Patent Application
20120074733
The present invention relates to a method for producing a metal component, in which a starting material is provided, the starting material is embossed and after the embossing is processed further to form a component, wherein the component comprises at least partially embossed regions. The invention also relates to an advantageous use of a metal component produced in this way. A starting material within the scope of the invention is understood to be a blank, a semi-finished product or a strip of metal.
In the production of metal components, in particular car body components, the production process has to satisfy various requirements. For example, in the production of car body components it is particularly important to satisfy the required strength properties with as low a component weight as possible, and also minimise the production costs. In order to meet these requirements various strategies are adopted in production processes for metal components and car body components of the prior art.
One possibility of reducing the component weight while retaining the same strength is to use variable wall thicknesses within a component. For example, in DE 10 2007 030 388 A1 a method and a device are disclosed for producing a hardened sheet metal component, in which flexibly rolled materials, so-called “Tailored Rolled Blanks”, are used. Alternatively blanks of different wall thicknesses welded to one another, so-called “Tailored Welded Blanks”, can also be used to produce metal components. A further possibility of optimising the weight of car body components from the prior art is to use embossed metal sheets. In this method a blank in the cold state is cold rolled between two rollers. At least one of the rollers has on its surface the structure required for the embossing. The employed material can be fed as a coil or, cut to length, as an individual blank to the roller. After the embossing the material is normally packaged and transported to the processing site. In order to provide crash-optimised components, inter alia the structure of the cold-rolled embossed blanks must be altered at the processing site. This is carried out for example by localised application of heat. The disadvantage of these methods from the prior art is that the production costs of crash-optimised components are raised. Furthermore, on account of the cold embossing rolling there is an increased wear of the rollers because of high rolling forces.
The technical object of the invention is accordingly to provide a method in which the production costs for crash-optimised components are reduced and at the same time there is reduced wear of the rollers.
This is achieved according to the invention in a generic method in which the starting material is hot embossed.
It had become known that in the hot embossing of the starting material significantly reduced forces are necessary to produce the embossings. In hot embossing the blank is previously heated to a temperature of above AC1, i.e. to more than 723° C., and is then embossed. In this way an at least partial structure transformation of the blank to an austenitic structure takes place before the embossing. An austenitic structure requires lower forming forces. The pressing force of the press or embossing roller is consequently less, so that the press or roller and the associated drive simply have to be designed for smaller forces and are subject to less wear. This leads to a cost reduction of the method compared to the embossing method of the prior art.
In a preferred embodiment of the method the starting material is hot embossed with a roller. The use of a roller for the hot embossing has the advantage that the embossing can be carried out continuously and this step of the production process can consequently be integrated better into a process sequence.
It has been found that particularly small forces are sufficient for good embossing results if the starting material is hot embossed above AC3. In this case a completely austenitic structure is present, so that in the hot embossing a complete structure transformation to martensite can take place. This results in particularly high strengths of the blanks after the hot embossing.
In a further preferred embodiment of the method according to the invention the starting material at least partially fully hardens in the embossed region. Due to the contact between the roller and the starting material in the region of the embossing, there is a cooling of the hot metal if the temperature difference between the roller or embossing punch and the starting material is sufficiently large. In this way a structure change can be achieved, resulting in a hardening process in particular in the base of the embossings. Thus, it is possible to produce in a simple manner metal components with local hardness differences that have for example a crash-optimised strength profile.
In a further preferred embodiment of the method the cooling can be specifically optimised in a targeted manner by actively cooling the embossing tool, in other words the embossing roller or the embossing punch, during the rolling. In this way in particular the cooling rate and thus the degree of hardening can be adjusted.
A further preferred embodiment of the method according to the invention is provided if the starting material consists of a steel alloy, in particular a manganese-boron steel. The requirements demanded of car body components in the automotive industry can be particularly well met with these materials. Furthermore, manganese-boron steel especially has a particularly high strength.
The properties of the metal component, for example the corrosion resistance, can in a further preferred embodiment be specifically adjusted if the starting material is coated metallically or organically/inorganically.
A further reduction of the production costs is achieved in yet a further embodiment if the starting material after the embossing is tempered to the processing temperature for the subsequent further processing. The thermal energy that was required for the tempering of the metal component for the heat embossing process can thus be at least partly used for the subsequent further processing. Accordingly, for the further processing the metal component does not have to be heated from for example room temperature to the processing temperature, but simply from the temperature after the embossing to the processing temperature. This leads to a significant energy saving.
A further preferred embodiment of the method according to the invention is provided if the starting material is hot formed and/or press hardened after the embossing. The processing temperatures required for the hot forming or press hardening are in a similar range as the preferred embossing temperature. Accordingly, after the embossing particularly little energy is necessary in order to bring the embossed semi-finished product to the desired processing temperature. Furthermore high degrees of forming can be achieved by hot forming and the component can be formed very flexibly.
Due to the press hardening of the embossed metal component a different hardness distribution in the metal component can be achieved if the non-embossed regions have direct contact with the surface of the press hardening tool and thus cool more rapidly than the embossed regions. In this way on the one hand the non-embossed regions can have a higher hardness than the embossed regions, while on the other hand in combination with the partial hardening of the embossed regions during the embossing process, a different or identical full hardening can be achieved in the embossed and in the non-embossed region.
In a further preferred embodiment of the method according to the invention the starting material is embossed with a microstructure. In this way particularly homogeneous properties, in particular strength and hardness properties of the metal component, can be achieved. Also the embossings provided with a microstructure can provide a good combination of high strength and large weight reduction. The microstructure can have any conceivable and in practice achievable shape or configuration. For example it is possible to emboss a microstructure with a roughness depth Ra of 50 μm to 500 μm.
A very flexible composite component is obtained in a further embodiment if a blank is used as starting material and after the embossing the blank is joined over its surface area to a further blank, preferably joined on the embossed side. These blanks are then preferably joined to one another by a cladding rolling and/or by combined hot rolling. In cladding rolling the blanks can be cohesively joined to one another without forming a positive engagement. In combined hot forming a positive engagement is produced, which joins both blanks to form a component. Optionally air gaps can be provided between the embossed blanks, which improves the expansion capability of the component. A joining can however also be effected by other known methods, for example by soldering. Particularly flexible properties are achieved in the production of the aforedescribed component if both blanks consist of different materials.
In a further embodiment of the method according to the invention the starting material is embossed specifically in the regions that contribute to the weight reduction. In this way it is possible to produce components that have roughly the same strength but weigh less.
In a further preferred embodiment of the method the starting material is embossed specifically in a stress-targeted manner, in particular with regard to the crash behaviour. On account of the material thinning that is achieved in the embossing and/or due to the hardness distribution in the component achieved during the embossing or due to the subsequent process steps, it is possible to adjust locally the hardness and/or strength properties of the component depending on the respective stress to be expected, in particular in the event of a crash.
The technical object is achieved in a second teaching if a hot-embossed metal component, preferably produced by the production process according to the invention, is used in a vehicle body, especially as a reinforcing element in a B column, a rocker panel or a longitudinal member. Due to the hot embossing the characteristic properties of crash-optimised components can be specifically adjusted in a simple way.
Further features and advantages of the invention can be derived from the following description of exemplary embodiments. In this connection reference is made to the accompanying drawings, in which:
A first exemplary embodiment of the method according to the invention is shown in
The blank 4 is tempered for the hot embossing and therefore preferably has a temperature above the AC3 temperature. The blank 4 in the present exemplary embodiment consists of a manganese-boron steel and is heated to a temperature of 900° to 950° C. After the heating the blank 4 is hot embossed in a rolling stand 6. The rolling stand includes an upper roller 8 and a lower roller 10, the upper roller 8 having a structured surface for the embossing. This is schematically illustrated in
The rolling stand 6 is simply illustrated diagrammatically, i.e. in particular it is not restricted to two rollers. It can also be designed as a four-roller or six-roller arrangement. The embossings 16 can be incorporated into the blank 14 also by a plurality of embossing rollers or by an embossing punch. The embossings 16 can also be incorporated on both sides of the blank 14, for example when also the lower roller 10 has raised portions. After the hot embossing procedure the embossed blank 14 or the embossed semi-finished product are processed further in a further work step 18 to form a component. This further work step 18 can include in particular forming procedures, press hardening procedures, but also machining and joining procedures.
A further exemplary embodiment of a rolling stand 26 for the hot embossing of the starting material is illustrated in
This effect can be intensified if the upper roller 44 is actively cooled. For this, the roller 44 may for example comprise a liquid cooling system in its interior. The depth of the embossings 48 is dimensioned in
After the embossing procedure the starting material as a rule has a temperature that is far above room temperature. In the following step 66 the embossed starting material is tempered for the further processing planned in the following step 68. In this connection use is made of the fact that, due to the already elevated temperature of the starting material after the hot embossing, less energy has to be expended in order to bring the starting material to the processing temperature, than in the case of cold-embossed blanks.
In particular the starting material after the embossing can at least in part still have a temperature above the AC1 temperature. For a further processing temperature above the AC1 temperature necessary in the following step 68, only a slight tempering of the starting material is therefore necessary. A processing temperature above the AC1 temperature is required in particular with hot forming and press hardening. Accordingly the starting material is preferably hot formed or press hardened in step 68.
If the embossed starting material is formed as a blank, then this blank can optionally also be joined to a further cold or hot blank, preferably on the embossed side.
An embossed blank 74 with embossings 76 on the upper side is illustrated in
By choosing different materials for the blanks 74 and 78, in particular different steel alloys with different strength and hardness properties, various components 82 can be fabricated in a very flexible way.
Instead of a firm connection between the blanks 74 and 78 it is also possible for the blanks to be joined to one another by way of a positive engagement by a rolling process or by combined forming. In
A further exemplary processing step of a hot-embossed starting material in the form of a blank is illustrated in
This production method can advantageously be combined with the partial hardening of the embossed blank during the hot embossing. By means of partial hardening of the blank in the embossed region due to the contact with the roller or with the embossing punch during the heat embossing and the hardening of the non-embossed regions in the press hardening tool 102, the embossed and non-embossed regions can be differently hardened either in the same way or by different cooling rates, so that it is possible for the thereby produced component to exhibit a large number of locally different hardness properties.
Finally
| Number | Date | Country | Kind |
|---|---|---|---|
| 102009025821.3 | May 2009 | DE | national |
This patent application is a continuation of PCT/EP2010/056677, filed May 14, 2010, which claims priority to German Application No. 10 2009 025 821.3, filed May 18, 2009, the entire teachings and disclosure of which are incorporated herein by reference thereto.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/EP2010/056677 | May 2010 | US |
| Child | 13297895 | US |
