Method for producing motor vehicle components by thermoforming, hot cutting and press hardening

Abstract

The invention relates to a method for producing motor vehicle components by means of hot forming, hot cutting and press hardening: providing a blank (6) made of a particularly hardenable steel sheet alloy, heating completely to a temperature greater than Ac1, in particular greater than Ac3, inserting into a combined forming and cutting die, fixing the inserted blank (6) in the forming and cutting die by means of a punch arranged in the inner region of the die, at least partially carrying out a circumferential edge trimming (10) before the start of the forming or during a period of up to 50% of the forming process and / or during at least 20%, preferably more than 30%, of the press stroke before the bottom dead point, carrying out the hot forming by means of one press stroke, and carrying out the edge trimming (10) and optionally the press hardening.

Description

Technical Field

[0001] This invention relates to a method for producing motor vehicle components by thermoforming, hot cutting, and stamping hardening. Background Technology

[0002] Methods for hot forming of sheet metal blanks are well known in the prior art. In particular, hot forming and stamping hardening are known. For this purpose, a sheet metal blank made of a hardenable steel alloy is heated to a temperature above Ac1 or Ac3. The blank heated in this way is then placed in a forming die and formed while hot. Then, in a direct hot forming process, the forming die is closed and rapidly cooled, thereby hardening the formed blank. According to the prior art, tensile strengths exceeding 1400 MPa can be easily achieved here. A notable aspect is that the hardened material structure can only be reworked mechanically, which incurs significant costs. For example, this increased cost includes edge trimming. Edge trimming is typically performed after the forming process to achieve particularly high component precision. Therefore, the outer contour precision of the component is exceptionally accurate. However, the problem is that the hardened blank can only be used under conditions of extensive design work and high abrasive wear on the die. Laser cutting also leads to higher manufacturing or production costs for the component. Cold trimming of hardened components is not recommended due to the risk of (micro)cracks.

[0003] When billets have different wall thicknesses, especially for example, welded billets (TWB), billets welded together from different wall thicknesses or steel alloys, edge trimming issues can be exacerbated as another characteristic. Weld protrusions beyond the billet edge contour, weld collapses (inward recesses), or billet misalignment between two interconnecting billets are all problematic and typically require re-trimming after the TWB is welded together. Summary of the Invention

[0004] This invention is achieved through a method of producing motor vehicle components by thermoforming, hot cutting, and stamping hardening.

[0005] The method according to the invention is used to manufacture motor vehicle components. Motor vehicle components may be, for example, a B-pillar, typically a pillar, sleeve, bumper, or bumper support, etc. In particular, reinforcing members with a cross-section at least partially U-shaped and without flanges can also be manufactured, for example, as insert members or patches, to reinforce the aforementioned components on the inner or outer side and form a partial double-sheet layer. They are manufactured by thermoforming and hot cutting, and optionally by stamping hardening in a combination die. All of this is performed in a single stamping stroke.

[0006] The method of the present invention comprises the following steps:

[0007] Provide blanks made of a special hardenable steel plate alloy;

[0008] Heat completely to a temperature greater than Ac1, especially greater than Ac3;

[0009] Insert the molding and cutting molds for the assembly;

[0010] The inserted blank is fixed in the forming and cutting die by punches arranged in the internal area of ​​the die;

[0011] At least partially, circumferential edge trimming is performed before the start of forming or during up to 50% of the forming process and / or during at least 20%, preferably more than 30%, of the stamping stroke before the bottom dead center.

[0012] Thermoforming is performed in a single stamping stroke, followed by edge trimming and stamping hardening.

[0013] According to the present invention, the method is characterized in that the blank is inserted before the forming begins or in the early stage of forming, and the trimming is completed during this period.

[0014] During trimming, there is only vertical cutting motion. The cutting die itself is driven solely by the stamping stroke. There is no other dedicated active drive device for the cutting die. There is also no wedge-shaped cross slide. No trimming occurs in the horizontal direction.

[0015] These measures according to the invention enable the production of components with C-shaped or cap-shaped cross-sections requiring high tolerances. Furthermore, components can be manufactured, particularly from welded blanks or blanks with different regions having varying wall thicknesses. In particular, re-trimming as a tolerance trimming is unnecessary. There is also no insertion tolerance compared to separate pre-insertion thermoforming dies and pre-performed pure blank trimming.

[0016] In addition, it is possible to produce formed components with U-shaped or C-shaped cross sections, thus enabling the production of flangeless components that cannot be cut after the forming process is completed or can only be cut in stamping at high cost due to the vertical orientation of the U-shaped or C-shaped legs.

[0017] Specifically, the method specifies placing the billet into the thermoforming mold at a temperature greater than 500°C, particularly greater than 550°C. The billet can also preferably be placed into the thermoforming mold at a temperature higher than AC1 or higher than AC3. Depending on the steel alloy used, the AC1 temperature exceeds 700°C, and the AC3 temperature exceeds 900°C.

[0018] To secure the blank in place, a guide stamp (vorauseilender stempel) is specifically arranged on the upper die. The blank, placed into the thermoforming die, is specifically positioned on the lower die block. The stamp is then lowered onto the blank, clamping it between the stamp and the lower die block to secure it in place. The hot cutting process then takes place. This can be completed before the actual forming process begins.

[0019] The hot cutting process is specifically performed as at least part, particularly the complete circumferential edge trimming of the blank. For this purpose, a cutting die with an outer circumferential running edge is set on the actual thermoforming die. Edge trimming can also be performed entirely in such a manner that: first, it is partially trimmed around the blank, particularly before the blank is heated. Then, the remaining edge trimming is performed during hot cutting in a local forming die, thus achieving a complete circumferential edge trimming overall. Specifically, subsequent edge trimming is no longer required. Specifically, laser or hard cutting is also unnecessary.

[0020] The cutting die can be arranged completely relative to the upper and lower dies. However, the cutting die can also be integrated into the upper and / or lower dies, and thus into the upper die block and / or lower die block.

[0021] As an alternative to complete edge trimming before the forming process begins, edge trimming can also be performed at the first moment or in the first stage of the forming process. In particular, edge trimming is performed when the blank itself is still completely flat, level, or has a low degree of deformation. This is especially true during periods when the forming progress is less than 50%, particularly less than 30%, and particularly less than 20%.

[0022] Alternatively or additionally, this time period can also be related to the total stamping stroke of the upper and lower dies relative to each other. Specifically, before reaching the bottom dead center, the cutting process has begun and ended at least 20%, preferably greater than 30%, and particularly greater than 50% of the stamping stroke, meaning the forming die is fully closed. In the case of 50%, this means that when the upper die descends onto the lower die, based on the entire stamping stroke, edge trimming has been completed by a maximum of 50%, particularly before the stamping stroke reaches the bottom dead center of the forming die.

[0023] After edge trimming, a thermoforming process is then performed or completed, followed by optional stamping hardening, especially if a hardenable steel alloy is used.

[0024] Edge trimming completely cuts off the blank, especially its wall thickness.

[0025] Specifically, edge trimming is performed at temperatures between 550°C and 700°C. According to the invention, at this temperature, an optimal value exists between the cutting capability of the steel and the abrasive wear on the cutting die, depending on the steel alloy used, and particularly an optimal value also exists in the material structure provided on the cutting edge.

[0026] If edge trimming is performed, the trimmed blank to be formed is specifically drawn into the interior of the resulting mold cavity. Any bent legs of the resulting motor vehicle component or formed component may then extend in a vertically oriented manner, making vertical trimming impossible.

[0027] According to the present invention, this is achieved by guiding edge trimming in the horizontal state of the blank.

[0028] Specifically, edge trimming of at least 20 mm, preferably greater than 30 mm, particularly greater than 50 mm, very particularly preferably greater than 80 mm, and particularly greater than 100 mm is completed before the thermoforming die reaches the bottom dead center.

[0029] In this intellectual property protection process, the terms "thermal forming mold" and "thermal cutting mold" are also used to refer to forming and cutting molds. Attached Figure Description

[0030] Further advantages, features, characteristics, and aspects of the invention are the subject of the following description. These contribute to a more readily understood understanding of the invention. Preferred embodiments and variations are illustrated in the schematic diagrams. In the drawings:

[0031] Figures 1a to 1c A forming and cutting die according to the present invention is shown;

[0032] Figures 2a to 2c It shows Figures 1a to 1c Variations;

[0033] Figures 3a to 3d The production of motor vehicle component 13, which is a hat-shaped component, is shown;

[0034] Figure 4a and Figure 4b Two precast blank areas are shown.

[0035] In the accompanying drawings, the same reference numerals are used for the same and similar components, even though they are not listed again for the sake of simplicity. Detailed Implementation

[0036] Figure 1a , 1b Figure 1c shows a forming and cutting die 1 according to the invention. For this purpose, the forming and cutting die 1 has an upper die 2 and a lower die 3. A guide die 4 is arranged in the upper die 2 itself, which clamps the blank 6 placed on the lower die block 5 of the lower die 3 onto the lower die block. The guide die 4 has previously been lowered. The blank 6 is thus fixed in place and can no longer be displaced, particularly in the horizontal direction H. Corresponding opposing cutting edges 9 are now arranged on the upper die block 7, which is part of the upper die 2, and on the sheet metal holder 8, which is part of the lower die 3.

[0037] By further reducing the upper mold block 5, such as Figure 1b As shown, edge trimming 10 is performed. Edge trimming 10 here corresponds to the subsequent outer peripheral component edge 11, as... Figure 1c As shown.

[0038] exist Figure 1b At this point in time, the forming process itself has not yet begun. However, edge trimming 10 has already been completed. By further lowering the upper mold block 7, the sheet metal holder 8 is lowered relative to the lower mold block 5. According to... Figure 1c The forming process then takes place in the formed mold cavity 12. The forming process is shown as complete and produces a U-shaped, flangeless motor vehicle component 13 in cross-section at least along its length. The motor vehicle component 13 is produced from a blank 6 to be formed. For this purpose, the blank 6 has been drawn into the internal space of the forming mold or the internal space of the mold cavity 12.

[0039] exist Figure 1a Cooling channel 19 can be seen, which is configured to cool all die components in contact with the forming blank for stamping hardening. Cooling channel 19 is located in other... Figures 1b-3c It is not shown in the diagram, but it is always set on the mold.

[0040] Figures 2a to 2c It shows Figure 1a The variation to c. Here, edge trimming 10 is also done entirely before forming begins. However, with Figure 1c The difference is that, instead of producing motor vehicle components 13 with a U-shaped cross-section, we produce components with a U-shaped cross-section according to... Figure 2c The vehicle component 13 has a hat-shaped cross-section. The flange 14 protrudes outward along the horizontal direction H. For this purpose, the sheet metal retainer 8 is specially constructed to be wider and is also used to form the mold cavity 12 when the upper mold 2 is fully lowered to the bottom dead center.

[0041] Figures 3a to 3d It shows something similar to Figure 2c The production of motor vehicle component 13 as a hat-shaped component. However, here, edge trimming 10 is performed at a later time, so it must be performed approximately at a time when at least 20 mm must still be covered before reaching the bottom dead center of the forming die in the stamping stroke direction 15. Here, also according to Figure 3b The inserted blank 6 is fixed in place on the lower die block by the guide die 4. However, according to Figure 3b The forming process has begun. Then, the cutting mold or the corresponding cutting edge 9 is used to perform the cutting according to... Figure 3cThe cutting operation. Here, for example, the forming process has been completed by about 20%, or the forming die has descended about 20% of the path to be covered in the stamping stroke in the stamping stroke direction 15. However, the edge trimming 10 is now completely completed, thus according to Figure 3d As the upper die block is further lowered and the lower plate retainer 8 is formed, the motor vehicle component 13 with a flange 14 protruding outward in the horizontal direction H is manufactured in the die cavity 12.

[0042] Figure 4 again shows two precast billet blanks. Figure 4a In this case, the blanks are welded together. There are two blank regions 6a and 6b with different wall thicknesses. Blank regions 6a and 6b are offset from each other by 16. This offset 16 can be ignored due to the circumferential edge trimming 10, because during the process according to the method of the invention… Figure 4a There is no more detailed setting for recutting the circumferential edge, and no need for final edge trimming 10 or similar process.

[0043] exist Figure 4b In this case, billet 6 is also shown as a welded billet. The weld 17 connecting the two billet regions 6a and 6b has a laterally protruding weld protrusion 18. In the case of circumferential edge trimming 10, this weld protrusion 18 is also removed.

[0044] List of reference numerals

[0045] 1- Molding and cutting molds

[0046] 2-Upper mold

[0047] 3-Lower mold

[0048] 4-Punching Die

[0049] 5-Lower mold block

[0050] 6-Bill

[0051] 7-Upper mold block

[0052] 8-Sheet metal retainer

[0053] 9-Cutting Blade

[0054] 10- Trimming

[0055] 11-Component edges

[0056] 12-Mold cavity

[0057] 13-Motor Vehicle Components

[0058] 14-Flange

[0059] 15 - Stamping stroke direction

[0060] 16-Offset

[0061] 17-Welding

[0062] 18-Weld protrusion

[0063] 19-Cooling Channel

[0064] 6a-Bill Area

[0065] 6b-Bill area

[0066] H - Horizontal direction

Claims

1. A method for producing motor vehicle components (13) by thermoforming, hot cutting and stamping hardening: Provide a billet made of a hardenable steel sheet alloy (6); Heat completely to a temperature greater than Ac1; Insert a molding and cutting mold (1) having an upper mold (2) and a lower mold (3), which reaches the lower dead point when the upper mold (2) is fully descending; The inserted blank (6) is fixed in the forming and cutting mold (1) by the punch (4) arranged in the internal area of ​​the mold; The circumferential edge trimming (10) is performed at least partially before the start of forming or at a position at least 20 mm before reaching the bottom dead center, the edge trimming (10) being driven by the stamping stroke of the forming and cutting die (1) itself; Thermoforming is performed in a single stamping stroke, followed by edge trimming (10) and stamping hardening.

2. The method according to claim 1, characterized in that, The edge trimming (10) is performed circumferentially throughout the entire process.

3. The method according to claim 1 or 2, characterized in that, The edge trimming (10) completely cuts off the wall thickness of the blank (6).

4. The method according to claim 1, characterized in that, The cross-section of the motor vehicle component (13) is U-shaped or cap-shaped.

5. The method according to claim 1, characterized in that, The edge trimming (10) is performed at 550°C to 750°C.

6. The method according to claim 1, characterized in that, After trimming, the blank (6) to be formed is pulled into the interior of the forming and cutting mold (1) through a further forming process.

7. The method according to claim 1, characterized in that, Formed welded blanks, wherein the blanks (6) have at least two regions having different wall thicknesses and / or different steel alloys.

8. The method according to claim 1, characterized in that, The edge trimming (10) is performed at a position greater than 30 mm before reaching the bottom dead center.

9. The method according to claim 8, characterized in that, The edge trimming (10) is performed at a position greater than 100 mm before reaching the bottom dead center.

10. The method according to claim 1, characterized in that, The punch (4) presses the blank (6) onto the lower die block (5) of the lower die (3) for fixation.

11. The method according to claim 1, characterized in that, All die components in contact with the blank forming the motor vehicle component (13) are actively cooled for stamping hardening.

12. The method according to claim 1, characterized in that, The blank (6) is fully heated to a temperature greater than Ac3.

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