Study of Process Parameters in Plasma ARC Machining Process

Abstract

Plasma arc cutting (PAC) is a widely used industrial process for the cutting of different types of metals in several operating conditions. PAC is considered a challenging technology compared to its main competitors: oxy-fuel and laser cutting, in particular for cutting of mild steel in the thickness range 8-40 mm. PAC of mild steel thin plates through a Cebora HQC Plasma Prof 164 plasma source, operating in the range 25-120 A, with a Cebora CP250G plasma torch have been studied. PAC of mild steel thin plates (thickness in the range 1-3 mm) are characterized by low current levels (25-45 A) and the use of O2 both as plasma gas and secondary gas. The aim of the work is the optimization of PAC of mild steel thin plates, both in terms of cut quality and performances of the consumables, to achieve cut quality standards and productivity levels usually obtainable through laser cutting processes. The first part of the work points out the main critical aspects of the considered cutting process, concerning both the obtained qualitative standards and the performances of the consumables, in particular of the nozzle, in terms of its service life. In the second part of the work, the optimization the process has been carried out 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 diffusers, and to optimize current profiles, in particular pilot arc current levels; while modeling and numerical simulation have allowed a better understanding of the physical phenomena concerning the critical aspects initially pointed out and to detect successful design solutions. The integration of the results of these two activities has allowed overcoming the critical aspects initially pointed out, improving plasma jet constriction and reducing plasma jet instabilities, leading to a better cut quality and performances of the consumables.