Method for producing a threaded bore and tapping tool bit

Abstract

A method for producing a threaded bore in a workpiece with a tapping tool bit, which, at its drill bit tip, has a main cutting lip and a thread profile trailing in a tapping direction (I) with at least one thread cutting tooth, wherein, in a tapping stroke (G), the main cutting lip produces a core hole and, at the same time, the thread profile forms an internal thread at the inner wall of the core hole until reaching an intended thread depth (t.sub.G), specifically with a tapping feed (f.sub.G) in the tapping direction (I).

Claims

1. A method for producing a threaded bore comprising: a workpiece and a tapping tool bit, the tapping tool bit has, at its drill bit tip, a main cutting lip and a thread profile, trailing in a tapping direction (I) with at least one thread cutting tooth, wherein, in a tapping stroke (G), the main cutting lip produces a core hole and, at the same time, the thread profile forms an internal thread on the inner wall of the core hole until an intended thread depth (t.sub.G) is reached, specifically with a tapping feed (f.sub.G) in the tapping direction (I) and at a tapping speed (n.sub.G) of the tapping tool bit synchronized therewith, wherein, after the tapping stroke (G), a reversing stroke (R) occurs in the opposite direction, in which the tapping tool bit is guided out of the threaded bore in a reversing direction (II), specifically with an opposite reversing feed (f.sub.R) and at a reversing speed (n.sub.R) synchronized therewith, so that the thread profile of the tool bit is guided out of the bore in the thread pitch of the internal thread, wherein, between the tapping stroke (G) and the reversing stroke (R), there occurs a groove forming step, in which the tapping stroke (G) is lengthened in the tapping direction (I) by a groove forming stroke (N), specifically to form a pitch-free encircling groove adjoining the internal thread, in which the thread profile can rotate in a stress-free manner.

2. The method according to claim 1, wherein, in the groove forming step, the tapping tool bit is moved beyond the intended thread depth (t.sub.G) until reaching an intended bore depth (t.sub.B) in the tapping direction (I), specifically with a groove forming feed (f.sub.N) and at a groove forming speed (n.sub.N) that are not synchronized with each other and/or are different from the tapping feed (f.sub.G) and from the tapping speed (n.sub.G).

3. The method according to claim 1, wherein, in the groove forming step, the thread profile of the tapping tool bit rotates completely in the encircling groove the threaded bore.

4. The method according to claim 1, wherein the encircling groove is formed during the groove forming stroke (N) by means of the main cutting lip and the thread cutting tooth of the thread profile.

5. The method according to claim 1, wherein, when the intended bore depth (t.sub.B) is reached, the groove forming feed (f.sub.N) is reduced to 0 and the groove forming speed (n.sub.N) is reduced to 0 for preparation of a reversal of direction required for the reversing stroke (R).

6. The method according to claim 1, wherein, at the start of the reversing stroke (R), the tapping tool bit is controlled in such a way that the thread cutting tooth is driven in a stress-free manner, without removal of material, into a thread pitch outlet, which opens into the encircling groove.

7. The method according to claim 1, wherein, during the tapping stroke (G), the groove forming stroke (N), and the reversing stroke (R), the rotational axis (B) of the tapping tool bit and the longitudinal axis (A) of the bore are aligned coaxially to each other.

8. The method according to claim 1, wherein the tapping tool bit is utilized as a pre-processing tool bit, and in that the pre-processed threaded bore is post-processed in a post-processing step by use of a finishing tool bit, wherein, as the finishing tool bit, a thread former, a helical thread former, or an axial thread former can be utilized.

9. The method according to claim 1, wherein the tapping tool bit itself is utilized as a finishing tool bit.

10. A tapping tool bit for producing a threaded bore in a workpiece, with a clamping shank and a tapping body that is adjoined to it, and along the longitudinal axis (A) of which, at least one chip groove extends up to a front-end main cutting lip at a drill bit tip, at which front-end main cutting lip, a chip surface bounding the chip groove and a front-end free surface of the drill bit tip converge, wherein, in the peripheral direction of the tool bit, the chip groove is bounded by at least one drill bit web, and the chip surface of the chip groove transitions, with the formation of an auxiliary cutting lip, into a back surface of the drill bit web on the outer peripheral side, and wherein the auxiliary cutting lip and the front-end main cutting lip converge at a radially outer main cutting corner, wherein, at the back surface of the drill bit web on the outer peripheral side, a thread profile with at least one thread-profile cutting tooth is formed, wherein the thread profile cutting tooth has a radially outer profile base cutting edge, which protrudes radially outward over the main cutting corner by a tooth height (r), wherein the tapping tool bit is formed with a cutting edge, with which an encircling thread countersink is produced in the bore opening of the bore, and in that the encircling thread countersink is produced during the groove forming step.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention and its advantageous embodiments and enhancements as well as the advantages thereof are explained in detail below on the basis of drawings.

(2) Shown are:

(3) FIG. 1 lateral cross sectional illustration, a threaded blind bore formed in a workpiece;

(4) FIG. 2 front view of a tapping tool bit in a view from the front;

(5) FIG. 3 lateral view of the tapping tool bit;

(6) FIG. 4 lateral view of the tapping tool bit;

(7) FIG. 5 side view producing the threaded blind bore;

(8) FIG. 6 lateral producing the threaded blind bore;

(9) FIG. 7 lateral producing the threaded blind bore; and

(10) FIG. 8 lateral producing the threaded blind bore.

DETAILED DESCRIPTION

(11) Shown in FIG. 1 is a finished threaded blind bore 1. The bore 1, which has a bore bottom 3, is worked to a target bore depth t.sub.B in a workpiece 5 by means of a so-called percussion drill processing, which will be explained later on the basis of FIGS. 5 to 8. At its bore opening, the bore 1 has an encircling thread countersink 7, which, in the further course, transitions downward into an internal thread 9. The internal thread 9 extends along the bore axis A to a useable intended thread depth t.sub.G. As further ensues from FIG. 1, a thread pitch 15 of the internal thread 9 opens with a thread outlet into an encircling groove 13. Said groove does not have a thread pitch and, as viewed in the axial direction, is formed between the internal thread 9 and the bore bottom 3. The thread pitch 15 has a radially outer thread root 17 as well as lateral thread flanks 19, which transition radially inward into an inner thread crest 21.

(12) The threaded blind bore 1 shown in FIG. 1 is made by use of the tapping tool bit 23 described below on the basis of FIGS. 2 to 4. In accordance therewith, at its drill bit tip 25, the tool bit 23 in FIG. 2 has three uniformly peripherally distributed, front-end main cutting lips 27 as well as a thread profile 29 trailing in the tapping direction I (FIG. 5 or 6).

(13) The tool bit 23 is constructed with a clamping shank 24 as well as with an adjoining tapping body 26, along the bore axis A of which a total of three chip grooves 28, which are distributed on the peripheral side, extend to the respective front-end main cutting lip 27 at the drill bit tip 25.

(14) At each main cutting lip 27, a chip surface 31, which bounds the chip groove 28, and a front-end free surface 33 of the drill bit tip 25 converge. In the peripheral direction of the tool bit, the respective chip groove 28 is bounded by a drill bit web 35. Overall, the thread tapping tool bit 23 shown in the figures has three drill bit webs 35. In this case, the chip surface 31 of the chip groove 28 transitions, with the formation of an auxiliary cutting lip 36, into a back surface 37 of the respective drill bit web 35 on the outer peripheral side. The auxiliary cutting lip 36 and the front-end main cutting lip 27 converge at a radially outer main cutting corner 39.

(15) At the back surfaces 37 of the three drill bit webs 35 on the outer peripheral side, the thread profile 29 has, in each case, a pre-cutting tooth 41, a middle cutting tooth 42, and a finishing cutting tooth 43. Each of the cutting teeth 41, 42, 43 is formed with a radially outer thread-root cutting edge 45 as well as with thread-flank cutting lips 47 in order to cut/to form the thread pitch 15 shown on the basis of FIG. 1. In this case, the cutting teeth 41 to 43 are designed with different geometries and are spaced at different axial distances a (only indicated in FIG. 5) from the drill bit tip 25 in order to cut the thread pitch 15 of the internal thread 9 shown in FIG. 1. By way of example, the pre-cutting, middle, and finishing cutting teeth 41, 42, 43 have different axial dimensions in the axial direction and/or different cutting tooth heights r (FIG. 2) in the radial direction. By way of example, the pre-cutting, middle, and finishing cutting teeth 41, 42, 43 become axially larger in the peripheral direction. The finishing cutting tooth 43 then cuts the entire internal thread contour. Alternatively to this, the finishing cutting tooth 43 can also be designed as a forming tooth in order to increase the thread strength.

(16) In addition, at the transition between the thread tapping body 26 and the clamping shank 24, the thread tapping tool bit 23 has a cutting edge 49 for formation of the thread countersink 7 shown in FIG. 1.

(17) Described below on the basis of FIGS. 5 to 8 is the method for producing the threaded blind bore 1 shown in FIG. 1: In accordance therewith, in FIG. 1, the tapping tool bit 23 is guided in a thread tapping direction I on the not yet predrilled tool bit 5 and a percussion drilling is carried out. In the tapping stroke G, the main cutting lips 27 produce a core hole and, at the same time, the trailing thread profile 29 produces the internal thread 9 at the inner wall of the core hole. The tapping stroke G occurs with a tapping feed f.sub.G and at a tapping speed n.sub.G synchronized therewith in a tapping rotational direction, specifically until the intended thread depth t.sub.G is reached (FIG. 6).

(18) Immediately afterwards, a groove forming step (FIG. 7) is carried out, in which the threaded bore stroke G is lengthened in the tapping direction I by a groove forming stroke N. In the groove forming stroke H [sic], in contrast to the thread forming stroke G, the groove-forming feed f.sub.N and the groove forming speed n.sub.N of the tapping tool bit 23 are not synchronized with each other and are different from the preceding tapping feed f.sub.G and from the tapping speed n.sub.G.

(19) In this way, by use of its precutting, middle, and finishing cutting teeth 41, 42, 43, the thread profile 29 produces the encircling groove 13 shown in FIG. 7, in which the thread profile 29 can rotate in a stress-free manner. The groove forming feed f.sub.N as well as the groove forming speed n.sub.N are set in such a way that an excessively large cutting stress placed on the cutting teeth 41 to 43 is prevented.

(20) When the intended bore depth t.sub.B is reached, both the groove forming feed f.sub.N and the groove forming speed n.sub.N are reduced to 0. Subsequently, for preparation of a reversing stroke R (FIG. 8), a reversal of the feed occurs. In the reversing stroke R (FIG. 8), the tapping tool bit 23 is guided out of the threaded bore 1 in a reversing direction II (FIG. 8), specifically with an opposite reversing feed f.sub.R as well as at a speed synchronized therewith. These parameters are of such values that the thread profile 29 of the tapping tool bit 23 is guided out of the threaded bore 1 in the thread pitch 15 of the internal thread 9 in a largely stress-free manner.

(21) At the start of the reversing stroke R, the tapping tool bit 23 is controlled by the fabrication unit in such a way that the cutting teeth 41, 42, 43 are each driven in a stress-free manner into the thread pitch outlet 11, which opens into the encircling groove 13. In the further course of the reversing stroke R, the thread profile 29 of the tapping tool bit 23 is then rotated in a stress-free manner outwards through the thread pitch 15 of the internal thread 9.

(22) As a finishing tool bit 18, it is possible to utilize a thread former, a helical thread former, or an axial thread former. Alternatively, the thread tapping tool bit 23 itself can be formed as a finishing tool bit 18.