Hollow beams and methods for manufacturing a vehicle body

Abstract

Hollow beam with a semi-shell-shaped profile section (3) having a shell base (7) and profile flanks (9) extending upwards therefrom, and defining an interior space (15) which is closed by a cover plate section (5), wherein the interior space (15) of the hollow beam (1) is subdivided by at least one bulkhead plate section (17) which is attached on the inside to the profile section (3) and at least one joint on the inside to the cover plate section (5), characterized in that the bulkhead plate section (17) has an actuating element (25) which, when actuated, allows the bulkhead plate section (17) to be adjusted between a pre-assembly state (V), in which the bulkhead plate section (17) has a reduced component cross-section and is spaced from the cover plate section (5) by a free joint gap (f), and an assembly state (Z), in which the bulkhead plate section (17) is joined to the cover plate section (5) by expanding its cross-section and at least partially utilizing the joint gap (f). is bringableand that the actuator (25) is thermally activatable, so that when heat is applied, the bulkhead part (17) changes from its pre-assembly state (V) to its assembled state (Z).

Description

[0001] The invention relates to a hollow beam, in particular a body hollow beam for a vehicle, according to the preamble of claim 1, a method for manufacturing a vehicle body according to claim 9 and a bulkhead sheet metal part according to claim 11.

[0002] The body structure of a vehicle uses elongated hollow beams with a closed cross-section as load-bearing elements, for example as vehicle pillars and / or in the vehicle floor as longitudinal beams and as transverse beams.

[0003] A hollow beam of this type consists of a semi-shell-shaped sheet metal profile and a cover plate. The sheet metal profile can have a U-shaped cross-section and a shell base as well as profile sides that extend upwards from it. Joining flanges project laterally from these upwards, which are, for example, spot-welded to the cover plate that closes the interior of the hollow beam. To increase the component stiffness, particularly with regard to crash safety, at least one bulkhead sheet metal section can be incorporated into the hollow beam. In common practice, this bulkhead sheet metal section has a base wall that divides the interior of the hollow beam, from which sheet metal tabs are angled at the edges. These tabs are spot-welded and / or adhesively bonded to the inner walls of the shell-shaped profile and the cover plate.The assembly of such a hollow beam of this type is carried out in the following process steps: First, in a first process step, the bulkhead sheet metal part is inserted into the still open interior of the shell-shaped profile section and secured there, for example, by resistance spot welding. Then, in a second process step (joining step), the cover sheet metal part is flange-connected to the shell-shaped profile section. In a subsequent process step, the cover sheet metal part is joined on the inside to a corresponding sheet metal tab of the bulkhead sheet metal part.

[0004] Immediately following the joining operations described above, the car body, including the bulkheads, undergoes an e-coating (e-coating) process. During this process, the car body, including the bulkheads, is heated to over 180°C. Different body components expand to varying degrees during this e-coating cycle due to their different materials and correspondingly different coefficients of thermal expansion. Thin-walled components naturally absorb heat more quickly and expand significantly faster, especially in the initial heating phase, than thick-walled components. Furthermore, external components come into contact with the e-coating bath earlier and therefore expand more rapidly, particularly in the initial phase, than internal components, which the e-coating bath must first reach.

[0005] The process sequence outlined above presents the following problem: Single-component adhesives are typically used to join such bulkheads. These adhesives only cure under the influence of heat during the e-coating bath. As with any adhesive bond, relative movement of the bonded components must be avoided as much as possible until the adhesive has cured, as this would impair the quality of the resulting bond. However, after the initial contact of the car body with the e-coating bath, the individual body components expand to varying degrees for numerous reasons, as described above. This leads to mechanical stresses within the car body, which, in the case of the still-curing adhesive bonds, cause the aforementioned relative movement and thus compromise the quality of the bond.

[0006] From DE 10 2004 044 509 B4 a method for connecting and stabilizing thermally and mechanically stressed, thin walls with a flat frame sheet part is known.

[0007] The object of the invention is to provide a hollow beam and a method for assembling a hollow beam that can be easily and reliably assembled.

[0008] The problem is solved by the features of claim 1, 9 or 11. Preferred embodiments of the invention are disclosed in the dependent claims.

[0009] The invention is generally based on the fact that the bulkhead plate component is no longer provided as a completely rigid component, which, due to tolerances, may not be able to be installed flawlessly in the hollow beam. Rather, according to the characterizing part of claim 1, an actuator is assigned to the bulkhead plate component, the actuation of which allows the bulkhead plate component to be adjusted between a pre-assembly state and an assembled state. In the pre-assembly state, the bulkhead plate component has a reduced component cross-section and is still spaced from the cover plate component by a free joining gap. In the assembled state, on the other hand, the bulkhead plate component can be brought into joint contact with the cover plate component by expanding its cross-section and at least partially utilizing the aforementioned joining gap. According to the invention, the actuator can be thermally activated.This means that with a suitably designed heat supply, the bulkhead sheet metal part is automatically (i.e., solely due to the heat supply) transformed from its pre-assembly state to its assembled state.

[0010] In one technical implementation, the thermally activated actuator can be integrally integrated into the bulkhead component. In this case, the actuator can be implemented as a bistable spring section that is adjustable between a first and a second equilibrium state by utilizing the so-called spring-load effect. In the first equilibrium state, the bulkhead component is in a cross-section-reduced pre-assembly state, while in the second equilibrium state, the bulkhead component is in a cross-section-expanded assembled state, ensuring a reliable joint (especially an adhesive bond) between the bulkhead component and the cover plate component.

[0011] The invention is particularly relevant to the aforementioned process sequence for manufacturing the vehicle body. In this process sequence, the invention is based on the premise that the e-coating step is conceptually divided into two phases: an initial warm-up phase and a subsequent steady-state phase. In the initial warm-up phase, the vehicle body is immersed in an e-coating bath and heated to the e-coating process temperature. This warm-up phase is accompanied by significantly different thermal expansions of the individual body components. In the subsequent steady-state phase, however, the vehicle body is heated to the process temperature essentially uniformly, so that no further thermal expansion of the body components occurs during this phase.

[0012] The invention utilizes the above situation as follows: The bulkhead component can be designed such that it remains in its pre-assembly state during both the assembly step and the heating phase of the e-coating step, in which the bulkhead component is not yet bonded to the cover sheet component. Only during the heat application occurring during the stationary e-coating phase is the bulkhead component thermally activated and brought into the assembled state, in which the adhesive bond between the bulkhead component and the cover sheet component is created and simultaneously cured.

[0013] According to the invention, the bulkhead is designed using suitable forming and joining processes such that the adhesive bond is only formed after heating in the e-coating bath. The joining partners to be bonded therefore do not yet have contact during the heating phase when immersed in the e-coating bath. For this purpose, a spring-loaded bulge is introduced into the bulkhead, which changes its state during the e-coating process. The process is irreversible, meaning that the state of the bulkhead remains unchanged after a single heating in the e-coating bath.

[0014] This results in the following advantages: The components to be joined do not yet have contact with each other during the heating phase when the car body is immersed in the e-coating bath. The inevitable mechanical stresses and the associated relative movements within the car body therefore have no negative impact on the quality of the resulting adhesive bond. The mechanical stresses that occur after the e-coating bath when the car body cools are unproblematic, as the adhesive has already cured by this time. Such stresses can therefore be easily withstood by the adhesive bond.

[0015] In a preferred technical implementation, the bulkhead plate consists of two sheets, which are welded together as a "tailor-welded blank" before forming: a core sheet and a frame sheet. The core sheet is typically made of a material with a relatively high coefficient of thermal expansion, such as aluminum. Its characteristic feature is its X-shape with rounded corners. The frame sheet is made of a material with a relatively low coefficient of thermal expansion, such as steel. Its characteristic features are its rectangular or trapezoidal shape, its central X-shaped cutout (corresponding exactly to the outer contour of the core sheet), and the tabs along its edge.

[0016] The frame sheet and core sheet are each sheet metal parts that generally have the same thickness. The production of a bulkhead sheet according to the invention is divided into the following steps: First, the frame sheet and core sheet are produced. The two sheet metal parts are, for example, laser-cut or punched from a coil or a sheet blank. Then, the frame sheet and the core sheet are joined together as a tailor-welded blank. The two sheets are generally welded together by FSW or laser welding. In any case, the weld seam must run continuously and be largely seamless, so that the entire outer contour of the core is welded to the frame sheet. Next, a basic curvature (2-dimensional) is applied, for example, using a 3-point bending roller, which creates a basic curvature with a constant radius in the entire bulkhead sheet.This radius varies depending on the dimensions and material combination of the bulkhead plate and is generally between 600 and 900 mm. This basic radius facilitates the subsequent formation of spring buckling. In particular, it ensures that a change in the shape of the bulkhead plate occurs during spring buckling (change in length due to the increased basic radius).

[0017] The bulge and tabs are then created. This is done, for example, by stretch forming, which introduces a spring-loaded bulge with two stable states into the center of the bulkhead plate. In this manufacturing step, tabs for later fastening of the bulkhead plate are also formed on at least three of the four edges; these are not shown in the illustrations presented here. At least one of these tabs is a "movable tab," meaning a tab that changes its angle or position during the transition between the two states of the bulkhead plate.

[0018] The two states of the bulkhead are, on the one hand, the "feeding" state and, on the other hand, the "joining" state. In the "feeding" state (i.e., the pre-assembly state), the bulkhead is placed in the e-coating bath. This state is relatively unstable, and the force required to transition between states is extremely low. The cross-section of the bulkhead has two high points in the direction of the original curvature and one low point in the opposite direction. The "joining" state (i.e., the assembly state) is very stable – the force required to transition between states is very high. The cross-section of the bulkhead has a simple curvature formed in the direction of the original curvature.

[0019] The joining of a bulkhead according to the invention is then divided into the following steps: First, the bulkhead is inserted into the outer sheet. This is done as before, for example by resistance spot welding. The previously formed tabs are required for this. Next, adhesive is applied to a movable tab. As before, a one-component adhesive is used here, which only cures during the e-coating process. The adhesive is applied to the movable tab of the bulkhead. Then the inner sheet is joined to the outer sheet.

[0020] Unlike previous methods, this process does not involve contact between the adhesive applied to the bulkhead and the inner sheet metal.

[0021] The resulting composite component is immersed in a cathodic dip coating (KTL) bath, heating the bulkhead sheet to over 180°C. The frame sheet of the bulkhead sheet expands only marginally compared to its core sheet (due to its low coefficient of thermal expansion). The core sheet, however, expands significantly, pushing the bulge beyond a zero line and thus bringing the bulkhead sheet into the "bonding" state. This causes the adhesive-coated movable tabs of the bulkhead sheet to snap outwards, creating an adhesive bond with the inner sheet.

[0022] This joining process is irreversible: After the bulkhead sheet cools, it remains in the "joined" state. This is due to the very stable nature of the "joined" state.

[0023] The "X-shape" of the core sheet metal part results in a continuous stress distribution within the spring bulge, which counteracts plastic deformation of the spring bulge during state transitions. Theoretically, a rectangular core sheet metal part could also be used, but then large stress peaks would occur in the transition area between the core sheet metal part and the frame sheet metal part during state transitions, leading to the aforementioned plastic deformations.

[0024] As mentioned above, the invention utilizes the so-called spring-buck effect. For this purpose, the spring-buck effect (also known as the "crack frog effect" or "hard oil canning") is introduced into the bulkhead sheet metal part by suitable forming operations, such as stretch forming. A bulge is formed into the base surface of the bulkhead sheet metal part. This bulge is designed such that a force applied in the opposite direction of its formation causes it to "flip" into a second equilibrium state. After this flip, the spring-buck is formed in the opposite direction. The base surface of the bulkhead sheet metal part is oriented to the inner cross-section of the hollow beam and can, for example, be rectangular or trapezoidal. In one embodiment, the bulkhead sheet metal part according to the invention can have three fixed, rigid sheet metal tabs that can be rigidly connected to the inner wall of the half-shell-shaped profile part.Rigid sheet metal tabs are attached to three of the four edges of the base. These tabs are bent upwards / downwards at an angle of approximately 90° to the base of the bulkhead. For example, three of the sheet metal tabs of the bulkhead can be connected to the shell-shaped profile by resistance spot welding. This can optionally be combined with bonding. The fixed, rigid sheet metal tabs undergo no or only minimal deformation during the transition of the bulkhead between the first and second equilibrium states.

[0025] In addition to the three fixed, rigid sheet metal tabs mentioned above, at least one movable sheet metal tab may be provided on the bulkhead component. This may be formed on the edge of the bulkhead component where no fixed, rigid sheet metal tab is formed. The movable sheet metal tab changes its angle to the base surface during the transition of the bulkhead component's state.

[0026] Further aspects of the invention are described below, which essentially relate to the component geometry of the bulkhead sheet metal part: The bulkhead sheet metal part can have a base wall dividing the interior of the hollow beam, which transitions at its edge side facing the cover sheet metal part into at least one angled, movable sheet metal tab that is movable between the pre-assembly state and the assembly state.

[0027] The spring bulge embossed into the base wall of the bulkhead sheet metal part can, upon thermal activation of the movable tab, impose a pivoting movement around a tilting axis. During this pivoting movement, the movable tab comes into contact with the cover sheet metal part, thereby utilizing the joining gap.

[0028] Preferably, the bulge can be realized as a dome-shaped base bulge in the base wall of the bulkhead component. In the pre-assembly state, the spring bulge can be formed into this base bulge, with its apex set back from the base bulge by one bulge depth. During thermal transformation to the assembled state, the spring bulge can snap over in the direction of the base bulge, utilizing this bulge depth. This results in an assembled state where the bulge flanks of the base bulge converge at the now raised apex of the spring bulge with essentially uniform (i.e., without a change in sign) slope.

[0029] The aforementioned tilting axis, around which the movable tab can pivot, can be realized as a pivoting web formed in the bulkhead base wall.

[0030] In a preferred embodiment, the bulge apex can be realized as a straight apex edge. This can be essentially parallel to the aforementioned tilting axis of the movable sheet metal tab. Alternatively, the spring bulge can also be formed as a circular indentation in the base curvature of the bulkhead sheet metal base wall.

[0031] In one technical implementation, the bulkhead blank can be realized as a tailor-welded blank. In this case, the bulkhead blank can be constructed from a circumferential frame blank that defines a recess into which a core blank is inserted. The core blank is contour-matched to the recess and welded to the edge of the recess. For optimal thermal activation of the bulkhead blank, it is preferred that the frame blank is made of a material with a low coefficient of thermal expansion and the core blank is made of a material with a high coefficient of thermal expansion.

[0032] The bulkhead base wall can, in addition to the movable sheet metal tab, have further rigid sheet metal tabs angled at its edges, as already described above. These rigid sheet metal tabs allow the bulkhead to be attached to the shell base and to the profile sides of the shell-shaped profile section. In contrast, the pivoting web formed in the base wall may not be connected to the shell-shaped profile section via sheet metal tabs at its axial end faces, but rather be free of any connection to the profile section in order to ensure smooth tilting movement of the movable sheet metal tab.

[0033] The base wall of the bulkhead can be extended beyond the tilting axis with at least one supporting leg, which transitions at a transition edge into the movable sheet metal tab projecting from it at a substantially right angle. In this case, the bulkhead acts as a two-armed lever arm, with the spring bulge formed on a first lever arm and the movable sheet metal tab formed on a second lever arm with respect to the tilting axis.

[0034] In the pre-assembled state, the supporting leg of the bulkhead plate component can be oriented essentially perpendicular to the cover plate component and spaced apart from it by the joining gap. The distance between the tilting axis and the transition edge is smaller than the distance between the tilting axis and a free edge of the sheet metal tab. This ensures that, during the transition to the assembled state, the movable sheet metal tab can be brought into contact with the cover plate component, at least partially utilizing the joining gap.

[0035] An embodiment of the invention is described below with reference to the accompanying figures.

[0036] They show: Fig. 1. A perspective drawing of an assembled hollow beam; Fig. 2 a bulkhead sheet metal part that can be installed in the hollow beam, both in standalone position and in the pre-assembled state; Fig. 3 to 6 each show views illustrating a process sequence for assembling the hollow beam; Fig. 7 to 9 views illustrating the manufacture of the bulkhead sheet metal part; and Fig. 10 A simplified block diagram illustrating a process sequence in car body manufacturing.

[0037] In the Fig. Figure 1 shows an assembled hollow beam 1, as it can be used as an example of a load-bearing element in the body structure of a motor vehicle. The hollow beam 1 is constructed in two parts, namely a semi-shell-shaped sheet metal profile part 3 and a cover sheet part 5. The semi-shell-shaped sheet metal profile part 3 has a shell base 7, from which profile walls 9 extend, transitioning into laterally angled joining flanges 11. The joining flanges 11 of the sheet metal profile part 3 are located in the Fig. 1 in flange connection with corresponding joining flanges 13 of the cover plate part 5.

[0038] The sheet metal profile part 3, together with the cover sheet part 5, defines a closed interior space 15, which is located in the Fig. 1 is divided by a bulkhead sheet metal part 17. The bulkhead sheet metal part 17 has a rectangular base wall 19 dividing the interior 15, from which rigid sheet metal tabs 21 are bent at the edges, which are joined 41 to the shell base 7 and to the profile walls 9 of the shell-shaped sheet metal profile part 3. In addition, the bulkhead sheet metal part 17 is bonded to the shell base 7 and the profile walls 9 of the shell-shaped sheet metal profile part 3 via two movable sheet metal tabs 23 ( Fig. 6) with the inside of the cover plate part 5. The movable sheet metal tabs 23 can be thermally activated by a spring bulge 25 formed in the base wall 19 ( Fig. 2 to 5) can be adjusted, specifically between a pre-assembly state V ( Fig. 2 to 5) and an assembly state Z ( Fig. 6), as will be explained later. The spring-loaded bulge 25 therefore generally acts as an actuator formed in the bulkhead part 17, which can be activated thermally (i.e. by the input of heat) in order to transfer the bulkhead part 17 from the pre-assembly state V to the assembled state Z.

[0039] The following is based on the Fig. 2. The component geometry of the bulkhead sheet metal part 17 according to the invention is described: A protrusion 26 is embossed into the base wall 19 of the bulkhead sheet metal part 17. The protrusion 26 is located in the Fig. 2 is designed in two parts, namely from a dome-shaped base bulge 28, which extends essentially over the entire base wall 19 of the bulkhead plate part 17, and into the spring bulge 25. The spring bulge 25 is in the Fig. 2 pre-assembly state V shown in the basic curvature 28, formed with a bulge depth t ( Fig. 3) spring bulge apex 27 set back from the base 28 ( Fig. 3) The spring-loaded bulge 25 can be removed during thermal transfer to the assembled state Z ( Fig. 1 or Fig. 6) snap over in the direction of curvature of the base curvature 28, using up the buckling depth t. In this case, the result is in the Fig. 1 or Fig. 6 Assembly state Z shown, in which the camber flanks of the base camber 28 with essentially uniform slope (without change of sign) meet the now raised spring bulge apex 27 ( Fig. 6) converge.

[0040] In the Fig. 3 The base wall 19 of the bulkhead plate section 17 transitions into a pivoting web 33, which defines a tilting axis K (described later) about which the movable plate tabs 23 can pivot or tilt. The base wall 19 extends beyond the tilting axis K with two support legs 35 spaced apart from each other by a recess 34. Each of these support legs 35 extends at a transition edge 37 ( Fig. 2) into a movable sheet metal tab 23 projecting from it at an essentially right angle.

[0041] As from the Fig. 2 or Fig. As further shown in Figure 7, the bulkhead sheet metal part 17 is not formed in one piece, but rather as a tailor-welded blank consisting of an outer frame sheet metal part 32 and an inner core sheet metal part 34. The outer circumferential frame sheet metal part 32 defines a sheet metal recess into which the core sheet metal part 34 is fitted and welded to the edge of the sheet metal recess. Furthermore, the core sheet metal part 34 is made of a material with a high coefficient of thermal expansion, while the frame sheet metal part 32 is made of a material with a low coefficient of thermal expansion. Both the movable tabs 23 and the rigid sheet metal tabs 21 are formed on the frame sheet metal part 32. In contrast, the spring bulge 25 is formed on the core sheet metal part 34.

[0042] To ensure a smooth tilting movement of the movable sheet metal tabs 23 between the pre-assembly state V and the assembly state Z, a pivoting web 33 formed in the base wall 19 ( Fig. 2), which defines a tilting axis K, spaced apart at its axial end faces from the profile walls 9 of the shell-shaped sheet metal profile part 3, i.e. without connection to the sheet metal profile part 3.

[0043] The following is a process sequence for assembling the [item] in the Fig. 1 shown hollow beam 1 based on the Fig. 3 to 6 described: In a first process step ( Fig. 3) First, the bulkhead sheet metal part 17 is attached to the shell-shaped sheet metal profile part 3 by means of spot welds 41 on the profile walls 9 and on the shell base 7 of the sheet metal profile part 3. In the Fig. 3 the bulkhead part 17 is in its pre-assembly state V, in which the bulkhead part 17 has a difference compared to the assembly state Z ( Fig. 6) occupies a reduced component cross-section.

[0044] Then, according to the Fig. 4 an adhesive application in which an adhesive 43 is applied to the outside of the movable sheet metal tab 23. Subsequently, according to the Fig. 5 The cover plate part 5 is joined to the sheet metal profile part 7 at spot weld points 44. In the Fig. 5 the bulkhead part 17 is still in the pre-assembly state V, in which the movable sheet metal tab 23 is spaced from the cover sheet part 5 by a joining gap f.

[0045] To create an adhesive bond between the bulkhead plate part 17 and the cover plate part 5, the bulkhead plate part 17 is subjected to heat. This leads to material expansion and material stresses in the area of ​​the spring bulge 25. The material stresses are relieved by the spring bulge 25 transitioning from its first equilibrium state (i.e., pre-assembly state V) to the second equilibrium state (i.e., assembled state Z), as described in the Fig. 6 is shown. The snapping or flipping of the spring-loaded bulge 25 simultaneously causes a tilting movement of the movable sheet metal tabs 23, which are bonded together ( Fig. 6) is brought with the cover plate part 5.

[0046] Based on the Fig. Figures 7 to 9 indicate process steps for manufacturing the bulkhead sheet metal part 17. Accordingly, the frame sheet metal part 32 and the core sheet metal part 34 are shown to have the same sheet thickness. The manufacture of a bulkhead sheet metal part 17 according to the invention is divided into the following steps: First, the frame sheet metal part 32 and the core sheet metal part 34 are manufactured separately. The two sheet metal parts 32, 34 are, for example, laser-cut or punched from a coil or a sheet metal blank. Subsequently, the frame sheet metal part 32 and the core sheet metal part 34 are joined together as a tailor-welded blank. The two sheets 32, 34 are welded together, for example, by FSW or laser welding.

[0047] Then the dome-shaped base 28 is inserted ( Fig. 8) This is done, for example, with a 3-point bending roller, which introduces a basic curvature with a constant radius into the entire bulkhead sheet. The spring bulges 25 are then formed ( Fig. 9) and the tabs 21, 23 are produced. The spring bulge 25 is formed centrally into the base curve 28 by stretch forming. In this manufacturing step, the tabs 21, 23 for later fastening of the bulkhead plate are also formed on at least three of the four edges of the bulkhead plate.

[0048] In the Fig. Figure 10 shows a simplified block diagram illustrating a process sequence for manufacturing a vehicle body. Accordingly, in an assembly step, the vehicle body is first assembled, forming the structure shown in the diagram. Fig. The hollow beam 3 shown in Figure 5, in which the adhesive bond between the bulkhead plate part 17 and the cover plate part 5 has not yet been established. After the assembly of the vehicle body, a KTL step is carried out in which the vehicle body is dip-coated. In the Fig. The e-coating (KTL) process is divided into a warm-up phase A and a steady-state phase S. In warm-up phase A, the vehicle body is immersed in an e-coat bath and heated to the e-coating process temperature. This occurs despite the different rates of thermal expansion of the body components. Warm-up phase A transitions into steady-state phase S, in which the vehicle body is heated to a virtually uniform e-coating process temperature, thus preventing any further thermal expansion of the body components.

[0049] The bulkhead sheet metal part 17 is designed according to the invention such that it remains reliably in its pre-assembly state V, in which the adhesive bond with the cover sheet metal part 5 has not yet been established, both during the assembly step and during the warm-up phase A of the e-coating step. Only through the heat input occurring in the steady-state phase S is the bulkhead sheet metal part 17 thermally activated and brought into its assembled state Z ( Fig. 1 or Fig. 6) transferred, in which the adhesive bond between the bulkhead part 17 and the cover plate part 5 is established and the adhesive 43 can cure.

Claims

[1] Hollow beam with a semi-shell-shaped profile part (3) having a shell bottom (7) and profile flanks (9) raised therefrom and defining an interior space (15) which is closed by a cover plate part (5), wherein the interior space (15) of the hollow beam (1) is subdivided by at least one bulkhead plate part (17) which is attached on the inside to the profile part (3) and at at least one joint on the inside to the cover plate part (5), characterized by, that the bulkhead part (17) has an actuator (25) which, when actuated, allows the bulkhead part (17) to be adjusted between a pre-assembly state (V), in which the bulkhead part (17) has a reduced component cross-section and is spaced from the cover plate part (5) by a free joining gap (f), and an assembly state (Z), in which the bulkhead part (17) can be brought into joining connection with the cover plate part (5) by expanding its cross-section and by at least partially using up the joining gap (f), and that the actuator (25) can be thermally activated, so that when heat is applied the bulkhead part (17) changes from its pre-assembly state (V) to its assembly state (Z). [2] Hollow beam according to claim 1, characterized by, that the actuator (25) is integrally integrated into the bulkhead part (17), and that the actuator (25) is a bistable spring section with two stable equilibrium states, in the first equilibrium state of which the bulkhead part (17) is in the pre-assembly state (V) and in the second equilibrium state of which the bulkhead part (17) is in the assembly state (Z), using a thermally activatable spring buckling effect. [3] Hollow beam according to claim 2, characterized by , that the bulkhead sheet part (17) has a base wall (19) dividing the hollow beam interior (15), which transitions on its edge side facing the cover sheet part into at least one angled, movable sheet metal tab (23) which is movable between the pre-assembly state (V) and the assembly state (Z). [4] Hollow beam according to claim 3, characterized by, that the bistable spring section (25) is a spring bump in the base wall (19) which, upon thermal activation of the movable tab (23) about a tilting axis (K), imposes a pivoting movement in which the movable tab (23) comes into joining connection with the cover sheet part (5) by breaking up the joining gap (f). [5] Hollow beam according to claim 4, characterized by, that the bulge (26) has a dome-shaped base bulge (28) in the base wall (19), and that in the pre-assembly state (V) the spring bulge (25) is formed into the base bulge (28), with a spring bulge apex (27) set back from the base bulge (28) by a bulge depth (t), and that during thermal transfer to the assembly state (Z) the spring bulge (25) snaps over in the direction of the bulge of the base bulge (28) while using up the bulge depth (t), and that in the assembly state (Z) the bulge flanks of the base bulge (28) converge with a uniform slope at the now raised spring bulge apex (27). [6] Hollow beam according to any one of claims 3 to 5, characterized by, that the base wall (19) has further rigid sheet metal tabs (21) which are angled at the edges and are attached to the shell base (7) and / or to the profile flanks (9) of the shell-shaped profile part (3), and that the pivot web (34) formed in the base wall (19) is free of connection to the profile part (3) at its axial end faces in order to ensure a smooth pivoting movement of the movable sheet metal tab (23). [7] Hollow beam according to one of the preceding claims, characterized by, that the bulkhead sheet metal part (17) is realized as a tailor-welded blank, with a circumferential frame sheet metal part (32) that delimits a sheet metal recess into which a core sheet metal part (34) is inserted, which is contour-adapted to the recess contour and welded to the edge of the sheet metal recess, and that the frame sheet metal part (32) has a material with a low coefficient of thermal expansion and the core sheet metal part (34) has a material with a high coefficient of thermal expansion, and / or that the core sheet metal part (34) is approximately X-shaped. [8] Hollow beam according to claim 7, characterized by , that the movable tab (23) and / or the rigid sheet metal tabs (21) are formed on the frame sheet metal part (32), and that the spring bulge is formed on the core sheet metal part (34). [9] A method for manufacturing a vehicle body, in which, in a process sequence, the vehicle body is first assembled by forming a hollow beam (3) according to one of the preceding claims, and subsequently, in a cathodic dip coating (CDC) step, the vehicle body is dip coated, wherein the CDC step (CDC) is divided into a warm-up phase (A), in which the vehicle body is immersed in a CDC bath and is heated to a CDC process temperature, with different thermal expansions of the body components, and into a stationary phase (S) in which the vehicle body is uniformly heated to the process temperature, so that no further thermal expansions of the body components take place. [10] Method according to claim 9, characterized by, that the bulkhead part (17) is designed such that it remains in its pre-assembly state (V) during the assembly step (Z) and the initial phase (A) of the e-coating step (e-coating), in which the bulkhead part (17) is not yet bonded to the cover sheet part (5), and that in the stationary phase (S) of the e-coating step (e-coating) the bulkhead part (17) is thermally activated and transferred to the assembly state (Z), in which the bond is created and cured. [11] Partition sheet metal part for installation in a hollow beam (1) according to any one of the preceding claims 1 to 8 according to a method according to claim 9.

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