Investigations of the Tensile Properties on Polycarbonate Thin-Wall Injection Molded Parts

Abstract

Effect of processing conditions including injection speed, melt temperature, mold temperature and packing pressure on tensile properties of polycarbonate (PC) thin-wall parts were investigated. Tensile test specimen with thickness of 2.5, 1.0 and 0.8 mm were injection molded under specified conditions. Tensile properties and residual stresses were measured experimentally. It was found that the residual stress plays a more significant role in influencing part tensile properties than flow-induced molecular orientation. Part thickness and injection speed are two key factors that affect residual stress most significantly within the current molding window. As part thickness decreases, residual stress increases resulting in the greater influence in reduction of part tensile strength, yield stress as well as Young’s modulus. Higher melt temperature and higher mold temperature would reduce residual stress whereas higher injection speed and higher packing pressure would increase residual stress. Associated with the decrease of residual stress, part’s tensile strength, yield strength and Young’s modulus increase with increased melt temperature, mold temperature and injection speed. On the other hand, higher packing pressure results in a decrease of part mechanical strength.