METHOD FOR AVOIDING EDGE CRACKS

Abstract

The present disclosure involves a method for determining the critical local expansion of a component with an eye toward the appearance of edge cracks based on an expansion of the component in the shaping process. Given a local expansion of the component at the edges that is smaller than the critical local expansion, no edge cracks arise that are larger than 1 μm. In particular, at least one expansion test is performed with at least one test component, and a critical overall expansion is determined with the at least one expansion test. The local maximum expansion of the test component is determined that the test component exhibits at the time of the critical overall expansion of the test component, and the local maximum expansion is the critical local expansion.

Claims

1-15. (canceled)

16. A method for determining the critical local expansion of a component to identify an appearance of edge cracks based on an expansion of the component in the shaping process so that given a local expansion of the component at the edges that is smaller than the critical local expansion, no edge cracks arise that are larger than 1 μm, the method comprising: performing at least one expansion test with at least one test component; and determining a critical overall expansion with the at least one expansion test; wherein a local maximum expansion of the test component is determined that the test component exhibits at the time of the critical overall expansion of the test component, and the local maximum expansion is the critical local expansion.

17. The method according to claim 16, further comprising performing a plurality of expansion test with a plurality of test components.

18. The method according to claim 16, further comprising graphically determining the critical overall expansion from at least one tensile force-expansion curve of the expansion test, wherein the critical overall expansion is numerically determined from values of the at least one expansion test.

19. The method according to claim 17, further comprising determining the critical overall expansion in several expansion tests, wherein a parameter for the difference in tensile forces between at least two tensile force-expansion curves is determined for at least two expansion tests, and once a prescribed value for the parameter has been reached, the existing overall expansion is the critical overall expansion.

20. The method according to claim 16, further comprising determining the local maximum expansion of the test component with finite element methods.

21. The method according to claim 16, further comprising determining the local maximum expansion via local expansion measurements on the test component.

22. The method according to claim 16, wherein the test component comprises the same material and same thickness prior to the expansion test as the component prior to shaping.

23. The method according to claim 22, further comprising fabricating the test component and component out of the same blank component.

24. The method according to claim 23, further comprising fabricating the test component and component with the same separating method.

25. The method according to claim 24, wherein the separating method is selected from the group consisting of punching and laser cutting.

26. A method for manufacturing a motor vehicle comprising: separating a component out of a blank component by a separating method; shaping the component; assembling the components into a body of the motor vehicle; wherein a geometry for shaping the components and a geometry for the components fabricated in the separating method is configured such that the local expansion at an edge of the component is less than a critical local expansion of the component relative to an appearance of edge cracks due to the expansion of the component while shaping the component such that no cracks larger than 1 μm are present on the edge of the component after shaping the component.

27. The method according to claim 26, further comprising determining the critical local expansion of the components with respect to the appearance of edge cracks due to an expansion of the component in a method wherein: at least one expansion test is performed with at least one test component; and a critical overall expansion is determined with the at least one expansion test; wherein a local maximum expansion of the test component is determined that the test component exhibits at the time of the critical overall expansion of the test component, and the local maximum expansion is the critical local expansion.

28. The method according to claim 27, further comprising determining the critical local expansion prior to shaping the component, and the geometry of shaping the component and the geometry of the component fabricated in the separating method are determined as a function of the critical local expansion determined to ensure that the expansion in particular at the edge is smaller while shaping the component than the clinical local expansion.

29. The method according to claim 26, wherein separating a component comprises punching the component out of a metal sheet unwound from a roll.

30. The method according to claim 26, further comprising assembling the component by at least one of a welding process and an adhesive bonding process.

31. The method according to claim 26, further comprising shaping the component by at least one of a bending process, deep drawing process and a shearing process.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The present disclosure will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements.

[0028] FIG. 1 is a tensile force-expansion curve with tensile force plotted on the abscissa and tension plotted on the ordinate for a test component fabricated via laser cutting;

[0029] FIG. 2 is a tensile force-expansion curve with tensile force plotted on the abscissa and tension plotted on the ordinate for a test component fabricated via punching;

[0030] FIG. 3 is a top view of a test component;

[0031] FIG. 4 is a top view of an imaginary part of the test component according to FIG. 3;

[0032] FIG. 5 is a top view of a component for manufacturing a body;

[0033] FIG. 6 is a side view of a blank component unwound from a roll; and

[0034] FIG. 7 is a side view of a motor vehicle.

DETAILED DESCRIPTION

[0035] The following detailed description is merely exemplary in nature and is not intended to limit the present disclosure or the application and uses of the present disclosure. Furthermore, there is no intention to be bound by any theory presented in the preceding background of the present disclosure or the following detailed description.

[0036] A motor vehicle 1 shown on FIG. 1 exhibits a body 2 made of steel. A drive engine 3, specifically an electric motor 4 and/or an internal combustion engine 5, drives the motor vehicle 1. The body 2 borders an interior space in which is located seats 6, specifically front seats 7 and rear seats 8, for accommodating passengers or persons.

[0037] The body 2 of the motor vehicle is assembled out of components 9 made of steel. The components 9 with varying geometries are joined together in a welding line via welding as the joining process. Before the components 9 are joined together, the components 9 are fabricated out of a blank component 19. The blank component 19 is a metal sheet, which is unwound from a roll 20. The components 9 with the varying geometries are fabricated out of the blank component 19 through punching with punching tools having a varying geometry. The components 9 here exhibit an outer edge 11 as one edge 10, and the components 9 can further also exhibit a borehole 14 and/or a recess 15. At the boreholes 14, an edge 12 here arises at the borehole 14, and at the recess 15, edges 13 arise at the recess 15.

[0038] After the components 9 have been punched out of the blank component 19, the components 9 as a rule have to be shaped, for example bent or deep drawn. The varying geometries for shaping and the varying positions for forming on the component 9 result in different local expansions on the component 9. The smaller a radius of curvature with which the initially flat component 9 is here bent, the greater the local expansion while shaping the component 9. Starting at a specific critical local expansion of the component 9 in the shaping process, edge cracks appear at the edges 10 starting at a specific size, e.g., 10 μm. Such edge cracks diminish the quality of the body 2, so that these edge cracks must be avoided starting at a specific size. The local expansions on the component 9 that arise while shaping can be calculated with the finite element method (FEM), for example, or by corresponding measurements. The geometry for shaping and/or the geometry of the components 9 after separated from the blank component 19 and prior to shaping is here prescribed by the structural requirements on the body 2, while these structural requirements can also be correspondingly adjusted and changed.

[0039] In a test or trial run for manufacturing the body 2 of the motor vehicle 1, the components 9 are fabricated out of the blank component 19 not by punching with a punching tool, but rather by laser cutting. This is done via laser cutting because punching tools are initially very expensive to manufacture, and when using laser cutting as the separation process, varying geometries for components 9 can be fabricated out of the blank component 19 only by reprogramming the laser cutting system. After the components 9 have been manufactured in this way in the test run, the components 9 are correspondingly shaped via corresponding tools for shaping, for example presses. However, structural changes arise at the edges 10 of the components 9 that are different during punching than during laser cutting. Punching is accompanied by micro-cracks along with embrittlement of the edges 10, so that the critical local expansion is resultantly smaller in components 9 made via punching than in components 9 made via laser cutting. In the test or trial run for manufacturing the body 2 of the motor vehicle 1, no edge cracks can thus arise initially on the edges 10 of the components 9 during the test or trial run performed with components 9 fabricated by laser cutting out of the blank component 19.

[0040] During the final and complete startup of the production line for manufacturing the body 2 of the motor vehicle, all components 9 are punched out of the blank component 19 by corresponding punching tools owing to the high number of components 9 to be fabricated. Three test components 6 are fabricated out of the blank component 19 via punching, and three additional test components 16 are fabricated via laser cutting. The three test components 16 made by laser cutting are sequentially subjected to an expansion test in a corresponding test device. FIG. 1 shows the three tensile force-expansion curves for these three test components 16. Expansion in % is plotted on the abscissa, and the tensile force kN is plotted on the ordinate. Given an expansion of roughly 15%, the maximum tensile force arises, after which a reduction in tensile force arises given a further expansion.

[0041] An operator uses this tensile force-expansion curve shown on FIG. 1 to manually determine a critical overall expansion ε.sub.k, either visually or with numerical methods. The critical overall expansion ε.sub.k is here larger than the expansion with a maximum tensile force, and, for example, measures a specific percentage value of expansion with the maximum tensile force, and the critical expansion is larger than the expansion with the maximum tensile force. The critical overall expansion ε.sub.k is here encountered at a value for expansion at which the tensile force-expansion curves for the three test components 16 do not yet essentially move apart, i.e., the difference in tensile forces is small given a respectively identical overall expansion. The critical overall expansion ε.sub.k for the test components 16 fabricated via laser cutting measures 25%.

[0042] In like manner, this expansion test is carried out with three test components 16 fabricated via punching out of the blank component 9. The critical overall expansion ε.sub.k for these three test components 16 fabricated via punching measures 23.5%. The expansion test is here performed as a tensile test, i.e., the test component 16 shown on FIG. 3 is exposed to a tensile force at the respective two end sections depicted on the left and right of FIG. 3, so that a tensile expansion of the test component 16 thereby arises. A local region 18 with a maximum expansion comes about in the middle of the test component 16 during the expansion test. The test component 16 exhibits two symmetrical axes that rest perpendicular one on the other, and a part of these two symmetrical axes is shown with dashed lines on FIG. 3. One fourth of the test component 16 as an imaginary part 17 of the test component 16, i.e., the left upper fourth on FIG. 3, which is imaginarily separated from the two symmetrical axes, is here subjected to a calculation process with the finite element method. This finite element method can be used to determine the expansion of the test component 16 at all local regions based on the symmetry of the arising local expansions, and to determine the local region 18 with the maximum expansion. The critical overall expansion ε.sub.k for the components 16 fabricated via punching is analogously determined, and measures 23.5%. The individual local expansions of the test component 16 at the time when the critical overall expansion is 23.5% can be determined with the finite element method, and the local region 18 with the maximum expansion can be determined from the latter. The critical local expansion of the test component 16, i.e., the local region 18 with the maximum expansion at the time when the critical overall expansion ε.sub.k for the test component 16, here measures 41%.

[0043] When manufacturing the components 9 by punching them out of the blank component 9 and then shaping the components 9, the geometry of the components 9 after punching, i.e., and thus the geometry of the punching tools and shaping geometry, i.e., for example also for the geometry of the tools for shaping, must be configured in such a way that the local expansions arising at the edges 10 of the components 9 in the shaping process are smaller than the critical local expansion of 41%. During final startup of the production line for the body 2 of the motor vehicle 1, the critical local expansion can be determined in advance so as to design the punching tools and/or tools for shaping the components 9 in such a way that the local expansions at the edges 10 of the components 9 are smaller than the critical local expansion of 41% in the shaping process, and hence that no edge cracks, for example those larger than 10 μm, advantageously arise on the edges 10 after the components 9 have been shaped.

[0044] Analogously, the critical local expansion can also be determined for the test components 16 fabricated through laser cutting from a blank component 19, and measures 51%. The critical local expansion for components 9 fabricated via laser cutting serves on the one hand as a comparative value for the critical local expansion for the components 9 fabricated via punching, and on the other for determining the difference in expansion.

[0045] Viewed as a whole, significant advantages are associated with the method according to the present disclosure for determining the critical local expansion and the method according to the present disclosure for manufacturing the motor vehicle. The critical local expansion of the components 9 starting at which edge cracks of a specific size arise can be easily determined with empirical methods, as described above. Because this critical local expansion starting at which relevant edge cracks arise is known, the geometry of the punching tools and/or the geometry of the tools for shaping the components 9 and/or the geometry of shaping can be designed in such a way prior to final startup of the process for manufacturing the body 2 of the motor vehicle 1 that the local expansions at the edges 10 of the components 9 are smaller than the critical local expansion in the shaping process. After final startup of the process for manufacturing the body 2 of the motor vehicle 1, no finishing of the edges 10 of the components 9 is thus required after shaping, in addition to which the punching tools and/or tools for shaping the components 9 also need not be changed out.

[0046] When determining the difference in expansion between the critical local expansion of components 9 fabricated via laser cutting and the critical local expansion of components 9 fabricated via punching, this determined difference in expansion can be used during conversion from the test run to final startup with the difference in expansion to indicate how much smaller the expansion in the shaping process during final startup must be than during the test run, so as to prevent any relevant cracks from arising during final startup. However, this presumes that no relevant cracks were encountered during the test run either. As a result, the costs for manufacturing the body 2 of the motor vehicle 1 can be reduced with little effort.

[0047] While at least one exemplary embodiment has been presented in the foregoing detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the present disclosure in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment, it being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope of the present disclosure as set forth in the appended claims and their legal equivalents.