Development of plasma cutting technique for C1220 copper, AA2024 aluminum alloy, and Ti-1,5Al-1,0Mn titanium alloy using a plasma torch with reverse polarity

Introduction. An important area of research in the field of plasma metal cutting is obtaining a metal cut face characterized by minimal roughness and geometric deviations. It is also important to minimize changes in the structure of the metal under the cutting surface caused by the temperature effects of the plasma jet, including the formation of dross. The solution to the problem of obtaining a quality cut is to optimize the parameters of the cutting process. The plasma arc current and voltage, cutting height and cutting speed are considered to be the main parameters that determine cut quality. However, insufficient attention has been paid to the processes of plasma metal cutting of thicknesses above 20 mm due to the limitations associated with the operation conditions of plasma torches with direct polarity currents. Accordingly, for cutting large thicknesses, the use of a plasma torch operating on currents of reverse polarity seems promising. The aim of this work is to develop the technique of plasma cutting of copper, titanium and aluminum alloy sheets up to 40 mm thick using a plasma torch operating on currents of reverse polarity. Results and discussion. Investigations show that for cutting aluminum alloy (Al 90.9–94.7 %; Cu 3.8–4.9 %; Mg 1.2-1.8 %; Mn 0.3–0.9 %) and titanium alloy (Ti 94.33–97.5 %; Al 1.5–2.5 %; Mn 0.7–2.0 %) it is possible to regulate the cutting speed in a wide range, while for rolled copper (Cu ≥99.96 %) and aluminum alloy with thickness of 40 mm the range of cutting speed regulation is rather narrow. While for aluminum alloy due to excessive precipitation of alloying elements from the solid solution in the heat-affected zone decrease of microhardness is observed, for titanium alloy the microhardness growth due to material hardening is characteristic. Changing the cutting mode parameters allows receiving more homogeneous macrogeometry of a cutting surface, smaller depth of a zone of melting of a material and a heat-affected zone and smaller changes of mechanical properties of a material in a zone of a cut. For the titanium alloy, almost all of the cutting modes used are close to optimum. For alloy aluminum and copper the modes providing the best cutting quality in the considered range of parameters are determined. According to the results of the work it can be concluded that plasma cutting on reverse polarity currents is effective for cutting rolled products of large thicknesses, but the technique requires further development in order to improve the quality of the resulting cut.