Device, system and method for forming a one-piece, at least partially tubular workpiece made of metal and corresponding use

Abstract

Device (V) for forming a one-piece, at least partially tubular workpiece (WS) made of metal, wherein the workpiece (WS) has a heating area (E); wherein the workpiece (WS) has an outer diameter (D1) and an inner diameter (d1) within the heating area (E) before forming; wherein the workpiece (WS) has an outer diameter (D0) and an inner diameter (d0) in a tubular section outside the heating area (E) before forming; wherein the device (V) comprises at least: a crushing pot (ST); a shrub thorn (SD); and a stop (ON); wherein the compression pot (ST) is multi-part, preferably two-part; wherein the compression pot (ST) has a receptacle (AW) for receiving the entire workpiece (WS) or at least a part of the workpiece (WS) including a heating area (E) of the workpiece (WS); wherein the recording (AW) has a first section (AW1), a second section (AW2) and a third section (AW3) along the central axis (MAW) of the recording (AW); where the inner diameter (d AW1 ) of the first section (AW1) of the fixture (AW) is 1.005 times to 1.040 times the outer diameter (D1) of the workpiece (WS) in the heating area (E) before forming; where the inner diameter (d AW2 ) of the second section (AW2) of the fixture (AW) is 1.002 times to 1.020 times the outer diameter (D0) of the workpiece (WS) in a tubular section outside the heating area (E) before forming; wherein the third section (AW3) of the recording (AW) is arranged between the first section (AW1) of the recording (AW) and the second section (AW2) of the recording (AW); wherein the third section (AW3) of the receptacle (AW) is designed as a circumferential annular groove (RN); where the inner diameter (d AW3 ) of the third section (AW3) of the inlet (AW) larger than the inner diameter (d AW1 ) of the first section (AW1) of the recording (AW); where the inner diameter (d AW3 ) of the third section (AW3) of the inlet (AW) larger than the inner diameter (d AW2 ) of the second section (AW2) of the recording (AW); wherein the length of the first section (AW1) of the fixture (AW), measured parallel to the central axis (MAW) of the fixture (AW), is greater than the length of the heating area (E) of the workpiece (WS), measured parallel to the central axis (MWS) of the workpiece (WS); wherein the shrub spine (SD) has a first section (SD1) and a second section (SD2) along the central axis (MSD) of the shrub spine (SD); wherein the compression mandrel (SD) in the area of ​​the first section (SD1) has an outer diameter (D SD1 ) which is 0.1 to 0.4 mm, preferably 0.2 to 0.3 mm, smaller than the inner diameter (d AW1 ) of the first section (AW1) of the recording (AW); wherein the compression mandrel (SD) in the area of ​​the second section (SD2) has an outer diameter (D SD2 ) which meets the following condition: D SD2 ≥ − 2.0 ⋅ ( D 1 2 − d 1 2 ) + d AW 1 2 , preferably D SD 2 ≥ − 1.6 ⋅ ( D 1 2 − d 1 2 ) + d AW 1 2 , wherein the length of the second section (SD2) of the upsetting mandrel (SD), measured parallel to the central axis (MSD) of the upsetting mandrel (SD), is at least 1.1 times the length of the heating area (E), measured parallel to the central axis (MWS) of the workpiece (WS); where the inner diameter (d AW3 ) the following condition is met in the third section (AW3) of the recording (AW): d AW3 ≤ 2.0 ⋅ d AW 1 2 − DSD 2 2 , preferably d AW 3 ≤ 1.6 ⋅ d AW 1 2 − 1.6 ⋅ DSD 2 2 ; wherein the compression spike (SD) is / are movably mounted relative to the compression pot (ST) and / or the compression pot (ST) is / are movably mounted relative to the compression spike (SD); wherein the compression mandrel (SD) is movably mounted in a direction parallel to the central axis (MAW) of the receptacle (AW); wherein the upsetting mandrel (SD) is suitable to apply a first force (F1) and a second force (F2) to the workpiece (WS), preferably to a first end face (S1) of the workpiece (WS), in a direction parallel to the central axis (MSD) of the upsetting mandrel (SD); wherein the stop (AN) is / are movable relative to the compression pot (ST) and / or the compression pot (ST) is / are movable relative to the stop (AN); wherein the stop (AN) is suitable to apply a first counterforce (GF1) and a second counterforce (GF2) to the workpiece (WS), preferably to a second end face (S2) of the workpiece (WS) opposite the first end face (S1), in a direction parallel to the central axis (MSD) of the upsetting mandrel (SD); where the first opposing force (GF1) is directed opposite to the first force (F1) and the second opposing force (GF2) is directed opposite to the second force (F2); wherein the compression pot (ST) and the compression mandrel (SD) are arranged or can be arranged in the device (V) such that the central axis (MAW) of the receptacle (AW) of the compression pot (ST) and the central axis (MSD) of the compression mandrel (SD) are concentric.

Description

Technical area

[0001] The present invention relates to a device for forming a one-piece, at least partially tubular metal workpiece according to claim 1, a corresponding system according to claim 6, a method for forming a one-piece, at least partially tubular metal workpiece according to claim 8 and a use according to claim 15. The method according to the invention can be used, for example, to form the following one-piece components or their precursors from at least partially tubular workpieces, but is not limited thereto: rotor shafts, drive shafts, stabilizers, shock absorbers, gas cartridges, scaffolding supports, shafts and tubular building blocks of all kinds. Background and state of the art

[0002] Hot forming processes for producing a one-piece hollow shaft with a projection on its outer circumferential surface by upsetting a tubular metal workpiece are known from the prior art. However, workpieces produced in this conventional manner have a continuous radial fold, i.e., a circumferential fold, on the inside of the workpiece in the area of ​​the projection due to wrinkling that occurs during forming. This reduces the mechanical stability of the workpiece, which is disadvantageous for a variety of applications of the workpiece, for example, in automotive engineering, or even precludes such applications.Such cracks or wrinkles occur particularly in hot forming processes that, by compressing the tubular workpiece to form the projection, provide such a high degree of deformation that the cross-sectional area of ​​the workpiece in the projection region is two to four times the cross-sectional area of ​​the workpiece in the projection region before forming or compared to an undeformed region of the tubular workpiece. Generic methods and devices are known to the person skilled in the art from the documents DE 10 2013 104 038 A1 and DE 41 04 707 A1. Object of the invention

[0003] An object of the present invention is therefore to provide a device or a system which makes it possible to reshape a workpiece which is originally at least partially, preferably completely, tubular and has a circular or substantially circular cross-section in a predetermined region or section in such a way that it has a projection on its outer circumferential surface in the predetermined region and the cross-sectional area of ​​the workpiece in the region of the projection is two to four times the cross-sectional area of ​​the workpiece in the same region or at the same point on the workpiece before reshaping, or the cross-sectional area of ​​the workpiece in the region of the projection is two to four times the cross-sectional area of ​​the workpiece in another region of the workpiece not affected by the reshaping. According to the invention, the workpiece does not have a radial fold orno circumferential gap or crack.

[0004] Furthermore, it is an object of the present invention to provide a corresponding method for forming a one-piece, at least partially tubular metal workpiece using the device or system according to the invention for producing the formed workpiece as described above without a radial fold on its inner circumferential surface in the region of the projection. Finally, it is an object to propose a corresponding use of the device or system according to the invention for producing the workpiece formed according to the invention. Definitions

[0005] In the context 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 a circle or a near circle. In the context of the present invention, “nearly a circle” or “essentially circular cross-section” with respect to the workpiece or a section thereof means that the outer diameter of the workpiece or the relevant section thereof, when measured or determined or viewed or seen or defined at the same point on the workpiece in two different directions perpendicular to the center axis of the workpiece, differs by a maximum of 1.0% between the two measurements. The same applies analogously to the inner diameter of the workpiece.The term "at least partially tubular workpiece" means that the above-described geometric properties of the tubular workpiece apply to at least one section of the workpiece, while the workpiece may have a shape deviating from a circular tube in another section, or preferably to the entire workpiece. The at least partially tubular workpiece to be formed according to the invention may have a length, measured or determined or viewed or seen or defined parallel to the center axis of the workpiece, of between 150 and 4,000 mm, preferably 200 to 1,000 mm, an outer diameter of between 20 and 406 mm, preferably between 30 and 120 mm, and preferably a thickness (= wall thickness = [outer diameter - inner diameter] / 2) of between 4 and 20 mm.

[0006] In the context of the present invention, the term “one-piece” with respect to the at least partially tubular workpiece also includes at least partially tubular workpieces which have a weld seam or a joining seam along the central axis of the workpiece.

[0007] In the context of the present invention, the term "metal" encompasses, for example, as the material for the workpiece, an element belonging to the metals, such as iron, alloys of two or more metals, such as stainless steel, or other alloys with an iron content of > 90%, such as steel. According to the invention, the definition of the term "metal" also includes an element or alloy that has a proportion of technically unavoidable impurities. The inventive definition of the term "metal" can be limited to iron and alloys with an iron content of > 90%, including steel and stainless steel. The definition of the term "metal" can preferably be limited to steel, including stainless steel, in particular one of the materials designated 1.2344 (X40CrMoV5-1), "NB5", material 1.7227 "42CrMoS4 + QT", material 1.7227 "42CrMoS4 + C", material 1.7225 “42CrMo4” or a boron-treated steel such as the material 1.1161 “26MnB5” in accordance with DIN EN 10083-3:2007-01.

[0008] In the context of the present invention, the term "concentric" with respect to the arrangement of central axes means an arrangement symmetrical around a common center, so that the central axes coincide. Furthermore, the term "concentric" can also encompass arrangements that exhibit minor, technically unavoidable deviations from the above definition of "concentric" in the strictly geometric sense.

[0009] The components of the device according to the invention, or at least a portion thereof, preferably the compression pot, the compression mandrel, and the stop, or a selection of said components or portions thereof, are preferably made of hard metal or hardened steel, in particular coated steel. The compression mandrel, or at least a portion thereof, is preferably made of hard metal.

[0010] All dimensions specified in the present application (e.g. outer diameter, inner diameter, length, wall thickness) of the workpiece and the components of the device according to the invention (in particular the upsetting pot, the upsetting mandrel and the stop) refer to room temperature, i.e. to 20 °C.

[0011] Within the scope of the present invention, the specified diameters of a component of the device according to the invention, including the inner and outer diameters, are always measured, determined, or viewed, or defined perpendicular to the longest axis of symmetry or center axis of the respective component, unless otherwise stated. The same applies analogously to the workpiece.

[0012] In the context of the present invention, the term “measured” in relation to a length dimension in formulations such as “measured parallel to ...”, “measured along ...”, “measured perpendicular to ...”, “measured in the direction of ...”, “measured from ...” is to be understood as synonymous with and interchangeable with “determined” or “viewed” or “when viewed”, “seen” or “when seen” and “defined”. Accordingly, these terms are mutually interchangeable. For example, “measured parallel to the central axis (MWS)” means the same as “determined parallel to the central axis (MWS)” or “viewed parallel to the central axis (MWS)” or “when viewed parallel to the central axis (MWS)” or “seen parallel to the central axis (MWS)” or “when viewed parallel to the central axis (MWS)” or “seen parallel to the central axis (MWS)” or “when viewed parallel to the central axis (MWS)” or “defined parallel to the central axis (MWS)”.Therefore, according to the invention, the term "measured" in the context discussed above does not necessarily include a measuring step, but merely defines the direction to which the length dimension refers. The same, namely the direction to which the length dimension refers, is expressed by the terms "determined," "considered" or "when viewed," "seen" or "when seen," and "defined."

[0013] In the context of the present invention, the "heating region E" means a partial region of the workpiece that is heated to at least 700°C for forming. The heating region may or may not comprise an end or an end section of the workpiece (referred to according to the invention as the "terminal heating region"). After the forming steps according to the invention have been carried out, the workpiece has a projection on its outer peripheral surface in the heating region or within the heating region. According to the invention, the expression "in the heating region" or "within the heating region" can refer to the entire heating region, a partial region thereof, or a single spatial location within the heating region.

[0014] If the heating region E does not encompass any end or end portion of the workpiece, i.e., is an internal heating region, the partial regions of the workpiece located between the heating region and each of the two ends of the workpiece are non-heating regions that have a temperature of less than 300°C during the implementation of at least steps (a), (b), (c), and (d) of the method according to the invention. These non-heating regions are also referred to as "cold regions K1, K2" in the context of this invention.

[0015] If the heating region E comprises one end or an end section of the workpiece, i.e., is a terminal heating region, the portion of the workpiece located between the heating region and the other, opposite end or the other, opposite end section of the workpiece is a non-heating region, which has a temperature of less than 300°C during the implementation of at least steps (a), (b), (c), and (d) of the method according to the invention. This non-heating region is referred to in the context of this invention as "cold region K."

[0016] According to the invention, “before forming” means a state, in particular a state of the workpiece, before the first upsetting is carried out according to step (b) and before the second upsetting is carried out according to step (d) of the method according to the invention, thus meaning the original state of the undeformed, at least partially tubular workpiece.

[0017] According to the invention, the AW defined as the inner diameter of the receptacle AW when viewed in a sectional view in which the receptacle AW is cut perpendicular to its central axis MAW.

[0018] According to the invention, D0 is defined as the outer diameter of the workpiece WS in a cold area K, i.e. in a tubular section outside the heating area E before forming, i.e. in the original state, when viewed in a sectional view in which the workpiece WS is cut perpendicular to its central axis MWS.

[0019] According to the invention, D1 is defined as the outer diameter of the workpiece WS in the heating area E before forming, i.e. in the original state, when viewed in a sectional view in which the workpiece WS is cut perpendicular to its central axis MWS.

[0020] According to the invention, D2 is defined as the outer diameter of the workpiece WS in the heating region E after the first upsetting according to step (b) of the method according to the invention, when viewed in a sectional view in which the workpiece WS is cut perpendicular to its central axis MWS. According to the invention, the term "after the first upsetting according to step (b) of the method according to the invention" means the state of the workpiece WS after carrying out the first upsetting according to step (b) but before carrying out the second upsetting according to step (d) of the method according to the invention, unless otherwise stated. The execution of the displacement according to step (c) has no influence on the outer diameter D2.

[0021] According to the invention, D3 is defined as the outer diameter of the workpiece WS in the heating region E after the second upsetting according to step (d) of the method according to the invention, when viewed in a sectional view in which the workpiece WS is cut perpendicular to its central axis MWS. According to the invention, the term "after the second upsetting according to step (d) of the method according to the invention" means the state of the workpiece WS after performing the first upsetting according to step (b), the shifting according to step (c), and the second upsetting according to step (d) of the method according to the invention, unless otherwise stated.

[0022] The above-defined outer diameters D0, D1, D2, D3 of the workpiece WS always refer to the maximum outer diameter of the workpiece WS in the specified range, e.g. in the heating range E D1, D2, D3 or outside the heating range E D0, taking into account the manufacturing tolerance of the workpiece WS, and taking into account the degree of deformation or upsetting (D1 = before the first upsetting; D2 = after the first upsetting and before the second upsetting; D3 = after the second upsetting), unless otherwise stated.

[0023] Alternatively, according to the invention, the outer diameters D0, D1, D2, D3 of the workpiece WS can also be defined as a function of the location x along the center axis MWS of the workpiece WS. For example, D1(x) is the outer diameter D1 of the workpiece WS before the first upsetting at location x in the heating area E along the center axis MWS between x0 (beginning of the heating area E) and x1 (end of the heating area E).

[0024] According to the invention, d0 is defined as the inner diameter of the workpiece WS in a cold area K, i.e. in a tubular section outside the heating area E before forming, i.e. in the original state, when viewed in a sectional view in which the workpiece WS is cut perpendicular to its central axis MWS.

[0025] According to the invention, d1 is defined as the inner diameter of the workpiece WS in the heating area E before forming, when viewed in a sectional view in which the workpiece WS is cut perpendicular to its central axis MWS.

[0026] According to the invention, d2 is defined as the inner diameter of the workpiece WS in the heating region E after the first upsetting according to step (b) of the inventive method, when viewed in a sectional view in which the workpiece WS is cut perpendicular to its central axis MWS. Here, the term "after the first upsetting according to step (b) of the inventive method" refers to the state of the workpiece WS after performing the first upsetting according to step (b) but before performing the second upsetting according to step (d) of the inventive method.

[0027] According to the invention, d3 is defined as the inner diameter of the workpiece WS in the heating region E after the second upsetting according to step (d) of the inventive method, when viewed in a sectional view in which the workpiece WS is cut perpendicular to its central axis MWS. Here, the term "after the second upsetting according to step (d) of the inventive method" refers to the state of the workpiece WS after performing the first upsetting according to step (b) and the second upsetting according to step (d) of the inventive method.

[0028] The above-defined inner diameters d0, d1, d2, d3 of the workpiece WS always refer to the minimum inner diameter of the workpiece WS in the specified range, i.e., in the heating range E or outside the heating range E, taking into account the manufacturing tolerance of the workpiece WS, and taking into account the degree of deformation (d0, d1 = before the first upsetting; d2 = after the first upsetting; before the second upsetting; d3 = after the second upsetting), unless otherwise stated.

[0029] Alternatively, according to the invention, the inner diameters d0, d1, d2, d3 of the workpiece WS can also be defined as a function of the location x along the center axis MWS of the workpiece WS. For example, d1(x) is the inner diameter d1 of the workpiece WS before the first upsetting at location x in the heating area E along the center axis MWS between x0 (beginning of the heating area E) and x1 (end of the heating area E).

[0030] According to the invention, D SD1 defined as the outer diameter of the compression mandrel SD in the region of its first section SD1 when viewed in a sectional view in which the compression mandrel SD is cut perpendicular to its central axis MSD in the region of its first section SD1.

[0031] According to the invention, D SD2 defined as the outer diameter of the compression mandrel SD in the region of its second section SD2 when viewed in a sectional view in which the compression mandrel SD in the region of its second section SD2 is cut perpendicular to its central axis MSD.

[0032] According to the invention, D SD3 defined as the outer diameter of the compression mandrel SD in the region of its optional third section SD3 when viewed in a sectional view in which the compression mandrel SD in the region of its optional third section SD3 is cut perpendicular to its central axis MSD.

[0033] According to the invention, D AN defined as the outside diameter of the stop AN in a cylindrical section of the stop AN when viewed in a sectional view in which the stop AN is cut in the region of this section perpendicular to its central axis MAN. Summary of the invention

[0034] The above-described object is achieved by the device according to claim 1. Thus, according to the invention, a device for forming a one-piece, at least partially tubular workpiece WS made of metal, preferably for carrying out at least steps (b), (c) and (d) of the method according to one of claims 8 to 14, wherein the workpiece WS has a heating area E; wherein the workpiece WS has an outer diameter D1 and an inner diameter d1 within the heating area E before forming; wherein the workpiece WS has an outer diameter D0 and an inner diameter d0 in a tubular section outside the heating area E before forming.

[0035] The device V comprises at least: a compression pot ST; a compression mandrel SD; and an attack ON; wherein the compression pot ST is multi-part, preferably two-part; wherein the upsetting pot ST has a holder AW for receiving the entire workpiece WS or at least a part of the workpiece WS, including a heating region E of the workpiece WS; wherein the holder AW has a first section AW1, a second section AW2, and a third section AW3 along the central axis MAW of the holder AW; where the inner diameter d AW1of the first section AW1 of the holder AW is 1.005 times to 1.040 times the outer diameter D1 of the workpiece WS in the heating area E before forming; where the inner diameter d AW2 of the second section AW2 of the holder AW is 1.002 times to 1.020 times the outer diameter D0 of the workpiece WS in a tubular section outside the heating area E before forming; wherein the third section AW3 of the receptacle AW is arranged between the first section AW1 of the receptacle AW and the second section AW2 of the receptacle AW; wherein the third section AW3 of the receptacle AW is formed as a circumferential annular groove RN; where the inner diameter d AW3 of the third section AW3 of the holder AW larger than the inner diameter d AW1 of the first section AW1 of the recording AW; where the inner diameter d AW3of the third section AW3 of the holder AW larger than the inner diameter d AW2 of the second section AW2 of the recording AW; wherein the length of the first section AW1 of the holder AW, measured or determined or viewed or seen or defined parallel to the central axis MAW of the holder AW, is greater than the length of the heating region E of the workpiece WS, measured or determined or viewed or seen or defined parallel to the central axis MWS of the workpiece WS; wherein the compression mandrel SD has a first section SD1 and a second section SD2 along the central axis MSD of the compression mandrel SD; Wherein the compression mandrel SD in the area of ​​the first section SD1 has an outer diameter D SD1 which is 0.1 to 0.4 mm, preferably 0.2 to 0.3 mm, smaller than the inner diameter d AW1 of the first section AW1 of the recording AW; wherein the compression mandrel SD in the area of ​​the second section SD2 has an outer diameter D SD2 which satisfies the following condition: DSD2≥−2.0⋅(D12−d12)+dAW12, preferably DSD2≥−1.6⋅(D12−d12)+dAW12; wherein the length of the second section SD2 of the upsetting mandrel SD, measured or determined or viewed or seen or defined parallel to the central axis MSD of the upsetting mandrel SD, is at least 1.1 times the length of the heating region E, measured or determined or viewed or seen or defined parallel to the central axis MWS of the workpiece WS; where the inner diameter d AW3 the recording AW in the third section AW3 meets the following condition: dAW3≤2.0⋅dAW12−DSD22, preferably dAW3≤1.6⋅dAW12−1.6⋅DSD22; wherein the compression mandrel SD is / are movably mounted relative to the compression pot ST and / or the compression pot ST is / are movably mounted relative to the compression mandrel SD; wherein the compression mandrel SD is movably mounted in a direction parallel to the central axis MAW of the holder AW; wherein the upsetting mandrel SD is suitable for applying a first force F1 and a second force F2 to the workpiece WS, preferably to a first end face S1 of the workpiece WS, in a direction parallel to the central axis MSD of the upsetting mandrel SD; wherein the stop AN is / are movably mounted relative to the compression pot ST and / or the compression pot ST is / are movably mounted relative to the stop AN; wherein the stop AN is suitable for applying a first counterforce GF1 and a second counterforce GF2 to the workpiece WS, preferably to a second end face S2 of the workpiece WS opposite the first end face S1, in a direction parallel to the central axis MSD of the upsetting mandrel SD; wherein the first counterforce GF1 is directed opposite the first force F1 and the second counterforce GF2 is directed opposite the second force F2; wherein the compression pot ST and the compression mandrel SD are arranged or can be arranged in the device V in such a way that the central axis MAW of the receptacle AW of the compression pot ST and the central axis MSD of the compression mandrel SD are concentric.

[0036] The device according to the invention enables the formation of a projection, such as a flange, on the outer circumferential surface of a metal workpiece which is at least partially tubular, by forming, wherein the workpiece in the region of the projection, more precisely on its inner circumferential surface in the heating region, has no circumferential or even partially present fold in the form of a gap or crack, although the workpiece in the region of the projection has a cross-sectional area which is approximately two to four times the cross-sectional area of ​​the workpiece in the region of the projection before forming, i.e. in the initial state, or in another area not affected by the forming, i.e. in a cold area outside the heating area, of the workpiece in which the workpiece still has its original round tube shape.According to the invention, the two-stage forming can be carried out in a single device, which saves space and facilitates and, above all, accelerates the implementation of the method according to the invention described below.

[0037] If the at least partially tubular workpiece represents an ideal round tube at least in part, the outer diameter D1 of the workpiece WS within the heating region E before forming is equal to the outer diameter D0 of the workpiece WS outside the heating region E, i.e. within a cold region K (before and / or after forming). If the at least partially tubular workpiece represents an ideal round tube at least in part, analogously, the inner diameter d1 of the workpiece WS within the heating region E before forming is equal to the inner diameter d0 of the workpiece WS outside the heating region E, i.e. within a cold region K, both before and after the forming according to the invention.

[0038] If the manufacturing tolerances customary in practice for real round tubes with a substantially circular cross-section are taken into account, it can be assumed within the scope of the present invention that, in the case of a real round tube, the difference between the outer diameter D1 of the workpiece WS within the heating area E before forming and the outer diameter D0 of the workpiece WS outside the heating area E, i.e. within a cold area K (before and / or after forming), is negligibly small (< 1%), so that within the scope of the present application the two outer diameters D1 and D0 are also regarded as being equal in terms of amount.Analogously, in the case of a real round tube, the inner diameter d1 of the workpiece WS within the heating area E before forming can be regarded as equal to the inner diameter d0 of the workpiece WS outside the heating area E, i.e. within a cold area K, both before and after the forming according to the invention.

[0039] Advantageously, the concept of the device according to the invention can be used for a large number of different, at least partially tubular workpieces, wherein the dimensions of the components of the device are selected depending on the dimensions of the workpiece to be formed (e.g. outer diameter, inner diameter and length of the workpiece).

[0040] Since the upsetting pot of the device according to the invention is designed in several parts, it is possible to place the undeformed workpiece into the opened device according to the invention, more precisely into the receptacle of the opened upsetting pot of the device according to the invention, and to remove it again from the device without any problems by opening the upsetting pot after the forming in the device and the formation of the projection.

[0041] Preferably, the multi-part upsetting pot can be locked not only hydraulically but also mechanically, whereby the mechanical stability of the device and in particular the hold of the workpiece in the device is further improved.

[0042] In the device according to the invention, the upsetting pot can be dimensioned such that it completely accommodates the workpiece. However, the invention is not limited to this. Rather, it is sufficient if at least a portion of the workpiece, including the heating area, is accommodated by the holder. For example, a cold area or part of a cold area can protrude from the holder and thus from the device.

[0043] More precisely, the axial length of the holder AW of the device V according to the invention is dimensioned such that it can accommodate at least the heating area E of the workpiece WS. If the workpiece WS has one or more cold areas as defined above, the axial length of the holder AW can be dimensioned such that, in addition to the heating area E, it can accommodate one cold area K or one of the two cold areas K1, K2 or even both cold areas K1, K2 in whole or in part. The holder AW of the device V according to the invention can also be dimensioned such that it completely accommodates the workpiece WS. Preferably, the holder AW is cylindrical at least in its first section AW1 and second section AW2.

[0044] The inner diameter d AW1and the length of the first section AW1 of the holder AW are dimensioned in the device according to the invention by being limited to the predetermined area such that the holder AW can accommodate the heating area of ​​the workpiece WS, even if, when carrying out the method according to the invention, it is heated to a temperature suitable for forming in the range from 700 to 1,450 °C and expands due to the heat in the process. Thus, the length of the first section AW1, measured or determined or viewed or seen or defined parallel to the center axis of the holder, is preferably 1.1 to 1.5 times, in particular 1.1 to 1.2 times, the length of the heating area E, measured or determined or viewed or seen or defined parallel to the center axis of the workpiece.

[0045] The inner diameter d AW2In the device according to the invention, the second section AW2 of the holder AW is dimensioned by being limited to the predetermined area such that the holder AW can accommodate a cold area of ​​the workpiece WS and can stably hold or support the workpiece despite the presence of the usual dimensional tolerances within the device. Thus, the second section AW2 of the holder AW represents a guide section for the workpiece within the device according to the invention if required. In the device according to the invention, the length of the second section AW2 of the holder AW is not particularly limited, as long as the above-described function of stably holding or supporting the workpiece in the closed device is ensured.

[0046] The inner diameter d AW2of the second section AW2 of the holder AW can be, for example, 0.05 to 0.5 mm, preferably 0.1 to 0.4 mm, larger than the outer diameter D0 of the workpiece WS outside the heating area E in the initial state before forming. In absolute terms, the inner diameter d AW2 of the second section AW2 of the receptacle AW may be, for example, 5 to 50 mm, preferably 10 to 40 mm.

[0047] Due to the dimensioning of the outer diameter of the compression mandrel SD in its first section SD1, it is ensured that the compression mandrel can be easily removed from the holder, more precisely from the first section AW1 of the holder AW or, if the first section AW1 of the holder AW does not include an end section or terminal section of the holder AW, from an adjacent end section of the holder, which, for example, has the same inner diameter as the inner diameter d AW2 of the second section AW2 of the holder AW, and can also be guided sufficiently safely during movements of the compression mandrel within the holder along the central axis of the holder.

[0048] In the area of ​​its second section SD2, the compression mandrel SD has an outer diameter D SD2which satisfies the condition stated above or in claim 1. In addition, the outer diameter D SD2 of the second section SD2 of the compression mandrel SD smaller than the outer diameter D SD1its first section SD1. Due to this dimensioning of the second section SD2 of the upsetting mandrel SD, it is ensured, according to the inventor's knowledge, that the degree of deformation of the workpiece in the heating region during the first upsetting according to step (b) of the method according to the invention is limited to a level such that the formation of a fold or a gap on the inner peripheral surface of the workpiece in the heating region during the respective forming step provided according to the invention can be avoided. In this context, the inventor has found that this can surprisingly be achieved if the degree of deformation or upsetting is limited during the first upsetting such that the cross-sectional area of ​​the workpiece in the forming region during the first upsetting increases by less than a factor of 2, preferably by less than a factor of 1.6, compared to the cross-sectional area at the same point on the workpiece before the first upsetting.In this case, a limitation to the factor 1.6 can be achieved by the preferred condition for the outer diameter D stated above or in claim 1. SD2 can be achieved.

[0049] Analogously, in the device according to the invention, the inner diameter d AW3 of the receptacle AW in the third section AW3 is limited to the extent that it meets the condition stated above or in claim 1. In addition, the inner diameter d AW3 of the third section AW3 of the holder AW larger than the inner diameter d AW1 of the first section AW1 and larger than the inner diameter d AW2of the second section AW2 of the holder AW. According to the inventor's knowledge, this dimensioning of the third section AW3 of the holder AW ensures that the degree of deformation of the workpiece in the heating area is also limited during the second upsetting according to step (d) of the method according to the invention to such an extent that the formation of a fold or a gap in the heating area due to the deformation can be avoided. In this context, the inventor has found that this can surprisingly be achieved if, even during the second upsetting, the degree of deformation or upsetting is limited such that the cross-sectional area of ​​the workpiece in the forming area increases by less than a factor of 2, preferably by less than a factor of 1.6, compared to the cross-sectional area at the same point after the first upsetting (and before the second upsetting). A limitation to a factor of 1.6 can be achieved by the above orpreferred condition for the inner diameter d specified in claim 1. AW3 of the third section AW3.

[0050] Overall, therefore, using the device according to the invention, a high degree of deformation can be achieved on the workpiece, with a cross-sectional enlargement of the workpiece in the heating or forming area of ​​up to a factor of 4, preferably up to a factor of 2.56, and with the formation of a projection arranged on the outer circumferential surface of the workpiece, without wrinkling occurring on the inner circumferential surface of the workpiece in the heating area. It is also a finding of the present inventor that if the above-described cross-sectional ratio factor is limited to a maximum of 1.6 for each upsetting process, i.e., with a total factor of a maximum of 2.56 for both upsetting processes, wrinkling on the workpiece is definitely avoided.Furthermore, for the vast majority of applications of the present invention, wrinkling on the workpiece can be effectively avoided even up to a cross-sectional ratio factor of 2.0 for each upsetting process, i.e. with a total factor of at most 4.0 for both upsetting processes.

[0051] In the device according to the invention, the third section AW3 of the holder AW is designed as a circumferential annular groove, the contour of which (when viewed in a sectional view of the device, cut along the center axis of the holder) characterizes the size and shape of the projection of the workpiece on its outer circumferential surface when the device according to the invention is used for forming a workpiece that is at least partially tubular, for example within the scope of the method according to the invention.

[0052] The contour of the annular groove is not particularly limited and can, for example, have the shape of a rectangle, a semicircle, a semi-ellipsoid, or any other desired shape with straight, curved, or freely shaped flanks. Preferably, the third section AW3 of the receptacle AW is rotationally symmetrical about the central axis of the receptacle. However, a non-rotationally symmetrical shape of the third section AW3 of the receptacle AW is also possible in the device according to the invention.

[0053] The shape of the annular groove RN is also not particularly restricted with regard to its dimensions. Thus, the length LN of the annular groove RN, measured or determined or viewed or seen or defined parallel to the central axis of the receptacle, at the point of its greatest extent can be, for example, 3 to 50 mm, preferably 4 to 12 mm. Additionally or independently of this, the depth TN of the annular groove RN, measured or determined or viewed or seen or defined perpendicular to the central axis MAW of the receptacle AW and from the level of the inner circumferential surface of the second section AW2 of the receptacle AW, at the point of its greatest extent can be, for example, 2 to 20 mm, preferably 3 to 10 mm (see also Fig. 5b).

[0054] According to the invention, the length of the second section SD2 of the upsetting mandrel SD, measured or determined or viewed or seen or defined parallel to the central axis MSD of the upsetting mandrel SD, is at least 1.1 times the length of the heating region E, measured or determined or viewed or seen or defined parallel to the central axis MWS of the workpiece WS. Preferably, the length of the second section SD2 of the upsetting mandrel SD, measured or determined or viewed or seen or defined parallel to the central axis MSD of the upsetting mandrel SD, is 1.1 to 1.5 times, in particular 1.1 to 1.2 times, the length of the heating region E, measured or determined or viewed or seen or defined parallel to the central axis of the workpiece.

[0055] If the workpiece has an internal heating region E according to the above definition, then the length of the second section SD2 of the upsetting mandrel SD, measured or determined or observed or seen or defined parallel to the central axis MSD of the upsetting mandrel SD, can be the sum of at least 1.1 times the length of the heating region E and the length of a cold region K lying between the heating region and one end of the workpiece, which cold region is in contact with the upsetting mandrel SD during the first and / or second upsetting according to steps (b) and / or (d) of the method according to the invention, wherein the lengths of the heating region E and the cold region K are each measured or determined or observed or seen or defined parallel to the central axis MWS of the workpiece WS.

[0056] Optionally, the upsetting mandrel SD can additionally have a third section SD3 along the central axis MSD of the upsetting mandrel SD, wherein the third section SD3 is arranged between the first section SD1 and the second section SD2. The third section SD3 can, for example, be designed as a linear, continuous, step-shaped or freely formed transition between the first section SD1 and the second section SD2. In this case, the length of the second section SD2 of the upsetting mandrel SD, measured or determined or viewed or seen or defined parallel to the central axis MSD of the upsetting mandrel SD, is exactly as defined above, namely at least 1.1 times the length of the heating region E. The length of the third section SD3 of the upsetting mandrel SD, measured or determined or viewed or seen ordefined parallel to the central axis MSD of the upsetting mandrel SD, can correspond, for example, to the length of the terminal cold region K of the workpiece which is in contact with the upsetting mandrel SD during the first and / or second upsetting according to steps (b) and / or (d) of the method according to the invention, wherein the lengths related to the regions of the workpiece WS are each measured or determined or viewed or seen or defined parallel to the central axis MWS of the workpiece WS.

[0057] A particular advantage of the device according to the invention is that both the first upsetting and the second upsetting (steps (b) to (d) of the method according to the invention) can be carried out with one and the same device, more precisely with the upsetting pot, the upsetting mandrel and the stop of the device according to the invention, as defined in this description. Thus, with the device according to the invention, neither the outer tool (upsetting pot) nor the inner tool (upsetting mandrel and stop) needs to be changed between the first upsetting and the second upsetting, which on the one hand simplifies the design of the device according to the invention, and on the other hand significantly facilitates and accelerates the implementation of two successive forming processes, in particular the implementation of the method according to the invention.The accelerated implementation also results in less cooling of the workpiece during the implementation of the method according to the invention.

[0058] The movable bearing enables relative movement of the upsetting mandrel to the upsetting pot and / or relative movement of the upsetting pot to the upsetting mandrel. The movable bearing of the upsetting mandrel allows, on the one hand, the interaction of the upsetting mandrel and the stop to achieve axial compression of the workpiece. On the other hand, the movable bearing also enables displacement of the workpiece within the holder by moving the upsetting mandrel and, if applicable, the stop. For the reasons stated above, the stop is also mounted so that it can move relative to the upsetting pot and / or vice versa.

[0059] The upsetting of the workpiece in the axial direction can be achieved by the upsetting mandrel applying a sufficiently large force to the workpiece WS located in the fixture, preferably to a first end face S1 of the workpiece WS at a first end E1 of the workpiece, in a direction parallel to the center axis MSD of the upsetting mandrel SD. The force can be applied to the workpiece WS, for example, by an upsetting edge SK or another suitable part of the upsetting mandrel SD. The force required for upsetting is determined on the one hand by the material properties (composition, structure, manufacturing process and current temperature) of the workpiece, and on the other hand by the dimensions (length and in particular wall thickness) of the workpiece.

[0060] Accordingly, the stop of the device according to the invention is designed such that it can apply a sufficiently large counterforce to the workpiece in a direction opposite to the force of the upsetting mandrel, parallel to the center axis of the upsetting mandrel. The stop preferably applies the counterforce to a second end face S2 of the workpiece WS, opposite the first end face S1, at the opposite, second end E2 of the workpiece. The counterforce can be applied to the workpiece WS, for example, by an upsetting edge AK or another suitable part of the stop AN.

[0061] In order to be able to apply the forces discussed above to the workpiece for accomplishing the upsetting and / or displacement of the workpiece in the device, the upsetting pot ST and the upsetting mandrel SD are arranged in the device V or can be arranged for the inventive forming such that the central axis MAW of the receptacle AW of the upsetting pot ST and the central axis MSD of the upsetting mandrel SD are concentric. Preferably, the upsetting pot, the upsetting mandrel, and the stop are arranged in the device or can be arranged for the inventive forming such that the central axes of the receptacle of the upsetting pot, the upsetting mandrel, and the stop are concentric. This arrangement prevents the components from tilting when moving along the central axis of the receptacle.

[0062] Preferably, the stop AN of the device according to the invention has a cylindrical section, when viewed in a sectional view in which the stop AN is cut perpendicular to its central axis MAN in the region of this section. The cylindrical section of the stop AN can be designed as a round tube or a solid cylinder and can serve as a guide section of the stop in the receptacle of the compression pot. For this purpose, at least this section of the stop preferably has an outer diameter D AN which is 0.1 to 0.3 mm, in particular 0.2 mm, smaller than the inner diameter d AW2 of the second section AW2 of the recording AW.

[0063] Advantageous embodiments are the subject of the dependent claims.

[0064] In the device according to the invention, the first force F1 and the first counterforce GF1 are each related to a first cross-sectional area A1 and can each be between 200 and 600 N / mm2 , especially between 280 and 450 N / mm 2 , The second force F2 and the second counterforce GF2 are each related to a second cross-sectional area A2 and can each be between 300 and 600 N / mm 2 , especially between 400 and 550 N / mm 2 , The first cross-sectional area A1 is calculated using the following formula: A1=π / 4⋅(D12−d12); and the second cross-sectional area A2 is calculated using the following formula: A2=π / 4⋅(dAW12−DSD22).

[0065] The inventor has determined that the first force F1 to be transmitted from the upsetting mandrel to the workpiece for carrying out a first upsetting stroke is preferably between 200 and 600 N / mm 2 , especially between 280 and 450 N / mm 2 , based on a first cross-sectional area A1, where A1 = π / 4 · (D1 2 - d1 2). The upsetting mandrel accordingly has a corresponding drive, such as a servo motor, which enables the application of such a force to the workpiece, preferably to the first end face S1 of the workpiece WS at the first end of the workpiece.

[0066] Furthermore, the inventor has determined that the second force F2 to be transmitted from the upsetting mandrel to the workpiece for carrying out a second upsetting stroke is preferably between 300 and 600 N / mm 2 , especially between 400 and 550 N / mm 2 , relative to a second cross-sectional area A2, where A2 = π / 4 · (D2 2 - d2 2 ) = π / 4 · (d AW1 2 - D SD2 2). The upsetting mandrel accordingly has a corresponding drive, such as a servo motor, which enables the application of such a force to the workpiece, preferably to the first end face S1 of the workpiece WS at the first end E1 of the workpiece.

[0067] Accordingly, the first counterforce GF1 to be transmitted from the stop AN to the workpiece for carrying out a first upsetting stroke is preferably between 200 and 600 N / mm 2 , especially between 280 and 450 N / mm 2 , relative to a first cross-sectional area A1, where A1 = π / 4 · (D1 2 - d1 2 ). Similarly, the second counterforce GF2 transmitted from the stop to the workpiece for performing a second upsetting stroke is preferably between 300 and 600 N / mm 2 , especially between 400 and 550 N / mm 2 , relative to the second cross-sectional area A2, where A2 = π / 4 · (D2 2 - d2 2 ) = π / 4 · (dAW1 2 - D SD2 2 ) is.

[0068] This enables the stop AN to hold the workpiece WS in its axial position during upsetting against the first force transmitted by the upsetting mandrel. The stop accordingly has a corresponding drive, such as a servo motor, which enables the application of such a force to the workpiece, preferably to the second end face S2 of the workpiece WS at the other end of the workpiece. The second end face S2 is located at the second end E2 of the workpiece, which is opposite the first end E1 of the workpiece with the first end face S1.

[0069] Because the upsetting mandrel and the stop are suitable for transmitting the above-described forces or counterforces in the respectively intended direction to the workpiece in the device according to the invention, it is possible, on the one hand, to hold the workpiece inserted into the device in its axial position with respect to its central axis or to displace it axially and, on the other hand, to carry out the two upsetting strokes according to steps (b) and (d) of the method according to the invention. Through the interaction of the forces acting on the workpiece by the components of the device according to the invention and the geometry of these components discussed above, compliance with the maximum forming line discussed above in each forming step can be ensured.

[0070] Furthermore, the device according to the invention can be limited in such a way that the compression pot ST, preferably the compression pot ST and the compression mandrel SD, can be tempered to a temperature between 120 and 200 °C, preferably between 140 and 160 °C; and / or that the device V has a tempering device TE for tempering the upsetting pot ST, preferably the upsetting pot ST and the upsetting mandrel SD, to a temperature between 120 and 200 °C, preferably between 140 and 160 °C; and / or that the stop AN has at least one section which has an outer diameter D AN which is 0.1 to 0.3 mm, preferably 0.2 mm, smaller than the inner diameter d AW2 of the second section AW2 of the recording AW.

[0071] Tempering the components of the device according to the invention to a temperature between 120 and 200 °C, preferably between 140 and 160 °C, significantly reduces friction between the workpiece and the device during the two upsetting strokes. Furthermore, the possibility of tempering the components of the device according to the invention is advantageous when a lubricant, for example, a water- or alcohol-based one, is used and the dispersant or solvent of the lubricant is to be removed before inserting the workpiece into the device or, at the latest, before upsetting it.

[0072] If the stop AN has at least one cylindrical section (solid cylinder or tube) having an outer diameter D AN which is 0.1 to 0.3 mm, preferably 0.2 mm, smaller than the inner diameter d AW2of the second section AW2 of the AW holder, it is ensured that the stop can be easily accommodated in the holder, more precisely by the second section AW2 of the AW holder or by an adjacent end section of the holder, even taking into account manufacturing tolerances and temperature-related dimensional changes / expansion, and can also be guided sufficiently safely during movements of the stop within the holder along the central axis of the holder.

[0073] Furthermore, the device according to the invention can comprise: a device I for heating the workpiece WS in the heating area E or in a part thereof to a temperature in the range of 700 to 1,450 °C, preferably 1,000 to 1,450 °C; wherein the device I carries out the heating of the heating area E of the workpiece WS preferably by means of induction, irradiation or flame treatment.

[0074] Heating the heating area of ​​the workpiece to a temperature within the temperature range specified above makes it possible, depending on the material composition and dimensions of the workpiece, in particular its wall thickness, to thermally soften the material of the workpiece in the heating area sufficiently to carry out the two compression strokes intended according to the invention. This applies in particular to compliance with the lower limit of the temperature range. On the other hand, compliance with the specified upper limit of the temperature range prevents, again depending on the dimensions and the material used, excessive liquefaction of the workpiece material, which would lead to one or more defined compressions, as intended to be achieved with the device according to the invention.Of course, the person skilled in the art will be able to determine, thanks to his general technical knowledge or by carrying out routine tests, the appropriate temperature required to carry out the upsetting strokes according to the invention within the claimed temperature range as a function of the material and dimensions of the workpiece once the workpiece has been selected or determined.

[0075] In order to bring the heating area of ​​the workpiece to a suitable temperature within the temperature range provided by the invention, a device which operates by induction has proven particularly useful in the experience of the inventor.

[0076] To determine the temperature of the workpiece in the heating area, the usual measures known to the person skilled in the art can be used, in particular non-contact measuring methods such as infrared thermometers.

[0077] Furthermore, the device according to the invention can be characterized in that the annular groove RN is rotationally symmetrical, zigzag-shaped or wave-shaped around the central axis MAW of the receptacle AW; and / or that the annular groove RN has a V-shaped, U-shaped, semicircular, rectangular or trapezoidal contour when viewed in a sectional view cut along the central axis MAW of the receptacle AW; and / or that the length LN of the annular groove RN at its greatest extent is 3 to 50 mm, preferably 4 to 12 mm, measured or determined or viewed or seen or defined parallel to the central axis MAW of the receptacle AW; and / or that the depth TN of the annular groove RN at the point of its greatest extent is 2 to 20 mm, preferably 3 to 10 mm, measured or determined or observed or seen or defined perpendicular to the central axis MAW of the receptacle AW. According to the invention, the depth TN of the annular groove RN is measured or determined or observed or seen or defined perpendicular to the central axis MAW of the receptacle AW at the point of its greatest extent in this direction (cf. also Fig. 5b).

[0078] The above-mentioned variants of the shape of the annular groove RN of the upsetting pot holder demonstrate the high flexibility and adaptability of the device according to the invention with regard to the shape of the projection on the outer circumferential surface of the workpiece in the heating area desired by the user of the device.

[0079] The object of the invention is further defined by the system according to claim 6.

[0080] A system S is proposed, comprising a one-piece, at least partially tubular workpiece WS made of metal and the device V for forming the workpiece WS according to one of claims 1 to 5, or consisting of a one-piece, at least partially tubular workpiece WS made of metal and the device V for forming the workpiece WS according to one of claims 1 to 5; wherein the workpiece WS has a heating area E; wherein the workpiece WS has an outer diameter D1 and an inner diameter d1 within the heating area E before forming; wherein the workpiece WS has an outer diameter D0 and an inner diameter d0 in a tubular section outside the heating region E, ie in a cold region K, before forming; wherein the device V is preferably suitable for carrying out at least steps (b), (c) and (d) of the method according to one of claims 8 to 14.

[0081] The mandatory and optional features, advantages, and modifications discussed above in connection with the device according to the invention, as well as their advantages, apply analogously to the system according to the invention. The same applies to the shape of the workpiece to be formed using the device of the system.

[0082] Furthermore, the system according to the invention can be limited in such a way that the workpiece WS can be arranged in the device V in a first arrangement such that the first section AW1 of the holder AW completely overlaps the heating area E, and the third section AW3 of the holder AW does not overlap, not even partially, with the heating area E, when viewed in a sectional view cut along the central axis MAW of the holder AW. In this case, the workpiece WS can be arranged in a second arrangement in the device V in such a way that the third section AW3 of the holder AW at least partially overlaps, preferably completely, with the heating area E, when viewed in a sectional view cut along the central axis MAW of the holder AW.Furthermore, the workpiece WS and / or the upsetting mandrel SD can be arranged in the device V in the first arrangement and in the second arrangement such that the second section SD2 of the upsetting mandrel SD completely overlaps with the heating region E, when viewed in a sectional view cut along the central axis MAW of the holder AW.

[0083] The object of the invention is further achieved by the method according to claim 8.

[0084] A method is proposed for forming a one-piece, at least partially tubular workpiece WS made of metal using the device V according to one of claims 1 to 5 or the system S according to claim 6 or 7; wherein the workpiece WS has a heating area E; wherein the workpiece WS has an outer diameter D1 and an inner diameter d1 within the heating area E before forming; wherein the workpiece WS has an outer diameter D0 and an inner diameter d0 in a tubular section outside the heating area E before forming; wherein the workpiece WS has a first cross-sectional area A1 within the heating region E; where the first cross-sectional area A1 is calculated according to the following formula: A1=π / 4⋅(D12−d12), the method comprising at least the following steps: (a) heating the heating region E of the workpiece WS to a temperature of 700 to 1,450 °C, preferably 1,000 to 1,300 °C; wherein the temperature difference between any two points on the workpiece WS within the heating region E is at most 100 °C; (b) first upsetting the workpiece WS in a direction parallel to the central axis MWS of the workpiece WS, such that the workpiece WS has a second cross-sectional area A2 in the heating region E after the first upsetting, wherein the ratio A2 / A1 of the second cross-sectional area A2 to the first cross-sectional area A1 satisfies the following condition: (A2 / A1)≤2.0, preferably (A2 / A1)≤1.6; where the second cross-sectional area A2 is calculated according to the following formula: A2=π / 4⋅(dAW12−DSD22), wherein the workpiece WS in the heating region E has a temperature of 700 to 1,450 °C, preferably of 1,000 to 1,300 °C, during the first upsetting; whereby the temperature difference between any two points on the workpiece WS within the heating range E is not more than 100 °C; wherein the workpiece WS or a part thereof including the heating area E is arranged in the receptacle AW of the upsetting pot ST of the device V during the first upsetting; wherein the workpiece WS is arranged during the first upsetting such that the central axis MWS of the workpiece WS is concentric with the central axis MAW of the holder AW of the upsetting pot ST; wherein the workpiece WS is arranged during the first upsetting such that the first section AW1 of the holder AW completely overlaps the heating area E, when viewed in a sectional view cut along the central axis MAW of the holder AW; wherein the workpiece WS is arranged during the first upsetting such that the third section AW3 of the holder AW does not overlap, not even partially overlap, with the heating area E, when viewed in a sectional view cut along the central axis MAW of the holder AW; wherein the upsetting mandrel SD of the device V or a part thereof is arranged inside the workpiece WS during the first upsetting; wherein the workpiece WS and / or the upsetting mandrel SD are / is arranged during the first upsetting such that the second section SD2 of the upsetting mandrel SD completely overlaps with the heating area E, when viewed in a sectional view cut along the central axis MAW of the holder AW; wherein the stop AN of the device V is in contact with the workpiece WS during the first upsetting; and the first upsetting is effected by the action of the upsetting mandrel SD and the stop AN on the workpiece WS; (c) after the first upsetting according to step (b) and before the second upsetting according to step (d), displacing the workpiece WS and / or the upsetting pot ST in a direction parallel to the central axis MAW of the holder AW, so that the workpiece WS is arranged such that the third section AW3 of the holder AW at least partially overlaps with the heating region E, preferably completely overlaps when viewed in a sectional view cut along the central axis MAW of the holder AW; wherein the displacement preferably takes place by moving the upsetting mandrel SD and the stop AN and / or the upsetting pot ST in a direction parallel to the central axis MAW of the holder AW; (d) second upsetting of the workpiece WS in a direction parallel to the central axis MWS of the workpiece WS, such that the workpiece WS has a third cross-sectional area A3 in the heating region E or in at least a part of the heating region E after the second upsetting, wherein the ratio (A3 / A2) of the third cross-sectional area A3 to the second cross-sectional area A2 satisfies the following condition: (A3 / A2)≤2.0, preferably (A3 / A2)≤1.6; where the third cross-sectional area A3 is calculated according to the following formula: A3=π / 4⋅(dAW32−DSD22), wherein after the first upsetting and before the second upsetting, no heating of the workpiece WS in the heating region E, preferably no heating of the workpiece WS, takes place; wherein the workpiece WS in the heating region E has a temperature of 650 to 1,200 °C, preferably 800 to 1,100 °C, during the second upsetting; wherein the workpiece WS or a part thereof including the heating region E is arranged in the receptacle AW of the upsetting pot ST of the device V during the second upsetting; wherein the workpiece WS is arranged during the second upsetting such that the central axis MWS of the workpiece WS is concentric with the central axis MAW of the holder AW of the upsetting pot ST; wherein the workpiece WS is arranged during the second upsetting such that the third section AW3 of the holder AW at least partially overlaps, preferably completely overlaps, with the heating region E when viewed in a sectional view cut along the central axis MAW of the holder AW; wherein the upsetting mandrel SD of the device V or a part thereof is arranged inside the workpiece WS during the second upsetting; and wherein the upsetting pot ST and / or the upsetting mandrel SD are / is arranged during the second upsetting such that the third section AW3 of the receptacle AW completely overlaps with the second section SD2 of the upsetting mandrel SD, when viewed in a sectional view cut along the central axis MAW of the receptacle AW; wherein the workpiece WS and / or the upsetting mandrel SD are / is arranged during the second upsetting such that the second section SD2 of the upsetting mandrel SD completely overlaps with the heating area E, when viewed in a sectional view cut along the central axis MAW of the holder AW; wherein the stop AN of the device V is in contact with the workpiece WS during the second upsetting; and The second upsetting is effected by the action of the upsetting mandrel SD and the stop AN on the workpiece WS.

[0085] In the method according to the invention, a metal workpiece is formed in or by means of the device according to the invention described above or by means of the system according to the invention.

[0086] The principle of the invention is explained below using the sequence of the method according to the invention: First, in step (a) of the method according to the invention, the heating area of ​​the metal workpiece is brought to a temperature in the range from 700 to 1,450 °C, preferably from 1,000 to 1,300 °C. This step can take place inside or outside the device according to the invention, for example by means of a device I for heating the heating area, in particular an induction device. It is important that the heating of the heating area takes place homogeneously, i.e. that the temperature difference between any two points on the workpiece within the heating area is at most 100 °C. Such a high level of homogeneity of heating is necessary in order to achieve a uniform, symmetrical upsetting result in the subsequent method steps (b) and (d).

[0087] Thus, the workpiece can either be heated in the device according to the above conditions, or the workpiece, heated in its heating area as described above, can be introduced into the device according to the invention. The workpiece can be introduced into the device, for example, by placing the workpiece in the lower part of the receptacle of the open compression pot and then closing the multi-part compression pot. Alternatively, the workpiece can be introduced from the outside through an opening in the receptacle into the closed compression pot.

[0088] Already during insertion of the workpiece into the holder, the workpiece can be arranged in the holder of the upsetting pot in such a way that the first section AW1 of the holder AW completely overlaps the heating area E, when viewed in a sectional view cut along the central axis MAW of the holder AW. Alternatively, the workpiece can also be inserted into the holder in any axial position and the workpiece can be displaced, for example with the aid of the upsetting mandrel and / or the stop, along the central axis of the holder in such a way that the overlap condition defined above or in claim 8 is met.

[0089] Subsequently, the workpiece is first upset in a direction parallel to its central axis. During the first upset, the workpiece must be positioned in the upset pot holder such that the overlap condition described above is met. This can be achieved, as explained above, by carefully placing the workpiece in the desired position in the fixture, more precisely in the upset pot holder. Alternatively, the workpiece can be placed anywhere in the holder and then moved along its central axis, for example, with the aid of the upset mandrel and / or the stop, such that the overlap condition described above is met.

[0090] The non-overlap of the third section AW3 of the receptacle AW of the upsetting pot ST with the heating region E of the workpiece WS during the first upsetting according to step (b) of the method according to the invention means an arrangement in which, when viewed in a sectional view cut along the central axis MAW of the receptacle AW, the third section AW3 of the receptacle AW and thus the annular groove RN are so far removed from the heating region E that there is no overlap, not even partial, between these two regions. The two regions can preferably be arranged relative to one another such that their edges are spaced apart from one another.

[0091] Typical non-overlapping arrangements are in Fig. 1. In Fig. 1 shows a schematic simplified representation of the lengths of the third section AW3 of the holder AW and the heating area E along the central axis MAW / MWS of the holder AW and the workpiece WS. Fig. 1a and Fig.1b shows the non-overlapping of the third section AW3 of the holder AW of the upsetting pot ST with the heating area E of the workpiece WS during the first upsetting according to step (b). Fig. Figure 1a shows an arrangement in which the third section AW3 is located away from the heating area E and does not overlap with it. In Fig. 1b, the third section AW3 and the heating area E touch each other in the respective edge area, but there is no overlap.

[0092] Furthermore, the heating zone during the first upsetting must have a temperature within the claimed temperature range, and the homogeneity of the temperature distribution within the heating zone, as defined above or in the claim, must be ensured. This is achieved by uniformly heating the workpiece in the heating zone in step (a) of the method, for example by induction, to a temperature within the specified temperature range. Depending on the material and dimensions of the workpiece (in particular, material and wall thickness), the person skilled in the art will determine the temperature within the claimed temperature range to which the heating zone is to be heated in order to achieve a suitable consistency, plasticity, or flowability for the upsetting according to claim 1.Thus, a person skilled in the art can determine the optimal temperature to which the heating zone of the specific workpiece to be formed during the upsetting processes provided for in the invention should be heated, for example, through simple experiments, computer-aided simulation programs, based on specialist literature, or their general specialist knowledge. For example, for a steel workpiece (material 1.7227 42CrMoS4 + QT) with a diameter of 58 mm and a wall thickness of 8 mm, they will choose a temperature of approximately 1,300 °C.

[0093] Since the device according to the invention makes it possible, as the inventor has already demonstrated in practical tests, to suitably position the workpiece in the receptacle of the upsetting pot within a few seconds after completion of heating and then to upsetting it a first and second time, cooling of the heating area of ​​the workpiece usually plays a subordinate role when using the device according to the invention or when carrying out the method according to the invention due to the achievable speed. Consequently, the temperature of the heating area of ​​the workpiece drops between the completion of heating and the execution of the second upsetting stroke after step (d) due to cooling in a cooler environment (specifically: the gas atmosphere surrounding the workpiece, usually at room temperature (20°C), or the upsetting pot of the device surrounding the workpiece), but not to such an extent that it would be outside the intended temperature window for the forming process.the temperature would be too low for the second compression.

[0094] Should the person skilled in the art, when setting up the method according to the invention, determine that the temperature of the heating region in the specific case, i.e., for the specific workpiece, has dropped too far, at least for the second upsetting in the device according to the invention, due to cooling in an environment cooler than the heating temperature in step (a) of the method according to the invention, and thus the workpiece in the heating region no longer has sufficient plasticity or flowability, he or she can attempt to either shorten the time period between the end of heating and the performance of the second upsetting and / or to select a higher heating temperature within the claimed range in step (a). On the other hand, the person skilled in the art will only increase the heating temperature to such an extent that the workpiece in the heating region is not too soft for the intended upsetting in step (a).When carrying out the method according to the invention, it is crucial that the temperature in the heating region E is sufficiently high for the two upsetting strokes and thus the formability if the two upsetting strokes according to the invention are carried out in quick succession.

[0095] In addition, the person skilled in the art can calculate, based on the heat capacity of the material of the workpiece to be formed, or determine by simple tests or simulations how quickly the heated workpiece cools down at the temperature of the usual or intended working environment (usually room temperature: 20 °C). In order to ensure, for a given workpiece, that the temperature of the heating area is within the claimed range and at a temperature suitable for hot forming / hot upsetting the specific workpiece in step (b), the heating temperature in step (a) will be selected such that it is at a temperature such that the heating area is sufficiently plastic, formable or flowable during the two upsetting strokes for the successive upsettings of steps (b) and (d), i.e. within the claimed temperature windows.Naturally, a person skilled in the art will take into account the properties of the specific workpiece to be processed, in particular its material properties and wall thickness, when selecting or setting the specific heating temperature. It is precisely through the use of the device according to the invention when carrying out the method according to the invention that the two upsetting strokes can be carried out one after the other within such a short time, namely within a few seconds, that problems during the second upsetting stroke due to insufficient formability caused by an excessive drop in the temperature of the workpiece in the heating area are avoided. Thus, the device according to the invention allows the two upsetting strokes in the method according to the invention to be carried out one after the other so quickly that the formability of the workpiece in the heating area does not change significantly / relevantly from the first to the second upsetting stroke.

[0096] During the first upsetting step, the workpiece deforms due to the temperature-induced plasticity or flowability of the material in the heating zone and the forces applied to the workpiece. The workpiece in the heating zone contacts the inner circumferential surface of the holder and the outer circumferential surface of the upsetting mandrel, which are each located opposite the heating zone and thus overlap with it—as seen in a sectional view cut along the workpiece's center axis. This results in a wall thickening of the workpiece within the heating zone and an overall shortening of the workpiece length, measured or determined or observed or seen or defined in the direction of its center axis.Thanks to the targeted selection of the inner diameter of the first section AW1 of the holder AW and the outer diameter of the second section SD2 of the upsetting mandrel SD, the invention allows for the targeted control and, above all, defined limitation of the wall thickening, or in other words, the cross-sectional area ratio (A2 / A1) in the heating area of ​​the workpiece during the first upsetting. Furthermore, the limitation of the wall thickening in the heating area E during the first upsetting is ensured by adhering to the non-overlap condition.

[0097] According to the invention, by limiting the cross-sectional area ratio (A2 / A1) to ≤ 2.0 or preferably ≤ 1.6, it is possible to limit the degree of deformation during the first compression to a level that, according to the inventor's knowledge, effectively prevents the formation of wrinkles on the inner circumferential surface. Compliance with the cross-sectional area ratio is achieved, on the one hand, by the specific arrangement of the workpiece in the holder, fulfilling the overlap and non-overlap conditions discussed above, and, on the other hand, by the selection of the inner diameter d AW1 of the first section AW1 of the holder AW and the outer diameter D SD2 of the second section SD2 of the compression mandrel.

[0098] During the second upsetting, the workpiece deforms due to the still existing, temperature-induced plasticity or flowability of the material in the heating area and the second forces applied to the workpiece in such a way that the workpiece in the heating area rests against the inner circumferential surface of the section of the holder that is now adjacent to the heating area, i.e. at least partially overlapping, due to the displacement of the previously performed step (c) of the method, namely the third section AW3 of the holder AW. The circumferential annular groove of the third section is filled by the material of the workpiece, whereby the projection on the outer circumferential surface of the workpiece is formed in the shape predetermined by the annular groove.In the same section of the workpiece, namely in the heating area, its inner side has been in contact with the outer circumferential surface of the upsetting mandrel since the first upsetting, and this does not change during the second upsetting. The outer circumferential surface of the upsetting mandrel remains a spatial limitation for the inward flow of the workpiece material during the second upsetting. During the second upsetting, within the heating area, due to the material projecting into the annular groove, which represents a spatial limitation for the outward flow of the workpiece material, there is a further thickening of the wall of the workpiece and a further shortening of the length of the workpiece, measured or determined or observed or seen or defined in the direction of its central axis. Thanks to the targeted choice of the inner diameter of the third section AW3 of the holder AW or.According to the invention, the shape of the annular groove and the outer diameter of the second section of the upsetting mandrel SD allows the second wall thickening or, in other words, the cross-sectional area ratio (A3 / A2) in the heating area of ​​the workpiece during the second upsetting to be specifically controlled and, above all, definedly limited.

[0099] A complete overlap of the third section AW3 of the holder AW with the heating area E of the workpiece WS during the second upsetting according to step (d) of the method according to the invention means an arrangement in which, when viewed in a sectional view cut along the central axis MAW of the holder AW, the third section AW3 of the holder AW and thus the annular groove RN are arranged relative to the heating area E in such a way that the length of the third section AW3 of the holder AW and thus of the annular groove RN, measured or determined or viewed or seen or defined parallel to the central axis MAW of the holder AW, is arranged completely within the length of the heating area E, ie that the annular groove RN of the upsetting pot ST and the heating area E of the workpiece WS completely overlap. Correspondingly, a partial overlap, e.g. 90%, means that a part, e.g. 90%, of the length of the third section AW3 of the holder AW orthe annular groove RN is arranged within the length of the heating region E, while the remaining part, e.g. 10%, is arranged outside. According to the invention, the second upsetting according to step (d) of the method according to the invention can take place as soon as there is even just a partial overlap, of e.g. 10%. Thus, when the upsetting pot ST is moved relative to the workpiece WS, the second upsetting can begin from the point in time at which the third section AW3 of the holder AW and the heating region E of the workpiece WS partially overlap, since from this point in time the space of the annular groove RN is accessible for the material moved during forming and is thus available for material reception.

[0100] So in Fig. 1c shows a partial overlap of the third section AW3 of the holder AW of the upsetting pot ST with the heating area E of the workpiece WS (approx. 50% overlap). Finally, in Fig.1d shows a complete overlap of the third section AW3 of the holder AW of the upsetting pot ST with the heating area E of the workpiece WS (100% overlap). In an analogous manner, the complete overlap of the first section AW1 of the holder AW with the heating area E (cf. Fig. 1e and Fig. 1f), of the second section SD2 of the compression mandrel SD with the heating area E (cf. Fig. 1g and Fig. 1h) or the third section AW3 of the receptacle AW with the second section SD2 of the compression mandrel SD.

[0101] In a similar way to the first upsetting, by limiting the cross-sectional area ratio (A3 / A2) to ≤ 2.0 or preferably ≤ 1.6, it is possible to limit the degree of deformation during the second upsetting to a certain level, so that, according to the inventor's findings, wrinkling on the inner circumferential surface can be effectively avoided even during further forming. Compliance with the cross-sectional area ratio is ensured, on the one hand, by the specific arrangement of the workpiece in the holder, while fulfilling the overlap condition discussed above, and, on the other hand, by the selection of the inner diameter d AW3 and the shape of the third section AW3 of the holder AW and the outer diameter D SD2 of the second section SD2 of the compression mandrel.

[0102] Overall, the method according to the invention succeeds for the first time in achieving a high degree of deformation, expressed as a cross-sectional area ratio of up to 4.0, when forming a metal workpiece that is at least partially tubular, by combining the following measures and features, without wrinkling occurring on the inner circumferential surface of the workpiece in the forming area: • Division of the forming work into at least two upsetting strokes; • Restriction to a moderate degree of deformation per upsetting stroke by a predetermined tool geometry in the vicinity of the heating area; • individual adjustment of the tool geometry in the vicinity of the heating area for each upsetting stroke; • Determination of a suitable temperature regime for each compression stroke.

[0103] Since the two upsetting strokes, apart from the displacement according to step (c), which can be carried out quickly with the device according to the invention (within 0.5 to 2.5 seconds), can be carried out practically immediately one after the other in the same device, the temperature conditions suitable for the respective forming stroke can be easily maintained.

[0104] Overall, within the scope of the method according to the invention and with the aid of the device according to the invention, the individual method steps can be carried out, for example, in the time periods listed in the following table: Step Task Duration [s] preferred duration [s] (a) Heating the heating area 2 to 20 2 to 10 (b) first compression 0.5 to 2.5 0.5 to 1.5 (c) Moving the upsetting pot or workpiece 0.5 to 2.5 0.5 to 1.5 (d) second compression 0.5 to 2 0.5 to 1 sum Heating and forming (steps (a) to (d)) 3.5 to 27 3.5 to 14 sum Forming (steps (b) to (d)) 1.5 to 7 1.5 to 4

[0105] The values ​​presented in the table clearly show that the forming steps according to the invention can be carried out within a few seconds, despite the sequencing of the upsetting strokes (b) and (d) with an intermediate displacement step (c). This means that, on the one hand, the temperature of the workpiece in the heating area required for forming can be maintained even during the second upsetting stroke, and, on the other hand, there is no longer any need to heat the heating area again before the second upsetting stroke. This significantly simplifies and shortens the process according to the invention, in particular simplifying the handling of the workpiece, since it no longer needs to be removed from the device before the second upsetting stroke. Furthermore, energy is saved by eliminating the need for a second heating step.Furthermore, the structural design of the device according to the invention can be kept simple, since the possible provision of a second device for heating the heating area and of components that would be required for reheating the workpiece in the heating area can be omitted.

[0106] Preferred embodiments of the method according to the invention are the subject of the dependent claims.

[0107] Thus, in the method according to the invention in step (a), the heating of the workpiece WS in the heating region E can be carried out by means of induction, irradiation or flame treatment, preferably by means of a device I for heating the workpiece WS; and / or the workpiece WS can rotate during heating.

[0108] The claimed heating methods, especially induction, are proven methods for heating the workpiece in the heating zone, enabling rapid and uniform heating. According to the inventor's experience, a particularly uniform heat distribution within the workpiece's heating zone can be achieved if the workpiece WS rotates during heating.

[0109] Thus, in the method according to the invention, in step (b), the first upsetting of the workpiece WS can be carried out by the upsetting mandrel SD applying a first force F1 in a direction parallel to the central axis MWS of the workpiece WS to the workpiece WS, preferably to a first end face S1 of the workpiece WS; and in that the stop AN applies a first counterforce GF1 to the workpiece WS in a direction parallel to the central axis MWS of the workpiece WS, preferably to a second end face S2 of the workpiece WS opposite the first end face S1, wherein the first counterforce GF1 is opposite to the first force F1; wherein the first force F1 relative to the first cross-sectional area A1 is preferably 200 to 600 N / mm 2 , especially 280 to 450 N / mm 2 , is; and wherein the first force F1 is preferably applied by moving the compression mandrel SD relative to the compression pot ST, preferably at a speed between 20 and 200 mm / s, in particular at a speed between 80 and 100 mm / s; and wherein the first counterforce GF1 relative to the first cross-sectional area A1 is preferably 200 to 600 N / mm 2 , especially 280 to 450 N / mm 2 , is; and wherein the first counterforce GF1 is preferably applied by the stop AN being fixed or moved relative to the compression pot ST, preferably at a speed between 0 and 200 mm / s, more preferably at a speed between 20 and 200 mm / s, in particular at a speed between 80 and 100 mm / s.

[0110] The first upsetting can be accomplished, for example, by applying the first force F1 through the upsetting mandrel, parallel to the axis, and simultaneously applying the first counterforce GF1 through the stop to the workpiece. This is particularly simple if the two forces are applied to the opposite end faces of the at least partially tubular workpiece, i.e., the first force F1 to the first end face S1 and the first counterforce GF1 to the second end face S2 of the workpiece WS. The forces to be applied naturally depend on the properties of the workpiece to be formed and are specified in relation to the first cross-sectional area A1 of the workpiece within the heating range E: 200 to 600 N / mm 2 , especially 280 to 450 N / mm 2The magnitudes of the first force F1 and the first counterforce GF1 can be equal. However, this is not necessarily the case. The two forces can also be set differently, for example, if the goal is to simultaneously shift the workpiece within the fixture while compressing it, i.e., if the compression is to be linked to a movement of the workpiece. Depending on the desired direction of movement of the workpiece within the fixture, the first force can be greater than the first counterforce, or vice versa.

[0111] Applying the force and counterforce in a direction parallel to the central axis MWS of the workpiece WS and thus parallel to the central axis of the holder has the advantage, on the one hand, that this is particularly easy to implement with regard to the design of the device according to the invention, since movement of the upsetting mandrel and / or stop only needs to be possible along one axis. On the other hand, applying the force and counterforce purely axially parallel without force vector components perpendicular to the central axis of the workpiece ensures the most uniform, rotationally symmetrical upsetting of the workpiece in the heating area in the device according to the invention when carrying out the method according to the invention. In addition, tilting of the workpiece in the holder is prevented and friction between the workpiece and the inner circumferential surface of the upsetting pot holder is minimized, thereby minimizing the energy required for forming.

[0112] In a preferred embodiment of the method according to the invention, the first force F1 is applied to the workpiece by the upsetting mandrel touching the workpiece at the first end face S1 at a first end E1 of the workpiece and moving it parallel to the center axis of the workpiece in the direction of the workpiece at a speed between 20 and 200 mm / s, in particular between 80 and 100 mm / s. The stop applies the first counterforce GF1 to the workpiece by the stop touching the workpiece at the second end face S2 at the second end E2 of the workpiece opposite the first end E1 and holding the second end E2 with respect to its axial position relative to the upsetting pot or moving it parallel to the center axis of the workpiece in the direction of the workpiece and thus in the opposite direction to the upsetting mandrel at a speed between 20 and 200 mm / s, in particular between 80 and 100 mm / s.

[0113] In the method according to the invention, the second upsetting of the workpiece WS can be carried out in step (d) by the upsetting mandrel SD applying a second force F2 in a direction parallel to the central axis MWS of the workpiece WS to the workpiece WS, preferably to a first end face S1 of the workpiece WS; and in that the stop AN applies a second counterforce GF2 to the workpiece WS in a direction parallel to the central axis MWS of the workpiece WS, preferably to a second end face S2 of the workpiece WS opposite the first end face S1, wherein the second counterforce GF2 is opposite to the second force F2; wherein the second force F2 relative to the second cross-sectional area A2 is preferably 300 to 600 N / mm 2 , especially 400 to 550 N / mm 2 , is; and wherein the second force F2 is preferably applied by moving the compression mandrel SD relative to the compression pot ST, preferably at a speed between 20 and 200 mm / s, in particular at a speed between 80 and 100 mm / s; and wherein the second counterforce GF2 relative to the second cross-sectional area A2 is preferably 300 to 600 N / mm 2 , especially 400 to 550 N / mm 2 , is; and wherein the second counterforce GF2 is preferably applied by the stop AN being fixed or moved relative to the compression pot ST, preferably at a speed between 0 and 200 mm / s, more preferably at a speed between 20 and 200 mm / s, in particular at a speed between 80 and 100 mm / s.

[0114] The forces acting on the workpiece during the second upsetting after displacement according to step (c) can be carried out in a manner analogous to the first upsetting, as described above. However, it should be noted that due to the interim, albeit slight, cooling of the workpiece in the heating area due to the time delay from the first upsetting and the resulting reduced plasticity or flowability of the workpiece's metallic material, the applied second force and / or second counterforce is / are typically larger relative to the second cross-sectional area now present in the heating area.

[0115] According to the invention, it is advantageous that both the tools—i.e., the upsetting mandrel, stop, and upsetting pot—used for the second upsetting operation can be identical to those used for the first upsetting operation. Furthermore, the same points of application of the force on the workpiece can be used for the second upsetting operation, preferably the two faces at the opposite ends of the workpiece. Both contribute to the fact that the first upsetting stroke and the second upsetting stroke can be carried out directly and in quick succession.

[0116] Furthermore, in the method according to the invention, before step (b) and / or before step (d), an outer peripheral surface of the upsetting mandrel SD and / or an inner peripheral surface of the upsetting pot ST, preferably an inner peripheral surface of the receptacle AW of the upsetting pot ST, can be wetted with a lubricant, preferably with a graphite-water mixture; and preferably the upsetting mandrel SD and / or the upsetting pot ST are heated to a temperature of 120 to 160 °C, preferably 150 °C, after wetting and before upsetting.

[0117] The use of a suitable lubricant, as described above, significantly reduces friction between the workpiece and the fixture parts. A graphite-water mixture has proven particularly suitable for the present invention, with a preferred mixing ratio of 1:4 (C:H2O). This reduces wear on the fixture parts and the energy required to carry out the process.

[0118] By optionally heating the surfaces wetted with the lubricant to the specified temperatures before upsetting, the solvent or dispersant of the lubricant can be removed quickly and sufficiently safely before upsetting.

[0119] In addition, in the process according to the invention, the compression pot ST or the compression pot ST and the compression mandrel SD can have a temperature between 120 and 200 °C, preferably between 140 and 160 °C, at least during the implementation of steps (b) and (d).

[0120] Tempering the upsetting pot ST or the upsetting pot ST and the upsetting mandrel SD to a temperature within the specified temperature range at least during the execution of steps (b) and (d) of the method also reduces tool wear during the upsetting strokes and the required upsetting energy. Furthermore, tempering the tools, in particular the upsetting pot into whose holder the workpiece is inserted, ensures that the cooling of the workpiece area heated in step (a) occurs more slowly than if the workpiece were exposed to a cooler ambient temperature, such as room temperature 20 °C.

[0121] In addition, in the method according to the invention in step (a), the duration of heating of the workpiece WS can be 2 to 20 seconds, preferably 2 to 10 seconds; and / or in step (b), the duration of the first upsetting of the workpiece WS may be 0.5 to 2.5 seconds, preferably 0.5 to 1.5 seconds; and / or in step (c), the duration of the first upsetting of the workpiece WS may be 0.5 to 2.5 seconds, preferably 0.5 to 1.5 seconds; and / or in step (d), the duration of the second upsetting of the workpiece WS may be 0.5 to 2 seconds, preferably 0.5 to 1 second; and / or steps (a), (b), (c) and (d) may be carried out together within 25 seconds, preferably 15 seconds, in particular 12 seconds.

[0122] In a particularly preferred embodiment, the individual steps of the method according to the invention, or at least some of them, are limited to the aforementioned durations. According to the inventor's findings, these durations are sufficient to carry out the individual method steps, so that the method and thus the desired overall upsetting can be carried out in a very short period of time and without the need for reheating between the two upsetting strokes, as already discussed above.

[0123] Furthermore, a one-piece, formed workpiece WS made of metal is disclosed, produced by means of the device V according to one of claims 1 to 5 or by means of the system S according to claim 6 or 7, and / or with the method according to one of claims 8 to 14, from a one-piece, at least partially tubular workpiece WS made of metal; wherein the workpiece WS has a heating area E; wherein the workpiece WS has an outer diameter D1 and an inner diameter d1 within the heating area E before forming; wherein the workpiece WS has an outer diameter D0 and an inner diameter d0 in a tubular section outside the heating area E; wherein the workpiece WS in the heating region E has a first cross-sectional area A1 before forming and a third cross-sectional area A3 after forming, wherein the ratio (A3 / A1) of the third cross-sectional area A3 to the first cross-sectional area A1 fulfills the following condition: (A3 / A1) ≤ 4.0, preferably (A3 / A1) ≤ 2.56; where the first cross-sectional area A1 is calculated according to the following formula: A1=π / 4⋅(D12−d12), where the third cross-sectional area A3 is calculated according to the following formula: A3=π / 4⋅(D32−d32), where D1 is the outer diameter of the workpiece WS in the heating area E before forming; where (d1) is the inner diameter of the workpiece WS in the heating area E before forming; where D3 is the outer diameter of the workpiece WS in the heating area E after forming; where (d3) is the inner diameter of the workpiece WS in the heating area E after forming; and wherein the workpiece WS in the heating area E after forming has no radial fold on its inner circumferential surface.

[0124] Furthermore, a one-piece, formed metal workpiece WS is disclosed, produced by means of the device V according to one of claims 1 to 5 or by means of the system S according to claim 6 or 7, and / or with the method according to one of claims 8 to 14, from a one-piece, at least partially tubular metal workpiece WS; preferably workpiece WS according to claim 15; wherein the workpiece WS has a cross-sectional area A0 in a tubular section outside a heating region E and a third cross-sectional area A3 in the heating region E, wherein the ratio (A3 / A0) of the third cross-sectional area A3 to the cross-sectional area A0 satisfies the following condition: (A3 / A0) ≤ 4.0, preferably (A3 / A0) ≤ 2.56; where the cross-sectional area A0 is calculated using the following formula: A0=π / 4⋅(D02−d02), where the third cross-sectional area A3 is calculated according to the following formula: A3=π / 4⋅(D32−d32), where D0 is the outer diameter of the workpiece WS in a tubular section outside the heating area E; where d0)is the inner diameter of the workpiece WS in a tubular section outside the heating area E before forming; where D3 is the outer diameter of the workpiece WS in the heating area E; where d3 is the inner diameter of the workpiece WS in the heating area E; and wherein the workpiece WS has no radial fold on its inner circumferential surface in the heating area E.

[0125] The particular advantage of the formed workpiece according to the invention is that, on the one hand, a high degree of deformation can be provided on a metal workpiece that is at least partially tubular and includes a projection, such as a flange, on its outer peripheral surface. The high degree of deformation is expressed by a ratio of the cross-sectional area in the formed region to the cross-sectional area at the same point on the workpiece before forming or to the cross-sectional area at another, non-formed point on the workpiece, which according to the invention is over 2.0 and up to 4.0, but at least between 2.0 and 2.65. On the other hand, the workpiece does not have any circumferential or even partially present fold in the form of a gap or crack in the region of the projection, more precisely on its inner peripheral surface in the heating region, i.e. in the region where the projection is arranged on the outside.As a result, the mechanical stability of the formed workpiece according to the invention is significantly improved compared to conventionally formed workpieces with a comparable degree of deformation, which, however, exhibit a radial fold on the inner circumferential surface in the heating region. Thus, upon further examination of the formed workpiece, for example, by applying an etching agent to the ground cut surface during a cut along the center axis of the workpiece or by another conventional method used by a person skilled in the art to visualize fiber orientations in metal structures, it can be observed that the fiber orientation in the heating region in which the deformation took place, although slightly fanned out in accordance with the degree of deformation, runs essentially parallel to the center axis of the workpiece (cf. ). Fig.4a). In contrast, the fiber paths of workpieces conventionally formed with a single upsetting stroke, which have comparable degrees of deformation, show sections in the heating area in which the fiber path clearly has a component radially outward towards the center axis of the workpiece and where the fold F is visible on the inner circumferential surface (cf. Fig. 4b).

[0126] Furthermore, the advantages discussed above in connection with the device according to the invention or with the method according to the invention also apply analogously to the workpiece formed according to the invention.

[0127] Furthermore, the workpiece WS formed according to the invention can have a projection AU on its outer circumferential surface within the heating region E.

[0128] As already discussed above in connection with the contour of the annular groove of the upsetting pot holder of the device according to the invention, the shape of the projection is also not particularly limited and can, for example, have the shape of a rectangle, a semicircle, a semi-ellipsoid, or any other desired shape with straight, curved, or freely shaped flanks. Preferably, the projection on the outer circumferential surface is rotationally symmetrical about the center axis of the workpiece. However, a non-rotationally symmetrical shape of the projection is also possible.

[0129] The shape of the overhang is also not particularly restricted with regard to its absolute dimensions. Thus, the length LA of the overhang AU, measured, determined, viewed, seen, or defined parallel to the central axis MWS of the workpiece WS, at its greatest extent can be 3 to 50 mm or more precisely < 3 to < 50 mm, preferably 4 to 12 mm or more precisely < 4 to < 12 mm, measured, determined, viewed, seen, or defined parallel to the central axis MWS of the workpiece WS (cf. Fig.5c). Additionally or independently of this, the depth TA of the projection AU, measured or determined or observed or seen or defined perpendicular to the central axis MWS of the workpiece WS, i.e. how much the projection AU projects beyond the outer peripheral surface of the workpiece in the direction perpendicular to its central axis MWS, at the point of its greatest extent can be 2 to 20 mm, more precisely < 2 to < 20 mm, preferably 3 to 10 mm, more precisely < 3 to < 10 mm. In this case, the depth TA of the projection AU is measured or determined or observed or seen or defined from the level of the outer peripheral surface of the cold area K of the workpiece adjacent to the heating area E (cf. also Fig. 5c).

[0130] The design variants of the projection AU described above demonstrate the high flexibility and adaptability of the device according to the invention with regard to the shape of the projection on the outer circumferential surface of the workpiece in the heating area desired by the user of the device.

[0131] Finally, the object of the invention is achieved by the use of claim 15. All features, advantages, and embodiments of the device according to the invention or the system according to the invention as well as the method according to the invention can also apply accordingly to the use according to the invention.

[0132] Thus, the use of the device V according to one of claims 1 to 5 or of the system S according to claim 6 or 7 for forming a one-piece, at least partially tubular workpiece WS made of metal is proposed, preferably for avoiding the formation of folds on the inner circumferential surface of the workpiece WS when forming a one-piece, at least partially tubular workpiece WS made of metal. Further disclosure of the invention

[0133] The upsetting mandrel SD and / or the stop AN of the device according to the invention can each independently have an internal pin or other centering aid for the workpiece WS. This makes it even easier to implement the above-described concentric arrangement of the various components of the device according to the invention.

[0134] The compression mandrel SD of the device according to the invention can be one- or multi-part and does not have to be made of the same material throughout. For example, the first section SD1 and the second section SD2 can be two-part and made of different materials. The same applies if a third section SD3 is also present.

[0135] The above-defined first, second, and third cross-sectional areas A1, A2, A3 of the workpiece according to the invention can also be defined, analogously to the outer and inner diameters, as a function of the location x along the center axis MWS of the workpiece WS. The following applies: (A2(x) / A1(x)) ≤ 2.0 or (A2(x) / A1(x)) ≤ 1.6 or (A3(x) / A2(x)) ≤ 2.0 or (A3(x) / A2(x)) ≤ 1.6 for each location x in the heating region E along the center axis MWS between x0 (beginning of the heating region E) and x1 (end of the heating region E). Accordingly, (A3(x) / A1(x)) ≤ 4.0 or (A3(x) / A1(x)) ≤ 2.56 applies for each point x in the heating range E along the central axis MWS between x0 (beginning of the heating range E) and x1 (end of the heating range E). Embodiments of the invention

[0136] Exemplary embodiments of the present invention are discussed below in conjunction with the accompanying drawings. The drawings attached to this application are not necessarily drawn to scale, but rather are intended to illustrate the principle underlying the present invention. Fig. 1 typical arrangements of the non-overlapping of the third section AW3 of the receptacle AW of the upsetting pot ST with the heating area E of the workpiece WS during the first upsetting according to step (b) of the method according to the invention ( Fig. 1a and Fig. 1b); typical arrangements of partial overlapping ( Fig. 1c) and complete overlapping ( Fig.1d) of the third section AW3 of the receptacle AW of the upsetting pot ST with the heating area E of the workpiece WS during the second upsetting according to step (d) of the method according to the invention; typical arrangements of the complete overlap ( Fig. 1e and Fig. 1f) of the first section AW1 of the receptacle AW of the upsetting pot ST with the heating area E of the workpiece WS during the first upsetting according to step b) of the method according to the invention; and typical arrangements of the complete overlap ( Fig. 1g and Fig. 1h) of the second section SD2 of the upsetting mandrel SD with the heating region E of the workpiece WS during the first upsetting according to step (b) and during the second upsetting according to step (d) of the method according to the invention; Fig. 2 a preferred embodiment of the method according to the invention for forming a tubular workpiece WS in a terminal heating region E thereof; Fig. 2a an undeformed, tubular workpiece WS in its initial state; Fig. 2b heating of an undeformed, tubular workpiece WS in a heating region E according to step (a) of the method according to the invention; Fig. 2c an insertion of the undeformed, tubular workpiece WS into a device V according to the invention with an open upsetting pot ST, an upsetting mandrel SD and a stop AN; Fig. 2d an arrangement of the undeformed, tubular workpiece WS in a holder AW of the upsetting pot ST with the upsetting pot ST closed and the upsetting mandrel SD and stop AN applied before the first upsetting is carried out; Fig. 2dd a detailed view of or section from the Fig. 2d; Fig.2e an arrangement of the partially formed workpiece WS in the holder AW of the upsetting pot ST with the upsetting pot ST closed and the upsetting mandrel SD and stop AN applied after carrying out the first upsetting according to step (b); Fig. 2f an arrangement of the partially formed workpiece WS in the holder AW of the upsetting pot ST with the upsetting pot ST closed and the upsetting mandrel SD and stop AN applied after carrying out the displacement according to step (c) and before carrying out the second upsetting according to step (d); Fig. 2g an arrangement of the formed workpiece WS in the holder AW of the upsetting pot ST with the upsetting pot ST closed and the upsetting mandrel SD and stop AN applied after carrying out the second upsetting according to step (d); Fig.2h an arrangement of the formed workpiece WS in the holder AW of the upsetting pot ST with the upsetting pot ST closed and the upsetting mandrel SD and stop AN applied after carrying out the second upsetting according to step (d); Fig. 2i a workpiece WS formed according to the invention; Fig. 2ii a detailed view of or section from the Fig. 2i; Fig. 3 shows a further preferred embodiment of the method according to the invention for forming a tubular workpiece WS in a non-terminal heating region E thereof ( Fig. 3a to 3i); Fig. 4a shows a simulated fiber path in a workpiece WS formed according to the invention; Fig. 4b shows a simulated fiber path in a workpiece WK formed conventionally in an upsetting stroke; Fig.5a / 5b Detailed views of the annular groove RN of the receptacle AW of the compression pot ST and for the inventive determination of the length LN and the depth TN of the annular groove RN; and Fig. 5c a detailed view of the projection AU at the forming area or heating area E of the workpiece WS and for the inventive determination of the length LA and the depth TA of the projection AU.

[0137] Fig. Figure 1 shows a simplified schematic representation of the non-overlapping, partial overlapping and complete overlapping of the third section AW3 of the holder AW of the upsetting pot ST with the heating area E of the workpiece WS. Fig. 1 shows a simplified schematic representation of the lengths of the third section AW3 of the holder AW and the heating area E along the central axis MAW / MWS of the holder AW and the workpiece WS.

[0138] In this case, Fig. 1a and Fig.1b shows the non-overlapping of the third section AW3 of the receptacle AW with the heating region E during the first compression according to step (b). Fig. Figure 1a shows an arrangement in which the third section AW3 is located away from the heating area E and does not overlap with it. Fig. 1b, the third section AW3 and the heating area E touch each other in the respective edge area, but there is no overlap. Fig. Figure 1c shows a partial overlap (approximately 50%) of the third section AW3 of the image AW and the heating area E along the central axis MAW / MWS. Finally, the Fig. 1d a complete overlap of the third section AW3 with the heating area E.

[0139] The Fig. 1e and Fig. 1f show a complete overlap of the first section AW1 of the image AW with the heating area E, where in Fig.1f the two sections AW1 and E end at the same axial position (right edge of the respective area in Fig. 1f). The Fig. 1g and Fig. 1h show a complete overlap of the second section SD2 of the compression mandrel SD with the heating area E, where in Fig. 1h the two sections SD2 and E end at the same axial position (right edge of the respective area in Fig. 1h).

[0140] Fig. Figure 2 shows an embodiment of the method according to the invention, in which a tubular workpiece WS made of metal is formed using the device according to the invention. The undeformed workpiece WS, shown in Fig. 2a, is a round tube, for example, with an outer diameter D1 of 51 mm, an inner diameter d1 of 32 mm and a wall thickness of 9.5 mm, and is made of the material 42CrMoS4 + QT. In the representation of the Fig.2, the tubular workpiece WS has a terminal heating area E, as can be seen in particular from the following detailed Fig. 2b.

[0141] In step (a) of the method according to the invention, the heating region E of the workpiece WS is heated to a temperature of, for example, 1,300 °C using a device I for heating the workpiece WS in the heating region E, which in this case is an electrically operated induction coil (cf. Fig. 2b), while the cold area K of the workpiece WS is not heated. A particularly homogeneous heating of the heating area E can be achieved, for example, by rotating the workpiece WS around its central axis MWS during heating (not shown).

[0142] After completion of step (a), the workpiece WS heated in the heating area E is placed in the opened device V according to the invention, as shown in Fig.2c, and the device V is closed by joining the multi-part compression pot ST. The closed state is shown in Fig. 2d. The device V comprises an upsetting pot ST, an upsetting mandrel SD and a stop AN. ​​The upsetting pot ST has a holder AW, which has a first section AW1, a second section AW2 and a third section AW3. The third section AW3 is arranged between the first section AW1 and the second section AW2 and is designed as a circumferential annular groove RN (here in the form of a groove with a flat base and beveled edges, in the contour). In the present example, the workpiece WS is placed in the upsetting pot such that the heating area E of the workpiece WS completely overlaps with the first section AW1, when viewed in a sectional view cut along the central axis MAW of the holder AW, as in Fig. 2c / 2d. The inner diameter dAW2 of the second section AW2 of the holder AW is 0.2 to 2% larger than the outer diameter of the workpiece outside the heating area E. This section therefore lies comparatively close to the workpiece and thus ensures good guidance or holding of the workpiece WS in the fixture V perpendicular to the central axis MWS. In contrast, the inner diameter d AW1 of the first section AW1 of the holder AW is 0.5 to 4.0% larger than the outer diameter D1 of the workpiece WS in the heating area E before forming, i.e. in the initial state, and is therefore usually larger than the inner diameter d AW2 of the second section AW2, which is particularly evident in the Fig. 2dd, which shows a detailed view of the Fig.2d. The gap SP between the outer peripheral surface of the workpiece and the receptacle in the region of the first section AW1 serves in particular to take into account the radial expansion of the workpiece in the heating region when heating it to a temperature to which the heating region E is heated according to the method according to the invention in step (a).

[0143] In the Fig. Figure 2d shows the state in which the workpiece WS, heated in the heating area E, is inserted into the device V in the axial position provided according to the invention, and the upsetting pot is closed. Furthermore, the upsetting mandrel SD and the stop AN are each positioned on an end face S1 / S2 of the tubular workpiece. The upsetting mandrel SD has an outer diameter D in the area of ​​its first section SD1. SD1 , which is 0.1 to 0.4 mm, and thus slightly smaller than the inner diameter d AW1of the first section AW1 of the AW holder. This ensures good guidance of the upsetting mandrel in the AW holder of the upsetting pot ST. In the area of ​​its second section SD2, the upsetting mandrel has an outer diameter D SD2 which is smaller than the inner diameter d1 of the workpiece, which is why the second section SD2 can be inserted into the interior of the workpiece. The transition between the second section SD2 and the first section SD1 represents a compression edge SK, which enables the application of a first force F1 to the first end face S1 of the workpiece WS at a first end E1 of the workpiece.

[0144] In the present embodiment, the stop AN has two sections, of which the section with the smaller outer diameter can be inserted into the interior of the workpiece. The transition between the two sections forms an upsetting edge AK, which enables the application of a first counterforce GF1 to a second end face S2 of the workpiece WS at a second end E2 of the workpiece, which is opposite the first end E1 of the workpiece. In the present example, the workpiece protrudes from the upsetting pot and the stop is positioned on the workpiece outside the upsetting pot. The protrusion of the workpiece from the upsetting pot is not a problem as long as the heating area E of the workpiece is completely accommodated in the upsetting pot.Accidental, uncontrolled forming of the workpiece in the protruding area is not possible because the workpiece in the protruding area has not been heated, and in particular not to the forming temperature provided for in the invention, and therefore cannot be formed despite the application of force provided for in the invention.

[0145] Alternatively, the workpiece WS can also be completely accommodated in the holder AW of the upsetting pot ST. For this purpose, a stop AN is selected whose section with the larger outer diameter has an outer diameter that is slightly smaller than the inner diameter d AW2 of the second section AW2 of the holder, so that the stop can move freely in the axial direction within the second section AW2 of the holder and is also securely guided by the inner circumferential surface of the second section AW2 of the holder.

[0146] The transition from the Fig. 2d to Fig. Figure 2e shows the execution of the first upsetting stroke according to step (b) of the method according to the invention. The first force F1 is applied to the first end face S1 of the workpiece WS by the upsetting pot ST, more precisely via its previously described upsetting edge SK, while the upsetting mandrel moves parallel to the workpiece's center axis in the direction of the workpiece (in the Fig. 2d or 2e to the left). At the same time, the stop AN applies a first counterforce GF1 to the second end face S2 of the workpiece WS via its upsetting edge AK (in the Fig.2d or 2e to the right) and thus holds the second end of the workpiece in its axial position. Due to the action of the upsetting mandrel and the stop, the workpiece in the heating area E, which has a temperature in the range provided according to the invention at the time of the first upsetting, is compressed in such a way that the material in the heating area E flows radially outwards and inwards with an increase in the wall thickness of the workpiece until it abuts the inner circumferential surface of the first section AW1 of the holder AW on the outside and the outer circumferential surface of the second section SD2 of the upsetting mandrel SD on the inside. As a result, after the first upsetting is complete, the workpiece in the heating area is shortened in its axial length and its wall thickness is increased.According to the invention, excessive compression is prevented by the claimed definition of the lower limit value for the outer diameter of the compression mandrel in the region of the second section SD2 and the upper limit value of the inner diameter d. AW2 the receptacle AW in the second section AW2 is avoided. More precisely, due to the essential limitations of the device according to the invention and the method according to the invention discussed above, the deformation of the workpiece in the heating region E can be controlled such that the cross-sectional area ratio A2 / A1 in the heating region E of the workpiece, the cross-sectional area of ​​the workpiece in the heating region E after the first upsetting and the cross-sectional area at the same point before upsetting does not exceed a value of 2.0 or preferably 1.6. This can ensure that no wrinkling occurs on the inner peripheral surface of the workpiece in the heating region.

[0147] The transition from the Fig. 2nd to Fig. 2f shows the displacement of the compression pot ST in a direction along the central axis of the holder AW relative to the workpiece (in the Fig. 2e or 2f to the right) according to step (c) of the method according to the invention. After displacement, the workpiece WS is arranged in the holder such that the third section AW3 of the holder AW, which has the annular groove RN, almost completely overlaps with the heating area E in the present example, when viewed in the Fig. 2f.

[0148] As soon as the overlap condition according to the invention is fulfilled, the second compression stroke can be carried out, which is here referred to as the transition from the Fig. 2f to Fig.2g. Analogous to the first upsetting stroke, the second force F2 is applied to the first face S1 of the workpiece WS by the upsetting pot ST, more precisely via its upsetting edge SK, while the upsetting mandrel moves parallel to the center axis MWS of the workpiece in the direction of the workpiece (in the Fig. 2f to the left).

[0149] At the same time, the stop applies a second counter force GF2 to the second face S2 of the workpiece WS (in the Fig.2f to the right) and thus holds the second end of the workpiece in its axial position. Due to the action of the upsetting mandrel and the stop, the workpiece is upset again in the heating area so that the material in the heating area flows radially outwards with a further increase in the wall thickness of the workpiece until it abuts the inner circumferential surface of the third section AW3 of the holder, i.e. the surface of the annular groove RN. Since the inside of the workpiece in the heating area E is already in contact with the outer circumferential surface of the second section SD2 of the upsetting mandrel SD from the first upsetting stroke, the second upsetting stroke essentially causes the workpiece to project outwards into the annular groove RN, while the inside remains essentially unchanged. In addition, the axial length of the workpiece is further shortened with the second upsetting stroke.During the second upsetting stroke, the temperature of the heating region E is reduced compared to the first upsetting stroke due to cooling through heat dissipation into the workpiece's surroundings, since the second upsetting stroke is performed after the first upsetting stroke. However, if the temperature condition of the heating region defined in step (d) is maintained, to the inventor's knowledge, the heating region is still sufficiently plastic or flowable and thus formable at the time the second upsetting stroke is performed. The design of the device according to the invention and the sequence of the method according to the invention allow the two consecutive upsetting strokes to be performed so quickly that a sufficiently high temperature is still ensured in the heating region of the workpiece during the second upsetting stroke in order to perform the second upsetting stroke while achieving the desired degree of deformation.

[0150] Thanks to the targeted selection of the shape of the third section AW3 of the holder AW and the supporting function of the second section SD2 of the upsetting mandrel SD on the inner peripheral surface of the workpiece in the heating region E, a further wall thickening in the heating region E can be achieved according to the invention, forming the projection AU on the outer peripheral surface of the workpiece. Due to the device and method conditions according to the invention, as defined in the independent claims, it is ensured that the cross-sectional area ratio A3 / A2 in the heating region E, i.e. the ratio of the cross-sectional area of ​​the workpiece in the heating region after the second upsetting to the cross-sectional area at the same point after the first upsetting, does not exceed a value of 2.0 or preferably 1.6.This ensures that no wrinkles will form on the inner peripheral surface of the workpiece in the heating area E even during the second upsetting.

[0151] The Fig. Figure 2g shows the workpiece formed with two upsetting strokes after completion of the second upsetting stroke in the closed fixture. In the example considered here, the outer diameter D3 of the workpiece WS in the heating area E in the projection area is 63 mm, the inner diameter d3 is 26 mm, and the wall thickness is 17.25 mm. This results in a total degree of deformation, i.e. the cross-sectional area ratio A3 / A1 in the heating area E of 2.09. In the next step ( Fig. 2h) the formed workpiece WS is exposed by removing the stop AN and the upsetting mandrel SD from the device V and opening the upsetting pot ST. Finally, Fig. 2i and in the detailed view of the Fig.2ii shows the workpiece formed according to the invention with the wall thickening in the heating area E and the projection AU on the outer peripheral surface of the workpiece WS.

[0152] The Fig. 3, more precisely the Fig. 3a to 3i, represent a further preferred embodiment of the method according to the invention, in which a tubular workpiece is formed with a non-terminal heating region E. In the following description, all features, circumstances and conditions that are identical to the Fig. 2 are omitted for the sake of simplicity and only differences to this embodiment are described.

[0153] As can be seen in particular from the Fig.As can be seen in Figure 3b, the undeformed, tubular workpiece WS is not heated at its first end, but rather the heating region E is located inside. A first cold region K1 is located between the heating region E and the first end E1 of the workpiece WS, while a second cold region K2 is located between the heating region E and the second end E2 of the workpiece WS.

[0154] The compression mandrel SD used for forming according to the present embodiment of the device according to the invention has, in addition to the above-described first section SD1 and second section SD2, a third section SD3, which represents a transition from the first section SD1 to the second section SD2. The third section SD3 has a length that approximately corresponds to the length of the first cold region K1 of the workpiece when viewed in a sectional view in which the compression mandrel SD is cut perpendicular to its central axis MSD. The outer diameter D SD3of the third section SD3 is 0.2 to 2.0% smaller than the inner diameter d0 of the workpiece in the first cold area K1. The presence of the third section SD3 improves the holding or guidance of the workpiece WS in the holder AW and limits the flow possibilities of the workpiece material in a direction parallel to the central axis MWS of the workpiece WS at the boundary between the heating area E and the first cold area K1 during the first and second upsetting (see in particular Fig. 3d). The individual procedural steps described in the Fig. 3b to 3h are shown, are analogous to the ones shown in the Fig. 2b to 2h and described above are carried out. In particular, the overlap and non-overlap conditions defined above and in the claims also apply to this embodiment, as with all embodiments of the invention.

[0155] Finally, in Fig.3i shows the workpiece WS formed according to this embodiment with the wall thickening in the non-terminal heating area E and the projection AU on the outer circumferential surface of the workpiece WS.

[0156] The Fig. Figure 4a shows a simulated fiber path in the forming area of ​​a workpiece WS formed according to the invention with a total of two strokes. As can be seen, the fiber path in the area where the forming took place fans out slightly according to the degree of forming, but runs essentially parallel to the center axis of the workpiece (see Figure 4a). Fig. 4a). In addition, the inner peripheral surface of the workpiece in the heating / forming area is smooth and without wrinkles.

[0157] If, however, the same workpiece is formed under the same conditions in a single upsetting stroke, with approximately the same total degree of deformation of > 2 (ratio of the cross-sectional areas before and after forming), then the grain of a workpiece WK formed in this way clearly exhibits a component radially outward toward the center axis of the workpiece WK, particularly near the inner circumferential surface of the workpiece WK in the forming area. In addition, a fold F is clearly visible on the inner circumferential surface of the workpiece WK (see Fig. 4b).

[0158] To clarify the dimensions of the annular groove RN of the AW holder, the detailed views of the Fig. 5a and Fig. 5b. This shows Fig. 5a a section of the sectional view of the Fig. 2d, where the tubular workpiece WS is accommodated in the holder AW of the upsetting pot ST. Furthermore, the upsetting mandrel SD, the end section of which is shown on the right in the Fig.5a, is introduced into the interior of the workpiece WS. As can be seen further, the annular groove RN, which is formed in the area of ​​the third section AW3 of the holder AW of the upsetting pot ST, is rotationally symmetrical about the central axis of the holder MAW, which is simultaneously the central axis MWS of the workpiece WS and the central axis MSD of the upsetting mandrel SD. As can be seen in the further detailed view of the Fig. 5b, the first section AW1 and the second section AW2 of the receptacle AW of the compression pot ST are arranged to the right and left of the third section AW3 of the receptacle AW of the compression pot ST. According to the invention, the length LN of the annular groove RN is measured or determined or observed or seen or defined at the point of its greatest extent parallel to the central axis MAW of the receptacle AW (see also Fig.5b). In the device V according to the invention, the length LN of the annular groove RN is typically and preferably identical to the length of the third section AW3 of the receptacle AW, measured or determined or viewed or seen or defined parallel to the central axis MAW of the receptacle AW. However, the device V according to the invention is not limited to this, since the third section AW3 of the receptacle AW can have a greater length than the length LN of the annular groove RN.

[0159] According to the invention, the depth TN of the annular groove RN is measured or determined or observed or seen or defined perpendicular to the central axis (MAW) of the receptacle (AW) at the point of its greatest extent in this direction (see also Fig. 5b). As can be seen from the Fig. 5b, the depth TN of the annular groove RN is between the level (horizontal dashed line in the Fig.5b) the inner circumferential surface of the second section (AW2) of the receptacle (AW) and the groove base of the annular groove RN are measured or determined or observed or seen or defined, perpendicular to the central axis MAW of the receptacle AW. The length LN and depth TN of the annular groove RN, as defined and determined according to the invention, are shown in the Fig. 5b indicated by double arrows.

[0160] Analogous to the above description of the annular groove RN and its dimensions, Fig. 5c an enlarged section of the Fig.2i, which represents the overhang AU at the forming area or heating area E of the workpiece WS formed according to the invention with two upsetting strokes. According to the invention, the length LA of the overhang AU at the point of its greatest extent parallel to the central axis MWS of the workpiece WS can be 3 to 50 mm or more precisely <3 to <50 mm, preferably 4 to 12 mm or more precisely <4 to <12 mm, measured or determined or viewed or seen or defined parallel to the central axis MWS of the workpiece WS. In addition, according to the invention, the depth TA of the overhang AU at the point of its greatest extent can be 2 to 20 mm, more precisely <2 to <20 mm, preferably 3 to 10 mm, more precisely <3 to <10 mm, measured or determined or viewed or seen or defined perpendicular to the central axis MWS of the workpiece WS. According to the invention, the depth TA of the projection AU is or is measured from the level of the outer circumferential surface of the cold area K adjacent to the heating area E.determined or considered or seen or defined (horizontal dashed line in the . Fig. 5c). Strictly speaking, the projection AU in the technically real embodiment of the invention must have slightly smaller dimensions in terms of its length and depth than the corresponding dimension of the annular groove with the aid of which it was formed. To express this, the "more precise" ranges < 3 to < 50 mm / < 4 to < 12 mm / < 2 to < 20 mm / < 3 to < 10 mm are also given above. The length LA and depth TA of the projection AU, as defined and determined according to the invention, are in the Fig. 5c indicated by double arrows.

Claims

[1] Device (V) for forming a one-piece, at least partially tubular workpiece (WS) made of metal, wherein the workpiece (WS) has a heating area (E); wherein the workpiece (WS) has an outer diameter (D1) and an inner diameter (d1) within the heating region (E) before forming; wherein the workpiece (WS) has an outer diameter (D0) and an inner diameter (d0) in a tubular section outside the heating region (E) before forming; wherein the device (V) comprises at least: a compression pot (ST); a compression mandrel (SD); and an attack (AN); wherein the compression pot (ST) is multi-part, preferably two-part; wherein the upsetting pot (ST) has a receptacle (AW) for receiving the entire workpiece (WS) or at least a part of the workpiece (WS) including a heating region (E) of the workpiece (WS); wherein the receptacle (AW) has a first section (AW1), a second section (AW2) and a third section (AW3) along the central axis (MAW) of the receptacle (AW); where the inner diameter (d AW1 ) of the first section (AW1) of the holder (AW) is 1.005 times to 1.040 times the outer diameter (D1) of the workpiece (WS) in the heating area (E) before forming; where the inner diameter (d AW2 ) of the second section (AW2) of the holder (AW) is 1.002 times to 1.020 times the outer diameter (D0) of the workpiece (WS) in a tubular section outside the heating area (E) before forming; wherein the third section (AW3) of the receptacle (AW) is arranged between the first section (AW1) of the receptacle (AW) and the second section (AW2) of the receptacle (AW); wherein the third section (AW3) of the receptacle (AW) is formed as a circumferential annular groove (RN); where the inner diameter (d AW3 ) of the third section (AW3) of the holder (AW) is larger than the inner diameter (d AW1 ) of the first section (AW1) of the recording (AW); where the inner diameter (d AW3 ) of the third section (AW3) of the holder (AW) is larger than the inner diameter (d AW2 ) of the second section (AW2) of the recording (AW); wherein the length of the first section (AW1) of the holder (AW), measured parallel to the central axis (MAW) of the holder (AW), is greater than the length of the heating region (E) of the workpiece (WS), measured parallel to the central axis (MWS) of the workpiece (WS); wherein the compression mandrel (SD) has a first section (SD1) and a second section (SD2) along the central axis (MSD) of the compression mandrel (SD); wherein the compression mandrel (SD) in the region of the first section (SD1) has an outer diameter (D SD1 ) which is 0.1 to 0.4 mm, preferably 0.2 to 0.3 mm, smaller than the inner diameter (d AW1 ) of the first section (AW1) of the recording (AW); wherein the compression mandrel (SD) in the region of the second section (SD2) has an outer diameter (D SD2 ) which satisfies the following condition: DSD2≥−2.0⋅(D12−d12)+dAW12, preferably DSD2≥−1.6⋅(D12−d12)+dAW12, wherein the length of the second section (SD2) of the compression mandrel (SD), measured parallel to the central axis (MSD) of the compression mandrel (SD), is at least 1.1 times the length of the heating region (E), measured parallel to the central axis (MWS) of the workpiece (WS); where the inner diameter (d AW3 ) of the recording (AW) in the third section (AW3) meets the following condition: dAW3≤2.0⋅dAW12−DSD22, preferably dAW3≤1.6⋅dAW12−1.6⋅DSD22; wherein the upsetting mandrel (SD) is / are movably mounted relative to the upsetting pot (ST) and / or the upsetting pot (ST) is / are movably mounted relative to the upsetting mandrel (SD); wherein the compression mandrel (SD) is movably mounted in a direction parallel to the central axis (MAW) of the holder (AW); wherein the upsetting mandrel (SD) is suitable for applying a first force (F1) and a second force (F2) to the workpiece (WS), preferably to a first end face (S1) of the workpiece (WS), in a direction parallel to the central axis (MSD) of the upsetting mandrel (SD); wherein the stop (AN) is / are movably mounted relative to the compression pot (ST) and / or the compression pot (ST) is / are movably mounted relative to the stop (AN); wherein the stop (AN) is suitable for applying a first counterforce (GF1) and a second counterforce (GF2) to the workpiece (WS), preferably to a second end face (S2) of the workpiece (WS) opposite the first end face (S1), in a direction parallel to the central axis (MSD) of the upsetting mandrel (SD); wherein the first counterforce (GF1) is opposite to the first force (F1) and the second counterforce (GF2) is opposite to the second force (F2); wherein the upsetting pot (ST) and the upsetting mandrel (SD) are arranged or can be arranged in the device (V) in such a way that the central axis (MAW) of the receptacle (AW) of the upsetting pot (ST) and the central axis (MSD) of the upsetting mandrel (SD) are concentric. [2] Device according to claim 1, wherein the first force (F1) and the first counterforce (GF1) are each related to a first cross-sectional area (A1) and are each between 200 and 600 N / mm 2 , especially between 280 and 450 N / mm 2, and wherein the second force (F2) and the second counterforce (GF2) are each related to a second cross-sectional area (A2) and each between 300 and 600 N / mm 2 , especially between 400 and 550 N / mm 2 , and where the first cross-sectional area (A1) is calculated according to the following formula: A1=π / 4⋅(D12−d12); and where the second cross-sectional area (A2) is calculated according to the following formula: A2=π / 4⋅(dAW12−DSD22). [3] Device according to claim 1 or 2, wherein the upsetting pot (ST), preferably the upsetting pot (ST) and the upsetting mandrel (SD), can be tempered to a temperature between 120 and 200 °C, preferably between 140 and 160 °C; and / or wherein the device (V) has a tempering device (TE) for tempering the upsetting pot (ST), preferably the upsetting pot (ST) and the upsetting mandrel (SD), to a temperature between 120 and 200 °C, preferably between 140 and 160 °C; and / or wherein the stop (AN) has at least one section which has an outer diameter (D AN ) which is 0.1 to 0.3 mm, preferably 0.2 mm, smaller than the inner diameter (d AW2 ) of the second section (AW2) of the recording (AW). [4] Device according to one of claims 1 to 3, wherein the device (V) further comprises: a device (I) for heating the workpiece (WS) in the heating region (E) or in a part thereof to a temperature in the range of 700 to 1,450 °C, preferably 1,000 to 1,450 °C; wherein the device (I) carries out the heating of the heating region (E) of the workpiece (WS) preferably by means of induction, irradiation or flame treatment. [5] Device according to one of claims 1 to 4, wherein the annular groove (RN) is rotationally symmetrical, zigzag-shaped or wave-shaped around the central axis (MAW) of the receptacle (AW); and / or wherein the annular groove (RN) has a V-shaped, U-shaped, semicircular, rectangular or trapezoidal contour when viewed in a sectional view cut along the central axis (MAW) of the receptacle (AW); and / or wherein the length (LN) of the annular groove (RN) at its point of greatest extent is 3 to 50 mm, preferably 4 to 12 mm, measured parallel to the central axis (MAW) of the receptacle (AW); and / or wherein the depth (TN) of the annular groove (RN) at the point of its greatest extent is 2 to 20 mm, preferably 3 to 10 mm, measured perpendicular to the central axis (MAW) of the receptacle (AW). [6] System (S) comprising a one-piece, at least partially tubular workpiece (WS) made of metal and the device (V) for forming the workpiece (WS) according to one of claims 1 to 5, or consisting of a one-piece, at least partially tubular workpiece (WS) made of metal and the device (V) for forming the workpiece (WS) according to one of claims 1 to 5; wherein the workpiece (WS) has a heating area (E); wherein the workpiece (WS) has an outer diameter (D1) and an inner diameter (d1) within the heating region (E) before forming; wherein the workpiece (WS) has an outer diameter (D0) and an inner diameter (d0) in a tubular section outside the heating region (E) before forming; wherein the device (V) is preferably suitable for carrying out at least steps (b), (c) and (d) of the method according to one of claims 8 to 14. [7] System (S) according to claim 6, wherein the workpiece (WS) can be arranged in a first arrangement in the device (V) such that the first section (AW1) of the holder (AW) completely overlaps the heating area (E), and the third section (AW3) of the holder (AW) does not overlap, not even partially, with the heating area (E), when viewed in a sectional view cut along the central axis (MAW) of the holder (AW); and wherein the workpiece (WS) can be arranged in a second arrangement in the device (V) such that the third section (AW3) of the holder (AW) at least partially overlaps the heating area (E), preferably completely overlapped when viewed in a sectional view cut along the central axis (MAW) of the receptacle (AW); and wherein the workpiece (WS) and / or the upsetting mandrel (SD) can be arranged in the device (V) in the first arrangement and in the second arrangement such that the second section (SD2) of the upsetting mandrel (SD) completely overlaps with the heating area (E), when viewed in a sectional view cut along the central axis (MAW) of the holder (AW). [8] Method for forming a one-piece, at least partially tubular workpiece (WS) made of metal using the device (V) according to one of claims 1 to 5 or the system (S) according to claim 6 or 7; wherein the workpiece (WS) has a heating area (E); wherein the workpiece (WS) has an outer diameter (D1) and an inner diameter (d1) within the heating region (E) before forming; wherein the workpiece (WS) has an outer diameter (D0) and an inner diameter (d0) in a tubular section outside the heating region (E) before the forming; wherein the workpiece (WS) has a first cross-sectional area (A1) within the heating region (E); where the first cross-sectional area (A1) is calculated according to the following formula: A1=π / 4⋅(D12−d12), the method comprising at least the following steps: (a) heating the heating region (E) of the workpiece (WS) to a temperature of 700 to 1,450 °C, preferably 1,000 to 1,300 °C; wherein the temperature difference between any two points on the workpiece (WS) within the heating region (E) is at most 100 °C; (b) first upsetting the workpiece (WS) in a direction parallel to the central axis (MWS) of the workpiece (WS), such that the workpiece (WS) has a second cross-sectional area (A2) in the heating region (E) after the first upsetting, wherein the ratio (A2 / A1) of the second cross-sectional area (A2) to the first cross-sectional area (A1) satisfies the following condition: (A2 / A1)≤2.0, preferably (A2 / A1)≤1.6; where the second cross-sectional area (A2) is calculated according to the following formula: A2=π / 4⋅(dAW12−DSD22), wherein the workpiece (WS) in the heating region (E) has a temperature of 700 to 1,450 °C, preferably 1,000 to 1,300 °C, during the first upsetting; wherein the temperature difference between any two points on the workpiece (WS) within the heating area (E) is not more than 100 °C; wherein the workpiece (WS) or a part thereof including the heating region (E) is arranged in the receptacle (AW) of the upsetting pot (ST) of the device (V) during the first upsetting; wherein the workpiece (WS) is arranged during the first upsetting such that the central axis (MWS) of the workpiece (WS) is concentric with the central axis (MAW) of the holder (AW) of the upsetting pot (ST); wherein the workpiece (WS) is arranged during the first upsetting such that the first section (AW1) of the holder (AW) completely overlaps with the heating area (E), when viewed in a sectional view cut along the central axis (MAW) of the holder (AW); wherein the workpiece (WS) is arranged during the first upsetting such that the third section (AW3) of the holder (AW) does not overlap, even partially overlap, with the heating area (E) when viewed in a sectional view cut along the central axis (MAW) of the holder (AW); wherein the upsetting mandrel (SD) of the device (V) or a part thereof is arranged inside the workpiece (WS) during the first upsetting; wherein the workpiece (WS) and / or the upsetting mandrel (SD) are / is arranged during the first upsetting such that the second section (SD2) of the upsetting mandrel (SD) completely overlaps with the heating region (E), when viewed in a sectional view cut along the central axis (MAW) of the holder (AW); wherein the stop (AN) of the device (V) is in contact with the workpiece (WS) during the first upsetting; and wherein the first upsetting is effected by the action of the upsetting mandrel (SD) and the stop (AN) on the workpiece (WS); (c) after the first upsetting according to step (b) and before the second upsetting according to step (d), displacing the workpiece (WS) and / or the upsetting pot (ST) in a direction parallel to the central axis (MAW) of the holder (AW), so that the workpiece (WS) is arranged such that the third section (AW3) of the holder (AW) at least partially overlaps the heating region (E), preferably completely overlaps it, when viewed in a sectional view cut along the central axis (MAW) of the holder (AW); wherein the displacement is preferably carried out by moving the upsetting mandrel (SD) and the stop (AN) and / or the upsetting pot (ST) in a direction parallel to the central axis (MAW) of the holder (AW); (d) second upsetting of the workpiece (WS) in a direction parallel to the central axis (MWS) of the workpiece (WS), such that the workpiece (WS) has a third cross-sectional area (A3) in the heating region (E) or in at least a part of the heating region (E) after the second upsetting, wherein the ratio (A3 / A2) of the third cross-sectional area (A3) to the second cross-sectional area (A2) satisfies the following condition: (A3 / A2)≤2.0, preferably (A3 / A2)≤1.6; where the third cross-sectional area (A3) is calculated according to the following formula: A3=π / 4⋅(dAW32−DSD22), wherein after the first upsetting and before the second upsetting, no heating of the workpiece (WS) in the heating region (E), preferably no heating of the workpiece (WS), takes place; wherein the workpiece (WS) in the heating region (E) has a temperature of 650 to 1,200 °C, preferably 800 to 1,100 °C, during the second upsetting; wherein the workpiece (WS) or a part thereof including the heating region (E) is arranged in the receptacle (AW) of the upsetting pot (ST) of the device (V) during the second upsetting; wherein the workpiece (WS) is arranged during the second upsetting such that the central axis (MWS) of the workpiece (WS) is concentric with the central axis (MAW) of the holder (AW) of the upsetting pot (ST); wherein the workpiece (WS) is arranged during the second upsetting such that the third section (AW3) of the holder (AW) at least partially overlaps with the heating region (E), preferably completely overlaps when viewed in a sectional view cut along the central axis (MAW) of the holder (AW); wherein the upsetting mandrel (SD) of the device (V) or a part thereof is arranged inside the workpiece (WS) during the second upsetting; and wherein the upsetting pot (ST) and / or the upsetting mandrel (SD) are / is arranged during the second upsetting such that the third portion (AW3) of the receptacle (AW) completely overlaps with the second portion (SD2) of the upsetting mandrel (SD), when viewed in a sectional view cut along the central axis (MAW) of the receptacle (AW); wherein the workpiece (WS) and / or the upsetting mandrel (SD) are / is arranged during the second upsetting such that the second section (SD2) of the upsetting mandrel (SD) completely overlaps with the heating area (E), when viewed in a sectional view, cut along the central axis (MAW) of the receptacle (AW); wherein the stop (AN) of the device (V) is in contact with the workpiece (WS) during the second upsetting; and wherein the second upsetting is effected by the action of the upsetting mandrel (SD) and the stop (AN) on the workpiece (WS). [9] Method according to claim 8, wherein in step (a) the heating of the workpiece (WS) in the heating region (E) is carried out by means of induction, irradiation or flame treatment, preferably by means of a device (I) for heating the workpiece (WS); and / or wherein the workpiece (WS) rotates during heating. [10] Method according to claim 8 or 9, wherein in step (b) the first upsetting of the workpiece (WS) is carried out by the upsetting mandrel (SD) applying a first force (F1) in a direction parallel to the central axis (MWS) of the workpiece (WS) to the workpiece (WS), preferably to a first end face (S1) of the workpiece (WS); and in that the stop (AN) applies a first counterforce (GF1) to the workpiece (WS) in a direction parallel to the central axis (MWS) of the workpiece (WS), preferably to a second end face (S2) of the workpiece (WS) opposite the first end face (S1), the first counterforce (GF1) being opposite to the first force (F1); wherein the first force (F1) relative to the first cross-sectional area (A1) is preferably 200 to 600 N / mm 2 , especially 280 to 450 N / mm 2 , and wherein the first force (F1) is preferably applied by moving the compression mandrel (SD) relative to the compression pot (ST), preferably at a speed between 20 and 200 mm / s, in particular at a speed between 80 and 100 mm / s; and wherein the first counterforce (GF1) relative to the first cross-sectional area (A1) is preferably 200 to 600 N / mm 2 , especially 280 to 450 N / mm 2, and wherein the first counterforce (GF1) is preferably applied by the stop (AN) being fixed or moved relative to the compression pot (ST), preferably at a speed between 0 and 200 mm / s, more preferably at a speed between 20 and 200 mm / s, in particular at a speed between 80 and 100 mm / s. [11] Method according to one of claims 8 to 10, wherein in step (d) the second upsetting of the workpiece (WS) is carried out by the upsetting mandrel (SD) applying a second force (F2) in a direction parallel to the central axis (MWS) of the workpiece (WS) to the workpiece (WS), preferably to a first end face (S1) of the workpiece (WS); and in that the stop (AN) applies a second counterforce (GF2) to the workpiece (WS) in a direction parallel to the central axis (MWS) of the workpiece (WS), preferably to a second end face (S2) of the workpiece (WS) opposite the first end face (S1), the second counterforce (GF2) being opposite to the second force (F2); wherein the second force (F2) relative to the second cross-sectional area (A2) is preferably 300 to 600 N / mm 2 , especially 400 to 550 N / mm 2 , and wherein the second force (F2) is preferably applied by moving the compression mandrel (SD) relative to the compression pot (ST), preferably at a speed between 20 and 200 mm / s, in particular at a speed between 80 and 100 mm / s; and wherein the second counterforce (GF2) relative to the second cross-sectional area (A2) is preferably 300 to 600 N / mm 2 , especially 400 to 550 N / mm 2, and wherein the second counterforce (GF2) is preferably applied by the stop (AN) being fixed or moved relative to the compression pot (ST), preferably at a speed between 0 and 200 mm / s, more preferably at a speed between 20 and 200 mm / s, in particular at a speed between 80 and 100 mm / s. [12] Method according to one of claims 8 to 11, wherein before step (b) and / or before step (d) an outer peripheral surface of the upsetting mandrel (SD) and / or an inner peripheral surface of the upsetting pot (ST), preferably an inner peripheral surface of the receptacle (AW) of the upsetting pot (ST), is / are wetted with a lubricant, preferably with a graphite-water mixture; and preferably the upsetting mandrel (SD) and / or the upsetting pot (ST) is / are heated to a temperature of 120 to 160 °C, preferably 150 °C, after wetting and before upsetting. [13] Method according to one of claims 8 to 12, wherein the upsetting pot (ST) or the upsetting pot (ST) and the upsetting mandrel (SD) have a temperature between 120 and 200 °C, preferably between 140 and 160 °C, at least during the execution of steps (b) and (d). [14] Method according to one of claims 8 to 13, wherein in step (a) the duration of heating of the workpiece (WS) is 2 to 20 seconds, preferably 2 to 10 seconds; and / or wherein in step (b) the duration of the first upsetting of the workpiece (WS) is 0.5 to 2.5 seconds, preferably 0.5 to 1.5 seconds; and / or wherein in step (c) the duration of the first upsetting of the workpiece (WS) is 0.5 to 2.5 seconds, preferably 0.5 to 1.5 seconds; and / or wherein in step (d) the duration of the second upsetting of the workpiece (WS) is 0.5 to 2 seconds, preferably 0.5 to 1 second; and / or wherein steps (a), (b), (c) and (d) are carried out together within 25 seconds, preferably 15 seconds, in particular 12 seconds. [15] Use of the device (V) according to one of claims 1 to 5 or of the system (S) according to claim 6 or 7 for forming a one-piece, at least partially tubular workpiece (WS) made of metal, preferably for avoiding the formation of wrinkles when forming a one-piece, at least partially tubular workpiece (WS) made of metal.

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