A “Mold Filling” Model from Viscosity Measurements in a Strengthened Injection-Molded Reduced Glass Fiber Length Polyester Bulk Molding Compound

Abstract

Experimental viscosity measurements (50 to 100 Pas at mold walls, T = 273 to 373 K) of an injection-molded highly-lled glass ber reinforced polyester bulk molding compound (GFRP-BMC) whose ber length (l ber = 0.44 mm) was optimized for tensile mechanical strength agreed well with that previously calculated by Navier-Stokes equation from ber orientation mapping. The mapping was from 0.44 mm ber formulation molded sample exhibiting 60, 40 and 20% higher tensile strength, strain, and modulus, respectively than commercially used (l ber = 6.4 mm). Based on the viscosity measurements a new mold lling model is constructed with physical meaning to predict needed injection molding parameters pressure (dP), shot time (t s ) and shot weight (m s ) for various size dog-bone specimens varying length (L tot ), gauge length (L B ), width (w) and thickness (th) for the optimized formulation. Moreover, the Mooney-Rabinowitsch calculation is found to be a decent predictor for shear rates across specimen thickness and at mold walls measured from the mapping. This was without buying new equipment, using the existing injection molding machine to save cost.