Twist drill bit having a cutting tip with a stepped structure

Abstract

Twist drill bit having a cutting tip (3) with a stepped structure, consisting of a shank (1), a guide region (2) and the adjoining cutting tip (3) with a stepped structure, the stepped structure of which is interrupted by two flutes (5) winding about a drill bit axis (0), wherein the cutting tip (3) with a stepped structure has a drill bit tip (3.1) with a radius (r.sub.0), at which a pair of first main lips (4.1) are formed, and a multiplicity of coaxially arranged cutting steps (3.2), which each have a conical step portion (3.2.1), in which in each case a pair of further main lips (4.2.sub.a-4.2.sub.m) are formed, and a cylindrical step portion (3.2.2), wherein the cylindrical step portions (3.2.2) have, towards the shank (1), an increasingly large radius (r.sub.a-r.sub.m), wherein the difference between in each case one of the radii and the next one of the radii (r) is chosen such that, upon rotation about the drill bit axis (0), the pair of further main lips (4.2.sub.a-4.2.sub.m) arranged therebetween sweep in each case over an annular face (A.sub.a-A.sub.m), coaxial with the drill bit axis (0), on an imaginary plane (E) arranged perpendicularly to the drill bit axis (0), and the annular faces (A.sub.a-A.sub.m) have an identical surface area, such that, during drilling, an identical chip volume is carried away with each pair of the further main lips (4.2.sub.a-4.2.sub.m).

Claims

1. A twist drill bit, comprising a shank, a guide region, and a cutting tip, the twist drill bit comprising a drill bit rotary axis, the cutting tip comprising a plurality of cutting steps and two chip flutes winding about the drill bit rotary axis, each of the cutting steps coaxial with the drill bit rotary axis, each of the plurality of cutting steps comprising a conical step portion and a cylindrical step portion, each cylindrical step portion has a respective radius, in the plurality of cutting steps: in a sequence from a cutting step that is farthest from the shank to a cutting step that is closest to the shank, the respective radii are increasingly larger, the two chip flutes dividing each conical step portion into a pair of conical step portion sections and dividing each cylindrical step portion into a pair of cylindrical step portion sections, each conical step portion comprising a respective pair of main cutting edges, each main cutting edge: is adjacent to a respective chip flute of the two chip flutes, and spans a respective conical step portion section from a respective first intersection point with one cylindrical step portion to a respective second intersection point with another cylindrical step portion, the cutting step closest to the shank is a first of said plurality of cutting steps, the respective pair of main cutting edges of the first conical step portion is a first pair of main cutting edges, each of the first pair of main cutting edges extending from the respective first intersection point to the respective second intersection point, the respective first intersection point spaced from the drill bit rotary axis by a first radial distance, the respective second intersection point spaced from the drill bit rotary axis by a second radial distance, a first imaginary annular surface is defined in a plane perpendicular to the drill bit rotary axis, the first imaginary annular surface is defined by a first radially inner annular boundary and a first radially outer annular boundary, the first radially outer annular boundary defined by a first projection onto the plane of the respective first intersection point at the first radial distance via a 360 rotation of the drill bit about the drill bit rotary axis, the first radially inner annular boundary defined by a second projection onto the plane of the respective second intersection point at the second radial distance via the 360 rotation of the drill bit about the drill bit axis, the first imaginary annular surface having a first surface area defined by the first inner annular boundary and the first outer annular boundary, the cutting step furthest from the shank is a second of said plurality of cutting steps, the respective pair of main cutting edges of the second conical step portion is a second pair of main cutting edges, each of the second pair of main cutting edges extending from the respective first intersection point to the respective second intersection point, the respective first intersection point spaced from the drill bit rotary axis by a third radial distance, the respective second intersection point spaced from the drill bit rotary axis by a fourth radial distance, a second imaginary annular surface is defined by a second radially inner annular boundary and a second radially outer annular boundary, the second radially outer annular boundary defined by a third projection onto the plane of the respective first intersection point at the third radial distance via the 360 rotation of the drill bit about the drill bit rotary axis, the second radially inner annular boundary defined by a fourth projection onto the plane of the respective second intersection point at the fourth radial distance via the 360 rotation of the drill bit about the drill bit axis, the second imaginary annular surface having a second surface area defined by the second inner annular boundary and the second outer annular boundary, wherein the first radial distance is different from the third radial distance, wherein the drill bit rotary axis is stationary during the 360 rotation, wherein the first surface area is equal to the second surface area.

2. The twist drill bit recited in claim 1, wherein the first radial distance is the largest radial distance of all of said main cutting edges, and the fourth radial distance is the smallest radial distance of all of said main cutting edges.

Description

(1) Embodiments of the invention will be described in more detail below on the basis of drawings, in which:

(2) FIGS. 1a-1c show a twist drill bit having cutting tip with a stepped structure according to the prior art in various views,

(3) FIGS. 2a-2b show a first embodiment of a twist drill bit according to the invention having a cutting tip with a stepped structure in various views, and

(4) FIGS. 3a-3b show a second embodiment of a twist drill bit according to the invention having a cutting tip with a stepped structure in various views.

(5) The invention relates to a twist drill bit having a cutting tip 3 with a stepped structure (hereinafter drill bit), as illustrated in FIGS. 2a-2b and 3a-3b. In the same way as drill bits known from the prior art, as shown by means of an example in FIGS. 1a-1c, said twist drill bit has a shank 1, by means of which the drill bit can be clamped into a drill chuck of a drilling machine. Adjoining the shank 1, a guide region 2, which has a length in the direction of the drill bit axis 0, which is larger than the thickness of the material, which is to be drilled, follows in the direction of a drill bit axis 0. The cutting tip 3 with a stepped structure (hereinafter cutting tip 3), the stepped structure of which is interrupted by two chip flutes 5 winding about the drill bit axis 0, connects to the guide region 2. Its maximum outer diameter corresponds to the outer diameter of the guide region 2. The cutting tip 3 with a stepped structure has a drill bit tip 3.1, at which a pair of first main cutting edges 4.1 is formed. The first main cutting edges 4.1 are connected to one another via a chisel edge, which crosses the drill bit axis 0. Due to the fact that the hole diameter of the drill holes, which can be drilled by means of the drill bit, is produced by means of a plurality of main cutting edges, the radius r.sub.0 of the drill bit tip 3.1 can be small, and the first main cutting edges 4.1 can be embodied to be short, whereby the chisel edge can also be of a filigree embodiment, which allows for a good centering of the drill bit. Any number of cutting steps 3.2 connects to the drill bit tip 3.1, in each case formed by means of a conical step portion 3.2.1 and a cylindrical step portion 3.2.2. The first cutting step 3.2 is identified with a in the drawings, the last one with m, wherein the last cutting step 3.2 merges into the guide region 2. A pair of further main cutting edges 4.2.sub.a-4.2.sub.m is in each case formed in the conical step portions 3.2.1. The cylindrical step portions 3.2.2 have an increasingly larger radius r.sub.a-r.sub.m towards the shank 1. Due to the fact that this drill bit is not used to drill holes with different diameters, as with a step drill bit, but holes having an identical diameter, which corresponds to the diameter of the last cutting step 3.2, it is generally not important which diameter the individual cutting steps 3.2 have, as long as they become larger in the direction towards the shank 1. This makes it possible to select the diameters so that, as improvement compared to the prior art, at least approximately identical chip volumes are created by means of the individual cutting steps 3.2. It is shown in FIG. 1c how the surface areas of an annular surface A.sub.a-A.sub.m, machined by means of one of the first cutting steps 3.2 or one of the last cutting steps 3.2 towards the shank, respectively, differ when, as specified as being advantageous in the prior art, the main cutting edges run parallel to one another and have an identical height. FIG. 1b shows a top view onto such a drill bit, which is known from the prior art, in the direction towards the shank 1.

(6) It is essential for the invention that during the drilling, the pairs of the further main cutting edges 4.2, see FIGS. 2a-2b, or in each case two adjacent pairs of the further main cutting edges 4.2 together, see FIGS. 3a-3b, in each case sweep over an annular surface A.sub.a-A.sub.m with an identical surface area, whereby they remove an identical chip volume over the depth of the resulting drill hole.

(7) So that the removed chip volume of two adjacent pairs of the further main cutting edges 4.2 is identical, the difference of the radii r between two adjacent cylindrical step portions 3.2.2 or the radius r.sub.0 of the drill bit tip 3.1 and the radius of the first one of the conical step portions 3.2.1.sub.a, or in other words, one of the radii, with a next one of the radii is in each case selected so that upon rotation about the drill bit axis 0, the pair of the further main cutting edges 4.2.sub.a-4.2.sub.m arranged therebetween in each case sweeps over an annular surface A.sub.a-A.sub.m, which is coaxial to the drill bit axis 0, on an imaginary plane E, which is arranged perpendicularly to the drill bit axis 0, and the annular surfaces A.sub.a-A.sub.m have an identical surface area, in other words, that the projection of the further main cutting edges 4.2 in each case sweep over annular surface A.sub.a-A.sub.m of identical surface areas (see FIGS. 2a-2b with regard to this). The pairs of the further main cutting edges 4.2 can in each case have an identical length and can draw different cutting angles with the drill bit axis 0, or can have a different length and draw identical cutting angles with the drill bit axis 0. The length l.sub.a-l.sub.1 of the cylindrical step portions 3.2.2, which can generally be arbitrary for the function of the drill bit, thereby follows inevitably in both alternatives.

(8) In the case of a large number of cutting steps 3.2, the pairs of the further main cutting edges 4.2 are in each case short, whereby the change of the chip volumes of two adjoining cutting steps 3.2 is also smaller than in the case of longer further main cutting edges 4.2. The idea of the invention can thus also already be benefitted from when each pair of the further main cutting edges 4.2 does not remove an identical chip volume, but when a similar chip volume is ultimately removed via all pairs of the further main cutting edges 4.2. In practice, a similar chip volume is created, e.g., when, as shown in FIGS. 3a-3c, the difference between one of the radii and a next but one of the radii r is selected so that upon rotation about the drill bit axis 0, the two pairs of the further main cutting edges 4.2.sub.a-4.2.sub.m) arranged therebetween in each case sweep over an annular surface A.sub.a-A.sub.m, which is coaxial to the drill bit axis 0, on an imaginary plane E, which is arranged perpendicularly to the drill bit axis 0, and the annular surfaces A.sub.a-A.sub.m have an identical total surface area in pairs.

(9) In that the chip volume for the cutting steps 3.2 is identical or at least similar, the density of the chips removed via the chip flutes 5, after a complete penetration of the cutting tip 3 into a workpiece, is more homogenous in the chip flutes 5 than in the case of a drill bit according to the prior art, which facilitates, e.g., an extraction by suction of the chip volume.

LIST OF REFERENCE NUMERALS

(10) 0 drill bit axis 1 shank 2 guide region 3 cutting tip (with a stepped structure) 3.1 drill bit tip 3.2(.sub.a-3.2.sub.m) cutting step 3.2.1(.sub.a-3.2.1.sub.m) conical step portion 3.2.2(.sub.a-3.2.2.sub.m) cylindrical step portion 4.1 first main cutting edge 4.2(.sub.a-4.2.sub.m) further main cutting edges 5 chip flute l.sub.a-l.sub.1 length of a cylindrical step portion 3.2.2 r.sub.a-r.sub.m radius of a cylindrical step portion 3.2.2 r(.sub.0r.sub.a-r.sub.1 r.sub.m) difference between adjacent radii r.sub.0 radius of the drill bit tip 3.1 E imaginary plane A.sub.a-A.sub.m annular surface cutting angle