Patent Publication Number: US-2022212435-A1

Title: Hollow article with optimized internal structural members

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of prior U.S. Provisional Patent Application Ser. No. 62/702,690, filed Jul. 24, 2018, which is hereby incorporated by reference in its entirety for all purposes. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to hollow articles with internal structural members, and a process for manufacture. 
     BACKGROUND 
     Composite panels have many uses in industry and serve, for example, as load bearing structural panels or load floors in aviation and automotive applications. A principal application for composite panels is in the automotive sector where it is desirable to replace bulky and heavy prior art panel systems with light-weight structural constructs having a maximum of strength for a minimum of weight and cost. Conventional construction methodologies have incorporated materials such as plastics at excess amounts, due to a lack of intelligent manufacturing processes, where material usage is calculated based on an optimization process. It is therefore an ongoing desire to improve upon manufacturing processes of a composite panel that achieves predetermined performance criteria, while increasing material usage efficiency and reducing overall component weight. 
     SUMMARY OF THE INVENTION 
     According to an aspect of an embodiment, a composite panel includes a first skin layer, an intermediate structural core, and a second skin layer. The first and second skin layers are disposed on opposing sides of the intermediate structural core. The intermediate structural core provides a geometric array of structural members, the arrangement of which is defined using topology optimization. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing and other features and advantages of the invention will be apparent from the following description of the invention as illustrated in the accompanying drawings. The accompanying drawings, which are incorporated herein and form a part of the specification, further serve to explain the principles of the invention and to enable a person skilled in the pertinent art to make and use the invention. The drawings are not to scale. 
         FIG. 1  is a partial sectional perspective view of a load floor exemplifying an embodiment of the invention. 
         FIG. 2  is a sectional view of the load floor according to  FIG. 1 . 
         FIG. 3  is a sectional view of an alternative embodiment of a load floor, including a covering. 
         FIG. 4  is a sectional view of an alternative embodiment of a load floor, including a covering and a reinforcement layer. 
         FIG. 5  is a sectional view of an alternative embodiment of a load floor, including a reinforcement layer without a covering. 
         FIG. 6  shows an exemplary geometric array of structural members for a structural core of a load floor. 
         FIGS. 7 a  to 7 f    provide alternative geometric arrays based on topology optimization. 
         FIG. 8  shows a structural core having an open-cell configuration. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS OF THE PRESENT INVENTION 
     Specific embodiments of the present invention will now be described with reference to the Figures, wherein like reference numbers indicate identical or functionally similar elements. The following detailed description is merely exemplary in nature and is not intended to limit the invention or the application and uses of the invention. A person skilled in the relevant art will recognize that other configurations and arrangements can be used without departing from the scope of the invention. Although the description and drawings of the embodiments hereof exemplify the formation/use of structural members in load floors, the invention may also be used in other manufacturing arrangements where it is deemed useful. Furthermore, there is no intention to be bound by any expressed or implied theory presented in the preceding technical field, background, brief summary or the following detailed description. 
     Turning now to  FIG. 1 , shown in partial-sectional perspective view is a structural panel according to an embodiment of the invention. More specifically, shown is an exemplary article known as a load bearing structural floor commonly used in motor vehicles, which is herein referred to as a load floor  10 . The load floor  10  is generally formed as a composite panel, including at least two layers that cooperate to provide the desired form and performance or function. 
     As shown more clearly in  FIG. 2 , the load floor  10  includes three layers, namely a first skin layer  20 , an intermediate structural core  22 , and a second skin layer  24 . The first skin layer  20  and the second skin layer  24  are positioned or disposed on opposing sides of the intermediate structural core  22 . More specifically, the first skin layer  20  is positioned on a first side  26  of the structural core  22 , while the second skin layer  24  is positioned on a second side  28  of the structural core  22 . As the first and second sides  26 ,  28  are opposing sides of the structural core  22 , the first and second skin layers  20 ,  24  associated therewith are spaced apart or separated by gap G. 
     The first and second skin layers  20 ,  24  may be separately formed and attached to the structural core  22 , for example through a suitable weldment process such as but not limited to IR welding, and vibration welding, or through the use of a suitable adhesive such as but not limited to a high-bond adhesive tape or adhesive glue. The first and second skin layers  20 ,  24  may also be mechanically captured using retention features to lock in the ribs or core (i.e., with dove tail features, snap fit features or locating features in different directions C/C and F/A). It will also be appreciated that one or both of the first and second skin layers  22 ,  24  may be integrally formed with the structural core, as will be described in greater detail below. 
     In some applications, it is desirable to have a covering material applied to or disposed on one or both sides of the load floor  10 . For example, it may be desirable to apply a carpet material to one side of the load floor  10  so as to meet desired performance and/or aesthetics characteristics. As such, provided in  FIG. 3  is an alternative embodiment of the load floor  10  where a covering  30  is provided on an outside surface  32  of the first skin layer  20 . 
     The covering  30  may be applied to the first skin layer  20  using a suitable adhesive, although it will be appreciated that other attachment methodologies are possible, such as being integrally bonded where the first skin layer  20  is molded. The covering  30  may be a wide range of materials, including but not limited to carpet (woven or non-woven) and sheets of varying forms such as solid and perforated configuration. Suitable materials for coverings include, but are not limited to polypropylene, polyester, polyamide, vinyl and TPO. 
     In some embodiments, one or more reinforcement layers may be incorporated into the load floor  10 . For example, in the load floor  10  shown in  FIG. 4 , a single reinforcement layer  34  is provided as an intermediate layer between the outside surface  32  of the first skin layer  20  and the covering  30 . 
     In other embodiments, such as the load floor  10  shown in  FIG. 5 , the reinforcement layer  34  may be provided on the outside surface  32  of the first skin layer  20  without a further covering material added. 
     Similar to the covering  30 , the reinforcement layer  34  may be applied to the first skin layer  20  using a suitable adhesive, although it will be appreciated that other attachment methodologies are possible, such as being integrally bonded. 
     Exemplary reinforcement layers include, but are not limited to mesh, fabric and plastic. Exemplary mesh materials include metal, glass, plastic and carbon fibre. Exemplary fabrics may be woven or non-woven, and may include synthetic and/or non-synthetic materials, such as, but not limited to hemp, jute and leather. Exemplary plastics may include polyamide (e.g. aramid), and any filled synthetic resin containing organic or inorganic fillers, such as, but not limited to talc, mica, carbon fiber and glass. The reinforcement layer  34  may be continuous over the entire surface, or may be discontinuous, that is only partially cover the article. In some embodiments, the reinforcement layer  34  may alternatively or additionally be provided on an outside surface of the second outside layer  24 . 
     The structural core  22  provides the primary strength and rigidity of the structural panel and is generally regarded as a planar construct when the structural panel has the form of a load floor  10 . The structural core  22  provides an array of structural members  40 , generally arranged as a plurality of geometric cells arranged in repeating pattern over the planar area defining the load floor  10 . An exemplary array of structural members is shown in  FIG. 6 . 
     Each geometric cell includes at least one structural rib  42 , at least one structural node  44 , and at least one structural web  46 . The structural ribs  42  define the principle structure of the geometric cell, the structural nodes  44  are generally defined as the location where two or more structural ribs  42  intersect, and the structural webs  46  serve to interconnect adjacent geometric cells. The geometric cells, in particular the walls defining the cells, are aligned to extend transversely relative to the load floor  10  or stated another way, are aligned to extend across the thickness of the structural core  22 . Accordingly, in an assembled load floor  10  having first and second skin layers  20 ,  24 , the geometric array of structural members  40  of the structural core  22  span the gap G and fixedly engage to the respective first and second skin layers  20 ,  24 . 
     It will be appreciated that the load floor  10 , may be constructed in a variety of ways, to achieve the desired performance characteristics. In particular, the selection of the structural core  22  is central to achieving the desired functional form. Parameters to be considered in the design will include, but are not limited to the expected stress loads, the manner by which the load floor  10  will be supported (i.e. the location of the boundary supports) when in use, the localized stress loads in the vicinity of the boundary supports, the material properties, the dimension of the cell size, the optimization objective and the performance constraints. 
     An effective and efficient method of accounting for these parameters in the design of the structural core  22 , in particular the geometric array of structural members  40 , is topology optimization. Topology optimization is developed to find the quantity, location, shape of the key design features, and the connectivity of design domains. Topology optimization has the capability to achieve the optimal configuration of the structural core  22  based on rigorous mathematical algorithm under the predetermined stress load and loading attributes of the load floor  10 . Accordingly, for a given set of parameters inputted into the topology optimization algorithm, an optimal geometric array of the structural members is generated, depending on the constraints enforced on the algorithm. With an optimal geometric array of structural members determined, an appropriate manufacturing methodology may be selected to form the targeted the load floor  10 . 
     With reference now to  FIGS. 7 a  to 7 f   , shown are exemplary geometric arrays for the structural members  40  of the structural core  22 . For a given stress or load profile, topology optimization identified an optimal geometric cell configuration. Select stress or load profiles are provided in Table 1, which correspond to the geometric arrays provided in the figures. 

 
     Based on the optimal topology, detailed structural optimization methods such shape optimization and size optimization may be implemented to further tune the local shape and the thickness of the structural members  40 . The resultant geometric arrays may be subject to further geometry interpretation to ensure the design conforms to the available and/or selected manufacturing processes. For example, where the structural core  22  is to be formed using an injection molding process, the thickness of the structural ribs  42 , the structural nodes  44  and the structural webs  46  are selected to be at least 0.65 mm. It will be appreciated, however, that other thicknesses for one or more of the structural ribs  42 , the structural nodes  44  and the structural webs  46  may be above or below this selected value. It will also be appreciated that shapes can be continuous or discontinuous based on manufacturing requirements. Rib thicknesses, cell shape and spacing can vary locally based on load or support requirements. 
     The structural core  22  may be formed using an injection molding process. In one embodiment, the structural core  22  may be formed without a skin layer provided on either side. Accordingly, the structural core  22  would have an open-cell structure, composed solely of the structural members  40  with in an optimized geometric configuration based on topology optimization. An exemplary structural core  22  formed in accordance with this methodology is depicted in  FIG. 8 . In this form, the structural core  22  generally serves as a structural insert for other molding or manufacturing processes. 
     For example, the structural core  22  may be incorporated into a compression molding or vacuum forming process where the structural core  22  would receive one or both of the first and second skin layers  20 ,  24  using a suitable adhesive or bonding process. Alternatively, the structural core  22  may be incorporated into a blow molding operation where the structural core  22  is disposed as a structural insert within the parison. 
     In an alternative embodiment, the structural core  22  may be an integral geometric projection formed on at least one of the first and second skin layers. This may be achieved through an injection molding process, where the process of forming the skin layer includes the injection molding of the structural members  40  of the structural core  22  directly upon an inside surface of one of the first and second skin layers  20 ,  24 . In a subsequent manufacturing step (i.e., compression molding or vacuum forming), the opposing skin layer would be bonded to the opposing open-side of the structural members  40 , therein encasing the structural core  22  therebetween. 
     In another alternative embodiment, the structural core  22  may be integrally formed upon each of the first and second skin layers. In this arrangement, it will be appreciated that the assembled form of the structural panel has a targeted structural core thickness. Accordingly, the first skin layer  20  will be formed with a first portion of the structural members  40 , while the second skin layer  24  is formed with a second portion of the structural members  40 . The structural members  40  provided on each of the first and second skin layers  20 ,  24  are arranged to align on assembly, and the first and second portions are suitably dimensioned to form on assembly a structural core with the targeted structural core thickness. In one embodiment, the portions of the structural members  40  provided on each of the first and second skin layers includes 50% of the targeted structural core thickness. In another embodiment, one of the first and second skin layers is configured to receive &gt;50% of the portion of the structural members, with the opposing skin layer receiving a complementary portion to achieve the targeted structural core thickness. For clarity, the term portion is used relative to the targeted structural core thickness. For example, where the targeted structural core thickness is 1 cm, and wherein each of the first and second skin layers are configured to receive a 50% portion, the structural members  40  provided on each of the first and second skin layers will be 0.5 cm. 
     In addition to injection molding, the structural core  22  may be formed using a variety of 3-D printing (additive manufacturing) methodologies including, but not limited to free form fabrication (FFF), direct manufacturing (DM), fused deposition modelling (FDM), powder bed printing (PBP), laminated object manufacturing (LOM), stereolithography (SL), selective laser sintering (SLS), selective laser melting (SLM), selective heat sintering (SHS), electron beam melting (EBM), direct ink writing (DIW), digital light processing (DLP) and additive layer manufacturing. These systems are used for generating three-dimensional objects by creating a cross-sectional pattern of the object to be formed and forming the three-dimensional solid object by sequentially building up layers of material. These techniques generally include selectively depositing material layer by layer, selectively fusing or solidifying the material and removing excess material, if needed. With this approach, the structural core  22  can be made and used in a subsequent manufacturing process, such as the compression molding, vacuum forming, and blow molding processes mentioned above. 
     The load floor  10  is made from a thermoplastic material that has sufficient strength and rigidity to meet the desired performance characteristics. A non-limiting example of suitable materials includes polypropylene, polyethylene, ABS, ABS/PC, polyamide, PLA and PPS. To meet desired strength and rigidity requirements, the thermoplastic may additionally include a range of inorganic filler components, a non-limiting example of which includes glass, mica, calcium carbonate and talc, and/or organic filler components, a non-limited example of which includes jute, husk, and hemp. The structural core  22  and the first and second skin layers  20 ,  24  may be formed of the same material, or of different materials, depending on the intended application. 
     While various embodiments according to the present invention have been described above, it should be understood that they have been presented by way of illustration and example only, and not limitation. It will be apparent to persons skilled in the relevant art that various changes in form and detail can be made therein without departing from the scope of the invention. Thus, the breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments but should be defined only in accordance with the appended claims and their equivalents. It will also be understood that each feature of each embodiment discussed herein, and of each reference cited herein, can be used in combination with the features of any other combination. All patents and publications discussed herein are incorporated by reference herein in their entirety.