OPTIMIZATION OF PLASMA ARC CUTTING PROCESS, USING TAGUCHI METHOD

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 KALI-100 Plasma Arc Cutting Machine, operating in the range 25-120 A. PAC of mild steel thin plates (thickness in the range 5-15 mm) are characterized by low current levels (65-135 A) and the use of air 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 by using Taguchi Method and analysis of experimental tests and numerical simulations. Experimental tests have allowed a better design of consumables, in particular nozzle stand-off distance, pressure of air which is delivered by the compressor, and to optimize current profiles and torch travelling speed by using Taguchi Method a the statistical tool for measuring the optimum level of the process. The output parameters are kerf and Heat Affected Zone, both are undesirable so had to be minimize. Taguchi L9 orthogonal array is used having for parameters having three levels. Taguchi Method have allowed a better understanding of the physical phenomena concerning the critical aspects initially pointed out and to detect successful optimum 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.