Abstract:
A method for targeted influencing of the deformation behavior of a wall-like structure, in particular a rear wall structure of a vehicle seat, which structure is heated in at least one region at least section by section by means of a laser light source. According to the invention at least one region which influences a strength and/or a tension of the wall-like structure is selectively chosen and is lasered for increasing the strength of the wall-like structure and/or for reducing tensions within the wall-like structure. The wall-like structure is characterized in that in a selectively chosen region the structure has at least one laser-welded seam which is generated by a laser light source of a laser device, increases the strength of the wall-like structure and/or reduces tensions in the wall-like structure.

Description:
[0001]    This nonprovisional application is a continuation of International Application No. PCT/EP2014/069085, which was filed on Sep. 8, 2014, and which claims priority to German Patent Application No. 10 2013 217 969.3, which was filed in Germany on Sep. 9, 2013, and which are both herein incorporated by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The invention relates to a method for stabilizing a rear-wall structure in a seat structure, and a seat structure, producible by the method, with selectively determined laser-strengthened regions in the area of a rear wall. 
         [0004]    2. Description of the Background Art 
         [0005]    DE 10 2007 024 797 A1, which corresponds to U.S. Pat. No. 8,272,681, discloses a method for producing a profile component from a semifinished sheet metal part, which has a structurally increased strength at least in sections. The semifinished sheet metal part is formed in an at least single-stage bending process. The bending process with the subsequent separating and cutting operations on the semifinished sheet metal part is combined with a thermal treatment of the at least one spatially delimited region of the semifinished sheet metal part. The thermal treatment comprises at least one heating step and one cooling step following it. The at least one spatially delimited region has a structurally increased strength after cooling. Profile components with an open, with a partially open, or also with a completely closed profile cross section and with hardness properties adapted in a directed manner can be produced by the process. It is possible to produce a profile component, which in sections has hardened regions and in sections non-hardened regions. The hardened regions can be partially hardened, completely hardened, or also partially hardened in sections and completely hardened in sections. For example, the forming of the profile component in DE 10 2007 024 797 A1 occurs by roll profiling and the heating of locally defined regions for strengthening these regions occurs before, during, or after the forming. 
         [0006]    The local spatial heating of the semifinished sheet metal part can be achieved advantageously by the inductive generation of an electromagnetic field or by a conductive current flow by means of the electrical resistance (or by a combination of these two processes), therefore, by dissipation of electrical energy. In other embodiments, there is also the possibility that the heat is introduced into defined regions of the semifinished sheet metal part by one or more laser light sources, by an infrared radiation source, or by means of a gas burner. Laser light sources have the advantage that the laser light generated by them can be focused, for example, by simple means also on a relatively small spatially delimited region of the semifinished sheet metal part to bring about local heating to the desired temperature in this region. 
         [0007]    In the so-called laser strengthening, in which regions, hardened at least in sections, in the profile component can be created, a carbon steel is heated for short time above the austenitizing temperature and converted by rapid cooling to the harder martensitic microstructure. In this regard, the heat is produced via the absorption of the laser radiation on the surface. The quenching occurs by heat conduction into the material interior. The hardening depth in laser strengthening is limited by the heat transport and self-quenching. The temporal temperature profile is determined substantially by the spot geometry of the laser beam at the machining site and the rate of advance of the laser beam relative to material. Laser sources often used in welding and laser strengthening are primarily the CO 2  and Nd:YAG laser, whereby the rapidly evolving fiber lasers are currently also gaining increasing acceptance in different technical fields. 
         [0008]    DE 10 2011 101 700 A1 describes the use of laser strengthening for selectively influencing the deformation behavior of a seat part structure. The aim is to prevent the buckling and breaking of the seat structure in greatly stressed regions of a backrest adjuster particularly in the event of a crash. This is to be achieved by introducing short laser-welded seams in this region. The laser-welded seams by means of the above-described process cause an increase in strength locally in the introduced regions. 
         [0009]    It is known that larger components, such as metal sheets, are in a metastable state because of the manufacturing process. The effect known as the “clicker” effect indicates that another stable or metastable state can be assumed with a relatively low force application to the component. The effect often accompanied by a noise indicates tensions in the component. These tensions disadvantageously induce instabilities in the component. 
         [0010]    The “clicker effect” occurs particularly in flat components whose width and/or length are considerably greater than their wall thickness, particularly in the case of the mentioned metal sheets. It is also known to occur when metal sheets are used in car body construction and when metal sheets are used in seat structures. 
         [0011]    To increase the stability of seat structures, known methods focus on wall thickenings to reduce the motion tolerance of the seat structure. 
         [0012]    A drawback of these methods, nevertheless, is that they are cost-intensive and lead to an increased weight of the component modified in this way. 
         [0013]    Another approach is the embossing of so-called ribbed structures. The ribbed structures stabilize a flat component without increasing the weight of the component. 
       SUMMARY OF THE INVENTION 
       [0014]    It is therefore an object of the invention to provide a method for a wall-like structure, which eliminates or at least reduces tensions within the wall-like structure and particularly prevents the “clicker effect” occurring in wall-like structures. 
         [0015]    A further object is to create a structural component, which is used as a wall-like structure in car body construction or within a seat structure of a vehicle seat and which is free of the negative “clicker effect.” 
         [0016]    It is clear that, as explained, wall-like structures refer to flat components that are more likely to have a thin wall thickness, so that the “clicker effect” generally occurs in a disadvantageous way. 
         [0017]    In particular, a seat structure, particularly a backrest of a vehicle seat or of a bench seat, is to be equipped with a wall-like structure, which is cost-effective and, moreover, does not increase the weight of the seat structure. 
         [0018]    The seat pan of a seat part in which such a “clicker effect” is also to be prevented and can also be considered to be a wall-like structure, for example. 
         [0019]    The starting point for the invention is a method for the targeted influencing of the deformation behavior of a wall-like structure, particularly a rear wall structure of a vehicle seat, which structure is heated in at least one region at least in sections by a laser light source. 
         [0020]    It is provided according to an embodiment of the invention that at least one region influencing the strength and/or tension of the wall-like structure can be selectively chosen and can be lasered to increase the strength of the wall-like structure and/or to reduce the tensions within the wall-like structure. 
         [0021]    Special cooling is not necessary in the method, because the desired characteristic physical properties are formed by the self-cooling of the wall-like structure in the desired manner within the material. 
         [0022]    A rear wall structure of a vehicle seat in particular, which has at least one laser-strengthened region and, as will still be explained, a reduced-tension region, is created by the use of the method in an advantageous manner. 
         [0023]    The invention thus also proposes performing a laser strengthening in a wall-like structure. 
         [0024]    During laser strengthening, so-called welding curves are determined depending on the material at a predefinable beam power of the laser source as a function of the welding depth [in mm] and welding speed [in m/min]. These welding curves enable a comparison of the various usable laser sources. 
         [0025]    For this reason, laser strengthening is also called laser beam welding, which in the use proposed here is not used to join components to one another by welding but causes a remelting of the material in at least one region, provided for this, of the wall-like structure, particularly a back wall/rear wall of the backrest of the seat structure. 
         [0026]    The remelting in a first effect advantageously has the result that an increased strength of the material is achieved in the at least one region. 
         [0027]    The remelting in a second effect advantageously has the result that a reduction of tensions within the material is achieved in the at least one region. 
         [0028]    In the heat-affected zone of the resulting laser welding tracks, martensite formation similar to classical hardening was determined in higher carbon steel. 
         [0029]    The seam structure of the low-carbon steels remains ferritic. The increase in strength occurs by the “quench aging process” in which the carbon remains partially in the a-lattice in supersaturated solution due to the rapid cooling and causes an increase in the deformation resistance. 
         [0030]    The advantages of using the method are that the laser beam hardening leads to a local increase in strength, especially the yield point in the hardened regions of the seat structure. 
         [0031]    Depending on the material, there is an increase in the yield point between 4% and 12%. 
         [0032]    The increased local strength in the back wall/rear wall of the backrest of the seat structure leads to an increased energy absorption of about 10% in the event of a crash. 
         [0033]    A particular advantage is further that steel parts as well, particularly similar wall-like structures with a lower carbon content can be hardened by laser beam hardening. 
         [0034]    The method of the invention advantageously selectively chooses regions on a rear wall structure in which regions laser strengthening reduces or even prevents the component movement responsible for the “clicker effect.” The criteria forming the basis for the selective choosing of the regions will be discussed in greater detail below. 
         [0035]    The method can be performed in exemplary embodiments of the invention in different steps, whose sequence may be variable, whereby an exemplary variant will be explained after the relevant process steps are indicated. 
         [0036]    In an exemplary embodiment of the invention, the wall-like structure can be connected to a support structure, whereby the lasering is performed optionally before, after, or during connection, particularly welding, to the support structure. 
         [0037]    The support structure can be, for example, a peripheral profiled frame close to the outer contour of the wall-like structure, which together with the wall-like structure forms, for example, the backrest structure of the backrest of a vehicle seat. 
         [0038]    In addition, the support structure can gives the backrest structure an increased stability, necessary for seat structures of a vehicle seat. 
         [0039]    In another embodiment of the invention, before or after connection, particularly welding, to the support structure, a ribbed structure having elevations and depressions can be introduced, for example, embedded into the wall-like structure. 
         [0040]    In an embodiment of the invention, the elevations and depressions of the ribbed structure can run in a linear manner in the wall-like structure. 
         [0041]    The linear elevations and depressions in exemplary embodiments are introduced as straight lines and/or as curves into the wall-like structure. The selection depends on the surface area or wall thickness of the wall-like structure. In practice, further, openings or the like can be located within the wall-like structure, so that the elevations and depressions, technologically simpler to introduce as lines, are replaced or supplemented by elevations and depressions introduced as curves. The explanation makes it clear that the design of the ribbed structure advantageously can be very variable. 
         [0042]    The method is notable particularly in that the lasering is performed optionally before or after the introduction of the ribbed structure having elevations and depressions. 
         [0043]    The procedure in the mentioned preferred variant is as follows. 
         [0044]    In a first step, the ribbed structure is introduced into the wall-like structure. With the introduction of the ribbed structure, there is advantageously a desired increase in stability in the wall-like structure. On the other hand, tensions arise within the material during the embossing of the ribbed structure, said tensions that are the cause of the “clicker effect.” 
         [0045]    In a second step, the connection to the support structure takes place, particularly to the mentioned profile frame. As explained, the stability of the component assembly having the ribbed structure and comprising the wall-like structure and support structure is advantageously increased still further thereby. 
         [0046]    During the connection, particularly the welding of the wall-like structure and the support structure, it also occurs due to the heat input during welding that the wall-like structure within the support structure becomes tensed, so that there is also the resulting risk that the “clicker effect” is initiated in the wall-like structure. 
         [0047]    The described approach, however, has the advantage that the ribbed structure of the wall-like structure can also be made in the region where the support structure is attached. The support structure is welded onto the surface or the wall-like structure such that the ribbed structures are arranged below the bearing surface of the support structure. 
         [0048]    This design has the effect that the component assembly comprising the wall-like structure and support structure with a ribbed structure taken up to the edge regions of the support structure is especially stable. 
         [0049]    As explained, it is also possible in the second step to connect the wall-like structure first to the support structure and to introduce the ribbed structure in a subsequent third step. In this case, however, a ribbed structure may no longer be introduced below the support structure, as a result of which the previously explained effect of the special stability is lost. 
         [0050]    In the third step, finally in the wall-like structure at least one laser-welded seam is introduced in the selective region, chosen for this, of the wall-like structure. 
         [0051]    The chosen selective region, in other words, is a localizable partial region of the wall-like structure, which is to be given a higher strength and in which arising tensions are to be reduced or are reduced advantageously, so that a “clicker effect” no longer occurs. 
         [0052]    The region is chosen depending on the dimensions and/or the wall thickness of the wall-like structure and/or depending on the height of the elevations and/or the depth of the depressions and/or the geometric form of the ribbed structure in the wall-like structure and/or depending on the geometric design of the support structure. 
         [0053]    Adherence to the indicated parameters results in a more accurate specification of the arrangement of the ribbed structure and/or the arrangement of the laser-welded seam structure and/or the selection of the welding parameters. 
         [0054]    It is provided in an embodiment of the invention that at least one laser-welded seam or a laser-welded seam structure comprising a plurality of laser-welded seams can be lasered into the wall-like structure, whereby the at least one or the plurality of laser-welded seams of the laser-welded seam structure (appropriate for the ribbed structure) can be introduced running linearly as straight lines and/or curves. 
         [0055]    In an embodiment, the laser-welded seams can be lasered horizontally and/or vertically onto the elevations and/or into the depressions of the wall-like structure. Such an embodiment will be explained in greater detail as an exemplary embodiment in the following description section. 
         [0056]    In another embodiment, it is provided that the elevations and/or depressions of the wall-like structure can be formed diagonal relative to an imaginary horizontal line of the wall-like structure. Similar to this, the at least one laser-welded seam or laser-welded seams based on the imaginary horizontal line are also lasered diagonally into the wall-like structure onto the elevations and/or into the depressions. 
         [0057]    Thus, the wall-like structure can have a ribbed structure, which is formed both by substantially vertical and horizontal as well as by diagonally arranged elevations and/or depressions. The at least one laser-welded seam or laser-welded seams is/are then lasered according to the invention onto the elevations or into the depressions. 
         [0058]    In the exemplary embodiment described hereafter, the ribbed structure can be formed by substantially vertical and horizontal elevations and depressions, arranged orthogonal to one another. The invention is not limited to this embodiment, however, because the elevations and depressions of the ribbed structure can also be arranged at a predefinable angle to one another within the wall-like structure relative to the imaginary horizontal line of the wall-like structure. The at least one laser-welded seam or laser-welded seams then run then not in the vertical and horizontal elevations, but are also lasered onto the elevations and into the depressions arranged diagonally relative to the imaginary horizontal line. 
         [0059]    In other words, the laser strengthening can be performed in an especially advantageous manner in selectively chosen regions only after welding of the rear wall structure to a support structure, particularly to a profile frame. 
         [0060]    The warpage possibly arising during the welding of the two components is reduced in an advantageous manner by the introduction of at least one laser-welded seam, as soon as the components have been welded together. 
         [0061]    A composite assembly that is more stable and has no “clicker effect” is created in an advantageous manner by the introduction of the at least one laser-welded seam and by the reduction of the warpage. The reduction of the tensions results overall in a reduced warpage of the wall-like structure and thus in a more stable component, particularly based on tendency of the wall-like structure to bend suddenly out of the plane of the wall-like structure, i.e., “clicker effect”. 
         [0062]    The introduction of the at least one laser-welded seam together with the welding of the support structure to the wall-like structure is of particular advantage, because these steps can be performed in the same tool simultaneously or quickly with one another. There are no costs for the transport from one tool to another tool, costs can be saved by the elimination of a tool and transport equipment, and the production time is reduced. 
         [0063]    The introduction of the ribbed structure into the wall-like structure, particularly the embossing of the ribbed structure, therefore occurs in an advantageous manner before the welding of the rear wall structure to the support structure. 
         [0064]    In an embodiment of the invention, in some exemplary embodiments horizontal and vertical ribs are run in chosen regions over the entire surface of the wall-like structure, particularly the rear wall structure. 
         [0065]    Earlier welding of the support structure to the rear wall structure would prevent embossing in terms of ribbing of the rear wall structure in the region of the support structure. The stabilization could therefore only be achieved in the interior of the support structure. 
         [0066]    An advantage of the later introduction of the laser-welded seam structure into the rear wall structure is that by the introduction of the ribbed structure and by the welding process during the connection of the rear wall structure to the support structure, induced tensions in the material can be reduced later by the subsequent laser welding. 
         [0067]    The wall-like structure forming within the method is explained in detail in the description. 
         [0068]    Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0069]    The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus, are not limitive of the present invention, and wherein: 
           [0070]      FIGS. 1 a  and 1 b    show a course of laser-welded seams on a rear wall structure of a vehicle seat according to an embodiment of the invention; 
           [0071]      FIG. 2 a    shows a vehicle seat with a seat part and a backrest part, whereby the backrest part has a wall-like structure with a support structure; 
           [0072]      FIGS. 2 b , 2 c , and 2 d    show laser-welded seam structures; 
           [0073]      FIGS. 3 a  and 3 b    show an exemplary embodiment of the arrangement of a support structure on a rear wall structure and a ribbed structure and a laser-welded seam structure arranged thereon; and 
           [0074]      FIG. 4  shows a relationship of two selected parameters in the laser welding process for creating strengthening lines on a wall-like structure, the rear wall structure. 
       
    
    
     DETAILED DESCRIPTION 
       [0075]    In the text below, the terms horizontal (from left to right) and vertical (from top to bottom) refer, for example, to a course of laser-welded seams  21 ,  22  and ribs  11 ,  12  in the plane of the rear wall structure in relation to the position of rear wall structure  10  shown in the figures. 
         [0076]      FIG. 1 a    shows by way of example the side, facing away from the upholstery, of a rear wall structure  10  of a vehicle seat F or a bench seat or a bench seat, comprising a plurality of vehicle seats F, in a motor vehicle. 
         [0077]      FIG. 2 a    shows a schematically illustrated vehicle seat F. It comprises a seat part S and a backrest R, whereby the wall-like structure is a rear wall structure  10  of backrest part R. Rear wall structure  10  is connected to a support structure  30 , particularly a profile frame. 
         [0078]    The invention will be described in greater detail with reference to the rear wall structure  10 , which is connected to support structure  30 . 
         [0079]    A ribbed structure  1112  embossed into the metal sheet of rear wall structure  10  can be seen in  FIG. 1   a.  Ribbed structure  1112  runs both vertically and horizontally. 
         [0080]    Elevations  11  and depressions  12  of the ribbed structure in the exemplary embodiment are arranged orthogonal to one another within rear wall structure  10 . 
         [0081]    Cut-outs for seat belt attachment, backrest adjustment, and attachment of rear wall structure  10  are shown in the left top edge region, in the right bottom edge region, and in the middle upper region. 
         [0082]    In a selected middle region, two horizontal laser-welded seams  21 , introduced in the shape of lines in rear wall structure  10 , run parallel to one another. 
         [0083]    In the initial example, horizontal laser-welded seams  21  run virtually over the entire width of rear wall structure  10 . 
         [0084]    A detail enlargement of rear wall structure  10  is shown in  FIG. 1   b.    
         [0085]    It can be seen by means of the enlargement that elevations  11  and depressions  12  of ribbed structure  1112  are each introduced close to the side edge of rear wall structure  10 . 
         [0086]      FIG. 1 b    shows, furthermore, that two horizontal laser-welded seams  21  (shown hatched) are run from an edge region over the middle region of rear wall structure  10 . Two horizontal laser-welded seams  21  are arranged one above the other at a small distance to one another in the middle region of rear wall structure  10 . 
         [0087]    Rear wall structure  10  in a selectively chosen region is strengthened by the arrangement of the two laser-welded seams  21 , whereby laser-welded seams  21 ,  22  in an embodiment of the invention are arranged within elevation  11  of ribbed structure  1112 . They exert the effects described below very effectively there, as tests have shown. 
         [0088]    The selectively chosen region of the laser-welded seam structures in this exemplary embodiment was chosen in a targeted manner over the entire width of rear wall structure  10 . 
         [0089]    This arrangement has the result that rear wall structure  10  is strengthened over the entire width. 
         [0090]    The strengthening is the greatest in the middle region due to the arrangement of the two horizontal laser-welded seams  21  one above the other, so that the greater tensions present in this middle region of rear wall structure  10  are prevented. 
         [0091]    The strength, particularly the bending strength of rear wall structure  10  in the middle of the rear wall structure is enhanced, on the one hand, by the laser strengthening in this region in an advantageous manner by the arrangement of the two horizontal laser-welded seams  21  one above the other. 
         [0092]    On the other hand, a heat input in the region, critical due to tension, of rear wall structure  10  occurs twice here by the introduction of heat by two laser-welded seams  21  lying very closely next to one another. 
         [0093]    This heating by the laser light source advantageously leads to a relaxation of the material structure of the illustrated rear wall structure  10  in the selected region. 
         [0094]    The laser strengthening lines can be introduced in the middle and/or at the edges in a ribbed structure  1112  in the selectively chosen region. 
         [0095]    The stabilizing effects of ribbed structure  1112  and laser-welded seam structure  20  are mutually strengthened thereby by the laser strengthening. 
         [0096]    It is provided that elevations  11  and depressions  12  of ribbed structure  1112  within rear wall structure  10  and horizontal and vertical laser-welded seams  21 ,  22  within rear wall structure  10  are arranged in each case orthogonal to one another. 
         [0097]    In an embodiment of the invention, a ribbed structure  1112  and a plurality of laser-welded seam structures  20  can be arranged on a rear wall structure  10 . 
         [0098]    The plurality of laser-welded seam structures  20  creates geometric forms, particularly laser-welded seams which are parallel to one another and are arranged at right angles to one another, particularly rectangles. 
         [0099]    Other possible arrangements of ribbed structures  1112  and associated laser-welded seam structures  20  are shown in an exemplary selection of three possible variants in  FIGS. 2 b  to 2 d    and are described hereafter. 
         [0100]    Shown are three schematic illustrations of rear wall structures  10  according to  FIG. 1 . 
         [0101]      FIG. 2 b    shows in a first variant three horizontal laser-welded seams  21 , parallel to one another and lying one above the other, as laser-welded seam structure  20 , which in each case run over the entire width of rear wall structure  10  and are arranged each in a horizontally running depression  12  (rib depression) of ribbed structure  1112 . 
         [0102]      FIG. 2 c    in a second variant shows a laser-welded seam structure  20 , introduced by laser strengthening. It is located in the central region of rear wall structure  10  and is made as a rectangle of two horizontal laser-welded seams  21 , running parallel to one another, and two vertical laser-welded seams  22 , substantially perpendicular thereto and likewise running parallel to one another. The horizontal and vertical laser-welded seams  21 ,  22  have their starting point and endpoint at an intersection or contact point of two lines. 
         [0103]    In a third variant according to  FIG. 2 d   , the horizontally running laser strengthening lines  21  extend beyond the points of intersection. Together with the vertically running laser-welded seams  22 , they form a rectangle as in  FIG. 2 c   , which is close to the center of rear wall structure  10 , but in the top middle region of rear wall structure  10 . 
         [0104]    However, the points of contact of vertical laser-welded seams  22  with the lower horizontal laser-welded seam  21  represent the starting point of vertical laser strengthening lines  21 . 
         [0105]    Structure  20  shown in  FIG. 2 d    by means of the laser strengthening alone or in combination with the shown ribbed structure  1112  represents an especially preferred variant, because it was determined that crossing laser-welded seams  21 ,  22  of laser-welded seam structure  20  affect especially advantageously the total strength of rear wall structure  10  and the reduction of tensions in rear wall structure  10 . 
         [0106]    All possible variants of the invention as shown in  FIGS. 2 b  to 2 d    have in common that they strengthen selectively chosen regions of rear wall structure  10 . 
         [0107]    The arrangement of laser-welded seams  21 ,  22  by means of their position, preferably on elevations  11  of ribbed structure  1112 , their length, and/or arrangement to one another within rear wall structure  10 , has a strengthening effect on the entire rear wall structure  10 . 
         [0108]    The arrangement of laser-welded seams  21 ,  22  in depressions  12  of ribbed structure  1112  is also conceivable according to the invention. 
         [0109]    Laser-welded seams  21 ,  22 , particularly in a preferred embodiment of the invention, are arranged parallel to the inner contour of support structure  30 , that is, running parallel to the inner contour of the profile frame. This design is especially advantageous, because the lines of action of support structure  30  run parallel to the lines of action of laser-welded seams  21 ,  22 . 
         [0110]    In particular, the bending strength of rear wall structure  10  is greatly increased thereby. 
         [0111]    Moreover, at least some of the horizontal and vertical laser-welded seams  21 ,  22  are arranged so that during the strengthening process they heat the material in selected regions by means of a laser light source. The selected regions are chosen so that the regions characterized by undesirable tensions are treated with heat, whereby these tensions are reduced during the heating by laser welding. 
         [0112]    In an embodiment of the invention, shown in  FIGS. 3 a  and 3 b   , it is provided that laser-welded seam structure  20  is arranged within the support structure, particularly profile frame  30 . 
         [0113]      FIG. 3 a    in this regard shows schematically two rear wall structures  10 , connected to one another, on the side facing away from upholstery. 
         [0114]    As in  FIGS. 1   a,    1   b  and  2   b  to  2   d , a ribbed structure  1112  is introduced, which in the shown exemplary embodiment was created by rib embossing. 
         [0115]    The laser-welded seam structure  20  introduced by means of the laser strengthening corresponds to the exemplary embodiment according to  FIG. 2   d.    
         [0116]    The difference between  FIGS. 2 c  and 3 a    is that rear wall structure  10  in the exemplary embodiment according to  FIG. 3 a    is connected to profile frame  30  as a support structure. 
         [0117]    It is mentioned at this point that other profile frames as well, which have only one top and bottom opposite support structure  30  of profiles or a support structure arranged opposite to the left and right, can be connected to rear wall structure  10 . As explained, ribbed structures  1112  or laser-welded seam structures  20  are adapted to this modified support structure  30 ; that is, other geometric arrangements are optionally formed for laser-welded seam structures  20 , which have not been described in greater detail here. 
         [0118]    Laser-welded seam structure  20  due to the laser strengthening in this exemplary embodiment is located within support structure  30 ; that is, laser-welded seams N;  21 ,  22  do not extend beyond the inner contour of support structure  30 . 
         [0119]    It is particularly made clear in  FIGS. 3 a , 3 a    that ribbed structure  1112  is formed in the bearing surface of profile frame  30  on the rear wall structure and even peripherally projects over the outer contour of profile frame  30 , as a result of which the ribbed structure is visible beyond profile frame  30 . 
         [0120]    It was already explained that this arrangement is possible, because ribbed structure  1112  was introduced before the attachment of profile frame  30  to rear wall structure  10 . 
         [0121]    In a sectional illustration through rear wall structure  10 , ribbed structure  1112 , particularly a depression  12  (rib depression) and thereto an elevation  11  (rib elevation) in the wall-like structure, is shown in  FIG. 3 b   . A distance Δx of 2 mm, for example, is selected between a depression and elevation. The wall thickness of rear wall structure  10 , therefore of the metal sheet, is, for example, about 0.5 mm. 
         [0122]    Shown is the alternative course of a laser-welded seam N;  21 ,  22 , which is shown hatched analogous to  FIG. 1   b;  unlike in the previous  FIGS. 1   a,    1   b,    2   b ,  2   c ,  2   d , it runs orthogonal to depression  12  and runs onto an adjacent elevation  11  of ribbed structure  1112  on one side or, as shown in  FIG. 3 b   , onto an adjacent elevation  11  of ribbed structure  1112  on both sides. 
         [0123]    It can be assured likewise advantageously by this orthogonal course that the strengthening effects of ribbed structure  1112  and laser-welded seam structure  20  due to the laser strengthening overlap and strengthen further, so that the “clicker effect” is prevented. 
         [0124]    The particular horizontal or vertical laser-welded seam N;  21 ,  22  in this embodiment runs orthogonal to at least one depression  12  onto at least one elevation  11  or even beyond the at least one elevation  11  to next depression  12 , in which the particular horizontal or vertical laser-welded seam N;  21 ,  22  continues and again crosses the particular depression  12  orthogonally. 
         [0125]    The orthogonal crossing of one or more depressions  12  or one or more elevations  11  of a laser-welded seam or a plurality of laser-welded seams N;  21 ,  22 , as shown in  FIG. 3 b   , also represents only one variant, however. 
         [0126]    It is also provided in other variants that one or more laser-welded seams N;  21 ,  22  cross one or more depressions  12  or one or more elevations  11  not orthogonally but at a predefinable angle. The one or the plurality of laser-welded seams N;  21 ,  22  in these variants therefore do not run in depressions  12  and/or on elevations  12 , but cross depressions  12  and/or elevations  12  at a predefinable angle, preferably orthogonally. 
         [0127]    The already mentioned course of ribbed structure  1112  beyond support structure  30 , that is, below support structure  30 , in each embodiment advantageously enables stabilization of the regions of rear wall structure  10 , which regions project on the edges beyond support structure  30 . 
         [0128]    It is necessary for this purpose to arrange ribbed structure  1112 , as explained, before the welding of rear wall structure  10  to profile frame  30 . 
         [0129]    Laser-welded seam structure  20  in the preferred process is introduced after the welding to profile frame  30 . 
         [0130]    The warpage, not to be prevented totally in the welding process during the connection of profile frame  30  to rear wall structure  10  and/or during the introduction of ribbed structure  1112 , is greatest within the inner contour of the profile frame, because this is a closed region, which permits no relaxation in a direction lying in the plane of rear wall structure  10 . The warpage can therefore be relaxed only orthogonally to the plane, as a result of which the “clicker effect” occurs, which is advantageously prevented by this invention, however. 
         [0131]    The introduction of a laser-welded seam structure  20  by laser strengthening by the method of the invention necessarily leads to a heating of critical regions and thus to a reduction of warpage. Moreover, the laser-strengthened regions are hardened and by the selection of the arrangement of laser-welded seam structure  20  by means of the laser strengthening strengthen the entire region in the interior of support structure  30 . The sum of the described effects makes the occurrence of a so-called “clicker effect” virtually impossible. 
         [0132]    Apart from the arrangement of laser-welded seam structure  20  by means of laser strengthening, the parameters for introducing the structure are critical for the combination of strengthening and relaxation of the entire rear wall structure. 
         [0133]    Critical process-engineering welding parameters in this case are the type of laser source, the power of the laser source, the focal spot diameter or defocus, the laser travel speed (rate of advance v), and the depth E and width of the strengthening track. 
         [0134]    A possible combination provides for the operation of an Nd:YAG laser (type of laser source) with a 4 kW burning power and a defocus of 30 mm. 
         [0135]      FIG. 4  shows the effect of the travel speed or rate of advance v of such a laser on the welding depth E during laser strengthening of a material HC300X, mentioned by way of example, in a 0.5 mm wall thickness based on a characteristic K and an associated interpolated characteristic K 1 . 
         [0136]    In order to produce the described positive and desired properties of the method of the invention, there can be especially no burn-through (E=100%) through the particular material. 
         [0137]    Laser-welded seam structure  20  can be introduced on one side or on both sides of rear wall structure  10 . 
         [0138]    Rear wall structure  10 , lasered according to the method of the invention, therefore has at least one laser-welded seam N;  21 ,  22  on at least one side or on both sides. 
         [0139]    For an optimal result, a minimum penetration depth of E=50% should be produced. 
         [0140]    In laser welding on both sides, the laser-welded seams N;  21 ,  22  are to be formed in different regions, because otherwise a burn-through of laser-welded seams  21 ,  22  may occur. 
         [0141]    The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are to be included within the scope of the following claims.