Abstract:
A method of manufacturing an assembly, including a structural member and an appearance feature formed therealong, is provided utilizing first and second molds. The method includes the steps of: injecting magnesium into the first mold to form the structural member; removing the structural member from the first mold; placing the structural member in the second mold; and injecting thermoplastic material into the second mold to overmold the appearance feature along a portion of the structural member.

Description:
BACKGROUND 
     The invention relates to structural components formed from magnesium and including appearance features overmolded thereto, and to a method for manufacturing these structural components. 
     It is well-known in the art to provide structural components or running boards for assisting individuals in either entering and exiting or accessing motor vehicles having a high ground clearance. These running boards may include at least one mounting bracket for mounting a step or platform alongside the motor vehicle. Various appearance features, such as covers, step mats, end caps, shields, and the like, are formed as separate elements that are secured to the mounting bracket and/or the step or platform. Each of these appearance features typically requires individual attachment to the mounting bracket or platform, takes up valuable packaging space, and limits styling flexibility. 
     SUMMARY 
     According to one aspect of the invention, a method of manufacturing an assembly, including a structural member and an appearance feature formed therealong, utilizes first and second molds. The method includes the steps of: injecting magnesium into the first mold to form the structural member; removing the structural member from the first mold; placing the structural member in the second mold; and injecting thermoplastic material into the second mold to overmold the appearance feature along a portion of the structural member. 
     According to another aspect of the invention, a method of manufacturing a running board assembly, including a platform, a mounting bracket, and an appearance feature, via first and second molds, includes the steps of: injecting magnesium into the first mold to form the platform; removing the platform from the first mold; attaching the mounting bracket to the platform; placing the platform and the mounting bracket attached thereto into the second mold; and injecting thermoplastic material into the second mold to overmold the appearance feature along at least one of the platform and the mounting bracket. 
     According to yet another aspect of the invention, a running board assembly for a motor vehicle includes a structural member including a platform formed from injection molded magnesium and adapted to be mounted to the motor vehicle. The platform includes a stepping surface extending between opposing ends. The running board assembly also includes an appearance feature injection molded onto the platform. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein: 
         FIG. 1  is a perspective view of a running board assembly including a platform, formed from magnesium, and a mounting bracket with appearance features overmolded thereto according to one embodiment; 
         FIG. 2  is a section view of the running board assembly including the platform and the mounting bracket; 
         FIG. 3  is a perspective view of a running board including a tubular member and appearance features overmolded therealong; 
         FIG. 4  is a cross-sectional view taken along lines  4 - 4  in  FIG. 3 ; 
         FIG. 5  is a cross-sectional view of the tubular member wherein the appearance feature is a step mat; and 
         FIG. 6  is a cross-sectional view of a mold for receiving the running board and mounting brackets for overmolding appearance features thereto. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Referring to  FIG. 1 , an assembly, generally shown at  10 , includes at least one structural member  12 ,  14  and at least one appearance feature overmolded to the at least one structural member  12 ,  14 . Each structural member  12 ,  14  is formed from injection molded magnesium. Each structural member  12 ,  14  is, therefore, a lightweight but generally rigid member. It is appreciated that the assembly  10  may be any of various parts or components for use in numerous industries. 
     In one embodiment of the invention, the assembly  10  is a running board assembly and the structural members  12 ,  14  are a platform and mounting brackets respectively. The platform  12  of the running board assembly  10  includes a stepping surface  16  for supporting individuals entering or exiting a motor vehicle. The platform  12  extends longitudinally between a pair of opposing ends  18 ,  20 , and laterally between an inboard end  22  and an outboard end  24 . 
     The mounting brackets  14  are fixedly secured to the platform  12  and adapted for attachment to the motor vehicle. The mounting brackets  14  mount, therefore, the platform  12  to the motor vehicle. It is appreciated that the platform  12  and the mounting brackets  14  may be formed as an integrally formed single piece or as separate pieces fixedly secured to one another. In the current embodiment, the running board assembly  10  includes a pair of mounting brackets  14  spaced apart from one another. Each mounting bracket  14  includes an outboard facing surface  26  and an inboard edge  28 . 
     The running board assembly  10  further includes at least one appearance feature overmolded to a portion of the platform  12  and/or the mounting brackets  14 . Each appearance feature is formed from a thermoplastic material. One appearance feature is an end cap  30  overmolded to the platform  12  at each opposing end  16 ,  18  thereof. The end caps  30  provide a finished look to the opposing ends  18 ,  20  of the platform  12 . 
     Another appearance feature is a shield  32  formed along the outboard facing surface  26  of the mounting brackets  14 . The shield  32  may also be formed along the outboard end  24  of the platform  12 , as shown in  FIG. 2 . The shield  32  protects the platform  12  and the mounting brackets  14  from damage from stone pecking as may occur during normal operation of the motor vehicle. 
     Another appearance feature for the platform  12  is a step mat, generally indicated at  34 , which is formed in a longitudinal direction along the stepping surface  16 . In the current embodiment, the step mat  34  includes a plurality of tread portions  36  each spaced apart from one another in a lateral direction. The step mat  34  provides traction to individuals stepping onto the platform  12 . 
     Referring to  FIGS. 3 and 4 , in another embodiment the structural member  12 ′ of the running board assembly  10 ′ is a tubular member extending between inboard-facing ends  38 ,  40 . The tubular member  12 ′ includes the stepping surface  16 ′ extending longitudinally between the opposing ends  38 ,  40 . In the current embodiment, the appearance feature is a cover  42  overmolded to the stepping surface  16 ′. The cover  42  extends continuously along the stepping surface  16 ′ in a lateral direction. In another embodiment, shown in  FIG. 5 , the appearance feature is the step mat  34 ′ including the plurality of tread portions  36 ′ formed along the stepping surface  16 ′ of the tubular member  12 ′ and spaced apart from one another in a lateral direction. 
     First and second molds are utilized in a method of manufacturing the assembly  10 ,  10 ′. The first step in the method for manufacturing the assembly  10  is forming the structural member  12  by injection molding magnesium into the first mold. The structural member  12  is removed from the first mold. The structural member  12  is placed in a second mold  44 . The second mold  44  includes a lower mold half  46  and an upper mold half  48  movable relative to the lower mold half  46 . The second mold  44  is closed and thermoplastic material is injected therein. As a result, the thermoplastic material is formed into one or more appearance features overmolded to a portion of the structural member  12 . A finishing operation may be conducted on the structural member  12  either after the step of forming the structural member by injection molding magnesium is completed or after the one or more appearance features are overmolded onto the structural member  12 . 
     In a method according to another embodiment of the invention, a method of manufacturing the running board assembly  10  begins with the step of injecting magnesium into the first mold to form the platform  12 . The platform  12  is then removed from the first mold. The mounting bracket  14  is attached to the platform  12  either by integrally molding the mounting bracket  14  with the platform  12  or by attaching the mounting brackets  14  to the platform  12  after molding thereof. The platform  12  and the mounting bracket  14  are placed in the second mold. The upper mold half  48  is closed against the lower mold half  46  and thermoplastic material is injected into the second mold to overmold the at least one appearance feature to at least one of the platform and mounting bracket. 
     It is appreciated that the above-described methods could be utilized to provide appearance features with various colors, materials, and textures. The running board assemblies  10 ,  10 ′ manufactured according to these embodiments can be produced at a lower cost due to reduced complexity, fewer part numbers, and lower labor requirements. Moreover, quality is improved through the use of fewer components, less variables and variation, and little or no warpage concerns. As an added benefit, there is greater flexibility with regard to overall styling. 
     The invention has been described in an illustrative manner. It is to be understood that the terminology, which has been used, is intended to be in the nature of words of description rather than of limitation. Many modifications and variations of the invention are possible in light of the above teachings. Therefore, within the scope of the appended claims, the invention may be practiced other than as specifically described.