EP3177416B1 - Method for producing hot-formed components - Google Patents

Description

The invention relates to a method for producing hot-formed components.

In today's automobile construction, the comfort for vehicle occupants is increasing through the use of special equipment. These include many electromechanical components such as sensors, motors, actuators, and are designed to make driving easier for the driver. At the same time as the comfort increases, however, the weight of the vehicle also increases. To counteract this, the state of the art attempts to design the structural components of the body to be lighter.

The structural components of the body are not only crucial to the stability of the vehicle, but also play a crucial role in safety in the event of a crash. In order to resolve this conflict of objectives between reducing the weight of structural components while maintaining or achieving high mechanical properties, it has proven successful in the past to produce structural components using hot forming. Hot forming processes are also described in the literature as form hardening or press hardening.

Two fundamentally different processes are known for producing form-hardened components, in particular for producing body components. In the direct hot forming process, a blank is first heated in a furnace to a temperature above the austenitizing temperature of the steel and then simultaneously formed and cooled in a tool, i.e. form-hardened. In the indirect hot forming process, a blank is first cold-formed to produce a fully formed and trimmed steel component. This is then heated in a heating system to a temperature above the austenitizing temperature of the steel and then form-hardened in a tool by rapid cooling. In both hot forming processes, the blank or a fully formed and trimmed steel component is thermomechanically formed in the tool after heating to the austenitizing temperature, with the thermomechanical forming taking place at a temperature above the final austenitizing temperature Ac3 (approx. 830°C), preferably between 900 and 1100°C. The formed workpieces are cooled using a cooling unit located in a closed tool body. This enables components with particularly high mechanical properties, especially with high strength, to be produced.

The patent specification DE 19723655 B4 shows a method for producing sheet steel products by heating a measured sheet steel, hot forming the sheet steel in a tool pair, hardening the formed product by rapidly cooling it from an austenitic temperature while still held in the tool pair, and then machining the product.

The DE 197 23 655 A1 describes a process for producing hardened components that have areas of lower hardness and areas of higher hardness. In these softer areas, a subsequent processing takes place. To create the softer areas, inserts are provided in the processing tools or gaps are provided between the tool and the workpiece. However, such systems have disadvantages in that they make it difficult to produce complex geometries. If the component geometry changes or if other areas of the component are to remain unhardened, this requires changes to the production tools. However, this involves a lot of modification work and is expensive. During the production of series components in large quantities, the tool is subject to high levels of wear. However, wear and tear also changes the properties of the components produced. In order to meet the requirements for dimensional accuracy and quality, the tools must be revised. This is associated with high costs and also leads to an interruption of the production process.

From the WO 2011/054575 A1 , on which the preamble of patent claim 1 is based, a method is known for producing components from sheet steel with regions of different ductility, wherein a component is produced from a sheet metal blank made of a hardenable steel alloy either by deep drawing and the deep-drawn component is subsequently at least partially austenitized by heat treatment and then quench hardened in a tool, or the blank is at least partially austenitized by heat treatment and formed while hot and quench hardened during or after that. In regions in which a desired higher ductility is to be achieved, at least one further sheet is applied to the blank so that the blank is heated up to a lesser extent there during the heat treatment than in the remaining region.

The WO 2010/139664 A1 relates to a method for hot forming a board made of an aluminum or steel alloy. Before forming, an insulating material is placed on at least one surface of the board, wherein the insulating material has a lower thermal conductivity than the circuit board and is made of paper or cardboard.

Based on this prior art, the present invention sets itself the task of specifying a method for producing hot-formed components in which different areas with different mechanical values can be formed in a component. It is a specific task of the invention to specify a method with which changes to the desired mechanical characteristics in a component can be implemented particularly quickly.

This object is achieved by a method according to independent claim 1. Advantageous embodiments of the method are specified in the subclaims.

• Erwärmen eines Halbzeugs, insbesondere einer Blechplatine oder eines vorgeformten Blechbauteils,
• Einbringen des Halbzeugs in ein Formwerkzeug, und
• Abkühlen der Halbzeugs in dem Formwerkzeug, wobei zumindest in einem Abschnitt eine Änderung des Werkstoffgefüges durchgeführt wird, dadurch gekennzeichnet, dass vor dem Einbringen des Halbzeugs in das Formwerkzeug in mindestens einem vorbestimmten Bereich des Halbzeugs eine Isoliereinrichtung aufgebracht wird, die form-, stoff- und/oder kraftschlüssig mit dem Halbzeug verbunden ist. Durch die Isoliereinrichtung wird der Wärmeübergang von dem Halbzeug an die Umgebung bzw. von der Umgebung an das Halbzeug lokal verändert in den vorbestimmten Bereichen. Vorbestimmte Bereich sind solche Bereich in denen das fertige Bauteil weichere, duktilere Eigenschaften aufweisen soll, als die übrigen Bereiche. In den vorbestimmten Bereichen weist das Bauteil ein duktiles Deformationsverhalten auf. Erfindungsgemäß werden somit Bauteile, beispielsweise Fahrzeugstrukturbauteile geschaffen, deren mechanische Eigenschaften, insbesondere deren Härte nicht homogen ist. Die Erzeugung von weichen, duktilen Bereichen kann mit dem erfindungsgemäßen Verfahren ohne hohe Investitionskosten erfolgen. Dadurch eignet sich das Verfahren sehr gut zum nachträglichen Anpassen der Bauteileigenschaften, selbst wenn eine Serienfertigung bereits im Gange ist.

To achieve this object, the invention teaches a method for producing a hot-formed component, in particular a sheet metal component made of steel, aluminum, magnesium or a combination of these materials, comprising the steps:

• Heating a semi-finished product, in particular a sheet metal blank or a preformed sheet metal component,
• Inserting the semi-finished product into a mold, and
• Cooling the semi-finished product in the mold, wherein a change in the material structure is carried out in at least one section, characterized in that before the semi-finished product is introduced into the mold, an insulating device is applied in at least one predetermined area of the semi-finished product, which is connected to the semi-finished product in a form-fitting, material-fitting and/or force-fitting manner. The insulating device locally changes the heat transfer from the semi-finished product to the environment or from the environment to the semi-finished product in the predetermined areas. Predetermined areas are those areas in which the finished component should have softer, more ductile properties than the other areas. In the predetermined areas, the component has ductile deformation behavior. According to the invention, components are thus created, for example vehicle structural components, whose mechanical properties, in particular their hardness, are not homogeneous. The production of soft, ductile areas can be carried out with the method according to the invention without high investment costs. This makes the method very suitable for subsequently adapting the component properties, even if series production is already underway.

In a first variant of the method, the insulation device is applied to the semi-finished product before heating. This ensures that the semi-finished product experiences less heat input in the predetermined area and does not reach a temperature above the austenitizing temperature AC3. Thus, after hardening, a structure with a lower ductility is formed in this predetermined area than in the rest of the component. The insulation device can be removed again after the semi-finished product has been heated before the semi-finished product is placed in a hardening tool. Alternatively, the insulation device can also remain on the semi-finished product while the semi-finished product is hardened in the hardening tool.

In a second variant of the method, the insulation device is only applied to the semi-finished product after it has been heated in the predetermined area. This means that the semi-finished product is heated over its entire length to a temperature above the austenitizing temperature AC3. It is then placed in the hardening tool with the insulation device attached to it and hardened. In the predetermined area, the warm semi-finished product is cooled more slowly than in the other areas, since the insulation device slows down the flow of heat from the semi-finished product into the tool.

In both process variants, a martensitic structure is created in the component that is characterized by high mechanical hardness. In the areas covered by the insulation device, a ferritic-pearlitic structure is created that is more ductile than the martensitic area(s).

The position of the insulation device on the semi-finished product can be changed depending on the position of the semi-finished product where more ductile areas are to be set. The insulation device covers the area of the semi-finished product that must not reach too high strength values in the finished component. In addition, depending on the mechanical properties to be achieved, various insulation devices that differ in their thickness or material can be applied to the semi-finished product.

According to a first embodiment of the invention, the insulating device can be designed as a permanent magnet and can be connected to the semi-finished product in a force-fitting manner. Since the semi-finished products are preferably designed as metal sheets, magnets are particularly suitable for use as insulating devices because they adhere to the semi-finished product automatically. A further advantage of permanent magnets is that they can be removed from the component without leaving any residue after hardening and cleaning or processing of the components is not necessary.

According to a second embodiment of the invention, an insulating device, which is designed as a film or tape, is applied to the semi-finished product. Due to their low thickness, tapes or films offer the advantage that they can be used in the manufacturing process without changes to the tools or with only minor tool changes. They are therefore particularly suitable for subsequent use in the manufacturing process during an already started production of series components. Such tapes or films can be designed in layers with a small layer thickness. To attach them to the semi-finished product, the tapes or films can be connected to the semi-finished product via an adhesion-promoting layer, for example an adhesive. Such a material connection advantageously results in a good hold of the insulating device on the semi-finished product.

According to a third embodiment, an insulating device, which is designed as a paste, is applied to the semi-finished product in a predetermined area. Such pastes can be, for example, copper pastes or similar pastes that have a low heat transfer coefficient. Pastes are also suitable for subsequent use in series production that has already begun.

According to a fourth embodiment, an insulating device, which is designed as a form-fitting coating, is applied in a predetermined area of the semi-finished product. This coating can be made of various materials that are correspondingly temperature-resistant. For example, such a coating can be made of an additional sheet metal that can be brought into engagement with the semi-finished product in the predetermined area. Alternatively, the coating can also be made of a temperature-resistant plastic that can be brought into form-fitting engagement with the predetermined area of the semi-finished product.

In all the embodiments described, several insulating devices can be arranged on the semi-finished product. These can all be arranged on a first side of the semi-finished product or on a side of the semi-finished product opposite the first side. Furthermore, the insulating devices can also be provided on both sides of the semi-finished product. They can be offset from one another or arranged on both sides of the semi-finished product in the predetermined area.

The invention is explained in more detail below with reference to the description of the figures. The description of the figures, the claims and the drawings contain features that a person skilled in the art would possibly also consider in a different combination in order to adapt them to corresponding applications of the invention.

They show in schematic representation

Fig. 1a to 1c

Process steps according to the first process variant

Fig. 2a to 2c

Process steps according to the second process variant, and

Fig.3

an exemplary structural component.

In the Figures 1a to 1c The process steps are shown that are carried out in direct hot forming according to a first variant of the process. In Fig. 1a the heating step is shown in which a semi-finished product 17, shown here as a circuit board, is heated. The heating can take place in an oven or with the help of another heat source. The insulation device 15 is already attached at a predetermined position and shields a predetermined area of the circuit board 17. The heat, shown as S-shaped curved arrows, only reaches the circuit board 17 to a lesser extent in this area and heats it in the predetermined area to a lower temperature than in the remaining areas of the circuit board 17.

Fig. 1b shows a forming tool 10 that can be used in presses for hot forming sheet metal blanks into sheet metal components 17. The forming tool 10 has a lower tool half 12u that sits on a base plate 11. The lower forming tool half 12u interacts with an upper forming tool half 12o. The mutually facing active surfaces of the upper forming tool half 12o and the lower forming tool half 12u are designed to correspond so that they function like the die and punch of a press tool. In the Fig. 1b In the example shown, the tool half 12o is designed as a punch and the tool half 12u as a die. Without departing from the scope of the invention, the upper and lower mold halves can be interchanged in terms of their arrangement, so that the upper tool functions as a die and the lower tool as a punch. The upper tool half 12o and the lower tool half 12u are movable relative to each other. The Fig. 1b The mold halves 12o, 12u shown can be moved apart and together again. When the mold halves are moved together, the semi-finished product 17, ie a piece of sheet metal or a sheet metal blank 17, gets between the mold halves and is surrounded by the active surfaces and formed. The Fig. 1b The state shown corresponds to an open position of the tool halves 12u, 12o during a forming process in which the component 17 is completely formed and can be removed from the forming tool 10. In the illustration, the insulating device 15 is removed from the sheet metal blank 17 after heating.

An insert 13 is provided in the lower mold half 12u, in which a cooling system having several cooling channels or cooling lines 14 is integrated. The use of such inserts 13 offers the advantage that different component contours can be embossed with a lower mold 12u, in that the insert 13 can be exchanged according to the desired component shape. The cooling lines 14 run essentially parallel to the surface of the Component 17 and thus also essentially parallel to the effective surface of the mold halves 12u, 12o. The cooling lines 14 thus follow the component surface at a certain distance into the insert 13 of the lower mold half 12u. The cooling channels enable targeted cooling of the semi-finished product 17 in the area of the cooling channels 14, so that the component is hardened and a structure is realized in the component with high mechanical strength.

In Figure 1c is out Fig. 1b known forming tool 10 is shown, however, in a closed position. In this state, the sheet metal part 17 is formed and hardened. Heat is extracted from the component 17 and dissipated via the cooling channels 14.

In the Figures 2a to 2c A second variant of the process is shown. In this variant, the board 17 is completely heated, as shown in the Fig. 2a The insulating device 15 is applied to the board 17 in a predetermined area before the board 17 is introduced into the mold 10, for example on a lower side of the semi-finished product 17, ie the side facing the lower tool half 12u. The board 17 with the insulating device 15 arranged thereon is then introduced into the mold 10, as shown in Figure 2b During forming and hardening, shown in Figure 2c the insulating device 15 influences the heat exchange between the semi-finished product 17 and the tool 10. The area of the semi-finished product 17 in which the insulating device 15 is arranged corresponds to a predetermined area in which high mechanical properties are not desired. Instead, an area with comparatively high ductility is to be created here. Due to the insulating device 15, the semi-finished product 17 experiences slower cooling in the predetermined area than in the other areas. As a result, a pearlitic-ferritic material structure is formed here, which gives the area a higher ductility.

Although the Figures 1a to 2c and 2a to 2c While the invention is described using the direct hot forming method, the invention can also be used in the indirect method. The sheet metal blank is first cold formed into a three-dimensional semi-finished product. This is then heated and then hardened without further forming or, if necessary, with only minor forming. After cold forming, either the first or the second variant as described above can be used, with the insulating device 15 being applied to a predetermined area of the three-dimensional semi-finished product before heating or before hardening.

In the figures, only the lower tool half 12u is provided with cooling channels 14. In further embodiments of the invention, the arrangement of cooling lines can alternatively also be arranged in the upper tool half 12o. In a further alternative embodiment, cooling channels 14 can be provided in both the upper tool half 12o and the lower tool half 12u.

Figure 3 shows a top view of a tool lower part 12u of the mold 10. As an example, a semi-finished product 17 is designed here for producing a B-pillar 18. The semi-finished product 17 is trimmed along the dashed contour in order to obtain the B-pillar 18 as a component. This can be carried out either before or after hot forming. Alternatively, other vehicle components or vehicle structural components can also be produced. These can in particular be A or C pillars, roof side frames, roof bows, sills, longitudinal or cross members.

List of reference symbols

10

Forming tool

11

Tool base plate

12u

Tool base

12o

Tool upper part

13

Tool use

14

Cooling lines

15

Insulation device

16

Component

17

Workpiece

Claims (5)

1. Method for producing a hot-formed component (17), in particular a sheet-metal component of steel, aluminium, magnesium, or of a combination of these materials, the method comprising the following steps:

   - heating a semi-finished product (16), in particular a metal blank or a preformed sheet-metal component,

   - introducing the semi-finished product (16) into a forming tool (10), and

   - cooling the semi-finished product (16) in the forming tool (10), wherein a modification of the material microstructure is carried out at least in a portion,

   wherein

   prior to introducing the semi-finished product (16) into the forming tool (10), an insulating installation (15) which is connected to the semi-finished product (16) in a form-fitting, materially integral, and/or force-fitting manner is applied in at least one predetermined region of the semi-finished product (16),

   characterized in that

   the finished component in the predetermined region has softer, more ductile properties than the remaining regions of the component, and the insulating installation (15)

   - either is configured as a permanent magnet and is connectable to the semi-finished product (16) in a force-fitting manner;

   - or is configured as a foil/film or tape and connected to the semi-finished product in a materially integral manner by way of an adhesion-promoting layer;

   - or is configured as a paste;

   - or is configured as a form-fitting cover coat which is brought to engage with the semi-finished product in the predetermined region.
2. Method according to Claim 1, characterized in that the insulating installation (15) is disposed on the semi-finished product (17) prior to heating.
3. Method according to Claim 1 or 2, characterized in that the insulating installation (15) is disposed on the semi-finished product (17) prior to heating, and is removed from the semi-finished product (17) post heating.
4. Method according to Claim 1 or 2, characterized in that the insulating installation (15) is disposed on the semi-finished product (17) prior to heating, and is left on the semi-finished product post heating of the semi-finished product (17) and during hardening.
5. Method according to Claim 1, characterized in that the insulating installation (15) is disposed on the semi-finished product (17) post heating, and remains on the semi-finished product (17) during hardening.

Images