Fastening arrangement for plastic to metal parts

In an automobile vehicle body having a metal substructure, a plastic panel for attachment to said substructure, fastening means fixedly attaching the panel to said substructure such that said plastic panel is slidable relative to said substructure, the improvement in said fastening means wherein:

• said plastic panel having inner and outer planar surfaces, at least one hole of predetermined diameter formed in said panel;
• said metal substructure having a planer portion defining inner and outer planer faces, said plastic panel inner surface in flush contact with said substructure planer portion inner face such that said one hole is aligned with an elongated slot in said substructure;
• a spring washer including a tubular sleeve portion defining an axial through bore of predetermined axial extent, an integral frusto-conical spring flange extending radially outwardly at one end of said sleeve portion, said sleeve portion other end extending through said substructure elongated slot and said plastic panel hole, said sleeve portion having a predetermined axial extent such that with the peripheral edge of said washer spring flange contacting said substructure outer face said washer sleeve portion other end is substantially flush with said plastic panel outer surface;
• a blind break-stem rivet having an elongated tubular rivet body formed with a rivet head at one end and an integral elongate shank, said rivet head having its undersurface formed with a thread-like concentric ring of a predetermined diameter terminating in an annular sharp crest extending a predetermined axial distance towards said shank;
• said rivet body shank being adapted to expand radially to form a blind end, an axial bore throughout said rivet head and shank, and a mandrel disposed in said body bore, said mandrel having an elongate stem which projects from the rivet head end of said body bore, a plug, and a breakneck joining said stem and said plug;
• said washer through bore having a predetermined diameter telescopically receiving said rivet elongated shank therethrough such that said rivet head undersurface annular sharp crest initially contacts said plastic panel outer surface in a line contact manner;
• whereby upon said rivet being set causing radial expansion of said shank to form a blind head when said mandrel is pulled to move said plug relatively towards said rivet head end of said body, wherein an axial clamping action is applied to said washer causing said washer radial spring flange to bias said rivet head annular sharp crest into pressure contact against said plastic panel outer surface;
• and
• wherein upon said attached plastic panel being heated to its thermal-relaxation temperature said plastic panel softens such that said annular sharp crest penetrates said plastic panel outer surface to a depth sufficient to relieve excess preloading of said spring flange providing a controlled sliding resistance of said washer spring flange with said metal substructure such that said plastic panel is slidable relative to said substructure upon thermal growth of said plastic panel.