DRILLING TOOL

Description

[0001] The invention relates to a drilling tool, in particular a twist drill for metallic materials, plastics or composite materials (composite materials), with a shank and a drill bit which has at least two main cutting edges (preferably three or more main cutting edges) on its front side, which are formed by adjacent chip and flank surfaces, wherein one of the main cutting edges extends at least as far as the longitudinal axis of the drill, and with straight or helical chip flutes.

[0002] Twist drills of the type mentioned are used in particular for drilling into solid material. Such a drilling tool according to the preamble of claim 1 is known from document DE 33 39 211 A.

[0003] The twist drills originally used in the state of the art have a wedge-shaped drill tip with two or more main cutting edges and secondary cutting edges arranged helically along the outer surface of the drill, with chip flutes arranged between them. This drill section, which contains the main and secondary cutting edges, is connected to a cylindrical shank as the clamping end. In twist drills with a wedge-shaped drill head, the wedge angle formed by the main cutting edges is 118° to 130°. Depending on the material, twist drills with different side rake angles are used.

[0004] To create a blind hole with a flat, level hole bottom, EP 1 748 859 B1 proposes a drill in which the two main cutting edges of the drill face form a common, continuous cutting edge that runs in a plane perpendicular to the drill's longitudinal axis. The two main cutting edges are thus oriented at an angle of 180° to each other. Such a drill has no forward-facing tip, so that the bottom of the hole is completely flat and level. The cutting edge formed by the main cutting edges should extend across the entire drill diameter and form a point-symmetrical arrangement with respect to the drill center.

[0005] However, drills with a wedge-shaped drill tip have the disadvantage that, especially for large drill diameters, a pilot hole with a narrow drill diameter must first be made, whereby the pilot hole determines the centering of the drill wedge tip.

[0006] Drills with a main cutting edge that runs linearly perpendicular to the drill's longitudinal axis practically do not allow for reliable centering. With handheld drills or those where the workpiece cannot be clamped relative to the drill holder, precise positioning of the drill hole is almost impossible.

[0007] It is therefore an object of the present invention to eliminate this disadvantage and to provide a drilling tool which, due to its design, enables reliable centering.

[0008] This object is achieved by a drilling tool according to claim 1, which is characterized in that the main cutting edges have an outer projecting cutting point located outside the longitudinal axis of the drill, seen in the direction of drilling progress, from which projecting cutting point the cutting edges drop towards the longitudinal axis of the drill and in that a trailing cutting edge is connected to the radially outermost projecting cutting point of the main cutting edges, which runs at an inclination of at least 10° with respect to the remaining lateral surface lying parallel to the longitudinal axis of the drill and which has a longitudinal axial extent of between 1.5 mm and 5 mm.

[0009] The combination of these measures ensures reliable centering. When the clamped drilling tool rotates, the radially outermost point of the main cutting edges or the main cutting edge defines a circle with a radius that either corresponds to the final hole diameter or almost corresponds to the final hole diameter. Unlike a drill head with a wedge-shaped drill tip, this ensures the local fixation of the drill during machining. The main cutting edges, which are inclined "backward" toward the longitudinal center of the drill, generate cutting forces during machining that effectively prevent the drill from deflecting sideways during drilling. The trailing cutting edges, which extend radially outward and are inclined at an angle of at least 10°, provide corresponding, and possibly supporting, forces.

[0010] Further developments of the invention are described in the subclaims. Thus, each of the main cutting edges, preferably each of the three main cutting edges, can be linear, convex, or concave when viewed in a cross-sectional view, preferably such that the linear main cutting edge or a connecting line of the end points of the convex or concave main cutting edge is inclined at an angle of between 3° and 20° to a transverse plane perpendicular to the drill's longitudinal center axis. An optimal angle is 10° ± 3°, as this provides an ideal compromise between drill centering and rapid drilling progress.

[0011] In order to prevent edge chipping between the trailing edge and the main cutting edge, there is a chamfer between the two cutting edges, which is preferably arranged at an angle between 40° and 50°, for example 45°.

[0012] According to a further preferred embodiment, the trailing edge is followed by another cutting edge with a convexly curved profile, preferably with a radius of curvature R between 1 mm and 1.5 mm. Such a curved profile of the (extended) trailing edge serves in particular to smooth the bore wall.

[0013] According to a further embodiment, an additional cutting edge for cutting a chamfer, preferably at an angle of 45°, can be provided between the drill bit and the shank for clamping the drilling tool. Such a chamfer prevents a sharp upper edge of the bore wall and, if necessary, serves as a centering aid for inserting pin-shaped tool parts, in principle known from the prior art.

[0014] As already mentioned, a main cutting edge is formed by a rake face and a flank face that adjoin each other. Preferably, the rake angle of the rake face is negative to enable a so-called "draw cut."

[0015] To improve chip breaking and thus facilitate chip removal via the helical chip forming grooves, a further embodiment of the invention provides chip forming elements in the rake faces of the main cutting edges. These elements are designed as chip forming grooves and / or chip forming elevations, in particular ribs. Chip forming grooves cause the chip flowing from the cutting edge to undergo a curvature, which leads to early chip breaking due to the chip forming groove itself or due to ribs arranged in the chip forming groove.

[0016] According to a further embodiment of the invention, the main cutting edges can have additional notches, preferably groove-shaped recesses, which are arranged at different axial distances, in particular from one main cutting edge to the next, so that the grooves follow different cutting paths as the drilling tool rotates. This measure significantly improves the cutting performance, i.e., the drilling progress.

[0017] Depending on the application, the one-piece drill body is made of a hard metal or a high-speed steel.

[0018] In order to improve the cutting performance in the area of ​​the drill's longitudinal axis, one of the main cutting edges used is designed to be longer than the other or remaining main cutting edges, i.e. one of the main cutting edges runs through the drill's longitudinal center axis and thus has a section that overshoots the drill's axis, whereas the other main cutting edge or the other main cutting edges end before the drill's longitudinal center axis.

[0019] Further details of the invention and preferred embodiments are explained below with reference to the drawings. Each of them shows a schematic diagram: Fig. 1 a simplified side view of a drilling tool, Fig. 2 a detailed view "X" according to Fig. 1 , Fig. 3 to 12 different schematic diagrams of various designs.

[0020] It should be noted that drilling tools with an insert shank and a drill bit with incorporated helical or linear chip-forming grooves are generally known. The chip chambers and the webs between the chip chambers are omitted from the drawings.

[0021] The drill according to the invention has in the Fig. 1 The version shown comprises a cylindrical clamping shank 20 and a shank portion 21 formed with the aforementioned chip grooves and the drill head. Between the clamping shank 20 and the shank portion 21, a chamfer 22 is provided at an angle γ of 45°, which serves to chamfer a drill hole edge. The drill bit has at least two main cutting edges 23, 24, which are inclined at an angle α with respect to a plane 27 vertical to the drill's longitudinal center axis 26. Fig. 3 , which shows a top view of the drill face, it can be seen that of the three main cutting edges 23, 24, and 25 used, one of the cutting edges 25 is extended and extends beyond the point determined by the drill's central longitudinal axis 26. The other main cutting edges 24 and 23 each end before the point determined by the drill's central longitudinal axis 26. In the "drilling center," the cutting work is therefore performed by the cutting edge 25 or its corresponding extension. The three main cutting edges 23, 24, and 25 used are arranged offset by 120° from one another.

[0022] The cutting edges 23, 24, and 25 can be linear or curved, namely concave or convex, when viewed in a cross-sectional view. Convex and concave curvatures of the main cutting edges result in an extended cutting edge. As a detailed view of the drill head in Fig. 2 shows, the main cutting edge 23 with its radially outer point 231 is followed by a chamfer 28 inclined at 45° to the longitudinal axis 26 of the drill, the width a1 of which can be selected to be comparatively small and less than 0.5 mm, because this chamfer 28 only serves to stabilize the edge area between the main cutting edge 23 and the trailing cutting edge 29. When the drilling tool is placed on the workpiece, this first comes into contact with point 231 of the drilling tool. This end of the main cutting edge 23 describes a drilling circle when the tool is rotating. The inclination of the main cutting edges 23, 24 and 25 effects a force distribution that effectively prevents the drill from deflecting to the side.

[0023] The chamfer 28 is followed by a trailing edge 29, which is straight in the part adjacent to the chamfer 28 (viewed in cross-section). This trailing edge 29 can transition at its rear end into a curved further edge 30 with a convex radius of more than 1 mm, for example 1.2 mm, before the diameter D1, which is determined by the band areas between the chip forming troughs, is reached.

[0024] Fig. 4 shows details of the first measures, namely the inclination of the main cutting edges 23 and 24 relative to a transverse plane 27 by an angle α, which lies between 3° and 20°, preferably 10° ± 5°. The trailing edge with a longitudinal axial extension by a dimension a of 1.5 mm to 5 mm, for example 3 mm, and its inclination by an angle β of 10° to 25°, preferably 15°, are the measures to ensure optimal drilling tool centering. In addition, and in Fig. 5 Shown is the division of the trailing cutting edge 29 into a linear part and a curved convex part 30 with a radius R. In the dimension a shown, the curved cutting edge portion is, for example, approximately 0.3 mm long.

[0025] Fig. 6 shows a drill body on whose drill head the respective main cutting edge is divided, namely into - related to the drilling progress - a front part 23' and 24' and respective rear parts 23" and 24", which are connected to one another via a connecting piece 23‴ and 24‴. As the drilling progresses, the marked end points 231 and 241 of the drilling tool first come into contact with the drill piece (not shown). As soon as the drilling tool has cut a drilling depth corresponding to the dimension c, the outer points 232 and 242 of the outer main cutting edges 23" and 24" first touch the workpiece, so that the continued main cutting edges 23" and 24" now begin their cutting work. The inclination of the connecting surfaces 23‴ and 24‴ by the angle ε is at angles of maximum 20°, preferably 10°. The areas 23" and 23‴ or 24" and 24‴ merge into each other via a groove with radius R1.The surfaces of areas 23' and 23" as well as 24' and 24" are offset parallel to each other.

[0026] Fig. 7 shows the already in Fig. 3 The main cutting edges 25, 24 and 23 shown in the drawing are provided with an over-center length of the main cutting edge 25 and three holes 31 through which a coolant can be fed to the drill tip. The coolant holes are parallel to the chip flutes and, depending on their shape, have a helical or straight course, as shown in Fig. 8 und 9 shown by lines 32 and 33. In the latter case, the angle at which the chip breaker grooves end at the drill tip is δ=30°.

[0027] Another alternative shows Fig. 10 , in which the main cutting edges 23 and 24 have additional notches 34 to 37. The distance of these notches from the drill center longitudinal axis 26, that is to say specifically the distance between the notches 35 and 36 on the one hand and 34 and 37 on the other hand, is preferably of different sizes, so that when the tool rotates, the notches describe different circular paths.

[0028] Fig. 11 shows an example of a drilling tool with a chamfer 38 inclined at 45°.

[0029] Out of Fig. 12 It should be clear that the cutting surface 39, which adjoins the main cutting edge 24, is arranged at a negative cutting angle. As can also be seen from Fig. 13As can be seen, at least one chip-forming recess 40 and at least one raised chip-forming element 41 are provided in the rake face 39. The chip-forming element 41 can have a rib-shaped configuration. The rake face at a negative rake angle, in conjunction with the chip-forming recess 40, causes a forced curvature of the chip running from the main cutting edge 24. Furthermore, the chip is undulated in the transverse direction by the raised chip-forming elements 41, which ultimately leads to chip breakage and thus prevents the formation of longer chips. This is of considerable importance with regard to chip removal via the chip flutes.

Claims

1. Drilling tool, in particular twist drill for metallic materials, plastics or composite materials (compound materials), with a shank (20) and a drill bit which has at least two main cutting edges, preferably three or more main cutting edges (23, 24, 25), on its end face, which are formed by respective adjacent chip and flank faces, wherein one of the main cutting edges extends at least as far as the longitudinal axis of the drill, and with straight or helical flutes, characterized in that the main cutting edges (23, 24, 25) possess an outer cutting point which lies outside the longitudinal axis (26) of the drill and projects as seen in the direction of the drilling progress, from which the main cutting edges (23, 24, 25) slope towards the longitudinal axis of the drill, and in that the radially outermost projecting cutting points (231, 241) of the main cutting edges (23, 24, 25) are adjoined by a drag cutting edge (29) which is inclined by at least 10° relative to the remaining lateral surface lying parallel to the longitudinal axis (26) of the drill and possesses a longitudinal axial extension (a) of between 1.5 mm and 5 mm.

2. Drilling tool according to claim 1, characterized in that the main cutting edges (23, 24, 25), preferably each of the three main cutting edges viewed in a cross-sectional view, are formed linear, convex or concave, preferably in such a way that the linear main cutting edge or a connecting line of the corner points of the concave or convex main cutting edge is inclined at an angle of 3°< α <20° to a transverse plane (27) lying perpendicular to the longitudinal axis (26) of the drill.

3. Drilling tool according to claim 1 or 2, characterized in that a chamfer (28) is arranged between the drag cutting edge (29) and the main cutting edge (23, 24, 25), preferably at an angle β between 40° and 50°.

4. Drilling tool according to one of claims 1 to 3, characterized in that the drag cutting edge (29) is followed by a further cutting edge (30) with a convex curved course, preferably with a radius of curvature R of between 1 mm and 1.5 mm.

5. Drilling tool according to one of claims 1 to 4, characterized in that a cutting edge (22, 38) for cutting a chamfer is arranged between the drill bit and the shank (20) for clamping the drilling tool, preferably at an angle ε of 45°.

6. Drilling tool according to one of claims 1 to 5, characterized in that the chip faces (39) of the main cutting edges (23, 24, 25) are arranged at a negative chip angle.

7. Drilling tool according to one of claims 1 to 6, characterized in that the chip faces (39) of the main cutting edges (23, 24, 25) have chip-forming elements which are formed as a chip-forming hollow (40) and / or chip-forming elevation (41), in particular a rib.

8. Drilling tool according to one of claims 1 to 7, characterized in that the main cutting edges (23, 24, 25) have notches (34 to 37), preferably groove-shaped recesses, wherein preferably an axial distance is selected which is different from main cutting edge (23) to main cutting edge (24), so that the grooves run through different cutting paths.

9. Drilling tool according to one of claims 1 to 8, characterized in that the one-piece drill body consists of a carbide or high-speed steel (HSS).

10. Drilling tool according to one of claims 1 to 9, characterized in that one of the main cutting edges (25) passes through the longitudinal central axis (26) of the drill and thus possesses a section which extends beyond the drill axis, whereas the other main cutting edge(s) (23, 24) end(s) in front of the longitudinal central axis (26) of the drill.