EP2907881B1 - Hot forming line and method for the preparation of hot formed sheet metal products - Google Patents

Description

The invention relates to a thermoforming line with a heating station and a forming station for the production of hot-formed and in particular press-hardened sheet metal products from metal blanks and a method for the production of hot-formed sheet metal products.

Press hardening is a process for producing high-strength complex vehicle components with high manufacturing accuracy. It combines deep drawing with a heat treatment with the goal of increasing the strength in one process. This manufacturing process requires a relatively high outlay because it involves heating and subsequent defined cooling of the formed sheet metal products in addition to the forming. The individual sub-processes exert a significant influence on the component properties.

By the DE 24 52 486 A1 includes a method for producing hardened sheet metal profiles from a metal plate in a prior art press hardening process. In this case, a board made of a hardenable steel is heated to a hardening temperature above the austenitizing temperature Ac3 and then hot-formed in a press tool and then hardened, while the sheet profile remains clamped in the press tool. Since the sheet metal profile at the Caused by the hardening process cooling is clamped in the press tool, we obtain a product with high and good dimensional stability.

The heating of the metal blanks in series production is currently for the most part in passage ovens, especially roller hearth furnaces, by convection and thermal radiation. Chamber furnaces are also used.

Furnace heating is an established heating process that allows homogeneous heating regardless of geometry. The furnace systems are usually heated electrically or with gas. The temperatures required for hot forming are between 780 ° C to about 1,000 ° C for steel sheets. In order to generally achieve the high thermoforming temperatures in the metal blanks, the residence time in the furnace plant must be designed accordingly. This is technically complex and makes a relatively large amount of space necessary.

Much faster is the inductive heating. It can be used both areal and locally. However, the homogeneity is dependent on the inductor geometry and clearly inhomogeneous than in the furnace heating. The efficiency of inductive heating is based primarily on the distance of the inductor to the component. The larger it is, the lower the efficiency. However, at a short distance, the energy loss due to the heat transfer to the inductor is significantly higher.

A thermoforming line with an inductively heated heater counts, for example by the DE 10 2012 110 650 B3 to the state of the art.

Systems for conductive heating are also known. In direct resistance heating technology, the metal board or area to be heated itself forms part of the circuit. A method and apparatus for conductive heating of metal sheets is disclosed in US Pat DE 10 2006 037 637 A1 described. There, the metal sheet is heated by a gripper-heating system, via which the energy is introduced, placed in a press tool consisting of a lower tool and an upper tool and reshaped.

From the DE 102 12 819 B4 The invention relates to processes for the production of metallic components by means of electrical resistance heating with subsequent hardening by rapid cooling, wherein areas are cooled or electrically and / or thermally bridged during resistance heating in order to remain below the austenitizing temperature in these areas, so that uncured in the sheet products Areas remain.

By the DE 10 2012 110 649 B3 includes a hot forming line for producing a hot-formed and press-hardened sheet steel product, in particular a motor vehicle component of the prior art. The thermoforming line has a tempering station, wherein in the tempering station locally different areas can be tempered to different temperatures. The temperature control is carried out by conductive conditioning, wherein for this purpose Temperierplatten be used, which are interchangeable.

A heating device with a lower heating unit and an upper heating unit for heating a metal circuit board is further from the EP 2 216 417 A2 out. Each heating unit has a heatable plate coming into contact with the board. The heating plate of the lower and / or the upper heating unit has a plurality of heating segments, which are arranged in a predetermined grid relative to each other and which are displaceable relative to each other in the plane defined by a contact surface between the heating segments and the board. The heating segments each have an integrated heating element in the form of a resistance heater.

The EP 2 182 081 A1 discloses a method and apparatus for thermal treatment of a coated sheet steel body. Again, the heating takes place via surface elements in the form of contact plates.

The object of the present invention is the development of a plant-technically improved thermoforming line with a rationally designed conductive heating system, which enables efficient heating of metal blanks for hot forming within the thermoforming line.

The solution of this problem consists according to the invention in a thermoforming line according to the features of claim 1.

Advantageous embodiments and further developments of the hot forming line according to the invention are the subject matter of the dependent claims 2 to 17.

A method for producing hot-formed sheet metal products in a hot-forming line according to the invention is the subject matter of claims 18 to 21.

The hot forming line according to the invention for the production of hot-formed and press-hardened sheet metal products from metal blanks comprises a heating station and a forming station. The heating station has a lower tool and an upper tool, between which a metal plate is accommodated for heating. The heating or heating of a metal plate in the heating station takes place conductively by indirect or indirect resistance heating. The heat is generated outside the metal plate and passes through its surface in the metal plate itself. For this purpose, the lower tool and / or the upper tool has an electrical resistance heating with at least one surface heating element. The heat transfer from the surface heating element to the metal plate takes place by heat conduction as a result of the at least indirect contact between the surface heating element and the metal plate to be heated.

According to the invention, the surface heating element is a heating plate with a plate body of an electrically conductive material, wherein the plate body is formed as a heating conductor. The plate body itself forms directly the heating conductor. The heating conductor defines a current path in the plate body. The heating element converts electrical energy into heat.

To heat a metal plate this is taken up between the upper tool and lower tool. For this purpose, a corresponding receiving space is provided between the lower tool and upper tool. According to the invention it is provided that the heating plate indirectly or indirectly comes into contact with the metal plate in contact. The heating surface of a heating plate is provided with an electrical insulation or an insulating layer.

The heating conductor is preferably configured to release from it the proper amount of heat for heating the metal board, which is supplied by heat transfer to the metal boards. In an advantageous embodiment of the invention, a heating conductor is formed in the plate body through at least one slot extending across the thickness of the plate body. In a further advantageous embodiment of the heating element is formed by at least one horizontal slot in the plate body. Preferably, the horizontal slot extends almost over the entire length or width of the plate body. The electrical line or the current path takes place over the region of the plate body which is not separated by the slot.

The heating conductor is configured through the slot guide in the plate body. In particular, the heating element is wound several times. For example, the heating element may meander or spiral. The heating conductor has a length which is longer than the shortest distance between the electrical contacts of the heating conductor. It can also be arranged or designed in a suitable heating circuit in a hotplate more than one heating element.

In another aspect of the invention, the plate body comprises at least two plate body layers. The plate body layers are arranged one above the other in the manner of a sandwich construction. Here, the plate body layers are electrically insulated from each other by an electrical insulation. Via a contact portion, the plate body layers are electrically connected to each other, so that a heating conductor defining the current path is formed. The contact portion may be a separate contact component. Preferably, the contact portion is an integral part of the plate body layers. In the region of the contact section, the plate body layers are not electrically insulated from one another, so that the current flows from one plate body layer over the contact section into the next plate body layer.

The plate body is made of an electrically conductive material. The material has a high specific resistance as well as a high heat resistance. One aspect of the invention provides that the plate body consists of a metallic Heizleiterwerkstoff. Alternatively, the plate body may also consist of a ceramic Heizleiterwerkstoff.

An austenitic stainless steel with the material number 1.4841 (EN material short name X15CrNiSi25-21), which is standardized in the standard DIN EN 10095, is a particularly advantageous heating conductor material in the context of the invention. This steel is heat resistant and is characterized by its good strength properties even at high temperatures. The range of application is preferably between 900 ° C to 1120 ° C.

The metallic heating conductor materials also include chromium-nickel alloys (CrNi). These can be used up to 1,200 ° C. Furthermore, ferritic chromium-iron-aluminum alloys (CrFeAl) can be used for temperatures up to 1400 ° C.

The ceramic heating conductor materials include silicon carbide (SiC). This is usually used up to temperatures of 1,600 ° C. Molybdenum disilicide (MoSi2) is also available for applications up to 1,850 ° C.

In the context of the invention, furthermore, a ceramic heating conductor material in the form of silicon-infiltrated silicon carbide (SiSiC) is considered to be advantageous. This is silicon carbide with embedded in the crystal metallic silicon. This heating conductor material can be used for operating temperatures of over 1,300 ° C. Furthermore, it has a very high compressive strength of about 2000 MPa, even at high temperatures. In addition, the heating conductor material is characterized by its good corrosion resistance and wear resistance. Furthermore, the high heat capacity and the low thermal expansion are advantageous.

Particularly useful is the heating plate added in a mount. The skirt surrounds or encloses the outer side edges of the heating plate. The enclosure serves both for thermal and electrical insulation as well as for mechanical stabilization. The enclosure may for example consist of a ceramic material.

Both the side edges and the back of the heating plate are advantageously provided with a thermal insulation. In addition, the enclosure and / or a thermal insulation can also be used to compensate for tolerances in the thickness or the insertion position of a metal plate.

In an advantageous embodiment of the heating station, a load distribution plate is arranged in the lower tool and / or in the upper tool. For this purpose, the lower tool and / or the upper tool can be integrated with incorporation of the load distribution plate in the tool frame of the heating station. The load distribution plate can be fixed in particular by spring elements on a press table.

According to the invention, the heating plate is provided with electrical insulation on its heating surface contacting the metal plate. This aspect provides to avoid direct contact between the heating plate and the metal plate by interposing an electrical insulation. The electrical insulation can be realized by a coating of the heating surface of the heating plate or a separate insulating layer or plate. As a result, the electrical current flow can be maintained even during the closing time or phase and thus during the heating of a metal plate. This is more advantageous because constantly changing switching cycles of the electrical system are avoided. Advantageously, the resistance heating on a number of selectively controllable, for example, on and / or turn-off, surface heating on. This makes it possible to heat different areas of the metal plate or not to heat areas of the metal board. The surface heating elements can also be heated differently via a controllable voltage or current supply in order to enable a partially different heating of a metal plate. Optionally, individual surface heating elements or groups of surface heating elements connected together in groups can be actuated. The driving also includes an optional switching on and / or off of Heizflächenelementen. Also several different components or metal boards can be heated in the same heating station by a demand-based circuit of the surface heating. This can be done individually or in groups.

Another aspect of the invention provides that the cross section of the heat conductor varies over its length. In particular, the heating conductor varies in its width. By a corresponding cross-sectional design of the heating element also a temperature or heating control is possible. Since the resistance in the heating conductor changes in proportion to its cross section, the desired amount of heat and the temperature in the course or over the length of the heat conductor or in sections of the heating element can be adjusted via the variation of the cross section.

The hot forming line according to the invention is not only suitable for heating flat metal blanks. Also metal blanks with varying thickness or cross-sectional profile, for example, so-called tailored blanks can be brought in the heating station to forming temperature and then hot-formed and press-hardened. For this purpose, one aspect of the invention provides that a receiving space for the metal plate is provided between the lower tool and the upper tool and the receiving space has a geometry adapted to the surface contour of the metal plate.

The receiving space between the lower tool and the upper tool can also be formed by or in the plate body itself. Depending on the board thickness, different heating temperatures can be set.

Thickness tolerances of the metal plates to be heated can be compensated. A tolerance compensation can be realized for example by a resilient mounting of the heat insulation of the lower tool and / or upper tool.

Also, a resilient mounting of the plate body is conceivable. Furthermore, tolerance compensation via an elastic deformability of the heat insulation itself is possible.

An advantageous embodiment of the hot forming line according to the invention further provides that the heating station can be at least one further heating device upstream or downstream. In particular, it can be provided that an additional heating device of the heating station is connected upstream. This design of the hot forming line provides a two-stage heating of a metal plate, in which the metal plate is first preheated in a first stage to a certain temperature. Thereafter, the preheated metal plate is transferred to the heating station and there heated or heated to forming temperature.

According to a further advantageous embodiment of the hot forming line according to the invention, the heating station and the forming station is arranged within a synchronous drive unit. Between heating station and forming station suitable transfer systems are integrated. The movement of the lower tool and the upper tool of the heating station and the lower tool and the upper tool of the forming station is synchronously preferably within a common synchronous drive unit with the same clock.

As mentioned, suitable board transfer systems are provided within the synchronous drive unit between the heating station and the forming station. It is understood that transfer devices or systems are also provided for the supply of the metal plate within the hot forming line to the heating station. The same applies to the removal of the hot-formed sheet metal products from the forming station and / or an optionally downstream additional cooling station.

In general, the forming and press hardening can be carried out in one tool. Also possible is a two-stage cooling or a two-stage hardening process. For this purpose, the heated metal plate is reshaped in the forming station and already cooled in the particular actively cooled forming station. Adjusting the final temperature and / or holding the reshaped Sheet metal product can be realized in a second cooling stage. For this purpose, the forming station is followed by a separate cooling station.

The movement and the clock control can be further improved by the fact that the heating station and / or the forming station and / or the cooling station of the thermoforming line are mounted in a machine frame. In this case, a station or all stations are necessarily mounted elastically within the machine frame. The flexible storage of the stations or moving tools of the stations extends the closing time or heating time in the heating of the metal plate and / or the forming and cooling in the forming stage and / or in the cooling stage. In particular, this results in a contact time between the upper tool and the lower tool which is extended relative to the cycle time.

The hot forming line according to the invention is characterized by a rationally designed conductive heating system, which enables efficient heating of metal plates for hot forming, in particular also press hardening within the hot forming line.

A method for the production of hot-formed and in particular press-hardened sheet metal products in a hot forming line according to the invention provides that a heating plate of the heating station is at least partially heated to a plate temperature between 1050 ° C and 1350 ° C. The hot plate has an overtemperature to the target temperature to which a metal board is to be heated. In the heating station then takes place at least partial heating of the metal plate from its initial temperature to the target temperature by contact of the metal plate with the heating plate. The target temperature is preferably between 850 ° C and 970 ° C. The heating of the metal plate is performed in a time of 10 seconds or less. In particular, the heating takes place in a time between 3 and 6 seconds.

One aspect of the invention provides that the overtemperature of the hot plates is between 20% and 30% above the target temperature of the metal blanks to which the metal blanks in the heating station are to be heated.

In a procedurally advantageous embodiment, the transfer of the heated metal plate from the heating station takes place in the forming station in a time of a maximum of 3 seconds. Heat losses can be minimized due to the low transfer time.

Also, the transfer of the formed metal plate or the sheet product from the forming station in the cooling station is carried out in a time of a maximum of 3 seconds. As a result, heat losses can be avoided and also a delay of the deformed sheet metal product can be prevented or minimized.

The hot-forming line according to the invention and the method is particularly advantageous for the production of hot-formed and press-hardened sheet metal products from metal blanks. The deformed sheet metal product is at least partially cured, in particular press-hardened while it is clamped in the forming tool. Here, the sheet metal product in the forming station in a time of less than or equal to (≤) 10 seconds, in particular in a time between 3 and 6 seconds at least partially cooled to a temperature of less than or equal to (≤) 250 ° C. The forming station can be connected downstream of a cooling station. The cooling and curing can then be carried out alone in the cooling station. It is also possible to cool the hot-formed sheet metal product both in the forming station and in a downstream cooling station. In a downstream cooling station is then carried out a further cooling or holding the sheet metal product at the cooling temperature. The cooling can be done for example in a plunge pool. Alternatively, cooling may also be carried out in a press hardening tool or a contact cooling station. This is in particular made of light metal with a high thermal conductivity and has cooling channels for Duchleitung a cooling medium.

Figur 1

eine grundlegende Ausführungsform einer Heizplatte in einer Draufsicht sowie in einem Längsschnitt und in einem Querschnitt;

Figur 2

eine Heizplatte mit äußerer Einfassung in einer Draufsicht sowie in einem Längsschnitt und einem Querschnitt;

Figuren 3 bis 7

unterschiedliche Ausführungsformen von Heizstationen, jeweils mit einer Ansicht von oben auf die Heizplattenanordnung sowie einer Querschnittsansicht auf die Heizstation;

Figur 8

einen Ausschnitt aus einer erfindungsgemäßen Warmformlinie;

Figur 9

einen weiteren Ausschnitt aus einer anderen Ausführungsform einer Warmformlinie;

Figur 10

eine Heizstation, eine Umformstation und eine Kühlstation innerhalb einer Synchronantriebseinheit mit der Darstellung von drei verschiedenen Betriebspositionen;

Figur 11

eine weitere Ausführungsform einer Heizplatte in einer Draufsicht sowie in zwei Seitenansichten;

Figur 12

eine weitere Ausführungsform einer Heizplatte mit der Darstellung eines Heizleiterverlaufs;

Figuren 13 bis 16

jeweils Varianten einer Heizstation mit der Darstellung einer Heizplatte bzw. von Heizplatten in einer Draufsicht sowie in einer Seitenansicht auf die Heizstation;

Figur 17

technisch vereinfacht eine Heizplattenanordnung in einer Heizstation, wobei jeweils eine Heizplatte des Unterwerkzeugs und eine Heizplatte des Oberwerkzeugs dargestellt ist und

Figur 18

eine weitere Ausführungsform einer Heizplatte in einer schematisierten Seitenansicht.

The invention is described below with reference to exemplary embodiments. Show it:

FIG. 1

a basic embodiment of a heating plate in a plan view and in a longitudinal section and in a cross section;

FIG. 2

a heating plate with outer enclosure in a plan view and in a longitudinal section and a cross section;

FIGS. 3 to 7

different embodiments of heating stations, each with a top view of the Heizplattenanordnung and a cross-sectional view of the heating station;

FIG. 8

a section of a hot forming line according to the invention;

FIG. 9

a further section of another embodiment of a thermoforming line;

FIG. 10

a heating station, a forming station and a cooling station within a synchronous drive unit with the representation of three different operating positions;

FIG. 11

a further embodiment of a heating plate in a plan view and in two side views;

FIG. 12

a further embodiment of a heating plate showing a Heizleiterverlaufs;

FIGS. 13 to 16

each variants of a heating station with the representation of a hot plate or hot plates in a plan view and in a side view of the heating station;

FIG. 17

technically simplifies a Heizplattenanordnung in a heating station, wherein in each case a heating plate of the lower tool and a heating plate of the upper tool is shown and

FIG. 18

a further embodiment of a heating plate in a schematic side view.

A hot forming line for the production of hot-formed and press-hardened sheet metal products from metal blanks comprises a heating station 1 for heating the metal blanks and a forming station 2 for shaping the metal blanks in the heated state. The heating station is in the figures with 1 and the Forming station marked with 2. A forming station 2 is shown in the FIGS. 8 . 9 and 10 ,

The basic structure of a heating station 1 is based on the representation of FIG. 3 described. In the FIGS. 4 to 9 and 15 to 18 carry corresponding components or component components the same reference numerals.

The heating station 1 has a lower tool 3 and an upper tool 4. Between lower tool 3 and upper tool 4, a receiving space 5 is provided between which a metal plate 6 is received for heating. The lower tool 3 and the upper tool 4 can be opened and closed by drive means. Here, the lower tool 3 and the upper tool 4 are moved relative to each other or moved away from each other. When a metal plate 6 is heated, the lower tool 3 and the upper tool 4 come into direct or indirect contact with the surface of the metal plate 6.

The lower tool 3 and / or the upper tool 4 have an electrical resistance heater 7 with at least one surface heating element. The surface heating element is a heating plate 8. The heating plate 8 has a plate body 9 made of an electrically conductive material. In the plate body 9, a heating element 11 is formed by at least one slot 10 or the plate body 9 itself forms the heat conductor 11. The heat conductor 11 defines the current path between the electrical contacts 12, 13 of the heating plate 8. The positive contact 12 (positive pole) is indicated in the figures by the sign "+" and the negative contact 13 (negative pole) is indicated by the sign "-". The slot 10 extends over the entire thickness d of the plate body 9. The width of a slot 10 is sufficiently dimensioned, so that an insulation between the mutually parallel Heizleiterabschnitten is ensured and no current flashover occurs. In principle, the slot 10 can also be filled by an electrical insulator material.

As in particular in the Figures 1 and 2 and 11 and 12, the heating conductor 11 is wound several times. In the embodiment of the heating plate 8 according to the Figures 1 and 2 the heating conductor 11 runs meandering. The heating conductor 11 is In this case realized by a plurality of individual spaced apart parallel juxtaposed slots 10 in the plate body 9. The individual slots 10 are each guided alternately from opposite side edges in the plate body 9. The individual slots 10 then each end a piece in front of the opposite side edge.

The plate body 9 of the heating plate 8 may consist of a metallic Heizleiterwerkstoff, in particular a stainless austenitic heat-resistant austenitic chromium-nickel steel 1.4841. Furthermore, the plate body 9 may consist of a ceramic heating conductor material, in particular of silicon carbide (SiC) or of silicon infiltrated silicon carbide (SiSiC).

The length of the heating conductor 11 is in each case greater or longer than the shortest distance k1, k2 between the electrical contacts 12, 13 of the heating conductor 11.

In the embodiment of a heating plate 8, as in the FIGS. 11 and 12 shown, the heating element 11 runs spirally.

As in the supervision of FIG. 11a is shown, the slot 10 is spiral, whereby the spiral heating conductor 11 is formed. By a constant distance of the slot 10 of the heating element 11 has a constant width b11.

Furthermore, the FIG. 11a it can be seen that the average length LS of the heating conductor 11 is longer than the shortest distance k2 between the electrical contacts 12, 13.

The FIGS. 11b and 11c further show two side views of the plate body 9 according to the FIG. 11a ,

The FIG. 11c It can be seen that the slot 10 extends over the entire thickness d of the plate body 9.

Another variant is by the FIG. 12 shown, in which a plurality of spirally extending heating plates 8 are arranged side by side, wherein the heating conductor 11 of each heating plate 8 is formed in each case by a slot 10.

Furthermore, by the FIG. 12 shown that in each case two heating conductors 11 are supplied via an electrical contact 13 and two electrical contacts 12 with voltage or current. Furthermore, it can be seen that the length LS of each heat conductor 11 is greater or longer than the shortest distance k2 between the electrical contacts 12, 13, respectively.

The FIG. 2 shows the heating plate 8 with its side edges 14, 15 enclosing enclosure 16. The enclosure 16 is used for mechanical stabilization and / or the thermal insulation of the heating plate. 8

The in the FIG. 3 shown heating station 1 has a lower tool 3 and an upper tool 4. In the upper tool 4 a total of five heating plates 8 are arranged in the embodiment shown here. The metal plate 6 to be heated is in the FIG. 3a ) shown in dashed lines. The metal plate 6 is used to produce a hot-formed and press-hardened B-pillar for a motor vehicle.

Both in the lower tool 3 and in the upper tool 4, a thermal insulation in the form of a lower insulating plate 17 and an upper insulating plate 18 is provided.

Further, a load distribution plate 19, 20 is provided both in the lower tool 3 and in the upper tool 4. The upper insulating plate 18 forms a heat insulation for the back 21 and the side edges 14, 15 of the or the heating plates 8. As in the FIG. 3b ), the metal plate 6 to be heated for the heating process rests on the lower insulating plate 17 of the lower tool 3. The directed to the metal plate 6 heating surface 22 of the heating plates 8 is separated by an electrical insulation in the form of an insulating layer 23 of the metal plate 6. The electrical insulating layer 23 may be designed as a coating of the heating surfaces 22 of the heating plate 8. Furthermore, the electrical insulating layer 23 may be embodied as an insulating layer of an electrical insulating material.

The arrangement of the heating plates 8 is matched to the outer contour or area of a metal plate 6 to be heated. The metal plates 6 can completely be heated to a predeterminable temperature, for example, the hardening temperature of the respective metal material, in particular the Austenitisierungstemperatur Ac3. It is also possible to heat the metal plates 6 partially differently, so that the metal plate has 6 areas or sections with mutually different temperatures. For this purpose, the heating plates 8 and the Heizflächenelemente are selectively controlled, for example, on and off or different heatable.

The heating station 1, as in the FIG. 4 shown, both in the lower tool 3 and in the upper tool 4, an electrical resistance heater 7 with surface heating elements in the form of heating plates 8. In order to avoid a direct contact of the heated metal plate 6 with the heating plates 8, both the heating surface or the heating surfaces 22 of the upper heating plates 8 and the heating surfaces 22 of the lower heating plates 8 are provided with a non-puncture insulating layer 23. The lower insulating plate 17 receives the heating plates 8 and forms a thermal insulation of the back sides 21 and the side edges 14, 15 of the heating plates 8. The heating station 1 in the embodiment according to FIG. 4 is suitable due to its design with a double resistance heater 7 in particular for the heating of thicker metal blanks 6.

At the heating station 1, as in FIG. 5 shown, three metal plates 6 are arranged in the transverse direction parallel to each other. The metal plates 6 shown here are used for the production of door impact beams.

The FIGS. 6 and 7 show heating stations 1, each with eight hot plates 8 and 8 '. The arrangement and heating of the heating plates 8, 8 'is selected so that portions of the metal plates 6 are tempered differently. Thus edge-side areas and / or middle areas of the metal plates 6 can be brought to different forming temperatures. For this purpose, the heating surface elements or the heating plates 8, 8 'are controllable and controllable. Optionally, heating plates 8, 8 'can be switched on or off. Thus, for example, in the embodiment according to FIG. 6 be set over the central or central heating plates 8 ', a greater temperature than in the outer heating plates 8. As a result, the metal plate 6 is heated more in the longitudinal direction in a central portion 24 as in board edge portions 24 'and in the lower and upper wing portions 24 ".

In contrast, in the embodiment according to FIG. 7 heated two metal plates 6, which are used for the production of A-pillars. Here, edge portions 24 "less heated by the central heating plates 8 '.

At the heating station 1, as in the FIG. 13 shown, the cross section of the heating element 11 varies over its length. This is realized via the distance a1, a2, a3 between the individual slots 10 in the plate body 9. As a result of the change in the cross section of the heating element 11 this is heated to different degrees. The electrical resistance changes inversely proportional to the cross section of the heating conductor 11. Consequently, Heizleiterabschnitte with larger cross section have a lower electrical resistance than Heizleiterabschnitte with a smaller cross section. Consequently, the heating conductor 11 is less strongly heated in heating conductor sections with a larger cross-section than in heating conductor sections with a smaller cross section. Accordingly, zones or regions are formed in the heating plate 8 which are heated to different degrees. The different zones or areas are in the FIG. 13b ) with> Ac3, <Ac1 and> Ac1. In the region> Ac3, a metal plate 6 is heated to a temperature above the austenitizing temperature Ac3. For this purpose, the heating plate 8 in this zone has a higher temperature (overtemperature) compared to the target temperature of the metal plate 6. The excess temperature is preferably> 1050 ° C, but in particular not more than 1350 ° C. In the area <Ac1, a temperature below the austenitizing temperature Ac1 and in the area or zone> Ac1 a temperature above the austenitizing temperature Ac1 is achieved. The heating plate 8 has in the zone <Ac1 a temperature of for example <800 ° C, whereas in the zone> Ac1 it has a temperature of> 800 ° C, but preferably a maximum of 950 ° C.

Also, the heating station 1 as shown by FIG. 14 comprises a lower tool 3 and an upper tool 4, wherein in the upper tool 4 surface heating elements in the form of heating plates 8 are provided. In this respect, reference is made here to the previous description. The cross-sectional view of FIG. 14c ), who cut the BB through the Figure 14a ) shows that the thickness of a heating conductor 11 varies. Edge portions 32 of the heat conductor 11 are thicker than the central portion 33 of the heat conductor 11. Since the resistance of the heat conductor 11 in the middle section with a smaller cross-section is greater than in the edge portions 32 with a larger cross-section of the heating element 11 is heated in the edge portions 32 less. Accordingly, edge regions 34 of the metal plates 6 are heated less strongly by this heating conductor configuration. As a result, no complete curing occurs at the edge portions 34 of the hot-formed and press-hardened components from the metal blanks 6.

The FIG. 15a ) and b) shows the embodiment of a heating station 1 for heating metal blanks 6, which have a different cross-sectional or thickness profile. The receiving space is matched to the surface contour of the metal plate 6 and has a metal plate 6 corresponding geometry. This is realized by the shape of the arranged in the upper tool 4 heating plates 8 and the plate body 9. The varying in their geometry sections of the metal plate 6 are in the FIG. 15b ) is characterized by s1 to s5. Similarly, the geometry of the receiving space 5 and the heating plates 8 also varies in this embodiment. Due to the smaller cross section of the heating element 11 in the section s3, the heating conductor 11 in the section s3 becomes hotter, for example, in the section s3 set a temperature of> 1.000 ° C. In contrast, the cross section of the heating element 11 in section s1 or s5 is larger, with the result that lower heating temperatures are present there, for example <950 ° C.

When in the FIG. 16 The embodiment of a heating station 1 varies both the cross-sectional profile of the heating plates 8 arranged in the lower tool 3 and the cross-sectional profile of the heating platens 8 integrated in the upper tool 4. The receiving space between the lower tool 3 and the upper tool 4 is adapted to the surface contour of the metal plate 6 shown here with broad-sided thickness gradients and has a corresponding geometry. The shortest distance k3 between the electrical contacts 12, 13 of the heating element 11 extends diagonally across the heating plate 8. The heating element 11 is multiple Meandering wound and has a multiple greater length than the shortest distance k3.

The FIG. 8 shows a section of a thermoforming line. Shown is a heating station 1 and a forming station 2. The heating station 1 and the forming station 2 are arranged within a synchronous drive unit 26. The synchronous drive unit 26 is a press, in particular an eccentric press. In time with the synchronous drive unit 26, the lower tool 3 or the upper tool 4 of the heating station 1 and the forming tools of the forming station 2 are moved relative to one another.

Outside the synchronous drive unit 26, a heater 27 connected upstream of the heating station 1 is provided. Here, a homogeneous preheating of the metal plates before they are transferred to the heating station 1.

The metal plate 6 is then heated in the heating station 1 to forming temperature and then transferred by a not shown here board transfer system in the forming station 2. In the heating station 1, the metal plate 6 can be heated homogeneously, that is, in total to the same forming temperature. It is possible, as described above, also a partially different heating of a metal plate 6. In the forming station 2, the metal plate 6 is hot-formed. Already in the forming station 2, the deformed metal plate 6 can be at least partially cooled and hardened. In the synchronous drive unit 26, a further cooling station 28 downstream of the forming station 2 is integrated. The still hot sheet metal product formed in the forming station 2 from the metal plate 6 is transferred by means of a transfer system, also not shown here, into the cooling station 28 and further hardened here either by further cooling. The cooling station 28 opens and closes in time, preferably synchronously with the heating station 1 and the forming station. 2

A variant of a hot forming line, in which two heating stations 1a and 1b, a forming station 2 and a cooling station 28 are arranged within a synchronous drive unit 26, shows the illustration of FIG. 9 , In the heating station 1a, a particularly homogeneous heating of a metal plate takes place to a certain preheating temperature. The metal plate is then transferred to the heating station 1 b and partially heated there further in certain areas or partially cooled by conditioning with non-heated heating plates 8. Subsequently, the temperature-controlled, that is, set in the temperature set metal plate is transferred to the forming station 2 and formed into a sheet metal product. Already in the forming station 2 also trimming operations, such as punching operations on the sheet metal product can be made. Transfer systems then transfer the sheet product into the cooling station 28. Here, if necessary, further perforation or trimming operations are carried out and the sheet metal product is press-hardened.

The FIG. 10 shows a technical schematic representation of a heating station 1, a forming station 2 and a cooling station 28, which are arranged together in a synchronous drive unit 26. During the drive movement of the synchronous drive unit 26, the upper tools and lower tools of heating station 1, forming station 2 and cooling station 28 are moved relative to each other. The heating station 1 and the forming station 2 and the cooling station 28 are elastically mounted on spring elements 30 in a machine frame 29 of the synchronous drive unit 26 shown only schematically here. The FIG. 10a ) shows the synchronous drive unit 26 in the open position. Accordingly, the heating station 1, the forming station 2 and the cooling station 28 are opened.

One recognizes a metal plate 6 in the heating station 1. In the forming station 2, the metal plate 6 is formed into a sheet product 31. In the cooling station 28, the hot sheet product 31 is cooled from a temperature above an austenitizing temperature and press cured. The FIG. 10b shows an operating situation in which the synchronous drive unit 26 is closed and the respective lower tools and upper tools with the metal plate 6 and the sheet product 31 come to rest. During the further closing movement, the machine frame 29 of the synchronous drive unit 26 with the heating station 1, the forming station 2 and the cooling station 28 is moved downward against the force of the spring elements 30. This is in the FIG. 10c ). The movement during closing and opening of heating station 1, forming station 2 and cooling station 28 is elastically supported by the spring elements 30.

In the FIG. 17 schematically an electrical resistance heating of a heating station is shown. The resistance heating has a surface heating element in the form of a heating plate 35 both in the lower tool (not shown here) and in the upper tool. A heating plate 35 has a plate body 36 made of an electrically conductive material. The plate body 36 is separated by a horizontal slot 37 over most of its length. Through the horizontal slot 37, the plate body 36 is formed as a heating conductor 38, which defines a current path. The current path is indicated by the arrows P. It can be seen that the slot 37 does not completely separate the plate body 36, so that at the end 39 of the plate body 36 it is not interrupted. The slot 37 may be filled with an electrical insulating material.

For heating a metal plate, it is received in the heating station 1 between the heating plates. In this case, the board comes in direct contact with the heating plates 35. The heating plates 35 are connected in parallel with each other and have the same resistance. During contact further current flow is possible for heating the heating plates 35 and thus the metal plate. Since the opposing areas of the heating plate 35, which are interconnected by the metal plate in the closed state, at each point have the same electrical potential (voltage level), there is no short circuit.

An alternative embodiment of a heating plate 40 is shown in FIG FIG. 18 shown. The plate body 41 of the heating plate 40 has two superimposed plate body layers 42, 43. Between the plate body layers 42, 43 an electrical insulation 44 is provided. The electrical insulation 44 extends over the substantial part of the length L of the plate body 41, so that they are partially isolated from each other electrically. At the end 45 of the plate body 41, a contact portion 46 is formed. In the contact section 46, the plate body layers 42, 43 contact each other and are electrically conductively connected to each other. In this way, a U-shaped heating conductor 47 is formed in the plate body 41. Again, the current path is indicated by the arrows P. Both in the FIG. 17 as well as in the FIG. 18 the shortest distance between the electrical contacts is marked k4. The Heating conductor 38 as well as the heating conductor 47 have a length which is longer than the shortest distance k4 between the electrical contacts "+" and "-".

In a method for producing hot-worked and press-hardened sheet metal products from metal blanks in a hot forming line according to the invention, the metal blanks are heated in a heating station 1 to forming temperature, then removed from the heating station 1 and transferred to the forming station 2 within a time T1 of less than 3 seconds. In the forming tool 2 then the transformation takes place to the sheet metal product. In the forming station 2 itself or a downstream cooling station 28, the hot sheet product is cooled at a cooling rate which is above the critical cooling rate of the metal material and cured in this way. The cooling takes place in a time T _K of less than or equal to (≤) 10 seconds, in particular in a time between 3 and 6 seconds. Here, the sheet product is cooled to a temperature T _E of less than or equal to (≤) 250 ° C.

The transfer of the erwämten metal plate from the heating station 1 in a downstream cooling station 28 takes place in a time t _T2 of a maximum of 3 seconds.

An advantageous aspect of the inventive method provides that a heating plate 8 of the heating station 1 is at least partially heated to a plate temperature T _P between 1050 ° C and 1350 ° C. A metal plate is then at least partially heated in the heating station 1, specifically from an initial temperature T1 to a target temperature T2, in that the metal plate comes into contact with the heating plate 8 of the upper and / or lower tool. The target temperature T2 is between 850 ° C and 900 ° C. The heating of the metal plate to the target temperature T2 takes place in a time t _E of less than or equal to (≤) 10 seconds, in particular in a time between 4 and 6 seconds.

Reference numerals:

1 -

heating station

1a -

heating station

1b -

heating station

2 -

forming station

3 -

lower tool

4 -

upper tool

5 -

accommodation space

6 -

metal board

7 -

resistance heating

8th -

heating plate

8th' -

heating plate

9 -

plate body

10 -

slot

11 -

heating conductor

12 -

Contact

13 -

Contact

14 -

Margin of 8

15 -

Margin of 8

16 -

mount

17 -

lower insulating plate

18 -

upper insulating plate

19 -

Load distribution plate

20 -

Load distribution plate

21 -

back

22 -

Heating surface of 8

23 -

insulating

24 -

midsection

24 '-

platinum section

24 "-

wing section

25 -

tempering

26 -

Synchronous drive unit

27 -

heater

28 -

cooling station

29 -

machine frame

30 -

spring element

31 -

sheet product

32 -

edge section

33 -

midsection

34 -

border area

35 -

heating plate

36 -

plate body

37 -

slot

38 -

heating conductor

39 -

End to 36

40 -

heating plate

41 -

plate body

42 -

Plate body layers

43 -

Plate body layers

44 -

insulation

45 -

End to 41

46 -

Contact section

47 -

heating conductor

d -

Thickness of 9

a1 -

distance

a2 -

distance

a3 -

distance

k1 -

distance

k2 -

distance

k3 -

distance

k4 -

distance

s1 -

section

s2 -

section

s3 -

section

s4 -

section

s5 -

section

B -

width

P -

arrow

L -

length

LS -

length

Claims (21)

1. Hot forming line having a heating station (1) and a forming station (2) for producing hot formed and in particular press-hardened sheet metal products (31) made of metal blanks (6), wherein the heating station (1) has a bottom tool (3) and a top tool (4) between which a metal blank (6) can be received for heating and the bottom tool (3) and/or the top tool (4) has an electric resistance heater (7) having at least one surface-heating element and the surface-heating element is a heating plate (8, 8', 35, 40) and the heating plate (8, 8', 35, 40) is in the form of a plate body (9, 36, 41) made of an electrically conductive material and the plate body (9, 36, 41) is formed as a thermal conductor (11, 38, 47) characterised in that the heating plate (8) is furnished with an electrical insulating layer (23) on its heating surface (22) contacting the metal blank (6).
2. Hot forming line according to claim 1, characterised in that the thermal conductor (11) has a length which is longer than the shortest distance (k1, k2, k3, k4) between the electrical contacts (12, 13) of the thermal conductor (11).
3. Hot forming line according to claim 1 or 2, characterised in that the thermal conductor (11, 38, 47) extends with multiple windings, in particular meander-shaped or spiral shaped.
4. Hot forming line according to any of claims 1 to 3, characterised in that the thermal conductor (11) in the plate body (9) is formed by at least one slit (10) which extends throughout the thickness (d) of the plate body (9).
5. Hot forming line according to any of claims 1 to 3, characterised in that the thermal conductor (38) in the plate body (36) is formed by a horizonal slit (37).
6. Hot forming line according to any of claims 1 to 3, characterised in that the plate body (41) comprises at least two plate body layers (42, 43) arranged on one another, wherein the plate body layers (42, 43) are at least in some areas electrically insulated from one another and are connected via a contact section in an electrically conductive manner with one another.
7. Hot forming line according to any of claims 1 to 6, characterised in that the plate body (9, 36, 41) is made of a metallic thermally conductive material.
8. Hot forming line according to any of claims 1 to 6, characterised in that the plate body (9, 36, 41) is made of a ceramic thermally conductive material.
9. Hot forming line according to any of claims 1 to 8, characterised in that the heating plate (8) is accommodated in a frame (16) surrounding its lateral edges (14, 15).
10. Hot forming line according to any of claims 1 to 9, characterised in that the resistance heater (7) has a number of selectively controllable surface-heating elements.
11. Hot forming line according to any of claims 1 to 10, characterised in that the cross-section of the thermal conductor (11) varies over its length.
12. Hot forming line according to any of claims 1 to 11, characterised in that between the bottom tool (3) and the top tool (4) is provided a receiving space (5) for the metal blank (6) and the receiving space (5) has a geometry which is adapted to the surface contour of the metal blank (6).
13. Hot forming line according to any of claims 1 to 12, characterised in that at least one further heating device (27) is connected upstream or downstream of the heating station (1).
14. Hot forming line according to any of claims 1 to 13, characterised in that the heating station (1) and the forming station (2) are disposed within a synchronous drive unit (26).
15. Hot forming line according to claim 14, characterised in that within the synchronous drive unit (26) between heating station (1) and forming station (2) is provided a blank transfer system.
16. Hot forming line according to any of claims 1 to 15, characterised in that a separate cooling station (28) is connected downstream of the forming station (2).
17. Hot forming line according to any of claims 1 to 16, characterised in that the heating station (1) and/or the forming station (2) and/or the cooling station (28) are resiliently supported in a machine mounting (29).
18. Method for the preparation of hot formed and in particular press-hardened sheet metal products in a hot forming line according to any of claims 1 to 17, characterised in that a heating plate of the heating station (1) is heated at least partially to a plate temperature T_P between 1,050 °C and 1,350 °C and in the heating station (1) the at least partial heating of a metal blank (6) from a starting temperature T1 to a target temperature T2 is carried out by contact of the metal blank (6) with the heating plate, wherein the target temperature T2 is between 850 °C and 970 °C and the heating takes place during a time t of less than or equal to (≤) 10 seconds, in particular in a time of between 3 and 6 seconds.
19. Method according to claim 18, characterised in that the transfer of the heated metal blank out of the heating station (1) into the forming station (2) is carried out in a time t_T1 of maximum 3 seconds.
20. Method according to claim 18 or 19, wherein a cooling station is connected downstream of the forming station, characterised in that the transfer of the formed metal blank out of the forming station (2) into a cooling station (28) is carried out in a time t_T2 of maximum 3 seconds.
21. Method according to at least one of claims 18 to 20, wherein the formed metal sheet product is at least partially hardened, in particular press-hardened, characterised in that the sheet metal product is cooled in the forming station (2) and/or a cooling station (28) connected downstream therefrom in a time t_K of less than or equal to (≤) 10 seconds, in particular in a time of between 3 and 6 seconds, at least partially to a temperature T_E of less than or equal to (≤) 250 °C.

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