A REVIEW OF RING-COMPRESSION TESTING AND APPLICABILITY OF THE CALIBRATION CURVES

The frictional conditions prevailing at the tool-material interface, in general, increase the redundant work in all metal-forming operations by increasing the load and energy requirements. Also, friction plays a significant role in determining the life of the tools, the formability of the work material and the quality of the finished product. In designing a metal-forming operation, it is necessary to quantify friction and evaluate the behaviour of various lubricants under the operating conditions of temperature and strain rate in order to optimize the processing route for producing the required shape and quality economically. The difficulty faced for quantitative evaluation of frictional conditions prevailing during actual forming operations, has led to the evolution of various tests, the ring-compression test having proven to be one of the best tests for quantitative evaluation of friction. Several researchers have analysed this process and generally the results of their analysis were presented in the form of calibration curves for specific ring geometries. This paper presents a review of the calibration curves developed by various researchers, and discusses their usefulness and limitations for quantitative evaluation of friction and flow stress. The experimental data obtained for some aluminium alloys is used for comparing the validity of the calibration curves.