DE202008016877U1 - Apparatus for producing partially hardened sheet steel components - Google Patents

Abstract

contraption for hardening steel components, wherein at least two mold halves (6, 7) are present, which at least partially cools down a heated steel component or a heated board at least one cooling shell (1) per mold half (6, 7), in particular device for performing the method according to any one of the preceding claims, in the cooling shells (1) workpiece side in the areas where a reduced or no hardness of the component is desired, recesses (4) in the surface (8) are present, wherein the recesses (4) for generating a Gas cushion during the pressing of the board or the component over Gas supply and gas discharge bores and in addition there is a device with the gas through the Feed holes can be introduced into the recesses.

Description

The The invention relates to a device for producing partially cured Sheet steel components with adjusted ductilities.

Around the increasing requirements in the vehicle construction regarding the Protection of passenger compartments in the event of a crash as well as weight savings to meet, are becoming increasingly important in motor vehicles solid steels used, which at lower weight a higher hardness than conventional motor vehicle steels have.

to Production of such components, it is known to heat boards and in a corresponding tool to reshape and cool rapidly to thereby achieve a press hardening. In addition are Various methods known in which the board partially or completely preformed to final geometry, then heated and either finished in an appropriate tool or only hardened by rapid cooling becomes.

The Press hardening of the components makes it possible, after the Heating and subsequent rapid cooling High-strength components with very tight cutting and shape tolerances manufacture.

From the PCT / EP 2005/008641 a method is known in which a virtually finished on final geometry component is placed in a tool, said component is clamped firmly in the region of the edges and is preferably supported only in the region of the positive radii. This component is placed in the heated state and is rapidly cooled in the mold to harden it. During this cooling, the component forms in the area of the positive radii to the mold, whereby it is dimensionally stable cooled. In other areas, the air-gap shapes may be located away from the component so as not to hinder the shrinkage of the component.

From the WO 2006/038868 A1 For example, there is known a method of hot working and tempering a metal sheet in which cutouts are provided in the mold halves so that retaining webs that hold the sheet metal part during cooling remain. In the areas where the mold halves are not adjacent to the sheet, softer zones of the final product should arise.

by virtue of the high brittleness and the low elongation values of Press-hardened components is in the crash load case the Danger that the components by the occurring high voltages tear or break. It is therefore necessary, targeted Areas leading to a component failure in a vehicle crash could, through areas of different mechanical Relieve material characteristics in a targeted manner. Here it is not sufficient only specifically to create areas of weakness, because of such Components are made high demands, making it mandatory necessary in all areas of the component, the mechanical Set parameters specifically and predict them safely.

task The invention is a device for producing partially hardened sheet steel components to create, with it succeeds, hardened sheet steel components with zones of different predictable to produce mechanical properties.

The The object is achieved with a device having the features of the claim 1 solved.

advantageous Further developments are in the dependent claims characterized.

According to the invention for a component made of sheet steel, a sub-range of the yield strength, tensile strength, elongation and ductility at faster Deformation in the event of a crash changed during manufacture. Hereby, the stresses occurring during the crash can be targeted be distributed to the component.

in this connection can according to the invention the mechanical Characteristics and the ductility of press-hardened or hot-formed components in precisely defined and exactly limited Partial areas are affected and without the entire part cross-section to weaken and also with a defined change also certain desired values.

According to the invention the press hardening tool used in the Areas for which greater ductility is required, provided with milled air cushions. The air cushions are chosen in their geometry so that there is a partial installation of the components in the active radii, so that deformation of the components during cooling is prevented, However, these areas in the ductility influenced specifically can be.

Around the cooling of the components also in the area of the air cushion with the respectively required for the ductility to achieve the best possible cooling time the air cushion with compressed air, which in temperature depending on the application cooled or heated or purged other gases.

Herewith a cooling rate is achieved, which is usually less than the cooling rate of the particular water-cooled mold halves.

The Air cushions are generally realized by the fact that in a mold half or mold surface shell Grooves and in particular shallow grooves circular disc-shaped Recesses or square flat recesses milled be, with these recesses with supply air and exhaust air ducts are equipped, preferably at a number of grooves an edge-side groove is formed with a Zuluftbohrung and then the grooves with each other with connecting holes are provided, through which the gas, for example, compressed air from a Groove passes to the other, while the opposite edge-side groove via a corresponding outlet opening features.

at The invention is advantageous in that a dimensional distortion the components is prevented because the geometry of the air cushion so it is chosen that the components on cooling abut the Anlageradien areas and thus the incipient on cooling Shrinking process and resulting part distortion positive being affected. In particular, the geometry of the Luftpolsternuten so chosen that the component in the form of a kind of lattice structure is held, consisting of the lying between the grooves and gives these limiting ridges.

The Invention will be explained by way of example with reference to a drawing, it shows:

1 strongly schematized and in an oblique top view a partially cut mold shell with milled air-cushion grooves and a component lying thereon;

2 a section through a closed mold according to the invention;

3 : a detail section according to 2 ;

4 an arrangement and geometry of possible air-cushion grooves on a sample mold half,

5 : a rear view of the mold half behind 4 ;

6 : a cut of the mold half behind 4 ;

7 : Cooling curve in the area of an air cushion groove;

8th : another cooling curve;

9 another cooling-cooling curve;

10 : Hardness results on the sample board at 1.5 mm sheet thickness;

11 : Hardness results on the sample board at 2 mm sheet thickness;

12 : the cooling curve without air cushion;

13 : the cooling curve at 3 mm air cushion thickness;

14 : an overview of cooling curves at different air cushion depths;

15 a tool according to the invention in cross-section;

16 a further embodiment of the tool according to the invention;

17 a renewed embodiment of the tool according to the invention;

18 a further cross section through a tool according to the invention with integrated ceramic pins;

19 : an enlarged detail of a tool according to the invention;

20 a further embodiment of the tool according to the invention with visible connection holes;

21 a cross section through an inventive tool with integrated in the air cushion induction coils;

22 : a cooling curve with a tool with a non-heated ceramic insert;

23 : a cooling curve of a tool with heated ceramic insert;

24 : the temperature profile in a two-part press hardening process;

25 : a comparison curve of the cooling of a sheet of 500 ° C at 30 ° C ambient temperature.

In 1 is the cooling shell according to the invention 1 shown in a partially sectioned view, in which they of a part of a component to be formed 2 is covered. One recognizes the supply air lines 3 , the interconnected Luftpolsternuten 4 and the exhaust pipes 5 , In this case, the Luftpolsternuten are circular disc-shaped recesses.

Seen on average one recognizes a tool shell 6 and a tool base 7 , wherein on the upper tool 6 and on the lower tool part 7 one cooling bowl each 1 is arranged. The cooling shells 1 essentially have a contour that the finished component 2 equivalent. In the cooling cups 1 can be recognized by the component 2 facing surfaces 8th the introduced Luftpolsternuten 4 , which have an air supply line 3 can be acted upon with a corresponding gas flow and the exhaust air lines 5 equipped with which the gas stream is derived.

In 3 , which represents a corresponding enlargement of the section, you can see that between the cooling shells 1 clamped workpiece, being in the cooling shells 1 the supply air lines 3 to the nearest diametrically opposed Luftpolsternuten 4 reach. It also recognizes the connection holes V of Luftpolsternuten 4 to allow a continuous gas flow.

The number of feed holes or lines 3 and drainage holes or pipes 5 is chosen so that an optimal gas flow is achieved, wherein it is important that when closing the tool in all Luftpolsternuten 4 a sufficient gas pressure to build the corresponding air cushion is present. In this respect, the gas flow must be adjusted so that a repeatable and process-safe delayed cooling during press hardening is possible.

In the first cooling phase (from the component insert) can by cold air, which flows through the air cushions, the temperature quickly to a desired temperature, z. B. 500 ° C are brought. Around to maintain this desired temperature for a certain time, is now in a second cooling phase hot air blown through the air cushion. This causes the component to open Desired temperature remains and so take place a homogeneous bainitic microstructure transformation can.

The 4 to 6 show the arrangement and geometry of Luftpolsternuten invention 4 in a test refrigerator.

The air cushion grooves shown 4 are flat, in the surface 8th the cooling shell 1 introduced recesses, which may have different shapes and diameters. It can be seen here, for example, circular disk-shaped Luftpolsternuten 4a , which are each arranged in groups, wherein the Luftpolsternuten 4a circular or cylindrical recesses are different from the surface 8th the cooling shell 1 extend into it.

In a further advantageous embodiment, the Luftpolsternut 4 as approximately square large air cushion grooves 4b formed, wherein the corner areas are rounded and the Luftpolsternuten 4b essentially the same depth into the interior of the cooling shell 1 extend, like the grooves 4a ,

In addition, it is possible the Luftpolsternuten 4 as rectangular, parallel to the longitudinal extent of the cooling shell 1 running grooves 4c train.

In a further advantageous embodiment, a plurality of small cylindrical grooves 4d formed as Nutenfeld, said Nutenfeld of grooves 4d , In particular, in order to be able to make a comparison, a same base area covered as the square groove 4b , Here are the remaining between the cylindrical grooves 4d remaining residual surfaces of the surface 8th almost as a grid pattern, which acts on a board to be placed.

In a further advantageous embodiment, the Luftpolsternut 4 as longitudinally extending grooves 4e formed, in the example shown, a plurality of longitudinally extending Luftpolsternuten 4e transverse to the longitudinal extent of the cooling shell 1 is arranged, wherein the Luftpolsternuten 4e have a small distance from each other, so that the remaining parts of the surface 8th as narrow strips are present.

In a further advantageous embodiment, the grooves 4 as Luftpolsternuten 4f elongated rectangular analogous to the grooves 4c formed, but these grooves with their longitudinal extent transverse to the longitudinal extent of the cooling shell 1 are arranged.

According to the invention in the areas where the component be formed ductile should, according to the contour of the component one or more the grooves shown may be present, in particular Also combinations of the grooves shown or Nutenfeldern available be.

With a mirror-symmetrical pair of the above-described experimental cooling pan cooling tests were carried out.

The corresponding experimental arrangements and cooling curves that could be achieved are in the 7 to 12 shown.

The tests were carried out on flat 600 × 300 mm flat boards using three sheet thicknesses, namely 1 mm, 1.5 mm and 2 mm. The boards were in this case heated in an oven, the furnace temperature was 910 ° C. The boards were taken out manually after reaching the target temperature from the oven and on one of the cooling shells 1 or mold halves 1 stored.

The Board storage in the tool takes place on so-called Sankyo pens.

The Temperature is during the pressing process with the help of a Thermocouple T recorded and recorded in the diagram, wherein the thermocouple T welded respectively to the board become.

Due to the air cushion, the cooling of the component in the air cushion area is significantly delayed. This is because air has a very low thermal conductivity and heats up during the cooling process to form a hot / hot air cushion ( 13 ). This causes the material does not convert martensitic over the original press hardening process, but a mixed structure is created. This mixed structure is significantly softer, more elastic and plastically deformable ( 12 . 13 ).

It is possible to produce different cooling rates by a variation of the air cushion shapes. Here, small air cushions dissipate the energy of the component much faster than large air cushions, which of course affects the component properties ( 7 . 8th . 9 ). The problem here is the bearing surfaces (holding areas / active radii) in which the component rests directly on the tool shell. These bearing surfaces are imperative to keep the component in shape and to size. Depending on the size of the bearing surface, these bearing surfaces can produce hard (actually undesirable) areas, since martensitic transformation takes place here, as in the original press hardening process on the cold tool.

Basically, it can be said that the larger the contact surface, the lower the reduction in the hardness of the air cushion. Different air cushion depths produce different cooling rates with the same contact surface and air cushion shape ( 14 ). The size, depth, shape, placement and number of air cushions is variable and also different depending on the component geometry.

Through the connection holes 5 it is possible during the pressing process hot or cold air to blow through the air cushion and thus the component temperature to a certain level, eg. B. 500 ° C for a certain time to keep ( 1 - 3 . 16 . 20 ). In addition, it is advantageous that the bearing surface on the tool shells (holding regions of the component) assume the temperature of the hot air flowing through. This can be ensured by directly below the surface extending communication holes and by the adjacent hot air cushion, so that the previously mentioned possibly hard holding areas are avoided.

According to the invention For this a nearly homogeneous bainitic structure also in the problematic holding areas are achieved.

Similar Like the variability of the air cushions are also the connecting bores in their size, depth, shape, placement and number variable and different depending on the component geometry.

A further embodiment according to the invention provides for the bearing surfaces to be formed in the holding regions of ceramic with low thermal conductivity ( 15 . 16 . 19 ), these ceramic bearing surfaces 5a or these ceramic inserts 5a can also be heated. Here are the air cushions, as in 15 or 16 shown, maintained.

The Size, shape, placement and number of ceramic Bearing surfaces is variable and is essentially of The component geometry determines, since these are the positive radii and Pad / or. Defined contact surfaces.

In a further advantageous embodiment ( 17 ) a full ceramic tool shell is used, which makes it possible to set a homogeneous structure. If such a ceramic tool shell is formed from a ceramic or a ceramic casting which is not heated, there is still a relatively hard but low-stress martensite ( 22 ). Is advantageously the ceramic or ceramic casting accordingly by a heating circuit 11 ( 17 ), a softer bainitic structure forms ( 23 ).

From Advantage is to select the ceramic so that the thermal conductivity is very low and the heat capacity as possible high. When using a ceramic, the temperature to be held is the Ceramic between 200 ° C and 300 ° C to a bainitic Form structure. If a cast ceramic is used, lies the temperature of the ceramic to be held at about 100 ° C.

In a further embodiment of the invention many small ceramic pins 14 arranged in the air cushion to provide sufficient support surface for the component ( 18 ). The small ceramic bearing surfaces through the pins 14 and the surrounding air cushion cause the energy to be slowly removed from the component in these areas, even at the support points. If necessary, there is the option of either the air cushion again 12 or the individual ceramic pins 13 ( 4 ) to heat. Again, of course, the size, shape, placement and number of ceramic bearing surfaces variable and also different depending on the component geometry.

In a further advantageous embodiment ( 21 ) are compared to the holding areas (active radii) in the tool and the holding area of the dividing induction coils 15 integrated or attached ( 21 ). The induction coils thus counteract the flow of energy. The inductors supply as much energy in the component as energy is dissipated via the contact surfaces. This allows a constant temperature of z. B. 500 ° C are generated in the holding areas. It is also possible in the air cushion, the induction coils 15 evenly distributed and so in the component for a certain time to produce a constant homogeneous temperature, whereby the microstructure can transform homogeneously bainitic.

Advantage of the integrated in the air cushion induction coils 15 is that the induction coil 15 do not have to work against the otherwise cooled directly on the component tool surfaces. Since the tool is cooled, the induction coils also do not heat because they are embedded in the tool.

The Air cushions also act as an insulating layer between the cooled tool and the hot component, wherein the tools are not heated by the induction coils since they are not ferromagnetic. Against the radiant heat of the Component, the induction coils by additional Insulating material or protected by deep embedding in the tool become.

If a heater is used to keep the component at a certain temperature for a certain time, it is sometimes necessary to carry out a two-part process ( 24 ). This is necessary in order to realize a cycle time reduction, wherein the process shown is a two-part press hardening process, which is suitable for partial areas of a component, as well as for complete components.

In There are two different pressing tools per press Component side or following the press a device for Stage (cool to room temperature). In the first one is through Heating the tool shell (air cushion or ceramic or induction, as already described) in certain component areas, the temperature brought a desired level and this temperature for held for a certain time. After the end of the holding time, the in certain areas still hot component by robot in placed a second pressing tool, wherein the component in this case while air the transfer continues to cool. Here it should be paid attention be that the temperature is not below the martensite start temperature decreases.

in the second pressing tool then becomes the still hot component area cooled quickly to room temperature, according to the usual, previous press hardening process. This two-part process allows a significant cycle time reduction compared to a single cycle Pressing tool.

at The invention is advantageous in that by the number, size and distribution of Luftpolsternuten and the enforced gas flow very sensitive the hardness of a quench hardened Component is adjustable.

1

cooling tray

2

component

3

supply air

4

Luftpolsternuten

4a

circular disk Luftpolsternuten

4b

nearly square large-area Luftpoluten grooves

4c

rectangular grooves parallel to the longitudinal extent of 1

4d

cylindrical Grooves, forming a groove field

4e

yourself longitudinally extending grooves

4f

elongated rectangular grooves transverse to the longitudinal extent of 1

5

exhaust pipes

6

Upper die

7

Tool part

8th

surface

11

heating circuit

12

bubble

13

pencils

14

ceramic pins

15

inductors

V

connecting bores

T

thermocouple

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• - EP 2005/008641 [0005]
• - WO 2006/038868 A1 [0006]

Claims (8)

Apparatus for hardening steel components, wherein at least two mold halves ( 6 . 7 ) are present, which at least partially cool down a heated steel component or a heated board on at least one cooling shell ( 1 ) per mold half ( 6 . 7 in particular apparatus for carrying out the method according to one of the preceding claims, wherein in the cooling shells ( 1 ) on the workpiece side in the areas in which a reduced or no hardness of the component is desired, recesses ( 4 ) in the surface ( 8th ) are present, wherein the recesses ( 4 ) for generating a gas cushion during the pressing of the board or the component via gas supply and gas discharge holes and also a device is provided, with the gas through the feed holes in the recesses can be introduced. Device according to claim 1, characterized in that the recesses ( 4 ) or Luftpolsternuten ( 4 ) occupy a contour or surface corresponding to the surface which is to have a reduced or no hardness. Apparatus according to claim 1 or 2, characterized in that in areas in which a reduced or no hardness is desired, a plurality of recesses ( 4 ) or Luftpolsternuten ( 4 ), which cover the area of reduced or non-existent hardness, leaving ridges between the air cushion grooves. Device according to one of the preceding claims, characterized in that the bearing surfaces or holding areas in the active radii of the component through below the surface extending connecting holes are arranged heated. Device according to one of the preceding claims, characterized in that relative to the holding areas or active radii in the tool induction coils ( 15 ) are integrated, which are arranged counteracting the energy termination of the sheet in the tool. Device according to one of the preceding claims, characterized in that the tool shell made of a ceramic or a ceramic casting is formed. Device according to one of the preceding claims, characterized in that the holding regions in the region of the active radii, in which the component rests, are formed of ceramic. Device according to one of the preceding claims, characterized in that in the Luftpolsternute ceramic pins as additional bearing surfaces for the Component are present.