6 Nonconventional Technologies Review 2017Romanian Association of Nonconventional Technologies Romania, March, 2017 SURFACE ROUGHNESS AT PLASMA CUTTING Laurențiu Slătineanu 1 ,Sanda Bangu 2 , Margareta Coteață 3 , Oana Dodun 4 , Mihai Boca 5 and Irina Beșliu 6 1 “Gheorghe Asachi” Technical University of Iaşi, Romania, slati@tcm.tuiasi.ro 2 “Gheorghe Asachi” Technical University of Iaşi, Romania, sandasist@yahoo.com 3 “Gheorghe Asachi” Technical University of Iaşi, Romania, mcoteata@tcm.tuiasi.ro 4 “Gheorghe Asachi” Technical University of Iaşi, Romania, oanad@tcm.tuiasi.ro 5 “Gheorghe Asachi” Technical University of Iaşi, Romania, mihaitzaboca@yahoo.com 6 “Ștefan cel Mare” University of Suceava, Romania,irina.besliu@yahoo.com ABSTRACT: Distinct cutting methods could be applied to separate parts from a plate workpiece. Nowadays, among such methods, the thermal plasma allows obtaining a relatively narrow slot, a high cutting speed and a cut surface appreciated as acceptable in certain situations. Essentially, the thermal plasma is generated by sending a gas through the electric discharge developed between the central electrode and the nozzle, as components of the plasma generator. The analysis of plasma cutting process showed that there are some groups of actors able to affect the heights of asperities generated by the cutting process on the cut surface. A full factorial experiment with three independent variables at two levels was designed and achieved by considering some of process input factors whose values could be easier modified, to investigate their influence on the value of the Ra surface roughness parameter. By processing the experimental results, a power type function was determined. The analysis of this empirical mathematical model and of the elaborated graphical representations highlighted the influence exerted by the cutting speed, plate workpiece thickness and current intensity on the Ra surface roughness parameter. KEYWORDS: plasma cutting, surface roughness, influence factors, experimental research, empirical mathematical model, cutting speed, workpiece thickness, current intensity 1. INTRODUCTION Plasma could be considered as a forth state of matter, together with the solid state, liquid state and gas state. In a certain extent,the physical properties of plasma are similar to those of gas state, but there are also distinct properties and this fact determined the physicists to consider plasma as a different state in comparison with the gas state. Essentially, the plasma could be obtained by increasing the gas temperature, by generating electrical discharges in gases and by irradiation. Within the field of machining processes, the plasma is obtained by electrical discharges. As a processing tool, the plasma could be applied in order to materialize processes characterized by material removal from workpiece (plasma beam cutting, drilling etc.), by material addition to the workpiece and without mass changing of the workpiece (for example, heat treatments by means of plasma).The plasma beam cutting is used in order to separate parts from plate type workpieces [7, 9, 10]. In comparison with other cutting processes applicable in similar situations (for example, laser beam cutting, oxygen flame cutting, abrasive water jet cutting etc.), the plasma beam cutting ensures a relatively narrow kerf, a higher cutting speed, a lower surface roughness of the obtained surfaces. A possible disadvantage is generated by the thickness of heat affected zone, generally higher in the case of plasma cutting, compared with other cutting methods. Bhuvenesh et al. investigated the roughness of surfaces obtained by manual plasma arc cutting[3]. They noticed an inverse proportional relation between the values of the Ra surface roughness parameter and the values corresponding to the material removal rate. They highlighted also that the dimensions of the dross offers a certain information concerning the roughness of the surfaces resulted by applying manual plasma arc cutting. The results of an experimental research concerning the quality of surfaces obtained by plasma cutting were published by Begic et al. [2]. They took into consideration the influence exerted by the cutting speed and plasma gas pressure on the Ra surface roughness parameter in the case of test pieces made of low alloy steel. One of the study conclusions highlights that the values of the Ra surface roughness parameters diminish when the plasma gas pressure increases and only a low variation of the Ra surface roughness parameter is generated when the cutting speed has higher values. Akkurt compared the results obtained by applying distinct cutting methods in the case of test pieces made of AISI 304 stainless steel [1]. He especially revealed that compared with the abrasive water jet cutting, the plasma cutting methods determine continuous changes in hardness values and the heat