drill

Abstract

Drill (2) which extends along an axis of rotation (4) and has a radius (r) and several main cutting edges (6), each extending from a cutting corner (8) located on the radius (r) in the direction of the axis of rotation (4), wherein a clearance surface (10) is connected to each of the main cutting edges (6) in a circumferential direction (U), which forms a clearance angle (α, β1, β2) to a horizontal plane (H) oriented perpendicular to the axis of rotation (4) and which transitions further into a flute (12), characterized in that - viewed in a vertical section parallel to the axis of rotation (4) - an outer section (18) of the clearance surface (10) in the region of the cutting corner (8) has a curved course and a section (16) near the center in the region of the axis of rotation has a straight course.

Description

Background of the invention

[0001] The invention relates to a drill which extends along an axis of rotation and has a radius and several main cutting edges, each extending from a cutting corner located on the radius in the direction of the axis of rotation, wherein a clearance surface is connected to each of the main cutting edges in the circumferential direction, which forms a clearance angle to a horizontal plane oriented perpendicular to the axis of rotation and which transitions into a chip groove.

[0002] For optimal drilling results, drill bits are typically ground on their front face, in the area of ​​the main cutting edges, using a face-grinding technique. This face is often conical and is created by a conical surface grind or a multi-surface grind. A drill bit tip with a ground conical surface can be found in US 2014 / 0308086 A1. Usually, a thinning cut is also performed in the area of ​​the drilling center, i.e., in the area of ​​the axis of rotation, to reduce the thickness of the drill core at the tip.

[0003] From JP 2002-036018 A a drill can be taken in which a radial end of a main cutting edge assumes a predetermined curved path, which is intended, among other things, to improve chip removal.

[0004] The design of the end geometry of the drill bit, including the main cutting edges and the clearance surfaces, significantly influences the properties of the drill bit.

[0005] Depending on the application, material selection, and machining parameters such as rotational speed, high loads occur during the drilling process, particularly due to friction. Chip removal via the flutes is also affected, with a particularly high frictional load occurring in the area of ​​the flanks immediately adjacent to the main cutting edge. Object of the invention

[0006] Based on this, the invention aims to provide a drill bit with a face geometry that results in a reduced friction load compared to conventional drill bits. Solution to the task

[0007] The problem is solved according to the invention by a drill bit which extends along an axis of rotation and has a radius and several main cutting edges, each extending from a cutting corner located on the radius towards the axis of rotation and thus to a center. A clearance surface adjoins each main cutting edge in a circumferential direction, forming a clearance angle with respect to a horizontal plane oriented perpendicular to the axis of rotation. The clearance surface then transitions into a flute in the circumferential direction. In a vertical section parallel to the axis of rotation and perpendicular to a radial, an outer section of the clearance surface in the region of the cutting edge corner has a curved profile, while a section closer to the center in the region of the axis of rotation has a straight profile.

[0008] In this context, radius refers to the nominal radius, which extends radially from the axis of rotation to the intersection point.

[0009] Viewed in vertical section, the outer section runs in particular along an arc-shaped line or is approximated to such an arc-shaped course by individual faceted surface sections.

[0010] The shape of the free surface, as seen in the vertical section, therefore varies from the axis of rotation towards the intersection point. While the free surface is straight in the section near the center, it is curved in the outer section.

[0011] The two sections connect directly to the main cutting edge in the circumferential direction.

[0012] The arc-shaped profile offers the particular advantage that the clearance angle changes and, in particular, increases in the circumferential direction, thus reducing the frictional load in this area. Due to the radial distance from the axis of rotation, the circumferential speed is higher in the area of ​​the cutting edge, and therefore in the outer section, than in the section near the center. The measure described above thus provides a targeted and effective way to reduce frictional load in high-speed areas.

[0013] The term "central section" preferably refers to a section that extends in a radial area greater than 0.1 or 0.2 times the radius. Furthermore, the central section preferably extends, for example, to at least 0.5 times the radius. The immediate area at the axis of rotation itself, and thus in the region of the foremost drill tip and especially in the area of ​​any typically applied point thinning, is therefore preferably not considered part of the central section, particularly since this immediate area at the axis of rotation is not usually precisely definable.

[0014] In contrast, the outer section with the curved profile is formed at least in a radially outer area, which is spaced 0.9 times the radius from the axis of rotation.

[0015] In a preferred embodiment, the clearance angle in the outer section is larger than the clearance angle in the section near the center. The clearance angle is preferably determined directly adjacent to the main cutting edge. This measure also takes into account the fact that the circumferential speed is higher in the outer section. The larger clearance angle in this outer section keeps friction low.

[0016] Preferably, the clearance angle in the section near the center with the straight course has a value in the range of 8° to 10°.

[0017] In the outer section, due to the curved shape, the value of the clearance angle increases in the circumferential direction from the main cutting edge, in particular from a first value to a second value.

[0018] The first value is preferably in the range of 10° to 20°.

[0019] Furthermore, the second value is preferably in the range of 20° to 40°.

[0020] The first value is preferably measured circumferentially at a first angular distance of 5° from the main cutting edge and the second value circumferentially at an angular distance of 15° from the main cutting edge.

[0021] Overall, the resulting free area with varying values ​​for the clearance angles achieves a particularly suitable design, leading to low frictional stress and thus low thermal stress on the drill bit.

[0022] According to a preferred embodiment, the outer section with its curved profile extends continuously into the clamping groove. This means that in the outer section, the free surface exclusively follows a curved profile extending into the clamping groove.

[0023] Alternatively, and especially additionally, in a preferred configuration, the section near the center extends in a straight line into the subsequent circumferential span groove. This means that in the section near the center, the open space extends exclusively along a straight line into the span groove.

[0024] The end of the free surface and the beginning of the groove extending circumferentially from the free surface are typically formed by a transition, for example, an edge. The groove is regularly oriented at a groove angle that is at least 1.5 or 2 times higher than the clearance angle of the section of the free surface immediately preceding the groove. The groove angle is defined by the angle at which a groove wall extending circumferentially from the free surface is oriented relative to the horizontal plane. This groove angle also depends, among other things, on the angle at which the groove is inclined relative to the axis of rotation. The groove angle is typically greater than 60°.

[0025] According to a particularly preferred embodiment, the clearance area is subdivided circumferentially by an imaginary, and in particular straight, dividing line into a first part facing the main cutting edge and a second part facing the flute. The dividing line runs from the inside out and intersects the main cutting edge at least at one outer intersection point. This outer intersection point is located, for example, at a radius greater than 0.7, greater than 0.8, and in particular greater than 0.9. Viewed in a vertical section, the first part of the clearance area is straight, and the second part is curved. In this embodiment, the area of ​​the clearance area section adjoining the main cutting edge, extending to the outer intersection point and forming the first part, defines the section near the center with the straight shape.In contrast, the radially outer area lying outside the intersection point defines the outer section with the curved path.

[0026] In a preferred embodiment, the dividing line intersects the main cutting edge at an internal intersection point. This point lies, in particular, in a region less than 0.2 times, and especially less than 0.1 times, the radius.

[0027] In this embodiment, with the two sections of the clearance area separated by the dividing line, the outer section with its curved profile extends continuously from the main cutting edge to the chip groove. In this embodiment, the section near the center with its straight profile is preferably followed circumferentially by an additional clearance area section with a curved profile.

[0028] The dividing line that separates the straight first part from the curved second part preferably runs in a straight line.

[0029] In a preferred embodiment, the dividing line is oriented parallel to a radial line that passes through the axis of rotation and through the intersection corner. Description of the characters

[0030] An exemplary embodiment is explained in more detail below with reference to the figures. These show, in some cases in simplified form: Fig. 1. A partial side view of a drill bit, Fig. 2 a top view of a front end face of the drill, Fig. 3 a partial sectional view along the section line AA according to Fig. 2, Fig. 4 a partial sectional view along the section line BB according to Fig. 2 as well as Fig. 5 A partial top view of the front end face of the drill with a drawn dividing line, by which a clearance surface is subdivided into a first part and a second part. Description of the exemplary embodiment

[0031] A in Fig. 1 and Fig. The drill 2 shown in a partial side view or a frontal top view is, for example, designed as a one-piece drill 2. However, the following explanations apply equally, for example, to modular drills in which a drill tip is interchangeably attached to a drill shank.

[0032] The drill 2 generally extends along a rotational axis 4, around which it rotates during operation. The drill 2 has several main cutting edges 6 on its front face, each extending outwards from a central tip located on the rotational axis 4 to a cutting corner 8. The main cutting edges 6 run – in the top view according to Fig. 2 viewed - each curved.

[0033] Preferably, the main cutting edges 6 continue continuously and steadily, and thus also without steps, from the cutting edge 8 to the axis of rotation 4. The drill 2 is therefore, for example, not designed as a step drill with stepped main cutting edge sections.

[0034] A radial distance between the axis of rotation 4 and each cutting edge 8 defines a radius r. The line connecting the axis of rotation 4 and each cutting edge 8 defines a radial R. In the exemplary embodiment, the drill 2 has a total of three main cutting edges 6. Alternatively, it may, for example, have only two main cutting edges 6.

[0035] In a circumferential direction U, a clearance surface 10 adjoins each main cutting edge 6. This clearance surface then transitions into a flute 12 in the circumferential direction U. The transition is represented in the figures by a curved line, which may be, for example, an edge or a rounded transition. A secondary cutting edge 14 extends from the cutting corner 8 along the flute 12.

[0036] In the area of ​​the axis of rotation 4, a point thinning may also be carried out. The end face of the drill bit with the clearance faces 4, the main cutting edges 6 and, if applicable, the point thinning, is formed by a suitable end face grinding.

[0037] According to the invention, each free space 10 has a special profile, as described below in connection with the Fig. 3-5 will be explained in more detail.

[0038] Specifically, the open area 10 has a central section 16 in the area of ​​the axis of rotation 4 and an outer section 18 in the area of ​​the intersection corner 8.

[0039] Viewed in a vertical section, as it appears in Fig. 3 and Fig. As shown in Figure 4, i.e. in a section plane parallel to the axis of rotation and perpendicular to the radial, the free surface 10 runs straight in the section 16 near the center and curved and arc-shaped in the outer section 18.

[0040] With respect to a horizontal plane H, which is oriented perpendicular to the axis of rotation 4, the free area 10 in the central section 16 is oriented under a constant, central free angle α, the value of which is preferably in the range between 8° and 10°.

[0041] In contrast, the convexly curved profile in the outer section 16 results in an increase in the outer clearance angle, from a first outer clearance angle β1 to a second outer clearance angle β2. The first outer clearance angle β1 is preferably in the range between 10° and 20°, and the second outer clearance angle β2 is preferably in the range between 20° and 40°.

[0042] The first outer clearance angle β1 is measured at a first angular distance γ1 from the main cutting edge 6, which is preferably 5°. The second outer clearance angle β2 is measured at a first angular distance γ2 from the main cutting edge 6, which is preferably 15°.

[0043] By means of this measure with the increasing clearance angle on the one hand in the radial direction, i.e. starting from the central section 16 to the outer section 18, and additionally in the circumferential direction U at the outer section 18, the clearance angle is specifically chosen to be increasingly larger in the areas where a circumferential speed increases during the drilling process due to the radial distance from the center.

[0044] According to a first design variant, the central section 16 as well as the outer section 18 extend in circumferential direction U to the beginning of the clamping groove 12.

[0045] According to a preferred embodiment, as exemplified in Fig. As shown in Figure 5, the respective open space 10 is subdivided into a first part 10A and a second part 10B. In the first part 10A, the open space 10 runs in a straight line when viewed in vertical section, as shown in Figure 5. Fig.5 is indicated by the straight arrow. In contrast, in the second part 10B, the free area 10 is curved in the vertical section, as indicated by the curved arrow. The first part 10A thus forms the central section 16. The second part 10B with the curved shape then adjoins this in the circumferential direction U.

[0046] The two parts 10A, 10B are separated from each other by a dividing line 20 (shown as a dashed line). In the exemplary embodiment, this line runs straight and parallel to the radial R. The dividing line 20 intersects the main cutting edge 6 at an outer intersection point S1 and preferably also at an inner intersection point S2. The outer intersection point S1 is preferably located in a region between 0.7 times the radius r and 0.9 times the radius r. The area of ​​the clearance surface 10 adjoining the outer intersection point S1 in the radial direction forms the previously described outer section 18. In this embodiment as well, this section is therefore continuously curved in the circumferential direction U up to the clamping groove 12.

[0047] In contrast, the inner intersection point S2 is preferably located at less than 0.2 times and especially at less than 0.1 times the radius r.

Claims

[1] Drill (2) which extends along an axis of rotation (4) and has a radius (r) and several main cutting edges (6), each extending from a cutting corner (8) located on the radius (r) in the direction of the axis of rotation (4), wherein a clearance surface (10) is connected to each of the main cutting edges (6) in a circumferential direction (U), which forms a clearance angle (α, β1, β2) to a horizontal plane (H) oriented perpendicular to the axis of rotation (4) and which subsequently transitions into a flute (12), characterized by , that - viewed in a vertical section parallel to the axis of rotation (4) - an outer section (18) of the free area (10) in the area of ​​the intersection corner (8) has a curved course and a section (16) near the center in the area of ​​the axis of rotation has a straight course. [2] Drill (2) according to the preceding claim, characterized by, that the centrally located section (16) has a straight course at least in a region greater than 0.1 times or greater than 0.2 times and preferably up to 0.5 times the radius (r). [3] Drill (2) according to any one of the preceding claims, characterized by , that the outer section (18) with the curved profile is formed at least in a region greater than 0.9 times the radius (r). [4] Drill (2) according to any one of the preceding claims, characterized by , that the value of the clearance angle (β1) at the main cutting edge (6) in the outer section (18) is greater than the value of the clearance angle (α) in the central section (16). [5] Drill (2) according to any one of the preceding claims, characterized by , that the clearance angle (α) in the central section (16) has a value in the range of 8° to 10°. [6] Drill (2) according to any one of the preceding claims, characterized by, that the clearance angle (β1,β2) in the outer section (18) starting from the main cutting edge (6) in the circumferential direction (U) increases from a first value to a second value. [7] Drill (2) according to the preceding claim, characterized by that the first value lies in the range of 10° to 20° [8] Drill (2) according to one of the two preceding claims, characterized by , that the second value lies in the range of 20° to 40°. [9] Drill (2) according to any one of claims 6 to 8, characterized by , that the first value in the circumferential direction (U) is measured at a first angular distance of 5° from the main cutting edge (6) and the second value in the circumferential direction (U) is measured at a second angular distance of 15° from the main cutting edge (6). [10] Drill (2) according to any one of the preceding claims, characterized by , that the outer section (18) with the curved course extends into the span groove (12). [11] Drill (2) according to any one of the preceding claims, characterized by , that the central section (16) with its straight course extends into the span (12). [12] Drill (2) according to any one of claims 1 to 10, characterized by , that the free surface (10) is subdivided in the circumferential direction (U) by a dividing line (20) into a first part (10A) facing the main cutting edge (6) and into a second part (10B) facing the clamping groove (12), wherein the dividing line (20) runs from the inside to the outside and intersects the main cutting edge (6) at least at an outer intersection point (S1), wherein, viewed in the vertical section, the first part (10A) is straight and the second part (10B) is curved, wherein the outer intersection point (S1) is preferably located at a distance greater than 0.7 times and, in particular, greater than 0.9 times the radius (r). [13] Drill (2) according to the preceding claim, wherein the parting line (20) further intersects the main cutting edge (6) at an inner intersection point (S2), which is preferably less than 0.2 times and particularly less than 0.1 times the radius (r). [14] Drill (2) according to one of the two preceding claims, wherein the parting line (20) is oriented in a straight line and in particular parallel to a radial (R) passing through the axis of rotation (4) and through the cutting corner (8).

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