METHOD FOR PRODUCEING A STEPPED CROSS-SECTIONAL TRAINING ON A ONE-PIECE, TUBE-SHAPED METAL WORKPIECE AND SYSTEM WITH A DEVICE FOR PERFORMING THE METHOD

Description

Technical field

[0001] The present invention relates to a method for producing a stepped cross-sectional reduction on a one-piece, tubular metal workpiece according to claim 1, and a system for carrying out the method according to claim 8. The method according to the invention can be used, for example, to produce the following one-piece components from tubular workpieces, but is not limited to: rotor shafts, drive shafts, shaft journals, stabilizers, shafts of all kinds which have a steep transition in the area of ​​the cross-sectional reduction, scaffold supports, scaffold frames for the construction industry and tie rods. Background and state of the art

[0002] Forming processes for tubular workpieces are known from the prior art, in which the tubular workpiece undergoes a significant reduction in wall thickness in the area of ​​the stepped cross-sectional reduction due to the forming process. This reduction in wall thickness in the forming area necessarily leads to a reduction in the mechanical stability of the formed workpiece.

[0003] Multi-part workpieces with a stepped cross-sectional reduction, which are joined together by welding, joining or other joining techniques, for example, exhibit the same disadvantage of reduced mechanical stability.

[0004] For a number of applications in this technical field, it is particularly advantageous if the stepped cross-sectional reduction is designed as an approximately right-angled stop edge. German patent application DE 10 2012 110 792 A1 of the same applicant discloses a method for producing right-angled stepped transitions. This avoids a reduction in wall thickness in the transition area. To prevent a local weakening of the wall thickness, the known method necessarily requires a preceding axial upsetting step before forming the stepped transition, in order to increase the wall thickness of the workpiece in a forming area.

[0005] Methods for producing step-shaped cross-sectional reductions on a one-piece, tubular workpiece made of metal are also known to those skilled in the art from documents DE 20 2008 017 196 U1, DE 10 2005 012 475 A1, GB 1 472 860 A and WO 2004 / 030 847 A1. Object of the invention

[0006] The object of the present invention is therefore to provide a forming process for producing a cross-sectional reduction in a tubular workpiece, with which a right-angled or nearly right-angled shoulder (stepped transition) can be created that is highly resilient and, in particular, withstands alternating bending and torsional stress. The process should, however, function without an additional upsetting step prior to shoulder formation, in which the wall thickness of the tubular workpiece in the forming area increases by at least 30%, preferably at least 20%, due to axial upsetting. Furthermore, a system comprising a one-piece, tubular metal workpiece and a device for carrying out the process is to be provided. Definitions

[0007] Within the scope of the present invention, the term "tubular workpiece" encompasses any shape of an elongated hollow body, preferably a tube, whose length is greater than its outer diameter. The cross-sectional shape of the tubular workpiece is not limited to a circle, but can also be elliptical or quasi-circular.

[0008] Within the scope of the present invention, the term "one-piece" with regard to the tubular workpiece means that it has at most one longitudinal weld seam, but otherwise no weld seam or joint. Preferably, according to the invention, the term "one-piece" means that the tubular workpiece has no weld seam or joint.

[0009] Within the scope of the present invention, the terms "reducing the cross-section" or "tapering the cross-section" of a tubular workpiece are understood to mean at least a partial reduction in the diameter of the tubular workpiece. Similarly, according to the invention, "cross-sectional tapering" is understood to mean a transition from a section of the tubular workpiece with a larger diameter to a section of the same with a smaller diameter. According to the invention, a section of the tubular workpiece which, after the forming process according to the invention, has a smaller diameter and the transition to a section of the tubular workpiece with a larger diameter (= original diameter of the workpiece in the same area before forming) is referred to as the "formed area".The section of the tubular workpiece that forms the transition from the section of the tubular workpiece with the smaller diameter to the section of the tubular workpiece with the larger diameter is referred to, according to the invention, as the "transition zone". By definition, the transition zone is part of the forming zone. In other words, the forming zone is a continuous section of the tubular workpiece which, as a result of the forming process according to the invention, has a reduced diameter compared to the state before forming or compared to the original diameter of the workpiece in the same area.

[0010] Within the scope of the present invention, the term "metal" includes any element belonging to the metals, such as iron, or non-ferrous metals, such as copper, alloys of two or more metals, such as stainless steel, or other alloys with a metal content of > 90%, such as steel. According to the invention, the definition of the term "metal" also includes any element or alloy containing technically unavoidable impurities.

[0011] Within the scope of the present invention, terms such as "approximately" or "nearly" with respect to a numerically definable or defined parameter mean a deviation of at most 5%, preferably at most 3%, from a specified numerical value. With respect to angles, the terms "approximately" or "nearly" mean a deviation of at most 3°, preferably at most 2°, and in particular at most 1°, from a specified angle. Summary of the invention

[0012] The problem described above is solved by the method according to claim 1. According to the invention, a method for producing a stepped cross-sectional reduction on a one-piece, tubular workpiece W made of metal is provided, comprising at least the following steps: (a) Reducing the cross-section of the tubular workpiece W in a forming area U thereof by means of a first forming tool UW1, thereby creating a transition area T in the forming area U; (b) Heating the tubular workpiece W in the forming area U or in a part thereof comprising the transition area T, to a temperature in the range of 700 to 1,450 °C, preferably 1,000 to 1,450 °C; (c) Forming the tubular workpiece W in the transition area T such that the tubular workpiece W forms a shoulder S in the transition area T, wherein a tangent WT at the inflection point of the shoulder S with a central axis MW of the tubular workpiece W forms an angle α of 45 to < 90°, preferably 65 to 75°; wherein during forming the tubular workpiece W has a temperature in the range of 700 to 1,450 °C, preferably 1,000 to 1,450 °C, in the transition area T;wherein the forming is carried out using a first upsetting cup ST1, a first upsetting ring SR1, a first upsetting guide SF1 and a first inner mandrel ID1; wherein the first upsetting cup ST1, the first upsetting ring SR1 and the first upsetting guide SF1 are arranged on the outer cylindrical surface of the tubular workpiece W, preferably each coaxial with the central axis MW of the tubular workpiece W; wherein the first upsetting cup ST1, the first upsetting ring SR1 and the first upsetting guide SF1 are arranged in this order towards an end E of the tubular workpiece W; wherein the first inner mandrel ID1 is arranged inside the tubular workpiece W;wherein an outer diameter of the first inner mandrel ID1, at least in a section AI1 of the first inner mandrel ID1 arranged opposite the transition region T of the tubular workpiece W during forming, is between 90 and 100% of the smallest inner diameter of the tubular workpiece W in the transition region T after reduction according to step (a) and before heating according to step (b); wherein an inner diameter of the first upsetting cup ST1 is between 100 and 110% of the outer diameter of the tubular workpiece W before reducing the cross-section in step (a); wherein an inner diameter of the first upsetting guide SF1 is between 100 and 110% of the outer diameter of the tubular workpiece W in the forming region U and outside the transition region T after reducing the cross-section in step (a) and before heating according to step (b);wherein an inner diameter of the first upsetting ring SR1 is between 100 and 115% of the outer diameter of the tubular workpiece W in the forming region U and outside the transition region T after reducing the cross-section in step (a) and before heating according to step (b); wherein the first upsetting ring SR1 has a contour of the inner circumferential surface with a rotationally symmetrical upsetting edge which is suitable to form the shoulder S during forming in the transition region T of the tubular workpiece W, wherein the tangent WT at the inflection point of the shoulder S forms an angle α of 45 to < 90°, preferably 65 to 75°, with the central axis MW of the tubular workpiece W;wherein, during forming, the first compression ring SR1 and the first compression guide SF1 and / or the first compression cup ST1 are moved parallel to the central axis MW of the tubular workpiece W such that the distance between the first compression ring SR1 and the first compression cup ST1 is reduced; and wherein, during forming, the first compression ring SR1 and the first compression guide SF1 are not movable relative to each other.

[0013] The inventive method produces a one-piece, formed workpiece with a steep shoulder. A wide variety of tubular workpieces of different diameters and lengths can be formed using this method. For example, tubular workpieces with a length of 150 to 4,200 mm can be processed according to the invention. Furthermore, the position of the shoulder along the length of the tube is largely freely selectable according to the inventive method, which underscores its high flexibility.

[0014] Since the workpiece is a single piece, it exhibits increased mechanical stability and strength compared to multi-part workpieces. Due to the absence of a weld or joining seam (the workpiece may at most have a longitudinal weld seam), the workpiece formed according to the invention has a homogeneous fiber orientation, which leads to higher internal material stability.

[0015] According to the invention, due to the single-piece design of the workpiece and the elimination of the need for upstream axial upsetting to thicken the wall, workpieces with inherently thinner wall thicknesses can be used, thus enabling a lightweight construction of the manufactured, tubular workpieces. This results in corresponding material and weight savings, which benefits both the manufacturing process and the subsequent use of the workpiece.

[0016] The particular advantage of the method according to the invention lies in the fact that, through the interaction of the first compression cup ST1, the first compression ring SR1, the first compression guide SF1, and the first inner mandrel ID1 during the forming of the tubular workpiece W in step (c), a forming (formation of the shoulder S in the transition region T) and a compression of the workpiece W in the transition region T are achieved in a single step. The material flow is specifically controlled to achieve the desired contouring and wall thickening of the workpiece in the transition region during forming. Thus, the first compression cup ST1, the first compression ring SR1, and the first compression guide SF1, with their predetermined inner diameters, prevent uncontrolled bulging or outflow of the workpiece material.Furthermore, the presence of the inner mandrel with its predetermined outer diameter inside the workpiece during step (c) prevents uncontrolled inward collapse or flow of the workpiece material. According to the inventive method, the inner diameters of the first upsetting cup ST1, the first upsetting guide SF1, and especially the first upsetting ring SR1 are each selected such that, during step (c), in the transition region T, preferably in the forming region U, the wall thickness can be increased to 1.01 to 1.6 times the wall thickness of the tubular workpiece at the same location on the workpiece before forming the workpiece W (= original wall thickness of the workpiece W). This is particularly advantageous when a further forming step (see Figure 1) is required.Step (d)) described below is provided in which the shoulder produced in step (c) is steepened to a tangent angle of 90°, because by increasing the wall thickness in step (c) as described above, a steep shoulder with a wall thickness corresponding to 1.01 to 1.6 times the wall thickness of the tubular workpiece at the same location on the workpiece before forming in step (c) is obtained in step (d).

[0017] With the method according to the invention, it is possible and preferred that the tubular workpiece W in the transition region T has a wall thickness after forming according to step (c) that is not reduced or even increased compared to the wall thickness of the workpiece W at the same location before the cross-sectional reduction according to step (a) (i.e., before the cross-sectional reduction was carried out). This results in even better mechanical stability of the formed workpiece in the transition region. It is even more preferred if the tubular workpiece W in the transition region T has a wall thickness after forming according to step (c) that is 100 to 160%, and in particular 101 to 150%, of the wall thickness of the workpiece W at the same location before the cross-sectional reduction according to step (a).

[0018] According to the invention, it is thus possible for the first time to form a step-shaped cross-sectional reduction on a one-piece tubular workpiece made of metal, which has a right-angled or almost right-angled shoulder in the transition area, without significantly reducing the wall thickness in the transition area compared to the original wall thickness of the workpiece and without requiring a step prior to forming for axial upsetting of the workpiece.

[0019] Thus, step (c) of the inventive method accomplishes several tasks simultaneously in one step: on the one hand, the shoulder S is formed from the cross-sectional narrowing in the transition area with a tangent angle (α) of 45 to < 90°, while on the other hand, a material reserve is created in the transition area, which allows a steepening of the shoulder in a further, optional forming step (see step (d) described below), without any further significant change in the wall thickness of the workpiece in the transition area, i.e., neither a thickening nor a thinning of the wall of the workpiece in the transition area compared to the original wall thickness.

[0020] Since in the first forming step (step (c)) the shoulder S is formed only up to a tangent angle of < 90°, preferably up to 80°, and not a full right angle, cracking at the step start on the inside of the workpiece in the transition area T, as explained in more detail below, is effectively avoided.

[0021] According to the invention, reducing the cross-section of the tubular workpiece in step (a) can be achieved by drawing in, kneading, or similar plastic metal forming techniques known to those skilled in the art. Drawing in (axial forming) is preferred because it does not require heating the workpiece.

[0022] Therefore, in step (a) of the method according to the invention, it can be provided that the forming area U, preferably the tubular workpiece W, is not heated to 80 °C or more, preferably to 40 °C or more, before and during the reduction.

[0023] This eliminates a separate process step required for heating and the energy required for it, thereby shortening the process according to the invention and making it more cost-effective.

[0024] According to the inventive method, the reduction of the cross-section in step (a) can be carried out in one or more partial steps or strokes. Thus, according to the invention, after the first reduction of the cross-section of the tubular workpiece described above, a further reduction of the cross-section of the tubular workpiece W in the forming area U of the tubular workpiece W in step (a) can be provided. This can be particularly useful if a step S with a relatively large dimension in the radial direction is to be produced (further reduction in the transition area), or if the workpiece is to have two or more steps at different locations in the forming area (creation of multiple step transitions). According to the inventors' experience, a reduction of the workpiece diameter of approximately 20 to 35% is achieved with a single reduction step or stroke.If a higher degree of reduction is desired, one or more additional strokes can be performed to reduce the cross-section. For further reduction of the cross-section of the tubular workpiece, a second forming tool UW2 or several additional forming tools can be used. The information disclosed above regarding the applicable process technology and the possibility of avoiding heating the workpiece applies analogously to further reduction.

[0025] In the inventive method, the transition area T is part of the forming area U and forms the transition from the original, unreduced cross-section of the tubular workpiece W at one end of the transition area T to a section of the forming area U with a reduced cross-section or diameter at its other end.

[0026] Heating in step (b) is necessary in the inventive process because otherwise, in step (c) and possibly in further steps, the stage S cannot be formed as sharply as desired, and / or cracking in the transition region T is to be expected. The inventors have observed so-called splintering or abrasion on the surface in the transition region T during cold forming below the temperature range specified in step (b), particularly below 700 °C. On the other hand, heating the workpiece or its transition region to a temperature above 1,450 °C is detrimental because the workpiece almost melts, and critical structural changes (coarse graining) can occur, or defined forming is no longer possible.

[0027] Prior to forming the tubular workpiece W in step (c) (and thus also before and during steps (a) and (b)), axial upsetting of the tubular workpiece W, whereby the wall thickness of the tubular workpiece W increases by at least 30%, preferably at least 20%, in at least one section of the forming area U, can be omitted. This eliminates the process steps of upsetting and, if necessary, the locally required heating of the workpiece compared to conventional methods, making the process shorter, more energy-efficient, and more cost-effective.

[0028] According to the invention, the first compression ring SR1 has a contour of the inner circumferential surface, which preferably has a rotationally symmetric compression edge, the tangent of which forms an angle of 45 to < 90°, preferably 65 to 75°, with the stroke direction or with the central axis MW of the tubular workpiece W during the forming process in step (c).

[0029] The first upsetting cup ST1, the first upsetting ring SR1, and the first upsetting guide SF1 can each be designed as a single piece, two pieces, three pieces, or even more pieces. For example, the first upsetting cup ST1 can be designed as a single piece. Preferably, however, the first upsetting cup ST1 is designed as a two-piece or multi-piece piece, which simplifies attaching the tool to the workpiece to be formed.

[0030] The first compression ring SR1 and the first compression guide SF1 can each be designed in two or more parts, which facilitates the replacement of the respective part. However, the first compression ring SR1 and the first compression guide SF1 can also be designed as a single piece or permanently connected to each other, which facilitates synchronous movement during the forming stroke.

[0031] The forming process in step (c) can preferably be carried out by moving the first compression ring SR1 and the first compression guide SF1 parallel to the central axis MW of the tubular workpiece W in the direction of the first compression cup ST1. Conversely, it is possible to move the first compression cup ST1 parallel to the central axis MW of the tubular workpiece W in the direction of the first compression ring SR1. In a further, alternative embodiment, both the first compression ring SR1 (together with the first compression guide SF1) and the first compression cup ST1 can be moved towards each other.

[0032] The forming process in step (c) can preferably be carried out until the first upsetting ring SR1 contacts the first upsetting cup ST1. In particular, the forming process in step (c) can be carried out until an end face of the first upsetting ring SR1 opposite the first upsetting cup ST1 contacts an end face of the first upsetting cup ST1 opposite the first upsetting ring SR1. Using the defined endpoint of the forming stroke, setting a defined, predetermined wall thickness of the tubular workpiece in the shoulder area is facilitated in a structurally simple manner. However, the endpoint of the forming stroke with respect to the first upsetting cup ST1 and / or the first upsetting ring SR1 can also be defined or determined in a manner other than the two described above.

[0033] Preferably, the first upsetting cup ST1 has a conical recess in the form of a rotationally symmetrical cutout at its end section STE1, which is located opposite the transition region T of the tubular workpiece W. This recess can serve to receive a quantity of the metal from the tubular workpiece W during the forming process according to step (c). Providing such a feature advantageously allows a portion of the metal from the tubular workpiece W to be stored during the forming process in step (c). This metal can then be advantageously used in a subsequent forming step, particularly during the final shaping of the shoulder S in step (d) or in an optional rolling step, to increase the wall thickness of the tubular workpiece W in the area of ​​the shoulder S.

[0034] Further advantageous embodiments of the method according to the invention are the subject of the dependent claims.

[0035] The inventive method can further comprise the step: (d) further forming of the tubular workpiece W obtained from step (c) in the transition area T such that the tangent WT at the inflection point of the shoulder S with the central axis MW of the tubular workpiece W forms an angle β of 80 to 90°, preferably 85 to 90°, preferably 87 to 90°; wherein during further forming the tubular workpiece W has a temperature in the range of 500 to 1,000 °C in the transition region T; wherein the forming is carried out using a second upsetting cup ST2, a second upsetting ring SR2, a second upsetting guide SF2 and a second inner mandrel ID2; wherein the second upsetting cup ST2, the second upsetting ring SR2 and the second upsetting guide SF2 are arranged on the outer surface of the tubular workpiece W, preferably each coaxially to the central axis MW of the tubular workpiece W; wherein the second upsetting cup ST2, the second upsetting ring SR2 and the second upsetting guide SF2 are arranged in this order towards the end E of the tubular workpiece W; wherein the second inner mandrel ID2 is arranged inside the tubular workpiece W;wherein an outer diameter of the second inner mandrel ID2, at least in a section AI2 of the second inner mandrel ID2 arranged opposite the transition region T of the tubular workpiece W during further forming, is between 90 and 100% of the smallest inner diameter of the tubular workpiece W in the transition region T after forming according to step (c); wherein the second upsetting cup ST2 is identical or structurally equivalent to the first upsetting cup ST1; wherein the second upsetting guide SF2 is identical or structurally equivalent to the first upsetting guide SF1 or wherein an inner diameter of the second upsetting guide SF2 is between 100.1 and 105% of the outer diameter of the tubular workpiece W in the forming region U and outside the transition region T after forming in step (c); wherein an inner diameter of the second upsetting ring SR2 is between 100 and 115% of the outer diameter of the tubular workpiece W in the transition region T after forming in step (c);wherein the second compression ring SR2 has an inner circumferential contour with a rotationally symmetric compression edge suitable for deforming the shoulder S during further forming in the transition region T of the tubular workpiece W such that the tangent WT at the inflection point of the shoulder S with the central axis MW of the tubular workpiece W forms an angle β of 80 to 90°, preferably 85 to 90°, preferably 87 to 90°; wherein during forming the second compression ring SR2 and the second compression guide SF2 and / or the second compression cup ST2 are moved parallel to the central axis MW of the tubular workpiece W such that the distance between the second compression ring SR2 and the second compression cup ST2 decreases; and wherein during forming the second compression ring SR2 and the second compression guide SF2 are not movable relative to each other.

[0036] The formation of the shoulder S in step (c) is preferably followed by a further forming step (step (d)) in which the shoulder S is made even steeper, preferably at approximately or exactly a right angle. The advantages of the two-stage shoulder formation in steps (c) and (d) are that, firstly, a very steep to right-angled shoulder S can be produced even with metals that are more difficult to form. Secondly, according to the invention, cracking at the shoulder base on the inside of the metal in the transition area T, which can occur during the formation of a steep shoulder in a single forming step depending on the composition, pretreatment, and properties of the metal, can be effectively avoided.

[0037] For the further forming process according to step (d), the residual heat remaining in the tubular workpiece W obtained from step (c) can be utilized, provided the temperature of the metal in the transition region T is between 500 and 1,000 °C. This means that if step (d) follows step (c) of the inventive process immediately or with only a short time delay, additional heating of the tubular workpiece W can be omitted. By avoiding a further heating step, the inventive process is simplified and becomes more energy-efficient. Consequently, heating of the tubular workpiece W, preferably of the transition region T, can be omitted between steps (c) and (d) and during step (d).

[0038] According to the invention, the second compression ring SR2 has a contour of the inner circumferential surface, which preferably has a rotationally symmetric compression edge, the tangent of which is at an angle of 80 to 90°, preferably 85 to 90°, preferably 87 to 90°, to the stroke direction or to the central axis MW of the tubular workpiece W during the forming process in step (d).

[0039] According to the invention, with reference to step (d) and / or to the device of the system according to the invention, the second inner mandrel ID2 may preferably have an outer diameter which corresponds to 90 to 100 % of the outer diameter of the first inner mandrel ID1.

[0040] In the inventive method, a right-angled or nearly right-angled shoulder can be produced on the tubular workpiece, making it possible to create a wide end face, such as a wide exhibition area, in the transition area of ​​a scaffold support.

[0041] Furthermore, the method according to the invention can also include the step: (e) before step (b), shortening the tubular workpiece W from the end E by removing material such that an axial length L of the forming area U is set to a predetermined length, preferably + / - 0.5 mm.

[0042] Shortening the tubular workpiece W according to claim 3 (step (e)) enables precise positioning of the shoulder S from the end of the workpiece when processing tubular workpieces with a variable tube length or seamless tubes or non-drawn tubes with uneven wall thicknesses. However, if the inventive method is used to process high-precision tubular workpieces with an exact, constant tube length, so-called precision tubes, step (e) is not required and can therefore be omitted.

[0043] Furthermore, according to the inventive method, during the forming process in step (c) and / or in step (d), the tubular workpiece W can be advanced from its end E towards the transition region T or axially towards the transition region T. This advancement can preferably be effected by means of a first tube stop RA1 (in step (c)) and / or a second tube stop RA2 (in step (d)), wherein the first tube stop RA1 is preferably attached to the first inner mandrel ID1 and the second tube stop RA2 is preferably attached to the second inner mandrel ID2.

[0044] The pushing of the tubular workpiece W from its end E towards the transition area T or in an axial direction to the transition area T according to claims 4 and 5 each advantageously contributes to preventing a thinning of the wall, i.e. a reduction of the wall thickness, of the tubular workpiece W in the transition area T, more precisely, in the area of ​​the shoulder S, even better.

[0045] Furthermore, the method according to the invention may also include at least one of the following steps: (f) after step (c) or (d), adjusting the temperature of the tubular workpiece W in the transition zone T or in part of the transition zone T to a temperature in the range of 350 to 1,450 °C; and / or (g) contour forming of the tubular workpiece W in the transition zone T using at least one rolling roller RR;

[0046] The contour forming of the tubular workpiece W in the transition region T in step (g) is preferably, but not necessarily, preceded by adjusting the temperature of the tubular workpiece W in the transition region T, or in a part thereof, to a temperature between 350 and 1,450 °C. This prevents the formation of abrasions, the so-called pitting, on the outer surface of the workpiece W in the transition region T, in contrast to contour forming of the cold workpiece.

[0047] By contour forming according to step (g), the workpiece W can be given its final shape of the lateral surface in the area of ​​the shoulder S in the transition zone. In this process, metal that has been carried outwards or flowed outwards can be transported radially inwards again to form a sharp-edged, preferably right-angled shoulder S with a sufficiently large wall thickness.

[0048] Furthermore, according to the inventive method, the tubular workpiece W can be spatially fixed by a clamping tool at least during the execution of one, several, or all steps of the method, preferably radially clamped and axially held. This facilitates the execution of precise forming strokes and the automated implementation of the inventive method.

[0049] The method according to the invention is preferably carried out using the device of the system according to the invention, as described below.

[0050] Furthermore, a one-piece, tubular workpiece W made of metal is disclosed, which has been or can be manufactured using the method according to one of claims 1 to 7.

[0051] The tubular workpiece W has a shoulder S in the transition region T, wherein a tangent WT at the inflection point of the shoulder S forms an angle of 45 to 90°, preferably 85 to 90°, preferably 87 to 90°, and in particular 89 to 90°, with the central axis MW of the tubular workpiece W. Preferably, the tubular workpiece W has a wall thickness in the transition region T, preferably in the forming region U, which is between 101 and 160%, preferably between 101 and 150%, of the wall thickness of the workpiece at the same location before the formation of the shoulder S, in particular before forming according to step (c), and / or which is between 101 and 160%, preferably between 101 and 150%, of the wall thickness of the workpiece W at a location of the workpiece W outside the forming region U (preferably outside all forming regions of the workpiece W, if several are present).

[0052] Even more preferably, the tubular workpiece W has a wall thickness in the transition region T, preferably in the forming region U, which is not reduced or even increased compared to the wall thickness of the workpiece W at the same location before the cross-sectional reduction according to step (a) (i.e., before the cross-sectional reduction was carried out), and / or which is not reduced or even increased compared to the wall thickness of the workpiece W at a location of the workpiece W outside the forming region U (preferably outside all forming regions of the workpiece W, if several are present). This results in even better mechanical stability of the formed workpiece in the transition region.Even more preferred is if the tubular workpiece W in the transition area T, preferably in the forming area U, has a wall thickness that is between 101 and 160%, in particular between 101 and 150%, of the wall thickness of the workpiece W at the same location before the cross-sectional reduction according to step (a), and / or that is between 101 and 160%, in particular between 101 and 150%, of the wall thickness of the workpiece W at a location of the workpiece W outside the forming area U (preferably outside all forming areas of the workpiece W, if several are present).

[0053] The problem defined above is further solved by the system according to the invention. Advantageous embodiments of the system according to the invention are the subject of the dependent claims. The advantages and device-related modifications discussed above in connection with the method according to the invention apply analogously to the system according to the invention.

[0054] A system consisting of a one-piece, tubular workpiece W made of metal and a device V for carrying out the method according to the invention is proposed, wherein the device V comprises at least: a first forming tool UW1 for reducing the cross-section of a tubular workpiece W made of metal in a forming area U of the tubular workpiece W; a device H1 for heating the tubular workpiece W in the forming area U or in a part thereof, which comprises a transition area T from a non-reduced to a reduced cross-section of the tubular workpiece W, to a temperature in the range of 700 to 1,450 °C, preferably 1,000 to 1,450 °C; a first upsetting cup ST1, a first upsetting ring SR1, a first upsetting guide SF1 and a first inner mandrel ID1; wherein the first upsetting cup ST1, the first upsetting ring SR1 and the first upsetting guide SF1 can be arranged on an outer cylindrical surface of the tubular workpiece W, preferably each coaxially to the central axis MW of the tubular workpiece W;wherein the first upsetting cup ST1, the first upsetting ring SR1 and the first upsetting guide SF1 can be arranged in this order towards an end E of the tubular workpiece W; wherein the first inner mandrel ID1 can be arranged inside the tubular workpiece W; wherein an outer diameter of the first inner mandrel ID1 is at least sectionally between 90 and 100% of the smallest inner diameter of the tubular workpiece W in the transition region T after reduction according to step (a) of the method and before heating according to step (b) of the method; wherein an inner diameter of the first upsetting cup ST1 is between 100 and 110% of the outer diameter of the tubular workpiece W before reducing the cross-section in step (a) of the method;wherein an inner diameter of the first upsetting guide SF1 is between 100 and 110% of the outer diameter of the tubular workpiece W in the forming area U and outside the transition area T after reducing the cross-section in step (a) of the process and before heating according to step (b) of the process; wherein an inner diameter of the first upsetting ring SR1 is between 100 and 115% of the outer diameter of the tubular workpiece W in the forming area U and outside the transition area T after reducing the cross-section in step (a) and before heating according to step (b);wherein the first compression ring SR1 has a contour of the inner circumferential surface with a rotationally symmetric compression edge which is suitable for forming the shoulder S in the transition region T of the tubular workpiece W, wherein the tangent WT at the inflection point of the shoulder S with the central axis MW of the tubular workpiece W forms an angle (α) of 45 to < 90°, preferably 65 to 75°; wherein the first compression ring SR1 and the first compression guide SF1 and / or the first compression cup ST1 are movably mounted parallel to the central axis MW of the tubular workpiece W such that the distance between the first compression ring SR1 and the first compression cup ST1 is variable;and wherein, during the forming process according to step (c) of the method, the first upsetting ring SR1 and the first upsetting guide SF1 are not movable relative to each other. In the apparatus of the system according to the invention, the first upsetting ring SR1, the first upsetting guide SF1, and the first inner mandrel ID1 are each movable relative to the first upsetting cup ST1. Preferably, the first upsetting ring SR1, the first upsetting guide SF1, and the first inner mandrel ID1 are separate tools from the first upsetting cup ST1. The first upsetting ring SR1 can be connected to the first upsetting guide SF1 by a material-locking, force-locking, or form-locking connection. Furthermore, the first inner mandrel ID1 can be movable relative to the first upsetting ring SR1 and the first upsetting guide SF1.

[0055] The device V of the system according to the invention may further comprise the following for carrying out step (d) of the method according to the invention: a second compression cup ST2, a second compression ring SR2, a second compression guide SF2, and a second inner mandrel ID2; wherein the second compression cup ST2, the second compression ring SR2, and the second compression guide SF2 can be arranged on the outer surface of the tubular workpiece W, preferably each coaxially with the central axis MW of the tubular workpiece W; wherein the second compression cup ST2, the second compression ring SR2, and the second compression guide SF2 are arranged in this order towards the end E of the tubular workpiece W; wherein the second inner mandrel ID2 can be arranged inside the tubular workpiece W; wherein an outer diameter of the second inner mandrel ID2 is at least sectionally between 90 and 100% of the smallest inner diameter of the tubular workpiece W in the transition region T after forming according to step (c); wherein the second compression cup ST2 is identical or structurally equivalent to the first compression cup ST1;wherein the second compression guide SF2 is identical or structurally equivalent to the first compression guide SF1, or wherein an inner diameter of the second compression guide SF2 is between 100.1 and 105% of the outer diameter of the tubular workpiece W in the forming area U and outside the transition area T after forming in step (c); wherein an inner diameter of the second compression ring SR2 is between 100 and 115% of the outer diameter of the tubular workpiece W in the transition area T after forming in step (c) of the process; wherein the second compression ring SR2 has a contour of the inner circumferential surface with a rotationally symmetric compression edge which is suitable to deform the shoulder S in the transition area T of the tubular workpiece W such that the tangent WT at the inflection point of the shoulder S with the central axis MW of the tubular workpiece W encloses an angle β of 80 to 90°, preferably 85 to 90°, preferably 87 to 90°;wherein the second compression ring SR2 and the second compression guide SF2 and / or the second compression cup ST2 are movably mounted parallel to the central axis MW of the tubular workpiece W such that the distance between the second compression ring SR2 and the second compression cup ST2 is variable; and wherein, during the forming process according to step (d) of the method, the second compression ring SR2 and the second compression guide SF2 are not movable relative to each other.

[0056] In this embodiment of the device of the system according to the invention, the second compression ring SR2, the second compression guide SF2, and the second inner mandrel ID2 are each movable relative to the second compression cup ST2. Preferably, the second compression ring SR2, the second compression guide SF2, and the second inner mandrel ID2 are separate tools from the second compression cup ST2. The second compression ring SR2 can be connected to the second compression guide SF2 by a material-locking, force-locking, or form-locking connection. Furthermore, the second inner mandrel ID2 can be movable relative to the second compression ring SR2 and the second compression guide SF2.

[0057] The device of the system according to the invention may further comprise one or more of the following for carrying out the process steps according to claims 3 to 5: A device for shortening the tubular workpiece W from its end E by removing material such that an axial length L of the forming area U can be adjusted to a predetermined length, preferably with an accuracy of + / - 0.5 mm; and / or a first pipe stop RA1, which is suitable for pushing the tubular workpiece W from its end E towards the transition area T or in an axial direction to the transition area T; and which is preferably attached to the first inner mandrel ID1; and / or a second pipe stop RA2, which is suitable for pushing the tubular workpiece W from its end E towards the transition area T or in an axial direction to the transition area T; and which is preferably attached to the second inner mandrel ID2;and / or a device H2 for adjusting the temperature of the tubular workpiece W in the transition region T or in a part of the transition region T to a temperature in the range of 350 to 1,450 °C; and / or a clamping tool for spatially fixing the tubular workpiece W, preferably a clamp or clamping jaw or a multi-segment clamping system. Further disclosure of the invention;

[0058] Unless otherwise specified, the process steps described in the claims and in the description are to be carried out in the specified order according to the invention.

[0059] During the single- or multi-stage reduction of the cross-section of the tubular workpiece W in step (a), the workpiece W in the forming area U can be treated with a lubricant to reduce friction during the reduction of the workpiece W in the forming area U.

[0060] According to the invention, and in particular with regard to the optional step (e) of the method according to the invention, the forming area U is defined as the area which extends - from the center of the tubular workpiece W to the end E of the tubular workpiece W which is closer to or encompassed by the forming area U - from the beginning of the transition area T to the end E of the tubular workpiece W.

[0061] In the process according to the invention, the forming strokes carried out in steps (c) and / or (d) are performed using a force exerted on the workpiece by the respective forming tool. This force is preferably between 100 and 1000 kN (10 to 100 tons) for pipe diameters of 20 to 150 mm, and in particular between 400 and 600 kN, with an initial diameter W of the tubular workpiece between 40 and 60 mm.

[0062] Advantageous embodiments of the present invention, in particular of the method according to the invention, are explained with reference to the following drawing. These show: Fig. 1 and 2 : a two-stage reduction of the cross-section of the tubular workpiece W in a forming area U of the same according to step (a) of the method according to the invention; Fig. 3 : Shortening the tubular workpiece W from the end E according to the optional step (e) of the method according to the invention; Fig. 4 : Heating the tubular workpiece W in the forming area U or in a part thereof according to step (b) of the method according to the invention; Fig. 5a bis 5d : Forming the tubular workpiece W in the transition area T to form a shoulder S according to step (c) of the method according to the invention; Fig. 6a and 6b: further forming of the tubular workpiece W obtained from step (c) in the transition area T according to the optional step (d) of the method according to the invention; Fig. 7 : Setting a temperature of the tubular workpiece W in the transition region T according to the optional step (f) of the method according to the invention; and Fig. 8 : contour forming of the tubular workpiece W in the transition area T by means of at least one rolling roller RR according to the optional step (g) of the method according to the invention.

[0063] During the execution of the inventive method, as described below in an exemplary embodiment and variations thereof, a tubular workpiece W made of metal is formed. The tubular workpiece W can be spatially fixed, preferably radially clamped and axially held, during individual or all process steps, for example by means of a clamping tool or the like; however, this has been omitted from the figures for the sake of clarity.

[0064] The Fig. 1 and 2 Figure 1 shows a two-stage reduction of the cross-section of the tubular workpiece W (step (a)). Thus, in Fig. 1 A first forming tool UW1 is moved from one end E of the workpiece W parallel to the central axis MW of the workpiece W towards the center of the workpiece W (see arrow in Fig. 1 ), thereby creating a forming area U with a reduced diameter d1 compared to the undeformed workpiece W. The forming area U is the section of the workpiece W with the reduced diameter d1 and further includes the transition area T, in which the workpiece W transitions from the initial diameter D1 to the reduced diameter d1.

[0065] In Fig. 2 The reduction process will be analogous to that in Fig. 1 The step described above is carried out, but a second forming tool UW2 with a smaller inner diameter than the first forming tool UW1 is used, resulting in a further reduction of the workpiece W's diameter in the forming area U (diameter d2). Heating the workpiece W is not required to perform the single- or multi-stage reduction process. The overall length of the workpiece W increases as a result of the single- or multi-stage reduction process. The single- or multi-stage reduction process as described above is not limited to simply moving the forming tool UW onto the fixed workpiece W (see arrow in Fig. 1 and 2 It is also possible that the workpiece W is moved onto a fixed forming tool UW.

[0066] After carrying out the single- or multi-stage reduction process, as described in Fig. 3 As shown, the tubular workpiece W is shortened from end E by material removal using a suitable tool KW such that an axial length L of the forming area U is set to a predetermined length (step (e)). The material removal can be carried out by any method known to those skilled in the art. If so-called precision tubes are used as the workpieces W, shortening the workpiece W can be omitted.

[0067] In the next step ( Fig. 4 The workpiece W is heated to a temperature in the range of 700 to 1450 °C in a portion of the forming area U, which includes or encompasses the transition area T (step (b)). The heating is preferably carried out using an induction coil IS, but can also be done by another known technique.

[0068] After heating the workpiece W, at least in the transition region T, the next step (c) of the inventive method involves forming the tubular workpiece W in the transition region T, thereby forming a shoulder S in the transition region T ( Fig. 5a , 5b and 5c ).

[0069] For this purpose, a first compression pot ST1, which is preferably designed in two parts for easier attachment, is arranged on the outer surface of the tubular workpiece W before forming according to step (c) such that an end face ST1SF pointing towards the end E of the workpiece is arranged at the transition area T of the workpiece W ( Fig. 5a ). The inner diameter of the first compression pot ST1 is between 100 and 110% of the outer diameter of the tubular workpiece W before reducing the cross-section in step (a).

[0070] A first internal mandrel ID1 is arranged coaxially to the central axis MW of the tubular workpiece W before forming according to step (c) ( Fig. 5a after 5b; see arrow in Fig. 5a ). In this case, the outer diameter of the first inner mandrel ID1 is at least in a section AI1 of the first inner mandrel ID1 arranged opposite the transition area T of the tubular workpiece W during forming between 90 and 100 % of the smallest inner diameter of the tubular workpiece W in the transition area T after reduction according to step (a) and before heating according to step (b).

[0071] A first compression ring SR1 and a first compression guide SF1, which in this example are designed as a single piece but can also be designed as multi-part pieces, are moved from the end E of the workpiece W in an axial direction parallel to the central axis MW of the workpiece W onto the workpiece W for forming (see arrow in Fig. 5b ), until the first crushing ring SR1 abuts the end face ST1SF of the first crushing pot ST1, which points towards the end E of the workpiece W, whereby this situation in Fig. 5c This is illustrated. In the final part of this movement of the first compression ring SR1 and the first compression guide SF1, until the first compression ring SR1 abuts the first compression cup ST1, the first compression ring SR1 engages the transition region T of the workpiece W and compresses the workpiece W in the transition region T, forming the shoulder S. The first compression ring SR1 has a contour on its inner circumferential surface with a rotationally symmetrical compression edge suitable for forming the shoulder S. During this compression stroke, due to the force acting from the compression edge in the axial direction towards the center of the workpiece W, material is pushed from the forming area towards the emerging shoulder S. This causes material to accumulate more in the area of ​​the shoulder S and also shortens the transition region T in the axial direction, i.e., the extent of the transition region T, considered parallel to the central axis MW of the workpiece W, is reduced.The shoulder S is reduced in size.

[0072] It is particularly advantageous if, during the formation of the shoulder S, the tubular workpiece W is pushed forward from its end E towards the transition area T or axially towards the transition area T. In the present example, this pushing is carried out by means of a first pipe stop RA1, which is positioned in the Fig. 5a bis 5c In the illustrated embodiment, it is attached to the first inner mandrel ID1 and exerts a force in the axial direction on the end E of the workpiece W.

[0073] The first upsetting cup ST1, the first upsetting ring SR1, and the first upsetting guide SF1 are arranged coaxially to the central axis MW of the tubular workpiece W on its outer surface during forming according to step (c). The inner diameter of the first upsetting ring SR1 is between 100 and 115% of the outer diameter of the tubular workpiece W in the forming area U and outside the transition area T after reducing the cross-section in step (a) and before heating according to step (b). Furthermore, the inner diameter of the first upsetting guide SF1 is between 100 and 110% of the outer diameter of the tubular workpiece W in the forming area U and outside the transition area T after reducing the cross-section in step (a) and before heating according to step (b).

[0074] In the Fig. 5a bis 5d According to the illustrated embodiment, the first compression pot ST1 has a conical recess F in the form of a rotationally symmetrical cutout at its end section STE1, which is located opposite the transition region T of the tubular workpiece W. This recess serves to receive a quantity of the metal material of the tubular workpiece W during the forming process according to step (c).

[0075] The configurations, arrangements, and / or movements of the first upsetting cup ST1, the first inner mandrel ID1, the first upsetting ring SR1, and the first upsetting guide SF1 described above define a space around the workpiece (outside and inside) that advantageously limits the material flow during forming step (c) (combined upsetting and shoulder forming step). In particular, the arrangement of the first upsetting cup (ST1), the first upsetting ring SR1, and the first upsetting guide SF1 around the outer surface of the workpiece W prevents or limits material from breaking out or bulging outwards, while the arrangement of the first inner mandrel ID1 inside the workpiece W prevents or limits material from buckling or breaking into the interior of the workpiece W.This not only allows the formation of a shoulder S with an inflection point tangent that forms an angle α of approximately 75° with the central axis MW of the workpiece W in the present example (see detailed view in . Fig. 5d According to the inventive method, in the shoulder S region, precisely enough material is accumulated in and around the transition area T so that the final workpiece W exhibits neither a significant reduction nor an increase in wall thickness in the transition area T, particularly in the shoulder S region, compared to the wall thickness of the workpiece W before the shoulder S is formed, especially before forming according to step (c). Depending on the material used, the desired shape, and the wall thickness of the shoulder S, the shape of the shoulder S and the wall thickness of the formed workpiece W in the forming area U can be precisely adjusted by varying the shape and inner or outer diameter of the tools interacting in the inventive method.

[0076] According to the inventive method, a further forming step (step (d); Fig. 6a ) connect, in which the shoulder S is set at a steep angle so that the inflection tangent of the shoulder S with the central axis MW of the tubular workpiece W forms a right or nearly right angle β (see detailed view in Fig. 6b For this purpose, the workpiece does not need to be locally reheated. Instead, the residual heat from the preceding step (c) can be used as long as the tubular workpiece W still has a temperature in the range of 500 to 1,000 °C in the transition zone T. This advantageously eliminates a further heating step.

[0077] Using a second upsetting cup ST2, a second upsetting ring SR2, a second upsetting guide SF2, and a second inner mandrel ID2, with an analogous design and arrangement of these components and execution of an analogous forming stroke, the shoulder S is steepened until a right or nearly right angle β is achieved. In the present example, the second upsetting cup ST2 (including the end face ST2SF facing the end E of the workpiece) is identical to the first upsetting cup ST1, and the second upsetting guide SF2 is identical to the first upsetting guide SF1, so that the corresponding components from step (c) can be used and no additional components are required. The second upsetting ring SR2 has an inner circumferential contour suitable for further steepening of the shoulder S, with a rotationally symmetrical upsetting edge.The second crushing pot ST2 also has the clearance F described above, in which a quantity of the metal material of the tubular workpiece W is received during the stroke to steepen the shoulder S according to step (d).

[0078] In the present example, the outer diameter of the second inner mandrel ID2 is at least in a section AI2 of the second inner mandrel ID2 arranged opposite the transition area T of the tubular workpiece W during further forming between 90 and 100 % of the smallest inner diameter of the tubular workpiece W in the transition area T after forming according to step (c).

[0079] In the next step ( Fig. 7The workpiece W is heated to a temperature in the range of 350 to 1450 °C in a part of the forming area U, which includes the transition area T (step (f)). The heating is preferably carried out using an induction coil IS, but can also be done by another known technique.

[0080] After heating the workpiece W, at least in the transition region T, a final step (step (g)) can be a rolling forming of the tubular workpiece W in the transition region T using at least one rolling roller RR, here using three rolling rollers. During rolling, the metal material previously incorporated into the clearance of the second upsetting cup ST2 can again be advantageously used to increase the wall thickness in the transition region T or at the shoulder S.

Claims

1. Method for producing a stepped cross-sectional taper on a one-piece, tubular workpiece (W) made of metal, comprising at least the following steps: (f) Reducing the cross-section of the tubular workpiece (W) in a forming zone (U) thereof by means of a first forming tool (UW1), thereby creating a transition zone (T) in the forming zone (U); (g) heating the tubular workpiece (W) in the forming zone (U) or in a part thereof comprising the transition zone (T), to a temperature in the range of 700 to 1,450 °C, preferably 1,000 to 1,450 °C; (h) Forming the tubular workpiece (W) in the transition zone (T) such that the tubular workpiece (W) forms a shoulder (S) in the transition zone (T), wherein a tangent (WT) at the inflection point of the shoulder (S) forms an angle (α) of 45 to < 90°, preferably 65 to 75°, with a central axis (MW) of the tubular workpiece (W); wherein, during the forming, the tubular workpiece (W) has a temperature in the transition zone (T) in the range of 700 to 1,450 °C, preferably 1,000 to 1,450 °C; wherein the forming is performed using a first upsetting pot (ST1), a first upsetting ring (SR1), a first upsetting guide (SF1), and a first inner mandrel (ID1); wherein the first upsetting pot (ST1), the first upsetting ring (SR1), and the first upsetting guide (SF1) are arranged on the outer shell surface of the tubular workpiece (W), preferably each coaxial with the central axis (MW) of the tubular workpiece (W); wherein the first upsetting pot (ST1), the first upsetting ring (SR1), and the first upsetting guide (SF1) are arranged in this order toward one end (E) of the tubular workpiece (W); wherein the first inner mandrel (ID1) is arranged inside the tubular workpiece (W); wherein an outer diameter of the first inner mandrel (ID1) at least in a portion (Al1) of the first inner mandrel (ID1) being located opposite to the transition region (T) of the tubular workpiece (W) during forming is between 90 and 100% of the smallest inner diameter of the tubular workpiece (W) in the transition region (T) after the reduction according to step (a) and prior to the heating according to step (b); wherein an inner diameter of the first upsetting pot (ST1) is between 100 and 110% of the outer diameter of the tubular workpiece (W) prior to reducing of the cross-section in step (a); wherein an inner diameter of the first upsetting guide (SF1) is between 100 and 110% of the outer diameter of the tubular workpiece (W) in the forming zone (U) and outside the transition zone (T) after reducing the cross-section in step (a) and prior to heating according to step (b); wherein an inner diameter of the first upsetting ring (SR1) is between 100 and 115% of the outer diameter of the tubular workpiece (W) in the forming zone (U) and outside the transition zone (T) after reducing the cross-section in step (a) and prior to heating according to step (b); wherein the first upsetting ring (SR1) has a contour of the inner circumferential surface with a rotationally symmetric upsetting edge suitable for forming the shoulder (S) during forming in the transition zone (T) of the tubular workpiece (W), wherein the tangent (WT) at the inflection point of the shoulder (S) forms an angle (α) of 45 to < 90°, preferably 65 to 75°, with the central axis (MW) of the tubular workpiece (W); wherein, during forming, the first upsetting ring (SR1) and the first upsetting guide (SF1) and / or the first upsetting pot (ST1) are moved parallel to the central axis (MW) of the tubular workpiece (W) such that the distance between the first upsetting ring (SR1) and the first upsetting pot (ST1) decreases; and wherein, during the forming, the first upsetting ring (SR1) and the first upsetting guide (SF1) are not movable relative to one another.

2. The method according to claim 1, wherein the method further comprises the step of: (i) further forming the tubular workpiece (W) obtained in step (c) in the transition zone (T) such that the tangent (WT) at the inflection point of the shoulder (S) forms an angle (β) of 80 to 90°, preferably 85 to 90°, and most preferably 87 to 90°, with the central axis (MW) of the tubular workpiece (W); wherein, during the subsequent forming, the tubular workpiece (W) has a temperature in the range of 500 to 1,000 °C in the transition zone (T); wherein the forming is performed using a second upsetting pot (ST2), a second upsetting ring (SR2), a second upsetting guide (SF2), and a second inner mandrel (ID2); wherein the second upsetting pot (ST2), the second upsetting ring (SR2), and the second upsetting guide (SF2) are arranged on the outer shell surface of the tubular workpiece (W), preferably each coaxial with the central axis (MW) of the tubular workpiece (W); wherein the second upsetting pot (ST2), the second upsetting ring (SR2), and the second upsetting guide (SF2) are arranged in this order toward the end (E) of the tubular workpiece (W); wherein the second inner mandrel (ID2) is arranged inside the tubular workpiece (W); wherein an outer diameter of the second inner mandrel (ID2) at least in a portion (AI2) of the second inner mandrel (ID2) being located opposite to the transition region (T) of the tubular workpiece (W) during further forming is between 90 and 100% of the smallest inner diameter of the tubular workpiece (W) in the transition zone (T) after forming according to step (c); wherein the second upsetting pot (ST2) is identical or of the same construction as the first upsetting pot (ST1); wherein the second upsetting guide (SF2) is identical or of the same construction as the first upsetting guide (SF1), or wherein an inner diameter of the second upsetting guide (SF2) is between 100.1 and 105 % of the outer diameter of the tubular workpiece (W) in the forming region (U) and outside the transition region (T) after forming in step (c); wherein an inner diameter of the second upsetting ring (SR2) is between 100 and 115% of the outer diameter of the tubular workpiece (W) in the transition zone (T) after forming in step (c); wherein the second upsetting ring (SR2) has a contour of the inner circumferential surface with a rotationally symmetric upsetting edge that is suitable for forming the shoulder (S) during further forming in the transition zone (T) of the tubular workpiece (W) in such a way that the tangent (WT) at the inflection point of the shoulder (S) forms an angle (β) of 80 to 90°, preferably 85 to 90°, more preferably 87 to 90°, with the central axis (MW) of the tubular workpiece (W); wherein, during the forming, the second upsetting ring (SR2) and the second upsetting guide (SF2) and / or the second upsetting pot (ST2) are moved parallel to the central axis (MW) of the tubular workpiece (W) in such a way that the distance between the second upsetting ring (SR2) and the second upsetting pot (ST2) decreases; and wherein, during forming, the second upsetting ring (SR2) and the second upsetting guide (SF2) are not movable relative to one another.

3. The method according to claim 1 or 2, wherein the method further comprises the step of: (j) prior to step (b), shortening the tubular workpiece (W) from the end (E) by material removal such that an axial length (L) of the forming zone (U) is set to a predetermined length, preferably + / - 0.5 mm.

4. The method according to any one of claims 1 to 3, wherein during the forming in step (c), the tubular workpiece (W) is fed from its end (E) toward the transition zone (T) or in the axial direction toward the transition zone (T); wherein the feeding is preferably performed by means of a first tube stop (RA1), which is preferably attached to the first inner mandrel (ID1).

5. The method according to any one of claims 2 to 4, wherein during the forming in step (d), the tubular workpiece (W) is advanced from its end (E) toward the transition zone (T) or in the axial direction toward the transition zone (T); wherein the advancing is preferably performed by means of a second tube stop (RA2), which is preferably attached to the second inner mandrel (ID2).

6. The method according to any one of claims 1 to 5, further comprising at least one of the following steps: (k) after step (c) or (d), setting a temperature of the tubular workpiece (W) in the transition zone (T) or in a portion of the transition zone (T) to a temperature in the range of 350 to 1,450 °C; and / or (I) contour-forming forming of the tubular workpiece (W) in the transition zone (T) by means of at least one rolling roller (RR).

7. The method according to any one of claims 1 to 6, wherein the tubular workpiece (W) is spatially fixed by a clamping tool (SW), preferably radially clamped and axially held, at least during the performance of the steps of the method.

8. A system comprising a one-piece, tubular workpiece (W) made of metal and a device (V) for carrying out the method according to any one of claims 1 to 7, wherein the device (V) comprises at least: a first forming tool (UW1) for reducing the cross-section of a tubular workpiece (W) made of metal in a forming zone (U) of the tubular workpiece (W); a device (H1) for heating the tubular workpiece (W) in the forming zone (U) or in a portion thereof comprising a transition zone (T) from a non-reduced to a reduced cross-section of the tubular workpiece (W) to a temperature in the range of 700 to 1,450 °C, preferably 1,000 to 1,450 °C; a first upsetting pot (ST1), a first upsetting ring (SR1), a first upsetting guide (SF1), and a first inner mandrel (ID1); wherein the first upsetting pot (ST1), the first upsetting ring (SR1), and the first upsetting guide (SF1) can be arranged on an outer shell surface of the tubular workpiece (W), preferably each coaxial with the central axis (MW) of the tubular workpiece (W); wherein the first upsetting pot (ST1), the first upsetting ring (SR1), and the first upsetting guide (SF1) can be arranged in this order toward one end (E) of the tubular workpiece (W); wherein the first inner mandrel (ID1) can be arranged inside the tubular workpiece (W); wherein an outer diameter of the first inner mandrel (ID1) is, at least in sections, between 90 and 100 % of the smallest inner diameter of the tubular workpiece (W) in the transition zone (T) after reducing according to step (a) of the method and prior to the heating according to step (b) of the method; wherein an inner diameter of the first upsetting pot (ST1) is between 100 and 110 % of the outer diameter of the tubular workpiece (W) prior to the reducing of the cross-section in step (a) of the method; wherein an inner diameter of the first upsetting guide (SF1) is between 100 and 110 % of the outer diameter of the tubular workpiece (W) in the forming zone (U) and outside the transition zone (T) after reducing the cross-section in step (a) of the method and prior to heating according to step (b) of the method; wherein an inner diameter of the first upsetting ring (SR1) is between 100 and 115 % of the outer diameter of the tubular workpiece (W) in the forming zone (U) and outside the transition zone (T) after reducing the cross-section in step (a) and prior to heating according to step (b); wherein the first upsetting ring (SR1) has a contour of the inner circumferential surface with a rotationally symmetric upsetting edge suitable for forming the shoulder (S) in the transition zone (T) of the tubular workpiece (W), wherein the tangent (WT) at the inflection point of the shoulder (S) forms an angle (α) of 45 to < 90 °, preferably 65 to 75 °, with the central axis (MW) of the tubular workpiece (W); wherein the first upsetting ring (SR1) and the first upsetting guide (SF1) and / or the first upsetting pot (ST1) are mounted so as to be movable parallel to the central axis (MW) of the tubular workpiece (W) in such a way that the distance between the first upsetting ring (SR1) and the first upsetting pot (ST1) is variable; and wherein, during the forming according to step (c) of the method, the first upsetting ring (SR1) and the first upsetting guide (SF1) are not movable relative to one another.

9. The system according to claim 8, wherein the device (V) further comprises: a second upsetting pot (ST2), a second upsetting ring (SR2), a second upsetting guide (SF2), and a second inner mandrel (ID2); wherein the second upsetting pot (ST2), the second upsetting ring (SR2), and the second upsetting guide (SF2) can be arranged on the outer shell surface of the tubular workpiece (W), preferably each coaxial with the central axis (MW) of the tubular workpiece (W); wherein the second upsetting pot (ST2), the second upsetting ring (SR2), and the second upsetting guide (SF2) are arranged in this order toward the end (E) of the tubular workpiece (W); wherein the second inner mandrel (ID2) can be arranged inside the tubular workpiece (W); wherein an outer diameter of the second inner mandrel (ID2) is, at least in sections, between 90 and 100 % of the smallest inner diameter of the tubular workpiece (W) in the transition zone (T) after forming according to step (c); wherein the second upsetting pot (ST2) is identical or of the same construction as the first upsetting pot (ST1); wherein the second upsetting guide (SF2) is identical or of the same construction as the first upsetting guide (SF1), or wherein an inner diameter of the second upsetting guide (SF2) is between 100.1 and 105 % of the outer diameter of the tubular workpiece (W) in the forming zone (U) and outside the transition zone (T) after forming in step (c); wherein an inner diameter of the second upsetting ring (SR2) is between 100 and 115 % of the outer diameter of the tubular workpiece (W) in the transition zone (T) after forming in step (c) of the method; wherein the second upsetting ring (SR2) has a contour of the inner circumferential surface with a rotationally symmetric upsetting edge that is suitable for upsetting the shoulder (S) in the transition zone (T) of the tubular workpiece (W) in such a way that the tangent (WT) at the inflection point of the shoulder (S) forms an angle (β) of 80 to 90 °, preferably 85 to 90 °, more preferably 87 to 90 °, with the central axis (MW) of the tubular workpiece (W); wherein the second upsetting ring (SR2) and the second upsetting guide (SF2) and / or the second upsetting pot (ST2) are mounted so as to be movable parallel to the central axis (MW) of the tubular workpiece (W) in such a way that the distance between the second upsetting ring (SR2) and the second upsetting pot (ST2) is variable; and wherein, during forming according to step (d) of the method, the second upsetting ring (SR2) and the second upsetting guide (SF2) are not movable relative to one another.

10. The system according to claim 8 or 9, wherein the device (V) further comprises one or more of the following: a means for shortening the tubular workpiece (W) from the end (E) by material removal such that an axial length (L) of the forming zone (U) is adjustable to a predetermined length, preferably with an accuracy of + / - 0.5 mm; and / or a first tube stop (RA1), which is suitable for advancing the tubular workpiece (W) from its end (E) toward the transition zone (T) or in the axial direction toward the transition zone (T); and which is preferably attached to the first inner mandrel (ID1); and / or a second tube stop (RA2), which is suitable for advancing the tubular workpiece (W) from its end (E) toward the transition zone (T) or in the axial direction toward the transition zone (T); and which is preferably attached to the second inner mandrel (ID2); and / or a device (H2) for setting the temperature of the tubular workpiece (W) in the transition zone (T) or in a portion of the transition zone (T) to a temperature in the range of 350 to 1,450 °C; and / or a clamping tool (SW) for spatially fixing the tubular workpiece (W), preferably a clamp or clamping jaw or a multi-segment clamping system.