Method for the forming production of a hollow shaft

Abstract

Method for forming the production of a hollow shaft (200) having a bore (210) with at least three bore sections (211-217) differing in cross-section, comprising the following process steps: - Providing a rotationally symmetrical preform (100) with an internal bore (110), wherein this preform (100) is a forging; - Heating the preform (100); and - Radial forming of the heated preform (100) to simultaneously produce an outer shape and an inner bore shape, wherein the inner bore shape is produced using a multifunctional mandrel (410) which has at least three mandrel sections (411-413) that differ in cross-section, and wherein the preform (100) is elongated at least twice in the axial direction (L).

Description

[0001] The invention relates to a method for the forming production of a hollow shaft which has several bore sections that differ in cross-section.

[0002] Hollow shafts of the aforementioned type are further processed, in particular, into transmission shafts for vehicle transmissions.

[0003] German patent application DE 10 2008 036 226 A1 discloses a method for manufacturing a hollow shaft from semi-finished products, comprising a sequence of process steps that enables the optimal production of a hollow shaft in mass production with regard to manufacturing time, material and resource consumption, and investment costs. The method includes the following steps: producing a preform by forging; performing a heat treatment on the preform; forming the preform into an at least partially hollow intermediate form by bore forming; and rotary swaging of the intermediate form into a hollow shaft with a substantially uniform wall thickness along the length of the hollow shaft.

[0004] The invention was based on the objective of providing a further advantageous method for manufacturing a hollow shaft of the type mentioned above.

[0005] This problem is solved by a method according to the invention with the features of claim 1. Preferred further developments and embodiments result analogously for all subject matter of the invention both from the dependent claims and from the following explanations.

[0006] For an understanding of the invention, explicit reference is also made to the explanations in DE 10 2008 036 226 A1 of the same applicant.

[0007] WO 2011 / 120062 A1 discloses a method for manufacturing wheel axles. EP 0 721 816 B1 discloses a method for manufacturing a hollow profile, and DE 10 2007 018 184 A1 discloses a method for manufacturing a workpiece that is at least partially hollow.

[0008] The inventive method for forming a hollow shaft which has a bore with at least three bore sections differing in cross-section (i.e., in cross-sectional size and / or shape) comprises at least the following process steps: - Providing a rotationally symmetrical preform with an internal bore, wherein this preform is a forging; - Heating the preform; and - Radial forming of the heated preform to simultaneously produce an outer shape and an inner bore shape, wherein the inner bore shape is produced using at least one multifunctional mandrel which has at least three mandrel sections with different cross-sections, and the preform is elongated at least twice in the axial direction.

[0009] Radial forming, performed on a radial forming machine, is an incremental forming process similar to rotary swaging. In this process, the workpiece, which has an internal bore, is plastically deformed by several, and in particular four, pulsating pressure hammers or radial hammers that deliver synchronous radial blows to the workpiece. The workpiece rotates together with an internal mandrel relative to the hammers. The material is formed radially onto the internal mandrel located in the internal bore, which, according to the invention, is designed as a multifunctional mandrel. It is also deformed axially along the internal mandrel or multifunctional mandrel, so that the material flows in a defined manner in at least one axial direction along the multifunctional mandrel. This results in axial elongation of the workpiece, so that the finished hollow shaft has a significantly greater axial length than the preform.In particular, the length ratio is > 2 (greater than two), meaning the preform is elongated at least twice, and especially at least 2.5 or 3 times, in the axial direction during radial forming. The main direction of deformation is generally the axial direction, achieving high degrees of deformation, e.g., Phi > 3 (greater than three). Preferably, the preform is elongated in both axial directions during radial forming, i.e., undergoes an axial change in length caused by deformation.

[0010] The hollow shaft to be manufactured has several bore sections with differing cross-sections, meaning axial sections arranged one after the other in the axial direction of the hollow shaft. The individual axial sections fulfill different functions, as explained in more detail below. According to the invention, the internal bore shape of the hollow shaft is produced using at least one multifunctional mandrel, which has several mandrel sections with differing cross-sections. The mandrel sections are axial sections arranged one after the other in the axial direction of the multifunctional mandrel. With the aid of a multifunctional mandrel, several bore sections with differing cross-sections can be produced, particularly in a single forming operation, with the respective external shape of a mandrel section determining the internal shape of a bore section. The mandrel sections thus function as functional units for shaping the internal bore shape.-contour. According to the invention, several internal mandrels, including those of conventional type, can also be used.

[0011] The hollow shaft is manufactured according to the invention by forming and thus without the use of chips. However, machining steps can follow the forming process. Preferably, the hollow shaft manufactured according to the invention is subsequently further processed into a transmission shaft for a motor vehicle transmission (e.g., longitudinal or transverse transmission). The hollow shaft or transmission shaft preferably has an axial length of 150 mm to 600 mm.

[0012] The method according to the invention allows for more design freedom than previously known methods. Furthermore, the hollow shaft can be manufactured faster and with less tooling. Further advantages of the invention, such as a favorable fiber orientation on the manufactured hollow shaft, are explained below.

[0013] The internal bore in the preform can be a through bore or a blind bore. In particular, it is a circular cylindrical internal bore. Preferably, the internal diameter of the bore in the preform corresponds to the maximum internal diameter of the bore in the hollow shaft to be manufactured, and / or the external diameter of the preform corresponds to the maximum external diameter of the hollow shaft to be manufactured.

[0014] Preferably, during radial forming, at least one bore section on the hollow shaft to be manufactured is produced with internal teeth. Preferably, the internal teeth are splined (or internal splined) teeth whose radially inward-facing teeth are designed, in particular, with threading chamfers. The internal teeth and, optionally, the threading chamfers on their teeth are produced solely by radial forming. For this purpose, the multifunctional mandrel has at least one corresponding mandrel section designed with a corresponding tooth geometry (or tooth profile).

[0015] The temperature during radial forming is preferably at a moderate level, thus saving heating energy. Preferably, the preform is heated to a temperature between 200°C and 800°C before radial forming, more preferably to a temperature between 200°C and 600°C, and particularly to a temperature below 600°C. During radial forming, it has a corresponding forming temperature, which, however, decreases gradually during the forming process. Post-heating is generally not required.

[0016] Preferably, the preform has a simple geometric shape. The preform is a forged part, and such preforms can be produced cost-effectively. Forged preforms can, for example, be manufactured in large quantities on a horizontal forging press. The material used is, for example, a case-hardening steel. It is particularly preferred that the wall thickness of the preform with an internal bore is at least 10 mm, preferably at least 15 mm, and especially at least 20 mm, which results in a short axial length. Due to the short axial length, the internal bore can be produced cost-effectively by simple drilling or punching. Furthermore, the preform can have compact dimensions.

[0017] A device for producing a hollow shaft, which has a bore with several bore sections differing in cross-section, by radial forming of a heated preform, comprises: - several radial hammers capable of delivering synchronous radial blows to the preform; and - at least one multifunctional mandrel which has at least three mandrel sections that differ in cross-section.

[0018] The device according to the invention is particularly suitable for manufacturing a hollow shaft using the method according to the invention.

[0019] The device may include further device components, such as a drive device for the rotary drive of the workpiece and the multi-function mandrel relative to the radial hammers, a drive device for bringing about a relative movement between the workpiece and the radial hammers, a control device, clamping devices and the like.

[0020] The multifunctional mandrel has several mandrel sections with differing cross-sections. The multifunctional mandrel has at least three differing mandrel sections. Preferably, at least one mandrel section is designed to produce internal teeth, particularly with threading chamfers, on the hollow shaft to be manufactured and has a corresponding tooth geometry, as already explained above. The multifunctional mandrel can have at least one mandrel section for producing a lightweight undercut. Preferably, the multifunctional mandrel has several mandrel sections, particularly adjacent or axially aligned, for producing lightweight undercuts, especially with different bore diameters. Preferably, the multifunctional mandrel is made of steel, and in particular tool steel, and has a polished surface.

[0021] A hollow shaft produced using the method and / or the apparatus according to the invention has a bore with at least three bore sections differing in cross-section. Furthermore, the produced hollow shaft can be characterized by at least two, and preferably at least three or four, of the following features: - the (defined) wall thicknesses in the area of ​​at least two adjacent bore sections are different, resulting in a wall thickness jump between the bore sections in question; - the (defined) wall thicknesses in the area of ​​at least two adjacent bore sections are identical, so that there is no wall thickness jump between the bore sections in question; - at least one bore section is formed with an internal toothing, the internal toothing being produced by radial forming; - at least one bore section is designed as a lightweight undercut, as explained in more detail below, whereby this lightweight undercut was created by radial forming; - at least one bore section is designed as a bearing point with high fit quality, whereby this bearing point was produced by radial forming and is in particular free of post-processing; - the outer shape has at least one solid band, as explained in more detail below; - the bore is closed at one axial end.

[0022] In summary, the invention offers the following advantages (this is not an exhaustive list): - economical method for manufacturing a one-piece, weight-optimized and preferably also load-optimized hollow shaft; - Suitability for the production of large quantities (mass production); - short process chain and low equipment costs; - High lightweight construction potential for the hollow shaft to be manufactured is created and utilized; - no material loss during radial forming and therefore optimal material yield; - high degree of dimensional stability and only low manufacturing tolerances (no concentricity problems); - the hollow shaft is fully formed after radial forming; no further forming steps are required; - Utilization of degrees of freedom and potentially high degrees of deformation in radial forming; - the preform can be manufactured and / or provided cost-effectively; - advantageous material fiber orientation in the hollow shaft and / or high surface quality (notch- and groove-free), whereby the inner surface of the bore can remain without post-processing, i.e., post-processing-free; - comparatively low energy input for manufacturing the hollow shaft and / or high energy efficiency of the energy used.

[0023] The invention is explained in more detail below by way of example and in a non-limiting manner with reference to the schematic figures. The features shown in the figures and / or explained below can be general features of the invention, irrespective of specific combinations of features. The directional terms used refer to the representations shown in the figures. The features of the embodiments shown and / or explained can be combined with one another within the scope of the invention. Fig. Figure 1 shows a preform and the hollow shaft produced from it in two sectional views. Fig. Figure 2 shows two sectional views of another preform and the hollow shaft produced from it. Fig. Figure 3 illustrates the radial forming process for manufacturing a hollow shaft in a cross-sectional view.

[0024] Fig. Figure 1 shows a cylindrical preform 100 having an internal bore 110. The hollow shaft 200 shown is produced from the preform 100 by radial forming. The hollow shaft has a bore 210 with at least three bore sections 211 to 217 differing in cross-section. Transitions are provided between adjacent bore sections so that there are no abrupt changes in cross-section. Both the preform 100 and the hollow shaft 200 are axially symmetrical with respect to the longitudinal and rotational axes L, respectively.

[0025] The hollow shaft 200 is subsequently further processed into a transmission shaft by machining, for example by milling a toothed groove into the solid collar 201 on its outer circumference. Several such solid collars can be provided.

[0026] Gear teeth or splined connections can also be milled into the outer circumference of the hollow shaft 200 at other axial locations. Due to its hollow design, the hollow shaft 200, and the transmission shaft manufactured from it, is relatively lightweight, yet very durable due to the forming process used in its production.

[0027] The bore of the hollow shaft 200 has, for example, seven axial bore sections 211 to 217, whose cross-sections differ in size and shape. The individual bore sections 211 to 217 can be considered separate functional units. The left-hand bore section 213 is a bearing point designed with a high degree of precision. A rolling bearing can be inserted into bore section 213 through the outer, larger-diameter bore sections 211 and 212. To the right of bore section 213, which serves as a bearing point, are three larger-diameter bore sections 214, 215, and 216. These have an undercut contour in the radial direction relative to bore section 213 and serve as lightweight undercuts. The hollow shaft 200 thus has several functional units of the same type, but with different designs, arranged directly one behind the other in the axial direction.To the right of bore section 216, a bore section 217 with a smaller diameter follows, forming the right-hand end of bore 210. Bore section 211, forming the left-hand end of bore 210, is designed with an internal splined connection. At the open end of bore 210, the teeth 218 of the internal splined connection are formed with threading chamfers 219, as can be seen in the enlarged detail view. The radially inwardly pointing teeth 218 are thus tapered in the axial direction toward the left-hand bore opening. The inner walls of bore sections 211 and 213 represent functional surfaces.

[0028] The in Fig. The hollow shaft 200 shown in Figure 1 has different wall thicknesses in bore sections 211 to 217, whereby the wall thickness can also vary within a bore section (see, for example, bore sections 215 and 216). The wall thickness in adjacent bore sections can therefore differ. Likewise, individual bore sections or even all bore sections can have the same wall thickness. The respective wall thickness results, for example, from a compromise between the required strength and the desired lightweight construction, possibly also taking into account an advantageous mass distribution.

[0029] The hollow shaft 200 is produced from the preform 100 by radial forming using a multi-functional mandrel which has at least three mandrel sections with different cross-sections, as shown below. Fig. 3. Explained using examples.

[0030] Fig. Figure 3 shows a partially formed preform 100' (hereinafter also referred to as the workpiece), into whose inner bore 110' an axially symmetrical multi-functional mandrel 410 with several mandrel sections 411, 412, and 413 is inserted. By means of radially acting hammers or radial hammers 420, the material of the workpiece 100', clamped in a workpiece holder (e.g., a chuck), is formed radially onto the multi-functional mandrel 410, whereby the workpiece 100' is always only partially formed at one axial point at a time. The respective outer shape of the mandrel section determines the inner shape of the bore section to be produced. By axially moving the workpiece 100' (including the multi-functional mandrel 410) relative to the hammers 420, each axial point is successively formed, whereby the material flows in a defined manner in the axial direction along the multi-functional mandrel 410.During radial forming, the workpiece material 100' is drawn axially over the internal mandrel 410. The multifunctional mandrel 410 shown has a toothed geometry in the mandrel section 412 for generating an internal splined connection. Preferably, the multifunctional mandrel 410 is made of a heat-treated steel material.

[0031] According to this procedure, the in Fig. The hollow shaft 200 shown in Figure 1 is manufactured as follows. After a multifunctional mandrel, designed according to the bore sections 214, 215, 216, and 217 to be produced, is positioned in the inner bore 110 of the heated preform 100 (with a defined axial relative position), the sections located to the right of the solid collar 201 are formed in a first forming operation, whereby the outer and inner contours of the hollow shaft 200 to be produced are successively created simultaneously. The respective inner contour is defined by the mandrel sections, and the respective outer contour is defined by adjusting the radial hammer positions. Optionally, the bore can be closed on the right side by radial forming. Subsequently, the area to the left of the solid collar 201 is formed up to the left-hand axial end of the bore section 214.The multi-function mandrel is then pulled out of the partially formed hollow shaft to the left and replaced by another multi-function mandrel, which is designed according to the bore sections 211, 212 and 213 to be produced, and the partially formed hollow shaft is re-clamped. In a second forming operation, the hollow shaft 200 is now fully formed by forming the sections located to the left of the solid collar 201, including a precisely formed internal splined connection with threading chamfers in bore section 211.

[0032] The process steps described above are carried out automatically by the radial forming machine used. By designing the hollow shaft 200 for manufacturability, it can potentially be produced using only one multi-functional mandrel.

[0033] The inner surface of bore 210 does not require post-processing after radial forming. This also applies in particular to the internal splined connection in bore section 211.

[0034] As in Fig. As illustrated in Figure 1 with dashed lines, the inner diameter of the inner bore 110 in the preform 100 corresponds to the maximum bore diameter of the bore 210 in bore section 214 of the hollow shaft 200 to be manufactured, and the outer diameter of the preform 100 corresponds to the outer diameter of the solid collar 201 on the hollow shaft 200 to be manufactured. During radial forming of the preform 100, a diameter reduction is thus carried out in the sections to be formed on the outer and / or inner circumference. In particular, it is intended that no radial forming, and therefore no diameter reduction, takes place in the area of ​​the solid collar 201, either on the outer or inner circumference. The solid collar 201 thus has the outer circumference of the preform 100 on its outer side and the inner circumference of the inner bore 110 of the preform 100 on its inner side.

[0035] Fig.Figure 2 shows another preform 100a, which is T-shaped in the longitudinal section shown, and the hollow shaft 200a produced from it by radial forming using a multi-function mandrel. The hollow shaft 200a has a bore 210a with three bore sections 211a, 212a, and 213a. Starting with the preform 100a provided as a forging, the hollow shaft 200a can be produced in a single forming operation using a multi-function mandrel, analogous to the preceding explanations. The bore section 212a can also be designed as a lightweight undercut, deviating from the embodiment shown. Reference symbol list 100 preforms (blanks) 110 mm internal bore 200 hollow shaft 201 massive bundle (accumulation of material) 210 bore 211 Bore section (with splined connection) 212 Drilling section 213 Drilling section 214 Drilling section 215 Drilling section 216 Drilling section 217 Drilling section 218 teeth (internal spline) 219 Threading chamfers (sharpening) 400 Device for radial forming 410 Multifunctional mandrel 411 Spine section 412 Spindle section 413 Spindle section 420 radial hammers L Longitudinal axis (axis of rotation)

Claims

[1] Method for forming a hollow shaft (200) having a bore (210) with at least three bore sections (211-217) differing in cross-section, comprising the following process steps: - Providing a rotationally symmetrical preform (100) with an internal bore (110), wherein this preform (100) is a forging; - Heating the preform (100); and - Radial forming of the heated preform (100) to simultaneously produce an outer shape and an inner bore shape, wherein the inner bore shape is produced using a multifunctional mandrel (410) which has at least three mandrel sections (411-413) that differ in cross-section, and wherein the preform (100) is elongated at least twice in the axial direction (L). [2] Method according to claim 1, characterized by, that the inner diameter of the inner bore (110) in the preform (100) corresponds to the maximum bore diameter of the bore (210) in the hollow shaft (200) to be produced and / or the outer diameter of the preform (100) corresponds to the maximum outer diameter on the hollow shaft (200) to be produced. [3] Method according to claim 1 or 2, characterized by , that the preform (100) is elongated at least 2.5 times or 3 times in the axial direction (L) during radial forming. [4] Method according to any of the preceding claims, characterized by , that the preform (100) is elongated in both axial directions during radial forming. [5] Method according to any of the preceding claims, characterized by , that the preform (100) is heated to a temperature between 200°C and 800°C and in particular to a temperature between 200°C and 600°C before radial forming.

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