Patent Publication Number: US-2017361544-A1

Title: Method for  producing a part by adding material

Description:
FIELD OF THE INVENTION 
     The invention relates to a method for producing parts made of plastic material for a motor vehicle, such as exterior or interior bodywork parts. 
     BACKGROUND OF THE INVENTION 
     In a known manner, a motor vehicle part made of plastic material is produced by molding. It may then undergo surface treatment and be stored. 
     Depending on the functions of this part, it may be necessary to add reinforcement elements so that it does not deform. Functional elements may also be added, such as elements to attach the part to the vehicle structure, elements to attach cables of electronic sensors and detectors and other plastic decorative parts. These elements are generally molded separately and stored. 
     The elements are then applied, for example, using clips, by bonding or by welding on the parts, depending on the requirements of each customer. 
     Thus, a large number of parts and various elements are stored, referenced and handled in order to meet the request of a customer. 
     OBJECT AND SUMMARY OF THE INVENTION 
     The invention aims in particular to simplify the method for producing motor vehicle parts, especially by simplifying the storage and handling of the elements applied thereto. 
     To this end, the invention relates to a method for producing a part made of plastic material for a motor vehicle, said part comprising at least one first section to which at least one second section is applied, in which the first section is produced, wherein the second section of the part made of plastic material is produced by three-dimensional printing directly on the first section of the part. 
     Thus, since the method can be used to produce the second section of the part directly on the first section of the part, all the operations related to storage of the second section, i.e. storage, referencing and handling, are avoided. 
     Thus, the second section does not need to be attached by bonding, welding or clipping to the first section. There is therefore no need to provide for additional assembly steps. 
     Since the second section is produced by three-dimensional printing, the structure of the second section can be modified very easily. It can be adapted according to the options selected by the customer. This method therefore offers considerable flexibility in the geometry and number of parts applied to the first section of the part. 
     Thus, for parts produced in limited numbers, this method avoids the fixed costs associated with the production of a specific mold for each section to be applied to the first section of the part in order to meet the part customization requests expressed by a customer. 
     Using this method, it is also possible to consider producing spare parts without having to keep all the molds to produce each section of the plastic part. 
     The production method and the part obtained using this method may further comprise one or more of the following characteristics, taken alone or in combination. 
     Advantageously, the first section of the part comprises at least one area for mechanically attaching the second section to the first section. Since the first and second sections of the part are attached together mechanically, it is possible to apply a second section whose plastic material is different from the plastic material of the first section. This therefore avoids the problems associated with the compatibility of the materials of the two sections, which may therefore be of different types. 
     Preferably, the mechanical attachment area comprises a three-dimensional network of ribs. The second section of the part is therefore blocked in at least two directions. This three-dimensional network of ribs can be relatively complex and the insertion of the first section of the part into the second section of the part during its three dimensional-printing also blocks the two sections relative to each other in the third direction. 
     The first section of the part could also comprises at least two attachment areas, each attachment area defining a surface and a normal to this surface, the two normals not being parallel to each other. Thus, the blocking of the second section of the part relative to the first section is increased in the third direction for each attachment area. 
     Furthermore, the second section of the part may comprise a functional element and/or a reinforcement element. It is therefore possible to increase the mechanical resistance of the part to deformation over some of its surface or locally, as required, and/or provide functional elements such as elements used to attach the part to the vehicle structure or elements used to attach cables, sensors and other decorative or style components such a painted or chromium-plated trim, for example. 
     Advantageously, to produce the first section of the part, the method comprises the following steps:
         producing at least one metal block having a three-dimensional network of ribs which are complementary to the ribs of the three-dimensional network of the first section,   placing the metal block in a mold at the location of the first section where the three-dimensional network is to be created,   molding the first section of the part.       

     This allows a mold to be customized according to the attachment areas required on the first section of the part. Thus, with the same mold, it would be possible to have several metal blocks and produce, depending on the metal blocks placed in the mold, a wide variety of first sections of the part. The three-dimensional network of ribs which are complementary to the ribs of the network of the first section of the metal block can be obtained by spark erosion or by three-dimensional printing of metal powder. 
     Preferably, the material of the first section of the part comprises polypropylene, polyamide, acrylonitrile butadiene styrene, polystyrene-b-poly(ethylene-butylene)-b-polystyrene, alone or mixed. 
     Furthermore, the material of the second section of the part comprises polypropylene, polyamide, acrylonitrile butadiene styrene, polystyrene-b-poly(ethylene-butylene)-b-polystyrene, alone or mixed. 
     The production method may also comprise a step, before producing the second section by three-dimensional printing, in which surface treatment is applied to the first section of the part. Thus, the first section of the part can be stored after receiving surface treatment. The types of surface treatment include, for example, steps of painting or chromium-plating the first section of the part. The surface treatment also comprises the steps required to make the paint, chromium-plating or other surface treatment adhere to the first section of the part. 
     The plastic part may be a bodywork part. A bodywork part means either an exterior bodywork part or an interior bodywork part. By way of non-limiting example, a bodywork part can be a front or rear bumper skin, a rocker box, a door, a boot door, a roof or boot spoiler, a wing, interior trim parts of the motor vehicle. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       We will now describe several embodiments of the invention given as non-limiting examples in reference to the drawings, on which: 
         FIG. 1  is a cross-sectional view of a first part made of plastic material obtained by the method of the invention; 
         FIG. 2  is a larger-scale view of a detail of  FIG. 1  showing a cross-sectional view of a three-dimensional network of ribs; 
         FIGS. 3 to 5  are top views of three examples of three-dimensional networks of ribs; 
         FIG. 6  is a diagrammatic view of a mold for producing the first section of the part according to the method of the invention; 
         FIG. 7  is a cross-sectional view of a second part made of plastic material obtained by the method of the invention; 
         FIG. 8  is a partial perspective view of a third part made of plastic material obtained by the method of the invention. 
     
    
    
     MORE DETAILED DESCRIPTION 
       FIG. 1  shows a cross-sectional view of a part  10  made of plastic material for a motor vehicle obtained by the method of the invention. 
     This part  10  comprises a first section  12  to which at least one second section  14  is applied. These two sections are made of plastic material. 
     The first section comprises an area  16  for mechanically attaching the second section  14  to the first section  12 . 
     The second section  14  of the part  10  can act as mechanical reinforcement for the first section  12  of the part. It can also be used to attach other elements to the part  10  and/or to attach the part  10  to the motor vehicle. 
     As can be seen on  FIG. 2  which is a larger-scale view of the mechanical attachment area  16  of  FIG. 1  and on  FIGS. 3 to 5 , the mechanical attachment area  16  comprises a three-dimensional network  18  of ribs  20 . 
       FIGS. 3 to 6  show different embodiments of the three-dimensional network  18 . In these top views, we see that the three-dimensional network  18  may take various forms. 
     The ribs  20  may be arranged together so as to form a continuous network of ribs  20  having, for example, a plurality of ribs  20  parallel to each other and connected to each other by other ribs  20 , as shown on  FIGS. 3 and 4 . 
     The three-dimensional network  18  may also be formed by ribs  20  which form crosses in pairs, the crosses being distributed over the attachment area  16 , as shown on  FIG. 5 . 
     We will now describe the method for producing the part  10 . 
     The part  10  made of plastic material is obtained by producing the first section  12  by molding and then by printing the second section  14  directly on the first section  12  using the three-dimensional printing technique. 
     Advantageously, mechanical attachment areas  16  can be provided on the first section  12 . 
     These mechanical attachment areas  16  may be materialized on the first section  12  by three-dimensional networks  18  of ribs  20 . These three-dimensional networks  18  are obtained by the presence, in a mold  22  for producing the first part  12 , of areas having a three-dimensional network  24  of ribs  26  which are complementary to the ribs  20  of the three-dimensional network  18  of the first section  12 . 
     Preferably, these areas having a three-dimensional network  24  of ribs  26  are formed on a metal block  28  applied in a section  30  of the mold  22  for producing the first section  12 . 
     Thus, depending on the number of metal blocks  28  present in the mold  22  and the presence or absence of an area  24  having a three-dimensional network of ribs  26  on these metal blocks  28 , it is possible to produce in the same mold  22  first sections  12  of a part  10  having mechanical attachment areas  16  arranged at different locations on the first section  12  and/or having different three-dimensional networks  18  of ribs  20 . 
     Thus, by replacing the metal block  28  by another metal block not provided with an area  24  having a three-dimensional network of ribs  26 , a first section  12  is obtained which, in the area of this metal block, does not have a three-dimensional network  18  of ribs  20 . 
     Furthermore, three-dimensional printing of the second section  14  on the first section  12  can be carried out after a step of surface treatment of the first section, for example by applying one or more coats to make a paint adhere to the first section  12  and by applying a coat of paint or chromium-plating. 
       FIG. 7  shows a diagrammatic cross-sectional view of a bodywork part for motor vehicle, for example a bumper skin  32 . Note that this bumper skin  32  is not flat. Typically, this bumper skin  32  has a thickness of a few millimeters, while it may have a length of over one meter. Also, the bumper skin  32  comprises a first “appearance” section  12 , which is visible from outside the vehicle and a second section  14  used to reinforce the first section  12  to prevent in particular the bumper skin  32  from deforming and denting if pressure is exerted on it. The second section  14  may also comprise functional elements used to attach the bumper skin to the vehicle or to attach other elements to the bumper skin, such as park distance control (PDC) sensors which assess the distance to an obstacle located in the sensor&#39;s field of view like a camera or a radar. 
     In this cross-sectional view, the first section  12  comprises three mechanical attachment areas  16 ′,  16 ″ and  16 ′″ each having a three-dimensional network  18  of ribs  20 . Each attachment area  16 ′,  16 ″,  16 ″ defines a surface and a normal  34 ′,  34 ″,  34 ′″ to this surface. The normals  34 ′,  34 ″,  34 ′″ are not parallel to each other in pairs. 
     Since at least two of the normals  34 ′,  34 ″,  34 ′″ are not parallel to each other, the second section  14  cannot be removed from the first section  12 . 
       FIG. 8  shows a partial perspective view of a bodywork part  36  for a motor vehicle. This part  36  comprises a skin made of plastic material forming the first section  12  of the part  36  and a second section  14  having a continuous three-dimensional network  38  of ribs  40  forming a honeycomb which mechanically strengthens the skin, and therefore the first section  12 . As can be seen on  FIG. 8 , ribs  40  are fitted with clips  42  in order, for example, to attach cables to the part  36  or to attach the part  36  to the motor vehicle. 
     The second section  14  of the part  36  also comprises another functional element  44  arranged between ribs  40  and attached to these ribs. This element  44  locally strengthens the first section  12  of the part  36  and acts as a means of attaching another element (not shown) to the part  36 . 
     Obviously, numerous modifications can be made without leaving the scope of the invention.