On parameters affecting metal flow and friction in the double cup extrusion test

Friction and lubrication in metal-forming processes are usually evaluated b y a process test with a friction-sensitive divided flow like the ring-compr ession test. Parameters affecting metal flow are not only friction, but als o strain hardening, tool geometry etc. The current friction models applied in numerical simulations often involve strain hardening because friction is expressed as a function of the flow stress or the flow shear stress. The d ouble cup extrusion test is considered to be one of the process tests for d etermination of friction. In this test, varying heights of the upper and lo wer cups will develop with different friction and strain hardening conditio ns. In the present paper, an investigation of this test has been carried ou t experimentally and theoretically. Both annealed and work-hardened AA6082 specimens were extruded with varying degree of reduction and different lubr icants. A friction model with constant absolute value excluding the influen ce of strain hardening on friction was adopted in FEM simulations, in order to more clearly study the individual influence of strain hardening and fri ction on the metal flow (upper and lower cup height ratio) without interfer ence between the two parameters. The predicted results show a good agreemen t with the experimental data. The influence of material strain hardening. f riction and tool geometry on the metal flow in the test has been investigat ed. By comparisons of the cup height ratio as a function of the punch trave l estimated by experiments and FEM simulations, the friction has been evalu ated. The parameters affecting the friction have also been discussed.