Experimental measurement of the resistant load in injection pultrusion processes

Injection pultrusion (IP) process is a manufacturing technique for producing advanced fiber reinforced polymers having constant cross-section. Unlike the traditional pultrusion process, in which fibers are impregnated passing through an open bath of liquid resin, in IP the uncured polymer is directly injected within the advancing reinforcement in a close chamber generally connected to the die. This paper investigates the resistant forces evolution in IP process at different pulling speeds. Resistant loads are mainly due to the interaction between the advancing material and the die cavity walls, inducing residual stress and, eventually, internal defects. These loads are typically classified in three main contributes, namely fiber collimation, viscous drag and solid friction. The latter two are directly related to the resin degree of cure, and, therefore, the overall resistant load is dramatically sensitive to the changes in operative parameters. In this paper, the resistant force acting along the die cavity has been measured using a dedicated experimental setup. Measurements were performed during the pultrusion of glass-reinforced polyester with different pulling speeds to evidence the variations in resistant load as a function of the process velocity.