Method for producing three-dimensionally formed components formed with a metallic sheet and at least one metallic reinforcing element

Abstract

Method for producing three-dimensionally formed components which are formed with a metallic sheet (1) and at least one metallic reinforcing element (2), in which in a first procedural step i) at predetermined positions of a surface of the metallic sheet (1) elevations are formed by a locally defined energy input, which is carried out with at least one defined two-dimensionally deflectable laser beam (5), and / or by welding with filler material, whereupon in a second procedural step ii) the at least one metallic reinforcing element (2) is placed on the surface of the metallic sheet (1) on which the elevations have been formed, and in a third procedural step iii) with at least one lower electrode (4) which is arranged opposite the surface of the metallic sheet (1) on which the elevations have been formed, and at least one upper electrode (3) with the surface of the at least one metallic reinforcement element (1) which faces away from the surface on which the at least one metallic reinforcement element (2) bears against the elevations, are brought into electrically conductive contact, whereby the metallic sheet (1) and the at least one metallic reinforcement element (2) are connected to one another in a materially bonded manner by electrical resistance welding in the region of the elevations and in a fourth procedural step iv) a three-dimensional forming process for obtaining a finished component is carried out on the locally defined interconnected metallic sheet (1) and the at least one metallic reinforcing element (2) using at least one forming tool

Description

[0001] The invention relates to a method for producing three-dimensionally formed components formed from a metallic sheet and at least one metallic reinforcement element. Metallic sheets with appropriately adapted edge contours, as well as three-dimensional semi-finished products, can be used as reinforcement elements. The latter should ideally have a flat, planar surface on which material-to-material connections with the respective metallic sheet can be formed.

[0002] The invention can be used in all industrial sectors where there is a requirement to locally reinforce sheet metal components with another sheet metal component or generally to bond two flat sheet metal components together over a large area. Particularly suitable areas of application are: → Automotive industry: Body construction → Rail vehicle construction, wagon construction → Commercial vehicle construction.

[0003] So-called patchwork blanks are currently used for the local reinforcement of structural components made of sheet metal. In this case, another flat sheet is welded onto the flat sheet metal blank prior to sheet forming, and the resulting composite blank (or patchwork blank) is then subjected to a forming process. The subsequent forming process can include hot forming. Currently, the two blanks (base blank + reinforcement patch) are welded using resistance spot welding (WPS) through a large number of individual points distributed across the surfaces of the two sheets. This is done to prevent detachment or relative movement of the sheets during forming, and to achieve an optimal reinforcement effect in the component after forming. The production of the very large number of weld points is very time-consuming and inefficient (approximately 1 second per weld point).Furthermore, the unavoidable damage and bulging of the sheet metal surface caused by the spot welding process cause problems in the subsequent forming process, which lead to increased tool wear of the forming tools used.

[0004] For example, it is known from KR 10 2019 0 029 338 A to join a sheet metal to a reinforcing sheet metal, whereby elevations are formed on the reinforcing sheet metal by forming, before the sheet metal and reinforcing sheet metal are joined together by electrical resistance welding and then formed together.

[0005] It is therefore an object of the invention to provide possibilities for the production of three-dimensionally formed reinforced components with which the productivity and service life of forming tools can be increased.

[0006] According to the invention, this object is achieved by a method having the features of claim 1. Advantageous embodiments and further developments can be realized with features recited in dependent claims.

[0007] The invention comprises a novel and significantly more effective joining method for creating a large-area connection between a metallic sheet and at least one metallic reinforcement element, which are joined together prior to three-dimensional forming. These joining partners are to be joined together in a preferably flat, large-area connection area in a material-to-material manner at predetermined positions. This can be used, among other things, to solve the problem described above for joining a metallic sheet as a base plate and one or more reinforcement elements.

[0008] The process proceeds as follows: in a first process step i), elevations are formed at predetermined positions on the surface of the metallic sheet by applying a locally defined energy input and / or by deposition welding with filler material. The deposition welding can be performed using conventional arc welding processes or by laser beam welding with added filler material.

[0009] Subsequently, in a second method step ii), the at least one metallic reinforcement element is placed onto the surface of the metallic sheet on which the elevations have been formed, and in a third method step iii), at least one lower electrode is arranged opposite the surface of the metallic sheet on which the elevations have been formed, and at least one upper electrode is brought into electrically conductive contact with the surface of the at least one metallic reinforcement element facing away from the surface on which the at least one metallic reinforcement element rests against the elevations. As a result, the metallic sheet and the at least one metallic reinforcement element are bonded together in a point-to-point, materially bonded manner in the region of the elevations by electrical resistance welding.In this case, an electric current flows from an electrical voltage source from the upper to the lower electrode through the metallic sheet and the at least one metallic reinforcing element, which leads to the formation of spot welds in the area of ​​elevations.

[0010] Subsequently, in a fourth process step (iv), a three-dimensional forming process is carried out on the locally defined interconnected metallic sheet and the at least one metallic reinforcement element using at least one forming tool to obtain a finished component. The forming process can, if necessary, be carried out in several stages using several forming tools or as hot or cold forming.

[0011] In the first method step i), in an alternative according to the invention, a locally defined energy input for forming elevations can be carried out using at least one laser beam that can be deflected in a defined two-dimensional manner. For this purpose, the laser beam can originate from a laser beam source and be directed onto a reflective element that can be pivoted along two axes aligned perpendicular to one another, or two successively arranged reflective elements in its beam path, each of which is directed around a reflective element that can be pivoted perpendicular to the axis of the other reflective element and thus impinges on predetermined positions on the respective surface of the metallic sheet to form elevations there. Such an optical structure for deflecting laser beams is usually referred to as scanner optics.

[0012] During the first process step i), compressive forces can be applied to at least two diametrically opposed edge surfaces. For this purpose, the metal sheet can be clamped on two opposite sides, and the compressive forces can be introduced into the metal sheet from at least one side, for example, using a piston-cylinder arrangement or linear motors. The locally defined energy input of the laser beam creates mechanical stresses during the temperature changes for heating and cooling. This stress, particularly in thin metal sheets, leads to the formation of protrusions at the pre-irradiated predetermined positions due to stress-induced deformation.

[0013] Alternatively, when carrying out the first method step i), the metallic sheet can also be arranged with its surface, which is opposite the surface on which elevations are formed, placed on a surface of a forming tool, on which elevations are formed according to the locally defined positions, and a compressive force is exerted, so that at the predetermined positions, as a result of the locally defined energy input into the metallic sheet by the at least one laser beam, elevations can be formed by deformation on the metallic sheet in surface areas that have been heated by means of the energy of the laser beam.

[0014] With these two alternatives for forming raised portions described above, deformations also occur on the opposite surface of the metal sheet. However, these are burr-free depressions that only have a very slight impact on the respective forming tool during the forming process according to the fourth process step iv), and far less so than with conventional spot welds.

[0015] In the first process step i), elevations should be formed which protrude with a height in the range of 0.1 mm to 0.5 mm, preferably up to 0.4 mm, above the respective surface of the metallic sheet on which the elevations are formed.

[0016] Advantageously, in the third method step iii), an upper electrode and / or a lower electrode can be used, which consist of several individual segments, each of which is individually connected to an electrical voltage source and positioned relative to surface areas on which elevations have been formed. In this case, it can be achieved that an electrical current flow through the metallic sheet and the at least one metallic reinforcing element can occur essentially only in the area of ​​elevations. For this purpose, an upper and / or lower electrode can be segmented such that individual segments only electrically contact a predetermined small number of elevations in a surface area when the respective welded joints are formed by electrical resistance welding.

[0017] The invention has the significant advantage that the surfaces of the metallic sheet and of the at least one metallic reinforcing element, which come into contact with a forming tool during three-dimensional forming, are free of elevations, so that only a small amount of material is removed, if at all, thus resulting in significantly reduced wear.

[0018] The resistance welding process used in the third process step iii) can also be referred to as projection welding. The process is intended to be used in such a way that a large-area connection can be created between at least two joining partners, metallic sheet and metallic reinforcement element, in a single welding process with a maximum process time of 1 second. With reference to the application example mentioned at the beginning, the production of patchwork circuit boards, the welding of a reinforcement patch would be possible with a single, very short welding process. In order to use this process for joining two completely flat surfaces, it is essential to form locally defined elevations, so-called projections, on one of the two joining partners. Particularly in the above-mentionedFor the production of patchwork boards, it is not advantageous to introduce these elevations using a mechanical stamping process, as is usually the case, as this represents a complex additional process step that would be very time-consuming, especially given the large number of required elevations, or would require a large tool. A further disadvantage is the loss of flatness on both sides of the metal sheet and the metal reinforcement element due to a purely mechanical stamping process, as is common in the state of the art, which in turn would result in increased tool wear.

[0019] Therefore, conventional forming processes cannot be used to quickly form the elevations, but rather surface-modifying or, in particular, deposition processes, which ideally have little or no impact on the opposite side of the sheet metal, where no elevations are formed. One possibility is to create nub-like elevations on the surface of a metal sheet using a laser process and a deposition welding process.

[0020] Such laser nubs or laser structures are usually used to ensure defined gaps between two adjacent sheets (see DE10 2004 005 358 B4). For projection welding applications, elevations can be achieved with a required process time of between 30 ms and 180 ms for a single elevation formed in this way. When using scanner optics with which a laser beam can be deflected to predetermined positions, this positioning time between the individual elevations can be neglected. With this technology, almost any distribution and density of elevations on the surface of a metallic sheet can be realized without exceeding the cycle time of the subsequent processes.The distribution and arrangement of the protrusions can be adjusted to create a connection between the metal sheet and the at least one metal reinforcement element that is optimally adapted to the subsequent load or the requirements of the forming process. Due to the short process time, the formation of the protrusions is completely cycle-time-neutral (the forming process takes longer) and can also be performed on a moving, not yet formed component as a semi-finished product, i.e., even during partial transport. The respective metal sheets on which the protrusions are to be formed simply need to be moved past one or more laser scanner optics.

[0021] Another option for creating the necessary local elevations, as already mentioned, is the use of a build-up welding process. Processes that enable the rapid welding of local, ideally circular, elevations should be used. Suitable examples include arc welding processes, particularly process modifications that allow for the welding of small, spot-shaped welds (e.g., CMT printing developed by Fronius), or laser processes with wire-like filler material.

[0022] After preparing one of the surfaces to be joined, on which elevations have been formed, the actual welding process for joining the metallic sheet and the at least one metallic reinforcement element can be carried out using resistance projection welding with a flat upper and lower electrode. These two electrodes can cover the entire welding area with the introduced elevations (projections). To achieve optimal electrical current flow and to prevent unwanted shunts, it can be advantageous to segment the area into several individual surface electrodes instead of one large electrode. This would also reduce the electrical power requirement per welding segment and facilitate the electrical power supply via several welding machines. In principle, it would also be possible to integrate the welding process directly into a forming press by using the upper and lower electrode(s) simultaneously as forming tools.

[0023] However, the method can also be carried out in such a way that the method step i) is carried out on a surface of the metallic reinforcing element, which is preferably flat and planar, instead of the surface of the metallic sheet for forming the elevations.

[0024] With the invention, the number of connections and thus the connection width can be adjusted as desired by adjusting the number and arrangement of the raised portions to be formed. A cycle-time-neutral formation of the joining connection can be achieved, since the number of connection points on the raised portions only minimally influences the overall process time. There is no or only minimal influence on the external surfaces that later come into contact with the surface of a forming tool. The joining process of metallic sheet metal and metallic reinforcement element(s) can be integrated into a forming press.

[0025] The invention will be explained below by way of example.

[0026] It shows: Fig. 1 in schematic form possible implementation of process steps i) to iii).

[0027] In the first process step i), as shown on the left in Fig. 1, the formation of elevations on a surface of a metallic sheet 1 takes place using a laser beam 5, which is directed by a scanner optics 7 at predetermined positions on the surface of the metallic sheet 1 facing in the direction of the scanner optics 7. Elevations are thus formed in a locally defined manner at the predetermined positions. These positions can be predetermined depending on the loads to which a completely formed component is exposed during its use and / or during the three-dimensional forming process. The laser beam 5 is then deflected such that its focal spot can cause energy to be introduced at the predetermined positions, either directly into the material of the metallic sheet 1 and / or into a filler material for build-up welding to form elevations. The metallic sheet 1 can preferably be moved continuously past the scanner optics 7.

[0028] After all the elevations have been formed on the corresponding surface of the metallic sheet 1, in this example, a sheet as a metallic reinforcing element 2 is also placed on the surface of the metallic sheet 1 with the elevations, so that the elevations are in direct contact with each other with the corresponding surface of the metallic reinforcing element 2.

[0029] In the middle of Fig. Figure 2 illustrates the third method step iii). After positioning the metallic reinforcement element 2 relative to the metallic sheet 1 according to the second method step ii), the upper electrode 3 and lower electrode 4, each formed integrally with the electrical voltage source 6, are pressed against the outwardly facing surfaces of the metallic sheet 1 and the metallic reinforcement element 2 from oppositely arranged sides, so that surfaces of elevations are contacted with the corresponding surface of the metallic reinforcement element 2 and an electrical current flows there. Thus, spot welds 9 are formed by electrical resistance welding in the region of elevations, with which the metallic sheet 1 and the metallic reinforcement element 2 are firmly bonded to one another.

[0030] In a form not shown, at least one of the two electrodes 3 and / or 4 can also be formed from several individual segments, each of which is individually connected to the electrical voltage source 6 or to its own electrical voltage source. A specific number of elevations in a common surface area can then be covered with one segment, and spot welds 9 can then be formed in this surface area by means of an electrical current flow from the respective segment of one electrode 3 or 4 to the other electrode or a segment of the other electrode through the material of the metallic sheet 1 and the metallic reinforcing element 2.

[0031] A semi-finished product prepared in this way is shown in the right illustration of Fig. 1. This can be three-dimensionally formed in a conventional manner in the fourth process step iv) in a form not shown.

Claims

[1] Method for producing three-dimensionally formed components which are formed with a metallic sheet (1) and at least one metallic reinforcing element (2), in which in a first procedural step i) at predetermined positions of a surface of the metallic sheet (1) elevations are formed by a locally defined energy input, which is carried out with at least one defined two-dimensionally deflectable laser beam (5), and / or by welding with filler material, whereupon in a second procedural step ii) the at least one metallic reinforcing element (2) is placed on the surface of the metallic sheet (1) on which the elevations have been formed, and in a third procedural step iii) with at least one lower electrode (4) which is arranged opposite the surface of the metallic sheet (1) on which the elevations have been formed, and at least one upper electrode (3) with the surface of the at least one metallic reinforcement element (1) which faces away from the surface on which the at least one metallic reinforcement element (2) bears against the elevations, are brought into electrically conductive contact, whereby the metallic sheet (1) and the at least one metallic reinforcement element (2) are connected to one another in a materially bonded manner by electrical resistance welding in the region of the elevations and in a fourth procedural step iv) a three-dimensional forming process for obtaining a finished component is carried out on the locally defined interconnected metallic sheet (1) and the at least one metallic reinforcing element (2) using at least one forming tool [2] Method according to claim 1, characterized bythat during the implementation of the first method step i) compressive forces are exerted on at least two diametrically opposed edge surfaces or the metallic sheet (1) is arranged with its surface, which is opposite the surface on which elevations are formed, placed on a surface of a forming tool, on which elevations are formed according to the locally defined positions, and a compressive force is exerted in the process, so that elevations are formed on the metallic sheet (1) by deformation at the predetermined positions as a result of the locally defined energy input into the metallic sheet (1) carried out by the at least one laser beam (5). [3] Method according to one of the preceding claims, characterized bythat in the first method step i) elevations are formed which protrude with a height in the range 0.1 mm to 0.5 mm above the respective surface of the metallic sheet (1) on which the elevations are formed. [4] Method according to one of the preceding claims, characterized by that in the third method step iii) an upper electrode (3) and / or a lower electrode (4) is used, which consists of a plurality of individual segments, each of which is individually connected to an electrical voltage source (6) and is positioned to surface areas on which elevations have been formed. [5] Method according to one of the preceding claims, characterized by that the third and fourth process steps iii) and iv) are carried out together in a combined tool.

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