Method and device for producing shaped sheet metal parts at a low temperature

Abstract

The invention relates to a method for producing a shaped sheet-metal part from a panel or a semifinished part made of a material consisting of steel with at least 60 wt. % Fe and a residual austenite content of at least 5%, in which the panel or the semifinished part is at least partially cooled to a temperature below 20 C. before the shaping and is shaped at a temperature below 20 C. in a forming tool. The object of providing a method for producing load-compliantly configured components, which on the one hand permits industrial-scale use of low-temperature forming and is configured particularly simply, is achieved by reducing the material temperature of the panel or semifinished part to below 20 C. is carried out in a thermally regulated cooling apparatus.

Claims

1. A method for producing a shaped sheet-metal part from a panel or a semifinished part made of a material comprising of steel with at least 60 wt. % Fe and a residual austenite content of at least 5%, comprising a cooling step in which the panel or the semifinished part is at least partially cooled to a temperature below 20 C. prior to a shaping step and comprising a shaping step in which the panel or the semifinished part is shaped at said temperature below 20 C. in a forming tool, wherein reduction of the material temperature of the panel or the semifinished part to below 20 C. is carried out in a thermally regulated cooling apparatus.

2. The method according to claim 1, wherein the panel or the semifinished part is removed from the cooling apparatus and delivered to the forming tool immediately before the shaping process.

3. The method according to claim 1, wherein the forming tool, in which the panel or the semifinished part is cooled and subsequently shaped, is used as the cooling apparatus.

4. The method according to claim 3, wherein icing of the forming tool, and the panel and/or the semifinished part, is prevented by using deicing means before and during the shaping.

5. The method according to claim 1, wherein the panel or a semifinished part comprises a surface coating.

6. The method according to claim 5, wherein the surface coating contains zinc.

7. The method according to claim 1, the method further comprising producing a structural part from the sheet metal part such that it has regions with different strengths and incorporating the structural part into a motor vehicle.

8. The method according to claim 7, wherein the structural part comprises a pillar, support, large-area component, base plate, tunnel, end wall or wheel well of a motor vehicle.

9. The method according to claim 7, wherein the structural part comprises a B-pillar of a motor vehicle, at least one region of the roof connection of the B-pillar having a higher strength than the region of the B-pillar base.

10. The method according to claim 7, wherein the structural part comprises a longitudinal beam in the front region of a motor vehicle, and the longitudinal beam comprises a front region which has a lower strength than the rear region.

11. A method for producing a shaped sheet-metal part from a panel or a semifinished part made of a material comprising of steel with at least 60 wt. % Fe and a residual austenite content of at least 5%, comprising a cooling step in which the panel or the semifinished part is at least partially cooled to a temperature below 20 C. prior to a shaping step and comprising a shaping step in which the panel or the semifinished part is shaped at said temperature below 20 C. in a forming tool, wherein reduction of the material temperature of the panel or the semifinished part to below 20 C. is carried out in a thermally regulated cooling apparatus; wherein the forming tool, in which the panel or the semifinished part is cooled and subsequently shaped, is used as the cooling apparatus; and wherein the forming tool thermally regulates the panel to be shaped, or the semifinished part to be shaped, only in the regions in which a high yield point and tensile strength are required.

12. The method according to claim 11, wherein the wall thickness of the panel or of the semifinished part is from 0.5 mm to 1.80 mm.

13. The method according to claim 11, wherein the wall thickness of the panel or of the semifinished part is from 0.7 mm to 1.20 mm.

14. A method for producing a shaped sheet-metal part from a panel or a semifinished part made of a material comprising of steel with at least 60 wt. % Fe and a residual austenite content of at least 5%, comprising a cooling step in which the panel or the semifinished part is at least partially cooled to a temperature below 20 C. prior to a shaping step and comprising a shaping step in which the panel or the semifinished part is shaped at said temperature below 20 C. in a forming tool, wherein reduction of the material temperature of the panel or the semifinished part to below 20 C. is carried out in a thermally regulated cooling apparatus; wherein the forming tool, in which the panel or the semifinished part is cooled and subsequently shaped, is used as the cooling apparatus; and wherein icing is prevented by using mechanical deicing means and/or by using a protective gas to produce a protective gas atmosphere on the cooled regions.

15. The method according to claim 14, wherein the wall thickness of the panel or of the semifinished part is from 0.5 mm to 1.80 mm.

16. The method according to claim 14, wherein the wall thickness of the panel or of the semifinished part is from 0.7 mm to 1.20 mm.

17. A method for producing a shaped sheet-metal part from a panel or a semifinished part made of a material comprising of steel with at least 60 wt. % Fe and a residual austenite content of at least 5%, comprising a cooling step in which the panel or the semifinished part is at least partially cooled to a temperature below 20 C. prior to a shaping step and comprising a shaping step in which the panel or the semifinished part is shaped at said temperature below 20 C. in a forming tool, wherein reduction of the material temperature of the panel or the semifinished part to below 20 C. is carried out in a thermally regulated cooling apparatus; wherein the forming tool, in which the panel or the semifinished part is cooled and subsequently shaped, is used as the cooling apparatus; and wherein the cooling of the forming tool, the panel and/or the semifinished part is carried out using a protective gas, the protective gas preferably flowing through flow channels provided in the forming tool.

18. The method according to claim 17, wherein the wall thickness of the panel or of the semifinished part is from 0.5 mm to 1.80 mm.

19. The method according to claim 17, wherein the wall thickness of the panel or of the semifinished part is from 0.7 mm to 1.20 mm.

20. A method for producing a shaped sheet-metal part from a panel or a semifinished part made of a material comprising of steel with at least 60 wt. % Fe and a residual austenite content of at least 5%, comprising a cooling step in which the panel or the semifinished part is at least partially cooled to a temperature below 20 C. prior to a shaping step and comprising a shaping step in which the panel or the semifinished part is shaped at said temperature below 20 C. in a forming tool, wherein reduction of the material temperature of the panel or the semifinished part to below 20 C. is carried out in a thermally regulated cooling apparatus; wherein the forming tool, in which the panel or the semifinished part is cooled and subsequently shaped, is used as the cooling apparatus; and wherein the wall thickness of the panel or of the semifinished part is from 0.7 mm to 1.20 mm.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will be explained in more detail below with the aid of exemplary embodiments in connection with the drawings.

(2) FIG. 1 shows an outline diagram of one exemplary embodiment of the method for producing a shaped sheet-metal part.

(3) FIG. 2 is an alternative embodiment of the method represented in FIG. 1.

(4) FIGS. 3a) and 3b) show one exemplary embodiment of a forming tool for carrying out the method.

(5) FIG. 4 is another exemplary embodiment of a forming tool for carrying out the method for producing a shaped sheet-metal part.

(6) FIGS. 5, 6 and 7 show exemplary embodiments of advantageous uses of a correspondingly produced sheet-metal part.

DETAILED DESCRIPTION OF THE INVENTION

(7) FIG. 1 first shows an outline diagram of the method for producing a shaped sheet-metal part, in which a panel 1 is intended to be shaped in a forming tool 2. The forming tool 2 is represented as a simple deep-drawing tool. However, the forming tool 2 represents any forming tools, such as are used for the production of shaped sheet-metal parts from flat panels or already preshaped or cut semifinished parts. The panel 1 consists of a steel containing at least 60 wt. % Fe and a residual austenite content of at least 5%. Typical examples of these steel types are, for example, high-manganese steels or alternatively TRIP steels. In the case of these steels, particularly the residual austenite steels (TRIP steels), it is observed that during shaping at very low temperatures austenitic regions are partially converted into a martensitic structure, and a further yield point and strength increase is therefore achieved in addition to the work hardening. It has been found that this effect increases significantly at temperatures lowered further, so that the strengthening process, which also represents a so-called TRIP effect in addition to the conventional work-hardening effect, can lead to very high yield points and tensile strengths. With a RA-K 40/70 steel (TRIP steel), for example, the yield point can be increased from 410 MPa to more than 800 MPa. In the exemplary embodiment of the method as represented in FIG. 1, the panel 1 is first cooled in a cooling apparatus 3 to a temperature below 20 C., preferably a temperature of from 40 C. to 190 C. To this end, refrigerants, for example liquid nitrogen, dry ice or liquid oxygen, may be used in the cooling apparatus without entailing a safety risk for operating personnel of the device. The thermally regulated cooling apparatus may for example comprise closed circuits of the correspondingly cold refrigerants, which transfer the cold for example by direct metal contact to the panel or the semifinished part. Once the panel, which has a wall thickness of preferably from 0.5 mm to 1.8 mm, particularly preferably from 0.70 mm to 1.20 mm, has reached the shaping temperature, it is removed from the cooling apparatus shortly before the shaping process and delivered to the forming tool. The shaping is then carried out immediately, so that the temperature rise due to removal from the cooling apparatus is limited. Preferably, the forming tool 2 itself may also be thermally regulated, so that a significant temperature rise of the panel in the forming tool is prevented.

(8) As can be seen from FIG. 1, the cooling apparatus 3 provides discontinuous operation of the cooling of the panel 1. In contrast thereto, the cooling apparatus 3 represented in FIG. 2 allows continuous passage of the panel 1 or the semifinished part 1 through the cooling apparatus 3, so that the panel 1 or the semifinished part 1 is brought to the shaping temperature at the exit of the cooling apparatus 3. The panel 1 or the semifinished part 1 is then placed in the forming tool 2 immediately after leaving the cooling apparatus 3, and is shaped. As already mentioned above, the forming tool 2 is represented here merely generically as a deep-drawing tool. In principle, AHU/IHU [external high-pressure/internal high-pressure] forming tools and any other forming tools, which cause shaping and therefore strengthening in the sheet-metal part, are also suitable.

(9) One optional configuration of the forming tool is represented in the schematic perspective view in FIGS. 3a), b). The forming tool 4 represented in FIG. 3a) comprises an upper forming tool half 4a, arranged in which there are flow channels 5 that generate a cooled region 6 of the panel, which is then shaped at low temperature. To this end a refrigerant, for example liquid nitrogen or liquid oxygen, or alternatively carbon dioxide cooled to low temperature, flows through the flow channels and thereby cools the panel strongly in this region.

(10) During the shaping, very much greater strengthening by the TRIP effect takes place in the highly cooled regions than in uncooled regions, so that the sheet-metal part 7 produced comprises a region 7a which has much higher yield points and tensile strengths owing to the strong TRIP effect.

(11) In order to prevent icing of the forming tool of FIG. 3a), it is advantageous that when the tool is opened, the upper tool half 4a, which comprises the flow channels and is therefore particularly cold, also carries the refrigerant through the flow channels while the tool is being opened. In this way, icing of the tool surfaces is prevented because a protective gas atmosphere 8 is formed in the region of the strongly cooled surfaces of the forming tool.

(12) FIG. 4 in turn represents one exemplary embodiment of a forming tool, which comprises a closed circuit for the refrigerant. To this end, the schematically represented forming tool 9 comprises refrigerant channels 10 in the region of the stamp or die, through which a refrigerant regulated to a correspondingly low temperature flows. The panel 1, which is arranged between the two halves of the forming tool 9 and has flat contact therewith, is cooled very strongly in the region of the surfaces in contact with the cooled stamp, and is brought to a shaping temperature below 20 C. If there are possibly regions which are not meant to be brought to the corresponding temperature, means that additionally allow local heating of the panel 1 are provided in the stamp 11. These means may, for example, be configured as a heating cartridge or similar means releasing heat. Means for mechanical deicing are furthermore provided on the forming tool 9, and are represented schematically. The mechanical deicing means 12 consists of a holder for receiving a scraper 12a, which for example cleans the surface of the stamp 9 when the forming tool 9 is opened. It is also conceivable to use brushes instead of the scraper 12a. The forming tool 9 represented may in any event cool an inserted panel 1 to the shaping temperature below 20 C. in a relatively short time owing to the large-area contact, and therefore provide a simple and economical production process.

(13) FIGS. 5, 6 and 7 show typical exemplary embodiments of advantageous uses of the shaped sheet-metal part 1. In FIG. 5, by way of example, the use of the sheet-metal part as a B-pillar 13 of a motor vehicle 14 is represented schematically. The B-pillar 13 should preferably comprise a roof connection region 13b provided with a high yield point and tensile strength, and a pillar base 13a provided with a lower strength but with a greater elongation at break. With the method according to the invention, this B-pillar can be produced economically by the upper region of the B-pillar 13 being strongly cooled in the forming tool and subsequently shaped. In this way, a higher yield point and tensile strength are imparted to the upper region compared with the pillar base 13a. The same also applies in principle for the other pillars, the A-pillar 15 represented and the C-pillar 16.

(14) FIG. 6 shows two longitudinal beams of a motor vehicle bodywork, which comprise two different functions in one component. The longitudinal beam 17 is used on the one hand, in the event of impact, first to absorb the impact energy and deform at least partially, and on the other hand to protect the passenger compartment located in the rear region against further deformation. To this end, the longitudinal beams 17 are conventionally configured in such a way that the front region is more easily deformable and the rear region is formed as rigidly as possible. With the method according to the invention, it is now possible to produce a longitudinal beam 17 in such a way that its front region 17a has a lower strength than the rear region 17b, the rear region of the longitudinal beam 17b being strongly cooled in the forming tool. The effect achieved by this is that the yield points and the tensile strengths of the two regions differ significantly. In the part of the longitudinal beam 17 provided with a higher yield point, for example, as likewise in the other uses above, a yield point of more than 800 MPa is provided so that this region is formed particularly solidly. The region 17a, on the other hand, is formed softly in the same process, as this region of the forming tool is not thermally regulated. The use of possible tailored blanks, which require additional working step in order to provide a similar strength profile, can therefore be avoided.

(15) Lastly, FIG. 7 shows an example of an end wall 18, which is also preferably produced by the method according to the invention. The end wall 18 generally has a large area and has a relatively small thickness. Individual connection regions 19 are formed for example with a higher yield point and tensile strength, so that no reinforcements in the form of patches, tailored blanks or separate components are any longer necessary. Furthermore, the effects achievable by controlled thermal regulation of the forming tool are not only that specific regions of the end wall 18 exhibit significantly different deformation behaviour in the event of an impact, but also that local regions, which are used to accommodate equipment, for example brake boosters, air conditioning, etc., are provided with corresponding yield points and tensile strengths so that the end wall 18 can be configured load-compliantly without additional measures.

(16) In the typical uses of the sheet-metal part shaped according to the invention, as represented in FIGS. 5 to 7, it is readily possible in particular to provide cathodic corrosion protection on the basis of a surface coating containing zinc and/or an organic surface coating, since hot forming can be avoided.