METHOD FOR THE PRODUCTION OF SHEET METAL PARTS AND DEVICE THEREFOR
The invention relates to a method and to a device for producing sheet metal components with substantially reduced springback.
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The invention relates to a method and to a device for producing sheet metal components.
BACKGROUND OF THE INVENTIONMethods and devices for producing 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, and DE 10 2013 103 751 A1, wherein production is carried out in at least two stages (forming processes). In the first stage, a forming blank, in particular a flat forming blank, is formed to give a preform. Relative to the final component geometry to be produced, the preform has an excess of material, which is distributed as uniformly as possible. In the second stage, referred to as sizing, this additional excess material is compressed in the direction of the sheet plane. During this process, the inhomogeneous state of stress of the preform is realigned, and the unwanted, batch-dependent springback of the component, which occurs especially in the case of ultra-high-strength materials in combination with small sheet thicknesses, is therefore very largely avoided. DE 10 2018 210 174 A1 furthermore discloses the production of a flangeless sheet metal component of high dimensional accuracy by producing, from a forming blank, a preform with an opening angle of the bodies of less than 6°, which is then sized to give a final sheet metal component.
Various boundary conditions must be observed during the production of the preform. Thus, the lengths of the local developments of the cross section must change only within narrow limits, even when influencing variables such as friction, mechanical properties of the material batch employed, and tool wear vary. It is therefore necessary to design the preforming tool at least with a spaced outer blank holder or else preferably entirely without an outer blank holder (“crash forming” or else “stamping/edging”). This prevents the forming blanks being stretched to a greater or lesser extent in the preforming tool as a function of the abovementioned influencing factors in the course of producing a number of components and when using different material batches. Such uncontrolled stretching of the material from component to component would have the effect that the distribution of the excess material for the subsequent sizing operation would stray under certain circumstances from the permissible range of values that could be managed in a reliable process.
As a result, the tensile forces, particularly in the bodies, that occur during the production of the preform are reduced in comparison with conventional manufacture by deep drawing with an active outer blank holder. Sometimes, the absence of superposition of the forming region with tensile stresses means that preforms produced in this way spring back to such an extent that they can only be fed in to a limited extent, if at all, during the subsequent sizing process. Moreover, excessive deviations from the setpoint geometry have the effect that there may still be unwanted dimensional deviations in the final component even after sizing. This applies especially to deformations to the component, such as torsion, bending and/or curvature, which may not be sufficiently accommodated in the sizing process, with the result that there may still be unwanted torsion and/or bending of the final, sized components. This effect is reinforced in the case of higher/ultra-high strength materials, especially if the ratio of yield point to tensile strength Re/Rm assumes high values.
The previous concepts envisage producing a preform which corresponds substantially to the final geometry, with the effective surfaces of the preforming tool being designed substantially to match the effective surfaces of the sizing tool.
SUMMARY OF THE INVENTIONIt is therefore the underlying object of the invention to provide a method of the type in question and a device of the type in question by means of which it is possible to produce a final component geometry that has as little as possible or no deviation from the final component geometry (setpoint geometry).
This object is achieved by a method of the type in question having the features of patent claim 1.
This object is achieved by a device of the type in question having the features of patent claim 4.
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- at least one body, at least one transition between the base and the body, optionally, at least in some region or regions, a flange, and optionally, at least in some region or regions, a transition between the body and the flange in a preforming tool, which acts by means of its effective surfaces on the metal sheet, wherein the resulting sheet metal preform has excess sheet metal material, at least in some region or regions; and final forming of the sheet metal preform to give a sheet metal component in a sizing tool, which acts by means of its effective surfaces on the sheet metal preform, and in which the excess sheet metal material is compressed in the sheet plane, and as a result particularly the sheet thickness increases, at least in some region or regions. For this purpose, the effective surfaces of the preforming tool of the sheet metal preform to be produced are configured in such a way in comparison with the effective surfaces of the sizing tool of the sheet metal component to be produced that, when the preforming tool and the sizing tool are compared, a torsion angle difference of at least 0.2° is established on consideration of the differential angle between the main axes of inertia-said axes being oriented the same way with respect to the respective cross-sectional shape—through the centroids of two parallel cross-sectional areas, 100 mm apart, of the tool gap enclosed by the respective effective surfaces.
This method is known in the prior art as “conventional compensation of springback”, but is intended for production of final component geometries in a single stage forming process, cf. for example EP 3 771 502 A1, and therefore further measures in the form of an additional process, the sizing process, are no longer required. The process according to the invention is designed to be in at least two stages in at least two tools.
It has been observed that it is possible to produce a final component geometry which has as little as possible or no deviation with respect to the final component geometry (setpoint geometry), especially if the sheet metal preform produced is also already one which has as little as possible or no deviation with respect to the final component geometry. It is a matter of common knowledge from the prior art that it is advantageous in principle if the geometry of the sheet metal preform is produced in such a way that it corresponds as closely as possible to the final component geometry, which is established in the sizing tool. The springback-induced curvature of the bodies, in particular, should be avoided even in the preform within the scope of the possibilities of the method, which is characterized, for example, by reduced material flow control.
By means of the approach according to the invention, deformation (torsion/twisting and/or bending) of the sprung-back sheet metal preform relative to the final component geometry is avoided by appropriate configuration of the effective surfaces of the sheet metal preform, and therefore the better the sprung-back sheet metal preform corresponds to the final sheet metal component, the more dimensionally accurate will be the result after sizing and the simpler process management, especially in the sizing tool, but also in any other subsequent processes provided, can be.
The torsion angle difference is thus the angle increment when comparing the preforming tool and the sizing tool, on consideration of the differential angle between the main axes of inertia—said axes being oriented the same way with respect to the respective cross-sectional shape—through the centroids of two parallel cross-sectional surfaces, 100 mm apart, of the tool gap enclosed by the respective effective surfaces, and is at least 0.2°, in particular at least 0.5°, preferably at least 0.7°, preferably at least 1°, as a further preference at least 2° and, as a further preference, at least 3°.
Thus the conventional compensation of springback is tied strictly to geometrical degrees of freedom, which must be taken into account even in the configuration of the geometry of the sheet metal component. For this reason, inter alia, sheet metal components with hat-shaped cross sections (base-bodies-flanges), in particular, must be provided with a “body opening”. Depending on the body opening angle, which is generally in a range of 3 to 8°, there is the limited possibility of reproducing the springback to be expected, in particular that of the bodies, in the opposite direction in the tool. This should then produce sheet metal components which have the required dimensional accuracy after springback. The body opening angle of the final sheet metal component determines the maximum extent of possible compensation in the tool since only effective surfaces without an undercut in the working direction can be used. If the available space is not sufficient for compensation, the final geometry of the sheet metal component must be adapted or, alternatively, elements acting transversely to the working direction of the press must be used to retrospectively rectify the sheet metal component concerned at great expense, for example. These measures are therefore rendered superfluous by the process according to the invention.
Cumulatively or alternatively, the effective surfaces of the preforming tool are configured in such a way in comparison with the effective surfaces of the sizing tool that a curvature in the longitudinal extent of the pre-springback sheet metal preform that deviates by at least 1%, in particular by at least 2%, preferably by at least 5%, preferably by at least 7%, particularly preferably by at least 9%, from the variable curvature in the longitudinal extent of the sheet metal component to be produced is established at least in some region or regions in the sheet metal preform to be produced in comparison with the pre-springback sheet metal component to be produced. The variable curvature of a component can be described as the curvature of an imaginary B spline defined by the centroids of the local cross sections, i.e. the points of intersection of the cross section main axes. If a cut is made through the sheet metal component and the sheet metal preform every 50 mm, for example, along the main axis in the longitudinal extent of the component, the centroid of the cross section lines is determined, and these points of intersection are then connected by means of a B spline, it is possible in this way to preserve the lines of curvature of the sheet metal component and the (compensated) pre-springback sheet metal preform, and thus the effective surfaces of the, in particular compensated, preforming tool. If the curvature of the (compensated) pre-springback sheet metal preform deviates by more than 5%, for example, from the curvature of the sheet metal component to be produced at the same location or in the same region, the sheet metal preform counts as compensated in respect of the curvature of the sheet metal component in the longitudinal extent. 5% deviation—this means that a component radius of curvature of, for example, 500 mm (curvature=1/R) in the (compensated) sheet metal preform before springback would have to become a radius of curvature of 475 mm.
In this context, the sheet metal preform can be produced by any combination of forming methods in one or more steps. Preforming can comprise a forming step similar to deep drawing, for example. In particular, it is also possible to perform multistage forming, comprising, for example, stamping the base to be produced and raising the bodies to be produced or dropping the flanges to be produced. Any desired combinations of edging and/or bending and/or stamping are also conceivable. The deep drawing carried out, for example, for the purpose of preforming can be performed, in particular, in one or more stages. Forming can preferably be performed without active material flow control to produce the sheet metal preform.
Compression/sizing is understood to mean final forming of the sheet metal preform and can be achieved, for example, by one or more press operations. In the sheet metal preform produced, excess sheet metal material is provided at least in some region or regions. At least in some region or regions, the excess sheet metal material in the sheet metal preform has a developed length in cross section which is between 0.5% and 6% longer than the developed length of the fully formed sheet metal component (setpoint geometry). Here, the developed length of the cross sections of the sheet metal preform which are thus considered in this way is, in particular, from 0.7% to 4.3% longer than that of the fully formed sheet metal component. If the developed length of the cross sections were to vary too much on account of the process management during the production of the sheet metal preform, insufficient excess sheet metal material would be available for the subsequent sizing process if the developed length were too short, as a result of which the dimensional accuracy of the final component would be compromised. If, on the other hand, the developed length of the sheet metal preform cross section considered were too great, the sheet metal material, which would thus be overdimensioned, would collapse into corrugations during the subsequent sizing process, which could entail optical and/or dimensional defects. In addition, there would be an increased risk of tool damage due to excessive compression forces or projecting squeezed component regions, e.g. sheet edges.
The substantially fully formed sheet metal component can thus be understood as the finally formed sheet metal component. However, it is also possible for the fully formed sheet metal component to be subjected to additional processing steps that modify the sheet metal component, e.g. in order to introduce attachment holes or a small final trimming cut. However, the aim is to configure the sizing die in such a way that, apart from any subsequent forming operations that may be required, such as the dropping of flanges or the downstream introduction of stamped features, no further forming steps are necessary. Compressing the sheet metal material that is in excess at least in some region or regions in the sheet plane gives rise to compressive stress superposition within the sheet metal material, and homogenization of the inhomogeneous state of internal stress is produced, thereby making it possible to achieve high dimensional accuracy of the sheet metal component sized in this way.
The sheet metal preform produced and the fully formed sheet metal component essentially have a longitudinal extent and a transverse extent, with the longitudinal extent being larger in terms of dimensioning than the transverse extent in the case of most sheet metal components. Thus, “cross section” means a section through the transverse extent of the sheet metal preform/sheet metal component.
“Flange” refers to the provision in the longitudinal extent and/or transverse extent of a flange portion that is provided at least in some region or regions at least on one side of the sheet metal component, in particular on both sides of the sheet metal component, and is used, for example, for connection to other components and is also referred to as a joining flange. The body is provided in the longitudinal extent at least on one side of the sheet metal component, in particular on both sides of the sheet metal component, wherein the sheet metal component has a cross section which is, for example, substantially in the form of a hat, with a body on each of the two sides, wherein the bodies can be of identical design but can also be embodied with different depths, in particular along the longitudinal extent. There is an integral transitional region between the flange and the bodies. The base is formed integrally with the body over a further transitional region and, depending on the complexity of the sheet metal component to be produced, does not have to be limited to one plane but can also be provided in different planes in the longitudinal and/or transverse extent in some region or regions. The transitions between the individual planes in the base region can be embodied stepwise or in a curved manner; in particular, it is possible to refer to an “offset” embodiment. The sheet metal component can also have shapes other than those which are in the longitudinal extent or longitudinally axial, e.g. it can be of arcuate, C-shaped or L-shaped design.
In contrast to the conventional compensation of springback and compensation of the tool effective surfaces which is associated with the final component geometry, there is the possibility, when compensating the preform, to enlarge the body opening angle of the sheet metal preform relative to the final component geometry in order thereby to achieve more freedom for necessary compensatory measures without an undercut. An enlarged body opening angle of the sheet metal preform can be processed, in particular reduced again, if necessary to 0°, without problems in the sizing tool and has virtually no effect on the dimensional accuracy of the final component geometry. In the case of (even local) adaptation of the body opening, on the other hand, it is possible to achieve very good results in the subsequent sizing tool, especially for highly twisted sheet metal preforms. Thus, according to one embodiment of the method, it is advantageously possible to configure the effective surfaces of the preforming tool in such a way in comparison with the effective surfaces of the sizing tool that a body opening angle difference of at least 0.5°, in particular at least 1°, preferably at least 3°, preferably at least 5°, particularly preferably at least 8°, as a further preference at least 10°, is established at the same location in the sheet metal preform to be produced in comparison with the sheet metal component to be produced.
Here, the body opening angle is the angle by which the component body can be rotated inward to the maximum extent relative to the direction of action of the press ram about an axis oriented in the longitudinal direction of the sheet metal component in the transitional region between the body and the component base before an undercut results in the tool.
The body opening angle difference is the difference between the local body opening angle of the sheet metal preform, in particular the compensated sheet metal preform or the compensated preforming tool, and the local body opening angle of the sheet metal component at the same location or in the same cross section. In particular, the considered cross sections or cross-sectional areas of the sheet metal preform and of the sheet metal component are in the same plane.
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 less favorable is the springback and/or the torsion of the sheet metal preform, and therefore reliable process management can no longer be ensured in the sizing tool. In particular, the yield strength can be at least 500 MPa, preferably at least 600 MPa, preferably at least 700 MPa.
The object stated at the outset is achieved in a device of the type in question, having at least one preforming tool for preforming a metal sheet to give a sheet metal preform having, in cross section, a base, at least one body, at least one transition between the base and the body, optionally, at least in some region or regions, a flange, and optionally, at least in some region or regions, a transition between the body and the flange, which preforming tool acts by means of its effective surfaces on the metal sheet, wherein the sheet metal preform has excess sheet metal material, at least in some region or regions; and having at least one sizing tool for compressing the sheet metal preform to give a sheet metal component, which sizing tool acts by means of its effective surfaces on the sheet metal preform, and in which the excess sheet metal material is compressed in the sheet plane, wherein the effective surfaces of the preforming tool of the sheet metal preform to be produced are configured in such a way in comparison with the effective surfaces of the sizing tool of the sheet metal component to be produced that, when the preforming tool and the sizing tool are compared, a torsion angle difference of at least 0.2° is established on consideration of the differential angle between the two main axes of inertia-said axes being oriented the same way with respect to the respective cross-sectional shape—through the centroids of two parallel cross-sectional areas, 100 mm apart, of the tool gap enclosed by the respective effective surfaces, or the effective surfaces of the preforming tool are configured in such a way in comparison with the effective surfaces of the sizing tool that a curvature in the longitudinal extent of the pre-springback sheet metal preform that deviates by at least 1% from the variable curvature in the longitudinal extent of the sheet metal component to be produced is established at least in some region or regions in the pre-springback sheet metal preform to be produced in comparison with the sheet metal component to be produced.
The effective surfaces of the preforming tool have been adapted in such a way that the expected deviations in the sheet metal preform with respect to the setpoint geometry of the sheet metal component are reproduced in advance in the opposite direction. With the aid of FE simulation, it is possible, in particular, to predict that a sprung-back sheet metal preform will be deformed (twisted/torsioned upon itself) in the longitudinal extent by X° about the main axis, thus ensuring that the effective surfaces of the preforming tool are corrected and adapted in such a way that the sheet metal preform is torsioned in advance in the opposite direction by an approximately adequate amount. It is ensured that, after load relief, the sprung-back sheet metal preform corresponds substantially to the required setpoint geometry of the sheet metal component to be produced, and the sheet metal preforms produced can be inserted reliably into the sizing tool, and the sizing result can be improved.
In order to avoid repetitions, attention is drawn to the statements relating to the method according to the invention.
According to one embodiment of the device, the effective surfaces of the preforming tool are configured in such a way in comparison with the effective surfaces of the sizing tool that a body opening angle difference of at least 0.5° is established at the same location in the sheet metal preform to be produced in comparison with the sheet metal component to be produced.
According to one embodiment of the device, the device comprises a sizing tool having a sizing punch, a sizing die and one element or optionally a plurality of elements, wherein the element is arranged in the sizing die and can be moved relative to the sizing die. The contour of the sizing punch and of the sizing die corresponds substantially in the base, the body and the optional flange and the transitional regions between the base and the body and optionally the body and the flange to the setpoint geometry of the sheet metal component. Here, the element which is arranged in the sizing die is used to position the sheet metal preform on the sizing punch before the compression/sizing of the sheet metal preform. Alternatively, the sizing tool can comprise a sizing punch, a sizing die and one element or optionally a plurality of elements, wherein the element is arranged in the sizing punch and can be moved relative to the sizing punch.
If a final sheet metal component with a profile that is open downward in the press position is to be produced, for example, the sizing punch is arranged at the bottom and the sizing die at the top in the sizing tool, and they can be moved relative to one another. The element is arranged in the sizing die, is moved, in particular, by the ram stroke, i.e. together with the sizing die in the direction of the sizing punch, in the process pushes the sheet metal preform downward and positions it nonpositively, e.g. by means of a spring, drift pin, hydraulic cylinder or pneumatics, on the sizing punch. In the course of the further ram stroke, there is a relative movement between the sizing die and the element until, finally, the element is retracted flush in the sizing die in the bottom dead center position.
If, alternatively, a final sheet metal component with a profile that is open upward in the press position is to be produced, the sizing punch is arranged at the top and the sizing die at the bottom in the sizing tool, and they can be moved relative to one another. The element is arranged in the sizing punch, is moved, in particular, by the ram stroke, i.e. together with the sizing punch in the direction of the sizing die, in the process pushes the sheet metal preform downward and positions it nonpositively, e.g. by means of a spring, drift pin, hydraulics or pneumatics, in the sizing die. In the course of the further ram stroke, there is a relative movement between the sizing punch and the element until, finally, the element is retracted flush in the sizing punch in the bottom dead center position.
In another embodiment of the device according to the invention, the element or, optionally, a plurality of elements arranged in the sizing die is moved in a controlled manner by means, for example, of the ram stroke and/or additional control units in such a way, e.g. by means of springs, drift pins, hydraulics or pneumatics, that a defined distance is obtained between the element and the sizing punch during the closure of the sizing tool, and this distance is not undershot until the element has been retracted fully flush in the sizing die. This defined distance is preferably chosen in such a way that the force acting on the sheet metal component to be sized is not impermissible in the region of the element during the closure of the sizing die, and, for example, the surface of the fully formed component is not impermissibly damaged by the element, and/or the sizing process is not impermissibly hindered, and/or the material excess introduced in the base, for example, is not impermissibly deformed. Once the element has entered flush into the sizing die during the ram stroke, there can therefore be no further relative movement between the element and sizing die, as a result of which the element together with the sizing die forms a closed effective surface without an offset. In particular, the element ends substantially flush with the effective surface of the sizing die during closure, before the lower end position is reached.
According to another embodiment of the device, the device comprises a sizing tool having a sizing punch mounted on the press table, a sizing die mounted on the press ram, and a projecting element or optionally a plurality of projecting elements, wherein the projecting element is arranged in the sizing punch and can be moved relative to the sizing punch. The contour of the sizing punch and of the sizing die corresponds substantially in the base, the body and the optional flange and the transitional regions between the base and the body and optionally between the body and the flange to the setpoint geometry of the sheet metal component. Here, the projecting element which is arranged in the sizing punch is used to position the sheet metal preform in a predefined vertical position on the sizing punch before the compression/sizing of the sheet metal preform. The projecting element can project by up to 30 mm, in particular up to 15 mm or preferably up to 5 mm from the sizing punch, for example, but >0 mm. Positioning in a defined vertical position can have an advantageous effect on the position of the sheet metal preform during the closure of the sizing tool and, for example, can prevent trapping of the sheet metal preform between the moving parts of the sizing die, e.g. in the case where lateral slides are provided. Alternatively, the sizing tool can comprise a sizing punch, a sizing die and one projecting element or optionally a plurality of projecting elements, wherein the projecting element is arranged in the sizing die and can be moved relative to the sizing die.
If the sheet metal component is to be produced as a profile that is open downward in the press position, the sizing punch is arranged at the bottom and the sizing die at the top in the sizing tool, and they can be moved relative to one another. The element is arranged in the sizing punch so as to project and positions the inserted sheet metal preform nonpositively in a defined vertical position over the sizing punch, e.g. by means of springs, drift pins, hydraulics or pneumatics. During the closure of the sizing die arranged above the sizing punch, in the course of the further ram stroke, there is a relative movement between the sizing punch and the element until, finally, the element is retracted flush in the sizing punch in the bottom dead center position. In its lowermost position, the previously projecting element is preferably arranged in the sizing punch in such a way that a closed effective surface without an offset is obtained, and the element and sizing punch correspond substantially to the geometry of the sheet metal component to be produced.
In another embodiment of the device according to the invention, the element arranged in the sizing punch by means of a spring, hydraulics or pneumatics and projecting beyond the effective surface of the sizing punch is moved in a controlled manner, e.g. by way of the ram stroke or other control units, which may be driven by means of springs, drift pins, hydraulics or pneumatics for example, in such a way that the projecting element is already preferably recessed flush in the sizing punch even before the bottom dead center position of the press stroke is reached. It is thereby possible to ensure that, during the actual sizing process, the surface of the fully formed sheet metal component is not impermissibly damaged by the projecting element, and/or the sizing process is not impermissibly hindered, and/or the material excess introduced in the base, for example, is not impermissibly deformed.
In another embodiment of the device according to the invention, the projecting element or optionally the projecting elements in the sizing punch are combined with one leading element or optionally a plurality of leading elements in the sizing die.
The arrangement of one projecting element or optionally projecting elements can also be implemented analogously in the sizing die for a sheet metal component that is open upward in the press position. The combination of one projecting element or optionally a plurality of projecting elements in the sizing die can be implemented analogously with one leading element or optionally with a plurality of leading elements in the sizing punch.
According to one embodiment of the device, the device is integrated in a press line or transfer press. Particularly when producing mass-produced products, e.g. for products in the vehicle industry, products such as sheet metal components are, in particular, produced economically in press lines or transfer presses. The device according to the invention can be used economically in existing production lines in the form of interchangeable inserts which provide at least one preforming tool and at least one sizing tool. The use of the device according to the invention in compound progressive presses is also conceivable.
The invention is explained in greater detail below with reference to drawings. Identical parts are provided with the same reference signs. More particularly:
The method according to the invention for producing a sheet metal component (3) comprises at least two steps. On the one hand, the method comprises preforming a metal sheet (1) to give a sheet metal preform (2) having, in cross section (Q, Q1.1, Q 1.2), a base (2.1), at least one body (2.2), at least one transition (2.4) between the base (2.1) and the body (2.2), optionally, at least in some region or regions, a flange (2.3), and optionally, at least in some region or regions, a transition (2.5) between the body (2.2) and the flange (2.3) in a preforming tool (10), which acts by means of its effective surfaces (10.1, 10.2) on the metal sheet (1), wherein the sheet metal preform (2) has excess sheet metal material (4), at least in some region or regions. On the other hand, the method comprises final forming of the sheet metal preform (2) to give a sheet metal component (3) in a sizing tool (20), which acts by means of its effective 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 plane (E).
In this example, the sections of the preforming tool (10) and of the sizing tool (20) which are shown relate to a section in the region of one end of the sheet metal preform or one end of the sheet metal component. The effective surfaces (10.1, 10.2) of the preforming tool (10) of the sheet metal preform (2) to be produced are configured in such a way in comparison with the effective surfaces (20.1, 20.2) of the sizing tool (20) of the sheet metal component (3) to be produced that, when the preforming tool (10) and the sizing tool (20) are compared, a torsion angle difference (tdiff) of at least 0.2° is established on consideration of the differential angle between the two main axes of inertia (A2, A3)—said axes being oriented the same way with respect to the respective cross-sectional shape—through the centroids of two parallel cross-sectional areas (Q1.1, Q1.2, Q2.1, Q2.2) 100 mm apart.
Cumulatively or alternatively (not illustrated here), the effective surfaces (10.1, 10.2) of the preforming tool (10) can be configured in such a way in comparison with the effective surfaces (20.1, 20.2) of the sizing tool (20) that a curvature in the longitudinal extent of the sheet metal preform (2) that deviates by at least 1% from the curvature in the longitudinal extent of the sheet metal component (3) to be produced is established at least in some region or regions in the sheet metal preform (2) to be produced in comparison with the sheet metal component (3) to be produced.
Moreover, the effective surfaces (10.1, 10.2) of the preforming tool (10) can be configured in such a way in comparison with the effective surfaces (20.1, 20.2) of the sizing tool (20) that a body opening angle difference (zdiff) of at least 0.5° is established at the same location in the sheet metal preform (2) to be produced in comparison with the sheet metal component (3) to be produced.
A flat metal sheet (1) is, for example, uncoiled as a defined blank or forming blank from a metal coil (not illustrated) and cut to length, and made available to the subsequent process. The metal sheet (1) is preferably produced from a steel material, preferably from a relatively high strength steel material, e.g. with a material thickness of between 0.5 and 4 mm. Alternatively, it is also possible to use aluminum materials or other metals.
According to the invention, it is envisaged that the metal sheet (1) is first of all preformed by conventional methods in such a way 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 by means of crash forming, for example, or, alternatively, by means of deep drawing with a spaced blank holder or, alternatively, by means of deep drawing. The sheet metal preform (2) is produced in a preforming tool (10), for example, wherein the flat metal sheet (1) is inserted into the open preforming tool (10) by suitable means (not illustrated here), and in which the effective surfaces (10.1, 10.2) of the preforming tool (10) act on the metal sheet (1). By means of the excess sheet metal material (4) provided in the sheet metal preform (2), at least in some region or regions, during the production of the sheet metal preform (2), the excess sheet metal material (4) required for compression/sizing, particularly in the base (2.1) of the sheet metal preform (2), e.g. in the form of introduced corrugations, stamped features, bulges, arched formations, and/or particularly in the bodies (2.2) and/or in the optional flanges (2.3) of the sheet metal preform (2), e.g. by extension thereof, is allowed for in the preforming tool (10). The production of the sheet metal preform (2) is not limited to one preforming tool (10) but, depending on the complexity of the sheet metal component (3) to be produced, can take place in two or more stages or in preforming tools (not illustrated here). The configuration of the sheet metal preform (2) is distinguished by flexibility and, through geometrical degrees of freedom, allows many possibilities for achieving a suitable sheet metal preform (2). This sheet metal preform (2) should be oriented geometrically as close as possible to the final geometry of the sheet metal component (3).
After preforming, the sheet metal preform (2) is removed from the preforming tool (10), which exhibits springback and/or torsion due to a nonuniform introduced state of stress in the sheet metal preform (2). In the configuration of the preforming tool (10), compensatory measures in the form of modified effective surfaces (10.1, 10.2) in comparison with the effective surfaces (20.1, 20.2) of the sizing tool (20) can be taken in order to obtain a sheet metal preform (2) which comes as close as possible to the setpoint geometry of the sheet metal component (3). Fluctuations in the springback and/or torsion are compensated in the sizing tool (20), and therefore complex correction grinding operations are not required here. The same applies to fluctuations that may result from batch changes and/or wear on the preforming tools and/or the tribological properties of the tools and material. At least in some region or regions, the sheet metal preform (2) has a developed length in cross section which is between 0.5% and 6% longer than the developed length of the sheet metal component (3).
The sheet metal preform (2) is removed from the preforming tool (10) and still has a deviation from its setpoint geometry caused by various influencing variables. The sheet metal preform (2) is placed in a sizing tool (20), which comprises a sizing punch (21) and a sizing die (22). Furthermore, the sizing tool (20) can comprise an element (23) which is arranged in the sizing die (22) and can be moved relative to the sizing die (22). Before closure of the sizing tool (20), the inserted sheet metal preform (2) is first of all fixed or clamped securely in position between the element (23) and the sizing tool (21). During the process of closure, the effective surfaces (20.1, 20.2) act on the sheet metal preform (2) and, by virtue of compressive stress superposition, the excess sheet metal material (4) is compressed in the sheet plane (E), with the result that the sheet metal preform (2) is fully formed into a sheet metal component (3) corresponding substantially to the setpoint geometry. The compressive stress superposition or compression in the sheet plane (E) is accomplished by action on the excess material in the sheet metal preform (2) in the form, for example, of cross-sectional segments of the component extended in a rectilinear or undulating manner while simultaneously locking the sheet metal preform by way of its edges in cross section (Q). This is accomplished, for example, by the locking feature (21.1) in the sizing punch (21). In particular, it is also possible to arrange slides (not illustrated) for locking the edges of the metal preform in the sizing tool.
The torsion angle difference (tdiff) thus corresponds to the angle increment of the differential angle between the main axes of inertia (A2, A3)—said axes being oriented the same way with respect to the cross-sectional shape—of the effective surfaces (10.1, 10.2) of the preforming tool (10) of the sheet metal preform (2) to be produced in comparison with the effective surfaces (20.1, 20.2) of the sizing tool (20) of the sheet metal component (3) to be produced, between the main axes of inertia (A2, A3)—said axes being oriented the same way with respect to the cross section—of the effective surfaces (10.1, 10.2) of the preforming tool (10) in comparison with the effective surfaces (20.1, 20.2) of the sizing tool (20) in two parallel cross sections (Q1.1, Q1.2, Q2.1, Q2.2) 100 mm apart. The cross sections (Q1.1, Q2.1) and (Q1.2, Q2.2) are, for example, congruent, i.e. they are each determined at the same location on the sheet metal preform (2) and on the sheet metal component (3), and in the preforming tool (10) and the sizing tool (20). The main axes of inertia (A2, A3) can be congruent, for example.
In terms of method, a sheet metal component (3) made from a steel material with a yield strength of 440 MPa and a thickness of 1.5 mm was first of all designed in the context of FE simulation, and it was then implemented in terms of tooling. Relatively high and ultra-high strength steel materials have shown in the past that the sheet metal preforms produced by means of the previous procedure deviate from the desired setpoint geometry to such an extent, on account of their tendency for highly pronounced unwanted springback and/or torsion effects, that neither reliable insertion into the sizing tool nor a satisfactory sizing result can be achieved. Here, the difference between the sheet metal preform and the setpoint geometry refers particularly to excessive springback-related torsion of the overall sheet metal preform (2′). In
The invention is not restricted to the embodiments shown. Other shapes of sheet metal component are likewise possible and require correspondingly adapted tool contours. In addition to flanged sheet metal components, it is also possible to produce flangeless sheet metal components with substantially reduced springback. In particular, the tools (10, 20) can be designed as interchangeable tools and can be used in a production line, particularly in a press line, transfer press or compound progressive press.
Claims
1. A method for producing a sheet metal component, wherein the method comprises at least two steps:
- preforming a metal sheet to give a sheet metal preform having, in cross section (Q), a base, at least one body, at least one transition between the base and the body, at least in some region or regions, a flange, and at least in some region or regions, a transition between the body and the flange in a preforming tool, which acts by means of its effective surfaces on the metal sheet, wherein the sheet metal preform has excess sheet metal material, at least in some region or regions; and
- final forming of the sheet metal preform to give a sheet metal component in a sizing tool, which acts by means of its effective surfaces on the sheet metal preform, and in which the excess sheet metal material is compressed in the sheet plane (E);
- wherein the effective surfaces of the preforming tool of the sheet metal preform to be produced are configured in such a way in comparison with the effective surfaces of the sizing tool of the sheet metal component to be produced that, at least on of (i) when the preforming tool and the sizing tool are compared, a torsion angle difference (tdiff) of at least 0.2° is established on consideration of the differential angle between the two main axes of inertia—said axes being oriented the same way with respect to the respective cross-sectional shape—through the centroids of two parallel cross-sectional areas, 100 mm apart, of the tool gap enclosed by the respective effective surfaces; and
- (ii) that a curvature in the longitudinal extent of the sheet metal preform that deviates by at least 1% from the curvature in the longitudinal extent of the sheet metal component to be produced is established at least in some region or regions in the sheet metal preform to be produced in comparison with the sheet metal component to be produced.
2. The method as claimed in claim 1, wherein the effective surfaces of the preforming tool are configured in such a way in comparison with the effective surfaces of the sizing tool that a body opening angle difference (zdiff) of at least 0.5° is established at the same location in the sheet metal preform to be produced in comparison with the sheet metal component to be produced.
3. The method as claimed in claim 2, wherein a steel sheet with a yield strength Re of at least 400 MPa is used.
4. A device for producing a sheet metal component, for carrying out a method as claimed in claim 3, having at least one preforming tool for preforming a metal sheet to give a sheet metal preform having, in cross section, a base, at least one body, at least one transition between the base and the body, at least in some region or regions, a flange, and, at least in some region or regions, a transition between the body and the flange, which preforming tool acts by means of its effective surfaces on the metal sheet, wherein the sheet metal preform has excess sheet metal material, at least in some region or regions; and having at least one sizing tool for compressing the sheet metal preform to give a fully formed sheet metal component, which sizing tool acts by means of its effective surfaces on the sheet metal preform, and in which the excess sheet metal material is compressed in the sheet plane; wherein the effective surfaces of the preforming tool of the sheet metal preform to be produced are configured in such a way in comparison with the effective surfaces of the sizing tool of the sheet metal component to be produced that, at least one of (i) when the preforming tool and the sizing tool are compared, a torsion angle difference (tdiff) of at least 0.2° is established on consideration of the differential angle between the two main axes of inertia—said axes being oriented the same way with respect to the respective cross-sectional shape—through the centroids of two parallel cross-sectional areas, 100 mm apart, of the tool gap enclosed by the respective effective surfaces; and (ii) that a curvature in the longitudinal extent of the sheet metal preform that deviates by at least 1% from the curvature in the longitudinal extent of the sheet metal component to be produced is established at least in some region or regions in the sheet metal preform to be produced in comparison with the sheet metal component to be produced.
5. The device as claimed in claim 4, wherein the effective surfaces of the preforming tool are configured in such a way in comparison with the effective surfaces of the sizing tool that a body opening angle difference of at least 0.5° is established at the same location in the sheet metal preform to be produced in comparison with the sheet metal component to be produced.
6. The device as claimed in claim 5, wherein the sizing tool has a sizing punch, a sizing die and at least one element of, wherein the element is arranged in the sizing die and can be moved relative to the sizing die.
7. The device as claimed in claim 6, wherein the sizing punch is arranged at the bottom and the sizing die at the top in the sizing tool.
8. The device as claimed in claim 5, wherein the sizing tool has a sizing punch, a sizing die and at least one element of, wherein the at least one element is arranged in the sizing punch and can be moved relative to the sizing punch.
9. The device as claimed in claim 8, wherein the sizing punch is arranged at the top and the sizing die at the bottom in the sizing tool.
10. The device as claimed in claim 6, wherein the at least one element arranged in the sizing die is moved in a controlled manner by at least one of means of the ram stroke and additional control units in such a way that a defined distance is obtained between the element and the sizing punch during the closure of the sizing tool.
11. The device as claimed in claim 10, wherein the at least one element ends substantially flush with the effective surface of the sizing die during closure, before the lower end position is reached.
12. The device as claimed in claim 8, wherein the at least one element arranged in the sizing punch is moved in a controlled manner by at least one of means of the ram stroke and additional control units in such a way that a defined distance is obtained between the element and the sizing die during the closure of the sizing tool.
13. The device as claimed in claim 12, wherein the element ends substantially flush with the effective surface of the sizing die during closure, before the lower end position is reached.
14. The device as claimed in claim 13, wherein the device is integrated in one of a press line, transfer press and compound progressive press.
Type: Application
Filed: Aug 12, 2022
Publication Date: Oct 10, 2024
Applicant: ThyssenKrupp Steel Europe AG (Duisburg)
Inventors: Martin KIBBEN (Dinslaken), Lars BODE (Düsseldorf), Michael LINNEPE (Wickede), Peter SIECZKAREK (Tönisvorst), Daniel NIERHOFF (Bottrop)
Application Number: 18/681,609
