Currently, the controllers for achieving a desired injection velocity setpoint profile are independent of processing conditions in plastic injection molding. The dynamics of the reciprocating screw during injection mold filling is complex and temperature-dependent. This complexity is based on process parameters that are nonlinear, which can vary spatially in time. Open-loop tests were performed on two polymers at three melt temperatures and three mold-fill velocity regimes: low, medium, and high. These tests were based on close-loop injection mold-fill setpoints and a derived voltage velocity relationship for the injection velocity hydraulic valve. The results of the open-loop tests show that mold-filling injection velocity is polymer- and melt temperature-dependent. (C) 2004 Society of Plastics Engineers.