Investigation of friction factor in forging process of Ti-6Al-4V through isothermal ring compression test

1. Introduction

Friction at the tool/workpiece interface in the forging process has a significant effect on the tool life, load and energy requirement, formability and the quality of the finished part [1]. In the metal forming simulation, friction factor is a key parameter that must be considered in the model to obtain reasonable results. In the precision forging of the aerofoil sections, the friction factor has a significant effect on the pressure distribution at tool/workpiece interface and consequently elastic deflection of the tool [2]; therefore the precise determination of the friction factor is important. Several methods are developed to determine the magnitude of the friction factor, such as: compression test [3], T-shape test [4], spike test [5] and ring compression test. The ring compression test is the most common method to determine the friction factor in the metal forming processes.

The ring compression test was introduced by Kunogi [6] and was further developed by Male and Cockcroft [7]. The mathematical models of the ring compression test were developed by Kunogi [6], Kudo [8] and Avitzur [9]. The ring compression test involves axially forging of ring shaped specimens between two flat platens. The change in the internal diameter of the ring is sensitive to frictional forces and according to its value may increase, decrease or remain constant. For a frictionless condition, the ring deforms like a solid disk, so internal diameter increases. Increasing the frictional forces impedes outward flow of metal and beyond a critical value, the internal diameter decreases [1].

With assumptions of no barreling, von Mises stress-strain laws and constant friction factor, Avitzur developed an optimum upper bound mathematical solu...

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...esults show that the friction factor of the glass used in this study increases with increasing the temperature. At the temperature of 900 °C strain rate does not show a considerable effect on the friction factor but at 850 and 950 °C increasing the platen velocity decreases the friction factor significantly.

The results of this study provide insight into the frictional interaction in the precision forging process. It can be utilized for accurate simulation of material flow in the die; hence optimization of the parameters in the forging process and also a better design of required tooling can be achieved.

Acknowledgement

The financial support for these works was partially provided by MAPNA group under grant No. RD-THD-91-05 which is appreciated. The authors extend their sincere gratitude toward Professor Mohammad Habibi Parsa for his invaluable scientific advice.