DE102013008853A1 - Plant and method for hot forming of blanks - Google Patents

Abstract

The present invention relates to a system for hot forming of blanks (P) with at least one heating device (4) and at least one pressing device (2) arranged downstream of the at least one heating device (4), with at least one reheating device (6) downstream of the pressing device (2). is provided for at least partial heat application to the blanks formed in the pressing device.

Description

The invention relates to a system for hot forming of blanks, as well as a corresponding method for hot forming of blanks.

State of the art

The hot forming of sheet metal is a relatively new development trend in component manufacturing, especially for vehicle bodies. In the context of this application, sheets used in this context are also called "sinkers", in accordance with common usage in the field of shaping technology. A circuit board is usually a suitably cut, punched, joined and / or preformed sheet metal. However, the measures according to the invention can be used not only for appropriately prepared sheets but also for the starting materials used in each case. The invention therefore extends to all workpieces or semi-finished products which can be formed in a corresponding shaping process, for example by pressing and / or deep-drawing.

Hot forming allows components with high strength and complex geometry to be produced without springback and allows a significant reduction in weight in the case of the hereby described. B. manufactured bodies and an increase in safety, for example, occupants of a corresponding vehicle.

Due to the increasing demands on strength and rigidity of structural components, in particular in the vehicle, increasingly high and very high strength steels are used. Increasing the strength allows a reduction of the vehicle weight, which in particular allows reduced pollutant emissions and fuel consumption. With current vehicle models, the use of hot-formed components can save more than 30 kg in weight.

Hot forming processes are essentially combined forming and tempering techniques. By using appropriate steels, such as manganese-boron steels, it is possible to achieve strengths of up to 1,500 MPa. Press hardening methods include, for example, heating boards to a temperature above the complete austenitizing temperature, e.g. B. above 850 ° C, and then cool the board quickly in the tool. This forms the desired martensite structure with the desired strength. The combination of forming with quenching in a tool is sometimes referred to as compression or form hardening.

In the hot forming of ultra-high-strength materials for automotive bodies z. B. so-called roller hearth furnaces used for preheating the boards. The heating of such ovens is usually carried out by means of jet pipes, which are heated electrically or by gas burners. In order to achieve the shortest possible process cycle times, a certain "supply" of preheated components in the system is advantageous. The heat treatment time for the tempering of the steel is an essential parameter that defines the cycle time of a corresponding press. Roller hearth furnaces have a length of up to 40 meters and therefore require appropriate structural conditions, including an efficient removal of excess heat. Even rotary drum ovens, which are used as an alternative to roller hearth furnaces for preheating of components, have corresponding disadvantages. They too are heated by means of jet pipes and are rather unsatisfactory in terms of their efficiency.

Press-hardened components are characterized by their high strength and rigidity. As mentioned, this can be reduced sheet thicknesses and thus saved weight. However, the problem is the low elongation at break of press-hardened components, which in downstream manufacturing operations such. B. welding of other parts, can lead to cracking. For this reason, it is desirable certain areas z. As a body component form-hardened, and other areas of the same component in such a way that they have a higher ductility and thus can absorb more energy by plastic deformation.

Previous approaches that are used to produce such locally different properties, so-called "tailored properties", include the targeted influencing of alloy components of corresponding semi-finished products, the production of so-called "tailored welded blanks", ie boards that are joined from different materials, the partial (Local) heating by means of inductive or conductive heating technologies, the partial tempering of certain areas of the press-hardening tools by local heating and the masking of certain component areas to suppress the heating (and thus austenitizing) in a corresponding roller hearth furnace. However, such methods are expensive, often not satisfactory as a result and cause excessive costs.

Thus, there is a need for improved ways to provide boards with locally different characteristics.

Disclosure of the invention

Against this background, the present invention proposes a system for hot stamping of blanks, as well as a corresponding method for hot forming of blanks with the features of the independent claims. Preferred embodiments are subject of the dependent claims and the following description.

By inventively provided at least partial reheating, which is performed only after the forming or press hardening of the boards in the pressing device can be in a particularly effective way boards or components provide locally different properties. In particular, according to the invention very complex shapes at any point with the desired material properties, eg. B. increased ductility provided.

Advantages of the invention

As previously mentioned, the term "boards" in the context of this application comprehensively understood. The term includes sheets, semi-finished products, joined and / or preformed components, which are hot-formed in a corresponding system, in particular press-hardened.

A particularly advantageous aspect of the invention relates to the use of a premixing hydrogen-oxygen burner or fuel gas-oxygen burner. Such types of burners are basically, for example from the DE 103 45 411 A1 , known. For example, premixing fuel gas oxygen burners are used for so-called fire polishing of glass parts, in particular parts made of lead crystal or soda-lime glass. In this case, at least part of the surface of the glass part is heated and melted with the burner flame. Corresponding burners are also known as so-called Hydropox burners and are sold under this brand name by the applicant.

Premixing fuel gas-oxygen burners, in particular hydrogen-oxygen burners, are characterized by a particularly high heat transfer efficiency. In contrast to so-called external mixing burners, a gas mixture of fuel gas and oxygen is already fed to a burner head of a premixing fuel gas-oxygen burner and not first generated in a corresponding burner head. Premixing burners produce particularly hard flames, which are suitable for melting larger surface areas, which may also have pits or other irregularities. This constitutes, as found according to the invention, a decisive advantage over externally mixing burners. In externally mixing burners, only a soft flame can be produced, which in particular can not penetrate into corners, holes or depressions of a surface. The use of a premixing burner thus enables, in particular, local heating of areas, in particular of differently shaped areas, of corresponding boards. Although prolonged heating by means of an external mixing burner would also achieve a high temperature possible, but there is a risk that the board heats up altogether, not only in the desired areas.

According to a particularly preferred embodiment of the system according to the invention, the at least one reheating device is spatially orientable and / or spatially displaceable. For example, the reheating device used according to the invention can be mounted on an industrial robot. This allows the exact guidance and orientation of the post-heating device along or over the surface of the formed board, which thereby in the desired areas (partially) evenly to a desired temperature range, eg. B. between 650 and 850 ° C, in particular 700 ° C-800 ° C, in particular about 750 ° C can be heated.

Preferably, the heating device (for particular complete heating of the board before forming in the pressing device) is designed as Austenitisierungseinrichtung. Preference is given to complete austenitization. Austenitizing provides the desired material properties with which a subsequent pressing with simultaneous cooling or quenching and then a further at least partial heating (postheating) can be carried out. A corresponding Austenitisierungseinrichtung is for, in particular local, heating the boards to a temperature of 750-1.050 ° C in particular from 800-1000 ° C, for example, 850-950 ° C, furnished. A corresponding temperature depends on the respective materials and is above an austenitizing temperature. This is for example in the mentioned manganese-boron steels at about 850 ° C. If a corresponding board is preheated to a temperature just below the austenitizing temperature, the austenitizing temperature can be quickly reached or exceeded by a corresponding burner, in particular in predeterminable areas of the board. In such a cooling during the pressing or forming, the boards are preferably cooled to temperatures of 100 ° C-200 ° C, with a cooling to any Temperature between room temperature and 250 ° C is possible.

A corresponding system advantageously also has at least one loading device for loading the system with the blanks and / or at least one transfer device for transferring the blanks into the at least one pressing device of the system and / or at least one transfer device for transferring the blanks to the reheating device.

Advantageously, the at least one heating device comprises at least one paternoster oven. As paternoster, which are basically known, for example, vertical paternoster furnaces are used, which have improved energy efficiency and in particular the advantage of conventional roller hearth furnaces, which, as mentioned build large and therefore require appropriate structural conditions to replace. Paternoster furnaces are for example electrically or fuel-heated and operable in corresponding temperature ranges, so that an efficient and reliable heating is ensured.

The respective temperatures to be set depend on the particular material of the boards. For example, as noted, the complete austenitizing temperature of manganese-boron steels is about 850 ° C. The person skilled in the art can easily derive corresponding temperatures from available material parameters.

It proves to be advantageous to also form the heating device with at least one premixing hydrogen-oxygen burner or fuel gas-oxygen burner. This is also a very effective, in particular area heating of boards possible.

Although such a heating device, in particular Austenitisierungseinrichtung, heating device is preferably used in the present invention for a complete Austenitisierung a board, it is also possible for partial heating, in particular austenitizing, ie for heating or austenitizing certain regions or local areas of boards be educated. At least one burner flame of a premixing hydrogen-oxygen burner can be directed onto the region (s) provided for partial heating, in particular austenitizing. A corresponding burner arrangement thus enables, in particular, a defined, local austenitization of regions in which, for example, by press hardening, a high local strength can subsequently be achieved. In the non-austenitized areas, however, sufficient ductility of the material after press hardening is ensured. So it would be z. B. conceivable to provide a desired ductility in first areas of the board by means of such partial heating by the heating means, ie before forming, and in second areas of the board by means of heating by the reheating device, ie after forming.

Advantageously, a heating device, in particular an austenitizing device, is provided in a corresponding system with a preheating device in the form of a structural unit. This allows compact, small-scale and energy-efficient plants that require, for example, only a heat or temperature insulation.

A method according to the invention comprises loading blanks into a system according to the invention, at least locally heating or austenizing the blanks in a heating device, in particular an austenitizing device, shaping them in a pressing device by pressing and then at least partially heating them in a reheating device. As explained, the pressing process may be a press hardening process.

The inventive system for hot forming of boards, and the inventive method equally benefit from the advantages explained above.

It is understood that the features mentioned above and those yet to be explained below can be used not only in the particular combination given, but also in other combinations or in isolation, without departing from the scope of the present invention.

The invention is illustrated schematically with reference to an embodiment in the drawing and will be described in detail below with reference to the drawing.

figure description

1 shows a system for hot forming of boards according to a preferred embodiment of the invention in a schematic representation.

2 shows a combustion head for use in an embodiment of the invention in a schematic representation.

3 shows a method for hot stamping of boards according to an embodiment of the invention in the form of a flowchart.

In the figures, the same or equivalent elements may carry identical reference numerals and will not be explained repeatedly for the sake of clarity.

1 shows a plant for hot stamping of boards according to a preferred embodiment of the invention. The plant is in total with 10 designated. It has a loading device 3 in which corresponding blanks P, for example punched-out pieces of sheet metal, can be loaded in the direction of the arrow (lower horizontal arrow) into a corresponding installation. A heating device 4 is provided, which is a schematically illustrated Paternosterofen 4a having. The boards P are in the arrow direction in a lower portion of the heating device 4 introduced, lifted up (illustrated by vertical arrow) and continuously heated during lifting. It is possible to use the boards in the paternoster furnace 4a to heat up so that they austenitize. In the 1 however, an embodiment is shown in which the heating device 4 one downstream of the paternoster furnace 4a provided Austenitisierungseinrichtung 4b having. In this case, the paternoster oven serves to preheat the boards.

In an upper area of the paternoster furnace 4a leave the boards P this again in the direction of arrow (upper horizontal arrow). They then go through the austenitization device 4b that have a burner 14 which is symbolized in the present case as dreiflam-miger burner. The burner 14 can have any number of burner flames. The burner 14 can also be designed mobile and subordinate different areas of a board P successively act. For this purpose, corresponding movement devices can be provided which, for example, can also be controlled fully automatically using a corresponding control. The boards P pass through the austenitizing device 4b in the direction of the arrow, where they are heated to a temperature (eg 900 ° C.) which is above an austenitizing temperature of the corresponding material.

The boards P then go into a transfer device 5 and become a press tool 8th transferred. The pressing tool 8th Forms the boards in the desired manner, wherein simultaneously with the forming a cooling of the boards to about 200 ° C or less takes place.

As a result of this cooling or quenching, which preferably takes place at a rate of greater than 30 K / sec, a martinsite or hardened structure is formed in the austenized regions of the blank.

As mentioned, the formed blanks in this state have a temperature of about 200 ° C. In this state, the formed boards are now by means of a Nacherwärmungseinrichtung 16 containing at least one premixing hydrogen-oxygen burner 18 or fuel gas-oxygen burner, partially heat-stressed. As a result, the hardened structure is converted to a mixed structure at the heat-stressed points of the formed blank, which has improved properties, for example with respect to ductility.

The reheating device 16 For example, it can be mounted on an industrial robot (not shown), thus providing three-dimensional movability and orientability of the burners 18 is available. This allows the exact guidance of the burner 18 along the component surface, which thereby can be uniformly heated in the desired areas to temperatures between about 650 and 850 ° C. The structural change provided by this leads z. As to a reduction in hardness and increase in elongation or extensibility. In experiments carried out z. B. Improvements of the expansion values can be realized by up to 18 percent.

The burners 18 can be made in any geometry (even with small diameters, for example for welding spot areas), and are thus able to heat a wide variety of areas on a component or a converted board P. The energy transfer is very efficient, and the treatment time can be limited to a few seconds.

There are significant advantages over other heating technologies, such as induction heating, which can not be used in three-dimensional geometries or board shapes, since, for example, inner radii can not be heated properly.

Even compared to conventional laser-based methods, the inventive method has advantages. While laser-assisted methods are generally capable of performing similar tasks, they must operate at significantly higher process cost due to the high energy density and relatively small focal area, for example to heat larger contiguous areas, making such methods relatively ineffective in practice.

With the method according to the invention can be partial areas of a board, in particular a three-dimensionally formed board, for example, hardened blanks made of UHS steel, subsequently in a very varied rich and effective Heat the method, wherein the elongation of the material can be increased to a value sufficient for a targeted deformation.

By means of the burners used according to the invention, burn spots, for example, of an area of up to 10 to 20 cm ^{2 can be} made available. Burners which can be provided by means of which burnt surfaces of a size of 2 cm × 2 cm or 4 cm × 2 cm prove to be particularly preferred.

In 2 is a preferred embodiment of an inventively usable burner head shown.

An inventively usable premixing burner head is in 2 With 22 designated.

With a pre-mixing hydrogen-oxygen burner used according to the invention, via a channel 221 features a hydrogen-oxygen mixture over the burner head 22 is fed, a very hard burner flame can be generated, which ensures a very good energy transfer. In particular, z. B. trained with recesses or more complex contours areas reliably acted upon with the necessary heat. The corresponding gas mixture thus already flows here as a mixture of fuel nozzles 223 and is lit there.

3 shows a flowchart of a method 100 according to a particularly preferred embodiment of the invention in a schematic representation. In a first process step 101 corresponding boards P are punched out of a sheet. These are in one process step 102 For example, by means of a loading device, loaded in a hot-forming plant according to the invention. This can be done continuously. In one step 103 the boards P are preheated in the system, for which purpose the previously explained means can be used. In one step 104 Austenitization is carried out, as also explained above. After austenitizing, the boards P become one step 105 transferred by a transfer device in a pressing tool and there in one step 106 deformed or pressed and quenched at the same time. After quenching in the press tool, the press-hardened blanks, which in this state may have complex three-dimensional shapes, are partially heated in the desired manner in the desired manner by means of a post-heating device, in particular a premixing hydrogen-oxygen or fuel gas-oxygen mixer (step 107 ), whereby a mixed structure with desired properties (eg improved extensibility) can be provided in the heated areas.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 10345411 A1 [0013]

Claims (11)

Plant for hot forming of boards (P) with at least one heating device ( 4 ) and at least one downstream of the at least one heating device ( 4 ) arranged pressing device ( 2 ) for forming the blanks, characterized in that downstream of the pressing device ( 2 ) at least one post-heating device ( 16 ) is provided for at least partial heat application of the formed in the pressing device boards (P). Plant according to claim 1, characterized in that the reheating device ( 16 ) at least one premixing hydrogen-oxygen burner or a premixing fuel gas-oxygen burner ( 18 ) having. Installation according to one of the preceding claims, characterized in that the reheating device ( 16 ) is formed spatially displaceable and / or orientable. Plant according to one of the preceding claims, in which the heating device ( 4 ) is designed as Austenitisierungseinrichtung. Plant according to one of the preceding claims, further comprising at least one loading device ( 3 ) for loading the system with blanks and / or at least one transfer device for transferring the blanks into the at least one pressing device and / or at least one transfer device for transferring the converted blanks to the at least one postheating device ( 16 ) having. Installation according to one of the preceding claims, characterized in that the heating device ( 4 ) comprises at least one paternoster furnace. Installation according to one of the preceding claims, characterized in that the heating device comprises at least one premixing water-oxygen burner or a premixing fuel gas-oxygen burner. Installation according to one of the preceding claims, characterized in that the pressing device ( 8th ) is formed such that the boards during their transformation to a temperature between room temperature and 300 ° C, in particular 150 to 250 ° C or less than 200 ° C are cooled. Installation according to one of the preceding claims, characterized in that in the reheating device ( 16 ) heated portions of the formed board to temperatures of about 650 to 850 ° C, in particular 700 to 800 ° C, in particular heated by 750 ° C. Method for hot forming of blanks, in which the blanks are charged in a plant according to one of the preceding claims, heated in a heating device of the plant to an austenitizing temperature, formed in a pressing device and thereby cooled, and then at least partially in a reheating device to a temperature from 650 to 850 ° C, in particular 700 to 800 ° C, in particular 750 ° C, are heated. A method according to claim 10, characterized in that coated blanks are hot formed, in particular that are coated with aluminum-silicon or zinc-coated blanks warm.

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