METHOD FOR THE PRODUCTION OF SHEET METAL PARTS AND DEVICE THEREFOR

[0001]The invention concerns a method and a device for the production of sheet-metal parts.

[0002]Methods and devices for producing precisely dimensioned sheet-metal parts 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 production takes place in at least two stages (forming processes). In the first stage, an in particular flat forming plate is formed into a preform. Compared with the geometry of the definitive sheet-metal part to be produced, the preform has a material surplus distributed as evenly as possible. This material surplus is compressed in the second stage, so-called calibration, in particular in the direction of the sheet plane. The non-homogenous stress state of the preform is re-aligned and hence the undesired, load-dependent spring-back of the sheet-metal part, which occurs in particular in ultra-high-strength materials in combination with low material thicknesses, is largely avoided.

[0003]When calibrating sheet-metal parts with (welding) flange, usually side slides are brought up to the calibration punch via wedge drivers when the calibration tool is closed, and remain there during the calibration process. During calibration, the edge of the preform flange rests on the slide, whereby the compressive stress superposition is achieved by compression of the material surplus. The contact between the preform and slide exists exclusively in the region of the edge of the preform flange. For sheet-metal parts with portions or substantial regions without (welding) flange however, there is no satisfactory concept. The former concepts provide for the production of a preform which substantially corresponds to the final geometry, wherein the preform tool is designed with its active faces substantially at the active faces of the calibration tool.

[0004]The invention is thus based on the object of providing a generic method and a generic device which can be used to produce precisely dimensioned sheet-metal parts which are flangeless at least in portions.

[0005]This object is achieved with a generic method with the features of claim 1.

[0006]This object is achieved with a generic device with the features of claim 5.

[0007]According to the teaching of the method of the invention, it is provided that the method for producing a sheet-metal part comprises at least two steps: preforming a sheet into a metal preform in a preforming tool, wherein the metal preform is configured as an open profile with an opening and in its longitudinal extent has at least one flangeless portion and, at least in regions, surplus sheet material; and final forming of the metal preform into a sheet-metal part in a calibration tool comprising at least one calibration punch and at least one calibration die, in which the surplus sheet material in the metal preform is compressed by a relative movement between the calibration punch and the calibration die, wherein during final forming, because of the relative movement, the edge of the metal preform present at least in the flangeless portion comes into contact with a punch shoulder of the calibration punch, rests thereon and is pressure-loaded, in particular so as to be compressed.

[0008]It has been found that precisely dimensioned sheet-metal parts can be produced which are flangeless at least in portions, and in particular can be calibrated or final-formed with a very low wing opening angle of less than 6° using a simplified calibration tool structure. During compression or calibration, by means of compressive stress superposition, at least the edge of the metal preform present in the flangeless portion can rest on the punch shoulder of the calibration punch. It must be ensured that during the calibration process, on closure of the calibration tool, the metal preform is not clamped between the calibration punch and the calibration die, which would lead to damage of the final-formed sheet-metal part and/or the calibration tool.

[0009]The wing opening angle is the angle through which the sheet-metal part wing can be rotated maximally inward relative to the action direction of the calibration tool (press ram) about an axis oriented in the longitudinal extent of the sheet-metal part, in the transitional region between the wing and the floor of the sheet-metal part, before causing an undercut in the tool.

[0010]Viewed in cross-section, the metal preform and the final sheet-metal part have at least one floor and at least two protruding wings, each with a transition between the floor and the two wings. Furthermore, depending on design of both the metal preform and the final sheet-metal part, in the longitudinal extent there is at least one flangeless portion. This means that either portions can be designed flangeless locally on one or both sides, or one side can be completely flangeless, and/or optionally the other side may be only partly flangeless. In particular, the metal preform and also the final sheet-metal part may be formed flangeless. For example, at least in portions, a flange may be connected to one of the wings, wherein both the metal preform and the final sheet-metal part may, at least in portions, have a transition between the wing and the flange. Preferably, the final sheet-metal part has portions with and without flange. The flangeless portion may however also be present only on one side of the metal preform, wherein the metal preform, depending on design, may however also have no flange on either side, at least locally, viewed in cross-section.

[0011]The metal preform may be produced by means of any combinable forming process in one or more steps. The preforming may comprise for example a deep-drawing forming step. In particular, multistage forming may be used, comprising for example embossing the floor to be produced and erecting the wings, or straightening the flanges to be optionally produced in portions. Any combination of trimming and/or bending and/or (pre-)embossing is conceivable. The deep-drawing carried out for example for preforming may in particular be single-stage or multistage. Preferably, forming without active material flow control may be used to produce the metal preform. Depending on embodiment, the preform tool is then designed accordingly.

[0012]Final forming of the metal preform means compression/calibration, which can be achieved for example by one or more pressing processes. In the produced metal preform, surplus sheet material is present at least in regions. This surplus sheet material in the metal preform has, at least in regions, in cross-section a straightened length which is between 0.5% and 6% longer than the straightened length of the final-formed sheet-metal part (nominal geometry). The straightened length of the resulting cross-section of the metal preform is in particular between 0.7% and 4.3% longer than that of the final-formed sheet-metal part. If, because of process control in production of the metal preform, the straightened length of the cross-sections varies too greatly, if the straightened length were too short, there would not be enough surplus sheet material for the following final forming, whereby the dimensional precision of the final sheet-metal part would be reduced. If the straightened length of the cross-section of the metal preform is however too large, during the following final forming, the over-dimensioned sheet material would collapse in waves, which may signify a visual and/or dimensional defect. In addition, there would be an increased risk of tool damage due to excessive compression forces or protruding, crushed regions of the sheet-metal part, e.g. sheet edges.

[0013]The substantially final-formed sheet-metal part can to this extent be considered definitively formed. However, it is possible that the final-formed sheet-metal part may be transferred into further processing steps modifying the sheet-metal part, such as the creation of connection holes and/or slight final trimming and/or the performance of secondary forming steps such as the production of additional local embossings, or for example straightening flanges on the ends of the sheet-metal part.

[0014]The produced metal preform and the final-formed sheet-metal part substantially have a longitudinal extent and a transverse extent, wherein in most sheet-metal parts, the longitudinal extent is larger than the transverse extent because of dimensioning. Thus a cross-section means a section through the transverse extent of the metal preform/sheet-metal part.

[0015]The metal preform is laid in the calibration tool such that its opening points downward and is positioned on the calibration punch. The advantage of laying the metal preform, produced as an open profile, with the opening pointing downward is that the metal preform can be positioned better and more easily. In particular, the calibration punch is arranged stationarily and the calibration die movably in the calibration tool.

[0016]Since the compression/calibration force generated on final forming is conducted into the calibration punch via the edge of the metal preform present at least in the flangeless portion, too great a gap between the edge of the metal preform in the calibration punch and in particular vertical die cheeks of the calibration die positioned above this, may lead to damage of the sheet-metal part and hence to high wear or damage of the calibration tool. Thus it is provided that during the relative movement, the calibration die passes by the punch shoulder of the calibration punch, at least in the region of the flangeless portion of the metal preform, with a minimum possible gap which may in particular correspond to between >0% and 20% of the material thickness of the inserted sheet, before the final forming begins by compression of the surplus material additionally introduced into the metal preform. Thus, in particular before starting the final forming, the edge of the metal preform is surrounded by stable tool faces on all sides before the edge of the metal preform rests on the punch shoulder on the calibration punch during final forming, and a final sheet-metal part geometry is produced in the actual calibration process.

[0017]According to an embodiment of the method according to the invention, the metal preform is provided with a floor which, during preforming, is loaded with a surplus sheet material at least in the region of the flangeless portion, such that a floor region pre-curved in the direction of the opening is produced during the preforming, so that the metal preform is positioned on the calibration punch at least via the pre-curved floor region, at least in the region of the flangeless portion of the metal preform, such that the edge of the metal preform present at least in the flangeless portion is arranged above the punch shoulder. The floor of the preform, at least in the flangeless portion, may have surplus sheet material which is distributed as evenly as possible on the floor (region) and for example, during production of the metal preform, is loaded with 2 to 5% added material (ratio of straightened length of metal preform<->sheet-metal part) in order to achieve a compressive stress superposition during final forming in the calibration tool, preferably such that the pre-curved floor region is positioned on the calibration punch before the start of the actual final forming, and during closure of the calibration tool, the wing(s) of the metal preform are securely arranged on the calibration punch above the punch shoulder and thus clamping between calibration die and calibration punch can be securely prevented.

[0018]According to an alternative or additional embodiment of the method of to the invention, the metal preform is provided with a floor in which, locally or in portions, embossings pointing in the direction of the opening are produced during the preforming, so that the metal preform is positioned on the calibration punch at least via the embossings, such that the edge of the metal preform present at least in the flangeless portion is arranged above the punch shoulder. The embossing(s) made locally or in portions in the floor of the preform during preforming may be distributed along the floor in the longitudinal extent, or only be made as local or partial embossings on the two ends of the metal preform viewed in the longitudinal extent. Thus a compressive stress superposition can be achieved on final forming in the calibration tool in that, before the start of the actual final forming, the metal preform is positioned on the calibration punch via the embossings in the floor, so that during closure of the calibration tool, the wing(s) of the metal preform is/are securely arranged on the calibration punch above the punch shoulder and thus clamping between the calibration die and calibration punch can be securely prevented.

[0019]According to a further alternative or additional embodiment of the method according to the invention, the metal preform is provided with a floor, wherein during insertion of the metal preform in the calibration tool, at least a part region of the floor comes into contact with at least one adjustable insert which is arranged in the calibration punch and spaced from the calibration punch on insertion of the metal preform, and the metal preform is positioned on the insert at least via the part region of the floor, at least in the region of the flangeless portion of the metal preform, such that the edge of the metal preform present at least in the flangeless portion is arranged above the punch shoulder. The or several inserts arranged in the calibration punch may be sprung or driven, for example via wedge drivers, hydraulically, pneumatically, electromechanically, electromagnetically, and additionally or alternatively used to achieve a compressive stress superposition on final forming in the calibration tool, preferably such that before the start of the actual final forming, the metal preform is positioned on the calibration punch so that during closure of the calibration tool, the wing(s) of the metal preform is/are safely arranged above the punch shoulder on the calibration punch and thus clamping between calibration die and calibration punch can be securely prevented.

[0020]In order to securely prevent clamping of the wing(s) between the calibration die and the calibration punch, preferably at least one of the three above-mentioned embodiments comprising a metal preform with pre-curved floor region, a metal preform with local or partial embossings in the floor, and/or adjustable inserts in the calibration punch, are taken into account during positioning of the metal preform on the calibration punch.

[0021]The above-mentioned object is achieved with a generic device with at least one preform tool for preforming a sheet into a metal preform, wherein the metal preform is configured as an open profile with an opening and in its longitudinal extent has at least one flangeless portion and, at least in regions, surplus sheet material; and with at least one calibration tool for final forming of the metal preform into a sheet metal part, wherein the calibration tool comprises at least one calibration punch and at least one calibration die, wherein the surplus sheet material in the metal preform is compressed by the relative movement between the calibration punch and the calibration die; wherein the metal preform can be positioned on the calibration punch with its opening at the bottom; wherein the calibration punch has at least one punch shoulder which is provided at least in the flangeless portion of the metal preform such that, by the relative movement, the edge of the metal preform present at least in the flangeless portion can be brought into contact with a punch shoulder of the calibration punch, can rest thereon and be pressure-loaded.

[0022]Preferably, a final sheet-metal part with a profile open at the bottom is produced in the calibration tool (press) so that the calibration punch is arranged at the bottom and the calibration die at the top in the calibration tool, and these are movable relative to one another. Thus preferably the calibration punch is arranged on a press table and the calibration die on a press ram of the calibration tool formed as a press. Depending on design of sheet metal part to be produced, at least portions are flangeless, wherein also portions with flange may be present; so that if there are flanged portions on one or both sides, corresponding portions in the calibration tool are adapted to the flanged portion so that a compressive stress superposition can be achieved in at least part of the flange portion. Preferably, the calibration tool is configured segmented accordingly, so that flangeless and any flanged portions on a metal preform can be final-formed into a sheet metal part.

[0023]To avoid repetition, reference is made to the statements relating to the method according to the invention.

[0024]According to one embodiment of the device, the calibration punch has at least one adjustable insert which is arranged in the calibration punch and can be spaced from the calibration punch. In particular, the at least one insert can be moved relatively in the calibration punch. The element(s) arranged in the calibration punch can be driven for example via the ram stroke and/or additional control units, which may be driven e.g. by means of springs, wedge drivers, hydraulics or pneumatics. Via the element, a defined spacing can be set between the metal preform and the calibration punch, via which a spacing of the edges, provided in particular in the flangeless portion, from the punch shoulder of the calibration punch can be set. During final forming or closure of the calibration tool, the element is retracted completely flush into the calibration punch.

[0025]According to one embodiment of the device, the calibration die may be formed in multiple pieces and has at least one adjustable die cheek at least in the flangeless portion of the metal preform. The die cheek may for example function as a leading blocking part to ensure that the edge of the metal preform is safely arranged above the punch shoulder when the leading die cheek has passed the punch shoulder and hence a closed calibration gap has closed.

[0026]According to an embodiment of the device according to the invention, the punch shoulder has a maximum extent of the material thickness of the inserted sheet plus >0 to 0.35 mm, in particular 0.01 to 0.20 mm, preferably 0.02 to 0.10 mm. This preferably ensures that on compressive stress superposition, the surplus sheet material can flow are far as the edge of the sheet-metal part; in particular, also in regions, a local thickening of the metal preform during calibration is permitted without tilting or other negative effect (damage to sheet-metal part and/or tool), in particular on opening of the calibration tool and/or on removal of the sheet-metal part from the calibration tool.

[0027]According to an embodiment of the device according to the invention, the device is integrated in a pressing line or a transfer press. In particular for production of mass products e.g. components for the automotive industry, products such as sheet-metal parts are produced particularly economically in pressing lines or transfer presses. The device according to the invention may be used economically in existing production lines, in the form of interchangeable inserts which provide at least a preforming tool and at least a calibration tool. Use of the device according to the invention in a follow-on press is conceivable.

[0028]The invention is explained in more detail below with reference to drawings. The same parts carry the same reference signs. The drawings show:

[0029]FIG. 1 a schematic, perspective illustration of the production of a metal preform,

[0030]FIGS. 2 to 5 a sequence of steps at different times in the production of a sheet metal part according to an embodiment of the method according to the invention, and a device according to the invention, in a schematic sectional illustration, and a part extract from the device in a schematic perspective illustration, and

[0031]FIG. 6 a schematic, perspective illustration of the sheet-metal part.

[0032]FIG. 1 shows in schematic, perspective illustration a production of a metal preform (2) from a sheet (1) in a preform tool (10), not shown in detail. The metal preform (2) may be produced in one or more steps by means of any combinable forming process. Reference sign (10) covers the preform tool, consisting of one or more tools which are suitable for creating a metal preform (2) from a sheet (1). The sheet (1) is for example unwound and cut as a defined blank or forming plate from a metal bundle/coil (not shown), and made available for further processing. Preferably, the sheet (1) is made of steel, preferably a high-strength steel, for example with a material thickness between 0.5 and 4 mm. Alternatively, aluminum materials or other metals may be used.

[0033]FIGS. 2 to 5 show in a schematic sectional illustration—and FIGS. 3 and 4 also, on the right-hand side, in a schematic perspective drawing—a partial extract of a device in longitudinal extent, and a sequence for performance of a method according to the invention and a device according to the invention, which relates at least to the embodiment of the calibration tool (20). The method according to the invention for producing a sheet-metal part (3), see FIG. 6, thus comprises at least two steps. Firstly, the method comprises preforming a sheet (1) into a metal preform (2) having in cross-section a floor and two wings, each with a transition between floor and wings.

[0034]The metal preform (2) or sheet-metal part (3) may comprise in the longitudinal extent (L) for example at least one flanged portion, here on the left side of the profile open at the bottom, and at least one flangeless portion (2.1). With at least one portion, viewed in the longitudinal extent (L), having a flange, which for example may be arranged on one side or also on both sides in different portions, in the region of the flange there is a transition between the wing and the flange. The statements below relate to an example with a portion in cross-section, wherein both sides of the metal preform (2) and accordingly two sides of the sheet-metal part are flangeless in at least one portion. Evidently only one side need be flangeless and the other side may have a flange in cross-section, or be completely flange-free (not shown).

[0035]The metal preform (2) is produced such that surplus sheet material (4) is provided which is arranged, preferably evenly distributed, in the metal preform (2) in the floor, or in the floor and in the transition between the floor and the wings. Further surplus sheet material may be present, in particular locally, in the metal preform (2), e.g. a further material addition respectively close to the two metal preform ends, in the floor and in a floor region (2.2) pre-curved in the direction of the opening (0) of the metal preform (2), so that the metal preform (2) can be positioned on the calibration punch (21) at least via the pre-curved floor region (2.2), at least in the region of the flangeless portion (2.1) of the metal preform (2), such that the edge (2.11) of the metal preform (2) present at least in the flangeless portion (2.1) is arranged above the punch shoulder (21.1), see FIG. 2.

[0036]Alternatively or additionally, the metal preform (2) is provided with a floor in which, locally or in portions, embossings (2.3) are provided pointing in the direction of the opening (Ö), see drawing on the right of the metal preform (2) in FIG. 1 during production of the preform, so that the metal preform (2) can be positioned on the calibration punch (21) at least via the embossings (2.3), see FIG. 3, such that the edge (2.11) of the metal preform (2) present at least in the flangeless portion (2.1) is arranged above the punch shoulder (21.1). The embossings (2.3) made in the floor may be distributed in the longitudinal extent (L) along the floor or be present only as local or partial embossings (2.3) on the two ends of the metal preform (2.3), viewed in the longitudinal extent (L). If a sheet-metal part is to be produced with a flange at least in portions, these embossings need not necessarily be made in the region of the flangeless portion (2.1) of the metal preform (2). The embossings (2.3) made serve not only as spacers but may also provide further surplus metal material, at least in portions, viewed locally or in part in the transverse extent of the metal preform (2).

[0037]Further alternatively or additionally, at least one adjustable insert (21.2) may be arranged in the calibration punch (21), see FIG. 4, which can be spaced from the calibration punch (21) so that at least a part region of the floor comes into contact with the insert (21.2) when the metal preform (2) is laid in the calibration tool (20), and the metal preform (2) is positioned on the insert (21.1) at least via the part region of the floor, at least in the region of the flangeless portion (2.1) of the metal preform (2), such that the edge (2.11) of the metal preform (2) present at least in the flangeless portion (2.1) is arranged above the punch shoulder (21.1).

[0038]The metal preform (2) is final-formed into a sheet-metal part (3) in a calibration tool (20) comprising at least one calibration punch (21) and at least one calibration die (22) in which, by relative movement between the calibration punch (21) and calibration die (22), the surplus sheet material (4) in the metal preform (2) is compressed, see FIG. 5, left illustration before final forming, right illustration in final forming. It has proved advantageous that during the final forming, because of the relative movement, the edge (2.11) of the metal preform (2) present at least in the flangeless portion (2.1) comes into contact with a punch shoulder (21.1) of the calibration punch (21), rests thereon and is pressure-loaded in order in particular to cause the desired, at least local compression of the metal preform during the further press stroke.

[0039]With the embodiment according to the invention, before final forming or before closure of the calibration tool (20), it can be ensured that the metal preform (2) can be positioned on the calibration punch securely against clamping, and flangeless portions (2.1) as well as optional flanged portions can be final-formed to precise dimensions. For final forming of the exemplary flanged portions (not shown in FIGS. 2 to 5), in particular slides (not shown) are provided in the calibration tool for blocking the flange edges of the metal preform, so that these portions too can undergo the compressive stress superposition similarly to the flangeless portions (2.1).

[0040]After the metal preform (2 has been laid in the calibration tool (20) such that the opening (Ö) of the metal preform (2) points downward and is positioned on the calibration punch (21), during the relative movement, the calibration die (22) passes by the punch shoulder (21.1) of the calibration punch (21) with a minimum possible gap, at least in the region of the flangeless portion (2.1) of the metal preform (2), before final forming is completed or the compressive stress superposition initiated. Before the start of the compression/calibration process, it is thus ensured that at least the die cheek (22.1) of the calibration die (22) has passed the punch shoulder (21.1) of the calibration punch (21), so that during compressive stress superposition, uncontrolled flow between the punch shoulder (21.1) and the edge (2.11)—which could lead to seizing—is prevented. The drawing does not show that the calibration die (22) may also be made in multiple parts, for example with at least one leading die cheek (22.1).

[0041]After completion of final forming, the calibration tool (20) is opened again and the precisely dimension sheet-metal part (3) can be removed. The opened calibration tool (20) is thus free again, to be reloaded with a new preform (2) for final forming.

[0042]Preferably, at least one of the three above-mentioned embodiments, comprising a metal preform (2) with pre-curved floor region (2.2), a metal preform with local or partial embossings (2.3) in the floor, and/or adjustable inserts (21.2) in the calibration punch (21), serves for positioning of the metal preform (2) on the calibration punch (21).

[0043]The invention is not restricted to the embodiment shown. Other forms of sheet-metal part are also possible and require correspondingly adapted tools, preform and calibration tools. In particular, the tools (10, 20) may be configured as interchangeable tools and be used in a production line, in particular in a pressing line, transfer press and/or follow-on press.