Molding of nonuniform object having undercut structure

Abstract

Various embodiments are disclosed herein that relate to the molding of an item having a non-uniform thickness and an undercut structure. One disclosed embodiment provides an injection molding device for molding a part having a non-uniform thickness and an undercut structure, the injection molding device comprising a pair of opposing end walls, a first mold surface being stationary with respect to the pair of opposing end walls, and a second mold surface being movable toward the first mold surface such that a first end of the second mold surface is movable a larger travel distance toward the first mold surface than a second end during a molding process. Further, the pair of opposing end walls comprises a slider with an undercut mold surface that is movable in a direction transverse to a direction in which the second mold surface is movable toward the first mold surface.

1 . A method of forming a part having a non-uniform thickness and an undercut structure, the method comprising:
 pressing an embossing master defining the undercut structure against an end of a part having a non-uniform thickness while heating the embossing master to soften the end; and   cooling the embossing master while maintaining contact between the embossing master and the end of the part having a non-uniform thickness to harden an embossed pattern into the end, the embossed pattern defining the undercut structure, thereby forming the part having the non-uniform thickness and undercut structure.   
     
     
         2 . The method of  claim 1 , further comprising molding the part having the non-uniform thickness before embossing the undercut structure into the end. 
     
     
         3 . The method of  claim 1 , wherein pressing the embossing master against the end of the part having a non-uniform thickness comprises softening a surface layer of the end less than 1 mm thick. 
     
     
         4 . The method of  claim 3 , wherein heating the embossing master comprises heating for between thirty seconds and one minute. 
     
     
         5 . The method of  claim 1 , wherein the end of the part having the non-uniform thickness comprises a curved end, and wherein the undercut structure of the embossing master has a curvature that matches the curved end of the part having the non-uniform thickness. 
     
     
         6 . The method of  claim 5 , wherein the curved end of the part having the non-uniform thickness is toroidal, cylindrical or spherical. 
     
     
         7 . The method of  claim 1 , further comprising controlling a positional accuracy of the embossing master relative to the curved end of the part having the non-uniform thickness and undercut structure via a precision fixture alignment guide. 
     
     
         8 . The method of  claim 1 , wherein pressing the embossing master while heating to soften the end of the part having the non-uniform thickness is at least partially controlled by a micropressure adjustment control. 
     
     
         9 . The method of  claim 1 , wherein the undercut structure defines a faceted Fresnel lens structure. 
     
     
         10 . A method of forming a light guide having an end comprising a faceted Fresnel lens structure, the method comprising:
 pressing a Fresnel lens embossing master against a curved end of a light guide blank while heating the Fresnel lens embossing master to soften the curved end of the light guide blank; and   cooling the Fresnel lens embossing master while maintaining contact between the Fresnel lens embossing master and the curved end of the light guide blank to harden an embossed pattern in the curved end of the light guide blank, thereby forming the light guide.   
     
     
         11 . The method of  claim 10 , wherein heating the Fresnel lens embossing master comprises induction heating the Fresnel lens embossing master. 
     
     
         12 . The method of  claim 10 , wherein pressing the Fresnel lens embossing master against the curved end of the light guide blank while heating comprises softening a surface layer of the light guide blank less than 1 mm thick. 
     
     
         13 . The method of  claim 10 , wherein heating the Fresnel lens embossing master comprises heating the Fresnel lens embossing master for between thirty seconds and one minute. 
     
     
         14 . The method of  claim 10 , wherein the light guide blank has a toroidally curved end. 
     
     
         15 . The method of  claim 10 , wherein the light guide blank has a cylindrically or spherically curved end. 
     
     
         16 . An embossing device configured to emboss a Fresnel lens pattern into a light guide blank, the embossing device comprising:
 a molding surface configured to contact an end of the light guide blank, where the molding surface comprises a faceted Fresnel lens structure, and the molding surface has a curvature matching a curvature of the end of the light guide blank; and   a heater disposed adjacent the molding surface and configured to heat the molding surface.   
     
     
         17 . The embossing device of  claim 16 , wherein the molding surface has one of a toroidal, cylindrical, and spherical curvature. 
     
     
         18 . The embossing device of  claim 17 , further including a thermal control for heating the device via induction. 
     
     
         19 . The embossing device of  claim 16 , wherein the embossing device comprises nickel chrome. 
     
     
         20 . The embossing device of  claim 19 , wherein an average roughness of the faceted Fresnel lens structure is between 2 and 10 nanometers when the embossing device is formed using the nickel chrome substrate.