Patent Application
20190283100
The invention relates to a method for producing an at least partially hardened profiled component, in which method a semi-finished product, after being heated up to a hardening temperature, is shaped in a forming tool by means of hydroforming or by means of pressing so as to produce the profiled component which, after being shaped in the forming tool, is hardened by means of quenching.
In particular, the invention relates to structural profiled components for motor vehicles such as, for example, A-pillars, B-pillars or other frame components that can be used for the production of monocoque car bodies. The profiled component can especially be an A-pillar for a convertible car.
On the one hand, such profiled components are subject to extremely high requirements in terms of their strength, for instance, in order to enhance the crash safety of motor vehicles. On the other hand, in modern automotive construction, these requirements run counter to the desire for a great deal of design flexibility as well as for lightweight construction.
The above-mentioned profiled components, which are especially used in automotive construction, are also subject to various requirements in terms of their mechanical strength. Such components should be configured so as to be, for example, mechanically stiffer in a first section, and more easily deformable in another section. For instance, an A-pillar or a B-pillar, as part of the crumple zone of a motor vehicle, should have a higher strength so that it does not fail in case of an impact in the area of the greatest load. On the other hand, by being deformed, that same component should convert as much impact energy as possible into deformation work. When it comes to A-pillars for convertibles, the A-pillars should provide sufficient support for the window frame of the windshield in order to create a survival space for the vehicle occupants, for example, in the eventuality of a vehicle roll-over. For this reason, such an A-pillar should exhibit a very high mechanical strength, especially in the transition area between the fender and the window frame. For this purpose, profiled components are sometimes used which have a non-uniform cross section along their extension in order to be very rigid, for example, in certain places in a certain direction. This means that the shape of the cross section along the extension of the component in question makes a transition, for example, from a round basic shape to a box-like shape and then again to a round or oval shape so that different places of the component are provided with the appertaining section-specific contours of the profile and the corresponding transitions of the various profile cross sections.
Such components can be produced, for instance, by means of the so-called U/O bending method in which a flat metal blank is used to first create a component with a U-shaped cross section and it is then shaped in a second work step to create a closed O-profile. At the same time, when it comes to such a U/O bending method, the component can be bent in the direction of its extension so that an extension that was originally configured as a straight line is shaped into a two-dimensional or three-dimensional extension curve. In this manner, for instance, a semi-finished product can be made which, in another work step, ensures a collapse of the cross section by means of a shaping mandrel that is inserted into the blank. Such a method is disclosed, for example, in European patent specification EP 2 205 370 B1. This method, however, entails the drawback that at least one end of the semi-finished product as well as one end of the finished component must have a sufficiently large cross sectional shape to accommodate the drawing mandrel. This restricts the design freedom during the development of the final shape.
European patent specification EP 2 282 853 B1 discloses a support core for such a U/O shaping method which is employed to shape blanks into a structured hollow profile. The support core has a plurality of support members connected to each other, whereby, when the individual support members are in a position where they have been pushed together, they form the inside contour of the hollow profile that is to be produced so as to be at least partially flat and they are connected to each other via coupling elements. In such a production method, a blank is first imparted with a U-shape. Then, the support core is inserted into the U-shaped blank in order to then shape the blank into a hollow profile by means of a U/O shaping process or by employing a rolling technique.
German patent specification DE 10 2009 003 668 A1 discloses a method and a device for the production of closed profiles, whereby a blank is placed onto the upward-facing edges of the side walls of a first die. A U-shaped punch is moved into the matrix of the first die, thereby pre-shaping the blank. Owing to the movement of the side walls of the first die relative to the matrix of the first die, the blank acquires an at least partially U-shaped cross section, whereby the U-shaped punch remains positioned in the matrix of the first die. The U-shaped punch is then removed from the U-shaped blank and from the matrix of the first die, and a support core is inserted into the U-shaped blank. Subsequently, a second die located opposite from the first die is put into position. Via the side walls of the second die, which rest on the side walls of the first die, the side walls of the first die are moved relative to the matrix of the first die, so that the U-shaped, bent blank is shaped into a profile with a closed cross section.
For the production of structural components for motor vehicles, it is also a known procedure to impart hollow profiles with their final shape by means of hydroforming. Towards this end, international patent document WO 98/54370 discloses a production method to blow-mold a heated hollow blank that, after having been expanded, is subsequently quenched in the same forming tool by introducing a cooling medium so that the component has already hardened when it is removed from the forming tool.
Other hydroforming methods are disclosed, for example, in international patent application WO 2010/105341 A1 and German patent application DE 10 2007 018 281 A1.
In the method known from international patent application WO 2010/105341 A1, sections of a tube having a round or circular cross-section are shaped in such a way that the cross-section along the extension of the tube is tapered. Then a bending method is employed to impart the thus-formed tube with a shape that follows a two-dimensional or three-dimensional curve. Subsequently, the thus-created semi-finished product is imparted with its final shape by means of hydroforming. In order to prevent material failure during the hydroforming due to cold-work hardening during the preceding forming steps, the semi-finished product has to undergo an intermediate heat treatment so that it can be shaped by means of the hydroforming step. Here, the semi-finished product can also consist of two profiled segments that have been welded together and that have already been pre-shaped so as to be conical, and after these profiled segments have been welded, they are bent in a bending machine so as to approximate the envisaged final shape. All in all, however, this method proves to be quite complex since the cold-work hardening that takes place during the production of the semi-finished product has to be compensated for by means of a heat treatment prior to the hydroforming process.
According to the method disclosed in German patent application DE 10 2007 018 281 A1, it is possible for the semi-finished product to consist of two pre-shaped tubular profiled segments. Here, the ends of the individual profiled segments are arranged in such a way that they can be slid into each other in order to ensure a gas-tight closure for the subsequent hydroforming process. This, in turn, requires for both ends of the profiled segments to undergo a special treatment—which is also subject to strict tolerance requirements—so as to achieve a gas-tight seal between the two profiled segments. In the final shape of the profiled component, both profiled segments are then joined by means of a positive-fit, radially circumferential connection which, however, has an influence on the final shape of the profiled component that is to be produced.
It would also be conceivable for the method disclosed in international patent application WO 98/543 70 A1 to be employed for a semi-finished product produced by means of the U/O profile forming method described above. Such a method, however, would entail the problem that, in order to produce the semi-finished product, which sometimes can have a length of more than one meter, there would be a need for special presses with an extremely large stroke of approximately more than one meter, in order to make it possible for the above-mentioned U/O forming method to be carried out. Moreover, such semi-finished products are developed iteratively together with the tool for the subsequent high-pressure forming process, whereby changes in shape due to production-related requirements for the semi-finished product as well as for the final product each mutually influence the other method. Consequently, the development of such a component has proven to be particularly complex.
Before this backdrop, the invention is based on an objective of putting forward an improved method and an improved semi-finished product for said method, thus allowing a simplification of the development process as well as a reduction in the investment costs for the requisite production machines.
The method according to the invention for producing an at least partially hardened profiled component provides that, to start with, a first profiled segment, which has a uniform cross-sectional shape along its extension, and a second profiled segment, which has a non-uniform cross-sectional shape along its extension, are joined together at a joint in order to form at least part of a semi-finished product, wherein the first and the second profiled segments have cross-sectional shapes that essentially match at the joint. After the semi-finished product has been heated up to a hardening temperature, it is then shaped in a forming tool by means of hydroforming or by means of pressing so as to produce the profiled component which is subsequently hardened inside the forming tool by means of quenching.
For instance, the first profile can be configured as a round tube. As an alternative, the first profiled segment can be configured as a uniform oval or box-like profile. Both profiled segments can be produced by means of profile rolling processes that are relatively simple and manageable, as a result of which the production costs for the individual sections of the semi-finished product as well as the investment costs for the requisite tools can be significantly reduced.
The invention also assumes that only a few areas, or even just one single area—for example, in the form of the second profiled segment having a non-uniform cross-sectional shape along its extension as the transition area has to be configured between two uniform profiled segments in order to meet the necessary requirements made of the mechanical properties. In this manner, for example, in the case of an A-pillar of a convertible, the total length of this second profile element can be reduced from about 1.5 m to about 0.4 m. This permits the use of considerably smaller and thus cheaper tools.
In comparison to a likewise conceivable subsequent joining of profiled sections that have already acquired their final shape in order to form the profiled component, the present method entails the advantage that any structural changes in the profiled segments are automatically compensated for if these changes result from the production process of the profiled segments or from the creation of the joined connection between the profiled segments. Owing to the heat treatment prior to the hydroforming process, such structural changes do not occur in the finished profiled component.
Therefore, the first profiled segment can be made in a way that is geometrically extremely simple and cost-effective, a process in which the cost-intensive shaping steps for producing the semi-finished product are then limited to the second profiled segment.
The shaping in the forming tool can be carried out by means of simple pressing. This is particularly the case for geometrically simple profiled components in which collapsing of the profile caused by the pressing procedure is not to be expected at all or else only to a tolerable extent. In contrast, if collapsing of the profile has to be prevented—that is to say, if it has to be ensured that the wall of the semi-finished product will come to rest against the contour of the forming tool—then hydroforming is employed.
In accordance with an advantageous embodiment of the method according to the invention, it is provided that, when the second profiled segment is produced, it is made with a connecting end whose cross-sectional shape essentially matches the cross-sectional shape of the first profiled component. This means that the adaptations of the cross-sectional shape needed for joining the profiled segments can be shifted to the second profile, which is more cost-intensive anyway, as a result of which the first profiled segment can be produced geometrically even more simply and in a less costly manner.
Preferably, the profiled segments can be joined by an integral bond, for instance, by means of welding, especially preferably by means of laser welding, particularly by means of orbital laser welding. Such joining operations allow a very simple production of the joined connection between the profiled segments. In this context, the profiled segments are especially preferably butt-welded, a measure that allows high throughput rates in the production facility.
In a refinement of the invention, it can be provided that at least a third profiled segment is joined to the first or to the second profiled segment, said third segment having either a uniform or a non-uniform cross-sectional shape along its extension. This allows the production of semi-finished products which, as a function of the desired final shape, are already pre-shaped and consequently are optimally adapted to the subsequent hydroforming process. This yields a very cost-effective semi-finished product for the production of a profiled component, some of whose sections, in turn, can be subject to different mechanical requirements or which, owing to the final design, have to be produced so as to exhibit markedly different degrees of deformation.
In a special manner, it can be provided that at least one of the profiled segments is made of a hardenable alloy. This means that the alloy in question can be hardened in that it is heated to a hardening temperature and subsequently quenched, in other words, it is quickly cooled off. In this context, the alloy preferably consists of steel, particularly a boron-alloyed steel. During the hardening procedure, the component is heated up to the hardening temperature.
As far as the terminology is concerned, it should be mentioned that the hardening temperature is a temperature above the structural transformation temperature which, for example, in the case of a steel material, causes a structural transformation into an austenitic structure. Due to the subsequent rapid cooling, i.e. the quenching, the structure is transformed into a martensitic structure that is permanently retained when the material is in its cooled state. In comparison to the initial structure, the martensitic structure is harder. In the case of hardenable alloys, the hardness of the material is particularly high after the hardening when compared to the hardness that prevailed before. Particularly well-suited for this are steel materials, especially preferably boron-alloyed steel grades. In this manner, at least partially high-strength steel components can be made. An example of such a steel grade is 22MnB5 (see the German publication titled SZFG material sheet 11-112, status as of May 2014, which can be downloaded at: http://www.salzgitter-flachstahl.de/fileadmin/mediadb/szfg/informationsmaterial/produktinformatione n/kaltgewalztes_feinblech/deu/22mnb5.pdf).
According to a preferred embodiment, the hydroforming is carried out by a pressurized gas that serves as the forming medium, especially at a pressure between 300 bar and 600 bar, whereby the quenching is carried out with a separate cooling medium which is conveyed into the forming tool, especially into the shaped profiled component, after the hydroforming process.
Using pressurized gas for shaping the semi-finished product into the finished component has the advantage that, on the one hand, the provision of the gas in the above-mentioned pressure range is considerably cheaper than the provision of a pressurized liquid of the type employed in hydroforming.
According to the invention, the hydroforming or pressing of the semi-finished product is carried out at a hardening temperature, for instance, above 950° C. This temperature has to be present before the beginning of the quenching in order for the desired hardening to be achieved. The high temperature during the shaping renders the steel more resilient so that it can be shaped by means of the pressurized gas at pressures that are well below the pressures normally employed during hydroforming.
Moreover, a gas fundamentally exhibits a lower thermal capacity and thermal conductivity than a liquid, so that the temperature of the semi-finished product is only negligibly lowered when the forming medium is introduced. In contrast, a gas or a liquid having a relatively higher thermal conductivity or thermal capacity is preferably employed as the cooling medium; for instance, water or a water-oil emulsion can be used as the cooling medium. Preferably, the method for the hydroforming and the subsequent quenching can be based on the method disclosed in international patent application WO 98/54370 A1.
In a preferred embodiment of the invention, it can be provided for the first profiled segment to be produced by means of a profile rolling method, especially by means of roller/roll profiling, while the second profiled segment is produced by means of a U/O bending method. An example of a U/O bending method is the so-called T3® method of ThyssenKrupp Steel, which is described, for example, in European patent specification EP 2 205 370 B1, in European patent specification EP 2 282 853 B1 or in German patent application DE 10 2009 003 668 A1.
Once the profiled segment has been shaped by means of roller/roll profiling or by means of the U/O bending method, the profile segment in question is joined at the seam of the sides that are bent onto each other, preferably by means of welding, to form a closed hollow profile that is sufficiently liquid-tight so that it can be expanded during the subsequent hydroforming process or at least so that, following a pressing operation, it can hold the cooling medium needed for the quenching. The structural changes and tensions introduced into the material by this welding operation and the resultant structural transformation processes are largely or completely compensated for when the material is heated up to a hardening temperature, so that the appertaining seam on the finished profiled components no longer, or almost no longer, constitutes a weak spot.
A semi-finished product for producing an at least partially hardened profiled component has at least two profiled segments whose extensions are arranged one after the other and which are joined together at a joint in such a way that the semi-finished product can be shaped by means of hydroforming or by means of pressing, whereby, along their appertaining extensions, the first profiled segment has a uniform cross-sectional shape while the second profiled segment has a non-uniform cross-sectional shape, and the profiled segments have essentially matching cross-sectional shapes at the joint.
A semi-finished product configured in this manner and preferably produced by means of the method described above can be adapted very well to the pressing process or to the hydroforming process, whereby, on the one hand, the strength properties of the produced profiled component are optimized with respect to the amount of material that has been used and shaped. In particular, this also makes it possible to meet the recent requirements for lightweight construction in modern motor vehicles since less material can be used in the areas of the profiled components that are less stressed.
In a preferred embodiment of the invention, the second profiled segment can be provided with a connecting end whose cross-sectional shape essentially matches the cross-sectional shape of the first profiled component. This has the advantage that the adaptations needed during the production in order to subsequently join the two profiled segments are concentrated in the second profiled segment, which is the one that is more complex to produce anyway, as a result of which the first profiled segment can be produced in a very cost-effective and simple manner.
Preferably, the profiled segments can be joined by an integral bond, for instance, by means of welding, especially preferably by means of laser welding, particularly by means of orbital laser welding. In this context, the profiled segments can have connecting ends that are preferably butt-welded at the joint. Such joining operations allow a very simple creation of the joined connection between the profiled segments. Here, the profiled segments are especially preferably butt-welded, a measure that allows high throughput rates in the production facility.
Preferably, it can be provided for the semi-finished product to have at least a third profiled segment that has either a uniform or else a non-uniform cross-sectional shape along its extension.
In this manner, the semi-finished product can already be pre-shaped as a function of the desired final shape so that it can be optimally adapted to the subsequent hydroforming process.
According to a special embodiment of the invention, it can be provided that the at least one profiled segment consists of an alloy that can be hardened by being heated up to a hardening temperature and subsequently quenched, whereby the alloy preferably consists of steel, particularly a boron-alloyed steel.
In the method according to the invention and the semi-finished product according to the invention, it can also be provided for the extension of the profiled segments and/or of the semi-finished product, at least in certain sections, to follow at least a straight line and/or a two-dimensional and/or three-dimensional curve.
As a result, the semi-finished product can already be pre-shaped or pre-bent so as to match the final shape of the profiled components so that the degrees of bending necessary during the hydroforming method can be reduced to an extent that is permissible for the material in question. In particular, it can be provided that the second profiled segment follows a two-dimensional and/or a three-dimensional curve, whereby the first profiled segment or else other profiled segments attached to the second profiled segment are shaped so as to be straight, in other words, so as to follow in the direction of the extension of a straight line. In this manner, complex production steps such as, for instance, the bending of the profiled segment or the creation of a bent shape, can be concentrated on the second profiled segment, which is already more cost-intensive to produce anyway.
The term “extension” of the appertaining profiled segment refers to the part that is subsequently shaped in the forming tool. A conical expansion that might be provided at one end of the profiled segment for attaching a feed connection piece for the hydroforming medium or for the cooling medium is not included under the concept of “extension”.
Additional objectives, advantages, features and application possibilities of the present invention ensue from the description below of an embodiment making reference to the drawing. In this context, all of the described and/or depicted features, either on their own or in any meaningful combination, constitute the subject matter of the present invention, also irrespective of their compilation in the claims or the claims to which they refer back.
In this context, the following is shown, at times schematically:
For the sake of clarity, identical components or those having the same effect are provided with the same reference numerals in the figures shown below.
In the present example, the profiled component 2 forms an A-pillar 8 of a convertible that has to be configured so as to be very stable in case the convertible rolls over. Here, especially the area between an upper tube 3 and a lower tube 4 has to be configured so as to be very stable, and in the present case, this area is formed by an intermediate piece 5.
On the upper right,
The second profiled segment 20 has a non-uniform cross-sectional shape 9, 10 along its extension 22, whereby in the present case, said shape expands starting at a connecting end 31 towards a connecting end 32 of the second profiled segment 20. Moreover, the extension 22 of the second profiled segment 20 follows an at least two-dimensional curve 30. By the same token, the two-dimensional curve 30 can also be a three-dimensional curve 30 which, in the views of
The second profiled segment, as an intermediate piece 5, has the two differently configured connecting ends 35, 36, whereby the connecting end 35 is shaped during the production of the profiled segment 20 in such a way that it essentially matches the first profiled segment 19. This means that the two connecting ends 31 and 35 can be, for instance, positioned so as to abut each other and can then be joined together by means of a simple welding operation.
The second connecting end 36—which lies on the second profiled segment 20 along the extension 22 opposite from the first connecting end 35—in turn, is shaped so as essentially match another connecting end 32 of a third profiled segment 21. The third profiled segment 21 is shown at the bottom of
It can be seen in
The gas that serves as the forming medium is subsequently vented from the forming tool 11 and replaced by a cooling medium that then performs the quenching 27 of the profiled component 2 and thus the hardening. The forming tool 11 and the heating device 17 can each be part of a physically interrelated hydroforming installation 18.
The formed and hardened profiled component 2 in its final shape can still be fed to an aftertreatment station 12 where, for instance, by means of laser cutting, any protruding edges or burrs or else conical expansions that might have been provided at the ends for the hydroforming 26 can then be removed.
The production method 34 schematically shown in
First of all, the profile production 23 is carried out for the first and second and optionally additional profiled segments 19, 2021 which are subsequently put together to create the semi-finished product 1 by means of joining 24. Then the semi-finished product 1 is brought to a hardening temperature, for instance, above 950° C., in order to subsequently impart the profiled component 2 with its final shape by means of hydroforming 26. The profiled component 2 is hardened by means of quenching 27 and by the structural transformation that takes place in this process. Subsequently, an aftertreatment 28 can be carried out in order to remove any protruding edges and burrs.
The method 34 according to the invention or the semi-finished product 1 according to the invention make it possible to produce partially as well as completely hardened profiled components. Putting together the semi-finished product 1 out of various profiled components 19, 20, 21 allows the use of profiled segments made of different materials having, for example, different hardening characteristics, so that in a single work step, differing degrees of hardening occur in the same profiled component 2 during the quenching 27 down from the hardening temperature.
The present invention is not restricted in terms of its configuration to the embodiments presented here. Rather, several variants are conceivable which make use of the solution presented here, even in the case of other types of configurations. It will be appreciated by those skilled in the art that changes could be made to the embodiments described above without departing from the broad inventive concept thereof. It is understood, therefore, that this disclosure is not limited to the particular embodiments disclosed, but it is intended to cover modifications within the spirit and scope of the present disclosure as defined by the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2016 123 265.3 | Jan 2016 | DE | national |
This application is a national stage application (under 35 USC § 371) of PCT/EP2017/079725, filed Nov. 20, 2017, which claims benefit of German application No. 10 2016 123 265.3, filed Dec. 1, 2016, the contents of each of which are incorporated by reference herein.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2017/079725 | 11/20/2017 | WO | 00 |
