РАСЧЕТ ТЕМПЕРАТУРНОГО ПОЛЯ УПРОЧНЕННОГО СЛОЯ ПРИ ЭЛЕКТРОМЕХАНИЧЕСКОЙ ПОВЕРХНОСТНОЙ ЗАКАЛКЕ

Abstract

The main methods of surface hardening during electromechanical processing (EMP) include finishing-hardening electromechanical processing (FHEMP) and electromechanical surface hardening (EMSH). EMSH, as compared with the FHEMP modes, features a slow processing speed (0.6…1.4 m/min), a long contact width of up to 5 mm, a significant electric current strength of the secondary circuit – 1200…3000 A. The article presents a three-dimensional model for predicting and determining the temperature fields of the hardened layer of U8 steel bushings during EMSH made in the ANSYS Workbench program. The authors carried out finite element modeling of the EMSH process consisting of successive transient structural strength analysis and transient thermal analysis. During EMSH, the thermomechanical cycle “heating – keeping – deformation – cooling” is carried out in the closed contact zone of the tool and the workpiece in hundredths of a second. It was found that during EMSH a temperature gradient is formed along the depth of the hardened zone as there is intensive cooling of the surface layer heated to 1559°C, as a result of heat removal by the underlying metal layers. After EMSH a fine-dispersed martensite is formed in the hardened zone. The study results are useful for developing the EMSH processing technology of the surface layer of bushings made of U8 steel based on the hardening mode with the following parameters: hardening speed of 1.2 m/min, the current strength in the secondary circuit of 1600 A, the secondary circuit voltage of 3 V; the width of the contact electric effect of 4 mm; the pressing force of the tool roller of 400 N.