OPTIMIZATION OF PLASMA ARC CUTTING OF MILD STEEL THIN PLATES

Plasma arc cutting processes (PAC) of mild steel thin plates through a Cebora HQC Plasma Prof 164 plasma source, operating in the range 25-120A, with a Cebora CP250G plasma torch have been studied. Plasma arc cutting of mild steel thin plates (thickness in the range 1-3mm) is characterized by low current levels (25-45A) and the use of O2 both as plasma gas and secondary gas. Intrinsic critical aspects initially pointed out concern both cut quality (unevenness of the cut, inclination of the cut surfaces and dross formation) and performance of the consumables (rapid and severe nozzle wear). The aim of the work is to report on the optimization procedure of PAC of mild steel thin plates, carried out with respect to both cut quality and, to achieve high cut quality standards, high performances of the consumables and productivity levels otherwise obtainable with laser cutting processes through the simultaneous planning and analysis of experimental tests and numerical simulations. Experimental tests have allowed a better design of consumables (in particular nozzle, electrode and gas diffusers) and the optimization of current profiles (in particular current levels during pilot arcing); on the other side, modeling and numerical simulation have allowed a better understanding of the physical phenomena evidenced by experimental results and to suggest successful design solutions. The integration of the results of these two activities has allowed the overcoming of the critical aspects initially pointed out, improving plasma jet constriction and reducing plasma jet instabilities, to obtain better cut quality and better performance of the consumables.