OBRABOTKAMETALLOV TECHNOLOGY Vol. 24 No. 2 2022 224 mm from the end of the extruded rod, which is 63 % of the rod diameter. At the same time, the established recommendations include the removal of metal at a length of up to 200 % of the rod diameter. It should be noted that the low strain fi eld in the press product front (output) part has been repeatedly confi rmed by experimental studies carried out by the coordinate mesh method [22, 23]. However, these studies were carried out on a model material, such as lead, as well as with much smaller geometric parameters. The fi nite element method application made it possible to set the real workpieces dimensions and the real deformable material properties for the solution. The practical value of the presented study lies in the fact that, according to the data obtained as a calculation result, it is possible to estimate the strain obtained by the rod in the initial non-stationary stage of extrusion and decide whether it is possible to use this metal for further forming or it should be sent for remelting. One of the problems that arise after the end of the extrusion process is that it is necessary to evaluate the fi nished product mechanical properties. This should be done by selecting a template that is located at a certain distance from the rod front end. This distance is regulated by the standard. What are the product properties at a smaller or greater distance from the specifi ed location remains unknown. It is possible that a part of the extruded rod has the necessary physical and mechanical properties level, but there is nothing to measure it with. It can be concluded that an easier way out is to send a potentially good metal to remelting. A solution to the problem by the fi nite element method allows building a strain distribution picture and linking this distribution with the properties distribution in the presence of pre-known functional dependencies. Another way to use the resulting solution is to use the extruded rod front part for re-extrusion on a lower power press to obtain a product of a lower diameter. In this case, as a fi rst approximation, the strain degree in the two stages of extrusion can be added using the additivity principle. The higher product properties will be achieved with a greater strain. Conclusions In the extrusion process with a low elongation ratio, the strain is distributed inhomogeneously both along the press product cross section and along its length. The difference between the strain (logarithmic) in the central part (on the axis) and on the extruded rod periphery may be higher than 300%. In the nonstationary initial extrusion stage the rod front part remains weakly deformed both at the periphery and in the center. It is often forces to send this part to remelting due to the insuffi ciently developed metal structure. At the same time, if boundary conditions are set on the minimum possible strain degree, it is possible to set the minimum metal length to be removed with using the calculation results by the fi nite element method, thereby reducing the waste mass sent to the remelting. Fig. 6. Strain rate distribution (1/sec) in the longitudinal section (shape of the deformation zone); W – maximum point References 1. Li H., Wu Y., Cao H., Lu F., Li C. Energy dissipation characteristics modelling for hot extrusion forming of aluminum-alloy components. International Journal of Precision Engineering andManufacturing – Green Technology, 2022, pp. 1–23. DOI: 10.1007/s40684-021-00410-y.
RkJQdWJsaXNoZXIy MTk0ODM1