EP2367644B1 - Method and rolling die for producing a screw - Google Patents

Description

Background of the invention

The present invention relates to a method of manufacturing a screw according to the preamble of claim 1 and to a rolling die according to the preamble of claim 9. (See FIG. 1 In a known method for producing a screw, a blank for forming the screw thread is rolled between two dies. In this case, a rolling profile is formed in each rolling die, which comprises a family of elongated depressions, which are intended to form the thread turn. Each rolling die has first and second ends spaced apart in the rolling direction, a blank being moved from the first towards the second end during rolling relative to the rolling die.

wobei d_G0 einem "zylindrischen Ersatzdurchmesser" des fertiggewalzten Gewindes entspricht, nämlich dem Durchmesser eines gedachten Ersatzzylinders, dessen Volumen pro Längeneinheit demjenigen des fertiggewaltzten Gewindes entspricht. d_dV ist eine Zugabe zum Walzdurchmesser, die zum Ausgleich des Axialschubs bestimmt ist und typischerweise weniger als 5 % von d_w0 beträgt.In general, blanks are used which have at least one cylindrical clearance which is formed into thread. Since in the rolling process by transverse pressure flow in the longitudinal direction of the thread occurs, it is common to the roll diameter d _w0 , ie to choose the diameter of the blank used so that the volume per unit length in the blank is slightly greater than or equal to that of the finished thread. For the rolling diameter d _w0 , therefore: $${\mathrm{d}}_{\mathrm{w}\mathrm{0}}\mathrm{=}{\mathrm{d}}_{\mathrm{G}\mathrm{0}}\mathrm{+}{\mathrm{d}}_{\mathrm{dV}}\mathrm{.}$$

where d _G0 corresponds to a "cylindrical equivalent diameter" of the finish-rolled thread, namely the diameter of an imaginary replacement cylinder whose volume per unit length corresponds to that of the finish-rolled thread. d _dV is an addition to the rolling diameter that is intended to compensate for axial thrust and is typically less than 5% of d _w0 .

If a screw with a desired thread form is to be produced in the rolling process, d _{G0 is} determined by this thread form, and d _dV results automatically during the rolling process. This means that for the production of a certain thread form in the rolling process always a very specific rolling diameter d _w0 must be selected, so there is no degree of freedom with respect to the choice of Durclunessers d _{w0 of} the section of the blank where the thread is to be formed.

In general, one will endeavor to use a simple cylindrical blank because it is easiest and most cost-effective to produce, and in this case the diameter of the blank is fixed by d _w0 . However, this often leads to problems in practice. For example, if a screw head is to be made by pressing a corresponding unthreaded portion of the blank, the predetermined diameter d _w0 is often simply too small. In this case, it is inevitable to use a variable diameter blank having a first, slimmer portion for forming the thread and a second, denser portion for forming the head. A similar situation arises in the manufacture of hanger bolts, ie bolts having two distinct, separate threads, typically a metric thread and a self-tapping wood thread. For both threads results in an associated required rolling diameter d _w0 ⁽¹⁾ or d _w0 ⁽²⁾ , which, however, will not be identical in the rule. Also in this case, it is inevitable to provide a blank having two sections of different diameters, which, however, substantially increases the manufacturing cost.

Another method according to the preamble of claim 1 is known from DE 60 2004 004 057 T2 known.

Summary of the invention

The invention has for its object to provide a method of the type mentioned, in which the problems described above are avoided.

This object is achieved by the method according to claim 1. In this method, a special rolling die according to claim 9 is used. Advantageous developments are specified in the dependent claims. According to the method of the invention, a rolling die is used in which the mean pitch of the center lines of the recesses, which is defined as the quotient of the changes in the positions of the center line in the direction transverse to the rolling direction, in a first region of the first end of the Rolling jaws different from the average pitch in a region of the second end of the rolling die, the said region of the first end - as viewed in the rolling direction - opposite.

Such a rolling die differs substantially from a conventional rolling die in which the center lines of all recesses are straight, parallel and equidistant. This means that in a conventional rolling die and the slope of the center lines of the wells are identical everywhere on the rolling die, and in particular at its first and second ends. Notwithstanding this, the invention proposes to vary the slope of the recesses along the rolling direction so that the average pitch in - viewed in the rolling direction - opposite areas at the first and second end of the rolling die are different from each other. In this case, "regions viewed in the rolling direction" designate those regions at the first and second end of the rolling jaw which are delimited by two lines parallel to the rolling direction.

With the variation of the pitch of the recess in the rolling direction, a volume transport of the blank material in the axial direction is accompanied, the extent of which depends on the variation of the slope of the (center lines of) recesses. This means that the rigid relationship between the effective diameter d _{G0 of} the finished thread, which is predetermined by the screw design, and the rolling diameter d _w0 no longer exists. Rather, it is possible to freely choose a blank diameter d ' _w0 within certain limits and, in turn, to suitably vary the pitch of the depressions along the rolling direction. The relationship between d _w0 , d ' _w0 , the pitch P _{1 of} the recesses at the first and the pitch P _{2 of} the recess at the second end of the rolling die results from the volume conservation as follows: $${{\mathrm{d}}_{\mathrm{w}\mathrm{0}}}^{\mathrm{2}}\mathrm{\cdot }{\mathrm{P}}_{\mathrm{2}}\mathrm{=}{{\mathrm{d\text{'}}}_{\mathrm{w}\mathrm{0}}}^{\mathrm{2}}\mathrm{\cdot }{\mathrm{P}}_{\mathrm{1}}\mathrm{,}$$

Note that P ₂ , ie, the slope of the recesses at the second end of the rolling die is determined by the thread pitch of the finished screw because the rolling process ends at the second end of the rolling die. Furthermore, as described above, d _w0 is _defined by the desired thread form, the cylindrical replacement diameter d _G0 and the addition d _dV . However, within certain limits, a desired modified rolling diameter d ' _{w0 are} chosen. For this purpose, according to the above equation, only the pitch P _{1 of} the depressions at the first end of the rolling die must be selected as follows: $$P_1=\frac{{d_{w0}}^2}{d{{\text{'}}_{w0}}^2}\cdot P_2\mathrm{,}$$

In this consideration, it has been assumed that the pitch P ₁ is identical for all cavities at the first end of the rolling die, and that the pitch P ₂ for all cavities at the second end of the rolling die is identical. However, the invention is by no means limited to this embodiment, but embodiments are also described herein for variable pitch screws, for the production of a rolling jaws is used, in which the pitches of the wells both at the first end to each other vary and at the second end to each other. In order to do justice to both cases, reference is made below to the "average slope" in certain areas.

Preferably, the mean pitch P ₂ in the area of the second end is greater than the mean pitch P ₁ in the opposite area of the first end, ie P ₂ > P ₁ . This corresponds to an extension of the blank during rolling and, according to the above equation, means that d ' _w0 > d _w0 . Thus, to produce a particular helical shape, a blank having a larger rolling diameter d' _w0 may be used than in a prior art rolling method in which the rolling diameter of the blank would be set to d _w0 . For example, the rolling diameter d ' _w0 can be _chosen so large that it allows the formation of a screw head by pressing.

Preferably, said mean slopes in said regions at the first and second ends differ by at least 2.5%, preferably at least 15% and most preferably at least 25% from one another.

Preferably, the rolled section is formed so that the average volume per unit length of the finish-rolled screw thread is at least 5%, preferably at least 17% and more preferably at least 27% lower than that of the blank.

An important application of the method is to uniformly stretch the blank in the course of rolling. This means that a thread is rolled from a cylindrical blank whose volume per unit length in the longitudinal direction of the thread is constant. In other embodiments, however, it may be advantageous if the rolled section is designed such that, starting from a cylindrical blank, a threaded section is rolled in which the volume varies per unit length. This is the case, for example, when a screw with a continuous thread variable pitch in the rolling process is to be produced. In this case, the term of a "continuous" thread indicates that it is a single, continuous thread, and serves to delimit against two separate threads, which are formed on the same screw.

A screw with a continuous thread with variable pitch is, for example, in the WO 2009/015754 described. By a suitable variation of the thread pitch can be generated when screwing the screw into a component an internal stress in the bond between the screw and the component. According to the teaching of the cited patent, the variation of the thread pitch is to be selected such that the residual stress of a composite stress, which occurs under load of the component, is opposite, so that at least the voltage peaks of the resulting composite stress are reduced under load of the component. Such a screw with variable pitch can, for example, for reinforcing components, for. As laminated supports, or used to introduce forces into a component.

It will be noted that a variable pitch lead screw in a low pitch range, i. lower pitch for forming the thread requires more material per unit length than in a high pitch area. If this additionally required material is missing during rolling, it may happen that the thread diameter decreases in the region of low thread pitch, or that the thread is not completely "filled" in the rolling process. The local lack of material is referred to below as "volume defect".

wobei P₂₁ die mittlere Steigung der (Mittellinie der) Vertiefungen in einem ersten Bereich am zweiten Ende des Walzbackens ist, die geringer ist als die mittlere Steigung P₂₂ der Vertiefungen in einem zweiten Bereich am zweiten Ende des Walzbackens, und wobei P₁₁ und P₁₂ die mittleren Steigungen in denjenigen Bereichen am ersten Ende des Walzbackens sind, die dem ersten bzw. dem zweiten Bereich des zweiten Endes - in Walzrichtung betrachtet - gegenüberliegen.In the context of the invention, it is possible, this volume defect by systematic variation of the slopes of the wells of the rolling die and a material transport caused thereby to compensate in the axial direction. For this purpose, according to one embodiment of the invention, the rolled section is therefore chosen such that the following inequality holds: $$\frac{P_{21}}{P_{11}}<\frac{P_{22}}{{\mathrm{<figure-callout\; id="12"\; label="P"\; filenames="imgf0001.png"\; state="\{\{state\}\}">P</figure-callout>}}_{12}}.$$

wherein P _{21 is} the mean slope of the (center line of) depressions in a first region at the second end of the rolling die that is less than the mean slope P _{22 of} the depressions in a second region at the second end of the rolling die, and P ₁₁ and P _{12 are} the average slopes in those areas at the first end of the rolling die, which are opposite to the first and the second region of the second end, as viewed in the rolling direction.

Additionally or alternatively, a volume defect can also be compensated for by selecting a smaller cross-sectional area of a thread tooth by varying the flank angle and / or the thread depth for the finish-rolled thread in a region of lesser thread pitch. Thus, the thread may have a sharper flank angle in the region of lower thread pitch than in a region of greater thread pitch. This can be maintained with less available material a constant thread diameter.

In the case of the rolling die, those depressions whose center lines have a greater pitch in the region of the first end of the rolling jaw are preferably made deeper in the region of the first end of the rolling jaw than those whose center line has a smaller pitch in the region of the first end of the rolling jaw. Since recesses of higher pitch are spaced further apart in the region of the first end, it is advantageous for the rolling process if these recesses are formed deeper. Preferably, the recesses in the region of the first end of the rolling die are V-shaped in cross-section and at least in depth at least to ± 10% proportional to the slope of the center line at the first end of the rolling die.

Brief description of the figures

Fig. 1A

eine Draufsicht auf einen Walzbacken nach dem Stand der Technik zum Walzen eines Gewindes mit konstanter Gewindesteigung sowie eines Rohlings und eines fertig gewalzten Gewindes;

Fig. 1B

eine Draufsicht auf eine Stirnfläche des Walzbackens von Fig. 1A an dessen erstem Ende;

Fig. 1C

eine Draufsicht auf eine Stirnfläche des Walzbackens von Fig. 1A an dessen zweitem Ende;

Fig. 2A

eine Draufsicht auf einen Walzbacken nach einer ersten Ausführungsform der Erfindung, sowie eines Rohlings und eines fertig gewalzten Gewindes;

Fig. 2B

eine Draufsicht auf eine Stirnfläche des Walzbackens von Fig. 2A an dessen erstem Ende;

Fig. 2C

eine Draufsicht auf eine Stirnfläche des Walzbackens von Fig. 2A an dessen zweitem Ende;

Fig. 2D und Fig. 2E

perspektivisch Ansichten des Walzbackens von Fig. 2A;

Fig. 3A

eine Draufsicht auf einen Walzbacken zum Herstellen einer Schraube mit veränderlicher Gewindesteigung ohne axialen Volumentransport;

Fig. 3B

eine Draufsicht auf eine Stirnfläche des Walzbackens von Fig. 3A an dessen erstem Ende;

Fig. 3C

eine Draufsicht auf eine Stirnfläche des Walzbackens von Fig. 3A an dessen zweitem Ende;

Fig. 3D

eine vergrößerte und vereinfachte Ansicht der Draufsicht auf den Walzbacken von Fig. 3A;

Fig. 4A

eine Draufsicht auf einen Walzbacken nach einer zweiten Ausführungsform der Erfindung sowie eines Rohlings und eines fertig gewalzten Gewindes;

Fig. 4B

eine Draufsicht auf eine Stirnfläche des Walzbackens von Fig. 4A an dessen erstem Ende;

Fig. 4C

eine Draufsicht auf eine Stirnfläche des Walzbackens von Fig. 4A an dessen zweitem Ende.

Further advantages and features of the invention will become apparent from the following description in which the invention with reference to two embodiments with reference to the accompanying drawings will be described. Show:

Fig. 1A

a plan view of a rolling die according to the prior art for rolling a thread with a constant pitch and a blank and a finished rolled thread;

Fig. 1B

a plan view of an end face of the rolling die of Fig. 1A at its first end;

Fig. 1C

a plan view of an end face of the rolling die of Fig. 1A at its second end;

Fig. 2A

a plan view of a rolling die according to a first embodiment of the invention, as well as a blank and a finished rolled thread;

Fig. 2B

a plan view of an end face of the rolling die of Fig. 2A at its first end;

Fig. 2C

a plan view of an end face of the rolling die of Fig. 2A at its second end;

FIGS. 2D and 2E

perspective views of the rolling of Fig. 2A ;

Fig. 3A

a plan view of a rolling die for producing a variable pitch screw without axial volume transport;

Fig. 3B

a plan view of an end face of the rolling die of Fig. 3A at its first end;

Fig. 3C

a plan view of an end face of the rolling die of Fig. 3A at its second end;

Fig. 3D

an enlarged and simplified view of the top view of the dies of Fig. 3A ;

Fig. 4A

a plan view of a rolling die according to a second embodiment of the invention and a blank and a finished rolled thread;

Fig. 4B

a plan view of an end face of the rolling die of Fig. 4A at its first end;

Fig. 4C

a plan view of an end face of the rolling die of Fig. 4A at its second end.

Description of the Preferred Embodiments

Fig. 1A FIG. 12 is a plan view of a prior art rolling die 10 that can be used to roll a constant pitch lead screw.

The rolling die 10 has a first end 12 and a second end 14. During rolling, a blank 16 is rolled from the first end 12 of the rolling die 10 toward the second end 14. On the surface of the rolling die 10, a rolled profile is formed, which is formed from a plurality of rectilinear, parallel and equidistant depressions 18. The recesses 18 in the region of the first and second end 12, 14 are in Figs. 1B and 1C can be seen, each showing a plan view of one of the end faces 20, 22 of the rolling die 10. A screw 19 with finished rolled thread is shown in the region of the second end 14 of the rolling die 10.

As in Figs. 1A, 1B and 1C As can be seen, the cross-section of the recesses 18 changes between the first and second ends 12, 14 of the rolling jaw 10. However, the cross-sections of all recesses 18 at the first end 12 are identical (see Fig. 1B ), and the same applies to the cross sections 18 at the second end of the rolling die 10 (see Fig. 1C ). Further, the center lines of the recesses 18 are rectilinear, parallel to each other and arranged equidistantly.

Fig. 2A shows a plan view of a rolling die 24, which is suitable for producing a screw 26 also shown with a continuous thread 28 with a constant pitch. The screw 26 can be made of the same blank 16, which in the embodiment of Fig. 1A has been shown and is rolled from a first end 30 of the rolling die 24 towards a second end 32. Figs. 2B and 2C show plan views of end faces 36 and 38 in the region of the first and second end 30, 32 of the rolling die 24th FIGS. 2D and 2E show perspective views of the rolling die 24th

As in Fig. 2A . 2D and 2E it can be seen, consists of the rolling profile of the rolling die 24 of a plurality of elongated recesses 34, unlike the dies 10 of Fig. 1A however, they are not straight, parallel and equidistant over their entire length. Instead, the recesses in the region of the first end 30 of the rolling jaw 24 are closer together than in the region of the second end 32, and the slopes of the center lines of the recesses, which are defined as the quotient of the changes in the position of the center lines in Direction transverse or parallel to the rolling direction, are less in the region of the first end of the rolling die than in the region of the second end. Between the first and second ends 30, 32 of the rolling die, the recesses 34 are suitably shaped around a smooth transition between the smaller pitch in the region of the first end 30 of the rolling die 24 and the greater pitch in the region of the second end 32 of the rolling die 24 manufacture.

Note that in the embodiment shown, the transition between the initial and the final pitch substantially occurs in a first length portion 25a of the rolling die that extends from the first end 30 to about ½ to ¾ of the total length. In a second, adjacent to the second end 32 length portion 25 b of the rolling die 24, the recesses 34 are similar to the conventional rolling 10 of Fig. 1A parallel and equidistant and therefore have a constant slope. In the first longitudinal region 25a of the rolling jaw 24, therefore, the blank is stretched when forming the thread, whereas in the remaining second longitudinal region 25b, ie at the end of the rolling stretch, only the thread 28 is further formed.

Out Fig. 2A to 2E It can be seen that with the rolling die 24 according to the first embodiment, a relatively slender screw can be produced from a relatively thick blank. Here, the ratio between the cylindrical equivalent diameter of the finished screw 26 and the blank 16 is approximately equal to the root of the ratio of the pitch of the recesses 34 at the first and second ends 30, 32 of the rolling die 24. It is therefore possible to make a screw with desired shape, the diameter of the blank within certain limits to choose freely and in turn to vary the slope of the wells at the first end 30 of the rolling die 24 relative to the slope at the second end 32 of the rolling die 24 accordingly.

Note that the screw 26 in the schematic representation of Fig. 2A shows only the rolled threaded portion, but the non-rolled portion of the blank has been omitted for the sake of simplicity. This unrolled portion of the comparatively thick blank may then be used, for example, to press a screw head or to form a metric thread thereon in another rolling operation to produce a hanger bolt (not shown in the figures).

In the embodiment of Fig. 2A For example, in the rolling process, the cylindrical diameter of the screw compared to that of the blank was reduced, but the cylindrical equivalent diameter of the finished thread or the volume per unit length remained constant in the finished thread. In some applications, however, it is advantageous to form the rolled section so that the volume per unit length in the finished thread is no longer constant. An application for this purpose are screws with continuous thread variable thread pitch, where in the area of low thread pitch, ie lower pitch, more material is required to form the thread. This will be explained in more detail in a second embodiment of the invention. However, before describing this second embodiment, reference is made to FIG Fig. 3A to 3D First, it will be explained how a rolling jaw can look like to form a thread with a variable pitch, in which initially there is no appreciable volume transport in the axial direction. Based on this geometry of the rolled section is then described how the desired axial volume transport can be caused.

Fig. 3A shows a plan view of a rolling die 40, which is suitable for a method for producing a screw 42 also shown with a continuous thread 44 variable pitch. The screw 44 can be made of the same blank 16, which in the embodiment of Fig. 1A has been shown and which is rolled from a first end 46 of the rolling jaw 40 toward a second end 48. 3B and 3C show plan views of end faces 52 and 54 in the region of the first and second end 46, 48 of the rolling die 40th

As in Fig. 3A can be seen, consists of the rolling profile of the rolling jaw 40 of a plurality of elongated recesses 50, unlike the rolling jaw 10 of Fig. 1A however not straightforward, not parallel and not equidistant. The geometry of the recesses 50 is determined by Fig. 3D described in more detail, in which the plan view of the rolling jaws 40 is shown enlarged, and in the sake of clarity, only the center lines 50 'of the respective elongated depressions 50 are located.

As in Fig. 3D can be seen, the center lines 50 'of each two adjacent recesses 50 are formed and arranged so that they can be brought by a shift in the rolling direction by a constant distance T in line. The centerlines 50 'have a slope defined as the quotient of the centerline position changes Δy and Δx, respectively in the direction transverse (y-direction) or parallel (x-direction) to the rolling direction. Due to the translation symmetry in the rolling direction, the slopes of each centerline at their intersections are identical to a line 56 parallel to the rolling direction. Incidentally, this pitch is proportional to the thread pitch in the section 58 corresponding to the line 56 of the finished screw 42 (see also FIG Fig. 3A ), ie the portion of the screw which is formed by a portion of the rolling jaw 40 which extends along the line 56.

In Figs. 3B and 3C It can be seen that the distances between adjacent recesses 50 in the y-direction, ie, a direction transverse to the rolling direction change both at the first and at the second end 46, 48 of the rolling jaw 40. This change in the distances reflects the variable thread pitch, since the distances represent a "local" pitch of the screw, so the local thread pitch of the screw. Note that the local thread pitch P = dy / dφ is proportional to the in Fig. 2D slope Δy / Δx shown, since a certain distance .DELTA.x during unrolling of the blank corresponds to a certain rolling angle .DELTA..phi.

It should be noted, however, that the average pitch of the recesses 50, as seen in the rolling direction, are identical in opposite regions at the first and second ends 46, 48 of the rolling die 40 herein. For explanation, see Fig. 3B a first region 60 of the first end and in Fig. 3C a first portion 62 of the second end of the rolling jaw 40 is shown. Each of these regions has six depressions 50, which means that the mean slope of the depressions 50 in the opposite regions 60, 62 is identical.

Further shows Fig. 3B a second region 64 of the first end of the rolling jaw 40, the width of which corresponds to that of the first region 60, but in which the mean slope of the recesses is greater, because only four recesses fit in this region 64. The second region 64 of the first end a second region 66 of the second end, in which the mean slope is greater than in the first portion 62 of the second end, but equal to that in the opposite portion 64 of the first end.

The fact that the average pitches in - viewed in the rolling direction - opposite sections 60/62 and 64/66 at the first and second ends 46, 48 of the rolling die 40 are identical, has the consequence that there is virtually no material volume transport in the axial direction of the blank (or γ-direction of the rolling jaw 40).

Another difference between the dies 40 of Fig. 3A to 3D and the rolling jaw 10 of Fig. 1A to 1C From the prior art is that such wells 50, whose center line in the region of the first end 46 of the rolling jaw 40 have a greater pitch, are formed deeper in the region of the first end 46 than those whose center line in the region of the first end 46 a has smaller slope, like Fig. 3B can be seen directly. When rolling 10 of Fig. 1B however, the depths of all depressions 18 at the first end 12 of the rolling die 10 are identical. By adjusting the milling depth of the recesses 50 in the region of the first end 46 of the rolling jaw 40 to the pitch of adjacent recesses 50 can be ensured that 50 peaks are formed between two adjacent recesses, all of which are at least approximately at the same level and thereby simultaneously come into contact with the blank 16 in contact. As Fig. 3B it can be seen, in the first embodiment, the recesses 50 in the region of the first end 46 of the rolling jaw 40 in cross-section V-shaped, and their depth is proportional to the slope of the center line 50 'in the region of the first end 46 of the rolling jaw 40, or to the spacing of adjacent recesses 50.

Since the blank 16 used is cylindrical and therefore has a constant volume per unit length, the screw 42 which was produced with the rolling jaw 40, a constant volume per unit length, because the geometry of the rolled profile of Fig. 3A is initially chosen so that a volume transport in the axial direction during rolling of the blank 16 is avoided. However, the finished screw 42 requires more material in an area of lesser thread pitch, where the turns are closer together. If the thread pitch varies greatly with the screw, it can happen that the thread is not "filled" in places, because there is not enough material, or that the diameter of the thread decreases in this area.

The lack of material in the area of lower thread pitch is referred to below as "volume defect". To compensate for the volume defect, three approaches are proposed herein:

First, instead of a cylindrical blank, a blank of variable section could be used. This blank would have a slightly larger diameter in areas where a threaded portion of low pitch is to be formed than in areas where a portion of comparatively large pitch is to be formed. However, this solution is disadvantageous in that it requires a complicated production of the blank.

A second solution is to vary the cross-sectional area of a thread tooth by varying the flank angle and / or the thread depth of the thread 44 so that the finish rolled thread has a smaller cross-sectional area of the thread tooth in a region of lesser thread pitch and thus the volume defect is compensated. Thus, the thread can have a more acute flank angle, so that the thread viewed in the longitudinal section of the screw is narrower and provided with a sharp edge and thus requires less material. This can be easily implemented in the die 40 by making the widths of the recesses 50 narrower and / or less deep at the second end 48 of the die 40 in areas of lesser thread pitch.

The third and preferred solution is to design the rolled profile to produce some targeted volume transport from areas of greater thread pitch to areas of lesser thread pitch that balance the volume defect. This third variant is described in the second embodiment, which is described below with reference to FIG FIGS. 4A to 4C is described.

Fig. 4A FIG. 12 shows a plan view of a rolling die 68 according to a second embodiment of the present invention having a first end 70 and a second end 72. On the die 68 is similar to in Fig. 3A a rolling profile consisting of a plurality of elongated, curved, non-parallel depressions 74 is formed. The course of the pits 74 is based on that of Fig. 3A which, however, has additionally been modified for a particular intended volume transport.

Figs. 4B and 4C again show the top view of the end faces 76 and 78 of the first and second end 70, 72 of the rolling die 68. As can be seen by comparing Fig. 3C and 4C detects, the rolled section in the second embodiment at the second end 72 of the rolling die 68 is identical to that at the second end 48 of the rolling jaw 40 of FIG. 3A to 3D , This is because the rolling operation at the second end is finished, and apart from the volume defect correction, the same type of screw is to be manufactured with both embodiments. The difference between the embodiments is in the shape of the rolled profile at the first end of the rolling die 68, as by comparison of FIG Fig. 4B and 3B can be seen.

According to the second embodiment of Figs. 4B and 4C the thread pitches in - viewed in the rolling direction - opposite portions of the first and second ends 70, 72 of the rolling die 68 are no longer identical. In Fig. 4B For example, a first portion 80 of the first end 70 of the die 68, which includes five dimples 74, is shown. This area is - viewed in the rolling direction - at the second end 72 of the rolling die 68, a region 82 opposite, fall in the six wells 74. In other words, the average pitch P ₁₁ in the first region 80 of the first end 70 is greater than the average pitch P ₂₁ in the first region 82 of the second end 72. This has the consequence that when rolling the blank 16, an axial material transport in the Area 82 corresponding portion of the thread takes place. Since the threaded portion corresponding to the region 82 is a low-pitch portion, the above-described volume defect in this region can be compensated in this manner.

The reverse effect occurs in a second region 86 at the second end 72 of the rolling jaw 52, which is opposite to a second region 84 at the first end 70 of the rolling jaw 68 - viewed in the rolling direction. As Figs. 4B and 4C 2, the average pitch P _{22 of} the second area 86 at the second end of the rolling die 68 is greater than the average pitch P ₁₂ at the opposite area 84, as viewed in the rolling direction, which means that a material transport corresponding to area 86 will occur Section of the thread takes place. This is useful because the corresponding area of the thread is a high pitch area where therefore less material per unit length is needed to form the thread.

wobei P₂₁ die mittlere Steigung der Vertiefungen in einem ersten Bereich am zweiten Ende des Walzbackens ist, P₂₂ die mittleren Steigungen der Vertiefungen in einem zweiten Bereich am zweiten Ende des Walzbackens und P₁₁ und P₁₂ die mittleren Steigungen in den Bereichen am ersten Ende des Walzbackens sind, die dem ersten und dem zweiten Bereich - in Walzrichtung betrachtet - gegenüberliegen, und wobei ferner gilt: P₂₁<P₂₂. Die obige Ungleichung definiert somit eine lokale Umverteilung von Material in axialer Richtung, die über eine globale Streckung oder Stauchung hinausgeht.It should be noted that by varying the thread pitch in - viewed in the rolling direction - opposite portions at the first and second ends of the rolling die both a global stretching or compression of the thread and a redistribution of materials in the axial direction can be achieved. For the correction of the volume defect described above, however, a global stretching or compression is not sufficient, but rather Material must be transferred from a higher pitch area to a lower pitch area. A criterion for such a redistribution is given by the following inequality: $${\mathrm{P}}_{\mathrm{21}}\mathrm{/}{\mathrm{P}}_{\mathrm{11}}\mathrm{<}{\mathrm{<figure-callout\; id="22"\; label="P"\; filenames="imgf0001.png"\; state="\{\{state\}\}">P</figure-callout>}}_{\mathrm{22}}\mathrm{/}{\mathrm{<figure-callout\; id="12"\; label="P"\; filenames="imgf0001.png"\; state="\{\{state\}\}">P</figure-callout>}}_{\mathrm{12}}\mathrm{.}$$

where P _{21 is} the mean slope of the recesses in a first region at the second end of the rolling die, P ₂₂ the average slopes of the recesses in a second region at the second end of the rolling die, and P ₁₁ and P ₁₂ the middle slopes in the regions at the first end of the rolling die facing the first and the second region, as seen in the rolling direction, and further wherein: P ₂₁ <P ₂₂ . The above inequality thus defines a local redistribution of material in the axial direction that goes beyond global stretching or compression.

wobei ΔV der Volumendefekt der i-ten Windung und d_G0 ein zylindrischer Ersatzdurchmesser des fertigen Gewindes ist, d.h. der Durchmesser eines Ersatzzylinders, der die gleiche Länge und das gleiche Volumen hat, wie das fertige Gewinde. Hierbei ist dp(i) die Steigungsänderung Δϕ, die proportional zu einer Änderung ΔX der Vertiefungen in Walzrichtung ist.The rolling dies of FIGS. 4A to 4C can for example be constructed as follows: Starting point of the rolling dies without volume transport, as in Fig. 3A is shown to be. The geometry of the wells of the rolling die without volume transport can then be based on a desired shape of the finished screw and using the in conjunction with FIGS. 3A to 3E construct named criteria. As explained above, the average pitches in - compared to opposite areas in the rolling direction at the first and second ends of the rolling die are initially identical. In a second step, the slopes at the first end can then be varied to produce the desired volume transport. For this purpose, a correction value dp (i) is preferably added to the slope of the i-th depression at the first end, which is calculated as follows: $$\mathit{dp}\left(i\right)=\frac{\mathrm{\Delta }V\left(i\right)}{{d_{G0}}^2\pi /4}.$$

where ΔV is the volume defect of the i-th turn and d _{G0 is} a cylindrical replacement diameter of the finished thread, ie the diameter of a replacement cylinder having the same length and volume as the finished thread. Here, dp (i) is the pitch change Δφ, which is proportional to a change ΔX of the pits in the rolling direction.

In this way, the slope corrections at the first end can be calculated for each turn. The correction leads to a displacement of the recesses at the first end of the rolling die, as a comparison of Fig. 4B With Fig. 4C makes it clear. The individual recesses may then be modified by smooth functions to result in the desired variation at the first end of the rolling die and the desired thread form at the second end of the rolling die.

Note that the dies 24, 40 and 68 of FIG Fig. 2 . Fig. 3 respectively. Fig. 4 continuously change the slopes of the centerlines of the wells. To put it clearly, this means that the recesses are not bent at any point, which would correspond to a sudden change in the thread pitch. Such leaps and bounds would be obtained, for example, by tapping together threaded sections with different but constant thread pitches in the finished screw. Such a die might be simpler in construction, but more expensive to manufacture than the dies disclosed herein. The rolling jaws shown here with the smooth, kink-free depressions can be produced in the milling process. This is not readily possible with rolling jaws with kinked depressions. Although the rolling jaws could be composed of several individually manufactured parts at the kinks. The inventor has found, however, that such a composite rolling jaw tends to be susceptible to wear. Alternatively, it would be possible to produce a rolling jaw with kinked recesses in an erosion process, which, however, is much more expensive than a milling process. Therefore, the rolling jaws proves to be particularly advantageous with a smooth, kink-free course of the wells.

LIST OF REFERENCE NUMBERS

10

dies

12

first end of the rolling 10

14

second end of the rolling 10

16

blank

18

deepening

19

screw

20

End face at the first end of the rolling 10th

22

End face on the second end of the rolling 10th

24

dies

25a

first length range

25b

second length range

26

screw

28

thread

30

first end of the rolling die 24

32

second end of the rolling jaw 24th

34

deepening

36

Front side at the first end of the rolling die 24th

38

Front side at the second end of the rolling die 24th

40

dies

42

screw

44

Thread of the screw 42

46

first end of the rolling jaw 40

48

second end of the rolling jaw 40

50

deepening

52

End face at the first end of the rolling jaw 40th

54

Front side at the second end of the rolling jaw 40th

56

Line parallel to the rolling direction

58

Section of the thread 42

60

first area at the first end of the rolling die

62

first area at the second end of the rolling jaw 40

64

second area at the first end of the rolling jaw 40th

66

second area at the second end of the rolling jaw 40th

68

dies

70

first end of the rolling die 68

72

second end of the rolling die 68

74

deepening

76

Front side at the first end of the rolling die 68th

78

Front side at the second end of the rolling die 68th

80

first area at the first end of the rolling die 68

82

first area at the second end of the rolling die 68

84

second area at the first end of the rolling die 68th

86

second area at the second end of the rolling die 68th

Claims (15)

1. A method for manufacturing a screw (26, 42), in which method a blank (16) is rolled between two rolling dies (24, 68), wherein
   in each rolling die (24, 68) a rolling profile is formed that comprises a host of elongated depressions (34, 74), and
   the rolling die (24, 68) comprises a first and a second end (30, 32; 70, 72) spaced apart from each other in the direction of rolling, wherein during rolling the blank (16) is moved relative to the die (24, 68) from the first end towards the second end,
   characterised in that
   the mean slope of the centre lines of the depressions (34, 74) in a region of the first end (30, 70) of the rolling die (24, 68) differs from the mean slope in a region of the second end (32, 72) of the rolling die (24, 68), which region - when viewed in the direction of rolling - is opposite the region of the first end,
   wherein the slope of a centre line is defined as the quotient of the changes in the positions of the centre line in the directions transverse and parallel to the direction of rolling, respectively.
2. The method according to claim 1, in which the above-mentioned mean slopes in the above-mentioned regions at the first end and at the second end differ from each other by at least 2.5%, preferably at least 10% and particularly preferably by at least 25% and/or
   in which the above-mentioned mean slope in the region of the second end (32) is larger than in the region of the first end (30) and/or
   in which the rolling profile is designed so that the mean volume per unit of length of the finish-rolled screw thread is smaller by at least 5%, preferably at least 17% and particularly preferably at least 27% than that of the blank (16).
3. The method according to any one of the preceding claims, in which the rolling profile is formed so that starting from a cylindrical blank (16) a thread section is rolled in which the volume per unit of length varies, wherein preferably the difference between the maximum value and the minimum value of the volume per unit of length of the thread section is at least 2%, preferably at least 4% and particularly preferably at least 6% of the maximum value of the volume per unit of length.
4. The method according to claim3, in which the screw has a continuous thread with a variable thread pitch, and the mean slope P₂₁ of the depressions (74) in a first region (80) at the second end (72) of the rolling die (68) is less than the mean slope P₂₂ of the depressions (72) in a second region (86) at the second end (72) of the rolling die (68), and wherein the following applies: $${\mathrm{P}}_{\mathrm{21}}\mathrm{/}{\mathrm{P}}_{\mathrm{11}}\mathrm{<}{\mathrm{P}}_{\mathrm{22}}\mathrm{/}{\mathrm{P}}_{\mathrm{12}}\mathrm{,}$$

   

   
   wherein P₁₁ and P₁₂ denote the mean slope in the regions (80, 84) at the first end (72) of the rolling die (68), which when viewed in the direction of rolling, are opposite the above-mentioned first and second regions (82, 86) of the second end (72), respectively.
5. The method according to claim 4, in which the depressions (74) in the region of the second end (72) are formed in such a manner that the finish-rolled thread in a region of a smaller thread pitch has a smaller cross-sectional area and/or a more acute flank angle of a thread ridge than in a region of a larger thread pitch,
   in which the depressions (74) in a first region at the second end (72) of the rolling die (68) where the mean thread pitch is smaller than in a second region at the second end (68) of the rolling die (68), are preferably narrower than in the second region, and/or
   in which such depressions (74) whose centre line in the region of the first end (70) has a larger slope, in the region of the first end (70) are deeper than those whose centre line in the region of the first end (70) has a smaller slope, wherein preferably the depression in the region of the first end (70) of the rolling die (24, 52) is V-shaped in cross section, and its depth is proportional, at least within ±10%, to the slope of the centre line.
6. The method according to any one of the preceding claims, in which, furthermore, a screw head is formed by pressing a non-rolled section of the blank (16).
7. The method for manufacturing a screw, in which the screw comprises two threads that are separate of each other, and at least one of the threads is rolled in a method according to one of claims 1 to 5,
   in which in particular the screw is a hanger screw that comprises a metric thread and a wood thread or dowel thread.
8. The method according to any one of the preceding claims, in which the slopes of the centre lines of the depressions (34, 74) vary continuously.
9. A rolling die (24, 68) for manufacturing a screw (26, 42), in which rolling die (24, 68) a rolling profile is formed that comprises a host of elongated depressions (34, 74), wherein the rolling die (24, 68) comprises a first and a second end (30, 32; 70, 72) spaced apart from each other in the direction of rolling, wherein during rolling the blank (16) is moved relative to the die (24, 68) from the first end towards the second end,
   characterised in that
   the mean slope of the centre lines of the depressions (34, 74) in a region of the first end (30, 70) of the rolling die (24, 68) differs from the mean slope in a region of the second end (32, 72) of the rolling die (24, 68), which region - when viewed in the direction of rolling - is opposite the region of the first end,
   wherein the slope of a centre line is defined as the quotient of the changes in the positions of the centre line in the directions transverse and parallel to the direction of rolling, respectively.
10. The rolling die (24, 68) according to claim 9, in which the above-mentioned mean slope in the above-mentioned regions at the first end and at the second end differ from each other by at least 2.5%, preferably at least 15% and particularly preferably at least 25% and/or
    in which the above-mentioned mean slope in the region of the second end (32) is larger than in the region of the first end (30) and/or
    in which the rolling profile is designed so that the mean volume per unit of length of the finish-rolled screw thread is smaller by at least 5%, preferably at least 17% and particularly preferably at least 27% than that of the blank (16).
11. The rolling die (68) according to any one of claims9 or 10, in which the rolling profile is formed so that starting from a cylindrical blank (16) a thread section is rolled in which the volume per unit of length varies,
    in which the difference between the maximum value and the minimum value of the volume per unit of length of the thread section is at least 2%, preferably at least 4% and particularly preferably at least 6% of the maximum value of the volume per unit of length.
12. The rolling die (68) according to claim 11, for manufacturing a screw with a continuous thread with a variable thread pitch, wherein the mean slope P₂₁ of the depressions (74) in a first region (80) at the second end (72) of the rolling die (68) is less than the mean slope P₂₂ of the depressions (72) in a second region (86) at the second end (72) of the rolling die (68), and wherein the following applies: $${\mathrm{P}}_{\mathrm{21}}\mathrm{/}{\mathrm{P}}_{\mathrm{11}}\mathrm{<}{\mathrm{P}}_{\mathrm{22}}\mathrm{/}{\mathrm{P}}_{\mathrm{12}}\mathrm{,}$$

    

    
    wherein P₁₁ and P₁₂ denote the mean slopes in the regions (80, 84) at the first end (72) of the rolling die (68), which when viewed in the direction of rolling, are opposite the above-mentioned first and second regions (82, 86) of the second end (72), respectively.
13. The rolling die (68) according to claim12, in which the depressions (74) in the region of the second end (72) are formed in such a manner that the finish-rolled thread in a region of a smaller thread pitch has a smaller cross-sectional area and/or a more acute flank angle of a thread ridge than in a region of a larger thread pitch,
    in which the depressions (74) in a first region at the second end (72) of the rolling die (68) where the mean thread pitch is smaller than in a second region at the second end (68) of the rolling die (68), are preferably narrower than in the second region.
14. The rolling die (68) according to claims 12 or 13, in which such depressions (74) whose centre line in the region of the first end (70) has a larger slope are deeper in the region of the first end (70) than those whose centre line in the region of the first end (70) has a smaller slope, wherein
    preferably the depressions in the region of the first end (70) of the rolling die (68) are V-shaped in cross section, and the depth of the depressions is proportional, at least within ±10%, to the slope of the centre line.
15. The rolling die (24, 68) according to any one of claims 9 to 14, in which the slopes of the centre lines of the depressions (34, 74) vary continuously.

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