Abstract:
A method of producing a molded article includes the steps of positioning an insert within a first mold, and filling the first mold with a low melt allow to form a lost core assembly. The lost core assembly includes an external shape corresponding to the desired cavity formed within the molded article. The inserts are supported within the lost core and form a part of the surface of the cavity of the completed molded article. The lost core assembly is over-molded with a thermoplastic or thermoset material. The alloy material is removed leaving the inserts within the molded article to form specific portions of the cavity.

Description:
This invention claims priority to U.S. Provisional application Ser. No. 60/368,244 filed Mar. 28, 2002. 

   BACKGROUND OF THE INVENTION 
   The subject invention is method of producing a plastic article utilizing a lost core process, and specifically a method of producing a plastic article by supporting inserts within a lost core assembly for positioning within the completed plastic article. 
   Conventional lost core-molding processes include the formation of a core defining a desired inner cavity configuration of the completed part. The core is formed from an alloy having a low melting temperature. The formed core is placed into a plastic injection mold and molded over by a thermoplastic or thermoset material to form the desired shape of the plastic article. The molded plastic article containing the core is submerged in a hot liquid bath to melt and drain the core material from the plastic article. 
   Many types of devices require specifically configured cavities to support rotating members. Further, the rotating members required supporting features composed of material capable of withstanding specific wear conditions. One example of such a device is an outboard assembly for a motorboat. The outboard assembly transfers power from an interior mounted engine to a propeller positioned within the water. Conventional outboard assemblies are fabricated from an outer housing cast in aluminum. The cast aluminum housing is finish machined to form the required inner mounting structures that support the drive components that drive the propeller. In addition, openings for mounting fasteners and the like are machined into the aluminum casting. The majority of costs associated with the production of an outboard are consumed by the cost of the finish machining operations. 
   There are several inherent problems associated with the use of aluminum as a material to fabricate an outboard. Although aluminum does not rust as a ferrous metal does in the presence of water, there is a certain amount of material loss associated with the constant immersion in water. Further, cast aluminum is often plagued by porosity that degrades the strength of the casting. Pure aluminum is typically to soft to be used without mixing other strengthening elements, at the sacrifice of corrosion resistance. Typically, bearing races and other surfaces supporting rotating drive components must be fabricated from sufficiently hard materials, thereby requiring inserts to be installed within the aluminum housing. 
   Accordingly, it is desirable to develop a method of producing a plastic article capable of accommodating rotating members and that substantially reduces finish machining and with economical materials. Further, it is desirable to develop an outboard assembly with economically beneficial materials and processes that is better suited for the water environment. 
   SUMMARY OF THE INVENTION 
   The present invention is a method of producing a molded article utilizing a lost core assembly supporting a plurality of inserts for positioning within the completed plastic article. 
   The method includes the steps of positioning at least one insert within a first mold and filling the first mold with a first material to form a lost core assembly. The inserts are held within the lost core assembly in a predetermined position. The lost core assembly is then placed into a second mold and over-molded with a second material to form the plastic article. Once the second material has sufficiently hardened, the plastic article, including the lost core assembly is removed from the second mold. The material comprising the lost core assembly is then removed leaving the inserts within the cavity formed by the lost core assembly. 
   Accordingly, the present invention provides a method of producing a plastic article containing inserts supporting rotating members or other internal components while substantially reducing costs. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The various features and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the currently preferred embodiment. The drawings that accompany the detailed description can be briefly described as follows: 
       FIG. 1  is a perspective view of a plurality of inserts and a first mold; 
       FIG. 2  is a perspective view of a completed lost core assembly within the first mold; 
       FIG. 3  is a perspective view of a completed lost core assembly; 
       FIG. 4  is a perspective view of the lost core assembly within a second mold; 
       FIG. 5  is a perspective view of a plastic article including the lost core assembly; 
       FIG. 6  is a perspective view during removal of a portion of the lost core assembly from the plastic article; and 
       FIG. 7  is a perspective view of the completed plastic article. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Referring to  FIGS. 1-3 , the present invention is a method of fabricating a plastic article. The method of the present invention is illustrated by the process of fabricating an outboard housing assembly  22  ( FIG. 7 ). The outboard housing assembly  22  is only one example of a plastic article that may be fabricated with the benefit of this disclosure. 
   The method includes a first mold  10  for forming a lost core assembly  12 . The lost core assembly  12  comprises a low melt alloy  15  including a mixture of components known to provide a specific predetermined melting point. The lost core alloy  15  comprises a combination of several elements mixed according to predetermined proportions to obtain a desired melting point. Examples of alloy components include lead, tin, bismuth, antimony, cadmium, copper, and the like. A worker knowledgeable in the art with the benefit of this disclosure would understand which combination of alloy elements are required to obtain a desired melting temperature. 
   A plurality of inserts  14  are placed into the first mold  10 . The first mold  10  is filled with alloy material  15  such that each insert  14  is positioned as required in the completed plastic article  22 . Each insert  14  includes inner and outer surfaces  16 ,  18 . The outer surface  18  includes attachment features  20  cooperating with a second material forming the plastic article to maintain each of the inserts  14  in the desired final position within the completed plastic article  22 . The internal surface  16  of the insert is held secure within the lost core assembly  12 . Each of the inserts  14  are positioned within the first mold  10  relative to other inserts  14 . The outer surface  18  of each insert  14  becomes encased in plastic and the inner surface  16  is exposed once the lost core material  15  is removed. 
   The lost core assembly  12  is molded to secure the position of each of the inserts  14  relative to each other and to include internal features  24  of the housing assembly  22 . The internal features  24  comprise support structures for rotating drive members (not shown) along with openings for fasteners and cavities through which the drive members extend. As appreciated, an outer surface  26  of the lost core insert  12  defines an inner surface of a completed housing assembly  22  for the housing assembly  22 . 
   Referring to  FIG. 4 , the lost core insert  12  is placed within a plastic injection mold  28  that defines a cavity  30 . The cavity  30  defines the outer surface configuration of the complete housing assembly  22 . Plastic injected into the cavity  30  is of a melting temperature compatible with the melting temperature of the low melt alloy  15  used to form the lost core assembly  12 . Therefore, hot liquid plastic entering the mold  28  does not does not melt or damage the lost core assembly  12 . Molten plastic material, shown schematically at  34 , entering the cavity  30  envelops the lost core insert  12  along with the inserts  14 . The plastic material  34  comprises known thermoplastic and thermoset materials. 
   The inserts  14  are secured within the housing assembly  22  and within the plastic material  34 . Securing of the inserts  14  is accomplished by attachment features  20  disposed on the outer surface  18  of each insert  14 . Preferably, the attachment feature  20  disposed on the outer surface  18  of each insert  14  is a knurled surface that cooperates with the plastic material  34  to secure the insert  14  in place. Alternatively, the attachment features  20  may be a groove including an undercut such that plastic material fills the groove and undercut to secure the insert  14  to the plastic material. A worker skilled in the art with the benefit of this disclosure would understand how to configure an attachment feature  20  to secure each insert within the housing assembly  22 . 
   Referring to  FIGS. 5-7 , once the plastic material  34  has hardened, the housing assembly  22  containing the lost core assembly  12  is removed from the plastic injection mold  28 . The housing assembly  22  including the lost core assembly  12  is submerged within a tank  40  containing liquid  42  at a temperature to melt the low melting alloy  15  without melting the plastic material  34 . The low melting alloy  15  melts and drains from the plastic housing  22  to expose an inner surface  32  of a cavity  36  formed within the outboard assembly  22 . The inner surface  32  of the cavity  36  is formed by the outer surface  38  of the lost core assembly  12 . The inserts  14  are attached to the inner surface  32  within the outboard assembly  22  by the attachment features  20 . The inserts  14  become an integral part of the inner surface  32  of the cavity  36 . Although a hot liquid bath is discussed, it is within the contemplation of this invention to use any type of operation of method of removing the lost core material form the housing assembly  22 . 
   The remaining plastic housing  22  includes an inner surface  32  as defined by the removed lost core assembly  12 . The inner surface  32  includes the inserts  14  along with the cavity  36  to support and surround drive members. Preferably, the inserts  14  require no additional machining and are spaced relative to each other within specific predefined tolerances such that the drive members may be assembled to the housing assembly  22  as molded. Alternatively, the inserts  14  may require minimal machining to provide threads or other features such as holes that are not compatible with the lost core process. A worker knowledgeable in the art would understand how to machine such features into the inserts  14  of the molded plastic housing  22 . 
   The completed plastic outboard housing  22  may be finished as desired by way of an outer cosmetic coating such as paint or an enamel coating. It is within the contemplation of this invention that the plastic outboard housing can be finished by way of any means known in the art. Alternatively, the plastic outboard housing  22  may be molded utilizing a plastic of the desired finished color such that further cosmetic finishing is not required. 
   The completed housing  22  substantially reduces or eliminates the amount of finish machining required to produce an outboard. Further, the plastic material is lighter than a comparable aluminum housing while being of comparable strength. In addition, the plastic material does not exhibit porosity, nor is the plastic material susceptible to corrosion problems encountered with an aluminum housing. The foregoing description is exemplary and not just a material specification. The invention has been described in an illustrative manner, and should be understood that the terminology used is intended to be in the nature of words of description rather than of limitation. Many modifications and variations of the present invention are possible in light of the above teachings. The preferred embodiments of this invention have been disclosed, however, one of ordinary skill in the art would recognize that certain modifications are within the scope of this invention.