Berezshnaya E. Development of scientific and technological fundamentals for improving efficiency and quality of wear-resistant electrocontact surfacing

The thesis is devoted to the development of scientific fundamentals and methods for automated calculation and design of the wear-resistant electrocontact surfacing process by strips, including the development of practical recommendations for improving the manufacturing electrode materials and restoring worn-out surfaces technologies. When designing recovery operations based on the electrocontact surfacing using the calculation methods for determining the technological conditions for increasing the surface layer, the following basic requirements are met. They ensure the necessary performance properties: adhesion strength of the welded layer to the substrate, wear resistance and fatigue strength. The work experimentally confirmed the effect of the strengthening coefficient on the sensitivity to the stress concentration applied to samples deposited by strips of structural carbon steels with subsequent heat treatment. Based on the results of experimental studies, a combined technology for the recovery of cylindrical parts working under cyclic loading conditions was developed. The proposed technology includes electrocontact surfacing operations followed by local heating of RF current and delayed cooling in a heat-insulating mixture containing graphite laminate compounds. The use of the developed combined technology for the restoration of parts made possible the reduction of the growth rate of the fatigue crack in the surface layer and the increasing of the deposited parts’ fatigue strength. On the basis of the experimental studies, the technology for electrode material fabrication was developed. It helps to obtain in the deposited surface layer a structure consisting of a plastic matrix (solid solution) and uniformly distributed solid components (iron borides), wherewith the loads perceived by the product surface are redistributed over the coating area, reducing the destruction probability. The proposed technology for manufacturing the electrode material provides high wear resistance and a breakdown stresses of the coating deposited by the electrocontact method. A numerical mathematical model of the electrocontact surfacing process by electrode strips is developed. It’s based on a numerical recurrence solution of the static equilibrium condition for the selected elementary volume of the thermal deformation hearth. A peculiarity of the proposed mathematical model is the correct consideration of the electrode material thermal characteristics distribution along the thermal deformation focus, which plays an important role in the formation of the joint during the surfacing process. The effect of the kinematic asymmetry magnitude coefficient on the change in the local energy-force characteristics of the process is established. The assumptions made under finite difference modeling are confirmed by the results of finite element modeling of the electrocontact surfacing by tapes. The sufficiency of the developed mathematical model is confirmed by experimental studies. It was experimentally established that an increase of kinematic asymmetry coefficient in the electrocontact surfacing process contributes to the increase in the adhesion strength. On the basis of the developed mathematical model, the technological regimes automated design of the electrocontact surfacing by tapes is performed. Based on the developed database of the electrocontact surfacing process initial parameters, a structural diagram was constructed and a simulation of the fuzzy process control module was implemented. Its implementation provides control over the regime parameters during the welding current pulse. Key words: electrode tape, electrocontact surfacing, finite-difference mathematical model, finite element model, electrocontact surfacing modes.