Abstract:
A method for producing a node structure includes providing at least two pre-manufactured profile components having respective profile ends provided with corresponding abutment surfaces; positioning the profile ends in a pressing tool so that a homogenous gap is formed between the abutment surfaces; performing a pressing process in the presence of a fiber-containing plastic mass in the pressing tool for generating a connecting node that form fittingly connects the profile ends, wherein the fiber containing plastic mass also enters into the gap.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
       [0001]    This application claims the priority of German Patent Application, Serial No. 10 2015 014 358.1, filed Nov. 6, 2015, pursuant to 35 U.S.C. 119(a)-(d), the content of which is incorporated herein by reference in its entirety as if fully set forth herein. 
       BACKGROUND OF THE INVENTION 
       [0002]    The invention relates to a method for producing a node structure with at least two profile components that are in particular made of a fiber reinforced plastic composite material. 
         [0003]    The following discussion of related art is provided to assist the reader in understanding the advantages of the invention, and is not to be construed as an admission that this related art is prior art to this invention. 
         [0004]    Vehicle body structures formed from profiles are known from the state of the art. Thus for example DE 44 23 642 C1 discloses a motor vehicle support frame which is composed of individual separately pre-manufactured frame profile components. The frame profile components can each be configured as fiber composite profile pieces, for example with a rectangular hollow profile cross section and in the consolidated or cured state are respectively connected framework-like via node pieces, which are also made of a fiber composite material, to form an integral frame structure. For manufacture of a node piece the frame profile components that are o be connected are inserted into the receiving pockets of a pre-manufactured fiber preform. In a forming tool the node piece is then generated under the influence of pressure and heat. 
         [0005]    It would be desirable and advantageous to provide an improved method for producing a node structure. 
       SUMMARY OF THE INVENTION 
       [0006]    According to one aspect of the present invention a method for producing a node structure includes providing at least two pre-manufactured profile components having respective profile ends provided with corresponding abutment surfaces; positioning the profile ends in a pressing tool so that a homogenous gap is formed between the abutment surfaces; performing a pressing process in the presence of a fiber-containing plastic mass in the pressing tool for generating a connecting node that form fittingly connects the profile ends, wherein the fiber containing plastic mass also enters into the gap. 
         [0007]    A further independent patent claim sets forth a vehicle body, in particular for a passenger car with a frame (space frame) that is constructed from profile components and with at least one node structure according to the invention. Preferably multiple profile components that form a frame section (for example the rear section front section or midsection structure) are made of fiber plastic composite material. These are in particular exclusively hollow profile components, which are connected with each other by means of node structures according to the invention. 
         [0008]    The profile ends of the profile components to be connected in a connecting node are configured with corresponding abutment surfaces, which means surface areas that face each other or confront each other in the connecting node and which in case of stress also serve as force transmission surfaces. The corresponding abutment surfaces can for example be configured as straight slanted surfaces, as concave and convex surfaces (or at least having concave or convex surface portions), as waved surfaces, as stepped surfaces and/or as surfaces that can be nested in each other, which is the subject matter of advantageous refinements. 
         [0009]    The gap between these abutment surfaces makes it possible that during the pressing process the fiber containing plastic mass, which is used for generating the connecting node, is also pressed between these abutment surfaces so that the node-side profile ends are optimally surrounded by the fiber containing plastic mass and thereby are integrated in a form fitting or also materially bonding manner. A homogenous or uniform gap ensures that the fiber containing plastic mass can fully fill the gap and that at any point of the gap substantially the same connecting properties are generated. A non uniform gap may for example lead to an asymmetric force flux in the event of stress on the produced node structure. 
         [0010]    The invention has many advantages. For example in the method according to the invention no pre-manufactured fiber prefrom, such as described in DE 44 23 643 C1, is required. Furthermore a node structure produced with the method according to the invention has excellent strength, stiffness and crash stability while also being lightweight. 
         [0011]    According to another advantageous feature of the invention the gap has a substantially constant width of at least 0.5 mm and at most 2.0 mm. The minimal gap width of at least 0.5 mm ensures a distance between the abutment surfaces that permits flow so that the profile ends positioned in the pressing tool can be ideally surrounded by the fiber containing plastic mass and thereby integrated in a form fitting/materially bonding manner. The maximal gap width of at most 2.0 mm ensures that in the produced connecting node the paths of force flux between the connected profile ends and their abutment surfaces are short. 
         [0012]    After the curing of the fiber containing plastic mass the pressing tool can be opened and the produced node structure removed. This node structure includes at least two profile components, in particular made of fiber plastic composite material, and a connecting node made of fiber plastic composite material or fiber containing plastic mass, and in particular short fiber containing plastic mass, in which the profile components are connected with each other at their profile ends (or at their node side profile ends in a form fitting and optionally materially bonding manner, wherein the profile ends connected in the connecting node are configured with corresponding abutment surfaces and these abutment surfaces are spaced apart from each other by a uniform gap (i.e. with substantially constant gap width) that is filled with fiber containing plastic mass. The node structure is thus an assembly made of at least two profile components. 
         [0013]    The term profile component means a longitudinal rod-like component with a defined cross sectional shape (profile), which can have a straight or also curved or bent axial extent. At least one profile component can also be a tubular hollow profile component with a closed cross section and with at least one profile chamber. The corresponding profile and hollow profile components are in particular made of consolidated fiber plastic composite material. The fibers can be carbon fibers, glass fibers and/or other fibers. Preferably they are long fibers, which are, for example also in a layered construction, arranged in accordance with a load path. The plastic material (matrix material) can be a thermoset or thermoplastic. 
         [0014]    The profile components can be pre-manufactured components, which are produced in a prior manufacturing process, optionally also by a supplier. The provision of these components includes for example confectioning, preparation, cleaning and/or testing of the profile components to be connected. The provision includes optionally also production of the abutment surfaces for example by mechanical processing, in particular by cutting and/or milling, wherein the abutment surfaces have to be produced at the lasted prior to insertion and positioning of the profile ends in the pressing tool. 
         [0015]    According to another advantageous feature of the invention, the profile components are produced from pre-manufactured profile semi-finished products (in particular rod products). It is also conceivable however to directly produce the profiles or profile components for example by pultusion (or optionally also by coiling or braiding). The profile components can be made of the same fiber reinforced plastic composite material or of different fiber reinforced plastic composite materials. 
         [0016]    According to another advantageous feature of the invention, at least one profile component of a node structure according to the invention is a hollow profile component made of fiber reinforced plastic composite material. In particular all profile component of a node structure according to the invention are hollow profile components made of fiber reinforced plastic composite material. 
         [0017]    The plastic mass that generates the connecting node can be a thermoset (resin) or a thermoplast. The fibers can preferably be short fibers (carbon fibers, glass fibers and/or other fibers, also mixed fibers and in particular recycled fibers) with a length of for example 1 mm to 100 mm, preferably 2 mm to 50 mm, and in particular 3 mm to 25 mm. Preferably the fiber-containing plastic mass used for generating the connecting node is adjusted to the fiber reinforced plastic composite material of the profile components or hollow profile components to be connected. 
         [0018]    The fiber-containing plastic mass for generating the connecting node can be introduced into the tool cavity prior to closing the pressing tool. The fiber-containing plastic mass for generating the connecting node can also be introduced into the tool cavity after closing the pressing tool by injection (similar to injection molding of the RTM technology). 
         [0019]    As described above at least one of the profile components can be a hollow profile component, wherein in particular it is provided that the node-side open profile end of this hollow profile component is closed by means of a closing element in order to prevent the fiber containing plastic mass from entering the hollow profile component during the pressing process. The closing element that is to be applied at the latest prior to inserting and positioning of the hollow profile component in the pressing tool is for example a cover, in particular made of fiber plastic composite material, or a stopper-like closing element made of a plastic foam material, which is in particular glued into the open profile end. 
         [0020]    According to another advantageous feature of the invention, the profile components and/or hollow profile components to be connected in a connecting node can have different cross sections or cross sectional dimensions and/or different wall thicknesses or wall strengths at least at their profile ends that are to be connected or at their node-side end sections. 
         [0021]    According to another aspect of the invention a node structure for a vehicle body, includes at least two profile components having respective profile ends configured with respective corresponding joining surfaces; and a connecting node in which the profile components are form fittingly connected with each other at the respective profile ends, said respective profile ends being spaced apart from each other by a homogenous gap which is filled with a fiber-containing plastic mass. 
         [0022]    The node structure can be manufactured with the method according to the invention. 
         [0023]    According to another aspect of the invention a vehicle body, includes a frame, wherein the frame includes profile components having respective profile ends configured with respective corresponding joining surfaces, and a connecting node in which the profile components are form fittingly connected with each other at the respective profile ends, wherein the respective profile ends are spaced apart from each other by a homogenous gap which is filled with a fiber-containing plastic mass. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0024]    Other features and advantages of the present invention will be more readily apparent upon reading the following description of currently preferred exemplified embodiments of the invention with reference to the accompanying drawing, in which 
           [0025]      FIG. 1  shows in a perspective view a vehicle rear section structure made of hollow profile components; 
           [0026]      FIG. 2  shows a perspective view of a node structure belonging to the vehicle rear section structure of  FIG. 1 ; 
           [0027]      FIG. 3A  shows in multiple sectional views possible configurations of abutments surfaces on two hollow profile components to be connected during the production of the node structure of  FIG. 2 ; 
           [0028]      FIG. 3B  shows a sectional view of another possible configuration of an abutment surface on two hollow profile components to be connected during the production of the node structure. 
           [0029]      FIG. 3C  shows a sectional view of another possible configuration of an abutment surface on two hollow profile components to be connected during the production of the node structure. 
           [0030]      FIG. 3D  shows a sectional view of another possible configuration of an abutment surface on two hollow profile components to be connected during the production of the node structure. 
           [0031]      FIG. 4  shows a sectional view of possible configurations of abutment surfaces of three hollow profile components to be connected during the production of the node structure of  FIG. 2 ; and 
           [0032]      FIG. 5  shows in sectional view steps of the production of connecting nodes during the production of the node structure of  FIG. 2 . 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0033]    Throughout all the Figures, same or corresponding elements may generally be indicated by same reference numerals. These depicted embodiments are to be understood as illustrative of the invention and not as limiting in any way. It should also be understood that the figures are not necessarily to scale and that the embodiments are sometimes illustrated by graphic symbols, phantom lines, diagrammatic representations and fragmentary views. In certain instances, details which are not necessary for an understanding of the present invention or which render other details difficult to perceive may have been omitted. 
         [0034]    The vehicle structure or vehicle rear section structure  100  show in  FIG. 1  is a part of a frame of a vehicle body. The vehicle rear section structure  100  includes multiple separately pre manufactured hollow profile components  120 ,  120   a ,  130 ,  130   a,    140 ,  140   a  and  150  made of fiber plastic composite material, wherein these are so called pultrusion profiles whose profile ends are fixedly connected with each other on connecting nodes or node sites  160  and  160   a.  typically the hollow profile components  120 ,  120   a,    130 ,  130   a,    140 ,  140   a  and  150  are configured differently, i.e., they have depending on the stress different cross sections and/or wall thicknesses and/or are made of different fiber plastic composite materials. The vehicle rear section structure  100  can also have closed profile components and/or profile components that are made of other materials (for example also metal), and which are in particular also integrated in the frame structure  100  via the connecting nodes  160  or  160   a.  In spite of its low weight the vehicle rear section structure  100  nevertheless has excellent strength, stiffness and crash stability. 
         [0035]    The hollow profile components that are connected in a connecting node  160  or  160   a  form together with this connecting node a node structure in the sense of the invention.  FIG. 2  shows such a node structure  110  for the frame region that is position in driving direction x on the left hand side. The integrated node structure  110  includes multiple hollow profile components  12   a,    130 ,  140 , and  150  whose profile ends are fixedly connected with each other in a connecting node  160 . 
         [0036]    In the following the production of such a node structure  110  is explained in more detail with reference to  FIGS. 3, 4 and 5 , wherein only the connection between the two hollow profile components  120  and  130  is explained. While not illustrated, the hollow profile components  120  and  130  can have different cross sections or cross sectional dimensions and/or different wall thicknesses or wall strengths at least at their end sections  121  and  131  that are to be connected. 
         [0037]    According to the invention the node-side profile ends to be connected are configured with corresponding abutment surfaces.  FIGS. 3  A-D show the profile ends  121  and  131  of the hollow profile components  120  and  130  with differently configured abutment surfaces  122  and  132 . The open profile ends  121  and  131  of the hollow profile components  120  and  130  to be connected are closed by closing elements  125  and  135  that are glued in by adhesive  126  or  136 . The closing elements  125  and  135  are made of a plastic foam material, in particular a temperature resistant and pressure resistant hard foam. The abutment surfaces  122  and  132  are preferably only generated after these closing elements  125  and  135  have been glued in, wherein the processing is in particular performed by mechanical processing such as cutting and/or milling. This process can also be referred to as contouring of the profile ends. 
         [0038]    In the embodiment shown in  FIG. 3A  the node-side profile ends are slanted, i.e., the abutment surfaces  122  and  132  on the profile ends  121  and  131  are configured as straight slanted surfaces. The node-side slanted surfaces  122  and  132  extend slanted (in the sense of non-perpendicular) relative to the longitudinal axes L 1  and L 2  of the hollow profile components  120  and  130 . In the embodiment shown in  FIG. 3B  the abutment surfaces  122  and  132  are configured as oppositely stepped surfaces. In the embodiment shown in  FIG. 3C  the abutment surfaces  122  and  132  are configured as waved surfaces with corresponding wave contours (which have concave and convex surface portions). In the embodiment shown in  FIG. 3 d    the abutment surfaces  122  and  132  are configured as surfaces that can be nested in each other. 
         [0039]      FIGS. 3  A-D show the corresponding abutment surfaces  122  and  132  on the profile ends  121  and  131  to be connected only schematically in 2D representations. Of course the shown abutment surfaces  12  and  132  have correspondingly configured three-dimensional surface contours. Furthermore the embodiments for abutment surfaces shown in  FIGS. 3  A-D can be changed or combined to form further embodiments. 
         [0040]    The corresponding abutment surfaces  122  and  132  shown in  FIGS. 3  A-D are configured so that they can be arranged with a homogenous gap between them (see  FIGS. 4 and 5 ), as explained in more detail below. The abutment surfaces  122  and  132  can be configured so as to enable improved force and/or torque transmission between the associated profile components  120  and  130  in spite of the presence of the gap. 
         [0041]      FIG. 4  shows an embodiment with complexly formed abutment surfaces for three profile ends  121 ,  131  and  141  that are to be connected in the connecting node  160 . The corresponding profile ends  121 ,  131  and  141  are prepared by mechanical processing, which results in specially formed abutment surfaces or joining surfaces, i.e., corresponding end shapes. The contouring is in particular carried out so that these profile ends  121 ,  131  and  141  can be positioned as close as possible to each other while maintaining homogenous gaps S with greatest possible abutment surfaces. Thus within a connecting node multiple abutment surface pairings that are configured with different surface contours and/or with different gap widths can be provided. In this way also more than two profile ends, or even up to five profile ends and more can be brought in very close proximity to each other in a connecting node which saves space while taking later load paths into account. 
         [0042]    For generating the connecting node  160  the closed profile ends  121  and  131  of the hollow profile components  120  and  130 , which are configured with corresponding abutment surfaces  122  and  132 , are inserted into a pressing tool  200  that generates the connecting node  160  as shown in  FIG. 5 a   . Correspondingly configuring the two-part pressing tool  200  makes it possible to also realize different connecting angles than the shown 180° connecting angle. The pressing tool  200  is configured to enable accurately fixing the profile ends  121  and  131  in position. The abutment surfaces  122  and  132  of the profile ends  121  and  131  to be connected are spaced apart by a homogenous or uniform gap S. The size of the gap or the gap width B is for example 0.25 mm to 3 mm and in particular 0.5 mm to 2.0 mm. 
         [0043]    In the tool cavity  230  of the lower tool  210  a short-fiber-containing plastic mass K is present which was introduced already prior to inserting and positioning the profile ends  121  and  131 . The plastic mass K is preferably a thermoset mass (resin). After the positioning of the profile ends  121  and  131  that are to be connected additional short-fiber-containing plastic mass K is applied or sprayed onto the connecting region, for example with the shown spray device  300 . 
         [0044]    Subsequently the pressing tool  200  is closed by lowering the upper tool  220  as shown in  FIG. 5 b    and a pressing process is performed. During this pressing process the defined amount of fiber-containing plastic mass K is distributed in the cavity  230 , wherein the profile ends  121  and  131  of the hollow profile components  120  and  130  arranged in the cavity  230  are surrounded form fittingly and wherein the fiber-containing plastic mass K is also pressed into the gap S. Hereby also a materially bonding connection between the plastic mass K, which forms the connecting nodes  160 , and the profile ends  121  and  131  is formed. The shape of the connecting node  160  is defined by the negative form of the tool cavity  230 . 
         [0045]    During the pressing process the closing elements  125  and  135  act as barriers and prevent the fiber-containing plastic mass K from entering the profile chambers of the hollow profile components  120  and  130 . This also allows establishing a high defined forming pressure in the tool cavity  230 . 
         [0046]    During production of the connecting node  160  only the profile ends  121  and  131  that are to be connected are inserted into the pressing tool  200 , so that the hollow profile components  120  and  130  protrude into the tool cavity  230  through openings in the pressing tool  200 . The pressing tool  200  is configured so as to enable accurately fixing the profile ends  121  and  131  in position. During the pressing process the sealing of the pressing tool  200  is accomplished by way of sealings  241  and  242 . The pressure-resistant closing elements  125  and  135  can stabilize the hollow profile walls in the sealing region and improve the sealing of the cavity. 
         [0047]    After the preferably thermoset plastic mass K is cured as a result of pressure and temperature the pressing tool  200  can be opened and the produced node structure  110  can be removed as shown in  FIG. 5 c   . The connecting node  160  can have wall thicknesses in the range from 1 mm to 15 mm, wherein the same but also different wall thicknesses can be provided. The closing elements  125  and  135  improve the strength, stiffness and crash stability of the node structure without noticeably adding weight. 
         [0048]    The short-fiber-containing plastic mass K can be pre-mixed and can be introduced into the tool cavity  230  prior to closing the pressing tool  200 , for example by means of the spray device  300  or the like. Furthermore a layered introduction is possible, wherein alternately fiber layers and plastic layers (resin layers) can be introduced. The short-fiber plastic mass K can also be introduced into the tool cavity  230  by injection after closing the pressing tool  200  (injection molding).