Method and device for producing sheet-metal components

Description

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

[0002] Deep drawing is a proven forming process commonly used to manufacture sheet metal components with complex geometries. The sheet metal, which is usually flat, is clamped between a blank holder and a die, and then drawn into the die by a punch. It is also common to produce the sheet metal component in several forming operations, using multiple tools.

[0003] Disadvantages of these conventional deep-drawing processes include, in particular, the tendency of the sheet metal component to spring back due to the inhomogeneous stress state after drawing and its sensitivity to batch variations. The expected springback is already taken into account during the design of the forming tools by incorporating classic compensation measures to counteract the anticipated springback in the opposite direction into the tool, in order to obtain a component with the highest possible dimensional accuracy after the inhomogeneous stress state is relieved.

[0004] Such compensatory measures on the tools can generally only be designed for a specific springback state. Furthermore, they are comparatively time-consuming to implement, complex, and usually require several iterations or tool correction loops to achieve the desired result.

[0005] However, it is problematic that after a change of material batch (especially after a change of the coil from which the sheets or circuit boards are manufactured) the dimensional accuracy of the sheet metal components can no longer be maintained, because the springback often differs.

[0006] Springback and a lack of process stability are the biggest obstacles to the use of high-strength steel or aluminum materials for the production of dimensionally accurate sheet metal components, such as body press parts, and pose major challenges for forming technology.

[0007] It is known from the prior art to effectively counteract the undesirable springback caused by applying compressive stress to the sheet metal components, which results in plastic deformation.

[0008] For example, German patent application DE 10 2007 059 251 A1, on which the preamble of claim 1 is based, German patent application DE 10 2008 037 612 A1, German patent application DE 10 2009 059 197 A1, German patent application DE 10 2013 103 612 A1 and German patent application DE 10 2013 103 751 A1 describe methods in which an excess of material is used to produce a dimensionally accurate component.

[0009] Typically, a preform is produced in one or optionally several process steps. This preform closely resembles the final shape of the component, with the key difference being the introduction of a defined excess of material in certain sections. In a subsequent process step, compressive stresses are selectively generated in the material through a specific upsetting process of the entire component. During this process, the component edge is supported, at least in some areas, by a form-fit against the calibration tool. This ensures that the excess material, which is primarily in the form of a larger development length, is preferably displaced only in the sheet thickness direction during the upsetting process. While this method eliminates the aforementioned disadvantages and minimizes material usage, it also has its own undesirable side effects.

[0010] It has been shown that, particularly in the production of the preform, measures are necessary to ensure a repeatable position of the preform's edges and thus of the preform edge, which is crucial for subsequent calibration. Ensuring a repeatable spatial position of the preform edge of the manufactured preform essentially ensures that the intended excess material for the subsequent calibration step is present in virtually every cross-section of the preform. The developed lengths of the local cross-sections considered in this way are, for example, approximately 1.0–3.0% larger than required for the final geometry of the sheet metal component.If the developed length of the cross-sections varies too much due to the manufacturing process of the preform, an insufficient amount of excess material would be available for the subsequent calibration step if the length is too short, thus impairing the dimensional accuracy of the sheet metal component. Conversely, if the developed length of the cross-section of the preform is too long, the resulting excess material would collapse into waves during the subsequent calibration process, potentially leading to visual and / or dimensional defects. Furthermore, this would place an unacceptable load on the calibration tool. Therefore, if the developed length of the local cross-sections of the preform varies too much, the positive-locking support of the preform's component edges against the calibration tool during the upsetting process, as described above, cannot be reliably achieved.

[0011] The aforementioned disadvantages are therefore related to the fact that the calibration effect is also applied via the preform edge, and this preform edge must be positioned with sufficient repeatability and reproducibility in the calibration tool shortly before the start of the actual compression and / or calibration process in order to achieve an optimal calibration effect.

[0012] To ensure that the spatial position of the preform edge and the local distribution of excess material meet the conditions required for calibration, special measures can be taken during the manufacturing of the preform. For example, a spaced blank holder can be used to minimize the influence of friction and thus the impact of batch variations on the developed length of the cross-sections. Deep drawing without a blank holder or with a spaced blank holder often allows for highly repeatable production of the local developments of the preform cross-sections and thus the position of the preform edge of the preform inserted in the calibration tool.

[0013] However, it has become apparent that, due to the geometry of certain sheet metal components, an exact position of the preform edges cannot be reliably achieved using the measures taken so far. Depending on the geometry to be produced, it may be desirable to use a sheet metal holder, at least in certain areas, to slow down the material flow during drawing to prevent unwanted wrinkling. While preformed parts produced in this way do conform to the required geometry, the developed length of the cross-sections varies to such an extent that these preformed parts cannot be processed, or can only be processed to a limited degree, in the subsequent calibration tool.

[0014] Starting from this premise, the object of the present invention is to provide a method by which the described disadvantages can be reduced or eliminated.

[0015] In a generic method for manufacturing sheet metal components, the problem is solved by the features of claim 1.

[0016] The proposed method involves a preformed part which, at least in certain areas of its cross-section, has excess developed length. Simultaneously, the preformed edges of the preformed part are arranged without positive locking, at least in certain areas, during calibration. An arrangement without positive locking, at least in certain areas, means that specific areas of the preformed edge can also be arranged with positive locking. Specifically, an arrangement without positive locking means that outward movement of the preformed edges, viewed in cross-section, is not prevented by positive locking. In other words, the preformed edges are not prevented from moving away, at least in certain areas, by positive locking. Therefore, it is no longer necessary to precisely position the preformed edges in the calibration tool, as they are not formed with positive locking within the tool.This allows for influencing the material flow, for example, by clamping the blank between a force-bearing sheet metal holder and the die for producing the preform. Typical negative effects of irregularities in the developed length of the preform in cross-section, such as waviness or cracking, can be reduced or avoided. As a result, forming processes can be used when forming the preform that were previously unusable due to the required precise positioning of the preform edges during subsequent calibration. For example, drawing with sheet metal holders, drawing beads, or in multiple drawing stages is now possible. The resulting irregular developed length of the preform in cross-section is unproblematic, depending on the batch and tribology, because the otherwise typical positive locking at the preform edges in the calibration tool is now at least partially absent.Finally, by trimming the calibration part after calibration, the sheet metal component can be achieved with its final geometry (finished dimensions) (in particular, the desired cross-sectional length of the sheet metal component). Advantageously, the trimming tool can be designed to closely match the target geometry and does not need to be adapted to the spring-back preform, as is common practice.

[0017] The sheet metal component preferably has a base area, a frame area, and / or an optional flange area. Accordingly, the calibration part preferably already has a base area, a frame area, and / or an optional flange area. Preferably, the preform also already has a base area, a frame area, and / or an optional flange area. The preform, for example, already has a near-net-shape geometry but is subject to undesired springback. In this respect, the preform can be considered a springback formed part.

[0018] The term "preformed part has excess developed length in cross-section, at least in certain areas" means, in particular, that the developed or stretched length of the preformed part in cross-section is greater, at least in certain areas, than required by the final geometry of the sheet metal component. Preferably, the preformed part has a developed length in local cross-sections, at least in certain areas, that is greater than required for subsequent calibration. For example, the developed length of the preformed part in cross-section is, at least in certain areas, more than 3%, and preferably more than 5%, greater than required by the final geometry of the sheet metal component.

[0019] The forming process, for example drawing or preferably deep drawing, is carried out in a drawing die. Advantageously, the proposed method can utilize deep drawing with draw beads, draw shoulders, and / or in a multi-stage deep drawing process, since a repeatable length of the development of the local cross-sections is not critical during calibration. The forming process can, in particular, include stretching.

[0020] Calibration is performed, for example, in a calibration tool. Calibrating the preformed part to the calibration part preferably includes at least partial upsetting of the preformed part.

[0021] The calibration part is trimmed, for example, using a trimming tool. This involves trimming (particularly with cutting blades or by laser beam cutting) the calibration part. During the trimming process, necessary through-holes and / or perforations are also made in the calibration part.

[0022] In one example, the calibration part is trimmed after calibration in a separate tool. However, it is also possible for the trimming to take place in the calibration tool itself, for example, after the calibration die has reached its final position.

[0023] In principle, forming, calibrating, and / or trimming can be carried out in separate fixtures. However, it is also possible for forming, calibrating, and / or trimming to be carried out, at least partially, in a combined fixture.

[0024] The circuit board, and thus the preformed part, the calibration part, and the sheet metal component with final geometry, are preferably made of an aluminum or steel alloy. For example, a high-strength steel, such as a multi-phase steel, is used.

[0025] According to the invention, the calibration part has a flange area, and the trimming of the calibration part includes the partial removal of this flange area. The preform also already has a flange area. The excess, developed length of the preform, at least in some areas of the cross-section, is then achieved, in particular, through the flange area. According to the invention, the flange area is at least partially compressed by calibrating the preform. The trimming then removes a portion or the entire flange area of ​​the calibration part. For example, the uncalibrated portion of the flange area can be removed by the trimming. Likewise, for example, a partially calibrated portion of the flange area can be removed by the trimming.

[0026] According to the invention, an undesired material flow towards the preform edges of the preform during calibration is reduced or prevented, at least in certain areas, particularly by means of a braking effect, especially through friction, force-fit, and / or positive locking, on the upper and / or lower surface of the sheet metal. This prevents excess material from flowing outwards and thus being unable to contribute to the calibration process. If the preform edges of the preform are arranged without positive locking at least in certain areas during calibration, this can be achieved, in particular, by exerting a braking effect on the upper and / or lower surface of the sheet metal during calibration. Preferably, the undesired outward material flow is counteracted exclusively in this way. For example, the preform, in particular the flange area of ​​the preform, is clamped in the calibration tool.

[0027] According to a preferred embodiment of the inventive method, the material flow during the forming of the blank into the preform is slowed down at least in certain areas, in particular by positive locking and / or frictional locking. By slowing down the material flow during forming, especially deep drawing, at least in certain areas, for example with a sheet metal holder, undesirable wrinkling can be reduced or avoided, and the preforms can be produced particularly advantageously, especially largely free of waviness, even with complex geometries. While this may result in batch-dependent changes in the length of the development of the local cross-sections of the preform, this is not problematic due to the at least partially non-positive locking arrangement of the preform edges during calibration.

[0028] To achieve a controlled material flow and thus an advantageous geometry of the sheet metal component without cracks and creases, a preferred embodiment of the inventive method employs one or more drawing beads, one or more drawing shoulders, and / or multi-stage forming during the forming process, particularly deep drawing, of the blank to create the preformed part. In this way, the existing limitations for producing a suitable preformed part can be significantly extended.

[0029] According to a preferred embodiment of the method according to the invention, the process is carried out without trimming, from the forming of the circuit board to the trimming of the calibration part after calibration. Thus, apart from the production of the circuit board, no intermediate trimming process takes place before calibration.

[0030] According to the invention, trimming the calibration part after calibration removes at least some of the calibrated areas. Preferably, at least some of the calibrated flange areas are removed by trimming after calibration. This ensures that the desired final geometry of the component can be achieved reliably, even if an additional developed length of the preform is generated in cross-section during the forming process, particularly deep drawing. Furthermore, it ensures that the final sheet metal component is calibrated substantially across its entire surface.

[0031] According to a preferred embodiment of the method according to the invention, the forming of the blank into the preform already includes compensatory measures aimed at producing a geometry of the preform that is particularly close to the final shape. For example, during deep drawing, for instance by appropriately designing the deep drawing tool, the preform is shaped (for example by overbending the frame area) against the expected springback. Due to the at least partially non-interlocking arrangement of the preform edges, fluctuations in the springback of the preform, or fluctuations due to batch changes, wear of the preform tool, or tribological properties, can be compensated for by calibration.

[0032] According to a preferred embodiment of the method according to the invention, the preform has excess material in a base region of the preform, in a frame region of the preform, in an optional flange region of the preform, and / or in one or more transition regions between these. It has been shown that excess material can be provided in these regions and used for calibration despite an arrangement that is at least partially free of form-fitting.

[0033] According to preferred embodiments of the inventive method, the sheet metal component, viewed in cross-section, is essentially hat-shaped, at least in certain sections. The sheet metal component may also exhibit cross-sectional changes along its main extent. Particularly in the case of hat-shaped sheet metal components viewed in cross-section, and especially in combination with cross-sectional changes, thinning, waviness, and cracks that frequently occur during manufacturing can be reduced or avoided using the described method.

[0034] A device for manufacturing sheet metal components shows Forming means for forming a blank into a preform such that the preform has at least some excess, developed length in cross-section; calibration means for calibrating the preform into a calibration part, at least in some areas, by at least partially utilizing the excess, developed length of the preform's cross-section, in particular for generating additional compressive stresses, such that the preform edges are arranged without positive locking at least in some areas during calibration; and trimming means for trimming the calibration part, at least in some areas, after calibration to produce the sheet metal component.

[0035] The device can comprise one or more tools for performing the different steps. In particular, the device can comprise a tool system with multiple tools. As already explained in connection with the described method, in contrast to the prior art, a device according to the invention does not provide, at least in some areas, a positive-locking fixation of the edges of the preform during calibration. The fact that the preform part has excess, unwound length in cross-section, at least in some areas, therefore does not negatively affect the calibration. Unnecessary material, for example, part of an optional flange area, can be removed by the trimming means.

[0036] According to preferred embodiments of the device, the forming means comprise a preforming tool with a preforming punch, a preforming die, and optionally a blank holder, and preferably one or more draw beads and / or one or more draw shoulders. The forming means can also be configured for multi-stage forming. As already explained, the developed lengths of the local cross-sections of the preform do not need to be achieved with repeatable accuracy during forming. This allows, in particular, the use of auxiliary components such as draw beads.

[0037] According to preferred embodiments of the device, the calibration means comprise one or more calibration tools with one or more calibration punches and one or more calibration dies. Sufficiently precise positioning of the preformed part can be achieved simply by the radius of the punch or die.

[0038] According to preferred embodiments of the device, the trimming means comprise one or more trimming tools for at least partially trimming the calibration part after calibration. For example, the trimming tool comprises one or more cutting blades. Alternatively or additionally, the trimming tool can be configured to perform laser beam cutting. The trimming tool can also be configured to perform any necessary through-holes and / or perforations.

[0039] Regarding further advantageous embodiments of the device, reference is made to the description of the method and its advantages.

[0040] The preceding and subsequent descriptions of process steps according to preferred embodiments of the method are intended to also disclose corresponding means for carrying out the process steps by preferred embodiments of the device. Likewise, the disclosure of means for carrying out a process step is intended to disclose the corresponding process step itself.

[0041] The invention will now be explained in more detail with reference to exemplary embodiments in conjunction with the drawing. The drawing shows in Fig. 1 shows an embodiment of a preforming tool for carrying out a forming step; Fig. 2 shows an embodiment of a spring-back preform after preforming; Fig. 3a shows an embodiment of a calibration tool for carrying out a calibration step; Fig. 4ab shows further embodiments of calibration tools for carrying out a calibration step; Fig. 5 shows an embodiment of a calibration part; and Fig. 6 shows an embodiment of a sheet metal component after trimming.

[0042] Fig. 1 Figure 1 shows an embodiment of a preforming tool 1 for carrying out a forming step according to an embodiment of a method according to the invention. The preforming tool 1 comprises a preforming punch 2 and a preforming die 4. An optional hold-down device 6 is also shown, which can be arranged, for example, on the ram pad or springs. The preforming tool 1 also has sheet metal holders 8 with draw grooves 8a. Draw shoulders 9 are also provided. Fig. 1 The circuit board has already been transformed into the preformed part 10 by deep drawing.

[0043] The circuit board was reshaped in such a way that the geometry of the preformed part 10 with a material reserve contained in the bottom area and / or in the frame area and / or in the flange area and / or in a transition area between bottom area and frame area and / or frame area and flange area corresponds to the geometry required at least for the subsequent calibration step.

[0044] The resulting preform 10 is characterized by the fact that its developed length in cross-section is, at least in some areas, greater than required for subsequent calibration. Therefore, common tools such as drawing beads 8a or drawing shoulders 9 can be used to manufacture the preform 10. It is also conceivable to produce the preform 10 in several forming stages, especially for particularly critical components. This significantly expands the previously applicable limits for manufacturing a suitable preform 10. Furthermore, it is conceivable to produce the preform in several forming stages using various combinations of drawing, bending, embossing, edging, etc.

[0045] When removed from the preforming tool 1, the preformed part 10 will spring back due to the inhomogeneous stress state, as shown in Fig. 2 The removed preformed part 10 (formed part) is then placed in a calibration tool 20, which replicates the desired final geometry plus the material addition in the area of ​​the preform edge, as shown in Fig. 3a , 3b The calibration tool 20 comprises a calibration punch 22, a calibration die 24 and top-hung hold-down or sheet metal holder 26.

[0046] In the Fig. 4a , b Alternative embodiments of calibration tools 30 and 40 for performing the calibration step are shown. Calibration tool 30 is designed as a two-part tool with a calibration punch 32 and a calibration die 34. A hold-down device is not required in this case. Calibration tool 40 comprises a calibration punch 42, a calibration die 44, and hold-down devices 46 suspended from the top. In this case, the flange area of ​​the preformed part 10' is formed without a shoulder.

[0047] In the described calibration tools 20, 30, 40, the preform 10, 10' (forming part) is fixed during the calibration process in such a way that material flow towards the preform edge is prevented during calibration. However, in these tools 20, 30, 40, the preform edges of the preform 10, 10' are arranged without positive locking, at least in some areas, during calibration. The preform 10, 10' is thus calibrated completely or at least partially without the preform edge being positively prevented from moving. Undesired material flow outwards towards the preform edge is thereby achieved only through the braking effect on the top and bottom surfaces of the sheet metal, but not through a braking effect at the preform edge itself.

[0048] Up to this point, no trimming of the preformed part 10, 10' or the calibration part has taken place. This means that the trim remnants, which are later to be removed by trimming (for example, by cutting), are at least partially calibrated in the calibration tool 20, 30, 40 of the resulting calibration part. In this way, a dimensionally accurate calibration part is obtained, which is then finally trimmed to become the final sheet metal component.

[0049] During the design of the preforming tool 1, compensatory measures, such as overbending the ribs, can already be implemented to obtain a preform 10, 10' that closely matches the final geometry. Fluctuations in the springback of the preform 10, 10' are largely compensated for during calibration, so that no time-consuming correction loops are required. The same applies to fluctuations resulting from batch changes and / or wear of the preforming tools and / or the tribological properties of the tools and material.

[0050] In Fig. 5 Figure 1 shows an embodiment of a calibration part 50, which was produced from the preformed part 10. The area to be cut off is indicated by the dashed lines 52. The trimming after calibration can be carried out in one or more steps and has the particular advantage that the trimming tools do not have to be adapted to the spring-back component, as is common practice, but can instead be designed to closely approximate the target geometry. In principle, however, it is also conceivable that the trimming after reaching the lower end position is integrated into the calibration tool 20, 30, 40 (not shown here).

[0051] A sheet metal component 60, produced by trimming from the calibration part 50 and having a finished dimension, is in Fig. 6 depicted.

[0052] In summary, the various exemplary embodiments of the described method and the described device can result in the following advantages in particular.

[0053] Regarding the initially required circuit board, a simplified cutting blade contour and reduced wear can result. Furthermore, simplified nesting is possible, as typically only one blade contour is needed.

[0054] With regard to the forming of the preformed part 10, 10', particularly complex components can be manufactured, some of which can only be produced by forming with aids such as sheet metal holders 8, draw beads 8a, draw shoulders 9, and / or by multi-stage forming. Furthermore, the work hardening of modern multi-phase steels can be utilized. This, in turn, can lead to reduced sheet thicknesses and thus to a reduced component weight, especially compared to a process involving embossing and raising while maintaining comparable component performance. Ultimately, areas prone to edge cracking can be reduced or avoided.

[0055] With regard to calibration, it can be advantageously achieved, particularly batch-independently and reliably, that the position of the preform edges in the calibration tool 20, 30, 40, which remains closed until shortly before the start of the upsetting and / or calibration process, has no influence on the calibration effect. This means that the preform 10, 10' can be optimally designed for the calibration step without considering the final sheet metal component edge. Furthermore, classic compensation by means of overbending or straightening can be dispensed with, although classic compensation can also be combined with the described method.It can also be advantageous that, due to the at least partially form-locking arrangement of the preform edges in the calibration tool, high surface pressures can no longer form in the area of ​​the preform edges supporting the tool during the upsetting and / or calibration process, thus increasing the service life of the calibration tool.

[0056] Regarding the trimming of the calibration part 50 to finished dimensions, known trimming methods that have been tested in series production can be used and optionally combined with the necessary through-holes and / or perforations.

Claims

1. Method for manufacturing sheet metal components, the method comprising: - forming a blank into a preform (10, 10'), wherein the preform (10, 10') has an excess unwound length in at least some areas of its cross-section; - calibrating the preform (10, 10') at least in some areas to form a calibrated part (50), using at least some of the excess developed length of the cross-section of the preform (10, 10') to build up additional compressive stresses, wherein the preform edges of the preform (10, 10') being arranged at least in some areas without a positive fit during calibration, whereby undesirable material flow in the direction of the preform edges of the preform (10, 10') during calibration is reduced or prevented at least in some areas by means of a braking effect on the upper side and / or lower side of the sheet metal; and - at least partial trimming of the calibrated part (50) after calibration to produce the sheet metal component (60), wherein the trimming of the calibrated part (50) after calibration removes calibrated areas at least in some areas, the calibrated part (50) has a flange area and the trimming of the calibrated part (50) comprises partial removal of the flange area, wherein the preformed part already has a flange area, characterized in that the flange area is at least partially compressed by the calibration of the preformed part.

2. Method according to claim 1, wherein the material flow during the forming of the blank into the preform (10, 10') is slowed down at least in some areas.

3. Method according to claim 2, wherein one or more drawing beads (8a), one or more drawing shoulders (9) and / or multi-stage forming are used when forming the blank into the preform (10, 10').

4. Method according to one of claims 1 to 3, wherein the method is carried out without trimming from the forming of the blank to the trimming of the calibrated part (50) after calibration.

5. Method according to one of claims 1 to 4, wherein the forming of the blank into the preformed part (10, 10') already comprises compensation measures with the aim of producing a geometry of the preformed part that is particularly close to the final geometry.

6. Method according to one of claims 1 to 5, wherein the preformed part (10, 10') has excess material in a bottom area of the preform (10, 10'), in a frame area of the preform (10, 10'), in an optional flange area of the preform (10, 10') and / or in one or more transition areas between these.

7. Method according to one of claims 1 to 6, wherein the sheet metal component (60), viewed in cross-section, is at least partially formed in a substantially hat-shaped manner.

8. Method according to one of claims 1 to 7, wherein the sheet metal component (60) has cross-sectional changes along its main extension.