Kondakov A. Technological support of the controlled formation of the parameters of surface layers of steels in the electroerosion processing with a wire electrode

Application of innovative developments in technology of processing of materials allows to expand use of high-quality materials of high hardness in mechanical engineering. During their processing, standard production methods are gradually being replaced by more progressive strategies, such as electroerosion treatment, electrochemical treatment, ultrasonic treatment and laser treatment. Electrical discharge machining (EDM) involves the complex involvement of numerous physical phenomena. Electric sparks between the cathode and the anode generate a large amount of heat over a small area of the part. The material of the part is removed due to the occurrence of melting and evaporation caused by high temperatures during the collapse of the discharge plasma channel. The parameters of the surface layers of steel parts, technical and technological characteristics of the process, which determine the mechanisms and results of their formation require further comprehensive system studies. The development of ideas about the formation of the parameters of the surface layers of steel parts during EDM treatment with a wire electrode will improve their performance, due to better forecasting and controlled formation of the specified micro geometry and physical and mechanical properties. The set of results of experimental and theoretical researches presented in the dissertation is a new solution of the actual scientific and technical problem of increase of efficiency of technological maintenance of forecasting and controlled formation of micro geometry and physical and mechanical properties of surface layers of steels at electroerosive processing by a wire electrode. An analysis of the state of problems and factors that affect the formation of surface quality during EDM treatment with a wire electrode. The detailed analysis of parameters of modern generators of technological current of electroerosive cutting machines and mechanisms of their influence on formation of a single erosion hole, productivity the process of cutting and quality of the formed surfaces is carried out. The influence of the characteristics of the wire electrode-tool on the process of electroerosive cutting is analyzed. The known models of surface formation during electroerosive treatment and features of formation of structure of surface layers are considered. The dissertation presents the developed and selected methods and equipment for the implementation of a set of experimental studies of controlled influence of the main parameters of EDM wire cutting on the formation of micro geometry, structure and physical and mechanical properties of surface layers of steels. An original method for determining stresses in the zone of thermal influence after EDM wire cutting in known simple technological schemes is proposed and adapted. Theoretical and experimental researches of processes of formation of geometry of a single erosion hole and microgeometry of surfaces formed by mass action of discharges at electroerosive wire cutting are described (WEDM). Regularities of change of energy efficiency of the process of destruction of structural steel 45 in the selected range of modes of operation of the generator are revealed. For a group of steels with known and sufficiently similar thermophysical characteristics (Steel 45, Steel 48, 40X, U10, X12M) a system of equations is obtained, which allows at the stage of designing the technological process of EDM for known discharge energy released at the anode, discharge duration and the coefficient of overlap of the holes to calculate the three basic parameters of roughness – Rz, Ra, Rq. The regularities of the occurrence and influence of vibrations of the wire tool electrode (WTE) on the formation of the micro geometry of the treated surfaces are obtained. A mathematical statistical model for calculating the effect of WTE vibrations on the micro geometry of treated surfaces has been developed. The results are given a systematic set of studies to determine the microhardness, structure and thickness of the thermal hardening zone in high-quality carbon structural Steel 45 after WEDM. The obtained results provide replenishment of the database and expansion of ideas about the patterns of influence of time-energy characteristics of process current pulses on the formation of a thermally strengthened layer by WEDM of high-quality carbon steels. The hypothesis that the WEDM of high-quality carbon steels with the use of discharge current pulses with energy and time parameters characteristic of modern EDM cutting machines has a dominant influence on the formation of the thickness of the thermally hardened layer has been put forward, substantiated and experimentally confirmed.