Drilling tool and method for producing drilling tool

Abstract

The drill tool (2) extends along an axis of rotation (4) and comprises at least three main cutting surfaces (6), each extending in the direction of the axis of rotation (4) starting from a cutting corner (8) arranged on a radius (r). The at least three main cutting surfaces (6) converge on the sharp drill tip (5), in particular in the absence of transverse cutting surfaces. Starting from the drill tip (5) and over its entire radial extent, each main cutting surface (6) adjoins an edgeless surface (10) comprising a clearance surface (14) and transitioning in each case into a respective flute (12).

Description

Field of the Invention

[0001] The present invention relates to a drill tool and a method for manufacturing a drill tool. Background Art

[0002] The geometry and design of the tip of a drill tool are generally crucial in a drill tool. In this context, the interaction of the cutting surface, the clearance surface, and the chip flutes is important.

[0003] Typical drill tools include two main cutting surfaces and chip flutes associated with each of them. The chip flutes generally extend in a helical manner along the axis of the drill tool. In addition to solid carbide drill tools in one piece, modular drill tools are also known, in which reversibly replaceable drill tools can be attached to the shaft.

[0004] A drill tool having two main cutting surfaces that are connected to each other at the center of the drill tool via a transverse cutting surface can be gleaned from EP 1 230 058 B1. The clearance surfaces are each designed as a curved surface of the respective main cutting surface, and the curved surface is designed to be edge-free in the direction of the chip flutes.

[0005] A drill tool including three main cutting surfaces that are interconnected via a transverse cutting surface and generally have a complex cutting geometry can be gleaned from US2011 / 0085868 A1.

[0006] In a drill tool, there is generally a problem of maximizing the positional accuracy at the start of a drilling operation. In particular, in the case of a smooth surface or a surface oriented obliquely to the longitudinal axis of the drill tool, there is generally a problem that the drill tool will be slightly laterally offset relative to the desired target position. In addition, the front of the drill tool is subjected to high mechanical friction loads, especially in the case of hard materials, which may lead to a high level of wear. Another problem in the case of carbide drill tools is that although they do have a high level of hardness, they also have a high level of brittleness, so a point load may cause scratching activity, which may lead to chipping of the drill tool material. Summary of the Invention

[0007] Based on this, an object of the present invention is to provide a drill tool and a manufacturing method thereof, wherein the drill tool is characterized by a high level of positional accuracy and low wear.

[0008] The object according to the invention is achieved by a drill which extends along a rotational axis and has at least three, preferably exactly three, main cutting surfaces. Starting from a cutting corner arranged radially, these cutting surfaces each extend in the direction of the rotational axis. The at least three main cutting surfaces converge at the drill tip. Additionally, starting from the drill tip and along the radial extent of the respective main cutting surface, the respective main cutting surface is circumferentially adjacent to an edge-free surface. This edge-free surface also includes at least a part of a clearance surface which, in each case, transitions into a respective chip flute.

[0009] It should first be emphasized that the respective main cutting surface extends as far as the drill tip and thus as far as the rotational axis. The drill tip is arranged on the rotational axis. The main cutting surfaces converge at a common point. Thus, the drill tip is pointed. Due to the very low or only minimal risk of lateral displacement at the start of the drilling operation, the pointed drill tip achieves a high level of initial positioning accuracy. In contrast, conventional drills including transverse cutting surfaces have this problem.

[0010] In the context here - within the manufacturing tolerances - a "pointed" surface should be understood to mean a surface with a diameter of less than 100 μm, in particular less than 20 μm. Thus, the drill tip is formed within the manufacturing tolerances by the position where the main cutting surfaces meet.

[0011] It should be particularly emphasized that the main cutting surface - starting from the drill tip and up to the cutting corner - is circumferentially adjacent to an edge-free surface which at least partly and preferably completely forms a clearance surface extending as far as the chip flute. The term "clearance surface" is generally understood to mean a surface which is adjacent to the respective main cutting surface, is inclined with respect to the horizontal plane (plane perpendicular to the rotational axis) and extends as far as the respective chip flute. The clearance surface forms a clearance angle with respect to such a horizontal plane and is typically in the range of a few degrees.

[0012] It should also be emphasized that this clearance surface which is edge-free adjacent to the respective main cutting surface extends as far as the pointed drill tip. In the case of conventional drills, typically at least one transverse cutting surface and also what is otherwise referred to as a "point" are introduced in the central region and formed by means of separate grinding. Steps are produced in the direction of the clearance surface by means of a separate grinding step and thus an edge is created. Then, by providing an edge-free design for each surface adjacent to the respective main cutting surface, wear is minimized due to the absence of an edge. This design is also particularly suitable for carbide drills because the absence of an edge in the highly stressed front region of the drill avoids point or line loads which can lead to high scratching activity and thus material chipping.

[0013] The stated object is also achieved by a method for producing such a drill, in which a non-edged surface is formed using a grinding method, and in which only one corresponding grinding step is provided for each non-edged surface. Thus, the entire non-edged surface is achieved in only a single continuous grinding step without multiple attachments of grinding disks. Preferably, the entire surface is ground in only a single grinding step, the entire surface adjoining a corresponding transverse cutting surface and extending in the circumferential direction as far as the chip flute, thus also including the entire clearance surface. The grinding disk and the drill are moved continuously and without relative removal with respect to each other in a suitable three-dimensional movement sequence. As a result of the continuous movement, the grinding disk thus moves continuously along a specified trajectory relative to the drill. Given that this relative movement does not stop or interrupt, the formation of edges is reliably avoided.

[0014] Thus, the term "non-edged" is specifically understood to mean the progression of a surface in which no sharp edge is formed between adjacent surface sections. The term "sharp edge" also refers to the transition between successive surface sections, the radius of which reaches a maximum of 3% of the drill diameter and preferably a maximum of 1% of the drill diameter in mm.

[0015] Further advantageously, the drill thus does not include a transverse cutting surface, i.e., it is designed without a transverse cutting surface. The particular advantage achieved thereby is that each radial section of the drill contributes to cutting, and no cutting action is achieved in the area of the transverse cutting surface as is the case with a conventional design including a transverse cutting surface. The absence of a transverse cutting surface particularly also supports a high level of positioning accuracy.

[0016] The term "transverse cutting surface" is generally understood to mean the cutting area located between the axis of rotation and the starting point of the tip.

[0017] In a preferred embodiment, the tip region of the drill is formed only by non-edged surfaces adjoining corresponding main cutting surfaces. Thus, in a drill including three cutting surfaces, the tip region is formed only by the three main cutting surfaces, the pointed drill bit, and the three non-edged surfaces. Herein, the tip region is defined as the foremost axial region of the drill, the foremost axial region extending from the drill bit to an axial length corresponding to at least 1 / 4, in particular at least 1 / 3, and preferably at least half of the radius. Thus, starting from the drill tip and at least as far as the thus-defined axial length, there are no edges on the surface adjoining the main cutting surface.

[0018] The tip region and thus its axial length starting from the drill tip preferably terminate at an axial length having a first full drill diameter, i.e., at the axial position of the drill where the drill bit at the end of the drill is tapered in the front region without grinding or other measures. The drill bit diameter is typically defined by the remaining circular diameter of the drill at a specified flute depth in the region of the flute. Thus, the drill bit diameter is typically defined by subtracting the flute depth from the nominal radius of the drill. In particular, this axial length thus also defines the axial position at which the clearance surface transitions into the respective flute, and thus the flute starts at this axial position. This transition to the flute is optionally achieved by rounding or chamfering.

[0019] In a preferred embodiment, exactly three main cutting surfaces are formed, and the three edge clearance surfaces are formed in particular in the manner of the tetrahedral surfaces of a degenerate tetrahedron that is twisted about the axis of rotation. Here, the term "degenerate tetrahedron" is understood to mean a three-dimensional structure conceptually formed by the three edge-free surfaces of the surfaces that initially formed a tetrahedron, which tetrahedron extends from a tetrahedron tip to a base, and the base of the tetrahedron is twisted about the axis of rotation while the tetrahedron tip is fixed simultaneously. The degenerate tetrahedron thus formed in particular forms the previously defined tip region.

[0020] In an advantageous embodiment, when viewed from above, the respective main cutting surfaces extend into the drill tip in a curved manner, in particular in a convexly curved manner. Thus, preferably, no linear progression of a transverse cutting surface is formed in the region of the drill tip. By means of the convex curvature, the near-central region of the main cutting surface (hereinafter also referred to as the central inner region) is thus arranged in front of the outer cutting surface section that is more outward in the radial direction during drilling.

[0021] In a preferred embodiment, the respective main cutting surfaces in this central inner region are thus designed to be continuously (i.e., uniformly) curved. Here, the term "near-central inner region" is understood to mean the near-central region starting from the axis of rotation, which extends in the radial direction by more than 1 / 4 of the radius, in particular by more than 1 / 3 of the radius and, for example, up to half of the radius. In this case, the radius of curvature can vary. The central inner region correspondingly adjoins another outer region, which correspondingly extends by at least 1 / 3 of the radius, for example, by at least half of the radius.

[0022] The main cutting surface preferably curves in a simple manner only in the central inner region and further over its entire length from the cutting corner to the tip of the drill tip, i.e., it does not include a plurality of reversely rotating (convex-concave) curved cutting surface segments.

[0023] Preferably, in addition to the curved cutting surface section in the central inner region, the main cutting surface further includes a linear section in the outer region. The entire main cutting surface is preferably formed by a (convex) curved cutting surface section in the central inner region and a linear cutting surface section in the outer region, the linear cutting surface section adjoining the curved cutting surface section and extending as far as the cutting corner.

[0024] The drill is preferably designed as a monolithic drill. In addition, the drill is preferably composed of cemented carbide.

[0025] In principle, there is also the option of designing the drill as a modular drilling tool including a shaft, the shaft having a replaceable drill tip part inserted on the front. This part has a specific geometry including a main cutting surface and an adjoining edge-free surface. Preferably, this drill tip part already includes a chip flute section, which then transitions into a chip flute formed in the shaft. Such a drill tip part is attached to the shaft in a suitable manner. Here, it is generally stipulated that the drill tip part rotates relative to the shaft about the rotational axis for insertion. Description of the Drawings

[0026] In the following, exemplary embodiments of the invention are explained in more detail with reference to the drawings. These drawings show the following partially simplified illustrations:

[0027] Figure 1 is a sectional side view of the drill,

[0028] Figure 2 is a top view of the front at the end of the drill,

[0029] Figure 3 is a sectional view through the drill at the axial length of the full drill diameter, and

[0030] Figure 4 is a sectional side view of the drill to illustrate the tip region. Detailed Description of the Invention

[0031] Respectively shown in Figure 1 and Figure 2 in sectional side view and front top view, the drill 2 is designed as an integral monolithic drill 2. However, the following statements equally apply to, for example, a modular drill in which the drill tip part is interchangeably attached to the drill shaft.

[0032] The drill 2 extends generally along the rotational axis 4 about which the drill rotates during operation. The front at the end of the drill 2 includes a plurality (specifically, a total of three) main cutting surfaces 6, each main cutting surface extending outward from the central pointed drill tip 5 on the rotational axis 4 as far as the cutting corner 8.

[0033] The radial distance between the axis of rotation 4 and the respective cutting corner 8 defines the radius r.

[0034] The respective edge-free surface 10 starts in the circumferential direction U, in particular along the entire length of the main cutting surface 6, and extends from the pointed drill tip 5 as far as the cutting corner 8, adjoining each main cutting surface 6. During its further progression, the edge-free surface 10 transitions into the chip flute 12 in the circumferential direction U. Thus, the edge-free surface 10 also defines the clearance surface 14. The transition from the edge-free surface 10 and thus the clearance surface 14 to the wall surface of the chip flute 12 is represented by a curve L in Figure 1 and Figure 2 which is designed as, for example, an edge or a rounded transition. Starting from the cutting corner 8, the respective auxiliary cutting surface 14 extends along the chip flute 12, the cutting surface adjoining the auxiliary cutting surface nose 16 in the circumferential direction U.

[0035] The drill 2 generally includes a tip region 20 which will be explained with reference to Figure 3 and Figure 4 In the present context, the longitudinally foremost region of the drill 2 is understood to extend from the drill tip 5 to a horizontal plane H which is oriented perpendicular to the axis of rotation 4 and defines the starting point of the chip flute 12. The tip region 20 has an axial length A which is defined by the distance from the drill tip 5 to the horizontal plane H. Starting from the drill tip 5, the full and thus maximum drill diameter D is first achieved at the horizontal plane H. The drill diameter D is generally defined as the diameter of the central region of the drill, which central region is referred to as the drill bit 22 of the drill and includes the circular surface in the region of the chip flute 12. The tip region 20 of this drill bit 22 tapers, and thus the drill diameter D tapers.

[0036] Thus, the tip region 20 is generally the foremost region of the drill where the chip flute 12 has (not yet) been formed. At least within the tip region 20, all the front surfaces are only designed as edge-free surfaces 10.

[0037] As can be seen in particular from the top view according to Figure 2 in the exemplary embodiment, the respective main cutting surface 6 initially extends linearly in the outer region 24 starting from the cutting corner 8, and then extends in a curved (i.e., convexly curved) manner in the central inner region 26. In the exemplary embodiment, the transition between the linearly extending outer region 24 and the central inner region 26 is approximately half of the radius r.

[0038] Thus, the main cutting surface 6 extends in a curved manner into the pointed drill tip 5 and thus as far as the axis of rotation 4.

[0039] Taking into account the front geometry of the drill tool 2 described herein, particularly in the tip region 20, it should be emphasized that, on the one hand, the main cutting surface 6 extends continuously from the cutting corner 8 to the pointed drill tip 5 located on the rotational axis 4 and meets at this location. Thus, no transverse cutting surface is formed in the central region of the rotational axis 4.

[0040] It should also be emphasized that the edge-free surfaces 10 directly adjoin the main cutting surface 6 over their entire length. In the exemplary embodiment, these edge-free surfaces 10 extend as far as the starting point of the respective chip flutes 12.

[0041] Positionally accurate attachment and drilling are achieved by means of this design. The edge-free surfaces 10 also minimize wear and stress on the front face. The drill tool 2 is in particular a solid carbide drill tool. Due to the edge-free design, the risk of local load peaks that could lead to material degradation is also particularly minimal.

Claims

1. A drilling tool (2) extending along a rotational axis (4) and including at least three main cutting surfaces (6), the at least three main cutting surfaces each extending in the direction of the rotational axis (4) starting from a cutting corner (8) arranged at a radius (r), characterized in that, Starting from the drill tip (5) and over its entire radial extent, the at least three main cutting surfaces (6) converge at the drill tip (5), and each cutting surface (6) adjoins a respective edge-free surface (10), the respective edge-free surface including a clearance surface (14) and in each case transitioning into a respective chip flute (12).

2. The drill tool (2) according to the previous claim, characterized in that, The main cutting surfaces (6) converge at the drill tip (5) without lateral cutting surfaces.

3. The drill tool (2) according to one of the preceding claims, characterized in that, The tip region (20) of the drill (2) is formed only by the edge-free surfaces (10), where the tip region (20) extends from the drill tip (5) up to an axial length (A) that corresponds to at least 1 / 4, in particular at least 1 / 3, and preferably at least 1 / 2 of the radius (r).

4. The drill tool (2) according to one of the preceding claims, characterized in that, Exactly three main cutting surfaces (6) are formed, and the three edge-free surfaces (10) are designed in the manner of the tetrahedral surfaces of a degenerate tetrahedron, the degenerate tetrahedron being designed to twist about the axis of rotation (4) within itself.

5. The drill tool (2) according to one of the preceding claims, characterized in that, The respective main cutting surface (6) extends in a curved manner into the drill tip (5).

6. The drilling tool (2) according to the previous claim, characterized in that, The central inner region (26) of the respective main cutting surface (6) extends continuously in a curved manner into the drill tip (5), where the central inner region is greater than 1 / 4, in particular greater than 1 / 3 of the radius (r).

7. The drill tool (2) according to one of the two foregoing claims, characterized in that, The respective main cutting surface (6) is curved only in one direction.

8. The drill tool (2) according to one of the preceding claims, characterized in that, It is designed as a monolithic drill (2), in particular made of hard metal.

9. A method for manufacturing a drill (2) according to one of the preceding claims, wherein the edge-free surfaces (10) are introduced in only one grinding step using a grinding method.

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