The influence of friction on the forming of flat workpiece with upsetting is investigated using the software complex Deform-3D during a virtual experiment. The following is shown: when the friction is great (i.e., the friction coefficient is greater than 0.5), forming takes place in accordance with the principle of least perimeter, confirmed in experiments on the upsetting of steel samples by Carl von Zobbe at the beginning of the last century. If the friction is close to zero, which is extremely rare in industrial conditions, rectangular samples during upsetting, increasing in size, retain their shape.Then we can highlight two kinematic schemes of metal flow. With minimal friction, a radial scheme of metal flow is observed, with great friction – a normal scheme of metal flow, which corresponds to the principle of least perimeter.In real deformation processes, when the friction is far from zero, any shape of the cross-section of the workpiece should tend to the circle. This statement is considered a classic axiom, although no one confirmed experimentally. All researchers confined to the study of the forming of workpieces of rectangular cross-section.We conducted laboratory experiments on the upsetting of plasticine samples of arbitrary shape. It has been established, that for any shape of the cross-section of a flat sample the principle of least perimeter is confirmed, i.e., with great degrees of deformation the cross-section of the workpiece turns into a circle.