EP3411163B1 - Device for producing hardened steel components and hardening method - Google Patents

Description

The invention relates to a method and an apparatus for producing hardened sheet steel blanks and sheet steel components thereof.

It has long been known, even in the automotive industry for body parts made of sheet steel to use hardened components. The advantage of hardened sheet steel components is that they result in a weight saving in body construction due to their considerably higher hardness or tensile strength (R _m ), since it is not necessary to use less solid and therefore solid components that would be significantly heavier.

In recent years, two processes have become established on the market for producing hardened sheet metal components.

The first method is the so-called direct method or press hardening. In this method, a board is punched from a sheet steel strip, which may also be provided with a corrosion protection coating made of metal, then heated this board and formed the heated board in a forming tool with a single stroke and cured at the same time. Here, the curing takes place in that the hardenable steel material gives off its heat to the forming tool. It is important that the heat is released at a speed above the critical hardening temperature. This quench hardening results in the heated board, which has an austenitic structure, subsequently having a substantially martensitic structure and thus the high tensile strength.

Normally, boron-manganese steels are used in this process, ie boron-alloyed manganese carbon steels, such as the most commonly used 22MnB5 for this purpose, although there are also a number of other suitable steels from the basically same alloy concept.

In the second method, the so-called form hardening, which was developed by the applicant, a sheet steel plate is cut out of a sheet steel strip optionally provided with a corrosion protection coating and then the sheet steel blank formed in a conventional multi-stage forming process to form a component. This component preferably has a final contour, which is about 2% smaller in all spatial directions than the finished contour of the component. Subsequently, this component is heated to the austenitizing temperature, so that the steel sheet structure becomes austenitic. The thermal expansion in this case means that this heated sheet metal component compensates for the 2% smaller production.

Subsequently, this austenitized sheet metal component is placed in a mold hardening tool, in which it is pressed and at the same time cooled, but practically no longer or only to a very small extent is formed. Again, the aforementioned steels are used and also here the critical hardness speed must be exceeded. The structure also results in the same way.

The advantage of the indirect method or form hardening is that geometries can also be made more complex.

The advantage of the so-called direct method or press hardening is that simple components can be produced faster.

One challenge in implementing the direct press hardening process is to heat the board.

Typically, the heating of the planar board in a conventional oven with a length of about 40 m, in particular 1.5 mm thick boards, for example, run through this oven for three minutes.

In addition, some attempts have been made to heat such boards by the application of hot metal body.

However, this results in a variety of problems.

In the case of classic radiant ovens, it is disadvantageous that they require a large amount of space, since the ovens are relatively large in size. In addition, it is disadvantageous that in case of failure a high rejects accumulates because all located in the oven boards, since they are left longer than planned in the oven, are no longer usable. Even in normal operation there is a strong oxidation of the surface, which is undesirable.

From the WO2013 / 000001 A1 a system for heating a component is known, which comprises a continuous furnace and a conveyor. The continuous furnace has heating elements which are arranged above and below the conveyor. The heating takes place by electrical resistance heating, wherein the heating elements can be controlled independently of each other with different heating power at least in groups. In this case, it is provided that the conveying device comprises a heating zone for heating the component, a heating zone for zone-wise heating of the component and a holding zone for a subsequent press hardening.

From the DE 10 2014 101 539 A1 For example, a hot-formed article is known for the production of hot-formed and press-hardened sheet metal products from metal blanks, which 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 is done by indirect resistance heating. The heat is generated outside the metal plate and passes through heat conduction into the metal plate itself. For this purpose, the lower tool and / or the upper tool on an electrical resistance heater with at least one surface heating element. 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. For this purpose, the plate body is slotted and provided for example with a slot which extends over the thickness of the plate body.

From the DE 10 2009 007 826 A1 For example, a heating apparatus for heating a metal circuit board having a lower heating unit and an upper heating unit is known. These heating units are adjustable between a closed, the board between them receiving heating position and a spaced-apart release position. Each heating unit has a heatable plate coming into contact with the board. It is provided that the heating plate of the bottom and / or the upper heating unit a plurality of Heater segments comprises, 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.

From the DE 10 2014 101 891 A1 a system for warming up workpieces, in particular for a thermoforming station is known, which has a warm-up device and at least one to be transported by the warm-up device goods carrier. The product carrier can be equipped with a workpiece and a tempering component for conductive heating of the workpiece is present, wherein the heating device has a movable electrode for electrically contacting the temperature control component.

In the known plate systems is disadvantageous that inductively heated plates have a low efficiency and the power distribution can be very poorly regulated. Even the already proposed Keramikheizelemente suffer from the fact that they have a low life, the power distribution is also poorly regulated and the driving effort is quite high for many small elements.

Known meandering solutions also have the disadvantage that the power distribution is unfavorable.

The object of the invention is to provide a device for heating sheet steel parts, with a rapid and homogeneous heating possible as the planar boards is ensured, which has a minimum space requirements, produced in case of disturbances low rejection and also ensures improved corrosion protection.

The object is achieved with a device having the features of claim 1. Advantageous developments are characterized in the dependent claims.

It is a further object of the invention to provide a method of heating sheet steel components using the apparatus.

The object is achieved by a method having the features of claim 12.

Advantageous developments are characterized in the dependent claims.

According to the invention, the boards are heated with heating modules designed according to the invention. In this case, a heating of the planar boards takes place under hot plates, wherein the high required power density and especially the uniform temperature distribution by a good heat conductive material, preferably copper and an electric heating can be realized. In this case, according to the invention mineral-insulated heating conductors are cast in copper, so that highest power densities can be achieved. Alternatively, other electrical heating elements, such as Hochtemperaturheizpatronen conceivable.

In accordance with the invention, optimum temperature homogeneity and the possibility of parts with different properties are achieved by modular design and modular control. In particular, when multiple, separately controlled heating modules are used for a board surface, in this case the mechanical properties can be adjusted very precisely by different degrees of hardness.

According to the invention, the copper is advantageously protected from oxidation by the fact that the copper and thus also the heat conductors cast in the copper are hermetically sealed in a heat-resistant stainless steel housing.

In addition, the plates may advantageously be provided with very wear-resistant and smooth coatings for longer service life and the lowest possible adhesion of corrosion layers, and in particular zinc, which may consist, for example, of chromium carbide or aluminum oxide and other known coatings.

Figur 1

stark schematisiert ein erfindungsgemäßes Heizmodul;

Figur 2

eine Anordnung mehrerer Heizmodule mit einer darunter angeordneten Platine in einer stark schematisierten Ansicht;

Figur 3

eine Aufheizpresse für Platinen mit einer Mehrzahl von Heizmodulen in einer seitlichen geschnittenen, stark schematisierten Ansicht;

Figur 4

die Vorrichtung nach Figur 3 in einem Horizontalschnitt durch die Heizmodule;

Figur 5

eine Heizmodulanordnung mit oberen und unteren Heizmodulen, wobei mittlere Heizmodule zudem über eine aktive Kühlung verfügen zur Erzeugung von Bauteilen mit unterschiedlichen mechanischen Eigenschaften;

Figur 6

eine Modulanordnung mit eingebauten funktionsfreien Modulen, um bestimmte Bauteilbereiche nicht aufzuheizen;

Figur 7

eine Anordnung von Heizmodulen mit Führungsbolzen und Federn zur Erzeugung einer gleichmäßigen Flächenpressung und zur Vermeidung von Verkippungen;

Figur 8

eine teilgeschnittene perspektivische Ansicht eines erfindungsgemäßen Heizmoduls mit Heizpatronen und Kupferkern;

Figur 9

das Heizmodul nach Figur 8 in einem Vertikalschnitt;

Figur 10

das Heizmodul nach Figur 8 in einem Horizontalschnitt;

Figur 11

das Heizmodul mit mineralisoliertem Heizkabel und Kupferkern in einer geschnittenen perspektivischen Ansicht;

Figur 12

das Heizmodul nach Figur 12 in einer Draufsicht;

Figur 13

das Heizmodul nach Figur 13 in einer Schnittansicht entsprechend der Schnittlinie A-A;

Figur 14

das Heizmodul nach Figur 12 in einer Schnittansicht entsprechend der Schnittlinie B-B;

Figur 15

einen Horizontalschnitt des Heizmoduls nach Figur 12 entsprechend der Linie C-C nach Figur 15;

Figur 16

das Heizmodul in einer Seitenansicht;

Figur 17

eine weitere Ausführungsform des erfindungsgemäßen Heizmoduls mit einer Kühlung;

Figur 18

das Heizmodul nach Figur 17 in einem Schnitt entlang der Linie A-A;

Figur 19

das Heizmodul nach Figur 17 in einer Darstellung, geschnitten entlang der Linie B-B;

Figur 20

das Heizmodul nach Figur 19 in einer Schnittansicht entlang der Linie C-C; [AP1]

Figur 23

eine teilgeschnittene perspektivische Ansicht entlang der Linie A-A gemäß Figur 17;

Figur 24

den Erwärmungsverlauf eines 1,5 mm dicken Stahlblechs zwischen 870°C heißen Platten.

The invention will be explained by way of example with reference to a drawing. It show here:

FIG. 1

highly schematic of a heating module according to the invention;

FIG. 2

an arrangement of several heating modules with an underlying board in a highly schematic view;

FIG. 3

a heating press for boards with a plurality of heating modules in a side cut, highly schematic view;

FIG. 4

the device after FIG. 3 in a horizontal section through the heating modules;

FIG. 5

a Heizmodulanordnung with upper and lower heating modules, wherein mean heating modules also have an active cooling to produce components with different mechanical properties;

FIG. 6

a module assembly with built-in function-free modules so as not to heat certain component areas;

FIG. 7

an arrangement of heating modules with guide pins and springs to produce a uniform surface pressure and to avoid tilting;

FIG. 8

a partially cutaway perspective view of a heating module according to the invention with heating cartridges and copper core;

FIG. 9

the heating module after FIG. 8 in a vertical section;

FIG. 10

the heating module after FIG. 8 in a horizontal section;

FIG. 11

the heating module with mineral insulated heating cable and copper core in a sectional perspective view;

FIG. 12

the heating module after FIG. 12 in a plan view;

FIG. 13

the heating module after FIG. 13 in a sectional view corresponding to the section line AA;

FIG. 14

the heating module after FIG. 12 in a sectional view corresponding to the section line BB;

FIG. 15

a horizontal section of the heating module after FIG. 12 according to the line CC after FIG. 15 ;

FIG. 16

the heating module in a side view;

FIG. 17

a further embodiment of the heating module according to the invention with a cooling;

FIG. 18

the heating module after FIG. 17 in a section along the line AA;

FIG. 19

the heating module after FIG. 17 in a representation, cut along the line BB;

FIG. 20

the heating module after FIG. 19 in a sectional view taken along the line CC; [AP1]

FIG. 23

a partially cutaway perspective view along the line AA of Figure 17;

FIG. 24

the heating course of a 1.5 mm thick steel sheet between 870 ° C hot plates.

A heating module 1 according to the invention is a cassette-like box-shaped element which has a plate-shaped or rectangular cavity 2 which has a flat plate 4 on a lower side 3 and side walls 5 which are perpendicular to the plate depart and a cover plate 6, which limit the box-like element 2 on all sides. At the top, an insulation 7 is arranged on the plate 6.

In the cavity 2 heating coils or heating elements 8 are arranged, which can be acted upon via an inlet and a discharge 9, 10 with power. In addition, advantageously, a temperature sensor 11 may be present, which is connected to a temperature controller 12, which regulates the flow of current.

In particular, in the case of a rectangular heating module 1, a plurality of mineral-insulated heating coils 8 are connected in series and arranged side by side, so that the heating module can be heated over the entire surface.

In addition to the heating elements 8, cooling coils or lines 9 (FIG. FIG. 5 ), so that the heating modules not only heated, but also can be cooled in particular with respect to adjacent heating modules.

A plurality of heating modules 1 can be combined to form a heating device 14 which, for example, comprises modules 1 arranged in such a way that they cover a board 15 to be heated accordingly.

Preferably, the heating modules 1 are arranged within a respective heating device 14, wherein the heating device 14 may be arranged once on a Aufheizpressenoberteil 16 and a Aufheizpressenunterteil 17 which are movable toward and away from each other, so that between the heating modules 1 of the respective heaters 14 a board 15 can be clamped and heated.

A corresponding heating device 14 may, for example, comprise six modules 1 ( FIG. 4 ), wherein the modules are included on the edge side of the heater 14 with an insulation 18. The number of modules is however arbitrary.

The heating devices 14 may also have at preferred locations cooled heating modules with cooling lines 9 or empty modules 20 or insulating blocks of insulating material, in whose areas no heating takes place ( FIG. 6 ).

The cavity 2 is inventively filled with copper, so that the heating element 8 are insulated by a non-electrically conductive mineral insulation against the copper and completely surrounded by copper and embedded to ensure a particularly good heat transfer. The plate 4, the side walls 5 and the top wall 6 are preferably made of heat-resistant or high heat-resistant stainless steel and include the good thermal conductivity core, in particular copper core ideally hermetically to prevent oxidation of the core.

In a further advantageous embodiment, the heating module 1 also has a copper core, but here heating cartridges are arranged. Here, the heating modules 1 are also formed on the region of the outer walls 5 with a complete insulation ( FIGS. 8 . 9, 10 ).

In a further advantageous embodiment ( FIGS. 11 to 15 ), the heating modules are also formed with mineral-insulated heating conductor and the copper core, wherein the heating modules have a uniform, in cross-section C-shaped insulation 20 in the formation as a single module in the side walls and the ceiling wall, the insulation 20 the actual heating area, consisting of the copper-filled stainless steel box with the mineral-insulated heating conductor, absorbs.

In order to keep the box on the insulation 20, in the box fasteners 21 are present, which are designed in particular as threaded columns which pass through the insulation 20 upwards and on the upper side 22 of the insulation by a counter-bearing plate 23 and are screwed against it. In addition, 23 contact poles 24 are arranged on the counter-bearing plate, which pass through the counter-bearing plate 23 and the insulation 22 and the heating elements 8 are formed contacting.

In a further advantageous embodiment ( FIGS. 17 to 23 ), the heating module is also formed so that the box 2 made of stainless steel, filled with copper and comprising arranged as Heizspiralen heating element 8, additionally comprises a cooling device in the form of a cooling coil 25 or cooling lines 25, wherein the cooling coil 25 from the outside with an inlet 26th and a drain 27 is provided.

The inlet 26 and the outlet 27 pass through both the insulation 20 and the plate 6 and extend into the copper core.

In the combination of heating modules 1, the insulation 20 can be removed to the ceiling insulation between the plate 6 and the counter-bearing plate 23 so that the heating modules are arranged adjacent to each other and allow uniform heating or cooling without temperature bridges.

In the invention, it is advantageous that a particularly good and highly effective heat transfer is realized by the coupling of mineral-insulated heating cables on the one hand and a copper core on the other hand, connected to a heat-resistant platinum-side stainless steel plate.

It can be seen from the heating course (FIG. 24) that within a few seconds a corresponding steel plate, which is 1.5 mm thick, heated under hot plates (preferably heated above 870 ° C.) to above the Ac 3 of the material, for example 850 ° C. in particular, the temperature range up to 700 ° C is crossed very quickly. Very fast means that this will take about 10 seconds.

In the invention, it is advantageous that, by using non-heatable or water-cooled modules in a heating device, certain areas which are not to be hardened can be left out. As a result, boards with different structures can be formed so that components with different mechanical properties (Taylored Property Parts = TPP) are achieved after press hardening.

Claims (13)

1. A device for heating sheet metal blanks, a heating device (14) being provided and the heating device (14) comprising at least one heating module (1), wherein the at least one heating module (1) is a box-like element which has a cassette-like design and comprises a plate-shaped or rectangular cavity (2) which has an underside (3) provided with a flat plate (4), at least one heating element (8) being arranged in the cavity (2) and formed as an electric resistance heating element, wherein the cavity (2), embedding the at least one heating element (8) and surrounding it, is completely filled with a material of good thermal conductivity, preferably copper, wherein the plates (4), the side walls (5) and the ceiling wall (6) surrounding the cavity (2) or the cavity (2) filled with copper are formed from a heat-resistant or high-temperature resistant stainless steel and connected to one another such that the core made of a material having good thermal conductivity, in particular a copper core, is hermetically sealed.
2. The device according to claim 1, characterized in that the heating module (1) additionally comprises cooling lines (9) for cooling the module (1).
3. The device according to any of the preceding claims, characterized in that the heating device (14) comprises heating modules (1) with heating elements (8) and/or heating modules (1) with heating elements (8) and cooling lines (9), and/or modules that are neither heated nor cooled.
4. The device according to any of the preceding claims, characterized in that a heating device (14) with at least one heating module (1) on a heating press upper part (16) and/or a heating press lower part (17) is disposed, which can be moved toward and away from each other, so that a blank (15) can be held in clamping fashion and heated between the heating modules (1) of the respective heating device (14).
5. The device according to any of the preceding claims, characterized in that the heating device (14) comprises unheated or cooled heating modules (1) at those places where a blank is not intended to be hardened.
6. The device according to any of the preceding claims, characterized in that the heating module (1), in the event of a singular arrangement in a heating device (14), is formed with an insulation (20) in the area of the outer walls (5) and in the area of the ceiling wall (6).
7. The device according to any of the preceding claims, characterized in that the insulation (20) has a C-shaped design in cross-section, wherein, in order to hold the box (2) on the insulation (20), connecting elements (21) are provided in the box which penetrate the insulation (20) starting from the plate (4), and a counter bearing plate (23) is provided on the upper side (22) of the insulation, which is penetrated by them and to which the connecting elements (1) are bound.
8. The device according to any of the preceding claims, characterized in that contact poles (24) are arranged on a side of the heating module (1) opposite the plate (4), which are formed so as to contact the heating elements (8).
9. The device according to any of the preceding claims, characterized in that in the event of a heating module (1) with one cooling line (9), the cooling line is formed outside with an inlet (26) and an outlet (27), wherein the inlet (26) and the outlet (27) penetrate the insulation (20) and the plate (6) and project into the copper core, so that they can supply the cooling line (9), (25) with a cooling agent.
10. The device according to any of the preceding claims, characterized in that in the event of a heating device (14) with a plurality of heating modules (1), the insulations (20) are formed such that they are arranged between uninsulated side walls (5) of the heating modules (1) so as to directly adjoin one another.
11. The device according to claim 1, characterized in that the heating element is designed as a heating cartridge or as a mineral-isolated heat conductor.
12. A method of operating a device according to claim 1, wherein the sheet metal blank is acted upon with heat at least on one side, wherein the sheet metal blank is brought into contact with a plate (4) of a heating module (1) of a heating device (14), wherein the heating module (1) electrically heated and the heat energy in the heating module is transferred from an electric resistance heating element (8) to a core having good thermal conductivity, preferably a copper core, and from said core, preferably a copper core, to the plates (6) and from the plate (6) to the blank.
13. The method according to claim 12, characterized in that a heating device (14) is formed with a plurality of heating elements (8) and the blank is selectively heated, not heated or cooled by the plurality of heating devices (8).

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