Hot-formed profile
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.
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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 INVENTIONThe 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.
BACKGROUNDIn 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.
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 INVENTIONIn 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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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:
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.
Claims
1. Method for producing a metal profile, wherein 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, wherein the metal component, before forming, is heated at least partially along at least one bending edge in such a way that strength is reduced in a heated region after heating.
2. Method according to claim 1, wherein the semi-finished product or the blank substantially consists of a high or maximum strength steel.
3. Method according to claim 1, wherein at least one bending edge is heated with a laser beam.
4. Method according to claim 1, wherein 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.
5. Method according to claim 1, wherein 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 W-shaped cross section.
6. Method according to claim 1, wherein at least two regions, separated by at least one bending edge, of the metal profile are bonded at least partly positively in a contact area.
7. Method according to claim 1, wherein the metal component is additionally heated in a region of at least one positively bonded join, so that the strength in the heated region is reduced after heating.
8. Method according to claim 1, wherein the size of heated regions of at least one bending edge and/or of the positively bonded join is adapted oriented on use.
9. Metal profile, produced in a method of claim 1, 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.
10. Metal profile according to claim 9, wherein the metal profile is at least partially closed.
11. Metal profile according to claim 9, wherein at least two regions, separated by at least one bending edge, of the metal profile are joined by at least one weld seam.
12. Metal profile according to claim 9, wherein the metal profile in a region of at least one positively bonded join exhibits a strength, which is reduced relative to the average strength of the metal profile.
13. Metal profile according to claim 9, wherein the size of the regions, heated after hot forming and hardening, with the strength reduced relative to the average strength of the remaining metal profile are adapted oriented on use.
14. Metal profile according to claim 9, wherein at least one bending edge and one contact region of the metal profile face each other.
15. (canceled)
16. (canceled)
17. Method according to claim 2, wherein the high or maximum strength steel comprises a manganese boron steel.
Type: Application
Filed: Sep 11, 2009
Publication Date: Apr 8, 2010
Applicant: ThyssenKrupp Steel AG (Duisburg)
Inventor: Lothar Patberg (Moers)
Application Number: 12/558,107
International Classification: B21D 37/16 (20060101); B21D 7/16 (20060101); B21D 53/88 (20060101);