CHARACTERIZATION OF FRICTION CONDITIONS UTILIZING THE RING COMPRESSION TEST

Characterizing the friction conditions in metal forming processes is important for controling surface quality, reduce die wear and optimizing final product dimensions [1,2]. The most accepted experimental method in the last few decades is the ring compression test [3]. In this method a ring specimen is plastically compressed between two flat dies. The dimensional changes of the inner diameter provide quantitative knowledge of the friction coefficient (μ) or friction factor (m). Nevertheless, in order to determine μ the experimental results need to be compared with numerical results, usually employing finite element methods (FEM). Isothermal conditions as well as constant friction are usually assumed throughout the experiment.

In this study, ring compression tests were investigated utilizing a coupled thermo-mechanical finite element analysis (FEA). Ring compression tests were conducted for several temperatures and lubrication conditions to validate the FE models. The coupled thermo-mechanical models were then used to investigate the sensitivity of the friction coefficient to deviations in temperature measurements, examining the validity of the isothermal assumption during experiments. In addition, the plastic strain which develops during deformation was computed for different experimental friction conditions and compared with metallographic results. The correlation between the friction coefficient, the plastic strain and the resulting microstructure will be presented.

References:

1. Dieter, G.E., Mechanical Metallurgy. McGraw-Hill, 1981.
2. A.T. Male, V. DePierre, “The validity of mathematical solutions for determining friction from the ring compression test”, Journal of Lubrication Technology, Vol. 92, pp. 389-397, 1970.
3. A.T. Male, M.G. Cockroft, “A method for determination of the coefficient of friction of metals under conditions of bulk plastic deformation”, Journal of the institute of Metals, Vol. 30, pp. 509-519, 1964.