AbstractA comprehensive study into the performance of 4 injection molding machines is reported, using identical mold, polymer, and processing conditions. Start‐up dynamics and process repeatability were directly compared across machine technologies. One servohydraulic, one proportional hydraulic and two servoelectric machines were used in the study, ranging in age from 14 years to 1 year old at the time of the study. Experiments were carried out at identical set molding conditions for a run of 400 parts and part quality and process parameters monitored. Results showed a significant start up period in each case, correlating strongly to mold temperature. Age of machine proved to be the most significant factor in determining process repeatability; modern machines having significantly lower variation than older ones. Differences between the operating characteristics of hydraulic and electric machines were detected, control of screw position in hydraulic machines being less repeatable, although this had a minor effect on part repeatability. Electric machines were found to use up to 4 times less energy than their hydraulic counterparts and operate more efficiently. POLYM. ENG. SCI., 45:857–865, 2005. © 2005 Society of Plastics Engineers