EP2344288A2

EP2344288A2 - Method and device for the non-cutting production of an outside thread on hollow metal work pieces

Info

Publication number: EP2344288A2
Application number: EP09767936A
Authority: EP
Inventors: Hilmar Gensert
Original assignee: Sieber Forming Solutions GmbH
Current assignee: Sieber Forming Solutions GmbH
Priority date: 2008-10-03
Filing date: 2009-10-02
Publication date: 2011-07-20
Also published as: WO2010037551A3; WO2010037551A2; CN102170981A; US20110185783A1; CN102170981B; KR20110084215A; JP2012504497A; DE102009048040A1

Abstract

The invention relates to a method for the non-cutting production of an outside thread on hollow metal work pieces for use as hollow screws, hollow shafts, threaded sleeves or fittings as stable connecting or fastening elements, and to a device suited for carrying out the method. Based on the disadvantages of the known prior art, a method is to be presented which is particularly suited for thin-walled work pieces and characterized by improved economic efficiency. Furthermore a device suited for carrying out the method is to be provided. As a proposed solution, within a multistage press (20) comprising a displaceable carriage (21) and a stationary work piece carrier unit (22), a wire section (27) as the base material is reshaped in one or more reshaping stages I to V into a finished hollow blank (4b). In the multistage press (20), the pre-fabricated hollow blank (4b) is inserted in a further stage VI into a multipart split tool (1, 8) having a cavity, the inside wall of which is provided with a negative threaded profile. In the closed state of the split tool (1, 8), at least one mandrel (6) is inserted into the central opening of the blank (4b) and the blank (4b) is widened, wherein the contours of the threaded profile is filled by a radial material flow and subsequently the finished work piece (4) is removed.

Description

Method and device for chipless production of an external thread on hollow metal workpieces

The invention relates to a method for chipless production of an external thread on hollow metal workpieces for use as hollow screws, hollow shafts, threaded sleeves or fittings as a stable connection or fastening elements, and a device suitable for carrying out the method. For the production of external threads on metallic workpieces, two classical types of processes are known, which are used in practice, depending on the size of the thread, the shape of the workpiece and / or the hardness of the metallic material, the rolling or cutting threads. When rolling or rolling machines are used with two or three driven round rollers or mutually moving flat jaws (parallel jaws). The thread can also be produced by means of lathes clamped in lathes, wherein the workpiece is driven.

The cold rolling of thread on thin-walled hollow parts by means of a profile rolling tool is z. B. from DE 195 36 817 A1.

The rolling or rolling of external threads on hollow cylindrical workpieces made of metal has gained in mass production in practice the greatest importance. However, a prerequisite for this is that the hollow cylindrical workpieces have a sufficient wall thickness. The wall thickness should be at least about 1/5 of the outer diameter / wall thickness on thread rolling on two-roll rolling machines and about 1/8 of the outer diameter / wall thickness on three-roll rolling machines.

If the ratio is below this value, then the thread can only be produced by machining or by means of rolling heads on lathes. Producing the thread on multi-spindle turning or tapping machines, however, is more material and time consuming than in a forming production. In the production of external threads by cutting shaping on automatic lathes by means of lathe tools, it is not possible to achieve a press-finished, cold-worked surface.

The invention has for its object to provide a method for chipless production of an external thread on hollow metal workpieces for use as hollow screws, hollow shafts, threaded sleeves or fittings as a stable connection or fastening elements, which is particularly suitable for thin-walled workpieces

CONFIRMATION COPY and is characterized by improved efficiency. Furthermore, a device suitable for carrying out the method is to be provided. According to the invention the object is achieved by the features specified in claim 1. Advantageous developments of the procedure are subject matter of claims 2 to 11. A suitable device for carrying out the method is the subject of claim 12. Further embodiments of the device are specified in claims 13 to 21.

According to the proposed procedure, cut-to-length metal wire or rod material is used as the starting material. The wire section is converted stepwise within a multi-stage press with a slidable carriage and a stationary tool carrier unit, in one or more extrusion or compression stages, to a finished hollow blank. Within the multi-stage press, the prefabricated hollow-shaped blank is inserted in a further stage into a multi-part jaw tool having a mold cavity whose inner wall is provided with a thread profiling designed as a negative. To form the external thread at least one mandrel is inserted or inserted on one side of the hollow workpiece in its central opening, wherein the workpiece is widened by means of the dome. Due to the expansion process, the contours of the thread profiling are filled by a radial flow of material (transverse extrusion presses) and thus the external thread is created. Finally, the finished workpiece is removed after opening the tool from this.

By means of the proposed procedure, external threads can be produced in a particularly economical manner on different hollow-shaped workpieces. As metallic workpieces come into question, which consist of kaltumformbarem material such as copper, aluminum or steel.

The manufactured externally threaded workpieces are intended for use as hollow screws, hollow shafts, threaded sleeves or fittings. These are used as stable connection or fastening elements.

If necessary, the inserted blank is fixed during the movement of the dome against an extension in the longitudinal direction.

The opening and closing movement of the jaws of the jaw tool and the movement of the dome can be triggered via the central drive unit of the multi-stage press. Of course, separate drives can be used, but this is associated with a higher cost.

The hollow-shaped workpieces can have a circular, oval or trilobular cross-sectional shape both inside and outside or inside and outside (in particular with screws) exhibit. The region of the workpiece which is to be provided with an external thread may also have a cavity, which is subdivided by a partition or other boundary into a plurality of cavity sections. In this case, a mandrel consisting of a plurality of mandrel sections is introduced into the cavity. The individual mandrel sections are adapted in their geometry to the respective cavity sections and at the same time cause a shaping of the corresponding threaded sections during the expansion process. The external thread produced can longitudinally interrupted threaded portions, which are, for example, in the places where the joints between the partition wall and the outer wall are. An application intended for this purpose are eg oil drain screws with two axial channels for the removal of oil.

According to a preferred variant of the method, the risk that material passes into the closing gap between the jaws of the baking tool during the thread pressing can be avoided by reducing the profile height of the thread profiling designed as a negative in the region of the closing edges of the jaws. As a result, no or only a weakened thread profiling is generated at the points of the blank, which are located in the region of the closing edges of the jaws. In the area of the closing edges of the jaws, the threads are lowered or practically no longer available.

Alternatively, within the multi-stage press, in one of the upstream process stages, on the portion to which the thread is to be formed, axially extending indentations or other preforms may be created. The indentations should then be located radially at the locations where the closing edges of the jaws of the baking tool lie.

The blank may also be designed so that the boundary wall surrounding the cavity, on which the thread is to be produced, is interrupted at one or more points. This takes place within one of the forming stages before the actual thread pressing.

It is advantageous that the method is also suitable for the formation of external threads on thin-walled hollow-shaped workpieces, which can be produced according to the known methods only with great effort. The minimum wall thickness of the hollow sections is u.a. depending on the depth of the thread flanks of the thread to be formed and the material of the blank.

Another advantage is that the expansion process of the threaded portion is work hardened while a bare surface is formed, so no more Post processing is required. The additional work hardening allows a stronger mechanical load of the threaded portion.

The required mechanical engineering expenses for generating the external thread are relatively small.

The thread to be formed can also consist of sections with different thread geometry. The thread profiling of the inner wall of the mold cavity is then formed accordingly.

The thread profiling can also be combined with other profilings. Thus, the external thread produced can be interrupted, for example, by recesses or round profiles, individually or in combination. Even outside the thread other profiles can be created above and / or below. Thus, in addition to the external thread can produce even more tailored to the purpose of the respective moldings profilings.

According to the known per se methods for producing external threads by rolling or rolling can be in addition to the thread in an economical manner no additional or additional profiles on the workpiece or blank in a process step produce.

The mandrel may be introduced into the cavity of the workpiece by axial or rotary or combined axial and rotary motion to produce the necessary pressing force for the required radial material flow. Alternatively, the workpiece can be moved over the mandrel or both are moved relative to each other. The mandrel can be made of high-speed steel or carbide.

The expansion process for forming the thread can be carried out stepwise with different thorns or mandrel sections in the outer circumference. Instead of a dome several mandrels of different dimensions can be used successively. This may be necessary in particular for relatively thick-walled hollow-shaped sections. The mandrel or mandrels may have different shape-forming zones in their geometry. A first section is designed so that it has a polygonal, preferably triangular or square, contact surface, the corners are slightly rounded. First, during the expansion process, the inner wall of the workpiece in the axial direction is radially expanded only at the points or areas at which the corners of the dome are in contact with the inner wall of the blank. As a result, material of the workpiece is pressed into the thread profiling only at these points. In the subsequent further expansion process is by means of the mandrel portion, the cross-sectional shape of the cavity adapted, the external thread produced in its final form. By these measures, an axial lengths of the workpiece is counteracted because the already completed in the first expansion step and solidified points of the thread profiling during the second expansion step an axial length brakes or allow only a small extent.

If necessary, the workpiece can be heated to forming temperature before or after insertion or insertion into the tool. The temperature depends on the wall thickness and the material of the workpiece.

Preferably, the expansion operation takes place in a multi-part jaw tool having a plurality, e.g. two, three or four, moving jaws. When forming threads with a relatively large tread depth considerable forces may be required to expand the workpiece. Thus, it can not be ruled out that during the expansion process, the jaws of the baking tool are slightly pushed apart at their closing points, which can form a longitudinal ridge at these points. To counter this, longitudinally extending narrow indentations are formed in the portion of the hollow workpiece intended to form the thread prior to the threading operation, which are located at the locations where the jaws of the jaw tool meet.

This prevents material from getting between the jaws during a slight opening of the jaws during the expansion process. The device suitable for carrying out the method consists of a multi-stage press with a movable slide and a stationary tool carrier unit, wherein within the multi-stage press at least one multi-part, movable in an open and closed position baking tool is arranged either on the carriage or the stationary tool carrier unit. This has a mold cavity with at least one central opening into which a hollow blank is inserted. The inner wall delimiting the mold cavity is equipped with a thread profiling designed as a negative. The device further comprises at least one stop for securing the position of the workpiece and at least one expanding mandrel or punch which can be inserted into the hollow workpiece and an ejector unit. Stamp and / or tool or the units on which they are mounted, are movable by means of a drive unit. The inserted into the mold cavity workpiece is released after the training of the workpiece by the opening movement of the tool for unloading.

The mold cavity defined by the inner wall of the pressing jaws should be dimensioned so that in the closed state of the jaws between the lateral surface of the insertable workpiece and the inner wall of the mold cavity is little play or touch contact.

The thread profiling of the jaws may be interrupted by other non-threaded profiles. Also outside the thread profiling such other profiles can be arranged.

Within the multi-stage press, for example, at least one stop for securing the position of the blank is provided during the expansion process. Preferably, the trained as a negative thread profiling of the jaws is designed so that in the region of the edge zones of the jaws of the outer thread diameter decreases continuously to both sides, i. the profile height decreases. This significantly reduces the risk that material may get between the jaws during the thread pressing process.

The limited by the inner wall of the jaws mold cavity is sized in size so that in the closed state of the jaws between the outer surface of the insertable blank and the inner wall of the mold cavity, there is little play or touch contact.

The thread profiling of the jaws can be interrupted by other profiles or the jaws are equipped with other profiles outside the thread profiling.

The movement of the carriage can be used to control the movement of mandrel or jaw tool as well as the opening and closing movement of the jaws. To move the jaws and a separate drive can be provided. About the movement of the carriage, a relative movement between the jaw tool and the mandrel is realized. The movement of the jaws can be done via a spring package that can be tensioned or relaxed by the movement of the carriage, or via a separate drive.

According to a further embodiment, the expanding mandrel may also have different form-forming sections, the section which can be inserted first into the workpiece being polygonal, and the corners or edges coming into contact with the workpiece being rounded.

The Aufweitdorn may also consist of several longitudinally divided sections or segments between which a clearance is arranged in the radial direction. The jaw tool consists of a single or multi-part outer ring, in which the pressing jaws are mounted radially displaceable, wherein the lateral surfaces of the pressing jaws and the inner surface of the ring are formed conical. The outer ring is available a slidable annular member which is movable over the carriage.

The expanding mandrel may have different shape-forming sections, wherein the first insertable into the workpiece section is polygonal. The reaching into contact with the workpiece corners or edges are rounded.

The invention will be explained in more detail below using an exemplary embodiment.

In the accompanying drawing show

1 is a two-part jaw tool in a simplified perspective view as a longitudinal section,

FIG. 2 a pressing jaw of the baking tool according to FIG. 1, FIG.

3 is a jaw tool with three pressing jaws in the closed state, in a simplified perspective view, as a longitudinal section,

FIG. 4 shows the jaw tool according to FIG. 3 during the expansion process, FIG.

5 shows the jaw tool according to FIG. 3 in the opened state, FIG.

6 is a section along the line A-A in Fig. 3,

7 shows a second embodiment of an expanding mandrel in a perspective view,

8 is a section along the line B-B in Fig. 7,

Fig. 9 shows a third embodiment of an expanding mandrel in perspective view and

10 is a section along the line C-C in Fig. 9.

11 shows the individual process steps for the production according to the invention of a pipe fitting within a multi-stage press, in a simplified representation, and

Fig. 12 shows a second embodiment of the baking tool as a cross-sectional view.

FIG. 11 shows in simplified form the process stages I to VI for the production according to the invention of a pipe fitting 4 with an external thread. Process stage I relates to the cutting to length of a section 27 of solid material (wire or rod-shaped material) fed from a supply roll by means of a shearing tool 19. The following process steps II to VI take place within a multi-stage press 20, which is designed as a 5-stage press is. The multi-stage press, not shown in more detail, has a machine frame with a sliding carriage 21 and a stationary tool carrier unit 22. The multi-stage press comprises a compression tool 23 (process stage II), a first reverse extrusion tool 24 (process stage IM), a second reverse extrusion tool 25 (Process step IV), a punching tool 26 (process step V) and a jaw tool 1, 8 as a pressing tool (process step VI). To produce a pipe fitting 4 with external thread, made of copper, in the process stages II to V from the cut wire section 27 a Blank 4b produced with ring collar. The individual tools of these process stages II to V each consist of two dies, an upper die 28a and a lower die 28b, with a central open mold cavity for receiving the blank 4b, a punch 29 and an ejector 30, in the opposite direction to the punch 29th is arranged.

The matrices 28a and 28b are each arranged on one of the two sides of the tool (carriage or tool carrier).

In the central cavity of the upper die 28a of the punch 29 is inserted and in the opposite, lower die 28b of the ejector 30 and the ejector 7. The movement of the punch 29 via the movement of the carriage 21 of the multi-stage press. If necessary, the matrices can also be designed as multi-part jaw tools. This depends on the geometry of the blank to be produced.

When punching, process step V, a sleeve-shaped stopper 7 is provided instead of a punch. The first die 28a is part of the carriage 21 and mounted on this. The second die 28b belongs to the stationary tool carrier unit 22. A reverse arrangement of the dies 28a and 28b would also be possible. After completion of a process step, the prefabricated blanks 4b are inserted by means of grippers or transport devices in the tool of the subsequent process step. Similarly, this also applies to the other process steps. The transformations of the blank in the process stages II to IV are preferably carried out as cold extrusion processes.

As shown in Figure 11, the supplied and cut wire rod or rod portion 4b of copper in the process stages II (upsetting), IM (first cupping), IV (second cupping) and V (punching) in particular by compression and extrusion processes a pipe fitting with collar reshaped. Finally, on one of the two cylindrical sections of the pipe fitting an external thread is to be generated. This takes place within the multistage press by a threaded press process (process step VI) by means of a multi-part jaw tool 1 or 8. The respective jaw tool 1, 8 is mounted analogously to the tools of the other process stages on the carriage 21 and the tool carrier unit 22, as shown in Fig. 11 ,

Specific embodiments of the jaw tools for producing an external thread are shown in Figures 1 to 6 and 12.

In the figures 1 and 2, a two-part jaw tool 1 is shown in longitudinal section, for further explanation of the process step VI. It consists of two pressing jaws of which only one pressing jaw 2 can be seen. The inner cavity delimiting the mold cavity wall of the press jaws 2 is provided with a trained as a negative thread profiling 3. After moving together the pressing jaws 2 in the closed position of the prefabricated pipe fitting or blank 4b is inserted with a collar in the mold cavity 5. The rear portion of the blank 4b, above the bundle of tubes, has a larger inner diameter than the tubular portion on which the thread is to be formed.

The inserted pipe fitting is supported from below by an ejector sleeve 7 inserted into the mold cavity, which serves as a stop, in order to prevent longitudinal expansion of the pipe fitting 4b during the pressing process.

To create an external thread on the tubular portion of the pipe fitting 4b, which projects into the mold cavity 5, an expanding mandrel 6 with a chamfered tip is inserted into the central opening of the pipe fitting 4b, from above. During the insertion of the expanding mandrel 6, a radial material flow is generated, wherein the contours of the formed as a negative thread profiling 3 of the inner wall of the pressing jaws 1 are filled with material and thereby on the tubular portion of the pipe fitting 4b an external thread is formed. The expansion process is completed when the expanding mandrel 6 is immersed in the sleeve 7. Subsequently, the mandrel 6 is moved back into the starting position and the jaw tool 1 is opened. The finished pipe fitting 4 with external thread is then removed by means of the ejector sleeve from the open jaw tool 1.

The rear portion 6a of Aufweitdornes 6 is reduced in its outer diameter to reduce the friction occurring during insertion. FIGS. 3 to 6 show a further embodiment variant as a jaw tool 8 with three movable jaws 10, 11, 12 (FIG. 6). The jaw tool 8 consists of an outer, axially displaceable ring 9, in which three jaws 10, 11, 12 are mounted radially movable, as part of the lower die. The outer surfaces of the jaws 10, 11 and 12 have a conical lateral surface 17 and the outer ring 9 has a corresponding conical inner surface 18, such that the jaws 10, 11 and 12 are movable within the outer ring 9 into an open and closed position , The jaws 10, 11, 12 have on their inner side or inner wall a thread profiling 3 as a negative. In the closed state of the jaws 10, 11, 12, the inner wall of the jaws bounded on both sides, up and down, open mold cavity. 5

On the outer ring 9 sits an annular member 13 (upper die), which is in communication with the movable carriage of the multi-stage press. The opening and closing movement of the jaws 10, 11, 12 is controlled by a spring plate (not shown). realized. With the feed movement of the carriage is stretched over the axial movement of the annular member 13, which is in contact with the ring 9, the spring assembly, wherein ring 9 is driven with the jaws 10, 11, 12 against a stop 14. When moving in the opposite direction, the spring assembly is relaxed while the ring 9 moves upward, with the jaws open. The device also still includes the Aufweitdorn 6 and the sleeve-shaped ejector 7, which also serves as a stop. The axial movement of the mandrel 6 is controlled by the movement of the carriage. In the figure 3, the jaw tool 8 is shown in the closed, tensioned state. The blank or pipe fitting 4b was taken over by means of a gripper device not shown in detail from the tool of the upstream process stage V and inserted into the mold cavity 5 of the baking tool 8. Loading takes place with the tool open. The pipe fitting 4b is supported by means of a spring-loaded ejector sleeve 7 acting from below. Subsequently, via the further advancing movement of the carriage, the expanding mandrel 6, from above, as shown in Fig. 4, inserted into the central cavity of the workpiece (pipe fitting). By the expansion process, as already explained above, an external thread is produced on the tubular portion of the pipe fitting 4b. After completion of the forming process, the expanding mandrel 6 and the annular member 13 are moved back to their original position. In this case, the spring assembly is relaxed, thereby moving the pressing jaws 10, 11, 12 in the open position (Fig. 5). In the open state of the baking tool, the pre-stressed ejector sleeve 7 is unlocked. This takes over the function as an ejector for the now finished molding. 4

Instead of the movement of the dome 6 and the closed jaw tool can be driven over the mandrel. This depends on the structural design of the multi-stage press.

In order to prevent a longitudinal ridge forming during the expansion process in the region of the closing edges of the jaw tool, longitudinally extending recesses or indentations 4a can be formed on the tubular portion of the blank on which the thread is to be produced. These must be arranged radially at the locations where the closing edges of the pressing jaws 10, 11, 12 of the jaw tool are, as shown in Fig. 6. The blank must then be inserted accordingly in the tool.

Another alternative to this is shown in FIG 12, in which the tool is shown in the closed state and without blank or pipe fitting. The formed as a negative thread profiling 3 of the individual jaws 10, 11, 12 is designed so that the pro- filhöhe or thread depth 3a of the individual threads each in the direction of the closing gap or edge of the jaws 10, 11, 12 is reduced. In the immediate area of the closing edges of the jaws 10, 11, 12 then no thread profiling as a negative longer exists.

This considerably reduces the risk that material may enter the closing gap as a result of the extrusion process.

The two aforementioned measures can also be combined with each other. FIGS. 7 to 10 show further embodiment variants with expanding mandrels of different configurations in terms of their geometry. The expanding mandrel 15 (FIGS. 7 and 8) has two different shaping zones. The upper portion 15a, which is first inserted into the cavity of the workpiece 4b is formed in its cross-sectional shape as a triangle 15b, wherein the corners are rounded. During the insertion of this section into the cavity of the workpiece 4b, at first only a flow of material in the area of action of these corners occurs in the contours of the thread profiling 3. The subsequent section 15c is adapted in its cross-sectional shape to the cavity, e.g. this has a circular cross-sectional shape in a tubular cavity. The expanding mandrel 16 shown in Figures 9 and 10 is used when the cavity of the workpiece 4b is divided into individual longitudinal chambers. The mandrel 16 has in its upper portion 16a, which is inserted into the divided cavity, two longitudinally extending mandrel portions 16b and 16c, between which a gap 16d is arranged. Over the lateral surfaces of the mandrel portions 16b and 16c of the radial material flow is then effected in the contours of the thread profiling. The external thread thus produced is interrupted in the longitudinal direction at the opposite points, where the gap or free space 16d is located.

Claims

claims

A method for chipless production of an external thread on hollow metal workpieces for use as hollow screws, hollow shafts, threaded sleeves or fittings as stable connection or fastening elements, characterized in that within a multi-stage press (20) with a sliding carriage (21) and a stationary Tool carrier unit (22) as a starting material wire or rod material (27) supplied and gradually, in one or more forming stages (Il to V) by extrusion and compression processes, to a finished hollow blank (4b) is formed and within the multi-stage press (20), in a further stage (VI) of the prefabricated hollow blank (4b) in a multi-part jaw tool (1, 8) with a mold cavity whose inner wall is provided with a formed as a negative thread profiling (3), inserted and, in the closed state of the baking tool ( 1, 8) into the central opening of the blank (4b ) introduced at least one mandrel (6, 15, 16) while the blank (4b) by means of the dome (6, 15, 16) is widened, wherein the contours of the thread profiling (3, 3a) are filled by a radial flow of material, and Finally, the finished workpiece (4) after opening the jaw tool (1, 8) is removed from this.

2. The method according to claim 1, characterized in that in the jaw tool (1, 8) inserted blank during movement of the dome (6, 15, 16) is fixed against expansion in the longitudinal direction.

3. The method according to any one of claims 1 or 2, characterized in that the opening and closing movement of the jaws (10, 11, 12) of the baking tool (1, 8) and the movement of the mandrel (6, 15, 16) over the Central drive unit of the multi-stage press (20) are triggered.

4. The method according to any one of claims 1 to 3, characterized in that the central opening of the hollow blank (4b) has a circular, oval or trilobular cross-sectional shape.

5. The method according to any one of claims 1 to 4, characterized in that the cavity of the blank (4b) by at least one partition in several hollow space sections is divided, and in the cavity of a plurality of mandrel sections existing mandrel (16) is introduced.

6. The method according to any one of claims 1 to 5, characterized in that the cavity of the blank (4b) surrounding the boundary wall is interrupted at one or more locations.

7. The method according to any one of claims 1 to 6, characterized in that in the region of the closing edges of the jaws (10, 11, 12) reduces the profile height (3a) formed as a negative thread profiling (3) and thereby at the points of the blank (4b), which are in the region of the closing edges of the jaws (10, 11, 12), no or only a weakened thread profiling is generated.

8. The method according to any one of claims 1 to 7, characterized in that the thread profiling (3) consists of several different in their geometry threaded portions, wherein during the expansion process threaded portions are produced with different thread geometry.

9. The method according to any one of claims 1 to 8, characterized in that thread profiling (3) are generated, which contain other profilings or outside the thread profiling other profiles are produced.

10. The method according to any one of claims 1 to 9, characterized in that for forming the external thread, a mandrel (15, 16) is used with different shaping zones, wherein the mandrel (15, 16) has a first portion with a polygonal contact surface with rounded corners and the inner wall of the blank (4b) is radially expanded only in the area of action of the corners, and subsequently has a second portion which is adapted to the cross-sectional shape of the cavity of the workpiece and takes over during the expansion process, the final formation of the thread.

11. The method according to any one of claims 1 to 10, characterized in that the hollow blank (4b) in the region which is intended for the formation of the thread, in the longitudinal direction extending narrow indentations (4a), which are arranged at the points where the jaws of the (2, 10, 11, 12) jaw tool (1, 8) meet.

12. Device for carrying out the method according to one of claims 1 to 11, characterized in that within a multi-stage press (20) with a movable carriage (21) and a stationary tool carrier unit (22) at least one multi-part, movable in an open and closed position Jaw tool (1, 8) either on the carriage (21) or the stationary tool carrier unit (22) is arranged, which has a mold cavity (5) with at least one central opening into which a hollow blank (4b) can be inserted, said the inner wall of the jaws (2, 10, 11, 12) delimiting the mold cavity (5) is equipped with a thread profiling (3) designed as a negative, and at least one expanding mandrel (6, 15, 12), which can be inserted into the hollow-shaped blank (4b) within the multi-stage press 16) is arranged, wherein Aufweitdorn (6, 15, 16) and / or jaw tool (2, 8) are movable by means of a drive unit.

13. The apparatus according to claim 12, characterized in that within the multi-stage press (20) except the jaw tool (1, 8) nor a compression tool (23), at least one reverse extrusion tool (24, 25) and a punching tool (26) are arranged in that the tools (23, 24, 25, 26) are equipped with dies (28a, 28b), one die (28a) being arranged on the carriage (21) and the opposite other die (28b) on the tool carrier unit (22).

14. Device according to one of claims 12 or 13, characterized in that at least one stop (7) for securing the position of the blank (4b) is provided during the expansion process.

15. Device according to one of claims 12 to 14, characterized in that the formed as a negative thread profiling (3) of the jaws (2, 10, 11, 12) is designed so that in the transition region to the edge zones of the jaws, the thread depth ( 3a) continuously reduced on both sides.

16. Device according to one of claims 12 to 15, characterized in that the through the inner wall of the jaws (2, 10, 11, 12) limited mold cavity (5) is dimensioned such that in the closed state of the jaws between the lateral surface of the insertable Blanks (4b) and the inner wall of the mold cavity (5) has little play or touch.

17. Device according to one of claims 12 to 16, characterized in that the thread profiling (3) of the jaws (2, 10, 11, 12) is interrupted by other profilings.

18. Device according to one of claims 12 to 17, characterized in that the jaws (2, 10, 11, 12) are equipped outside the thread profiling with other profiles.

19. Device according to one of claims 12 to 18, characterized in that for movement of the jaws (10, 11, 12), a separate drive is provided.

20. Device according to one of claims 12 to 19, characterized in that the expanding mandrel (15) has different shape-forming sections (15a, 15b, 15c), wherein the first in the blank (4b) insertable portion (15a) is polygonal, and the edges or edges reaching into contact with the blank (4b) are rounded.

21. Device according to one of claims 13 to 20, characterized in that the Aufweitdorn (16) consists of a plurality of longitudinally divided sections or segments (16 b, 16 c), between which in the radial direction, a free space (16 d) is arranged.