1. IntroductionFriction at the tool/workpiece interface in the forging process has a significant effect on tool life, load and energy requirements, formability and quality of the finished part [1]. In metal forming simulation, the friction factor is a key parameter that must be considered in the model to obtain reasonable results. In precision forging of airfoil sections, the friction factor has a significant effect on the pressure distribution at the tool/workpiece interface and consequently on the elastic deflection of the tool [2]; therefore the precise determination of the friction factor is important. Several methods have been developed to determine the magnitude of the friction factor, such as: compression test [3], T-shaped test [4], peak test [5], and ring compression test. The ring compression test is the most common method for determining the friction factor in metal forming processes. The ring compression test was introduced by Kunogi [6] and was further developed by Male and Cockcroft [7]. Mathematical models of the ring compression test were developed by Kunogi [6], Kudo [8], and Avitzur [9]. The ring compression test involves the axial forging of ring-shaped specimens between two flat plates. The variation of the internal diameter of the ring is sensitive to friction forces and based on its value it can increase, decrease or remain constant. In a frictionless condition, the ring deforms like a solid disk, so the internal diameter increases. Increasing the friction forces prevents the outward flow of the metal and above a critical value, the internal diameter decreases [1]. With the assumption of no barrel, von Mises' stress-strain laws, and constant friction factor, Avitzur developed an optimal mathematical solution for the upper limit. .... half of the paper ...... the results show that the friction factor of the glass used in this study increases with increasing temperature. At the temperature of 900 °C the strain rate does not show a considerable effect on the friction factor but at 850 and 950 °C increasing the plate speed significantly decreases the friction factor. The results of this study provide information on the interaction of friction in the precision forging process. It can be used for accurate simulation of material flow in the mold; thus it is possible to achieve parameter optimization in the forging process and also better design of the required tools. Acknowledgment Financial support for this work was partially provided by the MAPNA group under grant no. RD-THD-91-05 which is appreciated. The authors extend their sincere gratitude to Professor Mohammad Habibi Parsa for his valuable scientific advice.