Journal of Engineering Science and Technology Review 8 (3) (2015) 143-150 Research Article Fuzzy Logic Approach for the Prediction of Dross Formation in CO 2 Laser Cutting of Mild Steel Miloš Madić 1 , Miroslav Radovanović 1 , Žarko Ćojbašić 1 , Bogdan Nedić 2 and Marin Gostimirović 3 1 Faculty of Mechanical Engineering in Niš, University of Niš, A. Medvedeva, 18000 Niš, Serbia 2 University of Kragujevac, Faculty of Engineering, Serbia 3 University of Novi Sad, Faculty of Technical Sciences, Serbia Received 9 October 2015; Accepted 2 November 2015 ___________________________________________________________________________________________ Abstract Dross free laser cutting is very important in the application of laser cutting technology. This paper focuses on the development of a fuzzy logic model to predict dross formation in CO2 laser oxygen cutting of mild steel. Laser cutting experiment, conducted according to Taguchi’s experimental design using L25 orthogonal array, provided a set of data for the development of a fuzzy rule base. The predicting fuzzy logic model is based on using Mamdani-type inference system. Developed fuzzy logic model considered the cutting speed, laser power and assist gas pressure as inputs. Using this model the effects of the selected laser cutting parameters on the dross formation were investigated. Additionally, 3-D surface plots were generated to study the interaction effects of the laser cutting parameters. The analysis revealed that the cutting speed has the most significant effect, followed by laser power and assist gas pressure. The results indicated that the fuzzy logic modeling approach can be effectively used for the dross formation prediction in CO2 laser cutting of mild steel. Keywords: CO2 laser cutting, dross, fuzzy logic, mild steel __________________________________________________________________________________________ 1 Introduction Among various advanced machining processes, laser cutting is one of the most widely used thermal-based processes applied for contour cutting of a wide variety of materials. Numerous advantages such as convenience of operation, high precision, small heat-affected zone, minimum deformity, low waste, low level of noise, flexibility, ease of automation etc., along with technological improvements in laser cutting machines, made laser cutting technology more prevalent in today’s production systems. By focusing the laser beam on the workpiece surface, the high power density of the focused laser beam in the spot melts or evaporates material in a fraction of a second, while coaxial jet of an assist gas removes the evaporated and molten material from the cutting zone [1]. An important function of the assist gas is to protect lenses in the cutting head from the fumes formed during the laser cutting process. In laser cutting of metals two types of assist gasses are mainly used, oxygen and nitrogen. For carbon steels, oxygen is commonly used, whereby exothermic reaction provides additional energy which is used in the cutting process. In the case of stainless steel cutting, in order to achieve high cut quality nitrogen is commonly used. This is because some of the oxides such as CrO, which are normally formed when cutting with oxygen, have high viscosity and are difficult to eject from the cutting zone. In both the cases, the assist gas impinges on a section processed and drags away the molten metal in the cutting zone. Depending upon the laser cutting parameters, the molten layer thickness varies. Moreover, a jet of dross, consisting of small metal droplets is formed at the onset of melting leaving the cutting kerf [2]. The size of the droplets depends on the liquid metal Reynolds number, as well as the liquid and gas Weber numbers [3]. Laser cutting is a complex process characterized by a number of input parameters which determine efficiency of the entire process in terms of material removal rate, cut quality and cost. Majority of experimental studies dealt with the analysis of the effects of process parameters on kerf width, surface roughness and size of heat affected zone [4]. The reduced laser cut quality in the cutting of thinner steel sheets is attributed mainly to dross formation at the lower cutting edge [5]. Dross formation is one of the typical imperfections generated at the lower cut edges. If the applied laser energy, cutting speed, focus position and assist gas pressure are not controlled properly, incomplete melting occurs or traces of molten metal re-solidify over the cut sides forming undesired dross [6]. The mechanism behind the dross formation is very complex. The process is a consequence of the agglomeration of molten material which flows along the lower cut edge [7]. The dross formation depends on the liquid properties of the molten material, such as viscosity, density and surface tension, as well as laser and cutting properties, such as assisting gas velocity, kerf size and liquid layer thickness [2]. Jestr JOURNAL OF Engineering Science and Technology Review www.jestr.org ______________ * E-mail address: madic@masfak.ni.ac.rs ISSN: 1791-2377 © 2015 Kavala Institute of Technology. All rights reserved.