Abstract:
An injection-molded structural component, particularly for automotive front end carriers, with a hollow structural section, the hollow structural section including a section body having a cavity with an opening, a section lid secured to the section body via a hinge and hinge-folded onto the opening, and a fastener element for fastening the section lid to the section body such that the hollow structural section withstands dynamical load.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to injection-moulded structural components in high stiffness, high strength and low weight applications and their manufacture. More particularly, the present invention relates to injection-moulded front end carriers of automotive front end modules. 
     2. Brief Discussion of the Prior Art 
     Typically, structural components such as automotive front end carriers are manufactured by injection moulding and include rib-reinforced U-sections. However, these U-sections suffer from a limited stiffness. Also, their weight is increased by the reinforcement ribs. It would thus be desirable to replace the U-sections by hollow structural sections since the latter represent the better trade-off with regard to high stiffness vs. low weight. Yet, the implementation of hollow structural sections in injection-moulded structural components has failed so far because a hollow structural section, due to its closed cross-section, cannot be separated from the injection mould. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is a first object of the present invention to provide an injection-moulded structural component with a hollow structural section to ensure highest possible stiffness and lowest possible weight. 
     A second object of the present invention is to provide a particularly simple, quick and cheap method of manufacturing such a structural component. 
     These objects are achieved by an injection-moulded structural component with a hollow structural section, said hollow structural section comprising:
         a section body having a cavity with an opening;   a section lid secured to said section body via a hinge and hinge-folded onto said opening; and   a fastening means fastening the section lid to the section body onto the opening and preventing an unfolding of the section lid.       

     Thanks to the hinge-folded lid and the fastening means, one obtains a structural component with a stiff and lightweight hollow structural section that can be manufactured by injection-moulding. In particular, the resulting hollow structural section is able to withstand substantial dynamical load. 
     Said objects are also achieved by a method of manufacturing a structural component with a hollow structural section, in particular the structural component as described above, comprising the following steps:
         injection-moulding the structural component with a section body having an open cavity and a section lid secured to the section body via a hinge, wherein the section lid sticks out in an open position from the section body;   hinge-folding the section lid onto the section body thus closing the open cavity; and   fastening the section lid to the section body and onto the open cavity thus obtaining the hollow structural section, the fastening being such that an unfolding of the section lid is prevented.       

     According to preferred embodiments, the inventive structural component may have one, several or all of the following features, in all technically possible combinations:
         the fastening means comprises a circumferential welding seam;   the fastening means comprises a plurality of rivets;   the rivets have welded rivet heads;   the rivets are integrally formed with one of the section body or the section lid and extend through corresponding apertures in the other of the section body or the section lid;   each rivet has a shaft with a shaft broad side and a shaft narrow side, the shaft broad side of at least two different rivets having a different orientation;   a first rivet having a shaft broad side at a right angle to the shaft broad side of a second rivet;   it is made of reinforced plastic, such as glass-fibre reinforced plastic, in particular glass-fibre reinforced polypropylene;   it includes a reinforcing metal insert;   at least the section body, the section lid and the hinge are made from the same material;   it consists of an automotive front end carrier.       

     The inventive manufacturing method may have one, several or all of the following features, in all technically possible combinations:
         the fastening involves laser or ultrasonic welding;   the fastening involves riveting.       

     The invention also relates to an automotive front end module with a structural component as described above, and to a motor vehicle with such a front end module. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       The invention will now be described in detail with reference to the accompanying drawings, in which: 
         FIG. 1  is a perspective view of an automotive front end carrier according to the invention; 
         FIG. 2  is a perspective view of a portion of the hollow structural section of the automotive front end carrier of  FIG. 1 ; and 
         FIGS. 3 to 5  show the manufacture of the inventive front end carrier. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows an automotive front end carrier  10 . This carrier is part of the automotive front end module of a motor vehicle and supports the various elements which make up the front end module. 
     Preferably, the carrier  10  is made of plastic, in particular glass-fibre reinforced polypropylene and obtained by injection-moulding. 
     Carrier  10  has a generally rectangular shape. It includes an upper horizontal hollow structural section  12 , two vertical support beams  14  and  16 , a lower horizontal support section  18 , and a vertical strut  20  extending between the upper horizontal hollow structural section  12  and the lower horizontal support section  18 . 
     A portion  22  (delimited by dotted lines) of the hollow structural section  12  is shown in greater detail in  FIG. 2 . 
     The hollow structural section  12  comprises a section body  24 , a first section lid  26  and a first hinge  28  securing the first section lid  26  to the section body  24 . 
     Preferably, the first section lid  26  is a rectangular plate. In the present embodiment, the plate  26  has a plurality of fastening apertures  29  (cf.  FIG. 4 ). A first row R 1  of fastening apertures  29  is arranged along the lower end  31  of section body  24 , a second row R 2  of fastening apertures  29  is arranged along the centre  33  of section body  24 , and a third row R 3  of fastening apertures  29  is arranged along the upper end  35  of section body  24 . Preferably, the fastening apertures  29  have a rectangular shape. In this case, the fastening apertures  29  of the second row R 2  may be substantially at right angles to the fastening apertures of the other rows R 1  and R 3 . 
     Preferably, the section body  24  is a U-section defining a cavity  30  with a bottom  32  and an opening  34 . The cavity  30  may be subdivided in the longitudinal direction by a partition  36  extending from the bottom  32  to the opening  34 . The cavity  30  is delimited by two side walls  38  and  40 . The side walls  38 ,  40  each end in a fastening flange  42 ,  44 . 
     Each fastening flange  42 ,  44  and the partition  36  include a series of integral rivets  46 . Accordingly, the hollow structural section  12  has a lower row S 1  of lower rivets, a central row S 2  of central rivets, and an upper row S 3  of upper rivets. 
     Preferably, each rivet  46  has a rivet head  45  and a rivet shaft  47 . Each rivet shaft  47  may have a broad side  48  and a narrow side  50 . In this case, the shaft broad sides of the central rivets may substantially be at right angles to the shaft broad sides of the upper and lower rivets. 
     Each rivet shaft  47  extends through a corresponding fastening aperture  29  of the first section lid  26 . Each rivet head  45  covers a corresponding aperture  29 . 
     The first hinge  28  is made of a thin film connecting one fastening flange  42  to the first section lid  26 . 
     With reference to  FIG. 3 , the hollow structural section  12  may comprise a second section lid  52  with a second hinge  54 . The second section lid  52  operates in the same manner as the first section lid  26 . 
     In the following, the preferred method of manufacturing the front end carrier  10  will be described. 
     As a first step, an injection mould with a cavity in the shape of the front end carrier  10  is provided. Plastic, such as glass-fibre reinforced polypropylene, is injected into the mould, thus forming the front end carrier with opened section lids  26  and  52  as shown in  FIG. 3 . If desired, reinforcing metal inserts can be positioned inside the mould prior to injecting the plastic. These inserts reinforce the carrier  10  in areas that will be subjected to particularly high loads during operation. 
     After moulding, the front end carrier  10  as shown in  FIG. 3  is removed from the mould. At this stage, front end carrier  10  has a U-shaped upper structural section  12 ′ that will later on become hollow structural section  12 . The configuration of the portion  22  of the upper structural section  12 ′ is depicted in  FIG. 4 . 
     Subsequently, the section lids  26  and  52  are folded onto the section body  24  via the first and second hinge  28 ,  54 . The resulting configuration of portion  22  is shown in  FIG. 5 . Rivets  46  are inserted into fastening apertures  29 . 
     Finally, rivet heads  45  are melted by welding such as ultrasonic welding, thus fastening section lids  26  and  52  to section body  24 . The result is a hollow structural section  12  as shown in  FIGS. 1 and 2  adapted to withstand dynamical loads. 
     In a preferred embodiment, the residual heat still present in the front end carrier right after demoulding is used for folding the section lids  26 ,  52  onto the section body  24  and/or for riveting. Indeed, thanks to the residual heat, the hinges  28 ,  54  as well as the rivet heads  45  are still malleable. This advantageous use of the residual heat is only possible for plastics with a low glass transition temperature. For plastics with a high glass transition temperature, local heating of the hinges  28 ,  54  and the rivets  46  is needed prior to folding, respectively riveting. 
     In a variant of the manufacturing method, rivets  46  may be dispensed with and sections lids  26  and  52  may be fastened to section body  24  by laser welding their periphery. 
     The main advantages of the present invention can be summarised as follows:
         A hollow structural section can be implemented in a front end carrier in a single injection moulding step followed by a simple finishing involving folding and welding;   Thanks to the hollow structural section, the inventive front end carrier represents an ideal trade-off between the conflicting aims of minimising weight and maximising stiffness;   No additional component separate from the front end carrier is needed for the hollow structural section;   Since the inventive front end carrier is manufactured as one integral piece, it contracts evenly, which prevents warping.