Patent Application
20170321295
The present invention concerns a method for hot or warm forming of a workpiece and a production plant for hot or warm forming of a workpiece.
In hot and warm forming, uncoated or coated materials are generally used. To avoid corrosion during transport, a semifabricated piece in the form of a coil or a sheet can be provided partially, preferably entirely, with a corrosion protection oil or with lubricants. In addition, a contamination with dust or the like, especially in a coil or sheet warehouse, can likewise hardly be avoided as a rule.
Caused by thermal processes which occur upon reaching the desired temperature for the tempering process, a thermal decomposition of the substances which have been deposited on the semifabricated piece occurs. As a result of this thermal decomposition, contaminants remain on the semifabricated piece, which in turn reduce the quality of the fabricated semifabricated piece. A mechanical cleaning, such as by shot blasting, cannot always entirely remove the residues which occur, or it may in particular impair semifabricated pieces which are coated. Furthermore, large oil residues, such as those due to a large oil film, may lead to an intensified hydrogen absorption in the material during the processing of the semifinished piece. This may result in material embrittlement on account of the high strength. In the case of a micro-oiling, this behavior is not found, but then no adequate corrosion protection can be assured.
One object of the present invention is to provide a method for hot or warm forming of a workpiece with which the quality of the piece fabricated by the hot or warm forming is further improved beyond that of the prior art.
The present invention solves the object by a method for hot or warm forming of a workpiece, comprising the following method steps:
providing of the workpiece,
at least partial pretreating of the workpiece,
at least partial heating of the workpiece to a target temperature in a heating station and
at least partial forming and/or hardening of the workpiece,
wherein the workpiece is at least partially cleaned in a cleaning step between the pretreating and the heating of the workpiece.
As compared to the prior art, the workpiece is cleaned after the pretreating and before the heating for the forming and/or hardening and in particular is thereby freed of residues which have become deposited due to the pretreatment on the workpiece. In this way, the quality of the part fabricated after the forming of the workpiece is improved, since the likelihood of a depositing of contaminants which form from the residues during the heating of the workpiece and thus the likelihood of a permanent impairment of the workpiece is reduced. Furthermore, other contaminations such as dust can be removed from the workpiece in the cleaning step.
Preferably, it is provided that the cleaning step is done immediately before the heating. It is furthermore preferably provided that the workpiece as a finished part after the forming and/or hardening is a structural or chassis part of a motor vehicle. In particular, the workpiece is provided as a sheet metal piece, especially a flat metal sheet (direct hot forming) or a formed part having practically its final geometry (indirect hot forming), and the pretreatment is at least part of the manufacturing process for the sheet metal piece. Furthermore, it is preferably provided that the partial region of the workpiece which is supposed to be heated during the heating to the target temperature, preferably the entire workpiece, is specifically cleaned in the cleaning step. But it is also conceivable to clean specifically those partial regions of the workpiece for which an improved surface quality is desired on the finished part. Advantageous embodiments and modifications of the invention will be found in the dependent claims and in the specification making reference to the drawings.
According to a further embodiment of the present invention, it is provided that the workpiece in the cleaning step is at least partially chemically, mechanically and/or thermally treated. The chosen cleaning method is thereby preferably adapted to the workpiece such that the cleaning leaves the properties of the workpiece substantially unimpaired. In this way, one can advantageously ensure that no steps are taken with the cleaning step which endanger the quality of the subsequently fabricated part.
According to a further embodiment of the present invention, it is provided that the workpiece in the cleaning step is at least partially cleaned in a cleaning bath. During this chemical treatment of the workpiece, the contaminants are advantageously bound in a liquid of the cleaning bath. It is conceivable that the liquid in the cleaning bath will be exchanged by bringing the liquid into the cleaning bath and draining it out once more, for example it is pumped in a liquid circuit into the cleaning bath and again pumped out from the cleaning bath. Thanks to the binding of the contaminants to the liquid, it is advantageously prevented that the contaminants spread via the air and become deposited for example on plant parts. Furthermore, it is conceivable that the wet workpiece will be dried, for example with hot air, before the heating.
According to a further embodiment of the present invention, it is provided that the workpiece is in the cleaning step brushed. For this mechanical treatment in the cleaning step, it is conceivable that the workpiece is brought into contact with the brush and the workpiece is moved in the longitudinal direction, while the brush extends substantially along the transverse direction of the workpiece. In this way, the cleaning step can be advantageously integrated in the transport of the workpiece to the heating station, without the cleaning step occasioning any significant delay in the hot or warm forming. It is also conceivable that the brush or a system of brushes are arranged at the entrance to the heating station and in this way the cleaning of the workpiece is provided immediately before the heating. Alternatively, it is conceivable that the workpiece is cleaned manually. In manual cleaning with a brush, residues visible to the naked eye can be advantageously removed without major additional effort.
According to a further embodiment of the present invention, it is provided that the workpiece in the cleaning step is heated by a burner to a cleaning temperature. Preferably the workpiece is heated by one or more burners, preferably on both sides, especially all around and uniformly. It is conceivable that the burner is moved during the heating along the transverse direction or the longitudinal direction of the workpiece, preferably in oscillating manner. Thanks to the heating already done during the cleaning of the workpiece, relatively little heating energy is required to attain the target temperature in the heating station. Preferably the cleaning station with its burner is physically separate from the heating station in order to prevent contaminants which are present in the exhaust gases occurring during the heating to the cleaning temperature from depositing on the plant parts during the heating to the target temperature. But it is also conceivable that the cleaning step is carried out in the heating station by the burner responsible for the heating first heating the workpiece to the cleaning temperature and then to the target temperature, the target temperature being greater than the cleaning temperature. It is preferably provided that the air surrounding the workpiece is drawn off during the heating of the workpiece to a cleaning temperature, for example by means of an exhaust hood, in order to carry away the contaminants.
According to a further embodiment of the present invention, it is provided that the workpiece is transported or moved during the cleaning step. In this way, the cleaning step can be advantageously integrated in the hot or warm forming of the workpiece such that potential delays due to the cleaning step are kept as short as possible. If the cleaning step involves a thermal treatment, it is conceivable that the workpiece is moved by a burner belt along the conveyance direction past a burner, with the burner heating the workpiece as it moves past it. In particular, the workpiece is moved with a conveying mechanism along a conveyance direction and in this process it passes in succession through the cleaning station, the heating station, and reaches the forming and/or hardening die.
According to a further embodiment of the present invention, it is provided that the workpiece is transported from a cleaning station to a heating station between the cleaning step and the heating step. In the case of thermal cleaning, it is preferably provided that the transport path is covered in a shortest possible time in order to prevent the workpiece from cooling down again. In particular, it is conceivable that the conveying mechanism comprises heating elements which ensure that the workpiece basically maintains its cleaning temperature. Preferably, the workpiece is transported such that the workpiece does not become polluted or contaminated once more. In particular, the workpiece is moved with a conveying mechanism along a conveyance direction and thereby passes in succession through the cleaning station, the heating station, and reaches the forming and/or hardening die.
According to a further embodiment of the present invention, it is provided that the workpiece is heated during the heating for the forming and/or hardening with an additional burner to the target temperature. Preferably, the target temperature chosen is a temperature between 600° C. and 900° C. If a manganese-boron steel material is used preferably, it is preferably provided that the target temperature is reached above AC3, in order to transform the microstructure completely into austenite. If the target temperature lies below AC3 and above AC1, a mixed microstructure of austenite and ferrite is obtained. For example, it is provided that the speed with which the workpiece is heated to the cleaning temperature when using a burner is greater than the speed with which the workpiece is heated to the target temperature, especially when using a radiant furnace.
According to a further embodiment of the present invention, it is provided that the workpiece is coated with a protective material and/or in particular it is coated at least partially with a corrosion protection oil in order to prevent corrosion during transport.
According to a further embodiment of the present invention, it is provided that the burner and/or the additional burner is operated with a fuel gas and an oxygen-containing gas. Preferably, the heating power of the burner and/or the additional burner is adjusted by the mix ratio of the fuel gas and the oxygen-containing gas. In particular, an oxygen content is used to establish the maximum temperature in a burning flame of the burner and/or the additional burner. It is provided for example that a technical oxygen mixture is supplied to the additional burner wherein the oxygen content is preferably greater than 70% or especially preferably greater than 90%. Furthermore, it is provided that, in order to reach the target temperature with a desired speed at which the workpiece is heated, the distance between burner and workpiece, the oxygen content, and/or a conveying speed of the workpiece being transported along the conveyance direction are adjusted accordingly.
According to a further embodiment of the present invention, it is provided that the workpiece is arranged in a forming/hardening die for the forming and/or hardening. Preferably, the forming/hardening die is at least partially cooled and thereby advantageously ensures, for example, a partial hardening of the workpiece.
According to a further embodiment of the present invention, it is provided that the workpiece used is a flat metal sheet. For example, the workpiece is a workpiece fabricated substantially from a manganese-boron steel, especially 22MnB5, or it is a flat metal sheet with higher carbon content.
Another subject matter of the present invention is a production plant for hot or warm forming of a workpiece, especially for carrying out a method according to the invention, wherein the production plant comprises a cleaning station for cleaning a workpiece and a heating station for heating the cleaned workpiece.
As compared to the prior art, the production plant according to the invention has the advantage that, thanks to the cleaning station, it can be ensured that possible residues from a pretreatment of the workpiece are removed and thus the quantity of potential contaminants which might impair the quality of the subsequently fabricated part is reduced in advantageous manner.
According to a further embodiment of the present invention, it is provided that the production plant comprises a conveying mechanism. With the conveying mechanism, the workpiece can be advantageously transported through the cleaning station and the heating station to the forming/hardening die. It is conceivable that the conveying mechanism comprises conveying rollers.
According to a further embodiment of the present invention, it is provided that the cleaning station is structurally separate from the heating station. In this way, it can be advantageously ensured that the contaminants loosened by the heating of the workpiece to the cleaning temperature are distributed through the air and then become deposited on the plant parts of the heating station.
Further details, features and benefits of the invention will emerge from the drawings as well as the following specification of preferred embodiments with the aid of the drawings. The drawings only illustrate sample embodiments of the invention which do not limit the notions of the invention.
In the various figures, the same parts are always provided with the same reference number and therefore as a rule will respectively only be mentioned or designated once.
As an example of a cleaning step, the embodiment in
After the heating of the cleaned workpiece 1 it is provided that the workpiece 1 is placed in a preferably cooled forming and/or hardening die 30 and formed and/or hardened therein, as shown in
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2014 116 950.6 | Nov 2014 | DE | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2015/075809 | 11/5/2015 | WO | 00 |
