Method for the production of sheet metal parts and device therefor

Abstract

The invention relates to a method and a device (100) for the production of sheet metal parts (3) that are characterized by substantially reduced spring back.

Description

Technical field

[0001] The invention relates to a method for manufacturing sheet metal components. Technical background

[0002] Methods and devices for manufacturing dimensionally accurate sheet metal components are disclosed in the prior art, see, for example, DE 10 2007 059 251 A1, DE 10 2008 037 612 A1, DE 10 2009 059 197 A1, DE 10 2013 103 612 A1, DE 10 2013 103 751 A1, wherein the manufacturing process is carried out in at least two stages (forming processes). In the first stage, a blank, in particular a flat one, is formed into a preform. The preform has a material excess that is distributed as uniformly as possible compared to the final component geometry. This additional material excess is compressed in the second stage, the so-called calibration, in the direction of the sheet plane. The inhomogeneous stress state of the preform is thereby realigned, thus largely avoiding the undesirable, batch-dependent springback of the component, which occurs particularly with high-strength materials in combination with small sheet thicknesses.From DE 10 2018 210 174 A1 it is also known to produce a high-dimensionally accurate, flangeless sheet metal component by producing a preform with an opening angle of the sides of less than 6° from a blank, which is then calibrated to a final sheet metal component.

[0003] Various boundary conditions must be observed during the production of the preform.

[0004] The lengths of the local cross-sectional developments must therefore only change within narrow limits, even with varying influencing factors such as friction, the mechanical properties of the material batch used, and tool wear. It is therefore necessary to design the preforming tool with at least a spaced, outer blank holder, or preferably without any external blank holder at all (so-called "crash forming" or "embossing / folding"). This prevents the blanks in the preforming tool from stretching to varying degrees during the production of multiple components and when using different material batches, depending on the aforementioned influencing factors. Such uncontrolled stretching of the material from component to component would cause the distribution of excess material for subsequent calibration to potentially exceed the acceptable, process-reliable range.

[0005] In the production of the preform, reduced tensile forces occur, particularly in the frame, compared to conventional deep drawing with an active, external blank holder. Due to the lack of tensile stresses superimposed on the forming area, preforms produced in this way sometimes spring back so significantly that they cannot be, or can only be partially, used for subsequent calibration. Furthermore, excessive deviations from the target geometry can lead to unwanted dimensional deviations remaining in the final component even after calibration. This applies particularly to component deformations such as torsion, bending, and / or curvature, which may not be adequately captured during the calibration process, resulting in unwanted torsion and / or bending remaining even in final, calibrated components. This effect is more pronounced with high-strength / ultra-high-strength materials, especially when the yield strength ratio Re / Rm is high.The existing concepts envisage creating a preform which essentially corresponds to the final geometry, whereby the preform tool with its working surfaces is essentially designed to match the working surfaces of the calibration tool. Summary of the invention

[0006] The invention is therefore based on the objective of providing a generic method and a generic device with which a final component geometry can be produced that has as little or no deviation as possible from the final component geometry (target geometry).

[0007] This problem is solved by a generic method with the features of claim 1.

[0008] According to the teaching of the inventive method, the process for manufacturing a sheet metal component comprises at least two steps: preforming a sheet metal part into a sheet metal preform having in cross-section a bottom, at least one frame, at least one transition between bottom and frame, optionally at least partially a flange and optionally at least partially a transition between frame and flange in a preforming tool, which acts on the sheet metal with its working surfaces, wherein the resulting sheet metal preform has excess sheet metal material at least partially; and final forming of the sheet metal preform into a sheet metal component in a calibration tool, which acts on the sheet metal preform with its working surfaces and in which the excess sheet metal material is compressed substantially in the plane of the sheet metal, and thus, in particular, the sheet thickness increases at least partially.For this purpose, the effective surfaces of the preforming tool of the sheet metal preform to be produced are arranged in such a way as to ensure that, when comparing the preforming tool and the calibration tool, a torsional angle difference of at least 0.2° is set when considering the difference angle between the two principal axes of inertia oriented in the same direction with respect to the respective cross-sectional shape, through the centers of gravity of two parallel cross-sectional surfaces at a distance of 100 mm from the tool gap enclosed by the respective effective surfaces.

[0009] This method is known in the prior art as "classical springback compensation," but for the production of final component geometries in a single-stage forming process (see, for example, EP 3 771 502 A1), so that further measures in the form of an additional process, the calibration process, are no longer necessary. The process according to the invention is designed as a process with at least two stages in at least two tools.

[0010] It has been determined that a final component geometry can be produced that exhibits minimal to no deviation from the final component geometry (target geometry), particularly if a sheet metal preform is already produced that also exhibits minimal to no deviation from the final component geometry. It is generally known from the prior art that it is advantageous for the sheet metal preform geometry to be manufactured in such a way that it corresponds as closely as possible to the final component geometry set in the calibration tool. In particular, springback-induced curvature of the frame should be avoided in the preform itself, within the limitations of the process, which is characterized, for example, by reduced material flow control.

[0011] The inventive approach avoids deformation (torsion / twisting and / or bending) of the spring-back sheet metal preform relative to the final component geometry by appropriately designing the effective surfaces of the sheet metal preform, so that the better the spring-back sheet metal preform corresponds to the final sheet metal component, the more dimensionally accurate the result after calibration will be and the simpler the process control can be, especially in the calibration tool but also in any further subsequent processes.

[0012] The difference in torsion angle is therefore the angle increment when comparing the preforming tool and the calibration tool when considering the difference angle between the principal axes of inertia oriented in the same way with respect to the respective cross-sectional shape through the centroids of two parallel cross-sectional surfaces at a distance of 100 mm of the tool gap enclosed by the respective working surfaces and amounts to at least 0.2°, in particular at least 0.5°, preferably at least 0.7°, more preferably at least 1°, more preferably at least 2° and more preferably at least 3°.

[0013] The classic compensation for springback is therefore strictly bound to geometric freedoms, which must already be considered in the design of the final sheet metal component geometry. For this reason, among others, sheet metal components with hat-shaped cross-sections (bottom-side flanges) are provided with a so-called side opening. Depending on the side opening angle, which is typically in the range of 3 to 8°, there is then a limited possibility of representing the expected springback, particularly of the sides, in the opposite direction within the tool. This is intended to produce sheet metal components that exhibit the required dimensional accuracy after springback. The side opening angle of the final sheet metal component determines the maximum extent of possible compensation in the tool, since only working surfaces without undercuts in the working direction may be used.Should the available space for compensation be insufficient, the final sheet metal component geometry must be adjusted, or the component in question must subsequently be realigned at considerable expense, for example, using elements acting transversely to the working direction of the press. These measures are therefore unnecessary due to the process according to the invention.

[0014] Cumulatively or alternatively, the working surfaces of the preforming tool are configured, in comparison to the working surfaces of the calibration tool, such that, in the sheet metal preform to be produced before springback, a curvature in the longitudinal extent of the sheet metal preform before springback is set, at least in certain areas, which deviates by at least 1%, in particular by at least 2%, preferably by at least 5%, more preferably by at least 7%, and most preferably by at least 9% from the variable curvature in the longitudinal extent of the sheet metal component to be produced. The variable curvature of a component can be described as the curvature of an imaginary B-spline, which is defined by the centroids of the local cross-sections, i.e., the intersection points of the principal axes of the cross-sections. If, along the principal axis in the longitudinal extent of the component, e.g.,By creating a cross-section through the sheet metal component and the sheet metal preform every 50 mm, determining the centroid of each cross-sectional line, and then connecting these intersection points using a B-spline, the curvature lines of the sheet metal component and the (compensated) sheet metal preform before springback, and thus the effective surfaces of the compensated preform tool, can be obtained. If the curvature of the (compensated) sheet metal preform before springback deviates by more than 5% from the curvature of the sheet metal component to be produced at the same location or in the same area, the sheet metal preform is considered compensated with respect to the curvature of the sheet metal component in its longitudinal extent. A 5% deviation means that a component curvature radius of, for example, 500 mm (curvature = 1 / R) would have to become a curvature radius of 475 mm in the (compensated) sheet metal preform before springback.

[0015] The sheet metal preform can be manufactured using any combination of forming processes in one or more steps. Preforming can, for example, include a deep-drawing-like forming step. In particular, multi-stage forming is also possible, including, for example, embossing the base to be created and raising the sides to be created or setting down the flanges to be created. Any combination of folding and / or bending and / or embossing is also conceivable. The deep drawing performed for preforming, for example, can be carried out in a single stage or in multiple stages. Preferably, forming without active material flow control can be used to manufacture the sheet metal preform.

[0016] Upsetting / calibrating refers to the final forming of a sheet metal preform, which can be achieved, for example, through one or more pressing operations. The resulting sheet metal preform incorporates excess sheet material in at least some areas. This excess material has a developed length in the cross-section of the preform that is between 0.5% and 6% longer than the developed length of the finished sheet metal component (target geometry). Specifically, the developed length of these cross-sections of the sheet metal preform is between 0.7% and 4.3% longer than that of the finished sheet metal component.If the developed length of the cross-sections varies too much due to the manufacturing process of the sheet metal preform, an excessively short developed length would result in insufficient excess sheet material for the subsequent calibration process, thus compromising the dimensional accuracy of the final component. Conversely, if the developed length of the cross-section of the sheet metal preform is too long, the oversized sheet material would collapse into waves during the subsequent calibration process, potentially leading to visual and / or dimensional defects. Additionally, there would be an increased risk of tool damage due to excessive compression forces or protruding, pinched component areas, such as sheet metal edges.

[0017] The essentially finished sheet metal component can thus be understood as a fully formed sheet metal component. However, it is possible that the finished sheet metal component may undergo further processing steps that modify the component, such as the addition of connection holes and / or minor final trimming. The aim, however, is to design the calibration die in such a way that, apart from any necessary post-forming operations such as the removal of flanges or the subsequent introduction of embossing, no further forming steps are required. By compressing the excess sheet metal material, at least in certain areas, within the sheet plane, a superposition of compressive stresses occurs within the sheet metal, homogenizing the inhomogeneous residual stress state. This homogenization allows for high dimensional accuracy of the sheet metal component calibrated in this way.

[0018] Both the produced sheet metal preform and the finished sheet metal component essentially have a longitudinal and a transverse extent, with the longitudinal extent being larger than the transverse extent in most sheet metal components. Thus, a cross-section means a section through the transverse extent of the sheet metal preform / sheet metal component.

[0019] A flange is defined as a flange section, at least partially, extending longitudinally and / or transversely on at least one side of the sheet metal component, particularly on both sides. This flange section serves, for example, for connecting to other components and is also referred to as a joining flange. A frame is defined as a rim extending longitudinally on at least one side of the sheet metal component, particularly on both sides. The sheet metal component has, for example, a substantially hat-shaped cross-section, with a rim on each side. The rims may be identical or have different depths, particularly along their longitudinal extent. An integral transition area is provided between the flange and the rims.The base is integrally formed with the frame over a further transition area and, depending on the complexity of the sheet metal component to be produced, need not be limited to a single plane but can also be designed on different planes in its longitudinal and / or transverse direction. The transitions between the individual planes in the base area can be stepped or curved; in particular, a so-called cranked design can be used. The sheet metal component can also have shapes other than those in its longitudinal direction or longitudinal axis; for example, it can be arc-shaped, C-shaped, or L-shaped.

[0020] In contrast to the classic springback compensation and the tooling surface compensation tied to the final component geometry, preform compensation offers the possibility of increasing the frame opening angle of the sheet metal preform relative to the final component geometry. This provides more clearance for necessary compensation measures without undercutting. An increased frame opening angle of the sheet metal preform can be easily processed in the calibration tool, and in particular, reduced again if necessary to 0°, without significantly affecting the dimensional accuracy of the final component geometry. Furthermore, very good results can be achieved in the subsequent calibration tool by adjusting the frame opening (even locally), especially for highly twisted sheet metal preforms.According to one embodiment of the method, the working surfaces of the preforming tool can advantageously be arranged in comparison to the working surfaces of the calibration tool so that a difference in the flange opening angle of at least 0.5°, in particular at least 1°, preferably at least 3°, preferably at least 5°, particularly preferably at least 8°, and more preferably at least 10° is set at the same location in the sheet metal preform to be produced compared to the sheet metal component to be produced.

[0021] The frame opening angle is the angle by which the component frame, relative to the direction of action of the press ram, can be rotated inwards at most around an axis oriented in the longitudinal direction of the sheet metal component in the transition area between the frame and the component base, before an undercut occurs in the tool.

[0022] The difference in the frame opening angle is the difference between the local frame opening angle of the sheet metal preform, in particular the compensated sheet metal preform or the compensated preforming tool, and the local frame opening angle of the sheet metal component at the same location or in the same cross-section. In particular, the cross-sections or cross-sectional areas of the sheet metal preform and the sheet metal component under consideration lie in the same plane.

[0023] According to one embodiment of the method, a steel sheet with a yield strength (Re) of at least 400 MPa is used. The higher the yield strength of the steel sheet, the more unfavorable the springback and / or torsion of the sheet metal preform becomes, so that reliable process control in the calibration tool can no longer be guaranteed. The yield strength can be, in particular, at least 500 MPa, preferably at least 600 MPa, and more preferably at least 700 MPa.

[0024] The aforementioned problem is solved by a device of the generic type, comprising at least one preforming tool for preforming a sheet metal preform, the preform having in cross-section a base, at least one frame, at least one transition between base and frame, optionally at least partially a flange, and optionally at least partially a transition between frame and flange, the preform acting on the sheet metal with its working surfaces, wherein the sheet metal preform has excess sheet metal material at least partially; and at least one calibration tool for upsetting the sheet metal preform into a sheet metal component, the calibration tool acting on the sheet metal preform with its working surfaces, and in which the excess sheet metal material is upset in the plane of the sheet metal, wherein the working surfaces of the preforming tool for the sheet metal preform to be produced are arranged in such a way as to compare with the working surfaces of the calibration tool for the sheet metal component to be produced.that when comparing the preforming tool and the calibration tool, considering the difference angle between the two principal axes of inertia oriented in the same direction with respect to the respective cross-sectional shape, through the centers of gravity of two parallel cross-sectional surfaces at a distance of 100 mm from the tool gap enclosed by the respective working surfaces, a torsional angle difference of at least 0.2° is set, or the working surfaces of the preforming tool are arranged in comparison to the working surfaces of the calibration tool such that, in the sheet metal preform to be produced, before springback, a curvature in the longitudinal extent of the sheet metal preform before springback is set at least in some areas, which deviates by at least 1% from the variable curvature in the longitudinal extent of the sheet metal component to be produced.

[0025] The working surfaces of the preforming tool have been adapted to predetermine the expected deviations of the sheet metal preform from the target geometry of the sheet metal component in the opposite direction. In particular, using FE simulation, it can be predicted that a spring-backed sheet metal preform will deform (twist / torsion) by X° around its main axis in longitudinal extension. Therefore, the working surfaces of the preforming tool are corrected and adapted so that the sheet metal preform is intentionally twisted in the opposite direction by an approximately adequate amount. This ensures that, after unloading, the spring-backed sheet metal preform essentially corresponds to the required target geometry of the sheet metal component to be produced, and that the sheet metal preforms produced in this way can be reliably inserted into the calibration tool, thus improving the calibration result.

[0026] To avoid repetition, reference is made to the explanations of the method according to the invention.

[0027] According to one embodiment of the device, the working surfaces of the preforming tool are arranged in such a way as to ensure that a difference in the frame opening angle of at least 0.5° is set at the same location in the sheet metal preform to be produced compared to the sheet metal component to be produced.

[0028] According to one embodiment of the device, the device comprises a calibration tool with a calibration punch, a calibration die, and one or optionally several elements, wherein the element is arranged in the calibration die and is movable relative to the calibration die. The contour of the calibration punch and the calibration die essentially corresponds to the base, the frame, and the optional flange, as well as the transition areas between the base and frame, and optionally between the frame and flange, of the nominal geometry of the sheet metal component. The element arranged in the calibration die serves to position the sheet metal preform before upsetting / calibrating the preform on the calibration punch. Alternatively, the calibration tool can comprise a calibration punch, a calibration die, and one or optionally several elements, wherein the element is arranged in the calibration punch and is movable relative to the calibration punch.

[0029] For example, if a final sheet metal component with a downward-facing profile in the press position is to be produced, the calibration punch is located at the bottom and the calibration die at the top of the calibration tool and are movable relative to each other. The component is positioned in the calibration die and moves, particularly via the ram stroke, i.e., together with the calibration die, towards the calibration punch. This movement presses the sheet metal preform downwards and positions it securely on the calibration punch, for example, by means of a spring, wedge driver, hydraulics, or pneumatics. During the subsequent ram stroke, a relative movement occurs between the calibration die and the component until the component is finally flush within the calibration die at the bottom dead center.

[0030] Alternatively, if a final sheet metal component with an upward-facing profile in the press position is to be produced, the calibration punch is positioned at the top and the calibration die at the bottom of the calibration tool and are movable relative to each other. The element is located in the calibration punch and moves, particularly via the ram stroke, i.e., together with the calibration punch, towards the calibration die. This movement presses the sheet metal preform downwards and positions it securely in the calibration die, for example, by means of a spring, wedge driver, hydraulics, or pneumatics. During the subsequent ram stroke, a relative movement occurs between the calibration punch and the element until the element is finally flush with the calibration punch at the bottom dead center.

[0031] In a further embodiment of the device, the element arranged in the calibration die, or optionally several elements, is moved in such a controlled manner, for example via the plunger stroke and / or additional control units, which may be driven, for example, by springs, wedge drivers, hydraulics or pneumatics, that a defined distance is maintained between the element and the calibration plunger during the closing of the calibration tool, which is not undercut until the element is fully flush with the calibration die.This defined distance is preferably chosen such that, during the closing of the calibration die, no excessively large force acts on the sheet metal component to be calibrated in the area of ​​the element, and, for example, the surface of the finished component is not unduly damaged by the element, and / or the calibration process is not unduly hindered, and / or the excess material introduced, for example, into the base, is not unduly deformed. If the element is flush with the calibration die during the ram stroke, no further relative movement can occur between the element and the calibration die, so that the element and the calibration die together form a closed working surface without a step. In particular, during closing, the element is essentially flush with the working surface of the calibration die before reaching the lower end position.

[0032] According to a further embodiment of the device, the device comprises a calibration tool with a calibration punch mounted on the press table, a calibration die mounted on the press ram, and a projecting element or optionally several projecting elements, wherein the projecting element is arranged in the calibration punch and is movable relative to the calibration punch. The contour of the calibration punch and the calibration die essentially corresponds to the base, the frame, and the optional flange, as well as the transition areas between the base and frame and, optionally, between the frame and flange, of the nominal geometry of the sheet metal component. The projecting element, which is arranged in the calibration punch, serves to position the sheet metal preform at a predefined height on the calibration punch before upsetting / calibrating the sheet metal preform.The protruding element can, for example, extend up to 30 mm, in particular up to 15 mm, or preferably up to 5 mm, from the calibration die, but not more than 0 mm. Positioning it at a defined height can advantageously affect the position of the sheet metal preform when the calibration tool is closed and, for example, prevent the sheet metal preform from becoming jammed between moving parts of the calibration die, such as when lateral slides are provided. Alternatively, the calibration tool can comprise a calibration die, a calibration die, and a protruding element, or optionally several protruding elements, wherein the protruding element is arranged in the calibration die and is movable relative to the calibration die.

[0033] For example, if the sheet metal component is to be produced as a downward-facing profile in the press position, the calibration punch is located at the bottom and the calibration die at the top of the calibration tool and are movable relative to each other. The element is positioned protruding in the calibration punch and positions the inserted sheet metal preform at a defined height using a force-fit mechanism, for example, springs, wedge drivers, hydraulics, or pneumatics, above the calibration punch. As the calibration die, located above the calibration punch, closes during the progressive stroke of the ram, a relative movement occurs between the calibration punch and the element until the element is finally flush with the calibration punch at the bottom dead center.The previously mentioned element is preferably arranged in its lowest position in the calibration die in such a way that a closed effective surface without a step is obtained and the element and calibration die essentially correspond to the geometry of the sheet metal component to be produced.

[0034] In a further embodiment of the device, the element, which is arranged in the calibration punch by means of a spring, hydraulics, or pneumatics, and projects beyond the effective surface of the calibration punch, can be moved in such a way that the projecting element is preferably flush with the calibration punch before the press stroke reaches bottom dead center. This ensures that the surface of the finished sheet metal component is not unduly damaged by the projecting element during the actual calibration process, and / or that the calibration process is not unduly hindered, and / or that excess material, for example, in the base, is not unduly deformed.

[0035] In a further embodiment of the device, the protruding element or optionally the protruding elements in the calibration punch are combined with a leading element or optionally several leading elements in the calibration die.

[0036] The arrangement of a protruding element or optionally protruding elements can, analogously, also be implemented in the calibration die for a sheet metal component open upwards in the press position. The combination of a protruding element or optionally several protruding elements in the calibration die can, analogously, be implemented with a leading element or optionally several leading elements in the calibration punch.

[0037] According to one embodiment of the device, it is integrated into a press line or transfer press. Particularly in the production of mass-market products, for example, for the automotive industry, sheet metal components are manufactured most economically in press lines or transfer presses. The device can be economically integrated into existing production lines in the form of interchangeable inserts, each containing at least one preforming tool and at least one calibration tool. Use of the device in progressive die presses is also conceivable. Brief description of the drawings

[0038] The invention is explained in more detail below with reference to the drawings. Identical parts are identified by the same reference numerals. Specifically, the drawings show: Fig. 1 shows a sequence for the production of a sheet metal component according to an embodiment of the inventive method and the device in a schematic sectional view, and Fig. 2 shows a perspective view of a simulation of a sheet metal preform and a resulting sheet metal component. Description of the preferred embodiments (Best Mode for Carrying out the Invention)

[0039] In Figure 1A schematic cross-sectional view shows a sequence of an embodiment of a method or device (100) according to the invention. The method according to the invention for manufacturing a sheet metal component (3) comprises at least two steps. Firstly, the method comprises preforming a sheet metal part (1) into a sheet metal preform (2) having in cross-section (Q, Q1.1, Q1.2) a base (2.1), at least one frame (2.2), at least one transition (2.4) between the base (2.1) and the frame (2.2), optionally at least partially a flange (2.3), and optionally at least partially a transition (2.5) between the frame (2.2) and the flange (2.3) in a preforming tool (10), which acts on the sheet metal part (1) with its working surfaces (10.1, 10.2), wherein the sheet metal preform (2) has excess sheet metal material (4) at least partially.Secondly, the process includes finishing the sheet metal preform (2) into a sheet metal component (3) in a calibration tool (20), which acts on the sheet metal preform (2) with its working surfaces (20.1, 20.2) and in which the excess sheet metal material (4) is compressed in the sheet metal plane (E).

[0040] The sectional views of the preforming tool (10) and calibration tool (20) shown in this example refer to a section in the area of ​​a sheet metal preform end and a sheet metal component end, respectively. The working surfaces (10.1, 10.2) of the preforming tool (10) of the sheet metal preform (2) to be produced are configured in relation to the working surfaces (20.1, 20.2) of the calibration tool (20) of the sheet metal component (3) to be produced such that, when comparing the preforming tool (10) and the calibration tool (20) and considering the difference angle between the two principal axes of inertia (A2, A3) oriented in the same direction with respect to the respective cross-sectional shape, through the centroids of two parallel cross-sectional surfaces (Q1.1, Q1.2, Q2.1, Q2.2) spaced 100 mm apart, a torsional angle difference (tdiff) of at least 0.2° is established.

[0041] Cumulatively or alternatively (not shown here) the working surfaces (10.1, 10.2) of the preforming tool (10) can be configured in comparison to the working surfaces (20.1, 20.2) of the calibration tool (20) such that in the sheet metal preform (2) to be produced, compared to the sheet metal component (3) to be produced, at least in certain areas a curvature in the longitudinal extent of the sheet metal preform (2) is set which deviates by at least 1% from the curvature in the longitudinal extent of the sheet metal component (3) to be produced.

[0042] Furthermore, the working surfaces (10.1, 10.2) of the preforming tool (10) can be configured in comparison to the working surfaces (20.1, 20.2) of the calibration tool (20) so that a difference in the flange opening angle (zdiff) of at least 0.5° is set at the same location in the sheet metal preform (2) to be produced compared to the sheet metal component (3) to be produced.

[0043] A flat sheet (1) is, for example, unwound and cut to length as a defined blank or shaped sheet from a metal coil (not shown) and provided to the further process. Preferably, the sheet (1) is made of a steel material, preferably a high-strength steel material, for example with a material thickness between 0.5 and 4 mm. Alternatively, aluminum materials or other metals can also be used.

[0044] According to the invention, the sheet metal (1) is first preformed using conventional methods such that the geometry of the sheet metal preform (2) is provided with excess sheet metal material (4) for the subsequent process. The sheet metal preform (2) can be preformed, for example, by crash forming or alternatively by deep drawing with a spaced sheet metal holder or alternatively by deep drawing. The sheet metal preform (2) is produced, for example, in a preforming tool (10), wherein the flat sheet metal (1) is inserted into the open preforming tool (10) by suitable means (not shown here), and in which the working surfaces (10.1, 10.2) of the preforming tool (10) act on the sheet metal (1). The excess sheet metal material (4) provided at least partially in the sheet metal preform (2) during its production provides the excess sheet metal material (4) necessary for upsetting / calibration, particularly in the base (2).1) The sheet metal preform (2), for example in the form of incorporated waves, embossments, bulges, curves, and / or especially in the frames (2.2) and / or in the optional flanges (2.3) of the sheet metal preform (2), for example by extending them, is taken into account in the preforming tool (10). The production of the sheet metal preform (2) is not limited to one preforming tool (10), but can be carried out in two or more stages or preforming tools, depending on the complexity of the sheet metal component (3) to be produced (not shown here). The design of the sheet metal preform (2) is characterized by flexibility and offers many possibilities for achieving a suitable sheet metal preform (2) due to geometric freedom. This sheet metal preform (2) should be geometrically oriented as closely as possible to the final geometry of the sheet metal component (3).

[0045] After preforming, the sheet metal preform (2) is removed from the preforming tool (10). This preform exhibits springback and / or torsion due to an inhomogeneous, introduced stress state within the preform. In the design of the preforming tool (10), compensatory measures have been implemented in the form of modified effective surfaces (10.1, 10.2) compared to the effective surfaces (20.1, 20.2) of the calibration tool (20) to obtain a sheet metal preform (2) that closely approximates the target geometry of the sheet metal component (3). Fluctuations in springback and / or torsion are compensated for in the calibration tool (20), thus eliminating the need for complex correction loops. The same applies to fluctuations that may arise from batch changes and / or wear of the preforming tools and / or the tribological properties of the tools and material.The sheet metal preform (2) has, at least in some areas in the cross-section (Q), a developed length which is between 0.5% and 6% longer with respect to the developed length of the sheet metal component (3).

[0046] The sheet metal preform (2) is removed from the preforming tool (10) and still exhibits a deviation from its target geometry caused by various influencing factors. The sheet metal preform (2) is placed into a calibration tool (20), which comprises a calibration punch (21) and a calibration die (22). Furthermore, the calibration tool (20) can include an element (23) which is arranged in the calibration die (22) and is movable relative to the calibration die (22). Before closing the calibration tool (20), the inserted sheet metal preform (2) is first fixed or clamped securely in position between the element (23) and the calibration punch (21). During the closing process, the working surfaces (20.1, 20.2) act on the sheet metal preform (2) and, by means of superimposed compressive stress, the excess sheet metal material (4) is compressed in the sheet metal plane (E), so that the sheet metal preform (2) is finished to form a sheet metal component (3) that essentially corresponds to the target geometry.The superposition of compressive stresses, or upsetting in the sheet plane (E), is achieved by acting on the excess material in the sheet preform (2) in the form of, for example, straight or wave-shaped extended component cross-sectional segments, while simultaneously locking the sheet preform over its edges in cross-section (Q). This is done, for example, by the locking mechanism (21.1) in the calibration die (21). In particular, slides (not shown) can also be arranged in the calibration tool to lock the edges of the sheet preform.

[0047] The torsional angle difference (tdiff) thus corresponds to the angle increment of the difference angle between the principal axes of inertia (A2, A3) of the effective surfaces (10.1, 10.2) of the preforming tool (10) of the sheet metal preform to be produced (2), which are oriented in the same direction with respect to the cross-sectional shape, compared to the effective surfaces (20.1, 20.2) of the calibration tool (20) of the sheet metal component to be produced (3), in two parallel cross-sections (Q1.1, Q1.2, Q2.1, Q2.2) at a distance of 100 mm. The cross-sections (Q1.1, Q2.1) and (Q1.2, Q2.2) are, for example, identical, i.e. they are each defined at the same location on the sheet metal preform (2) and on the sheet metal component (3) respectively in the preforming tool (10) and calibration tool (20).The principal axes of inertia (A2, A3) can, for example, be congruent.

[0048] A sheet metal component (3) made of a steel material with a yield strength of 440 MPa and a thickness of 1.5 mm was first designed methodically using an FE simulation and subsequently implemented in the tooling. High-strength and ultra-high-strength steel materials have shown in the past that the sheet metal preforms produced using the previous method deviate from the desired target geometry to such an extent due to their tendency towards pronounced, unwanted springback and / or torsion effects that neither a secure insertion into the calibration tool nor a satisfactory calibration result can be achieved. The difference between the sheet metal preform and the target geometry relates in particular to excessive springback-induced torsion of the entire sheet metal preform (2'). Figure 2Reference numeral (2') shows the sheet metal preform that would result if a sheet metal preform (2') were conventionally produced from a higher-strength steel material. At the end of the sheet metal preform, the torsion at the conventionally produced sheet metal preform is very pronounced compared to the sheet metal component end of the finished sheet metal component (3) and cannot be sufficiently reduced or reliably processed further in subsequent processes. By designing the effective surfaces (10.1, 10.2) of the preforming tool (10) of the sheet metal preform (2) to be produced in comparison to the effective surfaces (20.1, 20.2) of the calibration tool (20) of the sheet metal component (3) to be produced with a between the principal axes of inertia (A2, A3) of the effective surfaces (10.1, 10.2) of the preforming tool (10) oriented the same with respect to the cross-section in two parallel cross-sections (Q1.1, Q1.2, Q2.1, Q2.2) By setting a torsional angle difference (tdiff) of at least 0.2° at intervals of 100 mm, the unwanted springback and / or torsion of the sheet metal preform (2) can be substantially compensated. For example, a counter-torsion to that which occurs during the conventionally manufactured alignment of the sheet metal preform (2') can be set and implemented on the tooling side, so that in the embodiment according to . Figure 2A torsional angle difference (tdiff) of 5° is set to preform a sheet metal preform (2) that closely approximates the target geometry. Based on FE simulations, a corresponding device (100) was implemented in the tooling, and the sheet metal preform (2) could be finished into a sheet metal component (3) with high process reliability in the calibration tool (20). Additionally, the working surfaces (10.1, 10.2) of the preforming tool (10) can be configured, in comparison to the working surfaces (20.1, 20.2) of the calibration tool (20), to ensure that a flange opening angle difference (zdiff) of at least 0.5° is set in the sheet metal preform (2) to be produced compared to the sheet metal component (3). Figure 2 This approach was also taken into account with a frame opening angle difference (zdiff) of 5°, in particular to prevent undercutting in the preforming tool (10).

[0049] The invention is not limited to the embodiments shown. Other sheet metal component shapes are also possible and require correspondingly adapted tool contours. In addition to flanged sheet metal components, flangeless sheet metal components can also be produced with substantially reduced springback. In particular, the tools (10, 20) can be designed as interchangeable tools and used in a production line, especially in a press line, transfer press or progressive die press.

Claims

1. Method for manufacturing a sheet metal component (3), wherein the method comprises at least two steps: - preforming a sheet metal (1) into a sheet metal preform (2) having, in cross section (Q), a base (2.1), at least one side (2.2), at least one transition (2.4) between the base (2.1) and the side (2.2), optionally at least in some areas a flange (2.3) and optionally at least in some areas a transition (2.5) between the frame (2.2) and flange (2.3) in a preforming tool (10) which acts on the sheet metal (1) with its working surfaces (10.1, 10.2), wherein the sheet metal preform (2) has excess sheet metal material (4) at least in some areas; and - finishing of the sheet metal preform (2) to a sheet metal component (3) in a calibration tool (20), which acts with its working surfaces (20.1, 20.2) on the sheet metal preform (2) and in which the excess sheet metal material (4) is compressed in the sheet metal plane (E); characterized in that - the working surfaces (10.1, 10.2) of the preforming tool (10) of the sheet blank (2) to be produced are arranged in such a way that, when comparing the preforming tool (10) and the calibrating tool (20) when viewing the difference angle between the respective cross-sectional shapes of the sheet blank (2) and the sheet component (3), the working surfaces (20.1, 20.2) of the calibrating tool (20) of the sheet component (3) to be produced are located in the sheet plane (E) of the sheet blank (2) and are positioned in such a way that the excess sheet material (4) is compressed in the sheet plane (E) of (3) to be such that, when comparing the preforming tool (10) and the calibrating tool (20) and viewing the difference angle between the two main axes of inertia (A2, A3) oriented in the same direction relative to the respective cross-sectional shape through the centers of gravity of two parallel cross-sectional surfaces (Q1.1, Q1.2, Q2.1, Q2.2) at a distance of 100 mm from the tool gap enclosed by the respective working surfaces (10.1, 10.2, 20.1, 20.2) enclosed by the respective effective surfaces (10.1, 10.2) of the preform mold (10) is set to a torsional angle difference (tdiff) of at least 0.2°, wherein the torsional angle difference (tdiff) corresponds to the angle increment of the difference angle between the main axes of inertia (A2, A3) oriented in the same direction relative to the cross-sectional shape; and / or - the working surfaces (10.1, 10.2) of the preforming tool (10) are arranged such that, in comparison with the working surfaces (20.1, 20.2) of the calibration tool (20) are designed such that, in the sheet metal preform (2) to be produced in the preforming tool ( ), at least in some areas, a curvature in the longitudinal extension of the sheet metal preform (2) is produced in comparison to the sheet metal component (3) to be produced is set in the sheet metal preform (2) to be produced in comparison to the sheet metal component (3) to be produced, which deviates by at least 1% from the curvature in the longitudinal direction of the sheet metal component (3) to be produced, wherein the variable curvature of a component is defined as the curvature of an imaginary B-spline defined by the centers of gravity of the local cross sections, i.e., the intersections of the main axes of the cross sections.

2. Method according to claim 1, wherein the working surfaces (10.1, 10.2) of the preforming tool (10) are arranged in such a way that, in comparison to the working surfaces (20.1, 20.2) of the calibration tool (20) are designed such that a frame opening angle difference (zdiff) of at least 0.5° is set at the same point in the sheet metal preform (2) to be produced compared to the sheet metal component (3) to be produced.

3. Method according to claim 1 or 2, wherein a steel sheet with a yield strength Re of at least 400 MPa is used.

4. Method according to one of the preceding claims, wherein the calibration tool (20) comprises a calibration punch (21), a calibration die (22) and an element (23) or optionally several elements, wherein the element (23) is arranged in the calibration die (22) and is moved relative to the calibration die (22).

5. Method according to claim 4, wherein the calibration punch (21) is arranged at the bottom and the calibration die (22) at the top of the calibration tool (20).

6. Method according to any of claims 1 to 4, wherein the calibration tool (20) comprises a calibration punch (21), a calibration die (22) and an element (23) or optionally several elements, wherein the element (23) is arranged in the calibration punch (21) and is moved relative to the calibration punch (21).

7. Method according to claim 6, wherein the calibration punch (21) is arranged at the top and the calibration die (22) is arranged at the bottom of the calibration tool (20).

8. Method according to claim 4, wherein the element or optionally several elements arranged in the calibration die are moved in a controlled manner via the ram stroke and / or additional control units ( ) in such a way that a defined distance between the element and the calibration punch is obtained during the closing of the calibration tool.

9. Method according to claim 8, wherein during closing, before reaching the lower end position, the element is substantially flush with the effective surface of the calibration die.

10. Method according to claim 6, wherein the element or optionally several elements arranged in the calibration punch are moved in such a way via the ram stroke and / or additional control units that a defined distance between the element and the calibration die is obtained during the closing of the calibration tool.

11. Method according to claim 10, wherein the element is essentially flush with the effective surface of the calibration die during closing before reaching the lower end position.

Images