Three-dimensional, thin-walled automotive structural component

Abstract

Three-dimensional, at least partially thin-walled, motor vehicle structural component with at least one traction machine receiving area (1) and at least two receiving areas (2), wherein the traction machine receiving area (1) is designed to receive an electric drive machine for driving a motor vehicle and wherein such receiving area (2) is designed to fix this motor vehicle structural component to a motor vehicle structure and wherein the traction machine receiving area (1) is connected in one piece to these receiving areas (2) by means of at least one thin-walled support structure (4) and wherein the motor vehicle structural component or at least one such thin-walled support structure (4) has a spatial extension of at least 150 mm along one coordinate axis of an arbitrarily arranged three-dimensional, orthogonal coordinate system and at least 150 mm along another coordinate axis of this coordinate system and at least 50 mm along a third coordinate axis of this coordinate system (5) and wherein said motor vehicle structural component comprises or consists of an aluminum material as a component and wherein the mass of said motor vehicle structural component is 15 kg or more and wherein a maximum wall thickness of such a thin-walled supporting structure (4) is less than 8 mm and wherein the thin-walled motor vehicle structural component has, at least in sections, residual compressive stresses generated by work hardening.

Description

[0001] The invention relates to a three-dimensional, thin-walled automotive structural component. A body structure for a passenger car body is known from DE 10 2022 113 070 B3.

[0002] The invention is described below using a motor vehicle structural component for a battery-electric motor vehicle, so-called BEV; this is not to be understood as a limitation of the invention. In a battery-electric motor vehicle, the energy storage device accounts for a large proportion of the total vehicle weight, which also increases the need to use structural components of the motor vehicle with the lowest possible weight in order not to increase the overall weight of the vehicle too much. It is known from the prior art to manufacture complex motor vehicle structural components, such as the housing of the electric traction motor, from light metal. Therefore, BEVs frequently use cast aluminum components produced by die casting, permanent mold casting, gravity casting, or sand casting. In this sense, aluminum is understood to mean an aluminum alloy suitable for the requirements.

[0003] Aluminum has the advantage, particularly compared to steel, of being easy to handle, inexpensive to procure, and highly recyclable. However, the disadvantages, particularly in the case of large and thin-walled structural components (large in this sense meaning structural components weighing 20 kg or more), are that defects in the structure can occur during the solidification of the aluminum. In the case of these components, which are manufactured using a die-casting process, the structure of the component can be negatively affected by solidification “without pressure” or “under low pressure” in certain areas. Particularly in the case of large and thin-walled components, a sufficiently high pressure cannot be guaranteed across the entire extent of the structural component for the entire casting process, particularly to reliably avoid the problems mentioned above.Such manufacturing results in reduced mechanical properties due to a "loose" microstructure. Automotive structural components are therefore usually assembled as assemblies of several smaller components or designed as "thick-walled" structural components to counteract the lower strength of the structural component by using a larger geometry.

[0004] Against this background, it is an object of the invention to provide a three-dimensional, thin-walled automotive structural component with improved mechanical properties compared to the prior art, and a manufacturing method for producing such a component. This object is achieved by an object according to patent claim 1 and by a method according to patent claim 4.

[0005] In the sense of the invention, a three-dimensional, thin-walled motor vehicle structural component, with at least one traction machine receiving area and at least two receiving areas, is to be understood as a motor vehicle component in which at least one traction motor, in particular an electric drive motor for providing drive power to overcome driving resistances of a motor vehicle, can be accommodated and which can be accommodated on a motor vehicle structure or, when mounted in the motor vehicle, forms part of such a motor vehicle structure.

[0006] This traction machine receiving region of the motor vehicle structural component is designed to receive an electric drive machine for driving a motor vehicle and preferably this traction machine receiving region is also designed to receive a transmission device for transmitting drive power from or to this electric drive machine.

[0007] Such a receiving region of the motor vehicle structural component is designed in particular for securing this motor vehicle structural component to a motor vehicle structure. For the purposes of the invention, a motor vehicle structure is understood to mean a load-bearing body component or a motor vehicle chassis component. Furthermore, this traction machine receiving region is integrally connected to these receiving regions by means of at least one thin-walled support structure. In particular, such a thin-walled support structure differs from this traction machine receiving region or such a receiving region in that it has a smaller wall thickness, and furthermore, such a thin-walled support structure has a spatial extension in an arbitrarily arranged three-dimensional, orthogonal coordinate system which has an extension of at least 150 mm in two directions of this coordinate system and of at least 50 mm in the third direction.Figuratively speaking, the thin-walled supporting structure has a not insignificant size, so that the problem of uneven solidification can arise when the automotive structural component solidifies.

[0008] This motor vehicle structural component has an aluminum material, in particular an aluminum alloy, as one component, and the motor vehicle structural component is preferably made of this aluminum material. As explained, this motor vehicle structural component is a large component with a not inconsiderable mass, which, within the meaning of the invention, is understood to mean a mass of the motor vehicle structural component of 15 kg or more.

[0009] Such a thin-walled motor vehicle structural component furthermore has, at least in sections and preferably in the region of the thin-walled support structure, a low wall thickness, which in the sense of the invention is understood to mean a maximum wall thickness of less than 8 mm, preferably less than 6 mm and more preferably less than 4 mm. The thin-walled support structure is preferably designed as a thin-walled region in this sense. In particular, such a maximum wall thickness is measured in a straight section, in particular of the thin-walled support structure, and in particular not at a curve or a transition between several walls, ribs or the like. Further preferably, the motor vehicle structural component also has at least one thick-walled region; in particular, such a traction machine receiving region or such a receiving region is designed as a thick-walled region.In particular, "thick-walled" within the meaning of the invention means a wall thickness of 10 mm or more. Particularly at transitions from a thick-walled to a thin-walled section of the automotive structural component, structural deficiencies in the microstructure of the aluminum material may occur after casting the automotive structural component.

[0010] It is further proposed that at least one region of the thin-walled motor vehicle structural component exhibit residual compressive stresses generated by systematically introduced strain hardening. In particular, such strain hardening reduces or eliminates structural deficiencies. In particular, systematically introduced strain hardening makes it possible to harden one or more regions of the motor vehicle structural component, thus at least reducing or even completely avoiding the previously explained problems in the manufacture of such components. Furthermore, it is particularly possible to produce large and complex structures with different wall thicknesses, in particular thick-walled and thin-walled regions, as a single-piece cast component.

[0011] In a preferred embodiment, at least one thin-walled support structure is integrally connected to this traction machine receiving area by means of a so-called transition area. This transition area has residual compressive stresses generated at least partially or entirely by work hardening. In particular, such residual compressive stresses give the transition area improved properties compared to a state without residual compressive stresses. In a preferred embodiment of the invention, the motor vehicle structural component has a plurality of thin-walled support structures and a plurality of transition areas.

[0012] In a preferred embodiment, at least one further transition region is provided, wherein such a thin-walled support structure is integrally connected to such a receiving region by means of such a further transition region. This further transition region has compressive residual stresses generated at least partially or completely by work hardening. In particular, due to such compressive residual stresses, the further transition region has improved properties compared to a state without compressive residual stresses; more preferably, the work-hardened microstructure of the motor vehicle structural component is converted from a loosened to a compacted or hardened state by means of this work hardening. In a preferred embodiment of the invention, the motor vehicle structural component has a plurality of receiving regions, a plurality of thin-walled support structures and a plurality of further transition regions.

[0013] Furthermore, a method for producing a three-dimensional, at least partially thin-walled, motor vehicle structural component, which comprises or consists of an aluminum material as one component, is proposed. In particular, the thin-walled motor vehicle structural component is designed according to one of the previously explained embodiments. Preferably, the motor vehicle structural component is produced using an aluminum casting process; in particular, the proposed manufacturing method thus comprises at least one aluminum casting process step.Furthermore, after casting, the motor vehicle structural component is partially re-compacted using a mechanical compaction process by at least one mechanical compaction process step, wherein in the sense of this invention and such re-compaction is to be understood as the planned application of a mechanical load resulting in residual compressive stresses, at least in one region of this motor vehicle structural component.

[0014] In contrast to prior art manufacturing, in which a complex vehicle support structure is assembled from multiple individual parts, the proposed process combines a support structure normally consisting of multiple individual parts into a single component, the so-called vehicle structural component. Areas with weak spots that inevitably occur during the casting process, particularly those with defects, are subsequently compacted and thus strengthened in a subsequent process step. In particular, the two-stage production of the vehicle structural component makes it possible to manufacture large components with partially thin-walled sections as a single, high-strength component made of light metal.

[0015] In a preferred embodiment, the method for at least partially recompacting the motor vehicle structural component is selected from a group of mechanical compaction methods which - rolling, - knurling, - Needles and - Squeezing includes.

[0016] For the purposes of the invention, squeezing is understood to be a process for mechanical recompaction. This recompaction occurs at a time when the metallic casting material is no longer completely liquid after introduction, but is semi-crystalline and still has a viscosity that allows local redistribution of the metallic casting material by applying pressure. During recompaction, a compression punch (squeeze pin) is pressed into the semi-crystalline aluminum material of the automotive structural component at a non-critical area of the automotive structural component in order to locally apply pressure to the automotive structural component. This pressure propagates through its aluminum material, thereby reducing the size of cavities in the area of the defects and preferably closing pores.

[0017] For the purposes of the invention, rolling is understood to be a mechanical densification process in which at least one roller processes the motor vehicle structural component, or at least a region of this component with lower strength, under pressure. If the pressure applied by the at least one roller exceeds the yield point of the aluminum material in the processed region of the motor vehicle structural component, the resulting cold deformation deforms and thereby strengthens the structure of the motor vehicle structural component in this region. Furthermore, knurling is preferably at least similar to rolling.

[0018] In the sense of the invention, needling is understood to mean a method in which a needling tool with at least one needle applies pressure to at least one area of the motor vehicle structural component, so that the structure of the motor vehicle structural component is compacted in this area.

[0019] In particular, the aforementioned methods for mechanically re-compacting at least one region of the motor vehicle structural component have proven to be particularly efficient methods for this process step.

[0020] In a further preferred embodiment of the manufacturing method, it comprises a heat treatment step. For the purposes of the invention, a heat treatment step is understood to mean at least one targeted heating and preferably targeted cooling of at least one region of the thin-walled motor vehicle structural component. Furthermore, such a heat treatment step is provided at least before or after the mechanical compaction process, or more preferably before and after the mechanical compaction process. In particular, the properties of the motor vehicle structural component can be further influenced by means of a heat treatment step.

[0021] In the following, individual features and developments of the invention are explained in more detail with reference to the figures. Combinations of features other than those shown are also possible in principle. It shows: Fig. 1: a highly schematic, three-dimensional, at least partially thin-walled automotive structural component Fig. 2: a schematic flow of the proposed method for manufacturing a three-dimensional automotive structural component.

[0022] In Fig. 1 shows a three-dimensional, partially thin-walled motor vehicle structural component with a traction machine receiving area 1 and at least four receiving areas 2 in a 2D representation. The traction machine receiving area 1 is designed to accommodate an electric traction machine, which is provided for driving a motor vehicle. The receiving areas 2 are designed to secure this motor vehicle structural component to a motor vehicle structure (not shown). The traction machine receiving area 1 has a thick-walled section 3 and is integrally connected to these receiving areas 2 by means of a respective thin-walled support structure 4.The motor vehicle structural component, or rather its thin-walled supporting structure, has a spatial extension of more than 150 mm in two directions of the orthogonal coordinate system 5 and an extension of more than 50 mm in the third spatial direction, i.e., in each case in the direction of the coordinate axes of this coordinate system 5. Furthermore, the motor vehicle structural component has an aluminum material as one component, and the mass of this motor vehicle structural component is more than 15 kg despite the fact that it is made of light metal. In the area of the thin-walled supporting structure, the motor vehicle structural component has a maximum wall thickness of less than 8 mm.In the transition area from the thin-walled support structure 4 to the traction machine mounting area 1, in particular to its thick-walled section 3, i.e., in the so-called transition area 6, defects in the material, so-called blowholes and / or pores, can arise during the cooling of the liquid aluminum material. The automotive structural component has been work-hardened in the transition area 6 using a mechanical compaction process, thus generating residual compressive stresses at least there. The mechanical hardening reduces or eliminates the initially present blowholes or pores, thus making it possible to design the automotive structural component as a single-piece component.

[0023] The disadvantages resulting from the size and weight of the automotive structural component, particularly when it is designed as a traction machine housing for a motor vehicle, have a limiting effect. The aforementioned design with thin-walled sections can result in structural deficiencies such as fine porosities in the transition areas from thick-walled to thin-walled, which have a negative impact on mechanical parameters such as fatigue strength but also on corrosion requirements. It is known from the prior art that such deficiencies can be reduced or avoided through casting technology. Such measures include, for example, a very "clean" casting melt (very low density index), or complex local post-feeding (particularly a local increase in the solidification pressure), or the design of appropriate post-feed paths, in particular to maintain directional solidification until the end.This results in disadvantages for lightweight construction, as such thin walls must be "thicker" compared to a component without such problems. This ultimately leads to a more expensive component, particularly in terms of increased cycle time, increased costs, increased weight, etc. To put it simply, a component not designed according to the invention is "oversized" because either the wall thickness is increased at an immediately critical point to increase safety, or the wall thickness is increased at another point to improve solidification at the immediately critical point.

[0024] The invention counteracts these problems of “over-dimensioning” by locally densifying the structure, in particular by means of local rolling, local knurling, local needling or local squeezing or re-squeezing, which is carried out in a cause- or load-oriented manner.

[0025] In a motor vehicle structural component designed to accommodate a traction machine, for example, fine porosity in the structure occurs in area 9 of a connector (high-voltage connector 8). Fine porosity is defined as a pore size of 0.1-1.5 mm or 0.1-0.4 mm in pore diameter. Such fine porosity has a negative impact on properties such as corrosion resistance and fatigue strength. Local re-rolling of external geometries, such as in area 9, or of contact surfaces: a) Fine porosity eliminated, b) improves the surface quality and c) the fatigue strength is increased by introducing compressive stresses.

[0026] This mechanical process is carried out after heat treatment of the automotive structural component, but can also take place before this.

[0027] In Fig.2 is a schematic flow chart of a proposed method for producing a three-dimensional, at least partially thin-walled motor vehicle structural component which has or consists of an aluminum material as one component.

[0028] In the first step, the motor vehicle structural component is manufactured using an aluminum casting process 101 and, after casting, this motor vehicle structural component is further compacted in a second step, at least in some areas, using a mechanical compaction process 102, thus introducing residual compressive stresses into this motor vehicle structural component and at least reducing structural deficiencies. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2022 113 070 B3

[0001]

Claims

[1] Three-dimensional, at least partially thin-walled, motor vehicle structural component with at least one traction machine receiving area (1) and at least two receiving areas (2), wherein the traction machine receiving area (1) is designed to receive an electric drive machine for driving a motor vehicle and wherein such receiving area (2) is designed to fix this motor vehicle structural component to a motor vehicle structure and wherein the traction machine receiving area (1) is connected in one piece to these receiving areas (2) by means of at least one thin-walled support structure (4) and wherein the motor vehicle structural component or at least one such thin-walled support structure (4) has a spatial extension of at least 150 mm along one coordinate axis of an arbitrarily arranged three-dimensional, orthogonal coordinate system and at least 150 mm along another coordinate axis of this coordinate system and at least 50 mm along a third coordinate axis of this coordinate system (5) and wherein said motor vehicle structural component comprises or consists of an aluminum material as a component and wherein the mass of said motor vehicle structural component is 15 kg or more and wherein a maximum wall thickness of such a thin-walled supporting structure (4) is less than 8 mm and wherein the thin-walled motor vehicle structural component has, at least in sections, residual compressive stresses generated by work hardening. [2] Three-dimensional, thin-walled automotive structural component according to claim 1, characterized by that a transition region (6) from such a thin-walled support structure (4) to this traction machine receiving region (1) has residual compressive stresses generated at least in some regions by work hardening. [3] Three-dimensional, thin-walled motor vehicle structural component according to one of the preceding claims, characterized by that a further transition region (10) from such a thin-walled support structure (4) to at least one such receiving region (2) has residual compressive stresses generated at least in regions by work hardening. [4] Method for producing a three-dimensional, thin-walled motor vehicle structural component from an aluminum material, wherein the motor vehicle structural component is produced by an aluminum casting process (101) and wherein after the casting of the motor vehicle structural component, this component is at least partially re-compacted using a mechanical compaction process (102) and whereby residual compressive stresses are introduced into this automotive structural component. [5] Method according to claim 4, characterized by that this mechanical compaction process is selected from a group of processes which - rolling, - knurling, - needles, - Squeezing includes. [6] Method according to one of the preceding claims, characterized by that the thin-walled motor vehicle structural component is subjected to a heat treatment process at least in part or entirely before or after the mechanical compaction process.

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