EP4015657B1 - Thermal treatment of components - Google Patents

Description

The invention relates to a method and a device for the thermal treatment of metallic components, in particular steel components for a motor vehicle.

In the automotive industry in particular, it is known to specifically harden steel components through thermal treatment. To do this, steel components such as B-pillars are thermally treated differently in certain areas. This results in different ductility in certain areas, which is advantageous for the crash behavior of such components. In this way, occupants can be protected by a hard area of the B-pillar at seat height, while soft areas in the upper and lower areas of the B-pillar absorb energy through deformation.

From the EP 2 336 374 A1 A method for the thermal treatment of a workpiece is known in which the workpiece is heated in a furnace and simultaneously cooled in one section. From the EN 10 2016 118 252 A1 A method for the thermal treatment of a metallic component is known in which a temperature difference between areas of the component is set in a tempering station.

The different thermal treatment of the components in different areas is regularly the limiting factor for the cycle time of an overall process.

The object of the present invention is to accelerate the thermal treatment of components, which differs from region to region, based on the described prior art.

This object is achieved with a method and a device according to the independent claims. Further advantageous embodiments are specified in the dependent claims. The features presented in the claims and in the description can be combined with one another in any technologically reasonable manner.

1. a) Erwärmen des Bauteils in einem ersten Ofen,
2. b) Halten des Bauteils an einem Ausgang des ersten Ofens, so dass ein erster Bereich des Bauteils außerhalb des ersten Ofens abkühlt, während ein zweiter Bereich des Bauteils innerhalb des ersten Ofens verbleibt,
3. c) Transfer des Bauteils von dem ersten Ofen in eine Temperierstation,
4. d) lokal unterschiedliches thermisches Behandeln des Bauteils in der Temperierstation.

According to the invention, a method for the thermal treatment of metallic components is presented. The method comprises for each of the components:

1. a) Heating the component in a first oven,
2. b) holding the component at an exit of the first furnace so that a first region of the component cools outside the first furnace while a second region of the component remains inside the first furnace,
3. c) Transfer of the component from the first oven to a tempering station,
4. d) locally different thermal treatment of the component in the tempering station.

Components can be thermally treated using the described method. The components are preferably steel components. The steel is preferably 22MnB5. For example, components for a motor vehicle, in particular B-pillars, can be thermally treated using the described method. After the thermal treatment, the components are preferably press-hardened in a press and thus hot-formed. The method preferably includes, for each of the components, as a further step that the component is transferred to a press after the thermal treatment and is press-hardened there. In this case, the described method is a method for the thermal treatment and press-hardening of metal components.

The method comprises steps a) to d). For a specific component, these are carried out in the order given. Preferably, several components are thermally treated one after the other, with the thermal treatment of one component being started before the thermal treatment of a previous component is completed. In steps a) to d), the component passes through the first oven and the tempering station. The first oven and the tempering station are different components that are spatially separated from one another.

In step a), the component is heated in the first furnace, preferably to a temperature above the austenitizing temperature of the component. Preferably, the heating takes place to a temperature above the AC3 temperature of the component. A furnace is understood to mean a device which is brought to an adjustable temperature inside and into which a component can be introduced. Over time, the component takes on the temperature prevailing inside the furnace. The heat is transferred to the component by thermal radiation. The first furnace is preferably a continuous furnace. A continuous furnace is a furnace through which the component can be moved, the component being heated as it passes through the furnace. The first furnace is preferably a roller hearth furnace. In the first furnace, the component is preferably heated by burners, in particular Gas burner. This allows the component to have a particularly evenly distributed temperature. The entire component is heated in the first oven. The component is completely taken up by the first oven. In addition, heating by a particularly large temperature difference can be achieved with an oven. With an oven, a component can be heated from room temperature to a temperature in the range of the AC3 temperature of the component. Such extensive heating is not possible with many other heating methods, or at least not without disproportionate effort.

Heating in an oven is particularly in contrast to heating by so-called "direct energization". This would make it difficult to heat the component evenly and to a sufficiently high level. With direct energization, the speed of heating is more important. In addition, direct energization requires contact with the component. In step a) of the process described, heating is preferably carried out without contact. This does not exclude the component being moved through the first oven using transport rollers and thus being in contact with the transport rollers. Heating is contactless if the heat is introduced into the component via a gas and/or thermal radiation.

In step b), the component is held at the exit of the first oven in such a way that a first area of the component cools down outside the first oven, while a second area of the component remains inside the first oven. The component is at rest for this step. For a treatment time, it is located at the exit of the first oven in such a way that the component is partly inside and partly outside the first oven. The part of the component held outside the first oven in step b) is the first area of the component. The part of the component held inside the first oven in step b) is the second area of the component. The component therefore protrudes from the exit of the first oven. The protruding first area of the component cools down in the process. This can happen because the component gives off heat via radiation.

The component can be moved in a transport direction through the first furnace and all subsequent elements of the device. It is preferred that the first region of the component is arranged in front of the second region of the component in the transport direction. This means that the first region leaves the first furnace first. Particularly preferably, a dividing line between the first region and the second region runs transversely to the transport direction. The method described is particularly suitable for such components because these components can be held particularly easily at the exit of the first furnace according to step b).

The second region remaining in the first furnace is exposed to a higher temperature than the first region. Depending on the temperature of the second region at the start of step b), the temperature of the second region in step b) can rise, remain constant or fall. If the temperature of the second region falls, this occurs more slowly than the cooling of the first region. After step b), the first region has a first temperature and the second region has a second temperature, the first temperature being lower than the second temperature, preferably by at least 100 K.

Due to the different thermal treatment of the two areas, the two areas can acquire different ductilities in the further course of the process. The first area and the second area are preferably each connected areas. The component preferably has exactly one first area, exactly one second area, a transition area between the first area and the second area and no further areas. A simple division of the component into two areas is easiest to achieve by step b). However, it is also conceivable that the first area and/or the second area are each made up of several non-connected sub-areas. This can be achieved by appropriately designing the exit of the first furnace.

In step b) of the process, the component is transferred from the first oven to the tempering station. "From the first oven" refers to the position in which the component was held for step b). It is therefore not necessary for the Component is completely in the first oven at the start of step c). The transfer according to step c) preferably takes place directly from the first oven to the tempering station. This means that the component does not pass through any further element between the first oven and the tempering station. The tempering station is arranged downstream of the first oven in the transport direction. During the transfer according to step b), the component can cool down. Preferably, the component is not actively cooled or heated during the transfer according to step b). This means that the component only cools down through radiation during the transfer.

In step d), the component is locally thermally treated differently in the tempering station. Preferably, a temperature difference of at least 200 K is achieved between different areas of the component.

Steps b) and d) result in a locally different thermal treatment of the component, which is divided into two steps. This division can speed up the process overall. This is particularly the case if the components are thermally treated at partially overlapping times. The components can be introduced into the first oven one after the other. Before a first component has reached the exit of the first oven, a second component can be introduced into the first oven. This is particularly the case with a continuous oven, through which a large number of components can be transported one after the other. As soon as the first component has reached the exit of the first oven, it can be treated there according to step b). The second component can still be transported through the first oven at the same time. Before the second component reaches the exit of the first oven, the first component can be transferred from the first oven to the tempering station. The first component can be thermally treated in step d) in the tempering station, while the second component is thermally treated at the exit of the first oven according to step b). Before a third component reaches the exit of the first furnace, the first component can be removed from the tempering station and the second component can be transferred from the first furnace to the tempering station. This process can be continued for any number of components. Compared to a design with a locally different thermal Treatment only in one tempering station, the process time for the locally different thermal treatment can be reduced by the described method to the extent that two components can be treated locally differently at the same time. Step b) can be understood as a local pre-cooling, through which the treatment time in the tempering station is reduced. Since step b) can be carried out for one component while the previous component is thermally treated in the tempering station according to step d), the total time for the locally different thermal treatment is shortened.

The method described can also be used to thermally treat several components at the same time, provided that the components are moved through the device next to one another. For example, a group of two to four components can be placed next to one another in the first oven and thus moved through the first oven at the same time. Steps b) to d) are also carried out simultaneously for the components in this group. This means that the device can be used to its full width. Different groups of components can be moved through the device one after the other and can thus be thermally treated in overlapping time.

The locally different thermal treatment in step d) can be carried out by increasing the temperature difference previously set in step c). However, it is not necessary for the first region to be treated uniformly in step d) and/or for the second region to be treated uniformly in step d). The locally different thermal treatment in step d) can also be carried out by dividing the component into different regions in a different way than for step b). This is particularly advantageous in that the temperature control station enables the component to be divided more precisely into regions. The temperature control station also enables the shape of the regions of the component to be freely designed, while the design of the exit of the first oven restricts the division for step b). For example, it may be possible for only one straight dividing line perpendicular to the transport direction to be possible between the first region and the second region in step b).

Nevertheless, the embodiment of the method is preferred in which in step d) the first region and the second region of the component are thermally treated differently.

In this embodiment, a locally different thermal treatment is carried out in steps b) and d) with the same division of the component into areas. This reinforces the locally different thermal treatment from step b) in step d). The two steps complement each other particularly well. In particular, a temperature difference obtained in step b) is not partially canceled out again in step d). In this embodiment, a particularly sharp division into the first area and the second area can be obtained.

In a further preferred embodiment of the method, a temperature of the second region of the component in steps b) and/or d) is kept within 200 K, in particular 150 K, of the value present at the start of step b). The "and" case is preferred.

In this embodiment, the temperature of the second region is preferably kept high enough to prevent the dissolution of previously formed austenite. In contrast to the cooled first region, the second region thus has lower ductility and higher strength. In this way, for example, the crash properties of a B-pillar for a motor vehicle can be specifically adjusted. Preferably, the temperature of the second region in steps b) to d) is kept high enough to prevent the dissolution of austenite.

In a further preferred embodiment of the method, the first furnace is a continuous furnace through which the component is conveyed in step a), wherein the component is stopped at the exit of the first furnace for step b).

The components can be transported through the first furnace one after the other. This means that a large number of components can be thermally treated automatically. For step b), the movement of the component is stopped so that the component is at rest for the duration of step b). This is advantageous because it allows a particularly sharp separation between the first area and the second area to be achieved. If the component were still moving during step b), the temperature in the component would decrease continuously over a larger transition area from the second area to the first area. A transition area can arise in particular if a part of the component that is at the front in the transport direction begins to cool earlier than a part that follows when it leaves the first oven. In order to keep the cycle time as short as possible and to achieve the most uniform strength possible in the first area, the component is preferably partially moved out of the first oven as quickly as possible and stopped as abruptly as possible.

For this purpose, the embodiment of the method is preferred in which the component for step b) is stopped by a stopper at the exit of the first furnace.

The stopper allows the component to be stopped particularly quickly. The stopper is preferably movable in such a way that the stopper can block the path of the component for step b) and can release the path of the component after step b).

In a further preferred embodiment of the process, step b) is carried out such that the first region cools to a temperature in the range of 500 to 750 °C.

This is particularly possible in the preferred embodiment of the method in which the component is held at the exit of the first furnace for 0.5 to 5 seconds in step b).

• e) Transfer des Bauteils aus der Temperierstation in einen zweiten Ofen,
• f) thermisches Behandeln des Bauteils in dem zweiten Ofen.

In a preferred embodiment, the method further comprises for each of the components:

• e) Transfer of the component from the tempering station to a second oven,
• f) thermally treating the component in the second furnace.

The first oven, the tempering station and the second oven are three different components that are spatially separated from each other. During the transfer from the transfer station to the second oven, the component can cool down. This is in contrast to a solution in which all process steps are carried out in the same facility if possible, without having to transfer the component.

Such solutions typically aim to keep the effort for component transfers to a minimum or to avoid them altogether. The spatial separation between the tempering station and the second oven also makes the design easier because the requirements for the tempering station and the second oven are different. Integrating both in one facility would therefore be correspondingly complicated.

What has been said about the first furnace applies accordingly to the second furnace. The second furnace is preferably a continuous furnace. The second furnace is preferably a roller hearth furnace. The entire component is thermally treated in the second furnace. The component is completely taken up by the second furnace. Thermal treatment in a furnace is in particular in contrast to heating by so-called "direct energization". Heating in the second furnace is preferably contactless. The second furnace is preferably arranged downstream of the tempering station in the transport direction. If the device has a press, the press is preferably arranged downstream of the second furnace in the transport direction.

The thermal treatment in the second furnace gives the component a different temperature in the first area and in the second area than would otherwise be the case. This means that after the pressing process has been completed, the desired structure with the desired strength values is present in the first area and in the second area. In this respect, the present embodiment is aimed at applications in which corresponding structure compositions are desired. The renewed thermal treatment in the second furnace also reduces a temperature difference between different areas of the component. Due to the smaller temperature difference between the areas, the geometric distortion of the components is reduced. In addition, this means that the components can lie flat on a roller hearth and can be reliably picked up by a press feed system.

The same applies to the order of steps a) to f) as was said above for steps a) to d). Continuing the example described above, the first component can be transferred from the tempering station to the second oven if the second component is transferred from the first furnace to the tempering station. The first component can then be thermally treated in the second furnace, while the second component is thermally treated in the tempering station and the third component is thermally treated at the exit of the first furnace.

As a further aspect of the invention, a device for the thermal treatment of metallic components is presented. The device comprises a first furnace, a tempering station and a control device. The control device is designed to carry out the method described.

The advantages and features of the method are applicable and transferable to the device, and vice versa. The method is preferably carried out with the device.

The device preferably has conveying means with which the components can be conveyed through the device. For example, the device can have transport rollers as conveying means via which the components can be conveyed through the first oven, the tempering station and, if present, the second oven and the press. The device is preferably designed such that the first oven, the tempering station and, if present, the second oven and/or the press can be passed through in the order mentioned without passing through further elements in between.

In a preferred embodiment, the device further comprises a transfer device for transferring the components from the first furnace to the tempering station, wherein the transfer device has a stopper for stopping the components at the exit of the first furnace.

The transfer device can be part of the previously described conveying means. The part of the conveying means arranged between the first oven and the tempering station can be regarded as a transfer device.

Fig. 1:

eine erfindungsgemäße Vorrichtung zur thermischen Behandlung von metallischen Bauteilen,

Fig. 2:

einen Temperaturverlauf bei einem erfindungsgemäßen Verfahren zur thermischen Behandlung von metallischen Bauteilen mit der Vorrichtung aus Fig. 1.

The invention is explained in more detail below with reference to the figures. The figures show a particularly preferred embodiment, to which the invention is, however, is not limited. The figures and the proportions shown therein are only schematic. They show:

Fig.1:

an inventive device for the thermal treatment of metallic components,

Fig. 2:

a temperature profile in a method according to the invention for the thermal treatment of metallic components with the device from Fig.1 .

Fig.1 shows a device 1 for the thermal treatment of metallic components 2. The device 1 comprises a first furnace 3, a tempering station 5 and a second furnace 6. The first furnace 3, the tempering station 5 and the second furnace 6 are arranged such that the components 2 can first pass through the first furnace 3, then the tempering station 5 and then the second furnace 6.

The device 1 also has conveying means 12. These serve to convey the components 2 through the device 1 with their elements. The transport direction is in Fig.1 from left to right. The first oven 3 and the second oven 6 are each designed as a continuous oven. The components 2 can be transported through the first oven 3 and through the second oven 6 by the conveying means 12. The part of the conveying means 12 arranged between the first oven 3 and the tempering station 5 is a transfer device 13 for transferring the components 2 from the first oven 3 to the tempering station 5.

1. a) Erwärmen des Bauteils 2 in dem ersten Ofen 3,
2. b) für 0,5 bis 5 Sekunden Halten des Bauteils 2 an einem Ausgang 4 des ersten Ofens 3, so dass ein erster Bereich 10 des Bauteils 2 außerhalb des ersten Ofens 3 auf eine Temperatur im Bereich von 500 bis 750 °C abkühlt, während ein zweiter Bereich 11 des Bauteils 2 innerhalb des ersten Ofens 3 verbleibt,
3. c) Transfer des Bauteils 2 von dem ersten Ofen 3 in die Temperierstation 5,
4. d) lokal unterschiedliches thermisches Behandeln des Bauteils 2 in der Temperierstation 5, indem der erste Bereich 10 und der zweite Bereich 11 des Bauteils 2 unterschiedlich thermisch behandelt werden,
5. e) Transfer des Bauteils 2 aus der Temperierstation 5 in den zweiten Ofen 6,
6. f) thermisches Behandeln des Bauteils 2 in dem zweiten Ofen 6.

The tempering station 5 has a nozzle 8 for discharging compressed air onto a part of the component 2 located in the tempering station 5. The device 1 also comprises a control device 7, which is designed to carry out a method for thermally treating components 2, in which the following steps are carried out for each of the components 2:

1. a) Heating the component 2 in the first oven 3,
2. b) holding the component 2 at an exit 4 of the first furnace 3 for 0.5 to 5 seconds, so that a first region 10 of the component 2 outside the first furnace 3 to a temperature in the range of 500 to 750 °C, while a second region 11 of the component 2 remains within the first furnace 3,
3. c) Transfer of the component 2 from the first furnace 3 to the tempering station 5,
4. d) locally different thermal treatment of the component 2 in the tempering station 5, in which the first area 10 and the second area 11 of the component 2 are thermally treated differently,
5. e) Transfer of the component 2 from the tempering station 5 into the second furnace 6,
6. f) thermally treating the component 2 in the second furnace 6.

For illustration purposes, Fig.1 Four components 2 are shown as an example. One component 2 is conveyed through the first furnace 3 as indicated by an arrow (step a)). A second component 2 was stopped by a stopper 9 and is at rest at the exit 4 of the first furnace 3 (step b)). A third component 2 is thermally treated locally in a different way in the tempering station 5 using the nozzle 8 and a heating device (not shown) (step d)). A fourth component 2 is conveyed through the second furnace 6 as indicated by an arrow (step f)).

Each component 2 is conveyed through the first furnace 3 in step a) and stopped at the exit 4 of the first furnace 3 for step b). For this purpose, the transfer device 13 has a stopper 9. The stopper 9 is movable in such a way that the stopper 9 can be moved into the transport path of the component 2 to stop a component 2. After step b) has been completed, the stopper 9 can be moved out of the transport path to clear the path for the component 2 again.

In step d), the first area 10 and the second area 11 of the component 2 are thermally treated differently in the tempering station 5. To do this, the first area 10 of the component 2 is cooled with the nozzle 8 of the tempering station 5, while the temperature of the second area 11 of the component 2 is kept within a window of +/-150 K around the value present at the start of step b). In step d), the temperature of the second area 11 of the component 2 is also kept within a window of +/- 150 K around the value present at the start of step b).

Fig. 2 shows a temperature curve for Fig.1 described method. The temperature of the component 2 is shown versus time t. The treatment time in the first oven 3 is given as t _O1 , the duration of step b) is given as a holding time t _H. The transfer time from the first oven 3 to the tempering station 5 is given as t _t1 , the treatment time in the tempering station 5 as t _temp , the transfer time from the tempering station 5 to the second oven 6 as t _t2 and the treatment time in the second oven 6 as t _O2 . Due to the different thermal treatment of the component 2 during the holding time t _H, the temperature curve shown with the holding time t _H splits into the temperature T ₁ of the first region 10 and the temperature T ₂ of the second region 11. After the component 2 has been thermally treated in the second furnace 6, the component 2 is transferred from the second furnace 6 into a press (not shown in the figures) and formed there. The component is cooled as quickly as possible in a water-cooled tool, for example.

By holding the component 2 at the exit 4 of the first furnace 3, the process is accelerated in that a component 2 can be pre-cooled according to step b), while the preceding component 2 is thermally treated in the tempering station 5 according to step d).

List of reference symbols

1

contraption

2

Component

3

first oven

4

Exit

5

Tempering station

6

second oven

7

Control device

8th

jet

9

stopper

10

first area

11

second area

12

Means of transport

13

Transfer facility

T

temperature

t

Time

TA

Austenitizing temperature of the component

T1

Temperature of the first area of the component

T2

Temperature of the second area of the component

tO1

Treatment time in the first oven

tH

Holding time at the exit of the first furnace

tt1

Transfer time from the first oven to the tempering station,

ttemp

Treatment time in the tempering station,

tt2

Transfer time from the tempering station to the second oven

tO2

Treatment time in the second oven

Claims (10)

1. Method for thermal treatment of metallic components (2), comprising, for each of the components (2):

   a) heating the component (2) in a first furnace (3),

   b) holding the component (2) at an outlet (4) of the first furnace (3), so that a first region (10) of the component (2) outside the first furnace (3) cools down, while a second region (11) of the component (2) remains within the first furnace (3),

   c) transferring the component (2) from the first furnace (3) to a temperature control station (5),

   d) subjecting the component (2) to locally different thermal treatment in the temperature control station (5).
2. Method according to Claim 1, wherein, in step d), the first region (10) and the second region (11) of the component (2) are subjected to different thermal treatments.
3. Method according to either of the preceding claims, wherein, in steps b) and/or d), a temperature of the second region (11) of the component (2) is kept within 200 K around the value it has at the start of step b).
4. Method according to one of the preceding claims, wherein the first furnace (3) is a continuous furnace, through which the component (2) is conveyed in step a), and wherein the component (2) is stopped at the outlet (4) of the first furnace (3) for step b) .
5. Method according to Claim 4, wherein for step b) the component (2) is stopped at the outlet (4) of the first furnace (3) by a stopper (9).
6. Method according to one of the preceding claims, wherein step b) is carried out such that the first region (10) is cooled down to a temperature ranging from 500 to 750°C.
7. Method according to one of the preceding claims, wherein, in step b), the component (2) is held at the outlet (4) of the first furnace (3) for 0.5 to 5 seconds.
8. Method according to one of the preceding claims, furthermore comprising, for each of the components (2) :

   e) transferring the component (2) from the temperature control station (5) to a second furnace (6),

   f) subjecting the component (2) to thermal treatment in the second furnace (6).
9. Apparatus (1) for thermal treatment of metallic components (2), comprising a first furnace (3), a temperature control station (5) and a controller (7), which is set up to carry out a method according to one of Claims 1 to 8.
10. Device (1) according to Claim 9, furthermore having a transferring device (13) for transferring the components (2) from the first furnace (3) to the temperature control station (5), wherein the transfer device (13) has a stopper (9) for stopping the components (2) at the outlet (4) of the first furnace (3).

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