International Scientific Journals
of Scientific Technical Union of Mechanical Engineering "Industry 4.0"

Bulk forming is one of the most effective and efficient manufacturing processes. Mass production of many of the items without any defects has been possible because of the advancements in cold bulk forming. The characteristic of a lubricant, especially coefficient of friction influences the interfacial friction during the forming process. This friction causes defects and many difficulties and has to be kept within limits so the proper choice of lubrication is very important for the quality of the formed product. The influence of lubricant’s coefficient of friction on different mechanical and electrical properties of cold extruded material has been investigated and described in this paper by performing many different tests and measurements for mechanical properties and electrical conductivity of the formed material. Coefficients of friction for four different lubricants were first obtained by ring test, and then these lubricants were used in cold extrusion process. The obtained experimental results describing the effect of lubrication on material properties were presented in a form of diagrams and have shown that choice of lubrication could influence some material properties.

Cold forming process in the plastic domain of deformation causes strain hardening in the formed material. Strain hardening can be used for practically all metals and alloys to increase most of mechanical characteristics, however ductility and some others are reduced. In the paper experimental researches of the influence of effective strain on change of main mechanical characteristics such as tensile strength, yield strength, impact toughness, and some other characteristics of cold formed material were carried out and analyzed.

The results of the experiments are presented in the form of graphs. Special mathematical models for determination of different properties were obtained. These models are especially helpful for prediction of mechanical and other properties of a cold formed material. Knowing the material properties and their changes during the cold forming processes is very important for quality of the product and for planning the right technology of the forming processes.

By using visioplasticity method the velocity field can be determined experimentally, and then the stresses can he obtained analytically from these experimental measurements. That means, strain rates and strains are calculated directly from the velocity field while the stress distribution is calculated from an analytical solution of the equilibrium equations and the constitutive equation relating the stress and strain for the material. This method can also provide detailed data of the pressure distribution on the die surface, which is important in the design of the die profile. In the paper cold forward extrusion through a conical die is illustrated by extruding copper alloy specimens with inscribed grid lines. Stress state distribution in plastic deformation region was analyzed using the visioplasticity method. From the flow lines of each element, the velocity and the strain rates are obtained. Finally, the stress components are calculated from the equilibrium and plasticity equations.