Abstract:
A method for producing a metal profile includes producing a metal component from a semi-finished product or a blank by a hot forming and hardening process and bending the metal component along at least one bending edge. Bending is simplified according to the invention in that, before forming, the metal component is heated along the bending edge in such a way that the strength is reduced in a heated region after heating. The metal profile, produced with this method, has at least one bending edge at which the strength of the metal profile is reduced. In addition the metal profile can be used in a motor vehicle body, in particular as A- and/or B-pillar.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of and priority to German Patent Application No. DE 10 2008 044 523.1, filed Sep. 15, 2008, the disclosures of which is incorporated herein by reference in its entirety. 
       FIELD OF THE INVENTION 
       [0002]    The invention relates to a method for producing a metal profile, in which a metal component is produced from a semi-finished product or a blank by a hot forming and press hardening process and the metal component is bent along at least one bending edge. The invention also relates to a metal profile with at least one bending edge, produced according to this method, as well as the use of the metal profile in a motor vehicle body. 
       BACKGROUND 
       [0003]    In many fields of application, particularly however in the automotive industry, high-strength metal components are used in order to obtain products which are as thin as possible and therefore as light-weight as possible with the same strength properties. For example side impact beams as well as A- or B-pillar reinforcements are produced from high or maximum strength steel alloys, whereby hot-formed heat-treatable steels, for example manganese boron steel, are increasingly being used. These steel alloys have to undergo hot forming with subsequent cooling in the tool in order to achieve a hardness as high as possible. A particularly preferred method in this case is the hot forming and press hardening process. With this method a semi-finished product or a blank, preferably made of a heat-treatable steel, is converted into the austenitic microstructure range by heating to temperatures of for example 900-1000° C. by hot-pressing and formed. Subsequently the pressed part, still in the tool, is quenched to temperatures between 100 and 200° C., as the result of which a martensitic structure and thus a usually throughout high-strength component is obtained. It is a disadvantage however when using such components that, due to the high strength, a further forming process is only possible at very high effort and also only to a limited extent and with limited precision. Furthermore, when using metal profiles made of heat-treatable steel, it is frequently desirable to optimally configure or accurately control the deformation behavior, for example of side impact beams or B-pillars of a motor vehicle. 
         [0004]    Patent Specification DD 253 551 A3 discloses a method for locally annealing work-pieces made of carbon steel, with reduction in the hardness and increase in the plasticity of the heated region being achieved by continuous heating of the work-pieces in the temperature range from the start point of martensite transformation up to the tempering temperature and subsequent localized heating of the surface by a laser to above the phase change temperature. 
       SUMMARY OF THE INVENTION 
       [0005]    In general, an aspect of the present invention is to provide a method for producing the metal profile which enables a metal profile with high strength to be produced at low cost. In addition another aspect of the present invention is to make available metal profiles which can be produced economically. Furthermore an advantageous use of the metal profiles shall be proposed. 
         [0006]    In accordance with a first teaching of the present invention the aspect described above is achieved in that the metal component, before forming, is heated at least partially along at least one bending edge in such a way that the strength is reduced in the heated region after heating. 
         [0007]    It has turned out that by locally heating a bending edge of a hot-formed and press-hardened metal component, preferably to temperatures above a phase change temperature, for example the austenite formation temperature, the strength at the bending edge can be reduced in such a way that the metal component can be formed at the bending edge to a greater extent and with substantially less effort. Due to the bending edge being heated to temperatures above the phase change temperature, the predominantly martensitic structure of a hot-formed and press-hardened metal component transforms into an austenitic microstructure. Thus, after cooling, the region can exhibit a non-martensitic structure with reduced strength for example. These regions can then be used as bending edges. 
         [0008]    Metal profiles with very high strength or stiffness can be achieved in accordance with a further embodiment of the inventive method in that the semi-finished product or the blank substantially consists of a high or maximum strength steel, preferably a manganese boron steel. In addition, bending of metal components made of such steels in the customary way is particularly problematic, so that by heating according to the invention much simpler and improved forming is achieved and some special forming processes are only rendered possible for the first time. 
         [0009]    A particularly narrow bending edge can be obtained in accordance with a further embodiment of the inventive method by heating at least one bending edge with a laser beam. A narrow bending edge brings about that the strength of the metal profile is only reduced in a very small region at the bending edge, so that overall the entire metal profile exhibits very high strength or, respectively, stiffness. A further advantage of heating with a laser beam is that a laser beam can be adjusted and controlled very exactly, so that very precise heating of the metal component at the bending edge is possible. Thus it is also conceivable for example that the bending edge is not heated continuously but only intermittently, in order to obtain even higher strength of the metal profile. 
         [0010]    According to a further embodiment of the inventive method the metal component is bent along at least one bending edge in such a way that a metal profile, which is at least partially closed, is produced by the bending. The bending can take place for example in such a way that at least two regions of the metal component, separated by at least one bending edge, are brought together at a contact region designed as contact edge. In particular the outside regions of the metal component can be bent in such a way that two opposite edges of the metal component abut together. Thus for example a tubular, flangeless metal profile can be produced. A further possibility is created by two contact regions of the metal component being arranged overlapping one another, so that the regions contact each other surface-to-surface. Partially closed metal profiles exhibit higher strength or stiffness than open metal profiles. The inventive metal profiles however are not limited to closed forms. It is also conceivable that, after forming, the metal profile has an open form which may be advantageous in certain applications on geometric grounds for example. 
         [0011]    A further embodiment of the inventive method is characterized in that the metal component exhibits a substantially W-shaped cross section, wherein optionally at least one bending edge is arranged substantially in the center of the cross section. The W-shaped cross section of the metal component for example permits a closed metal profile to be produced in a simple way, since closing can already be achieved by bending at just one bending edge. The arrangement of the bending edge in the center of the cross section is particularly advantageous, since the bending edge is thus arranged substantially in the center of the metal component and therefore both sides of the metal component have comparable strength. Consequently, this embodiment is particularly suitable for producing especially stable closed metal profiles, since with this arrangement the regions of reduced strength, that is to say the region of the bending edge and the contact region, are not close together. The metal component in this case can be designed mirror-symmetrically, particularly in respect of a face intersecting the bending edge. If the bending edge is not arranged in the center of the cross section, closed metal profiles with an asymmetrical arrangement of the bend and weld seam can be produced for example. These therefore may be specifically adapted to the use of the metal profiles. 
         [0012]    Increased stability of the metal profile is achieved in a further embodiment of the inventive method in which at least two regions, separated by at least one bending edge, of the metal profile are bonded at least partly positively in the contact region, in particular using a laser beam weld. Positively bonded metal profiles exhibit partially closed cavities, which provide particularly high resistance to bending forces. The positively bonded join in this case can be arranged in a contact region designed as contact edge or as contact surface. The connection can be continuous or intermittent. In the case of one contact region the positively bonded join for example can follow the contour around the region of the contact region or can also be partly arranged in the contact face of the contact region. In order to produce the positively bonded join, various connection techniques such as welding, soldering or gluing are conceivable. Welding at least two regions of the metal profile results in a particularly strong and permanent positive bond. The use of a laser beam for welding produces a very clean and narrow weld seam. The use of a laser beam is particularly advantageous if the heating of the bending edge is also performed with a laser beam, since in this way heating and welding can be carried out using the same tool. This leads to cost- and time-saving in production. 
         [0013]    In accordance with a further embodiment of the inventive method the metal component is additionally heated in the region of at least one positively bonded join, so that the strength in the heated region is reduced after heating. The advantage of this embodiment is that, in the region of the positively bonded join, the strength can be adjusted relative to the strength of the metal component at the bending edge. For example it is possible to ensure that the metal profile experiences particular deformations when certain force is applied to the regions of reduced strength. Also homogenization of the metal microstructure can be achieved by heating the region of the positively bonded join. Irregularities in the metallic microstructure, which may arise for example through temperature stress during welding, can lead to tension cracking due to the effects of temperature or force. This is prevented by the homogenization of the metallic microstructure. 
         [0014]    Controlled influencing of the strength and deformation properties of the metal profile can be achieved in a further embodiment of the inventive method in which the size of the heated regions of at least one bending edge and/or of the positively bonded join is adapted oriented on use. Thus a small region with reduced strength leads to high strength in the whole of the surrounding region and therefore of the entire metal profile, so that the latter only exhibits small deformation even when force is applied. In this way high strength metal profiles can be produced. On the contrary, a larger region with reduced strength constitutes a deformation region which, when force is applied, can become deformed and thus absorb deformation energy. This property may be relevant particularly in the case of B-pillars of motor vehicle bodies, since in this way deformation forces caused by an accident are absorbed by the bodywork and may affect to a lesser extent persons inside the vehicle. Especially metal profiles of high strength can be prevented from fracturing by providing deformation regions. If the regions of reduced strength at a bending edge and a positively bonded join are designed with the same size, the produced metal profile in the case of small regions has very high total strength whilst in the case of large regions it comprises particularly large deformation zones and therefore has particularly high energy absorption capacity. However, the regions with reduced strength can also have various sizes, as a result of which a certain side of the produced metal profile is particularly strong and thus particularly resistant to deformation forces, while another side can absorb the deformation forces especially well. In particular, with unequally-sized regions of the metal profile with reduced strength direction-aligned deformation capacity and, associated therewith, re-routing capability of the deformation forces can be achieved. 
         [0015]    The aspects described above are achieved in accordance with a second teaching of the present invention by a metal profile, produced according to anyone of the methods described above, with at least one bending edge, wherein the metal profile in the vicinity of at least one bending edge exhibits a strength, which is reduced relative to the average strength of the metal profile. 
         [0016]    Such a metal profile preferably consists of a high or maximum strength steel alloy, a manganese boron steel alloy for example. In this way, it is possible to design the metal profiles with very thin walls and thus reduce their weight. 
         [0017]    Particularly strong and rigid metal profiles are achieved in accordance with a further embodiment of the inventive metal profile in which the metal profile is at least partially closed. The partially closed form can be designed for example so that at least two regions, separated by at least one bending edge, of the metal profile are in contact by overlapping or abutting one another. In particular the metal component can have a tubular design. Since at least partially closed embodiments with no overlap need less material and thus are more light-weight, they are particularly suitable for use as A- or B-pillars of motor vehicle bodies. 
         [0018]    A particularly strong and stiff metal profile is achieved in a further embodiment of the inventive metal profile in which at least two regions, separated by at least one bending edge, of the metal profile are joined by at least one weld seam, in particular a laser weld seam. The weld seam in this case can be continuous or intermittent. The weld seam can be arranged in a region, in which the two regions of the metal profile lie against each other on a contact edge or surface-to-surface. Thus it is conceivable in the case of regions being in contact surface-to-surface, that the weld seam follows the contour around the region of the contact region or is partly arranged in the contact surface. 
         [0019]    The deformations arising when certain force is applied can be purposefully controlled in accordance with a further embodiment of the inventive metal profile, in which the metal profile in the region of at least one positively bonded join exhibits a strength, which is reduced relative to the average strength of the metal profile. Thus the strength in the region of the positively bonded join is adapted relative to the strength of the metal component at the bending edge. Deformations arising through application of force would therefore predominantly be allocated at the bending edge and the positively bonded join. 
         [0020]    According to a further embodiment of the inventive metal profile, the size of the regions, heated after hot forming and press hardening, with the strength reduced relative to the average strength of the remaining metal profile, is adapted oriented on use. The properties of the metal profile among other things depend on the size of the regions, which are reduced in strength, of the metal profile at the bending edge and/or the positively bonded join. Thus, with metal profiles with equally or differently sized small and/or large regions of reduced strength, very different needs can be met, for example in respect of their strength, stiffness or re-routing capability of deformation forces. 
         [0021]    High overall stability of the metal profile is achieved in accordance with a further embodiment of the inventive metal profile in which at least one bending edge and one contact region of the metal profile face each other. The regions, which are reduced in strength relative to the average strength of the metal profile, are spaced at a maximum from each other in this way. The metal profile can be designed mirror-symmetrically in respect of the face intersecting the bending edge and the contact edge. Naturally, asymmetrical metal profiles are also conceivable. 
         [0022]    The aspects described above are also achieved in accordance with a third teaching of the present invention by using anyone of the metal profiles described above in a motor vehicle body, in particular as A- and/or B-pillar. The high strength of the metal profiles permits small sheet metal thicknesses with constant or increased stiffness or, respectively, strength, so that the metal profiles are particularly light-weight. Overall this leads to weight reduction of the motor vehicle and thus to lower fuel consumption. The specific arrangement of deformation regions is further advantageous for improving passenger protection in the event of an accident, since the energy released on impact can be converted in a controlled way into deformation energy or, respectively, deformation forces can be re-routed. 
         [0023]    The stability of the metal profile may be further increased in another embodiment of the inventive use in which the metal profile is arranged so that the neutral axis runs through at least one bending edge and one contact region. The neutral axis in this case means the line which runs through the region of a component at which, due to its alignment with the bending direction, neither elongation nor compression occurs during a bending process. Thus in the case of a cylindrical homogeneous pipe, for example, the neutral axis runs, seen in cross section, perpendicularly to the bending direction through the center of the pipe diameter. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0024]    Further features and advantages of the present invention are described in detail in the description of a few exemplary embodiments, with reference being made to the appended drawing, wherein: 
           [0025]      FIG. 1   a  is a first exemplary embodiment of an inventive metal component, during the process for producing an inventive metal profile, in cross section, 
           [0026]      FIG. 1   b  is the first exemplary embodiment of an inventive metal profile in cross section, 
           [0027]      FIG. 1   c  is a second exemplary embodiment of an inventive metal profile in cross section, 
           [0028]      FIG. 1   d  is a third exemplary embodiment of an inventive metal profile in cross section, 
           [0029]      FIG. 2   a  is a fourth exemplary embodiment of an inventive metal profile in cross section, 
           [0030]      FIG. 2   b  is a fifth exemplary embodiment of an inventive metal profile in cross section, 
           [0031]      FIG. 3  is the second exemplary embodiment of an inventive metal component, during the process for producing an inventive metal profile, in cross section, 
           [0032]      FIG. 3   b  is a sixth exemplary embodiment of an inventive metal profile in cross section, 
           [0033]      FIG. 3   c  is the third exemplary embodiment of an inventive metal component, during the process for producing an inventive metal profile in top view and 
           [0034]      FIG. 4  is an exemplary embodiment of the use of two inventive metal profiles as A-pillar and B-pillar of a motor vehicle body. 
       
    
    
     DETAILED DESCRIPTION 
       [0035]      FIG. 1   a  shows in cross section a metal component  2 , hot formed and press hardened from a blank, during the production of an inventive metal profile in accordance with a first exemplary embodiment of the inventive method. The blank for example can consist of a high or maximum strength steel, preferably a manganese boron steel alloy, e.g. of the 22MnB5 type. The metal component  2  exhibits a left outside region  4  and a right outside region  6 , as well as a bending edge  8  arranged in-between. The left outside region  4  and the right outside region  6  were transformed, oriented on use, in the preceding hot forming and press hardening process, so that the metal component  2  exhibits a W-shaped cross section. The side edges  9  of the metal component  2 , after forming, point in the same direction. In the production process of the metal profile the bending edge  8  has already been heated by means of a laser beam, so that the metal component  2  exhibits lower strength at the bending edge  8  than in the left outside region  4  and in the right outside region  6 . 
         [0036]      FIG. 1   b  shows a first exemplary embodiment of an inventive metal profile  10  in cross section. The metal profile  10  was produced from a metal component  2  shown in  FIG. 1   a  by bending the left outside region  4  and the right outside region  6  around the bending edge  8 . The metal profile  10  exhibits an open cross section, which has a C-shape. The bending edge  8  exhibits a form modified by the compression and elongation forces arising during forming. 
         [0037]      FIG. 1   c  shows a second exemplary embodiment of an inventive metal profile  20  in cross section. The metal profile  20  was produced from a metal component  2  shown in  FIG. 1   a  by bending the left outside region  4  and the right outside region  6  around the bending edge  8 . The left outside region  4  and the right outside region  6  of the metal component  2  lie against one another in a contact region  22 . The metal profile  20  therefore exhibits a closed cross section. The left outside region  4  and the right outside region  6  of the metal component  2  are arranged overlapping in the contact region  22  and are welded together for example. 
         [0038]      FIG. 1   d  shows a third exemplary embodiment of an inventive metal profile  30  in cross section. The metal profile  30  was produced from a metal component  2  shown in  FIG. 1   a  by bending the left outside region  4  and the right outside region  6  around the bending edge  8 . The side edges  9  of the metal component  2  abut one another on a contact edge  34 . The left outside region  4  and the right outside region  6  of the metal component  2  are joined together on the contact edge  34  by a weld seam for example. 
         [0039]      FIG. 2   a  shows a fourth exemplary embodiment of an inventive metal profile  40  in cross section. The metal profile  40  was produced just as the metal profile  30  shown in  FIG. 1   d , the metal profile  40  additionally exhibiting a region  46  around the contact edge  34 , in which the metal profile has reduced strength. This was achieved for example with the welding process or else with an additional heating process, for example by means of a laser beam. At the same time the region  46  and the bending edge  8  in the case of the metal profile  40  are enlarged and formed in a comparable size. As a result of these two enlarged regions of reduced strength, which form deformation zones, the metal profile  40  in this region exhibits increased ductility and can well absorb powerful forces through deformation. 
         [0040]      FIG. 2   b  shows a fifth exemplary embodiment of an inventive metal profile  50  in cross section. The metal profile  50  was produced like the metal profile  40  shown in  FIG. 2   a , whereas the region  46  and the bending edge  8  however are constructed with a small size. Due to the small areas of the regions of reduced strength, the metal profile  50  exhibits general high strength and, when force is applied, only shows small deformations. The strength of the metal profile  50  can be further improved by a certain arrangement. If the bending forces predominantly work from one direction towards the metal profile  50  (see arrow), no compression or elongation forces act in the intersection of the plane A with the metal profile  50 . These regions of intersection are called neutral axis. Due to an arrangement of the region  46  and the bending edge  8  within the neutral axis, the force affecting these regions can be minimized. The strength and stability of the entire profile are optimized by this arrangement, since lesser forces also act on the regions of reduced strength. 
         [0041]    For the person skilled in the art it is obvious that the region  46  and the bending edge  8  can also be constructed with a different size and that the size can be adapted to the use. 
         [0042]      FIG. 3   a  shows the second exemplary embodiment of the metal profile in cross section having the form of a metal component  62 , hot-formed and press-hardened from a blank, during the production of an inventive metal profile. The metal component  62  exhibits a left outside region  64  and a right outside region  66 , as well as a bending edge  68  arranged in-between. The left outside region  64  and the right outside region  66  were formed by the preceding hot forming and press hardening process to a form suitable for use of the metal profile, being produced, as A-pillar of a motor vehicle. During the production process of the metal profile the bending edge  68  has already been heated by means of a laser beam, so that the metal component  62  exhibits lower strength at the bending edge  68  than in the left outside region  64  and in the right outside region  66 . 
         [0043]      FIG. 3   b  shows a sixth exemplary embodiment of an inventive metal profile  70  in cross section. The metal profile  70  was produced from a metal component  62  shown in  FIG. 3   a  by bending the left outside region  64  and the right outside region  66  around the bending edge  68 . The left outside region  64  and the right outside region  66  of the metal component  62  abut one another on a contact edge  74 . The metal profile  70  thus exhibits a closed cross section. The left outside region  64  and the right outside region  66  of the metal component  62  are joined together on the contact edge  74  for example by a weld seam. 
         [0044]      FIG. 3   c  shows the third exemplary embodiment of an inventive metal profile in top view having the form of a metal component  82 , hot-formed and press-hardened from a manganese boron steel blank during the production of an inventive metal profile, for use as A-pillar of a motor vehicle body. The metal component  82  exhibits a left outside region  84  and a right outside region  86 , as well as a bending edge  88  arranged in-between. The left outside region  84  and the right outside region  86  were formed oriented on use in the preceding hot forming and press hardening process. The side edges  89  of the metal component  82  in this case lie parallel to the line of sight. During the production process of the metal profile the bending edge  88  was heated by means of a laser beam so that the metal component  82  exhibits lower strength along the bending edge  88  than for example in the left outside region  84  or in the right outside region  86 . The upper end  90  and the lower end  92  of the metal component  82  respectively are adapted in their form for joining to the remaining bodywork of a motor vehicle. 
         [0045]      FIG. 4  shows a motor vehicle body  100  with an inventive metal profile  110  as A-pillar and an inventive metal profile  120  as B-pillar. The metal profile  110  for example can be produced from a metal component shown in  FIG. 3   c , with the left outside region  84  and the right outside region  86  being bent around the bending edge  88  in such a way that the side edges  89  contact each other and are welded together. The upper end  90  of the metal profile  110  is preferably positively bonded to the roof section  130  of the motor vehicle body  100 , the lower end  92  of the metal profile  110  preferably being positively bonded to the right side panel  132  of the motor vehicle body  100 . In order to influence the deformation behavior, the heated region can be up to 40 mm, preferably up to 25 mm, in width for example.