutting radius 22 and less than 3% of the nominal cutting radius, i.e. 0.15 mm.

[0058] The breadth (b) of the primary clearance surface along an outer portion of the cutting edge 11 is 0.53 mm, i.e. more than 10% and less than 30% of the nominal cutting radius 22, i.e. 1.5 mm. Specifically, this larger breadth (b) is present along a major portion of the main cutting edge 15 radially inward from the cutting corner 14.

[0059] The breadth (b) of the primary clearance surface 18 is constant substantially along the secondary cutting edge 16, broadens continuously along the transition portion 24 of the main cutting edge 15, and varies slightly along the outer portion of the main cutting edge 15 due to the concave curvature thereof.

[0060] Each forwardly facing front end surface 20 comprises a recess 25 delimited by a recess surface, which borders the primary clearance surface 18 along the minor transition edge 12, along the secondary cutting edge 16, and along a radially central portion of the main cutting edge 15 including the main transition edge 24. Radially outward, the recess surface borders the secondary clearance surface 21 and the axially forward, rotationally leading surface 31 of the chip flute 5.

[0061] Due to the recess 25, the portion of the primary clearance surface 18 that has the inventive narrow breadth (b) is located on a ridge. The ridge has a rotationally leading flank in form of the thinning surface 26 functioning as rake surface 17, and a rotationally trailing flank in form of the recess surface.

[0062] The recess surface is a concave surface comprising a curved bottom surface 27 extending axially rearward, a radially inner curved part surface 28 extending from the bottom 27 surface to the apex area 13, and a radially outer curved part surface 29, c.f. FIGS. 4 and 6.

[0063] As seen in the front end view of FIG. 3, the radially inner curved part surface 28 extends along the secondary cutting edge 16 of both cutting structures 10, and across the apex area 13. Specifically, the radially inner curved part surface 28 of the first cutting structure borders the thinning surface 26 of the second cutting structure, and the radially inner curved part surface 28 of the second cutting structure borders the thinning surface 26 of the first cutting structure. Due to the difference in concave curvature of the radially inner curved part surface 28 and the thinning surface 26, a common edge is formed at their intersection.

[0064] Each cutting structure 10 further comprises a coolant channel having a coolant opening 30. The coolant opening 30 is partly located in the recess surface, and partly in the rotationally leading surface 31 of the chip flute 5. Thus, the coolant opening 30 is located in the radially outer curved part surface 29 of the recess 25, wherein almost a radially inner and axially forward half of the perimeter of the coolant opening 30 is located in the recess surface.

[0065] As can best be seen in FIGS. 4-6, thanks to the inventive recess 25, coolant exiting through the coolant opening 30 is guided toward the secondary cutting edge 16. In combination with the inventive narrow breadth of the primary clearance surface 18 along the secondary cutting edge 16, the risk of material sticking to the clearance surface 18 is considerably reduced.