DE102017223164B3 - Device and method for producing a hot-formed and press-hardened sheet steel component - Google Patents

Abstract

The invention relates to a method and an apparatus for producing a hot-formed and press-hardened sheet steel component (7), with a heat treatment step in which a steel sheet semifinished product (11) is heat treated to above the material-specific austenitization temperature Ac3 of at least one sheet metal layer, and with an insertion step in which the heat-treated sheet steel semi-finished product (11) is placed in a hot state with an insertion temperature in a forming tool (6) and is hot-formed therein in a press-hardening step. According to the invention, at least one hot-rolled plating step takes place between the heat treatment step and the insertion step. In the hot rolling plating step, the heat-treated steel sheet semi-finished product (11) is hot roll-plated in the hot state.

Description

The invention relates to a method and a hot forming plant for producing a hot-formed and press-hardened sheet steel component according to the preamble of claim 1 or claim 7.

In a conventional hot forming process, a steel sheet is first heated to a process temperature above the material specific austenitizing temperature. Immediately thereafter, an inserting step takes place, in which the steel sheet is inserted into a hot-forming tool and press-hardened with an insertion temperature which corresponds approximately to the austenitizing temperature. By way of example, in the press-hardening step, the steel sheet can be cooled down to a removal temperature at which the hot-formed steel sheet can be removed from the forming tool.

Hot-forming steels, such as 22MnB5, exhibit a nearly complete martensitic structure after the hot-forming process with tensile strengths up to 1650MPa. The ductility of this structure is often characterized by the elongation at break. At 22MnB5 this is usually between 4% to 6%. In addition, the bending angle in the flake bending test according to VDA 238-100 is given as a further characteristic value for characterizing the ductility. For example, for 22MnB5 bending angles between 50 ° C and 65 ° C are to be expected. Lightweight construction with steel is essentially disadvantaged by the higher density of the lightweight material compared to other metallic construction materials (aluminum, magnesium, titanium).

All monolithic materials are limited in the combination of material properties, so that an alternative lightweight construction option is the use of sandwich materials to enable a favorable combination of optimum properties in the composite sheet. In the DE 10 2016 204 567 A1 or from the US 2013/0189539 A1 For example, such a composite sheet is produced by hot roll plating. In hot-roll cladding, first of all a steel sheet semi-finished product made of two flat metal products is provided, preferably made of different steel materials. These are stacked on top of each other and optionally welded together to produce a flat product package. Subsequently, the flat product package is heated to a hot rolling plating start temperature, which may be between 1100 ° C and 1300 ° C by way of example. After reaching the hot rolling plating start temperature, the flat product package is rolled in a rolling mill to a hot strip. After completion of the hot roll plating process, the hot strip is cut to either plates or sheets and stacked and made available to the processing industry. The hot strip can be rolled to cold strip if required.

From the US Pat. No. 9,644,252 B2 is a generic component with excellent anti-corrosion properties after painting and a method for its preparation is known. From the DE 10 2013 106 570 A1 is known a Siebstange, a bar screen and a method for producing a Siebstange.

The object of the invention is to provide a method and a hot forming plant for producing a hot-formed and press-hardened sheet steel component, which enables further efficiency improvements in comparison to the prior art.

The object is solved by the features of claim 1 or 7. Preferred embodiments of the invention are disclosed in the subclaims.

According to the hot rolling plating process is no longer decoupled process technology from the hot forming process, but rather the hot roll plating process is integrated directly into the hot forming plant. According to the characterizing part of claim 1 or 9, between the heating means, for example, a furnace in which the steel sheet semi-finished product is heat treated above the material-specific Austenitisierungstemperatur, and the forming tool, in which the hot forming takes place, a hot-rolling plating station interposed. The heat-treated steel sheet semifinished product is transferred in the hot state directly to the hot-rolling plating station, in which the heat-treated steel sheet semifinished product is hot-roll-plated. According to the invention, the fact is used that the process temperature of the steel sheet semifinished product produced in the heating device during the heat treatment is approximately in the range of the initial hot-rolling plating temperature. Therefore, both the hot-forming step and the hot-rolling plating step are assigned only a common heat treatment step, whereby the manufacturing process compared to the prior art is overall energetically favorable and feasible with reduced process duration. The process steps upstream of the hot-forming step are to be designed so that the insertion temperature at which the hot-rolled sheet steel semifinished product is inserted into the forming tool is selected above the martensite start temperature of at least one of the materials involved in order to ensure hardenability of the sheet steel semifinished product ,

It should be emphasized that in comparison to the above-mentioned prior art, no hot strips are produced in the hot-rolled plating step, but preferably hot-rolled cold-rolled sheet-metal packages are hot-rolled in the hot-forming process and hot-formed directly into sheet steel components.

With the invention it is achieved that steel sheets or steel sandwich plates can be produced in the hot forming process with optimum property combination including the reduction in density by use of, for example, metal foams. In addition to the mechanical and technological properties, the sheet thickness also has a considerable influence on the application potential. The invention optionally enables the variation of the sheet thickness in the semifinished product. For the implementation in a series production, only a compact hot-rolled plate framework is required, which can be implemented relatively inexpensively with comparable process times.

The hot rolling process step integrated in the hot forming process makes the material composite significantly more stable for the subsequent hot forming process step. In addition, as already mentioned, thickness differences can be set / rolled in. By rolling rather than pressing / pre-pressing done otherwise, the surface of the sheet steel semi-finished product becomes more uniform, less damaged (by sticking to the relatively cold tool), and the tool or rollers can be better cleaned if necessary. For larger sheet metal blanks you do not necessarily need a larger pressing tool. In addition, the pressure in the nip is precisely defined adjustable. Optionally, the rollers can be heated to achieve a defined and uniform temperature in the semifinished product. By an optional Verzurtungsschutz at least in the heating device (inert shielding gas), the mechanical-thermal compound can be improved in the hot-rolling plating step.

Particularly when using the sheet steel component in crash-sensitive areas of a vehicle, it is of relevance that the sheet steel component combines various properties: On the one hand, it must be high-strength, in order to ensure sufficient component stability in the event of a crash. On the other hand, the steel sheet part must absorb the impact energy by plastically deforming. These properties, which are difficult to combine with one another, can be realized in particular when the sheet steel component is produced as a composite material or as a composite sheet, which is constructed from sheet metal layers of different materials. According to a first embodiment variant, the hot-forming installation can have a stacking station upstream of the heating device, in which a sheet metal layer package or flat product package not yet roll-laminated is made available as a sheet steel semifinished product.

To avoid relative movements of the sheet metal layers, the sheet metal layer package can be fixed by embossing or spot welding, for example. In this case, spot welds can also be deliberately placed in load-transmitting component areas in order to better distribute the loads in the laminated core layers in the event of a crash.

The sheet-metal layer package is fed by means of a transfer device to the heating unit, in which it is heated in the heat-treatment step to above the material-specific austenitizing temperature of at least one material of the laminated sheet package, and thus into the region of a hot-rolling start temperature. Thereafter, the heat-treated sheet metal sheet package may be transferred to the hot-rolling plating station to start the hot-rolled plating step. Between exit of the laminated core from the heating unit and entry into the hot-rolling plating step, the optimum hot-rolled plating temperature can be set by means of a defined cooling phase in air. After hot-roll cladding, the steel sheet semi-finished product is inserted into the forming tool and the press hardening step is started.

Alternatively or additionally, a further stacking station may be provided between the heating device and the hot-rolling plating station. In this further stacking station, at least one non-heat-treated additional sheet metal layer can be stacked on the heat-treated sheet steel semifinished product. The resulting sheet-metal composite is hot-roll-plated in the process-related downstream hot-rolling plating station and then transferred further into the forming tool.

It is particularly preferred in view of increased lightweight and stability properties, if at least one sheet metal layer of the composite sheet is formed from a metal foam or at least a surface area in at least one sheet metal layer is recessed in a template and filled with the metal foam starting component. In this case, in a first process sequence, an as yet unfoamed starting component of the metal foam can form a material layer in the sheet metal layer package that has not yet been roll-laminated. The sheet metal layer package with the not yet foamed metal foam starting component is transferred into the furnace and heated there above the material-specific Austenitisierungstemperatur. As a result, the starting component is thermally activated, that is foamed to the metal foam. In the further course of the process, the hot-rolled plate station, in which the sheet steel semifinished product is mechanically thermally bonded and rolled to the intended sheet thickness. The rolled sheet steel semi-finished product is then fed to the forming tool in the further course of the process.

In the above case, therefore, in the heat treatment furnace, not only the preparation for the hot rolling plating step and the hot working step (that is, the heating of the steel sheet semi-finished product above the austenizing temperature and the hot rolling plating initial temperature) but also a thermal function is performed in another function Activation of the metal foam starting component.

Alternatively to the above process, the above-mentioned non-heat treated auxiliary sheet may optionally be a non-foamed metal foam starting component which is stacked in the stacking station between the furnace and the hot rolling station on the heat treated sheet steel semifinished product. Due to the high temperature of the sheet metal layer package above the martensite start temperature, the metal foam starting component is activated.

Tailored-rolled blanks are produced according to the invention in the hot-rolled plating step, which have surface areas with different sheet thicknesses which have been rolled into the sheet steel semifinished product.

Alternatively or optionally, in the hot-rolling plating step, at least one patch, that is to say a local reinforcing sheet fixed on a sheet-metal layer, can be rolled on. The fixation can be done for example by spot welding or embossing. Thereby, the number of required load transmitting welds can be reduced.

• 1 eine Anlagenskizze, anhand der die in der 2 angedeutete Prozessabfolge zur Herstellung eines warmumgeformten und pressgehärteten Stahlblechbauteils veranschaulicht ist;
• 2 in einem Blockschaltdiagramm die Prozessabfolge zur Herstellung des Stahlblechbauteils; und
• 3 und 4 jeweils Ansichten entsprechend der 1 und 2 gemäß einem weiteren Ausführungsbeispiel.

In the following, two embodiments of the invention will be described with reference to the attached figures. Show it:

• 1 an investment sketch, on the basis of which in the 2 indicated process sequence for producing a hot-formed and press-hardened sheet steel component is illustrated;
• 2 in a block diagram the process sequence for the production of the sheet steel component; and
• 3 and 4 each views according to the 1 and 2 according to a further embodiment.

In the 1 is roughly schematically sketched a hot forming plant, based on the first of the basic process sequence for the production of a hot-formed and press-hardened sheet steel component 7 is explained. The plant exemplifies a stacking station 1 , a continuous furnace 3 , a hot-rolling plating station 5 as well as a forming press 6 for hot forming and press hardening of sheet steel components 7 on. Furthermore, a storage station 9 provided in the manufactured sheet steel components 7 be stored.

In the 1 is in a first process step in the stacking station 1 First, a sheet metal layer package 11 , that is a flat product package, provided. The sheet metal layer package 11 forms the sheet steel semi-finished product from which the sheet steel component is produced in the hot forming plant 7 is formed. For this purpose, the sheet metal layer package 11 built from a series of stacked sheet metal layers, which have different material properties. In the stacking station 1 In addition, an indicated by arrows Fixieroperation F in which the sheet metal layers, for example, embossed or spot welded together to avoid relative movements of the sheet metal layers. Such a fixation operation F can also be found in the 3 indicated stacking station 17 respectively.

At the start of the process, the sheet metal layer package 11 by means of a transfer device 13 in the continuous furnace 3 transferred and heated there in a heat treatment step to a process temperature above the material-specific austenitizing temperature Ac3 of the steel sheet used, which may be 930 ° C by way of example. The so heated sheet metal package 11 is in the hot state via another transfer device 13 to the hot-rolling plating station 5 transferred, in which the sheet metal layer package 11 hot-roll-plated to a predefined sheet thickness. After completion of the hot-rolling plating step, the hot-rolled plated sheet steel semifinished product has 11 as before, a process temperature above the martensite start temperature of at least one material involved in sheet metal layer package, in which the steel sheet semi-finished 11 in the forming press 6 is inserted and hot-formed there in a press hardening step. After cooling to the removal temperature, the hot-formed sheet steel part 7 in the storage station 9 transferred.

By way of example, in the 1 shown middle sheet metal layer 15 of the laminated sheet package 11 be a non-foamed starting component of a metal foam. The foaming process of the metal foam starting component is during the oven 3 thermally activated heat treatment step. Subsequently, the steel sheet semi-finished product thus formed 11 with the middle foam core of the Hot Roll Plating Station 5 fed, in which the hot-rolling plating is performed.

In the 3 and 4 a hot forming process according to an alternative process sequence is shown. Consequently, the steel sheet semi-finished product 11 no longer a sheet metal package, as in the 1 and 2 but rather a single sheet steel layer in the continuous furnace 3 is transferred there and a heat treatment is heat treated to a temperature above the material-specific Austenitisierungtemperatur Ac3. Subsequently, the heat-treated steel sheet semi-finished product 11 a stacking station 17 supplied in the steel sheet semi-finished 11 with two additional, non-heat treated additional sheet metal layers 19 . 21 is stacked on top of each other. The resulting Blechlagenpaket is the hot-rolling station 5 fed, in which it is hot roll-plated to a predefined sheet thickness. In the further course of the process, the hot-rolled sheet steel semifinished product is used 11 in the forming press 6 inserted and thermoformed there in a Presshärteschritt.

LIST OF REFERENCE NUMBERS

1

stacking station

3

oven

5

Warmwalzplattier station

6

forming press

7

Sheet steel component

9

deposit station

11

Steel semi-finished

13

transfer device

15

Metal foam output component

17

another stacking station

19, 21

Additional sheet metal layers

F

fixing operation

Claims (9)

A process for producing a hot worked and press hardened sheet steel component (7), comprising a heat treatment step in which a steel sheet semi-finished product (11) is heat treated above the material specific austenitizing temperature Ac3, and an inserting step in which the heat treated sheet steel semifinished product (11 ) is inserted into a forming tool (6) in the hot state at an inserting temperature and hot-formed therein in a press-hardening step, wherein at least one hot-rolled plating step is performed between the heat-treating step and the inserting step, and wherein in the hot-rolling plating step the heat-treated sheet steel semifinished product ( 11) is hot roll-clad in a hot state, characterized in that surface areas with different sheet thicknesses are rolled into the sheet steel semifinished product (11) in the hot-rolled cladding step to form tailored-rolled blanks and / or that in the hot-roll cladding step at least one patch on the sheet steel -Halbzeug (11) is rolled. Method according to Claim 1 , characterized in that the steel sheet component (7) is made of a composite sheet, which is constructed of sheet metal layers of different materials, and that process technology before the heat treatment step, a not yet hot-rolled sheet metal stack as sheet steel semi-finished product (11) is provided in the heat treatment Step is heated to at least a hot-rolling plating start temperature. Method according to Claim 1 or 2 characterized in that between the heat treatment step and the hot roll plating step, a stacking step in which at least one non-heat treated auxiliary sheet metal layer (19, 21) is stacked on the heat treated sheet steel semifinished product (11). Method according to Claim 2 or 3 , characterized in that at least one sheet metal layer of the composite sheet of a metal foam (15) is formed or at least surface areas are recessed in a sheet-metal layer stencil-like and filled with metal foam. Method according to Claim 4 , characterized in that a not yet foamed starting component of the metal foam (15) forms a material layer or at least surface areas in the not yet hot-rolled sheet metal layer package (11), and that the foaming of the starting component (15) is thermally activated in the heat treatment step. Method according to Claim 3 and 4 characterized in that a non-foamed starting component (15) of the metal foam as the non-heat-treated auxiliary sheet metal layer or at least areas therein therein in the stacking step (stacking station 17) is stacked on the heat-treated steel sheet semifinished product (11). Hot-forming plant for producing a hot-formed and press-hardened sheet steel component (7), comprising a heating device (3) in which a steel sheet semifinished product (11) is heated above the material-specific austenitizing temperature Ac3 of at least one sheet metal layer, and with a forming tool (6) in which the heat-treated steel sheet semifinished product (11) is hot-formed in a press-hardening step, wherein a hot-rolling plating station (5) is arranged between the heating device (3) and the forming tool (6) is interposed, in which the heat-treated steel sheet semi-finished product (11) before hot-forming hot-rolled is characterized in that in the hot-rolling plating station (5) surface areas with different sheet thicknesses in the steel sheet semi-finished product (11) are rolled to form Tailored Rolled -Blanks and / or that in the hot rolling plating step, at least one patch on the steel sheet semi-finished product (11) is rolled. Hot forming plant after Claim 7 , characterized in that between the heating device (3) and the hot-rolling plating station (5) a stacking station (17) is interposed, in which at least one additional sheet-metal layer (19, 21) heat-treated in the heating device (3) does not heat-treat Steel sheet semi-finished product (11) is stacked. Hot forming plant after Claim 7 or 8th , characterized in that the heating device (3) is preceded by a stacking station (1) in which a sheet metal layer package as sheet steel semi-finished product (11) can be provided, and / or that in the stacking station (1) or (17) a fixing operation ( F) is feasible.

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