Method for producing a closed hollow profile for a vehicle axle

Abstract

A method for manufacturing a closed hollow profile (2) for a vehicle axle is presented and described, comprising the following steps: a) providing a blank (1) from a metal sheet, wherein the blank (1) has at least a length (L) in the longitudinal direction and at least a width (B) in the transverse direction or a shaped contour, b) forming the blank (1) to create an open profile with a channel (5) extending longitudinally along the blank (1), c) forming the side surfaces (6, 7) of the blank (1) to create a hollow profile (8) with a circumference (U) and a longitudinal gap (9), and d) joining the longitudinal gap (9). To enable reliable joining of the hollow profile (2) with high repeatability, it is proposed to form the blank (1) such that a compressive stress is created, particularly in the plane of the sheet, at least in the region of the longitudinal gap (9).

Description

[0001] The invention relates to a method for producing a closed hollow profile for a vehicle axle, comprising the following steps: a) providing a blank from sheet metal, the blank having at least one length in the longitudinal direction and at least one width or a shape contour in the transverse direction, b) forming of the blank, resulting in an open profile with a channel running in the longitudinal direction of the blank, c) reshaping of the side faces of the blank, resulting in a hollow profile with a circumference and a longitudinal gap, and d) joining the longitudinal gap.

[0002] A wide variety of axles and wheel suspensions are known in the field of chassis technology. Originally, axles created a rigid cross-connection between rotatably mounted wheels ("rigid axle"). The rigid connection between the two wheels was later abandoned. Instead, the wheel is mounted on a wheel carrier, which is movably connected to the vehicle body by several links ("independent wheel suspension").

[0003] The so-called “semi-rigid axle” represents a compromise between a rigid axle and an independent wheel suspension. Semi-rigid axles form - like rigid axles - a mechanical coupling of the two wheels. Nevertheless, semi-rigid axles - in contrast to rigid axles - allow a relative movement between the two wheels. This is usually achieved by targeted elastic torsional deformation of the cross member of the semi-rigid axle. The cross member is often a hollow profile. The torsional stiffness of the cross member usually varies along its length: at the two ends of the cross member, a high torsional stiffness is sought to enable a reliable connection of the side members and in the middle of the cross member a rather low torsional stiffness is sought to allow relative movement between the wheels enable. Against this background, it becomes clear that a quite complex geometry of the cross members is often required. Therefore, special requirements are placed on the manufacture of these components.

[0004] One possibility, known from the prior art, for producing such torsion profiles for axles consists in first producing a welded tube rolled to size in a separate, mostly continuous process and then pressing the finished tube in its middle section in a U-shape with a punch. to reduce the torsional stiffness in this section in a controlled manner. However, this manufacturing technique has several disadvantages. A disadvantage is that a material with a high bending capacity is required for the pressing of the tube. As a result, many high-strength or ultra-high-strength materials are out of the question. A further disadvantage lies in the limited freedom of design, since torsion profiles with a constant circumference can only be formed approximately with a constant circumference.

[0005] DE 10 2009 031 981 A1 discloses an alternative method for producing a torsion profile from a metal plate, which is intended to form the middle section—that is, the “cross member”—of a torsion beam axle. For this purpose, a rectangular metallic plate is formed into a hollow profile in several steps. The longitudinal edges of the blank are then welded together to form a closed hollow profile. A challenge of this method, however, lies in the creation of a reliable weld. Because of the multiple forming of the blank, the two longitudinal edges often spring back a little after the forming steps, so that there is no clean butt joint between the longitudinal edges for welding. Since the cross-sectional area of ​​the torsion profile changes along its length, the two longitudinal edges often also spring back to different extents along their length. This can lead to a gap with changing gap width, which further complicates the welding.

[0006] The invention is therefore based on the object of designing and developing the method described at the outset and previously explained in more detail in such a way that reliable joining of the hollow profile with high repeatability is made possible.

[0007] This object is achieved in a method according to the preamble of patent claim 1 in that the blank is deformed in such a way that compressive stress occurs at least in the area of ​​the longitudinal gap, in particular in the plane of the sheet.

[0008] The method according to the invention serves to produce a closed hollow profile for a vehicle axle. The hollow profile can in particular be a torsion profile, for example the cross member of a torsion beam axle. The method initially provides for the provision of a blank made of sheet metal, the blank having at least one length in the longitudinal direction and at least one width or shape contour in the transverse direction. The length is preferably significantly longer than the width. In particular, a plate can be rectangular and thus have a length in the longitudinal direction and a width in the transverse direction, or be designed as a shaped plate and have several lengths transverse to the longitudinal direction and several widths along the transverse direction. The method also provides for at least two forming steps: First, the blank is to be formed in such a way that an open profile with a channel running in the longitudinal direction of the blank is formed. A channel is understood to be an elongate trough or an elongate depression. Then the side surfaces of the blank should be shaped in such a way that a hollow profile with a circumference and with a longitudinal gap is created. The areas on the side next to the channel are referred to as side surfaces. Since the hollow profile has a longitudinal gap, it is not (yet) a closed hollow profile. Finally, the process provides for the joining of the longitudinal gap, whereby a closed hollow profile is created from the open hollow profile.

[0009] According to the invention, it is proposed that the blank be reshaped in such a way that a compressive stress arises at least in the area of ​​the longitudinal gap, in particular in the plane of the sheet metal. In particular, after steps b) and c) and before step d), a compressive stress should arise in the longitudinal gap, in particular in the plane of the sheet. The circuit board should therefore be shaped in such a way that contact is created between the two side surfaces of the circuit board that form the longitudinal gap. Contact can occur at one or more points along the length of the profile. Preferably there is continuous contact along the entire length of the longitudinal gap. The compressive stress created in the longitudinal gap has two advantages. Firstly, during profile forming, the compressive stress causes the areas near the edges to curve outwards. The curvature leads to the longitudinal edges touching tangentially, for example in the case of an edge joint, in order to form an exact I-joint and a desired exact distance between the longitudinal gap and the opposite area of ​​the hollow profile - the channel - is set. Second, the resulting compressive stress minimizes springback and prevents the component from popping open too much after removal from the forming die. These effects ensure safe and repeatable shaping and essentially stress-free joining of the longitudinal gap. A compressive stress can be achieved, for example, by an “excess of material”. The compressive stress in the area of ​​the longitudinal gap is preferably above the material yield point. The compressive stress is highest in the edge joint. The area next to the longitudinal gap (longitudinal gap area) is also affected by the resulting compressive stress, which can also contribute to avoiding springback, with the level of compressive stress decreasing outwards, away from the longitudinal gap.

[0010] According to one embodiment of the method, it is provided that the width or the shape of the blank is greater at at least one point than the circumference that occurs during the forming at the same point on the hollow profile. The use of blanks with a slightly increased width is a particularly simple way of obtaining a hollow profile with compressive stress in the longitudinal gap and the longitudinal gap area after the forming.

[0011] In a further development of the method, it is proposed that in step a) a blank made of steel, in particular made of a high-strength or ultra-high-strength steel or of a modern high-strength multi-phase steel (e.g. DP780, FB780 or CP800) is provided. Steel is characterized by good formability and very good strength values. In addition, the use of steel enables the production of torsion profiles with relatively thin walls and therefore low mass. In vehicle construction, a small quotient of "unsprung" masses (axles, wheels, etc.) to "sprung" masses (vehicle body) is aimed for in order to keep wheel load fluctuations low. Hollow sections made of steel with small wall thicknesses can make a contribution to this.

[0012] A further embodiment of the method provides that the board has a thickness in the range between 0.5 mm and 4.0 mm, in particular between 1.0 mm and 3.0 mm. Blanks with a thickness in the specified range have proven to be a good compromise between sufficient rigidity (the greatest possible thickness) and low weight as well as good formability (the smallest possible thickness). The blank can have a constant, consistent thickness or different thicknesses (so-called tailored blank, tailored strip or tailored rolled blank).

[0013] According to a further embodiment of the method, it can be provided that the blank has an elongation at break of less than 21%. By manufacturing the hollow profile from a flat plate, materials with a relatively low elongation at break can also be used, in contrast to manufacturing from a tube. This allows, for example, the use of high-strength and ultra-high-strength steels.

[0014] According to a further embodiment of the method, it is provided that the blank is formed in step b) by deep-drawing and / or stretch-forming and / or embossing-upsetting. Deep drawing is a variant of compression molding and enables the production of open hollow bodies. Deep drawing can be used in mass production and is therefore particularly suitable for the production of parts for vehicles. Stretch forming is one of the drawing processes and is characterized, for example, by a simple and cost-effective design. A preferably spaced-apart hold-down device can be used during the forming process in order to ensure that the material stretches as little as possible.

[0015] In a further development of the method, it is proposed that the blank be reshaped in such a way that a butt joint or an overlap joint is created. Both a butt joint and a lap joint represent good preparation for subsequent welding. The welding of the longitudinal gap can therefore take place immediately after the forming steps without any further preparation steps.

[0016] A further embodiment of the method provides that the blank is reshaped in such a way that the cross section at both ends of the open profile is approximately U-shaped. This shape is preferably formed after step b) and before step c), ie after the channel has been formed and before the side faces are finally formed into a hollow profile. The cross-sectional shape is preferably mirror-symmetrical. This form is, for example, in step V of figure 2 and figure 3 shown.

[0017] According to a further development of the method, it is proposed that the blank be reshaped in such a way that the cross section in the middle of the open profile is approximately W-shaped. This shape is preferably also formed after step b) and before step c), ie after the channel has been formed and before the side faces are finally formed into a hollow profile. The cross-sectional shape is preferably mirror-symmetrical. This form is, for example, in step V of figure 2 and figure 3 shown.

[0018] Finally, in a further embodiment of the method, it is proposed that in step d) the longitudinal gap is joined by welding, soldering, gluing or a mechanical joining method. Welding processes, soldering processes as well as gluing processes are material-to-material joining processes. With welding processes, thermally stable connections with high strength can be achieved. Adhesive bonding processes, on the other hand, have the advantage of lower energy requirements and the avoidance of thermally induced structural changes in the vicinity of the joint. Alternatively, the longitudinal gap can be joined using a mechanical joining process.

[0019] The invention is explained in more detail below with reference to a drawing that merely shows a preferred exemplary embodiment. Show in the drawing:

[0020] figure 1A: a circuit board made of a metal sheet with a rectangular shape,

[0021] figure 1B: a molded board made of a metal sheet,

[0022] figure 1C: a near-net-shape trimmed blank,

[0023] figure 2: the production of a closed hollow profile from a blank by the method according to the invention in seven steps in a perspective view,

[0024] figure 3: the production of a closed hollow profile from a blank by the method according to the invention in seven steps in a side view,

[0025] figure 4A: a closed hollow profile produced by the method according to the invention in a front view,

[0026] figure 4B: the closed hollow profile figure 4A in a plan view,

[0027] figure 4C: the closed hollow profile figure 4A in a side view, and

[0028] figure 5: the sequence of a method according to the invention in a schematic representation.

[0029] figure 1 shows a circuit board 1 from a metal sheet, which can be formed into a hollow profile in the method according to the invention. The circuit board 1 initially has a rectangular shape (rectangular plate) and has a length L in the longitudinal direction and a width B in the transverse direction ( figure 1A). After the shaping step b), the rectangular blank is subjected to a shape trimming, in particular of the edges running in the longitudinal direction. The circuit board 1 is alternatively a molded board ( figure 1B) which has several lengths L transversely in the longitudinal direction and several widths B longitudinally in the transverse direction or a corresponding shape contour. During the forming step b), the shaped blank is preferably deep-drawn with a spaced hold-down device, with trimming (final trimming) only taking place after joining. Another board 1 is alternatively in figure 1C, which as a molded blank cut close to the net shape has several lengths L transversely in the longitudinal direction and several widths B longitudinally in the transverse direction, or a corresponding mold contour.

[0030] In figure 2 is the production of a closed hollow profile 2 from a board 1 shown by the method according to the invention in seven steps in a perspective view. figure 3 shows the production of a closed hollow profile 2 from a board 1 by the method according to the invention in seven steps in a side view. The seven steps are used in both figure 2 as well as in figure 3 labeled I–VII.

[0031] In step I will make a flat board 1 provided from a metal sheet. The circuit board 1 was trimmed on the long edges and corresponds to the in figure 1B shown circuit board 1 . In step II was the circuit board 1 in the area of ​​both ends 3 reshaped so that each one paragraph 4 arises. The circuit board was formed by deep-drawing and / or stretch-forming 1 then reshaped in such a way that an open profile with a longitudinal direction of the board 1 running canal 5 arises (step III). In step IV, the canal 5 deformed in the opposite direction and now has a curved shape. The one next to the central channel 5 running side surfaces 6 ,7 the circuit board 1 were subsequently towards the canal 5 reshaped (Step V). Following this were the side faces 6 , 7 the circuit board 1 further formed, with a hollow profile 8 with a longitudinal slit 9 arises (step VI). A closed hollow profile 2 is finally created by welding the longitudinal gap 9 (Edge joint), with one the two side surfaces 6 , 7 connecting weld 10 arises (step VII).

[0032] figure 4A shows a closed hollow profile produced by the method according to the invention 2 in a front view. figure 4B shows the closed hollow profile 2 out figure 4A in a plan view and figure 4C shows the closed hollow profile 2 out figure 4A in a side view. As in particular in figure 4A and in figure 4B at the two uneven ends of the hollow profile 2 can be seen, was used for the production of the hollow profile 2 a board 1 used with trimmed transverse edges. Such a board 1 is for example in figure 1C.

[0033] In figure Finally, FIG. 5 shows the sequence of a method according to the invention in a schematic representation. The method comprises the following steps: a) Providing a circuit board 1 , b) Reshaping of the circuit board 1 (Channel 5 ), c) reshaping the circuit board 1 (side faces 6 , 7 ), and d) Joining the longitudinal gap 9 (edge ​​joint). Reference List 1 circuit board 2 closed hollow profile 3 end (of the circuit board 1 ) 4 paragraph 5 channel 6, 7 side surface (of the circuit board 1 ) 8 hollow profile 9 longitudinal gap 10 weld L Length (of board 1 ) B width (of board 1 ) U Circumference (of the hollow profile 8 ) QUOTES INCLUDED IN DESCRIPTION

[0034] This list of the documents cited by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Patent Literature Cited

[0035] DE 102009031981 A1

[0005]

Claims

[1] Method for producing a closed hollow profile ( 2 ) for a vehicle axle, comprising the following steps: a) Providing a circuit board ( 1 ) made from a sheet of metal, wherein the circuit board ( 1 ) has at least a length (L) in the longitudinal direction and at least a width (B) or a shape contour in the transverse direction, b) Shaping the circuit board ( 1 ), wherein an open profile with a longitudinal axis across the circuit board ( 1 ) running canal ( 5 ) arises, c) Shaping the side surfaces ( 6 , 7 ) the circuit board ( 1 ), wherein a hollow profile ( 8 ) with a circumference (U) and with a longitudinal slit ( 9 ) arises, and d) Joining the longitudinal gap ( 9 ), characterized by that the circuit board ( 1 ) is reshaped in such a way that at least in the area of ​​the longitudinal gap ( 9) a compressive stress is created. [2] Method according to claim 1, characterized by that the width (B) or the shape contour of the blank is larger at at least one point than the circumference (U) resulting from the forming process at the same point of the hollow profile ( 8 ). [3] Method according to claim 1 or 2, characterized by that in step a) a circuit board ( 1 ) is provided from steel, in particular from a high-strength or ultra-high-strength steel. [4] Method according to any one of claims 1 to 3, characterized by that the circuit board ( 1 ) has a thickness in the range between 0.5 mm and 4.0 mm, in particular between 1.0 mm and 3.0 mm. [5] Method according to any one of claims 1 to 4, characterized by that the circuit board ( 1 ) exhibits an elongation at break of less than 21%. [6] Method according to any one of claims 1 to 5, characterized by that the circuit board ( 1) in step b) is reshaped by deep drawing and / or stretch drawing and / or embossing-raising. [7] Method according to any one of claims 1 to 6, characterized by that the circuit board ( 1 ) is reshaped in such a way that a butt joint or a lap joint is created. [8] Method according to any one of claims 1 to 7, characterized by that the circuit board ( 1 ) is reshaped in such a way that the cross-section at both ends of the open profile is approximately U-shaped. [9] Method according to any one of claims 1 to 8, characterized by that the circuit board ( 1 ) is reshaped in such a way that the cross-section in the middle of the profile open on one side is approximately W-shaped. [10] Method according to any one of claims 1 to 9, characterized by that in step d) the longitudinal gap ( 8 ) is joined by welding, soldering, gluing or a mechanical joining process.