Development of devices for measuring contact friction forces in the processes of volumetric plastic deformation

Methods and means for studying the factor of plastic contact friction in the processes of volumetric plastic deformation of solid and hollow precision workpieces were discussed in the article. Estimation of the forces values required for overcoming friction resistance is important for the correct calculation and choice of technological variants for deformation processes, for assessing the properties of technological lubricants, as well as for the correct setting of initial conditions when simulating forming processes using various methods, including using FEM. An analysis of methods and means for assessing the conditions of contact friction in die forming processes was carried out, and a conclusion about the advantage of methods for directly measuring of friction forces in plastic deformation processes compared to ones for indirectly determining friction constants using deformation, kinematic, and force parameters was made. Designs of devices for measuring friction forces directly during the process of plastic deformation have been proposed and tested. Radial extrusion schemes have the advantages of identifying surfaces of directional influence by friction forces and recording them. Based on the results of measurements of friction forces, the effectiveness of several technological lubricants for cold and semi-hot extrusion of steel and aluminum alloys was assessed. The values of friction coefficients according to Siebel’s law have been refined. A correlation between friction stress and normalized pressure of extrusion was proposed, in which the flow stress of the near-contact metal layer was expressed through hardness indicators, and correction coefficients were found from experimental data of measuring friction forces. The proposed devices made it possible to expand the understanding of the contact friction factor in the processes of working by pressure, which is important for practice and for plastic deformation processes simulation.