Sink-free panels

Abstract

This invention proposes a method for eliminating 'sink' in molded glass fiber reinforced panels for automotive and other uses. Such panels are normally formed with integrally molded reinforcement shapes (ribs) and fastening locations (bosses), and a slight depression or 'sink' occurs in the exposed panel surface over the location of the ribs and bosses. The present invention proposes the elimination of this sink by utilizing innovative material and design techniques that compliment one another. The material approach makes use of dual reinforcements; normal chopped glass fibers reinforcement (1 inch or less in length) in combination with a long fiber reinforcement (2 inches or more in length) and preferably a continuous fiber reinforcement. The long fiber reinforcement is placed such that it is oriented in the panel to closely underlie the exposed panel surface. The short chopped fiber, but not the continuous fiber of the composite reinforcement, enters the rib to reinforce the same, while the continuous glass fibers bridge across the rib. The major design consideration is that the juncture points where the rib or boss meets the basic laminate have a sharp or minimum lead-in radius. This lead-in radius should be no greater than .005 - .01 inch, as contrasted with previously recommended 'generous' lead-in radii of from 1/8 to 1/4 inch. This geometry tends to minimize segregation of material flowing into the ribs and bosses as well as minimize the cross-sectional area of this juncture. The material and design approaches may be used separately to minimize 'sink' and, the visual distortion caused by that differential thermal shrinkage resulting from material non-uniformity and glass orientation as the rib fills and the resin exothermically cures.