Comparative Evaluation of Oxygen-Assisted and Compressed-Air Plasma Cutting of Low-Carbon Steel

Air plasma cutting technology is widely used for high-speed profiling of electrically conductive materials. The cut quality of surface and thermal effects is highly influenced by gas composition and process parameters. This study aims to systematically optimise and comparatively evaluate conventional compressed-air plasma cutting and an oxygen-assisted compressed-air plasma cutting process for 10 mm thick C-20 carbon steel plates. The investigation was conducted in two sequential stages using statistical Design of Experiments (DoE). First, a full-factorial design comprising 20 experiments was performed using compressed air to establish baseline process parameters and optimum operating ranges. Subsequently, a Central Composite Design (CCD) based on Response Surface Methodology (RSM) was employed for 20 additional experiments to model and compare pure compressed air with an oxygen-compressed air mixture. Cut quality was evaluated in terms of kerf width, dross height, bevel angle, surface roughness, maximum cutting temperature, and heat-affected zone (HAZ) length. The results demonstrate that the addition of oxygen improves plasma arc characteristics and produces substantial reductions in kerf width from 2.3 to 2.1 mm, dross height from 0.3 to 0.2 mm, bevel angle from 1.6 to 1.4 Radian, Avg.surface roughness from 1.2 to 0.2 µm, Max.surface roughness from 8.2 to 1.6 µm, Max. surface temperature from 1719.3 to 1607.8 °C and HAZ from 38 to 23.2 µm compared with conventional compressed-air cutting. Furthermore, microstructural analysis of the cut surfaces revealed a significant reduction in HAZ length when the oxygen-assisted gas mixture was employed. Overall, the findings demonstrate the potential of oxygen-assisted compressed-air plasma cutting to improve cutting efficiency and surface quality while reducing thermal effects, providing practical guidance for the optimisation of plasma-assisted manufacturing processes.