Model of the object of temperature control by electrostimulating action parameters

Technologies for pressure treatment of metal workpieces using powerful current pulses are becoming increasingly widespread both in Russia and abroad. Unique electromechanical processes are studied and improved in laboratory and production conditions. The process of applying an electric current to the workpiece is accompanied by a change in its physical properties as a result of the so-called electroplastic effect (EPE). At the same time, the temperature of the workpiece in the deformation zone increases. For high-quality and reliable operation of the drawing mill with electrostimulated drawing (ESW), it is necessary to use an automatic system for regulating the force and temperature. In order to implement the temperature control circuit, it is necessary to synthesize the transfer function of the control object – steel wire processed by pressure (rolling or drawing). Synthesis and analysis of parameters of the model of temperature control object are considered. The known relations are used: dependence of the pulse generator power on the calculated parameters (initial temperature, diameter, specific weight and electrical resistance of the workpiece, pulse duration); dependence of the RMS current of the generator on the amplitude and frequency of pulse reproduction; dependence of the magnetic permeability of the workpiece on its temperature; and dependence of the specific electrical resistance of the conductor material on temperature. In MATLAB – Simulink medium, a model of the temperature control object is synthesized as a function of the parameters of generator of high-power current pulses (amplitude and frequency), as well as the parameters of the workpiece to be processed (diameter, sample length, linear velocity, initial temperature, and resistivity at the initial temperature). The model is analyzed, and transients under different operating modes are presented. Using the developed model, the dependences of the temperature, power, and equivalent resistance on parameters of the generator and the workpiece are obtained for different generator pulse frequencies and workpiece diameters. The developed model can be used for laboratory studies of the electroplastic effect, as well as in production in auto-control systems with electrostimulated drawing in order to implement the object of regulation in the form of a model.

Enhancement of the tensile shear strength for joining low-ductility aluminium to high-strength steel by using electrically-assisted mechanical clinching (EAMC)

The present work studied the enhancement of the tensile shear strength for joining AA6061-T6 aluminium to galvanized DP590 steel via electrically-assisted mechanical clinching (EAMC) using an integrated 2D FE model. To defeat the difficulties of joining low-ductility aluminium alloy to high-strength steel, the electroplastic effect obtained from the electrically-assisted process was applied to enhance the clinch-ability. For this purpose, the results of experiments performed by the chamfering punches with and without electrically-assisted pre-heating were compared. Joint cross-section, failure load, failure mode, fracture displacement, material flow, and failure mechanism were assessed in order to study the failure behaviour. The results showed that the joints clinched at the EAMC condition failed with the dominant dimpled mechanism observed on the fracture surface of AA6061 side, achieved from the athermal effect of the electroplasticity. Besides, these joints were strengthened 32% with a much more fracture displacement around 20% compared with non-electrically-assisted pre-heating.

Analysis of the prospects of the application of the electroplastic effect in the processes of processing metals with pressure

The mechanical properties of metals change temporarily or permanently under the influence of a high density electric current in the deformation zone. This phenomenon is called electroplasticity, and its use makes it possible to intensify the process of pressure treatment of electrically conductive materials, including those that are difficult to machine using existing technologies. By now, there is no established point of view on the physical nature of the manifestation of electroplasticity, although this effect itself has already found practical application. The electrical plasticity of metals and their alloys was studied under various loading conditions, including tensile, compression, and bending tests. The article analyzes the theoretical mechanisms of the occurrence of electroplasticity described in scientific publications, the results of studies of the electroplastic properties of various metals or metal alloys, and recommendations for the practical application of the electroplastic effect.

ELECTROTECHNICAL COMPLEX FOR ELECTRODYNAMIC PROCESSING OF WELDED JOINTS

The composition of a two-channel switching power supply for electrodynamic processing of welded joints is determined, which consists in simultaneous action on a limited area of the electric current seam and compressive force of the electrode of such values that the electroplastic effect becomes possible. A linear electromechanical induction transducer is used to create the force pressure. The duration of the compressive phase of the power pulse is chosen to be longer than the duration of the current pulse, which reduces the probability of rupture of the electrical circuit and the release of thermal energy. By controlled delay of the beginning of the current pulse, synchronization of both factors of the electroplastic effect is achieved. The parallel inclusion of semiconductor devices that switch the discharge circuit alternately is proposed, which in the conditions of operation of electrical equipment with a pulse frequency of up to 10 Hz reduces the heat load. Experimental studies have shown a twofold increase in the number of cycles before the destruction of the samples with symmetrical bending. Comparison of two-channel and single-channel electrodynamic processing revealed a twofold reduction in power consumption in a two-channel device. References 8, figures 3, table 1.

Electroplastic effect in specimens of duplex stainless steel under tension

Duplex stainless steels (DSSs) possess a typical biphasic microstructure consisting of equal amount of ferrite and austenite, which provides better combination of the mechanical and corrosion properties compared to the austenitic grade. Despite their good processability, they suffer from embrittlement of secondary phases in a very specific temperature range 450 – 1000°C depending on the composition. Solubilizing treatment after processing is required to obtain a perfect balance between austenite and ferrite and moreover, to dissolve any secondary phases that could have been formed during processing. This implies very high energy consumption of forming processes due to a high temperature (above 1000°C) or high power needed for the forming machines. The electroplastic effect could be used to reduce the force needed to form the material and extend the forming limits. The effect consists in direct interaction between the electrons of the electrical current and the ions of the material. The current mode (e.g., continuous current, pulsed current, pulse duration and duty cycle) plays an important role in the occurrence and the extent of the electroplastic effect. The electroplastic effect is investigated under tension in two-phase duplex stainless steel UNS S32205. Tensile tests under different current conditions (current density and frequency) are compared to room temperature tests. The best effect in terms of reduction of the ultimate tensile strength and increase in the fracture strain is achieved by introducing a multi-pulse current with the maximum density and pulse duration.