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The paper deals with friction problems occur on the contact surface between the effect workpiece and tool and also size-effect during metal forming process. In the carried out numerical procedure the adaptation of the real isothermal conditions due to non-constant friction was investigated for original and resized experimental part. In scope of the paper two friction factors and one type of aluminium wrought alloy of the Al-Mg-Si-Cu system were used for numerical simulation, which were performed in QForm-2D/3D. Obtained results have shown that there is a functional dependency between deformation forces for original and resized forgings. It is quit independent from the friction factor and more depends on temperature.

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In industrial practice of rolling and hot forging, i.e. extrusion-type forging, abruptchanges in strain rate during the deformation of the material occur. For accurate numericalsimulation of a forging process, the experimental investigation of the effect of the transient changein strain rate on plastic flow behaviour is necessary. The present paper deals with the investigationof this effect on the flow stress of an AD-35 aluminium alloy during its deformation within thetemperature range of 350-450 °C. During continuous uniaxial compression loading of a cylindricalspecimen, the strain rate was either constant or abruptly increased or decreased from its initial valueat engineering strain of app. 26 %. The following strain-rate histories were applied: 1) constantstrain rate of 0.1, 1.0 and 10 s-1; 2) abrupt strain-rate increasing from 1.0 to 10.0 s-1; 3) abrupt strainratedecreasing from 10.0 to 1.0 s-1. The results of the experimental investigations corresponded tothe transient change in strain rate histories were used to verify the model of softening as well as themodel of hardening of the AD-35 alloy during the abrupt change of the strain rate. It allows todefine these models explicitly.

The paper contains the description of technique and the graphs for determination of the optimal curvature radius in the tool for isothermal forging with direct extrusion in axisymmetric matrix. This method is based on solving of the problem of minimizing of plastic deformation total power in flow of metal in axisymmetric matrix without curves, i.e. with free flow of material at the transition. Theoretical solution to the problem was verified experimentally.