Electrostimulated machining of metals

Abstract

New mechanical equipment requires structural materials whose high performance cannot be ensured by traditional methods. A promising approach to the shaping of steel is the use of powerful unipolar current pulses with the following characteristics: amplitude 10–15 kA; pulse frequency up to 400 Hz; pulse length up to 100 μs. The widespread industrial use of this technique is hindered by the low efficiency of the corresponding pulse generators, which also draw considerable power from the ac grid and are not sufficiently controllable. In the present work, a generator of powerful unipolar current pulses that is free of those defects is described. It includes a charging system connected to power capacitors; and a thyristor switch that discharges the capacitors to a low-resistance load. To reduce the power drawn from the grid, the generator includes a recharging device based on a thyristor, which is connected to a reverse-parallel thyristor switch. To permit regulation of the pulse amplitude and increase its power, the uncontrollable dc source in the charging system is replaced by two irreversible thyristor converters in series. That permits control of the voltage at the power capacitors. To optimize capacitor charging, a two-loop subordinate control system regulates the parameters of the pulse generator: the external control loop governs the voltage charging the capacitors, while the internal control loop governs the charging current. MATLAB Simulink software is used to create a model of the proposed generator. The model corresponds to the actual pulse generator used at Siberian State Industrial University to investigate the electrostimulated plastic deformation of metals and alloys. The model permits improvement in the characteristics of the pulse generator and its operating conditions. A benefit of the proposed generator over its counterparts is that the power drawn from the grid is considerably reduced, while the voltage charging the capacitor may be regulated in the range up to 600 V, with pulse frequencies up to 400 Hz. The generator may be used industrially—in particular, in rolling mills when drawing steel wire that is hard to deform.