EP1426454A1 - Method for producing a formed component with at least two regions of structure having different ductility and continuous furnace therefor - Google Patents

Abstract

Continuous furnace for heating metallic workpieces comprises two zones (1a, 1b) lying opposite each other and separated from each other by a thermal insulating separating wall (2). The workpiece (3) is placed in part of one zone and in part of another zone. A separate temperature regulation is carried out in both zones. An Independent claim is also included for a process for the production of a molded component using the above continuous furnace.

Description

The invention relates to a method for producing a molded component at least two structural areas of different ductility from a semi-finished product made of hardenable steel with heating in a continuous furnace and one Hardening process according to the preamble of claim 1 and a method for Production of a molded component with at least two areas different Ductility from a semi-finished product made of hardened steel with heating in one Continuous furnace according to the preamble in claim 7 and a continuous furnace Heating of metallic workpieces according to the preamble of claim 9.

It is known to use tool-hardened molded components for motor vehicle components Example chassis components such as handlebars or cross members or structural components such as door impact beams, B-pillars, struts or bumpers, with over the molded component distribute consistent material properties. This happens through a complete heating of the molded components with a subsequent hardening that can be followed by a starting process for compensation. In Various applications of automotive engineering are said to be over molded components certain areas have a high strength, other areas have a high strength Relative to this, have higher ductility. In addition to the reinforcement by Additional sheets or the joining of parts of different strength is it is already known to heat a component in this way treat that there are local areas of higher strength or higher ductility having.

DE 197 43 802 C2 shows a method, a molded component for Manufacture automotive components with areas of different ductility, by only partially heating an output board before or after pressing or with a previous homogeneous heating in the areas with desired higher ductility is specifically reheated. This is preferably done partial heating inductive.

DE 200 14 361 U1 describes a B-pillar, which also has areas of different strength. The B-pillar is manufactured in Thermoforming process, starting from a blank or a preformed longitudinal profile austenitized in an oven and then in is reshaped / hardened in a cooled tool. Large areas can be used in the oven Areas of the workpiece are insulated from the effects of temperature, whereby in these areas the austenitizing temperature is not reached and accordingly, there is no martensitic structure in the tool during hardening.

In mass production, continuous furnaces are often used in the mold for heating of roller hearth continuous furnaces or push-through furnaces with or without goods carriers used. DE 3441 338 A1 describes a method for heat treatment metallic workpieces using a continuous or push-through furnace and an apparatus for performing this method is disclosed. You can Workpiece batches of different treatment times, in particular Different case hardening depths when carburizing in two-step processes can be treated simultaneously by using a continuous or pusher furnace go through that with at least two of the workpieces one after the other continuous treatment chambers for the respective heat treatment of several Workpiece batches is provided. In particular, it can be a Continuous furnace act in which each treatment chamber as a rotary cycle furnace intermittently rotatable oven hearth is formed.

These methods show in their practical implementation in mass production however some problems arise. Isolation by encapsulation in the oven is technical complex, because every part needs its own insulation in each cycle, the insulation as a preparation process extends the thermoforming process as a whole and the insulation heats up with repeated use. This does one Mass production is expensive. The previously known ovens can heat different batches of workpieces to different extents, they are suitable but not for partial heating of the same workpiece.

The present invention is therefore based on the object of a method for Manufacture of a metallic molded component with at least two structural areas different ductility and a suitable continuous furnace for heating to further develop metallic workpieces so that they can be used for Are suitable for mass production.

This object is achieved by the invention in the characterizing part of claim 1 described method. Accordingly, it goes through a manufacturing process a molded component with at least two structural areas of different ductility from a semi-finished product made of hardenable steel with heating in one Continuous furnace and a hardening process, a board or a preformed component at least two at the same time during transport through a continuous furnace zones of the continuous furnace arranged next to one another in the direction of flow different temperature levels. Zone 1 of the continuous furnace is open set a temperature A and another zone 2 to a temperature B which is higher than temperature A. This heats up the semi-finished product in the areas in which it passes through the continuous furnace in zone 1 to temperature A and in Areas where it passes through zone 2 at temperature B. Then the semi-finished products heated to different degrees in this way using a thermoforming process and / or subjected to the hardening process. Through the hardening process arises in the before area 1 of the component heated to temperature A in relation to that Temperature B heated area 2 of the component more ductile structure and in area 2 a solid or high-strength structure.

Which temperature is chosen for the respective zone of the furnace depends on the desired properties of the component. If, for example, the base of a B-pillar for an automobile is to be ductile in relation to the rest of the B-pillar, a preformed component is introduced into the continuous furnace in such a way that it corresponds to area 1, which after the final shaping represents the B-pillar base to lie in zone 1 of the furnace. The rest of the component, which should be as high-strength as possible after the final shaping, extends over zone 2 of the continuous furnace. The temperature A in zone 1 is now set to a temperature below the AC ₁ temperature of the material. As a result, there is no structural change in area 1 during transport through the furnace. Consequently, during a subsequent hardening process, the unhardened initial structure remains in area 1 of the component and thus in the column base. The temperature B in zone 2 of the furnace is set to a temperature above AC ₃ in order to obtain the most complete structural transformation of the remaining component during transport through the continuous furnace. In a subsequent hardening process, a solid or high-strength structure is established over the rest of the B-pillar. In relation to this, the column base is ductile.

Depending on the requirements of the component, a different microstructure distribution can also be desired. In an advantageous exemplary embodiment, the temperature A in zone 1 of the furnace is set to a temperature above AC ₁ but below AC ₃ and the temperature B in zone 2 of the furnace is set to a temperature above AC ₃ in order to achieve different strength requirements. The component undergoes a partial structural change in area 1, with which it passes through zone 1, in area 2, with which it passes through zone 2, the structure changes almost completely. A subsequent hardening process therefore results in a mixed structure in area 1 and a structure that is firmer in area 2.

In particular for steel grades with a carbon content C> 0.8%, it is advantageous to set the temperature A in zone 1 just above AC ₁ , so that area 1 of the component is annealed and the structure is relaxed.

If the component has already received its final shape and adapts to the Heating process in the continuous furnace can only be followed by a hardening process heating of zone 1 of the continuous furnace can be dispensed with entirely. The Temperature A is then roughly the same as the ambient temperature of the furnace match. The component is only partially in zone 2 of the furnace in area 2 heated in which it should also be hardened.

If the component has not yet reached its final shape and a further thermoforming process may follow the heating process, apart from the requirements of the hardening process, the conditions of the thermoforming process must also be taken into account. Since the material of the material flows during the thermoforming process, it is particularly advantageous to set temperatures A and B as far apart as required for the desired structure to be finally set by the hardening process, but at the same time as narrow as possible within the limits of the ZTU diagram of the material possible to be placed next to each other in order to optimize the flow properties of the material. With a B-pillar, for example, which is only preformed and which should have an unhardened foot but a firm or high-strength structure over the rest of its area, it is therefore advisable to set the temperature A in zone 1 of the furnace, in which the area of the preformed component, which will later be the column base, to a temperature as close as possible to below AC ₁ . Temperature B in zone 2 of the furnace, in which the rest of the component is located, is set to a temperature as close to AC ₃ as possible. After the furnace has been heated, the component is then thermoformed and hardened. The B-pillar is end-shaped and has a relatively ductile base and a solid or high-strength structure in the rest of the area.

The last thermoforming step is preferably carried out at the same time as the hardening Forming tool instead.

In addition to a semi-finished product made of hardenable steel, the method according to the invention can also be used to process a semi-finished product made of hardened steel to produce a molded component with at least two areas of different ductility with heating in a continuous furnace. The peculiarity here is that the semi-finished product is already hardened over its entire length. The semifinished product can be a board or a preformed component that has already been preformed in one or more steps. In particular, the preforming can be cold-forming steps. The semi-finished product then simultaneously passes through at least two zones of the continuous furnace with different temperature levels which are arranged next to one another in the direction of the transit during the transport through a continuous furnace. The semi-finished product is introduced into the furnace in such a way that it comes to rest in zone 1 of the continuous furnace with area 1, which should have a solid or high-strength structure in the finished end component. Zone 1 is set to room temperature or to a temperature below AC ₁ . As a result, the existing hardness values of the semi-finished product in area 1 are largely retained. Area 2 of the component, which is to have a ductile structure in the finished end component, passes through the furnace in zone 2. Zone 2 is set to a higher temperature than zone 1, preferably to a temperature above AC ₁ , so that area 2 is soft-annealed to towards a complete structural transformation. This results in a more ductile structure in area 2 than in area 1. This furnace heating is then only followed by a hot forming and / or cooling process which does not reach the critical cooling rate which would lead to a renewed hardening of area 2.

This alternative method is suitable, for example, for dual-phase steels or Steel grades that have already been hardened in the coil.

Oven heating in a protective gas atmosphere is part of the prior art to carry out a reaction of the material with oxygen as possible prevention. It is therefore also with the oven heating described here advantageous to carry them out under a protective gas atmosphere. Depending on Temperature control, material properties and component requirements can Heating can also be carried out without protective gas.

The number of zones through which the component is guided is arbitrary and depends on the number of areas that are in each other in the finished part should receive a different structure. The inventive method makes itself the medium that has already been tried and tested in mass production Use oven heating. The continuous furnace as such is already on the Mass production adjusted. The main advantage of the invention is that Partially different heating is now easy and reliable in to be able to integrate the existing process chain.

The continuous furnace according to the invention for heating metallic workpieces is characterized by the fact that it has at least two in the direction of flow adjacent zones 1 and 2 is provided. Both zones are separated from each other by a thermally insulating partition so that the The workpiece passing through the furnace is located both in zones 1 and 2 is located in areas in Zone 2. There is a separate one in both zones Temperature control possible.

The type of continuous furnace is not important here. It can be both a roller hearth continuous furnace act, in which the workpieces on rollers the furnace can be transported, as well as a push-through furnace, in which a Workpiece batch from the impact of the subsequent workpiece batch by the Oven is pushed. The component to be heated can lie directly on the rollers or are on a product carrier such as a frame. The Oven according to the invention can be designed as a rotary hearth or rotary cycle oven, at which the direction of flow is not linear, but curved. The important thing is that the furnace with at least one parallel to the direction of flow Thermally insulating partition is provided, which in at least two in the oven Flow direction divided adjacent zones, which are separated are controllable from each other.

The partition does not completely separate the two zones, only to the extent that a component can be passed below the partition in such a way that it comes to rest in both zones 1 and 2 in zones. To minimize heat radiation from the warmer zone to the cooler zone the partition ends as close as possible to the surface of the component. at three-dimensional preformed components, it is particularly advantageous if both a thermally insulating partition on the furnace ceiling and on the furnace floor is attached, between which a workpiece can be transported continuously can. This enables a three-dimensional component with a Elevation at the desired location in two differently heated Separate areas. In order to adapt the furnace to different components, it is advantageous if the partition is transverse to the direction of the furnace is removably attached. This is done by a clever arrangement of the Heating elements and / or variably attachable heating elements allows.

If the workpieces are on a product carrier, it is particularly advantageous if on the respective goods carrier parallel to the direction of the furnace thermally insulating partition is attached to the oven with the merchandise support passes. In addition, the furnace itself can be one or more thermally insulating Partitions included, so that the oven in total again in at least two Zones is divided.

Appropriate regulation, cooling or insulation in the partition wall ensures that Temperature on the partition wall side to the cooler zone roughly the same Level as the temperature in the cooler zone kept to a to avoid temperature-increasing heat radiation from the warmer zone. moreover the transition area from Zone 1 to Zone 2 can be varied by varying the Partition in terms of width and insulation. This allows the Temperature gradient and thus the structure transition in the workpiece from area 1 to Range 2 can be set.

Figur 1 zeigt in Draufsicht einen Ofen 1 mit Trennwand 2, den eine B-Säule 3 durchläuft.

Figur 2 zeigt schematisch in Durchlaufrichtung einen Ofen 4 mit zwei Trennwänden 5, 5a, den eine Platine 7 durchläuft.

Figur 3 zeigt schematisch in Durchlaufrichtung einen Ofen 8 mit Trennwand 9, den ein Warenträger 11 mit einem geformten Bauteil mit Höhenerstreckung 12 und einer mitlaufenden Trennwand 9a durchläuft.

Figur 4 zeigt in Durchlaufrichtung einen Ofen 13, in dem eine Trennwand 14, 14a quer zur Durchlaufrichtung versetzbar angeordnet ist.

The furnace according to the invention is explained in more detail below with reference to the figures.

Figure 1 shows a top view of an oven 1 with a partition 2, through which a B-pillar 3 passes.

Figure 2 shows schematically in the direction of passage a furnace 4 with two partitions 5, 5a, through which a circuit board 7 passes.

FIG. 3 shows schematically in the direction of flow a furnace 8 with a partition 9, through which a goods carrier 11 with a shaped component with a height extension 12 and a moving partition 9a passes.

FIG. 4 shows a furnace 13 in the direction of passage, in which a partition 14, 14a is arranged such that it can be displaced transversely to the direction of passage.

FIG. 1 shows an oven 1 which is divided into two zones 1a and 1b by a partition 2. In the furnace there is a B-pillar 3, which lies with an area 3a, namely the column base, in zone 1a and with its area 3b, that is the remaining pillar, in zone 1b. The B-pillar 3 is made of a hardenable steel with an AC ₁ temperature of 740 ° C and an AC ₃ temperature of 850 ° C and is in its area 3a by a temperature setting in zone 1a of about 700 ° C to one Temperature of about 700 ° C and in its area 3b heated to a temperature of about 950 ° C to about 950 ° C by a temperature setting in zone 1b. In a subsequent final shaping step (not shown) combined with hardening in the shaping tool, a structure which is more ductile in relation to area 3b and a high-strength structure is established in area 3b of the B-pillar 3. As a result, a B-pillar 3 with a soft structure at the pillar base 3a is obtained.

FIG. 2 shows an oven 4 according to the invention with one on the oven ceiling 4a and one partition 5 and 5a attached to furnace bottom 4b in the direction of passage. There is a gap between the partitions 5 and 5a, which is a board 7 Rolls 6 passes. The arrow indicates the direction of rotation of the rollers 6. The circuit board 7 is therefore located both in zone 4c and in zone 4d of the furnace 4. In zone 4c Oven 4 has a cooler atmosphere than in Zone 4d. The partitions 5 and 5a are insulated on the side facing zone 4c so that a temperature-increasing heat radiation from zone 4d into zone 4c if possible is avoided. The circuit board 7 heats up in its regions 7a and 7b different levels.

Figure 3 shows a furnace 8 according to the invention in the direction of flow, the one Goods carrier 11 passes through with a component 12 with height extension. The arrow gives the direction of rotation of the rollers 10. The furnace 8 has a partition 9, which is attached to the furnace ceiling 8a and a partition 9b, which is on the furnace floor 8d is attached. The thermal insulation of zones 8b and 8c is due to the Partitions 9, 9a and 9b reached. The partition 9a is on the goods carrier 11 fastened and passed through the oven 8 with the goods carrier 11. To one To avoid heat radiation from the warmer zone 8b into the cooler zone 8c, In this case, the goods carrier 11 must be transported through the oven 8 to the goods carrier 11 so that there are no gaps between the moving partitions 9a arise. In particular, a component 12 with a vertical extension can be so precisely insert into zone 8c of the furnace 8 where in the finished component 12 a ratio to the rest of the component 12 more ductile structure is to be achieved.

Figure 4 shows a furnace 13 with a partition 14 on the furnace ceiling 13a and three partition walls 14a, 14b, 14c fastened to the furnace bottom 13b, between which Pass through rollers 15 and a board 16 transported on these rollers 15. The Dashed lines 16a and 16b indicate the contour of a not shown Component with height extension. To create a protective gas atmosphere in the furnace 13 is to be set, the furnace 13 for each zone is provided with a feed line 18 and 18a provided through which nitrogen is supplied to the furnace atmosphere. The partition 14 can be moved to the indicated positions 19 and 19a. About the transfer to be able to execute, the heating elements 17 on the furnace ceiling 13a to respective displacement positions 19 and 19a interrupted. The heating elements 17a on the furnace floor are separated anyway by the partitions 14a, 14b, 14c executed. Due to the variably attachable partition 14, the furnace 13 is flexible and use it for different components.

Claims (12)

Method for producing a molded component (3) with at least two structural areas of different ductility (3a, 3b) from a semi-finished product made of hardenable steel with heating in a continuous furnace (1, 4) and a hardening process,
characterized in that as a semi-finished product to be heated a plate (7) or a preformed component (3) during transport through a continuous furnace (1, 4) at the same time at least two zones (1a, 1b, 4c, 4d) of the continuous furnace arranged next to one another in the direction of flow (1, 4) passes through with different temperature levels, one zone 1 (1a, 4c) being set to a temperature A and another zone 2 (1b, 4d) being set to a temperature B above temperature A, so that the semi-finished product (3, 7) in the areas (3a, 7b) in which it passes through the continuous furnace (1, 4) in zone 1 (1a, 4c), heated to temperature A and in the areas (3b, 7a) in which it passes through zone 2 (1b, 4d), heated to temperature B, and then the semi-finished product (3, 7) thus heated is subjected to a thermoforming process and / or hardening process, as a result of which area 1 (3a, 7b ) of the component (3, 7) in relation to that on tempera B heated area 2 (3b, 7a) of the component (3, 7) more ductile structure and in the area 2 (3b, 7a) of the component (3, 7) a solid or high-strength structure. Method according to claim 1,
characterized in that the temperature A in zone 1 (1a, 4c) of the continuous furnace (1, 4) is set under AC ₁ and the temperature B in zone 2 (1b, 4d) of the continuous furnace (1, 4) is set via AC ₁ . Method according to claim 2,
characterized in that zone 1 (1a, 4c) of the continuous furnace (1, 4) is not heated if no further thermoforming process follows the furnace heating, but only a hardening process. Method according to claim 1,
characterized in that the temperature A in zone 1 (1a, 4c) of the continuous furnace (1, 4) above AC ₁ but below AC ₃ and the temperature B in zone 2 (1 b, 4d) of the continuous furnace (1, 4) above AC _{3 is} set. Method according to claim 1,
characterized in that the temperature A in zone 1 (1a, 4c) of the continuous furnace (1, 4) as close as possible to AC ₁ and the temperature B in zone 2 (1b, 4d) of the continuous furnace (1, 4) as close as possible to AC _{3 is} set. Method according to one of the preceding claims,
characterized in that the hardening process following the heating in the continuous furnace (1, 4) takes place simultaneously with a last hot-forming step in the forming tool. Method for producing a molded component (3) with at least two areas of different ductility (3a, 3b) from a semi-finished product made of hardened steel with heating in a continuous furnace (1, 4) and a molding and / or cooling process that does not reach the critical cooling rate reached,
characterized in that as a semi-finished product to be heated a plate (7) or a preformed component (3) during transport through a continuous furnace (1, 4) at the same time at least two zones (1a, 1b, 4c, 4d) of the continuous furnace arranged next to one another in the direction of flow (1, 4) passes through with different temperature levels, one zone 1 (1b, 4d) being unheated or set to a temperature A and another zone 2 (1a, 4c) being set to a temperature B above temperature A, so that the semi-finished product in area 1 (3b 7a) with which it passes through the continuous furnace (1, 4) in zone 1 (1b, 4d) does not heat up or heats up to temperature A and in area 2 (3a, 7b) which it passes through zone 2 (1a, 4c), is heated to a temperature B, as a result of which a solid or high-strength structure is retained in area 1 (3b, 7a) of the semi-finished product (3, 7) and in the area heated to temperature B. 2 (3a, 7b) of the semi-finished product (3, 7) in relation to the area 1 sets more ductile structure. Method according to one of the preceding claims,
characterized in that the heating takes place under a protective gas atmosphere. Continuous furnace (1, 4) for heating metal workpieces,
characterized in that the continuous furnace (1, 4) is provided with at least two zones 1 (1a, 4c) and 2 (1b, 4d) lying next to one another in the direction of the passage, which are thus separated from one another by a thermally insulating partition (2, 5, 5a) are separated that a workpiece (3, 7) passing through the furnace (1, 4) is located both in areas in zone 1 (1a, 4c) and in areas in zone 2 (1b, 4d) and in both zones (1a, 1b , 4c, 4d) separate temperature control is possible. Continuous furnace (4) according to claim 9,
characterized in that a thermally insulating partition (5, 5a) is arranged both on the furnace ceiling (4a) and on the furnace floor (4b), between which a workpiece (7) can be transported continuously. Continuous furnace (13) according to claim 9 or 10,
characterized in that the partition (14) is mounted transversely to the direction of passage of the furnace (13) so as to be displaceable (19, 19a). Continuous furnace (8) according to one of claims 9 to 11,
characterized in that when the workpieces (12) are transported through the continuous furnace (8) on a goods carrier (11) on the goods carrier (11) parallel to the direction of passage of the furnace (8) a thermally insulating partition (9a) is attached.

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