The invention relates to a drill bit according to the preamble of claim 1. The invention also relates to a device for producing a drill bit according to the preamble of claim 7 and to a method for producing a drill bit according to the preamble of claim 9. EP 0 843 772 Bl describes various variants for shaping and producing drill bits having a drill head which is made of carbide and is inserted into a slot-shaped connecting groove in an end region of the shank. Extending next to the connecting groove are transition surfaces of the shank which form the transition to a helix. The transition surfaces are each provided with surface sections, wherein the two surface sections are set against one another and converge at an intersecting edge. In particular, the two surface sections are each flat and are oriented at different angles both relative to the longitudinal axis of the shank and relative to the longitudinal extent of the connecting groove accommodating the drill head. The production of the drill bit having transition surfaces designed in such a way is complicated.

The problem addressed by the invention is to specify a drill bit, a method for producing it and a production device in such a way that especially simple production in a few operations is made possible.

For a drill bit mentioned at the beginning, the above problem is solved according to the invention by the characterizing features of claim 1.

The construction of the transition surface from surface curves which in each case originate from a parallel displacement of at least one segment of the groove base curve leads to ease of production and in particular to a drill bit which works effectively.

Transition surfaces m the context of the invention are planar regions of the shank which are arranged in particular on both sides of the connecting groove and which extend over most of the connecting groove. The transition surfaces form a substantial portion of the axial transition from the top marginal region of the connecting groove to the helix.

A "surface curve" of such a transition surface refers to any curve which extends over the transition surface and which lies completely in the transition surface. A "groove base curve" in the context of the invention is a curve along which the base of the connecting groove extends longitudinally. Individual recesses or the like which are incorporated in the base of the connecting groove do not influence the longitudinal extent of the base of the connecting groove in this context .

The transition surfaces arranged in particular on both sides of the connecting groove can be designed symmetrically at least in a region around the connecting groove. Depending on reguirements , however, said transition surfaces can also be surfaces which vary in shape and orientation. As mentioned above, the transition surfaces play a considerable part in the axial transition from the top marginal region of the connecting groove to the helix. Against this background, provision is preferably made for the transition surface to extend axially starting from the top marginal region of the connecting groove, preferably for it to extend axially at any rate in sections over more than half the depth of the connecting groove. In a preferred embodiment of the invention, the groove base curve has a straight course. A straight course of the groove base curve can be produced in an especially simple manner. In an alternative embodiment of the invention, the groove base curve has, at least in sections, a curved course. In an especially preferred manner, the curved course can have, at least in sections, the shape of part of a conic section, in particular an ellipse, circle or parabola.

Depending on reguirements, the groove base curve, in the course thereof, can also have a local minimum or a local maximum.

In general, the groove base curve, depending on reguirements imposed on the configuration of the transition surfaces, can have both curved and straight sections. It is possible to arrange straight sections in a row with angles provided in between, e.g. while forming a roof-shaped groove base curve overall.

The transition surface is preferably designed to be continuous and has no edges. This has proved to be especially advantageous for the removal of the drillings. In an especially preferred embodiment, the transition surface is even designed to be flat. This can be realized especially easily from the production point of view.

The outline of the transition surface can assume different shapes; for example, it can be rectangular or oval. However, the outline of the transition surface is preferably substantially trapezoidal.

Furthermore, in particular in the case of the flat transition surface, the transition surface is preferably inclined relative to the longitudinal axis of the shank. With the degree of the inclination of the transition surface, the removal of drillings can be specifically set. Especially good results have been shown at an angle of inclination of between about 30° and about 40°, in particular around about 35°.

The transition surface extends over a substantial part of the width of the shank, in particular over the entire width of the shank. This is very simple to achieve from the production point of view.

For a device mentioned at the beginning, the above problem is achieved by the characterizing features of claim 7. Steps for machining the shank can be saved or simplified by the arrangement of a second tool part next to the first tool part for the simultaneous incorporation of the connecting groove and at least one transition surface in the shank. In a preferred development of the device, a third tool part is arranged on the opposite side of the first tool part with respect to the second tool part and is rotatable together with the first tool part about the same rotation axis, wherein, at the same time as the connecting groove is incorporated, a second transition surface is shaped by the third tool part, said transition surface being arranged on the opposite side of the connecting groove with respect to the first transition surface. In the production method according to the invention, the connecting groove for accommodating the drill head and both transition surfaces adjoining the connecting groove can be produced simultaneously in one operation by such a device. The simultaneous incorporation of the connecting groove and a transition surface in the context of the invention refers to the fact that simultaneous removal of material for shaping the transition surface and of material for shaping the connecting groove takes place.

In an especially advantageous manner, at least one of the tool parts has a blade for the controlled removal of a chip from the shank. Thus, for example, the first tool part can be formed as a saw, the connecting groove being sawn in the shank. Alternatively or additionally, the second and/or the third tool part can be formed as milling tools with a milling blade for controlled cutting.

For a method mentioned at the beginning, the above problem is solved by the features of claim 9. A movement of the device and the shank relative to one another refers in the context of the invention to any relative movement resulting from an overlap of device and shank with resulting material removal for forming the connecting groove and the transition surface. In this case, either the device can be in a fixed position and the shank can be moved relative to the device or the shank can be clamped in a fixed position and the device can be moved relative to the shank, or both the shank and the device can be moved relative to the fixed location and relative to one another.

In this case, according to the device for producing a drill bit according to the features of either of claims 7 and 8, simultaneous removal of material of the transition surface and of material of the connecting groove is effected, at least over a section of the relative movement. As a result, in particular separate operations taking place in succession for shaping the connecting groove and the transition surface can be dispensed with.

In an advantageous development, the longitudinal axis of the shank and the rotation axis of the device are in this case disposed substantially perpendicularly to one another. As a result, the connecting groove can be slit parallel to the longitudinal axis of the shank in a simple manner. In principle, the longitudinal axis of the shank and the rotation axis can enclose largely any desired angles with one another, such that the vertical extent of the connecting groove is not necessarily oriented parallel to the longitudinal axis of the shank .

In an embodiment of the invention, the movement of the device relative to the shank runs along a straight line, wherein the straight line is disposed in particular perpendicularly to the longitudinal axis of the shank and, in a further preferred manner, runs through the longitudinal axis of the shank. As a result, inter alia, a flat connecting groove base can be formed, wherein transition surfaces which have a flat surface are advantageously formed.

In very general terms, the movement of the device relative to the shank runs along a machining trajectory. Such a machining trajectory can have largely any desired form. The machining trajectory preferably lies completely in a plane parallel to the longitudinal axis of the shank, wherein the longitudinal axis of the shank, in a further preferred manner, lies in this plane. For example, the machining trajectory can have the form of a curved line, in which case the curved line can pass through, in particular, a local maximum or a local minimum. The curved line can also have straight sections or the machining trajectory can consist of curved and straight sections or only of straight sections angled relative to one another. A completely straight line is also a machining trajectory in the context of the invention.

In addition, the above problem is achieved by a drill bit which is produced or can be produced according to the features of claims 9 to 12 according to a method according to the invention.

The drill bit according to the proposal is preferably configured as a masonry drill bit which is designed in particular for hammer operation. However, the solution according to the proposal can also be applied to all other conceivable types of drill bit. Further advantages and features of the invention follow from the exemplary embodiments described below and from the dependent claims .

Several exemplary embodiments of the invention are described below and are explained in more detail with reference to the attached drawings, in which:

1 shows a three-dimensional schematic view of a device according to the invention for producing a drill bit during machining of a drill bit according to the invention, fig. 2 shows a three-dimensional view of a first exemplary embodiment of a drill bit according to the invention having a shank and a drill head, fig. 3 shows a further three-dimensional view of the drill bit from fig. 2, fig. 4 shows a three-dimensional view of the shank of the drill from fig. 2 without inserted drill head, fig. 5 shows the shank of a drill bit according to a second exemplary embodiment according to the invention, fig. 6 shows a plan view of a half section of the drill bit from fig. 5 along the longitudinal axis of the shank,

7 shows a three-dimensional view of the shank of a further exemplary embodiment of a drill bit according to the invention,

8 shows a plan view of a half section of the drill bit from fig. 7 along the longitudinal axis of the shank.

The device shown in fig. 1 for producing a drill bit which comprises a shank 5 having a helix 6 and a drill head 9 exhibits a first central tool part 1 and two tool parts 2, 3 arranged on both sides of the tool part 1. The tool parts 1, 2, 3 are only shown schematically with respect to an enveloping form which results from rotation of the tool parts 1, 2, 3 about a common rotation axis la. The tool parts 1, 2, 3 are expediently accommodated on a common rotary shaft (not shown) for rotation therewith.

The central tool part 1 is a saw like a circular saw blade for machining a connecting groove 4 in a front end of the shank 5 of a drill bit.

The tool parts 2, 3 are peripheral milling cutters with milling blades (not shown), the milling blades having in particular a straight edge which is inclined by an angle W relative to a plane perpendicular to the rotation axis la.

In a known manner, the shank 5 of the drill bit has the helix 6 for removing drillings, the helix 6 ending at a front end region 7 of the shank 5. An insertion end of the drill bit for accommodating in, for example, a rotary hammer, said insertion end being arranged at the opposite end of the shank 5, is not shown in detail. Said insertion end can be in particular an SDS-plus® or SDS-max® insertion end.

In the present example, the helix 6 is shaped in a grinding or milling process, with rotation and simultaneous axial linear movement of the shank 5. When the helix 6 has been shaped, the rotary movement of the shank 5 is stopped and only the axial linear movement is continued, such that two steep, stepped flanks 8 are shaped in the end region 7 of the shank 5.

The end region 7 comprises the connecting groove 4, which extends in the form of a longitudinal slot over the entire width of the shank 5 and has a base 4a and two parallel side walls . A drill head 9 made of carbide is inserted into the connecting groove 4 and secured in a known manner by brazing. In the present example, the drill head 9 is provided with cutting edges 10 which extend outward from the longitudinal axis 5a of the shank 5. Here, the cutting edges 10 are preferably set against one another and form a substantially roof- shaped drill head 9 overall .

Here, two transition surfaces 11 of the shank 5 are formed on both sides of the connecting groove 4, wherein, in the present example, both transition surfaces 11 have been produced simultaneously with the milling-out of the connecting groove 4 by means of the device shown in fig. 1.

On account of the movement of the shank 5 and of the tool parts 1, 2, 3 relative to one another, the transition surfaces 11 are formed in the course of the production in such a way that said transition surfaces 11 each originate from a parallel displacement of a groove base curve 4b. The meaning of the term "groove base curve" was explained further above. Essential in the context of the invention is the principle that, by the simultaneous fashioning, explained in connection with fig. 1, of the connecting groove 4 and the transition surfaces 11 by means of rotating tool parts 1, 2, 3 and a movement of the shank 5 relative to the tool parts 1, 2, 3, transition surfaces 11 having surface curves 12 are produced which originate from parallel displacements of a groove base curve 4b. In the figures, in each case only a single surface curve 12 representing all further surface curves is shown.

In the course of the shaping of the connecting groove 4 and of the transition surfaces 11, the shank 5 or the tool part 1, 2, 3 in fig. 1 is moved in the direction of the groove extent 4c, which runs perpendicularly to the rotation axis la of the tool part 1, 2, 3 and perpendicularly to the longitudinal axis 5a of the shank 5.

A movement of the shank 5 relative to the tool part 1, 2, 3 in the direction of the rotation axis la is not effected in the present exemplary embodiment, but can in principle also be provided.

A relative movement of shank 5 and tool part 1, 2, 3 in the direction of the longitudinal axis 5a of the shank 5 is not provided in the first exemplary embodiment in the course of the production of the connecting groove 4 (straight machining trajectory), but can in principle be provided (non-linear machining trajectory, preferably completely in a plane oriented parallel to the longitudinal axis 5a and the groove extent 4c) . On account of the above-described relative movements and of the above-described shaping by the tool parts 1, 2, 3, a connecting groove 4 of substantially rectangular cross section having a straight, flat connecting groove base is produced. In addition, transition surfaces 11 arranged on both sides of the connecting groove 4 are produced, which transition surfaces 11 are likewise flat and have in the present case, but not necessarily, the same inclination angle W relative to the longitudinal axis 5a of the shank 5.

Narrow end faces 13 are located between the connecting groove 4 and the start of the transition surfaces 11, that is to say in the top marginal region of the connecting groove 4. The narrow end faces 13 are segments of an end face of the shank 5 which are left behind after the machining steps are carried out, which end face had the shape of a flat cone before the above machining steps due to a turning operation. This explains the fact that the flat end faces 13, shown in fig. 4 for example, have a slightly curved course of their margin. The end faces 13 are not transition surfaces in the context of the invention.

Fig. 5 shows a second exemplary embodiment of the invention, which in principle can be produced by the device schematically shown in fig. 1. In contrast to the first exemplary embodiment, the relative movement between the shank 5 and the device is not effected exclusively along a straight line in the direction of the groove extent 4c, but rather along a machining trajectory which lies completely in a plane oriented parallel to the groove extent 4c and the longitudinal axis 5a of the shank 5. The machining trajectory corresponds, at least over a segment, to the course of the groove base curve 4b.

In the example according to fig. 5, unlike in the first exemplary embodiment, no narrow end face has been left behind, and so the top edge of the connecting groove margin at the same time corresponds to a surface curve of the transition surfaces 11 of the end region 7 of the shank 5.

The transition surfaces 11 have a family of surface curves 12 which are each formed as section curves of the respective transition surface 11 with a section plane parallel to the grove extent 4c and the longitudinal axis 5a of the shank 5. Here, these surface curves 12 are each preferably a parallel displacement of at least one segment of the groove base curve 4b.

In this case, the groove base curve 4b is at the same time a segment of the movement trajectory of the relative movement of the shank 5 and the tool parts 1, 2, 3. The curved movement trajectory is in this case part of a conic section line, in particular part of a circular line. It has a local minimum or a deepest point which lies in the longitudinal axis 5a of the shank 5.

Shown in fig. 7 and fig. 8 is a further exemplary embodiment in which the groove base curve 4b forms a curved line inverted compared with the preceding example. Accordingly, the movement trajectory of the relative movement of shank 5 and tool part 1, 2, 3 has a local minimum in the longitudinal axis 5a of the shank 5. In the example according to fig. 7 and fig. 8, two narrow end faces 13 of the shank 5 have been left behind in the top marginal region of the connecting groove 4, as in the first exemplary embodiment. An exemplary surface curve 12, displaced parallel to the groove base curve 4b, of the transition surface 11 is depicted by a broken line in fig. 7 and results as a section curve between one of the transition surfaces 11 and a section plane parallel to the groove extent 4c and the longitudinal axis 5a.

Provided the above-described groove base curves 4b have a maximum or a minimum, the maximum or minimum preferably lies in the longitudinal axis 5a of the shank 5. In principle, however, provision may also be made for the maximum or the minimum to lie outside the longitudinal axis 5a. The resulting, asymmetrical configuration can be advantageous from the vibration point of view.

Finally, it may be pointed out that, here, the end-face connecting groove 4 of the shank 5 is preferably the only groove 4 extending over the entire shank width. However, it is also conceivable for a plurality of such connecting grooves 4 to be provided, which possibly intersect. For example, this plurality of connecting grooves 4, as viewed from above, run at an angle to one another, for example at an angle of 90° or 120°. In principle, however, provision may also be made for two connecting grooves 4, as viewed from above, to enclose only a small angle with one another, to run next to one another and to merge into one another at least in one region of the shank 5.