EP1990108A1 - Method for bending a high-tensile steel plate and workpiece manufactured according to this method - Google Patents

Abstract

The method involves providing a reverse spring angle for a side of a steel plate (1). Bends (6) are made on the plate, and run parallel to each other. The bends are provided with a detailed bending angle and a detailed bending radius (Rdet), which are smaller than a target bending angle and a target bending radius (Rsoll) of a work piece, respectively such that the detailed bending angle is equal to the target bending angle. The detailed bending radius is predetermined by a tool, and the plate has a tensile strength of more than 1.000 mega Pascal.

Description

The invention relates to a method for bending a high-strength steel sheet to a bending technically finished workpiece having the features of the preamble of claim 1 and with the features of the preamble of claim 8, as well as a bending finished workpiece with the features of the preamble of claim 10.

High-strength steel sheets with a tensile strength greater than 500 MPa, often with tensile strengths greater than 800 MPa or greater than 1,000 MPa, have increasingly found their way into the automotive industry in particular. In particular, reference may be made to the relevant recent specialist literature, in which the specific features of various high-strength steels are explained in detail ( Thyssen Krupp, 2005, "Forming behavior of higher and highest strength multiphase steels ").

The inventive method is concerned with a special method to bend a high-strength steel sheet in a reproducible manner at a certain bending angle. The high tensile strength of the high strength steel sheet, when bent, results in high and hard-to-predict springback. This has to do with the fact that the required for the maintenance of the bent state plastic deformation of the steel sheet in the bending area occurs much later than normal-strength steel sheets. As a result, this leads to significant tolerance problems of the bending technically finished workpieces and the need to constantly adjust the tools even during a series production of such a workpiece.

The problems explained above occur in particular where work has to be carried out with a relatively large bending radius, for example a bending radius of 20 mm and more. The invention is based on the problem, the known method in such a way and further develop that it is particularly aligned to the bending of a high-strength steel sheet.

The aforementioned problem is solved in a method having the features of the preamble of claim 1 by the features of the characterizing part of claim 1.

For the purposes of the present invention, a "finished by bending" workpiece is to be understood as one that is in any case no longer subjected to further bending for the area considered, but which can certainly be subjected to further processing such as punching, notching, etc., as well as further bending operations in other areas of the workpiece.

By the term "bending angle" is meant here the angle by which the flat, stretched steel sheet is bent relative to its initial position. So it is the outside angle measured against the stretched position of 0 °. The internal angle between the legs of the bent workpiece completes this bending angle to 180 °. A bend with a low bending angle thus has a large internal angle, it acts flat, while a bend with a large bending angle has a low internal angle and is pointed.

Normally, the bend radius followed in size the previously explained inner angle, which corresponds to the bending angle of the executed bend. Normally one will thus make a flat bend with a low bend angle and a large inside angle with a large bend radius.

According to the invention, however, it has been recognized that for bending a high-strength steel sheet with a tensile strength greater than 500 MPa, preferably greater than 800 MPa or even greater than 1000 MPa, an exactly reverse procedure leads to good results. A predetermined desired bending angle is according to the invention divided into a plurality of significant smaller detail bending angles. The desired bending angle is realized by a plurality of flat bends, which are laterally spaced and parallel to each other. On average, the bent, bending finished workpiece in the area of the overall bending has a polygonal pull-like structure.

Contrary to the hitherto customary procedure in the execution of "flat" bends the detail bending radius of the respective bends is set by the tool small, much lower than the target bending radius. As a result, a plastic deformation of the high-strength steel sheet is achieved at the bending vertexes of the individual, parallel bends, which could not be achieved with larger bending radii.

By adjusting the pressure in the operating equipment (press, roll forming machine), the exact settings can be determined empirically and adapted during batch changes. It is essential that the springback angle of the individual bends with the detail bending radii can be determined much more accurately and maintained than with larger bending radii.

Preferred embodiments and further developments of the teaching according to the invention are the subject of the dependent claims 2 to 7.

The previously indicated problem is solved in a sibling variant by a method having the features of claim 8.

According to the invention, it has been recognized that virtually no or only a very small plastic deformation takes place in the legs of the steel sheet extending from the bending elbow of a bend for the high-strength thin steel sheets concerned here. When pressing with a ram or a roll forming resulting in each case certain return spring angle in the positive direction for the outgoing from the bending vertex leg of the steel sheet. It has been recognized that one can compensate with these return spring angles directed in the negative direction return spring angle of the bend itself. In fact, this is done rather reversed, namely by deliberately increasing the bending radius of the bend so far that the plastic deformation of the steel sheet is reduced to the bending vertex so that even a sufficiently large negative springback angle is formed, which is the sum of the positive springback of the outgoing from the bending vertex leg Steel sheet is able to compensate.

Particularly preferred is a combination of the two methods explained above, which are independent of each other.

The subject matter of the invention is also a workpiece which is finished by bending technology and which has been produced by one of the methods explained above.

Such workpieces are in particular structural components of motor vehicle bodies, for example U-profiles, W-profiles, bumper cross-member profiles, or side impact protection profiles.

Fig. 1a)

in perspektivischer Ansicht ein Ausführungsbeispiel eines biegetechnisch fertigen Werkstückes aus einem hochfesten Stahlblech,

Fig. 1b)

einen Schnitt durch das Werkstück aus Fig. 1a) mit eingezeichneten Biegewinkeln und Biegeradien,

Fig. 2a)

ein Werkzeug zum Herstellen eines biegetechnisch fertigen Werkstücks mit eingelegtem, bereits gebogenem Stahlblech in einem Zustand vor Erreichen des Enddrucks,

Fig. 2b)

das Werkzeug aus Fig. 2a) bei Erreichen des Enddrucks.

In the following the invention will now be explained in more detail with reference to a drawing showing only exemplary embodiments. In the drawing shows

Fig. 1a)

a perspective view of an embodiment of a bending technically finished workpiece made of a high-strength steel sheet,

Fig. 1b)

a cut through the workpiece Fig. 1a ) with marked bending angles and bending radii,

Fig. 2a)

a tool for producing a workpiece with bending technology finished with inserted, already bent steel sheet in a state before reaching the final pressure,

Fig. 2b)

the tool off Fig. 2a ) when the final pressure is reached.

Based on Fig. 1 For example, the method according to the invention for bending a high-strength steel sheet having a tensile strength greater than 500 MPa, preferably greater than 800 MPa, particularly preferably greater than about 1000 MPa, can be explained particularly well with a bending-finished workpiece having a desired bending angle α and a nominal bending radius R _SOLL , The definition of the tensile strength values follows from the specialist literature already mentioned at the beginning ( Thyssen Krupp, 2005, "Forming behavior of higher and highest strength multiphase steels ").

Fig. 2 shows a typical press tool that can also be designed in the form of a Rollprofilierwerkzeugs with multiple stations, to realize the bending steps in the method according to the invention.

The drawing shows a steel sheet 1, in Fig. 1 in the form of the already bending technically finished workpiece, the in Fig. 2 has been produced with a lower tool 2 or a die and an upper tool 3 and a press ram shown.

Fig. 2 indicates that the steel sheet 1 during bending the area of the bending vertex 4 and the outgoing from the bending vertex 4 legs 5 is formed.

Fig. 1b ) shows marked the desired bending angle α or the total angle of the bending technically finished workpiece and the associated target bending radius R _SOLL , which results as a radius of the bending technically finished workpiece inscribed circle.

It is now provided that on the steel sheet 1 a plurality of mutually laterally spaced and parallel bends 6 are performed with a detail bending angle β, which is substantially smaller than the desired bending angle α, and with a predetermined by the tool detail bending radius R _DET which is much smaller than the target bending radius R _SOLL , such that the sum of the detail bending angles β is equal to the target bending angle α. The individual bending angles and radii are in Fig. 1b ). Between each two mutually parallel bends 6 with low detail bending angle β is in each case a straight intermediate piece. 7 Fig. 1b ) shows that this results in a cross-section polygonzugartige structure of the bending technically finished workpiece 1. The high tensile strength of the steel sheet 1 is evident from the fact that a plastic deformation is carried out only at the bends 6, the steel sheet in the spacers 7, however, has just stayed.

This in Fig. 1 illustrated embodiment shows an example that here the target bending angle α is 180 °, while the detail bending angle β, a total of six in number, only each 30 °. The nominal bending radius R _SOLL is in this example about 40 mm, the detail bending radii R _DET , however, are only about 4 mm. As a result, sufficient plastic deformation of the steel sheet is achieved at the bending vertexes 4 of the individual bends 6, so that the overall shape of the bending-technically finished workpiece 1 can be reproduced with high accuracy.

In principle, the detail bending angles β could be different. In the illustrated and preferred embodiment, however, it is such that the detail bending angle β are substantially equal. Essentially means the same within the usual tolerances, so that they can preferably be formed in one and the same tool. Even with the detail bending radii R _DET basically different bending radii could be realized differently. In the illustrated embodiment, all bending radii of the individual bends 6 but are essentially the same. Preferably, a ratio of 1/5 to 1/20, preferably from about 1/6 to about 1/10 of detail bending radius R _DET to set bending radius R _SOLL . In the present embodiment, this ratio is about 1/10.

In the illustrated embodiment, the lateral distances of the bends 6, so the widths of the straight intermediate pieces 7, are substantially equal.
The illustrated and preferred embodiment shows a steel sheet having a thickness of about 1.5 mm. The high strength steel sheets referred to herein typically have thicknesses of about 0.5 mm to about 2.0 mm. For this, reference may already be made to the reference already mentioned above.

Fig. 2 shows a press tool as an example of how to bend the high strength steel sheet in the process of the invention. Fig. 2 shows therein a special feature that represents an independent teaching according to the invention. In Fig. 2a ) it can be seen that before reaching the final pressure, that is, when the upper tool 3 has not yet been fully moved to the lower tool 2, in the region of the bending vertex 4 a linear contact on the one hand on the upper tool 3, on the other hand takes place on the right and left of the lower tool 2 (see the black dots). Especially in connection with the possibility of Rollprofilierens results from this linear system a reduction of the forces to be expended.

In Fig. 2b ) is shown that in this method in the given steel sheet for the given bending radius with the predetermined bending angle a spring back angle -γ and for the outgoing from the bending vertex 4 legs 5 of the steel sheet a return spring angle of + + δ is present. The outgoing from the bending vertex 4 springback would like to stretch the bent steel sheet again, the outgoing of the legs 5 springback is directed against the opposite. Based on this knowledge, it is realized according to the invention that the bending radius is dimensioned such that in any case approximately 2δ-γ = 0. As has already been stated above, the bending radius R provided by the upper tool 3 will be made so great that the plastic deformation of the steel sheet in the region of the bending vertex 4 is suitable. The return spring angle -γ, which starts from the bending vertex 4, is chosen so large that the sum of the return spring angle + δ, which emanate from the practically only elastically deformed legs 5, is just compensated.

Particularly preferred is a combination of the two methods explained above, which can be implemented independently of one another, because this advantageously influences the reproducibility of the bends in series production in two respects.

The invention is in addition to the method according to the invention also the bending technically finished workpiece as such, which is used in particular as a structural component of motor vehicle bodies.

Claims (11)

Method for bending a high-strength steel sheet with a tensile strength greater than 500 MPa to a work piece with bending properties and a desired bending angle α and a nominal bending radius R _SOLL ,
characterized,
that on the steel sheet a plurality of mutually laterally spaced and parallel bends are performed with a detail bending angle β, which is substantially smaller than the desired bending angle α, and with a predetermined by the tool detail bending radius R _DET , which is substantially less than the desired bending radius R _SOLL , such that the sum of the detail bending angle β is equal to the desired bending angle α. A method according to claim 1, characterized in that the steel sheet has a tensile strength greater than about 800 MPa, preferably greater than about 1000 MPa. A method according to claim 1 or 2, characterized in that the detail bending angles β are provided substantially the same. Method according to one of claims 1 to 3, characterized in that the detail bending radii R _DET are provided substantially the same. Method according to one of claims 1 to 4, characterized in that the detail bending radius R _{DET is} about 1/5 to 1/20, preferably about 1/6 to 1/10 of the desired bending radius R _SOLL . Method according to one of claims 1 to 5, characterized in that the lateral distances of the bends are provided substantially the same. Method according to one of claims 1 to 6, characterized in that the steel sheet has a thickness of about 0.5 mm to about 2.0 mm, preferably from about 0.8 mm to about 1.6 mm. A method for bending a high-strength steel sheet having a tensile strength greater than 500 MPa to a bending technically finished workpiece with a desired bending angle α and a target bending radius R _SOLL , wherein in the given steel sheet for the predetermined bending radius with the predetermined bending angle a Rückfederwinkel -γ and for the leg of the steel sheet emanating from the bending vertex has a springback angle of + δ each,
in particular method according to one of claims 1 to 7,
characterized,
that the bending radius is calculated so that 2 δ-γ = 0 in any case approximately applies. Method according to one of claims 1 to 8, characterized in that the bending-finished workpiece is a structural component of a motor vehicle body, in particular a U-profile, a W-profile, a side impact protection profile, a bumper cross member profile o. Bending technically finished, bent in a certain total angle α workpiece made of a high-strength steel sheet having a tensile strength greater than 500 MPa, in particular structural component of a motor vehicle body,
characterized,
that in the bent region of the workpiece on the steel sheet (1) a plurality of mutually laterally spaced and parallel bends (6) are provided with a detail bending angle β, which is substantially smaller than the total angle α, and
that the detail bending radius R _{DET of} the bends (6) is substantially less than the overall bending radius that can be recognized on the workpiece. Workpiece according to claim 10, characterized
that the steel sheet has a tensile strength of greater than about 800 MPa, preferably greater than about 1000 MPa and / or
that the detail bending angle β are substantially equal and / or
that the detail bending radii R _DET are substantially the same and / or
that the detail bending radius R _{DET is} about 1/5 to 1/20, preferably, about 1/6 to 1/10 of the desired bending radius R _SOLL and / or
that the lateral distances of the bends are substantially equal and / or that the steel sheet has a thickness of about 0.5 mm to about 2.0 mm, preferably from about 0.8 mm to about 1.6 mm.

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