A FORMING SHEET METAL PART FOR A VEHICLE FRAME AND CORRESPONDING PRODUCTION METHOD

Abstract

A forming sheet metal part (1) for a vehicle frame includes: a first portion (2) being locally heat-softened after the sheet metal part (1) has been formed out. The part (1) further includes a dedicated three-dimensional distortion-absorbing area (4), defining an internal boundary (6) within which the first portion (2) is to be locally heat-softened after the sheet metal part (1) has been formed out. The distortion-absorbing area (4) is dimensioned such that once said locally heat-softening step has been performed, the internal boundary (6) is adjacent to the first portion (2) and encloses the first portion (2) to absorb the dimensional distortions induced by the locally heat-softened first portion. The invention further relates to a method for producing a forming sheet metal part (1).

Claims

1. A forming sheet metal part for a vehicle frame comprising: a first portion of said sheet metal part being locally heat-softened after said sheet metal part has been formed out, wherein it further comprises: a dedicated three-dimensional distortion-absorbing area, defining an internal boundary within which said first portion is to be locally heat-softened after said sheet metal part has been formed out, and said distortion-absorbing area being dimensioned such that once said locally heat-softening step has been performed, said internal boundary is adjacent to said first portion and encloses said first portion to absorb the dimensional distortions induced by said locally heat-softened first portion.

2. The sheet metal part of claim 1, wherein said sheet metal part has a thickness between 0.5 and 8 mm, preferably between 0.5 and 6 mm, more preferably between 0.5 and 3 mm and especially preferably between 0.8 a 2.5 mm.

3. The sheet metal part according to claim 1, wherein said distortion-absorbing area has a height between 2 and 20 mm.

4. The sheet metal part according to claim 1, wherein said locally heat-softened first portion is distanced between 0 and 50 mm, and preferably between 0 and 10 mm to said internal boundary.

5. The sheet metal part according to claim 1, wherein said distortion-absorbing area comprises rounded edges and said internal boundary is defined by the inner tangency line of said rounded edges.

6. The sheet metal part according to claim 5, wherein said rounded edges have a radius between 2 and 20 mm and preferably between 2 and 10 mm.

7. The sheet metal part according to claim 1, wherein said first portion has an area between 100 mm.sup.2 and 50,000 mm.sup.2 and preferably between 100 mm.sup.2 and 15,000 mm.sup.2.

8. The sheet metal part according to claim 1, wherein said distortion-absorbing area is one of the group formed by a projection, a recess or a surrounding bump and in that said distortion-absorbing area encloses a flat portion for performing said locally heat-softened first portion.

9. The sheet metal part according to claim 8, wherein when said distortion-absorbing area is a surrounding bump, it further comprises a plateau of greater than 0 to 20 mm wide.

10. The sheet metal part according to claim 1, wherein said internal boundary is a closed boundary such as to completely enclose said locally heat-softened first portion.

11. A method for producing a forming sheet metal part with locally heat-softened portions comprising: a first forming step, for forming out said forming sheet metal part and a locally heat-softening step, after said first forming step, for locally heat-softened a first portion of said forming sheet metal part, wherein it further comprises a second forming step, prior to said heat-softening step, for forming a dedicated three-dimensional distortion-absorbing area, said three-dimensional distortion absorbing area defining an internal boundary within which said first portion is to be locally heat-softened, said distortion-absorbing area being dimensioned such that once said locally heat-softening step has been performed, said internal boundary is adjacent to said first portion and encloses said first portion to absorb the dimensional distortions induced by said heat-softening step.

12. The method according to claim 11, wherein said second forming step is carried out by hot or cold forming.

13. The method according to claim 11, wherein said first forming step is a stamping step and said first and second forming steps are performed simultaneously.

14. The method according to claim 11, wherein during said locally heat-softening step said first portion of said stamping part is heated between 300° C. and 1200° C. and preferably from 500° C. to 800° C.

15. The method according to claim 11, wherein said locally heat-softening step is carried out by irradiating said first portion with a laser beam having a power comprised between 500 W and 100 kW, preferably between 1 kW and 10 kW.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Further advantages and features of the invention will become apparent from the following description, in which, without any limiting character, preferred embodiments of the invention are disclosed, with reference to the accompanying drawings in which:

[0038] FIG. 1 shows a perspective view of a first embodiment of a forming sheet metal part according to the invention, in the shape of a longitudinal beam, the part having a distortion-absorbing area arranged on an edge of the sheet metal part and enclosing a locally heat-softened first portion.

[0039] FIG. 2 shows a top view of the distortion-absorbing area of the sheet metal part of FIG. 1.

[0040] FIG. 3 shows a detailed view of the cross-section of the distortion-absorbing area of the sheet metal part of FIG. 1.

[0041] FIG. 4A shows a numerical simulation of the deformation of the sheet metal part of FIG. 1, after the creation of the locally heat-softened first portion, when the part does not have a distortion absorbing area.

[0042] FIG. 4B shows a numerical simulation of the deformation of the sheet metal part of FIG. 1, after the creation of the locally heat-softened first portion, when the part has a dedicated distortion absorbing area according to the invention enclosing the first portion.

[0043] FIG. 5 shows a perspective view of a second embodiment of a forming sheet metal part according to the invention, in the shape of a longitudinal beam, the part having a distortion-absorbing area arranged in the center of the sheet metal part and enclosing a locally heat-softened first portion.

[0044] FIG. 6 shows a top view of the distortion-absorbing area of the sheet metal part of FIG. 5.

[0045] FIG. 7 shows a detailed view of the cross-section of the distortion-absorbing area of the sheet metal part of FIG. 5.

[0046] FIG. 8A shows a numerical simulation of the deformation of the sheet metal part of FIG. 5, after the creation of the locally heat-softened first portion, when the part does not have a distortion absorbing area.

[0047] FIG. 8B shows a numerical simulation of the deformation of the sheet metal part of FIG. 5, after the creation of the locally heat-softened first portion, when the part has a dedicated distortion absorbing area according to the invention enclosing the first portion.

[0048] FIGS. 9 to 11 show a perspective view of a third embodiment of a forming sheet metal part according to the invention, in the shape of a longitudinal beam, the part having a distortion-absorbing area arranged on an edge of the sheet metal part and enclosing a locally heat-softened first portion.

[0049] FIGS. 12A and 12B show a numerical simulation of the deformation of the sheet metal part of FIG. 9, after the creation of the locally heat-softened first portion, respectively without and with a distortion absorbing area.

[0050] FIGS. 13 to 15 show a perspective view of a fourth embodiment of a forming sheet metal part according to the invention, in the shape of a longitudinal beam, the part having a distortion-absorbing area arranged on an edge of the sheet metal part and enclosing a locally heat-softened first portion.

[0051] FIGS. 16A and 16B show a numerical simulation of the deformation of the sheet metal part of FIG. 13, after the creation of the locally heat-softened first portion, respectively without and with a distortion absorbing area.

[0052] FIGS. 17 to 19 show a perspective view of a fifth embodiment of a forming sheet metal part according to the invention, in the shape of a longitudinal beam, the part having a distortion-absorbing area arranged on an edge of the sheet metal part and enclosing a locally heat-softened first portion.

[0053] FIGS. 20A and 20B show a numerical simulation of the deformation of the sheet metal part of FIG. 17, after the creation of the locally heat-softened first portion, respectively without and with a distortion absorbing area.

DETAILED DESCRIPTION

[0054] FIGS. 1 to 3 show a first embodiment of a forming sheet metal part 1 for a vehicle frame according to the invention, such as e.g., a front rail for a car or any other type of vehicle comprising a metallic frame.

[0055] Even though the part 1 has been represented in the Figures without thickness for sake of simplicity, it preferably has a thickness between 0.5 and 8 mm; preferably between 0.5 and 6 mm, e.g., in cases where the part has an overlap of sheet metal parts. In other cases, the part 1 can have a thickness between 0.5 and 3 mm and especially preferably between 0.8 a 2.5 mm.

[0056] Also, the part 1 is depicted as a longitudinal straight beam. However, the part can have any desired configuration such as e.g., an A, B or C pillar, a hinge pillar, a rocker, a front or a rear rail, a body floor or any other vehicle frame part.

[0057] The sheet metal part 1 comprises a first portion 2 being locally heat-softened after said sheet metal part 1 has been stamped out. Preferably, the sheet metal part 1 is laser-softened. However, other locally heat-softening methods can be used, such as induction, resistive heating or the like.

[0058] In order to solve the problem of providing a forming sheet metal part 1 with an enhanced crash behaviour, but which simultaneously is easy to produce and maintains the required production quality without the part being out of tolerances after the heat treatment, the sheet metal part 1 comprises a dedicated three-dimensional distortion-absorbing area 4, defining an internal boundary 6 within which said first portion 2 is to be locally heat-softened, after the sheet metal part 1 has been formed out. This can be especially observed in FIGS. 2 and 3, in which the distortion-absorbing area 4 is formed by a semi-circular bump with rounded edges. As it is apparent from FIG. 2, the internal boundary 6 is defined in this case by the inner tangency line of the rounded edges. Also, in this case, the distortion-absorbing area 4 has a height of 10 mm with rounded edges having a radius of 5 mm. Therefore, taking the overall plane P1 of the part in the area where the heat-softening is to be carried out, the distortion-absorbing area 4 is in this case, a surrounding bump. The distortion-absorbing area 4 encloses then the flat portion 12 in which the first portion 2 is to be heat softened.

[0059] Therefore, the distortion-absorbing area 4 is dimensioned such that once the locally heat-softening step has been performed, the internal boundary 6 is adjacent to the first portion 2 and encloses said first portion 2 to absorb the dimensional distortions induced by said locally heat-softened first portion 2.

[0060] In the invention, the expression enclosing the first portion also includes the case in which the first portion lies on an edge of the part. As it is apparent from the FIG. 2, the free edge 8 is free from the bump. However, this does not lead the part 1 to go out of the tolerances, because the rest of the distortion-absorbing area 4, compensates the deformations induced by the heat and avoids the uncontrolled deformation of the sheet metal part occurring when no distortion-absorbing area 4 is available.

[0061] The expression enclosing the first portion neither excludes that the distortion-absorbing area 4 has small interruptions in its extension. For example, in the case of FIGS. 1 to 3, it is possible that the distortion absorbing area 4 is interrupted at the corners 10. However, this does not cause that the distortion-absorbing area 4 loses the distortion-absorption effect. Indeed, the effect in this case is somehow similar as when the heat-softened first portion 2 lies on a part edge.

[0062] Also, in order to guarantee an effective function of the distortion-absorbing area 4, the locally heat-softened first portion 2 is distanced a distance D1 comprised between 0 and 50 mm and preferably between 0 and 10 mm to the internal boundary 6. In this case, it must be pointed out that the distance D1 must not be constant in all cases to have an effective distortion-absorbing effect, as it is apparent from FIG. 18.

[0063] Preferably the first portion 2 has an area between 100 mm.sup.2 and 50,000 mm.sup.2 and preferably between 100 mm.sup.2 and 15,000 mm.sup.2 and is square or rectangular shaped.

[0064] The method for producing the forming sheet metal part 1 with locally heat-softened portions is as follows.

[0065] First starting from a sheet metal blank, a first forming step takes place in a forming die or a rolling device, for forming out the sheet metal part 1. The sheet metal part can be produced by methods such as cold stamping, press hardening, roll forming or indirect press hardening. Even though the part can be stamped both in cold or in hot conditions or by rolling, preferably the forming step is carried out by press hardening, also known as hot stamping.

[0066] Then a second forming step, for forming the three-dimensional distortion-absorbing area 4, takes place. Preferably this second forming step is carried out simultaneously with the first forming step, when the method used is either by cold stamping or press hardening. The second forming step defines an internal boundary 6 within which the first portion 2 is to be locally heat-softened.

[0067] Finally, the locally heat-softening step takes place, after the stamping step, for locally heat-softening a first portion 2 of said stamping part. Especially preferably the heat-softening step is carried out by irradiating the first portion 2 with a laser beam having a power comprised between 500 W and 100 kW and especially preferably between 1 kW and 10 kW. Then the first portion 2 is heated between 400° C. and 1,200° C. and preferably from 500° C. to 800° C. The distortion-absorbing area 4 is dimensioned such that once the locally heat-softening step has been performed, the internal boundary 6 is adjacent to the first portion 2 and encloses the first portion 2 to absorb the dimensional distortions induced by the heat-softening step.

[0068] FIGS. 4A and 4B show the effect of the creation of a distortion-absorbing area 4.

[0069] FIG. 4A shows the deformation of the sheet metal part 1, after the creation of the heat-softened first portion 4, in the case that no distortion absorbing area 4 is available. In this case, following distortion values are achieved.

TABLE-US-00001 TABLE 1 Sheet metal part with no distortion-absorbing area 4 Figure 4A Maximum distortion 2.280 mm Distortion in the center area A 2.280 mm

[0070] Instead, FIG. 4B shows the deformation of the sheet metal part 1, after the creation of the heat-softened first portion 4, when the part has a distortion absorbing area 4, thus reaching followings deformation values, as well as the following % deformation reduction.

TABLE-US-00002 TABLE 2 Sheet metal part with distortion-absorbing area 4 Figure 4B Maximum distortion 0.555 mm Distortion in the center area A 0.139 mm % Reduced Maximum Distortion 75.7% % Reduced Distortion in center area 93.9%

[0071] Therefore, from the previous table it is clearly derivable that the distortion-absorbing area 4 leads to a clear deformation reduction of the sheet metal part 1 after the locally heat-softening process has taken place. In particular, with the distortion-absorbing area 4, a 75.7% deformation reduction is achieved, relative to the maximum distortion over the sheet metal part. Additionally, in the center area of the heat softened part, even better results are achieved thanks to the surrounding bump, since a 93.3% deformation reduction can be obtained.

[0072] Below, further embodiments are described, having a plurality of features in common with the previous first embodiment. Therefore, from now on, only the distinguishing features are described, while for the common features, reference is made to the description above.

[0073] FIGS. 5 to 7 show a second embodiment of the sheet metal part according to the invention. As it is apparent, in this case, the distortion-absorbing area 4 is in the central area of the part. Again, for sake of simplicity a longitudinal U-shaped beam is shown, such as a car front rail. However, again the invention is applicable to any sheet metal part of a vehicle frame.

[0074] The distortion-absorbing area 4 is now a closed surrounding bump with rounded corners 10. More particularly, in this case the internal boundary 6 is a closed boundary such as to completely enclose the locally heat-softened first portion 2. In this case then the distortion absorbing area 4 provides for a more homogeneous and performing distortion absorbing effect as shown below in the comparative tables 3 and 4. Additionally, and differently to the embodiment before, the distortion-absorbing area 4 has further a plateau 14 between 0.1 and 20 mm wide.

[0075] Following deformation values were obtained in a sheet metal part without geometrical distortion absorber, corresponding to FIG. 8A.

TABLE-US-00003 TABLE 3 Sheet metal part with no distortion-absorbing area 4 Figure 8A Maximum distortion 1.369 mm Distortion in the center area A 1.369 mm

[0076] Instead, by providing a geometrical distortion absorber in the shape of a surrounding bump with an internal boundary 6 which is a closed boundary such as to completely enclose said locally heat-softened first portion 2, especially performing results were obtained as it is apparent from Table 4.

TABLE-US-00004 TABLE 4 Sheet metal part with distortion-absorbing area 4 Figure 8B Maximum distortion 0.350 mm Distortion in the center area A 0.350 mm % Reduced Maximum Distortion 74.4% % Reduced Distortion in center area 74.4%

[0077] FIGS. 9 to 11 show an embodiment, in which the distortion-absorbing area 4 is a projection having a cross-section of an isosceles trapezoid with rounded corners.

[0078] Table 5 shows the deformation results of a forming sheet metal part according to FIG. 12A, without a distortion-absorbing area 4.

TABLE-US-00005 TABLE 5 Sheet metal part with no distortion-absorbing area 4 Figure 12A Maximum distortion 2.280 mm Distortion in the center area A 2.280 mm

[0079] Again, as it is apparent from Table 6, thanks to the truncated pyramid like distortion-absorbing area 4 as the one in FIG. 12B, a maximum distortion reduction of 83% is achieved.

TABLE-US-00006 TABLE 6 Sheet metal part with distortion-absorbing area 4 Figure 12B Maximum distortion 0.388 mm Distortion in the center area A 0.388 mm % Reduced Maximum Distortion 83% % Reduced Distortion in center area 83%

[0080] The embodiment of FIGS. 13 to 15 is similar to the one of FIGS. 9 to 11, but in this case, the distortion absorbing-area 4 is a recess, having a cross-section of an inverted isosceles trapezoid with rounded corners.

[0081] Table 7 shows the deformation results of a forming sheet metal part according to FIG. 16A, without a distortion-absorbing area 4.

TABLE-US-00007 TABLE 7 Sheet metal part with no distortion-absorbing area 4 Figure 12A Maximum distortion 2.280 mm Distortion in the center area A 2.280 mm

[0082] Again, as it is apparent from Table 8, thanks to the inverted truncated pyramid like distortion-absorbing area 4 as the one in FIG. 16B, a maximum distortion reduction of 83% is achieved.

TABLE-US-00008 TABLE 8 Sheet metal part with distortion-absorbing area 4 Figure 16B Maximum distortion 0.540 mm Distortion in the center area A 0.488 mm % Reduced Maximum Distortion 76.3% % Reduced Distortion in center area 78.6%

[0083] Finally, in the embodiment of FIGS. 17 to 19, the height of the distortion-absorbing area 4 is variable. In this case, the U-shaped cross-section of the beam has been used to configure a section of the distortion-absorbing area 4, such that, only two lateral bumps are required.

[0084] Table 9 shows the deformation results of a forming sheet metal part according to FIG. 20A, without a distortion-absorbing area 4.

TABLE-US-00009 TABLE 9 Sheet metal part with no distortion-absorbing area 4 Figure 20A Maximum distortion 2.280 mm Distortion in the center area A 2.280 mm

[0085] Again, as it is apparent from Table 10, in this case the deformation reduction achieved is only of 44.6%. However, the technical effect of the distortion-absorbing area 4 is still apparent.

TABLE-US-00010 TABLE 10 Sheet metal part with distortion-absorbing area 4 Figure 20B Maximum distortion 1.260 mm Distortion in the center area A 1.260 mm % Reduced Maximum Distortion 44.6% % Reduced Distortion in center area 44.6%

[0086] Also, it must by pointed out, that the same part 1, can comprise a plurality of portions 2 being locally heat-softened in order to tailor the deformation behaviour of the part.

[0087] Finally, it cannot be discarded that the shape of the distortion-absorbing areas 4 is a combination of the embodiments explained before.

[0088] While the present disclosure has been illustrated and described with respect to a particular embodiment thereof, it should be appreciated by those of ordinary skill in the art that various modifications to this disclosure may be made without departing from the spirit and scope of the present disclosure.