Drill body of indexable insert drill and insert drill including such drill body

Abstract

1. A drill body (2) for an indexable insert drill comprising: at least two chip flutes (10a, 10b) spaced from one another circumferentially of the drill body by intermediate ribs (12a, 12b), each chip flute and each rib extending in a helically curved path; an insert mounting portion located at a transition between each chip flute and a front face of the drill body; and a coolant duct (20a, 20b) disposed on and extending along a respective one of the ribs (12a, 12b), each coolant duct extending in a helically curved path, the coolant duct having an upstream end (21) with an inlet opening (24a, 24b) and a downstream end (22) with an outlet opening (25a, 25b). Each coolant duct has a cross-sectional area that varies along the axial direction of the coolant duct such that the cross-sectional area at the outlet opening is smaller than the cross-sectional area at the inlet opening.

Description

[Technical field]

[0001] The present invention relates to a drill body for an indexable insert drill according to the preamble of claim 1. Furthermore, the present invention relates to an indexable insert drill comprising such a drill body. [Background technology]

[0002] An indexable insert drill is a drilling tool used to drill holes in a workpiece, comprising a drill body and one or more indexable cutting inserts removably mounted in respective insert mounts in a head portion at the front end of the drill body. Each individual cutting insert may comprise several identical cutting edges, thereby allowing each cutting insert to be moved to a different working position. When the cutting edge of the cutting insert wears out, the cutting insert may be repositioned in its insert mount and mounted in a new working position that places another cutting edge in an effective cutting position. To increase the useful life of the cutting insert, the interface between the cutting insert and the workpiece may be cooled and lubricated during the drilling operation by a flow of coolant, which may be supplied to the region of the cutting insert through one or more coolant ducts in the drill body. Furthermore, the flow of coolant to the interface between the cutting insert and the workpiece also helps to move chips formed during the drilling operation away from the cutting insert.

[0003] U.S. Pat. No. 6,030,155 discloses an indexable insert drill having a drill body with two helically curved chip flutes separated from each other by an intermediate rib formed in the drill body, with coolant ducts running in helically curved paths within each rib.

[0004] Object of the invention SUMMARY OF THE PRESENT EMBODIMENT It is an object of the present invention to provide a drill body for an indexable insert drill of the kind mentioned above, which has a new and preferred design. Summary of the Invention

[0005] According to the invention, this object is achieved by a drill body having the features defined in claim 1.

[0006] A drill body according to the present invention is elongated and has a rear end and an opposite front end, a central longitudinal axis of the drill body extending between the rear end and the front end of the drill body, the drill body comprising: a shank portion located at a rear end of the drill body and configured to be attached to a machine tool; a head portion located at the front end of the drill body; at least first and second chip flutes extending alongside one another along a portion of the drill body from the head portion to the shank portion, the chip flutes being separated from one another circumferentially of the drill body by intermediate ribs formed in the drill body and extending alongside the chip flutes, each chip flute and each rib extending in a helically curved path along an associated portion of the drill body; a first insert seat configured to receive a first cutting insert and disposed at a transition between the first chip flute and a front face of the drill body; a second insert seat configured to receive a second cutting insert and disposed at a transition between the second chip flute and the front face of the drill body; a coolant duct disposed within and extending along each of said ribs, each coolant duct extending in a helically curved path along at least a portion of an associated rib, each coolant duct having an upstream end with an inlet opening facing the rear end of the drill body and a downstream end with an outlet opening in the head portion; Equipped with.

[0007] Each coolant duct has a cross-sectional area that varies along the axial direction of the coolant duct such that the cross-sectional area at the outlet opening is smaller than the cross-sectional area at the inlet opening. By making the cross-sectional area at the outlet of each coolant duct smaller than the cross-sectional area at the inlet, the coolant pressure can be better maintained along the coolant duct, resulting in improved coolant flow characteristics at the outlet of the coolant duct and therefore improved cooling effectiveness.

[0008] Here, the cross-sectional area of ​​a coolant duct refers to the cross-sectional area of ​​the coolant duct when viewed in a cross section perpendicular to the central axis of the coolant duct.

[0009] According to one embodiment of the present invention, each coolant duct has a continuously decreasing cross-sectional area, at least along a part of its extension, when viewed in the direction from its upstream end to its downstream end. A continuously decreasing cross-sectional area of ​​the coolant duct means a smooth change in the cross-sectional area of ​​the coolant duct, which is favorable in terms of the characteristics of the flow of the coolant along the coolant duct, since abrupt changes in the cross-sectional area that could cause the formation of turbulences in the coolant duct are avoided. Particularly preferably, each coolant duct has a continuously decreasing cross-sectional area, when viewed from its upstream end to its downstream end.

[0010] According to an embodiment of the present invention, the coolant ducts are arranged closer to each other at their upstream end than at their downstream end. It may be advantageous to arrange the inlet openings of the coolant ducts closer to the longitudinal axis of the drill body and therefore closer to each other, so that all the coolant ducts can open into one and the same coolant supply duct arranged in the center of the rear part of the drill body. In such a case, the coolant is first introduced into the central coolant supply duct and then distributed from there to each individual coolant duct. Preferably, in the head part of the drill body, the position of the outlet openings of the coolant ducts is matched to the position of the insert mounts in such a way that the outlet openings of each coolant duct are arranged at essentially the same radial distance from the longitudinal axis of the drill body as the associated insert mount. Thereby, the coolant discharged from the outlet openings of the coolant ducts impinges on the interface between the workpiece and the cutting insert attached to the corresponding insert mount when the drill body rotates. Thereby, the outlet openings of the coolant ducts are preferably arranged on either side of the longitudinal axis of the drill body at a certain distance from the longitudinal axis of the drill body, such that there is a considerable distance between the coolant ducts at their downstream ends. Making the distance between the coolant ducts greater at their downstream ends than at their upstream ends can be achieved, for example, by extending the coolant ducts in respective spirally curved paths along the circumference of one and the same imaginary cone that widens when viewed in the direction from the upstream end of the coolant duct to the downstream end of the coolant duct. In this case, the distance between the coolant ducts increases continuously in the axial direction of the coolant duct when viewed from the upstream end to the downstream end of the coolant duct.

[0011] The outlet openings of the coolant ducts are advantageously located at the front face of the drill body.

[0012] Indexable insert drills often include a peripheral cutting insert mounted on a first insert mount, which is the outermost radially, and a central cutting insert mounted on a second insert mount, which is the innermost radially, located closer to the longitudinal axis of the drill body than the first insert mount. This results in the outlet openings of the coolant ducts associated with the peripheral cutting inserts being located at a greater radial distance from the longitudinal axis of the drill body than the outlet openings of the coolant ducts associated with the central cutting inserts. However, the inlet openings of the coolant ducts may be located at the same or essentially the same radial distance from the longitudinal axis of the drill body.

[0013] According to one embodiment of the invention, the coolant ducts are of equal length, have equal cross-sectional areas at the inlet openings and equal cross-sectional areas at the outlet openings, and the cross-sectional areas of the coolant ducts vary in the same manner along the extension of the different coolant ducts, such that the cross-sectional area of ​​one coolant duct at any axial distance from the inlet opening is the same as the cross-sectional area of ​​this coolant duct at the same axial distance from the inlet opening of each of the other coolant ducts, so that the flow characteristics of the coolant along the coolant ducts are the same for all coolant ducts.

[0014] According to one embodiment of the invention, at least one of the coolant ducts has a cross-sectional shape that varies along at least a portion of its extension. By varying the cross-sectional shape of the coolant duct in its axial direction, for example from a circular cross-sectional shape to an oval cross-sectional shape, the coolant duct can be adapted to obstacles that may be present in the drill body and enable the coolant duct to pass through the obstacles without having to change the spirally curved path of the coolant duct.

[0015] The material thickness of the drill body between the inner wall of each coolant duct and the peripheral surface of the drill body is preferably at least 0.75 mm throughout the coolant duct to ensure sufficient wear depth of the drill body.

[0016] Further advantageous features of the drill body according to the invention will become apparent from the dependent claims and the following description.

[0017] Furthermore, the present invention relates to an indexable insert drill comprising a drill body of the above-mentioned type and a cutting insert attached to an insert mount of the drill body.

[0018] Further advantageous features of the indexable insert drill according to the present invention will become apparent from the following description.

[0019] In the following, embodiments of the invention will be described by way of example with reference to the accompanying drawings, in which: FIG. [Brief description of the drawings]

[0020] [Figure 1] 1A-1D are various perspective views of an indexable insert drill in accordance with one embodiment of the present invention; [Diagram 2] 1A-1D are various perspective views of an indexable insert drill in accordance with one embodiment of the present invention; [Diagram 3] FIG. 3 is a front perspective view of the indexable insert drill of FIGS. 1 and 2 with the central cutting insert removed from the radially innermost insert mount of the drill body of the indexable insert drill; [Figure 4] FIG. 3 is another perspective view of the front of the indexable insert drill of FIGS. 1 and 2 with the peripheral cutting inserts removed from the radially outermost insert mount of the drill body; [Diagram 5] FIG. 3 is a side view of the indexable insert drill of FIGS. 1 and 2. [Figure 6A] FIG. 6 is a cross-sectional view taken along line AA in FIG. 5. [Figure 6B] FIG. 6 is a cross-sectional view taken along line BB in FIG. 5. [Figure 6C] FIG. 6 is a cross-sectional view taken along line CC in FIG. 5. [Figure 6D] FIG. 6 is a cut view taken along line DD in FIG. 5. [Figure 6E] FIG. 6 is a cross-sectional view taken along line EE in FIG. 5. [Figure 6F] FIG. 6 is a cross-sectional view taken along line FF in FIG. 5. [Figure 6G] FIG. 6 is a cross-sectional view taken along line GG in FIG. 5. [Figure 7] FIG. 7 is a rear end view of the indexable insert drill in the direction VII-VII of FIG. 5 . [Figure 8] FIG. 8 is a front end view of the indexable insert drill in the direction VIII-VIII of FIG. 5 . [Figure 9] FIG. 3 is a schematic diagram of coolant ducts and a central coolant supply duct included in the drill body of the indexable insert drill of FIGS. 1 and 2. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] An indexable insert drill 1 according to one embodiment of the present invention is shown in Figures 1-8. The indexable insert drill 1 comprises an elongated drill body 2 and is configured to rotate about an axis of rotation 3. The drill body 2 has a rear end 2a and an opposing front end 2b. A central longitudinal axis 4 of the drill body 2 extends through the center of the drill body between the rear end 2a and the front end 2b, and this longitudinal axis 4 is coincident with the axis of rotation 3 of the indexable insert drill 1.

[0022] A shank portion 5 at the rear end 2a of the drill body 2 forms a connection member that allows the drill body 2 to be attached directly or via an intermediate tool holder to a rotating spindle or the like of a drilling machine or other type of machine tool. In the illustrated embodiment, the shank portion 5 is conical and has a non-circular cross-sectional shape that is adapted to be inserted into a similarly shaped recess of a tool holder or spindle. The conical shape ensures a radially and axially play-free connection between the shank portion and the tool holder / spindle, while the non-circular cross-sectional shape ensures a non-rotatable fixation of the shank portion 5 to the tool holder / spindle. However, the shank portion 5 of the drill body 2 may have any other suitable shape.

[0023] A collar 6 is provided on the drill body 2 forward of the shank portion 5, which protrudes from the collar 6 in the axial direction of the drill body 2 on a first side of the collar 6. The drill body 2 further comprises an elongated helical portion 7 disposed on a second side opposite the collar 6 and extending in the axial direction of the drill body 2.

[0024] The drill body 2 includes a head portion 8 located at a front end 2b of the drill body forward of the helix 7. A first chip flute 10a and a second chip flute 10b are formed in the drill body 2 and extend alongside one another around the circumference of the helix 7. The chip flutes 10a, 10b extend from the head portion 8 towards the collar 6. The chip flutes 10a, 10b are separated from one another in the circumferential direction of the drill body 2 by intermediate ribs 12a, 12b formed in the drill body 2 and extending along the helix 7 alongside the chip flutes 10a, 10b. Each chip flute 10a, 10b and each rib 12a, 12b extends in a helically curved path along the helix 7 of the drill body.

[0025] In the illustrated embodiment, the helix 7 has a rear end located near the collar 6 from which it projects in the axial direction of the drill body 2. In this case, the chip flutes 10a, 10b and the ribs 12a, 12b terminate at the rear end of the helix 7 close to the collar 6. However, the drill body 2 may alternatively comprise an additional elongated portion between the collar 6 and the helix 7, in which the chip flutes 10a, 10b and the ribs 12a, 12b extend parallel, or at least essentially parallel, to the longitudinal axis 4 of the drill body 2 and thus also parallel, or at least essentially parallel, to each other. In the latter case, each chip flute 10, 10b has a first portion extending in a helically curved path along the helix 7 of the drill body and an adjacent second portion extending in a straight, or at least essentially straight, path along said further elongated portion of the drill body 2 between the helix 7 and the collar 6, and each rib 12a, 12b correspondingly has a first portion extending in a helically curved path along the helix 7 of the drill body and an adjacent second portion extending in a straight, or at least essentially straight, path along the further elongated portion of the drill body 2 between the helix 7 and the collar 6.

[0026] A first insert seating portion 14a configured to receive a first cutting insert 15a is arranged on the head portion 8 at the transition between the first chip flute 10a and the front face 9 of the drill body 2, and a second insert seating portion 14b configured to receive a second cutting insert 15b is arranged on the head portion 8 at the transition between the second chip flute 10b and the front face 9 of the drill body 2. In the illustrated embodiment, the first insert seating portion 14a constitutes a central insert seating portion and the second insert seating portion 14b constitutes a peripheral insert seating portion, the second insert seating portion 14b being located at a greater radial distance from the longitudinal axis 4 of the drill body 2 than the first insert seating portion 14a. Each insert seating portion 14a, 14b is open towards the front face 9 of the drill body 2 so that the cutting insert 15a, 15b attached to the insert seating portion can protrude in the axial direction of the drill body 2 past the front face 9 of the drill body 2. Additionally, the second insert mount 14b is open towards the periphery of the drill body 2 to allow a cutting insert 15b attached to the second insert mount to project radially of the drill body 2 past the periphery of the drill body 2. Each chip flute 10a, 10b is disposed within the drill body 2 forward of its associated insert mount 14a, 14b when viewed in the intended direction of rotation R of the drill body 2. In larger sized indexable insert drills, the head 8 may comprise two or more insert mounts 14a with associated cutting inserts 15a disposed adjacent to each other at the transition between the first chip flute 10a and the front face 9 of the drill body 2, and two or more insert mounts 14b with associated cutting inserts 15b disposed adjacent to each other at the transition between the second chip flute 10a and the front face 9 of the drill body 2.In larger size indexable insert drills, more than two chip flutes 10a, 10b, e.g., three or four chip flutes, may be present in the drill body 2 along with a corresponding number of intermediate ribs, and each chip flute may be associated with one or more insert mountings formed at the transition between the chip flute and the front face of the drill body.

[0027] In the illustrated embodiment, the first and second cutting inserts 15a, 15b are geometrically identical to one another. In the illustrated embodiment, each cutting insert 15a, 15b is releasably fixed to the associated insert mounting portion 14a, 14b by a fastening element 16 in the form of a screw that extends through a through hole 17 of the cutting insert 15a, 15b and engages with a threaded hole 18 in a tangential support surface 19 of the insert mounting portion 14a, 14b.

[0028] A coolant duct 20a, 20b is arranged on and runs along each of the aforementioned ribs 12a, 12b. Thus, in the illustrated embodiment, the first coolant duct 20a is arranged on the first of the ribs 12a and the second coolant duct 20b on the other rib 12b. Each coolant duct 20a, 20b has an upstream end 21 with an inlet opening 24a, 24b facing the rear end 2a of the drill body 2 and a downstream end 22 with an outlet opening 25a, 25b in the head 8. The coolant ducts 20a, 20b are arranged closer to each other at the upstream end 21 than at the downstream end 22.

[0029] In the embodiment shown, a central coolant supply duct 26 is provided in the drill body 2 at the rear of the drill body 2, and each coolant duct 20a, 20b opens into the coolant supply duct 26. In this case, the inlet openings 24a, 24b of each coolant duct 20a, 20b are therefore provided at the boundary between the coolant duct and the coolant supply duct 26. However, each coolant duct 20a, 20b may alternatively extend throughout the entire drill body 2, i.e. also through the collar 6 and the shank 5, and have an inlet opening at the rear face of the drill body 2. The inlet openings 24a, 24b of the coolant ducts 20a, 20b may be arranged at the same or essentially the same radial distance from the longitudinal axis 4 of the drill body 2. In the illustrated embodiment, the inlet opening 24b of the second coolant duct 20b is positioned at a somewhat greater radial distance from the longitudinal axis 4 of the drill body 2 than the inlet opening 24a of the first coolant duct 20a, as shown in FIG. 7.

[0030] A coolant supply duct 26 opens at a rear face 27 of the drill body 2 and passes through the shank portion 5 and the collar 6 .

[0031] In order to clearly visualize the coolant ducts 20a, 20b and the coolant supply duct 26, the boundaries between each of the coolant ducts 20a, 20b and the drill body, as well as the boundary between the coolant supply duct 26 and the drill body, are shown in FIG. 9.

[0032] In the illustrated embodiment, the outlet openings 25a, 25b of each coolant duct 20a, 20b are arranged at the front face 9 of the drill body 2. However, each coolant duct 20a, 20b may alternatively open into the associated chip flute 10a, 10b at a position closer to the front face 9 of the drill body 2. The outlet openings 25a, 25b of the coolant ducts 20a, 20b are arranged at different radial distances from each other from the longitudinal axis 4 of the drill body 2, corresponding to the radial positions of the associated insert seats 14a, 14b. Thus, the outlet opening 25a of the first coolant duct 20a associated with the radially innermost first insert seat 14a is located closer to the longitudinal axis 4 of the drill body 2 than the outlet opening 25b of the second coolant duct 20b associated with the radially outermost second insert seat 14b.

[0033] Each coolant duct 20a, 20b extends in a helically curved path along at least a portion of the associated rib 12a, 12b. In the illustrated embodiment, each coolant duct 20a, 20b extends in a helically curved path along the entirety of the associated rib 12a, 12b. However, if there is sufficient space available in the drill body 2 at the rear ends of the ribs 12a, 12b, the rear portions of each coolant duct 20a, 20b may be arranged to extend along a straight line parallel to each other and to the longitudinal axis 4 of the drill body 2. The front portions of each coolant duct 20a, 20b closest to the outlet openings 25a, 25b may also be arranged to extend along a straight line parallel to the longitudinal axis 4 of the drill body 2 or obliquely to the longitudinal axis 4 of the drill body 2.

[0034] The cross-sectional area of ​​each coolant duct 20a, 20b, i.e. the area when viewed in a cross section perpendicular to the central axis of the coolant duct, varies in the axial direction of the coolant duct such that the cross-sectional area at the outlet openings 25a, 25b is smaller than the cross-sectional area at the inlet openings 24a, 24b. Each coolant duct 20a, 20b preferably has a continuously decreasing cross-sectional area when viewed in a direction from its upstream end 21 to its downstream end 22, at least along a part of its extension. Preferably, each coolant duct 20a, 20b has a continuously decreasing cross-sectional area when viewed from its upstream end 21 to its downstream end 22, i.e. a continuously decreasing cross-sectional area over the entire coolant duct when viewed from the inlet openings 24a, 24b to the outlet openings 25a, 25b. However, the cross-sectional area of ​​each coolant duct 20a, 20b may remain constant along some parts of the coolant duct and decrease continuously along other parts of the coolant duct.

[0035] In the illustrated embodiment, the first and second coolant ducts 20a, 20b extend in respective helically curved paths along the circumference of one and the same imaginary cone extending when viewed in a direction from the upstream end 21 towards the downstream end 22 of the coolant ducts. However, each coolant duct 20a, 20b may extend in a helically curved path in any other suitable manner.

[0036] The coolant ducts 20a, 20b are preferably of equal length, have equal cross-sectional areas at the inlet openings 24a, 24b and equal cross-sectional areas at the outlet openings 25a, 25b. Furthermore, the cross-sectional areas of the first and second coolant ducts 20a, 20b preferably vary in the same manner along the extension of the coolant ducts such that the cross-sectional area of ​​the first coolant duct 20a at any axial distance from the inlet opening 24a of the first coolant duct is the same as the cross-sectional area of ​​the second coolant duct 20b at the same axial distance from the inlet opening 24b of the second coolant duct.

[0037] The material thickness of the drill body 2 between the inner wall of any coolant duct 20a, 20b and the surrounding surface of the drill body 2 is at least 0.75mm along the entire coolant duct, thus meaning that the minimum distance between a coolant duct 20a, 20b and the surrounding surface of the drill body 2 is 0.75mm.

[0038] In the illustrated embodiment, the cross-sectional shape is essentially circular along the entirety of the first coolant duct 20a, while the second coolant duct 20b has a cross-sectional shape that varies along a portion of its extension, as shown in Figures 6A-6G. In the illustrated example, the second coolant duct 20b has a circular cross-sectional shape at its inlet opening 24b and outlet opening 25b, and an oval cross-sectional shape in its intermediate portion. The first coolant duct 20a may also have a cross-sectional shape that varies along a portion of its extension.

[0039] The drill body 2 is manufactured from a metal material by 3D printing and subsequent surface milling of the outer surface of the drill body and drilling of various holes in the drill body. For this purpose, a "green body" having a shape corresponding to the outer shape of the drill body 2 to be formed is first manufactured by 3D printing. In the 3D printing, the shank part 5 and the collar 6 are formed without the central coolant supply duct 26, i.e. as solid parts. However, the coolant ducts 20a, 20b in the ribs 12a, 12b are formed in the 3D printing of the green body. The outer surface of the green body manufactured by 3D printing is then machined to obtain the desired surface finish, and the threaded holes 18 of the insert seating parts 14a, 14b and the central coolant supply duct 26 are formed in the green body by drilling, thereby manufacturing the final drill body 2. A hole for a coolant supply duct 26 is drilled in the green body in contact with the downstream end 21 of each coolant duct 20a, 20b such that the coolant duct inlet openings 24a, 24b are formed at the interface between the hole and the coolant duct.

[0040] The present invention is, of course, in no way limited to the above-described embodiments, on the contrary, many possibilities for modification thereof will be apparent to those skilled in the art without departing from the basic concept of the invention as defined in the appended claims.

Claims

1. A drill body for an indexable insert drill, the drill body (2) being elongated and having a rear end (2a) and an opposite front end (2b), a central longitudinal axis (4) of the drill body (2) extending between the rear end (2a) and the front end (2b) of the drill body, the drill body (2) comprising: a shank portion (5) located at the rear end (2a) of the drill body (2) and adapted to be attached to a machine tool; a head (8) located at the front end (2b) of the drill body (2); at least a first chip flute (10a) and a second chip flute (10b) extending side by side along a portion of the drill body (2) from the head portion (8) to the shank portion (5), the chip flutes (10a, 10b) being separated from one another in the circumferential direction of the drill body (2) by intermediate ribs (12a, 12b) formed in the drill body and extending side by side with the chip flutes (10a, 10b), each chip flute (10, 10b) and each rib (12a, 12b) extending in a helically curved path along the associated portion of the drill body; a first insert seat (14a) adapted to receive a first cutting insert and arranged at the transition between said first chip flute (10a) and the front face (9) of said drill body (2); a second insert seat (14b) arranged at the transition between said second chip flute (10b) and said front face (9) of said drill body (2), adapted to receive a second cutting insert; a coolant duct (20a, 20b) arranged in and extending along each of the ribs (12a, 12b), each coolant duct (20a, 20b) extending in a spirally curved path along at least a portion of the associated rib (12a, 12b), each coolant duct (20a, 20b) having an upstream end (21) with an inlet opening (24a, 24b) facing the rear end (2a) of the drill body (2) and a downstream end (22) with an outlet opening (25a, 25b) in the head portion (8); In a drill body comprising: each coolant duct (20a, 20b) has a cross-sectional area that varies in the axial direction of the coolant duct such that the cross-sectional area at the outlet opening (25a, 25b) is smaller than the cross-sectional area at the inlet opening (24a, 24b), Drill body.

2. 2. The drill body according to claim 1, characterized in that each coolant duct (20a, 20b) has, along at least a part of its extension, a continuously decreasing cross-sectional area when viewed in the direction from the upstream end (21) to the downstream end (22).

3. 2. The drill body according to claim 1, characterized in that each coolant duct (20a, 20b) has a cross-sectional area that decreases continuously when viewed from the upstream end (21) to the downstream end (22).

4. 2. Drill body according to claim 1, characterized in that the coolant ducts (20a, 20b) are located closer to each other at the upstream end (21) than at the downstream end (22).

5. 5. The drill body according to claim 4, characterized in that the coolant ducts (20a, 20b) extend in respective spirally curved paths along the periphery of one and the same imaginary cone which widens when viewed in the direction from the upstream end (21) of the coolant duct to the downstream end (22) of the coolant duct.

6. 2. The drill body according to claim 1, characterized in that the inlet openings (24a, 24b) of the coolant ducts (20a, 20b) are located at the same or essentially the same radial distance from the longitudinal axis (4) of the drill body (2).

7. 2. Drill body according to claim 1, characterized in that the outlet openings (25a, 25b) of each coolant duct (20a, 20b) are arranged on the front face (9) of the drill body (2).

8. 8. The drill body according to claim 7, characterized in that the first and second insert mounting portions (14a, 14b) are located at mutually different radial distances from the longitudinal axis (4) of the drill body, and the outlet openings (25a, 25b) of the coolant ducts (20a, 20b) are located at mutually different radial distances from the longitudinal axis (4) of the drill body (2).

9. 2. The drill body according to claim 1, characterized in that a central coolant supply duct (26) is provided in the drill body (2) at the rear of the drill body (2), and each coolant duct (20a, 20b) opens into the central coolant supply duct (26).

10. 2. The drill body according to claim 1, wherein the coolant ducts (20a, 20b) are of equal length, have equal cross-sectional areas at the inlet openings (24a, 24b), and have equal cross-sectional areas at the outlet openings (25a, 25b), and the cross-sectional areas of the coolant ducts (20a, 20b) vary in the same manner along the extension of the different coolant ducts, such that the cross-sectional area of one coolant duct at any axial distance from its inlet opening (24a, 24b) is the same as the cross-sectional area of the other one of the other coolant ducts at the same axial distance from its inlet opening (24a, 24b).

11. The drill body according to claim 1, characterized in that at least one of the coolant ducts (20a, 20b) has a cross-sectional shape that varies along at least a portion of the extension of the coolant duct.

12. 2. The drill body according to claim 1, wherein the material thickness of the drill body (2) between the inner wall of each coolant duct (20a, 20b) and the peripheral surface of the drill body is at least 0.75 mm throughout the coolant duct.

13. An indexable insert drill comprising the drill body (2) according to any one of claims 1 to 12 and cutting inserts (15a, 15b) attached to the insert mounts (14a, 14b) of the drill body.

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