Thread former and method for producing a thread

Abstract

A thread former for the chipless production of a thread has a plurality of pressing lands, which are each arranged at predefined separation angles (T) along a shaping curve. Each separation angle (T) is smaller than or equal to a predefined maximum separation angle (T.sub.max). For nominal thread former diameters (Da) between 6 mm and 20 mm, the maximum separation angle (T.sub.max) is determined such that the following condition: T.sub.max=sin.sup.−1((a×ND.sup.y+b×ND+c)×2×π); is met for i) 6≤ND<10 where a=−0.0008, b=0.00705, c=0.1325, y=2; ii) 10≤ND<12 where a=1.7924/(2×π), b=0, c=0, y=−0.408; or iii) 12≤ND≤20 where a=0.751/(2×π), b=0, c=0, y=−0.104; wherein T.sub.max is the maximum separation angle and ND is the amount of the nominal thread former diameter (Da) measured in millimeters.

Claims

1. A thread former for the chipless production of a thread, including a thread forming portion with a plurality of pressing lands which are each arranged at predefined separation angles (T) between adjacent pressing lands along a shaping curve, which encircles a tool axis (L), wherein: each separation angle (T) is smaller than or equal to a predefined maximum separation angle (T.sub.max); for nominal thread former diameters (Da) between 6 mm and 20 mm the maximum separation angle (T.sub.max) is determined such that the following condition:
T.sub.max=sin.sup.−1((a×ND.sup.y+b×ND+c)×2×π) is met for:
6≤ND<10 where a=−0.0008, b=0.00705, c=0.1325, y=2;  i)
10≤ND<12 where a=1.7924/(2×π), b=0, c=0, y=−0.408; and  ii)
12≤ND≤20 where a=0.751/(2×π), b=0, c=0, y=−0.104;  iii) T.sub.max is the maximum separation angle and ND is an amount of the nominal thread former diameter (Da) measured in millimeters; and the separation angle (T) is determined such that: (i) a number of pressing lands for at least one revolution along the shaping curve for nominal thread former diameters (Da) between 6 mm and less than 8 mm is precisely 6, and (ii) the number of pressing lands for nominal thread former diameters (Da) between 8 mm and less than 10 mm is precisely 7.

2. The thread former for the chipless production of a thread, including a thread forming portion with at least one pressing land, wherein: at least one flank, oriented in a direction of a longitudinal axis (L) of the thread former, of at least one pressing land, comprises in each case a first and a second part flank surface, which intersect along a line of contact which extends outward from a core diameter (Dk) of the thread former at an angle that differs from zero; and the line of contact extends substantially radially outward with reference to the longitudinal axis (L) of the thread former when viewed in axial projection and extends outward substantially parallel to the radial direction.

3. The thread former as claimed in claim 2, wherein: a line of contact extends through a tip of the thread former; and the line of contact shows a somewhat radial progression when viewed in axial projection parallel to the longitudinal axis (L) of the thread former.

4. The thread former as claimed in claim 2, wherein: the shaping curve or crest curve is determined in such a manner that a rectilinear line of contact is produced or imaged from the core diameter up to at least half of the pressing land; and the part flank surfaces contact one another in the line of contact such that, at a predefined radius, the respective pressing land comprises a maximum thickness at the line of contact when measured in cutting planes perpendicular to the shaping line.

5. The thread former as claimed in claim 1, wherein: each of the separation angles (T) is chosen additionally in such a manner that the number of pressing lands of the pressing lands present consecutively along the shaping curve comprising an uneven integral value for each revolution along the shaping curve; the separation angles (T) are chosen such that the number of pressing lands of the pressing lands present consecutively along the shaping curve is given for nominal thread diameters where ND≥8 or ND>8 by an uneven value.

6. The thread former as claimed in claim 5, wherein the separation angle (T) is determined in such a manner that: the number of pressing lands of the pressing lands present consecutively along the shaping curve for each revolution along the shaping curve for nominal diameters (Da) between 10 mm and less than 12 mm is at least 9; and the number of pressing lands for nominal diameters (Da) between 12 mm and 20 mm, is at least 11.

7. The thread former as claimed in claim 1, wherein: the pressing land comprises a thread former tip which projects radially outward with reference to the longitudinal axis (L) of the thread former; and the pressing land is asymmetric with reference to a center plane (E), which extends through the thread former tip and parallel to the shaping curve.

8. The thread former as claimed in claim 1, wherein: the pressing land comprises a tapping edge which points radially outward, and a free tapping edge which points radially outward; and a tapping angle which is defined by the tapping edge is greater with reference to a predefined measuring depth than a free tapping angle which is defined by the free tapping edge at the predefined measuring depth.

9. The thread former as claimed in claim 1, wherein: the pressing lands are arranged in groups to form multiple pressing webs; and each pressing web extends substantially parallel to the longitudinal axis (L) or helically to the longitudinal axis (L), and pressing lands which are placed one behind another along the shaping curve are arranged parallel to the longitudinal axis (L) with a thread pitch that is a multiple of the thread pitch of the thread former.

10. The thread former as claimed in claim 1, wherein: the surfaces of the pressing lands are smoothed at least in part by means of a polishing treatment; and the polishing treatment includes polishing with diamond dust.

11. A method for producing a thread in or on a workpiece, comprising the following steps: providing the workpiece; providing a thread former for the chipless production of a thread, the thread former including a thread forming portion with a plurality of pressing lands which are each arranged at predefined separation angles (T) between adjacent pressing lands along a shaping curve, the shaping curve encircling the tool axis (L), which encircles the tool axis (L), wherein: each separation angle (T) is smaller than or equal to a predefined maximum separation angle (T.sub.max); for nominal thread former diameters (Da) between 6 mm and 20 mm the maximum separation angle (T.sub.max) is determined such that the following condition:
T.sub.max=sin.sup.−1((a×ND.sup.y+b×ND+c)×2×π) is met for:
6≤ND<10 where a=−0.0008, b=0.00705, c=0.1325, y=2;  i)
10≤ND<12 where a=1.7924/(2×π), b=0, c=0, y=−0.408; and  ii)
12≤ND≤20 where a=0.751/(2×π), b=0, c=0, y=−0.104;  iii) T.sub.max is the maximum separation angle and ND is the amount of the nominal thread former diameter (Da) measured in millimeters; providing the thread by simultaneously rotating and moving the thread former in an axial-translatory manner; wherein the thread former is moved at a predefined rotational speed and a predefined axial feed speed.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention is explained in more detail below, in particular also with regard to further features and advantages, by way of the description of exemplary embodiments as examples and with reference to the accompanying drawings, in which:

(2) FIG. 1 shows a perspective view of a thread former,

(3) FIG. 2 shows an enlarged view of the thread former head of the thread former,

(4) FIG. 3 shows a top view of the thread former head looking in the direction toward the thread former tip,

(5) FIG. 4 shows an enlarged representation of a portion of a pressing land of the thread former and

(6) FIG. 5 shows a representation of the progression of the tapping and free tapping edges of a pressing land.

(7) Parts and components that correspond with one another in FIG. 1 to FIG. 5 are designated with the same reference symbols.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

(8) FIG. 1 shows a perspective view of a thread former 1 which is realized for the chipless production of a thread, for example of a female thread, on or in a workpiece, for example produced from one of the materials named further above.

(9) The thread former 1 includes a tool shank 2 for clamping in a motor-driven chuck (not shown), on the one end of which thread former is realized in a working region that is realized in the form of a thread former head 3.

(10) The thread former head 3 includes a plurality of pressing lands 4 which are arranged in a helical manner around the longitudinal axis L (in particular: tool axis, rotational axis), the helical progression of the pressing lands 4, which among other things defines the thread former profile of the thread former 1, corresponds to the thread pitch of the thread that is producible with the thread former head 3. The pressing lands 4 are arranged substantially in such a manner that the center plane thereof is angled corresponding to the pitch of the thread, extends transversely to the longitudinal axis L and is aligned substantially parallel to the helical progression.

(11) As can also be seen in particular from FIG. 2, which shows an enlarged view of the thread former head 3 of the thread former 1, the thread former head 3 includes in the thread profile elevations and indentation or furrows which are formed alternately by the pressing lands 4 and are arranged and aligned substantially parallel to the helical progression. The pressing lands 4 and respective corresponding indentations, when viewed in the direction of the longitudinal axis L, are normally, and in the exemplary embodiment shown, at the same distance to one another, which means that the pitch of the threads is constant.

(12) The pressing lands 4 of the exemplary embodiment shown as an example taper radially outward in the cross section of the center plane, said pressing lands being able to be realized in a rounded manner in the radially outermost region, in particular in the head or crest region 5 thereof.

(13) In the case of the cold forming tap 1 shown in the figures, it is provided that the working region, i.e. the thread former head 3, is tapered toward the tool tip 6, which is placed remotely from the tool shank 2, in a cone-shaped tapping region 7, wherein the pressing lands 4 are arranged gradually offset inwardly in the tapping region 7 with a largely unchanged overall form.

(14) As a result of the tapping region 7, a corresponding thread profile is gradually produced as a result of the increasing radial advancement of the pressing lands 4, and in addition penetration of the pressing lands 4 into the workpiece surface, e.g. the inner wall of a corresponding bore, for producing a female thread is made easier, it being possible to reduce the forming forces working at the pressing lands 4 overall.

(15) In the guide or calibration region 8 which connects to the run-up region 7, the radial advancement (in particular: the radial length) of the pressing lands 4 remains substantially constant, said region serving for guiding the cold forming tap in a thread produced by the run-up region as a result of forming, and where applicable for smoothing or calibrating the thread. Toward the end of the tool shank 2 the guide or calibration region 8 can merge into a region which decreases in a cone-shaped manner, in which the radial length of the pressing lands 4 decreases up to the level of the tool shaft.

(16) The increase in the radial advancement between adjacent or consecutive pressing lands 4 in the run-up region/tapping region is also designated as the forming height.

(17) For producing a female thread with a cold forming tap 1, as a rule a bore is first of all produced in the workpiece, which bore has an inside diameter that is smaller than the outside diameter Da, i.e. nominal diameter Da, of the cold forming tap 1 (see FIG. 3 which shows a top view of the thread former head looking toward the direction of the thread forming tip 6).

(18) The cold forming tap 1 is then introduced into the produced bore with the tool tip at the front at a defined axial feed and defined rotation about the longitudinal axis L in the thread forming direction R.

(19) In this case, the pressing lands 4 and/or associated forming surfaces, such as, for example, axially aligned flanks of the pressing lands 4 which will be explained in more detail further below, are pressed into the surface of the bore so that the thread is produced as a result of material forming, in particular cold forming.

(20) The material of the workpiece, as already mentioned, is, in this case, plastically deformed and displaced radially into the indentations between the pressing lands 4 of the thread former head 3.

(21) The torque increases when tapping until all of the pressing lands 4 are engaged. Once the cold forming tap 1 has been sufficiently rotated in, it is rotated out of the produced thread by rotating in the opposite direction, the sliding friction torque continually decreasing as it is rotated out.

(22) When the thread is produced as a result of forming the workpiece, not insignificant forces occur at the pressing lands 4, in particular friction forces which, on the one hand, influence the forming of the workpiece and, on the other hand, as mechanical stresses, have a decisive influence on the service life of the pressing lands 4. In particular, the radial advancement and form of the pressing lands 4 influence not only the forces occurring but also the quality and strength of the produced thread.

(23) In the case of the thread former according to the invention, the pressing lands 4, as shown in FIG. 1 to FIG. 4, can be arranged in such a manner along the shaping curve 9, which is defined by the pressing lands 4 and extends helically about the longitudinal axis L, that the pressing lands 4 are arranged in groups to form multiple pressing webs 10 (see FIG. 3).

(24) Each pressing web 10 of the exemplary embodiment shown as an example extends substantially parallel to the longitudinal axis L. However, other arrangements of the pressing lands 4 are also possible, for example in such a manner that the pressing webs 10 extend helically with respect to the longitudinal axis L, or that no defined pressing webs 10 are realized at least in portions along the longitudinal axis L, which can be the case, for example, with varying distances between pressing lands 4 in the direction of the shaping curve 9.

(25) The ordered arrangement of the pressing lands 4 into groups to form multiple pressing webs 10 produces grooves 11, which can be used, for example, for the purpose of supplying lubricant and/or coolant, between the pressing webs 10 adjacent in the circumferential direction.

(26) Further lubricant and/or coolant channels (not shown) can be realized, for example, in the interior of the tool shank 2 and of the thread former head 3, and open out, for example, into the region of the tool tip 6.

(27) The thread former 1 shown in FIG. 1 to FIG. 4 is a thread former 1 with a nominal diameter Da, i.e. an outside diameter Da, of 10 mm. In total, the thread former 1 shown comprises nine pressing lands 4, or pressing webs 10, per revolution about the longitudinal axis L, i.e. the tool axis L. In particular, such a realization and arrangement of the pressing lands 4 has proved advantageous with regard to low wear and a long service life with at the same time a high degree of thread quality and thread strength.

(28) In particular, the thread former 1 shown in FIG. 1 to FIG. 4 is realized in such a manner that the pressing lands 4 are arranged in each case at a predefined separation angle T (see FIG. 3) with respect to one another along the shaping curve 9, which encircles the tool axis L, i.e. longitudinal axis L, in a substantially helical manner.

(29) Corresponding to the underlying invention and to the conclusions underlying the invention regarding wear and thread quality and/or thread strength, each separation angle T between adjacent pressing lands 4 is smaller than or equal to a predefined maximum separation angle T.sub.max, the maximum separation angle T.sub.max being determined such that the following condition:
T.sub.max=sin.sup.−1((a×ND.sup.2+b×ND+c)×2×π),
is met for:
6≤ND<10 where a=−0.0008, b=0.00705, c=0.1325, y=2;  i)
10≤ND<12 where a=1.7924/(2×π), b=0, c=0, y=−0.408; or  ii)
12≤ND≤20 where a=0.751/(2×π), b=0, c=0, y=−0.104;  iii)
T.sub.max being the maximum separation angle and ND the amount of the nominal thread former diameter measured in millimeters.

(30) In particular, the three regions i), ii), und iii), which can also be claimed independently of one another, are produced from the above relationship.

(31) For the shown thread former 1 where Da=10 mm, a maximum separation angle of approximately 45.76 degrees is produced according to the above relationship. The actual or effective separation angle T of the embodiment shown as an example with a total of nine pressing lands 4, or pressing webs 10, per revolution is 40 degrees and is therefore actually smaller than the maximum separation angle Ta. The actual separation angles can be chosen, in particular, in such a manner that they are smaller than or equal to the maximum separation angle, and the number of pressing lands for each revolution corresponds to an integral, for example uneven, value.

(32) It should be noted that it is not necessary for all separation angles Ta to be identical. Rather, it is also possible for the pressing lands 4 to be arranged along the shaping curve using two or more than two different separation angles Ta.

(33) In the case of thread formers 1 according to the invention with a nominal diameter, i.e. outside diameter Da, of 12 mm, a maximum separation angle T.sub.max of approximately 35.45 degrees is produced with the above relationship.

(34) If the arrangement of the pressing lands 4 is chosen in such a manner that the number of pressing lands for each revolution along the shaping curve comprises an integral value, in particular an uneven integral value, which has proved to be particularly advantageous with regard to service life and thread quality, thus at a nominal diameter Da of 12 mm, for example, eleven pressing lands 4 can be provided per revolution, which corresponds to an effective separation angle T of 32.73 degrees which lies below the previously named maximum separation angle T.sub.max of 35.45 degrees.

(35) As already mentioned, there are advantages with regard to the service life of the thread former 1 and the service life of the pressing lands 4 for maximum separation angles according to the specified relationship, it being possible to achieve advantageous thread qualities and thread stability in particular at the same time.

(36) In particular, according to acquired knowledge for thread forming within the framework of the invention it has proved particularly advantageous when the separation angle is determined in such a manner that the number of pressing lands of the pressing lands 4 that are present consecutively along the shaping curve 9 for each revolution along the shaping curve 9 for nominal diameters Da between 10 mm and less than 12 mm is at least nine, in particular precisely nine, and that the number of pressing lands for nominal diameters of 12 mm or more than 12 mm, preferably for nominal diameters between 12 mm and 20 mm, is at least eleven, in particular precisely eleven.

(37) As can be seen from FIG. 2, FIG. 3 and in particular from FIG. 4, in which an enlarged representation of a portion of a pressing land 4 of the thread former 1 is shown, the flanks 13 of the pressing lands 4, which are oriented toward the tool tip 6, can each comprise a first part flank surface 13.1 and a second part flank surface 13.2.

(38) In particular, under the specified relationship for the maximum separation angle T.sub.max it has proved advantageous with regard to improved service lives and/or thread qualities when the first 13.1 and second part flank surface 13.2 intersect along a line of contact 14 which extends outward from the core diameter Dk of the thread former 1, the part flank surfaces 13 intersecting in a preferred manner at an angle which differs from zero and is in particular obtuse. The latter can mean, for example, that the pressing lands 4 comprise in each case the largest thickness measured in the longitudinal direction in radial sections parallel to the longitudinal axis L on the line of contact 14 in the circumferential direction.

(39) In the example of the thread former 1 in the exemplary embodiment shown, the line of contact 14 extends substantially radially outward with reference to the longitudinal axis L of the thread former 1, which has proved advantageous with regard to reduced wear.

(40) It can be seen in particular from FIG. 3 that the pressing lands 4 can be realized in such a manner that they each realize a thread former tip 12 which protrudes radially outward with reference to the longitudinal axis L of the thread former 1, the line of contact 14 opening out into the thread former tip 12.

(41) The thread former tips 12 provide the regions of the pressing lands 4 with the largest radial advancement when the thread is produced and exposed along with the part flank surfaces 13 and the line of contact 14 to comparatively high friction forces and torques.

(42) The lines of contact 13 beginning approximately at the core diameter Dk open out in each case in a thread former tip 12, edges 15 of the pressing lands 4 which point radially outward comprising a corresponding kink so that the line of contact 14 extends over the edges 15 which point radially outward, which can be seen in particular from FIG. 4.

(43) Consequently, it follows for the pressing land geometry shown that during thread production the radial advancement and radial/axial forming forces increase in opposition to the thread forming direction R toward the line of contact 14 and decrease again from the line of contact. In particular, with the special geometry of the pressing lands 4 and the (in particular: defined, restricted) distance between pressing lands 4, in particular between the thread former tips 12, e.g. in the circumferential direction, given by the maximum separation angle T.sub.max, advantageous service lives in the case of the thread former 1 and comparatively good thread qualities and strengths can be achieved corresponding to the invention.

(44) As can be seen in particular from FIG. 3, connecting lines, which connect in each case adjacent thread former tips 12 in the circumferential direction, produce a polygon P which is shown in FIG. 3 simply including three thread former tips 12. In the example of the thread former 1 in FIG. 1 to FIG. 4, each polygon observed along the shaping curve 9 for one revolution comprises nine (in numerals: 9) corners.

(45) As can be seen from FIG. 2 and FIG. 3, all pressing lands 4 in the present example are realized in such a manner that said cutting planes S (see FIGS. 3, 5 as an example) which extend through the thread former tip 4 and are perpendicular to the shaping curve 9 are realized asymmetrically.

(46) The thread former 1 of the exemplary embodiment shown is realized especially in such a manner that each of the pressing lands 4 comprises a tapping edge 15.1 which points radially outward, is oriented in the thread forming direction R and connects radially to the first part flank surface 13.1. In this respect the first part flank surface 13.1 can be designated as a tapping surface.

(47) In addition, each of the pressing lands 4 includes a free tapping edge 15.2 which points radially outward, is oriented in opposition to the thread forming direction R and connects radially to the second part flank surface 13.2. In this respect the second part flank surface 13.2 can be designated as a free tapping surface.

(48) According to a design, as shown in FIG. 5, the pressing land 4 can be realized in such a manner that a tapping angle defined by the tapping edge 15.1 with reference to a predefined measuring depth is greater than a free tapping angle defined by the free tapping edge 15.2 at the predefined measuring depth.

(49) In particular in the case of thread formers 1, which are realized in a manner corresponding to the described line of contact 14 and/or corresponding to the asymmetry relating to tapping edge 15.1 and free tapping edge 15.2, or tapping angle and free tapping angle, designs can be provided for which the maximum separation angle T.sub.max is determined as specified for nominal thread diameters Da of between 6 mm and less than 10 mm, and the actual separation angle T is determined in such a manner that precisely six pressing lands 4 are present for at least one, preferably for each, revolution along the shaping curve 9 for nominal diameters of between 6 mm and less than 8 mm, and that precisely seven pressing lands 4 are present for nominal diameters of 8 mm and less than 10 mm. Advantageously service lives and thread qualities and/or thread strengths are also produced for such designs.

(50) In further designs it can be provided that at least the first and second part flank surfaces 13 are smoothed by a polishing treatment, for example with diamond dust. In particular, as a result further advantages with regard to service life and thread quality can be achieved in addition to the special arrangement and geometry of the proposed pressing lands 4.

(51) As can be seen from the described exemplary embodiments, the thread former 1 proposed herein enables the production of a thread, a corresponding method being able to comprise the following steps: provide the workpiece; provide a thread former as claimed in one of the designs of the invention proposed herein; produce the thread by simultaneously rotating and moving the thread former in an axial-translatory manner, wherein the thread former is moved at a predefined rotational speed and a predefined axial speed.

(52) When the thread is produced, the tapping edges 13.1 and the tapping flanks 13.1, i.e. the first part flank surfaces 13.1, and the thread former tips 12 are advanced radially in particular in the tapping region 7, as a result of which the workpiece is formed at the worked surface, in particular cold formed, corresponding to the axial sequence of the pressing lands 4 and indentations between the pressing lands 4 so that a thread which corresponds to the structure of the thread former head 3 is produced.

(53) There is no further advancement in the radial direction in the region of the guide and calibration region 8 (apart from the advancement that occurs, where applicable, on account of the elastic spring-back of the material of the workpiece). As already mentioned, the guide and calibration region 8 is provided for the purpose of guiding the thread former head 3 in the thread produced by the tapping region 7 and/or to rework or calibrate the thread that has already been produced/that exists already.

(54) Overall, it is shown that with the thread former proposed herein for the chipless production of a thread with a plurality of pressing lands 4 which are each arranged at predefined separation angles T along a shaping curve 9, it is possible to in particular achieve advantageous service lives simultaneously with comparatively good thread quality and thread strength.

LIST OF REFERENCES

(55) 1 Thread former 2 Tool shank 3 Thread former head 4 Pressing land 5 Crest region 6 Tool tip 7 Tapping region 8 Guide region, calibration region 9 Shaping curve 10 Pressing web 11 Groove 12 Thread former tip 13 Flank 13.1 First part flank surface 13.2 Second part flank surface 14 Line of contact 15 Edge 15.1 Tapping edge 15.2 Free tapping edge L Longitudinal axis Da Outside diameter Dk Core diameter T Separation angle Tmax Maximum separation angle E Center plane P Polygon R Thread forming direction S Cutting plane