Tsibrii I. Mechatronic control system for melting titanium

The thesis is devoted to increasing efficiency of the process of titanium ingot production, which allows increasing productivity of melting and improving quality of ingots based on a mechatronic control system for electron beam melting with feedback on the melt temperature in the intermediate capacity and the melt level in crystallizer. The purpose of the thesis is the enhancement of these processes and increasing efficiency of the titanium ingots production by developing a mechatronic system for titanium melting control. It was found that the most unstable element of the mechatronic system is the intermediate capacity where charge falls randomly into the titanium melt, which affects the melt flow into the crystallizer and ingot pulling-out from it. Based on the coupled Fourier heat-conduction equation and Navier-Stokes equations, a non-stationary three-dimensional mathematical model of the process in the intermediate capacity of an electron-beam unit was developed, which takes into account changes in the heat source coordinates and the melt flow velocity. The simulations were done using the finite-element method and MATLAB software, the finite-difference method and the tridiagonal matrix algorithm. The influence of the velocity of the titanium melt flow, the heating power and its distribution over the intermediate capacity surface on the average temperature of the molten titanium and the ratio of the molten titanium volume to the total volume of the intermediate capacity was investigated. The analytical dependencies were obtained which allow setting the rational parameters of the titanium melt heating during the electron beam melting. Based on the simulation results, a method for controlling the trajectory of the electron beam motion with feedback on the titanium melt temperature was proposed, which enables reducing the titanium ingot melting time. The simulations of the titanium melt heating in the intermediate capacity were performed due to the proposed control method. It was found that the application of the proposed control method at the coefficient of heat distribution over the intermediate capacity surface equal to n = 50 ... 60% provides titanium melt heating within the required temperature range 1950-2200 K and the required stable flow of the titanium melt from the intermediate capacity into the crystallizer. Heat and mass transfer in the intermediate capacity was simulated for the case of the entry of an unmolten charge piece during the heating with temperature feedback. The average melting time of the charge piece was found to be 16 seconds. On the basis of the proposed method for controlling the electron beam motion trajectory, an algorithm was developed for simultaneous control of several electron beam guns with redistribution of their influence zones on the intermediate capacity surface. A method of the ingot pulling-out from the crystallizer by applying additional oscillation to the ingot using a hydraulic drive was developed. A design of the hydraulic membrane actuator for applying oscillation to the ingot of any mass was proposed. A mathematical model was proposed to describe stress and strain state of the actuator steel membrane. Using the finite-element method (ANSYS, COMSOL), the influence of the geometric parameters of the steel membrane on its stress and strain state and durability was investigated for a given oscillation amplitude. An analytical expression of the maximum stress in the oscillating steel membrane was derived depending on its geometric parameters. An engineering method was proposed to choose rational geometric parameters of the hydraulic membrane actuator. As compared to similar parameters of the VMO electron-beam unit, the application of the proposed mechatronic system with feedback on the melt temperature in the intermediate capacity and the melt level in crystallizer allows to reduce the energy consumption by 14%, increase the melting productivity by 16%, and, if taking into account the reduction of losses during the mechanical treatment of titanium ingot surfaces, increase the overall process performance by 18%.