THE EFFECTS OF MILLING PARAMETERS ON SURFACE ROUGHNESS OF STAINLESS STEEL X22 CR MO V 12 1

ABSTRACT Stainless Steels have several uses in different industries and include an extensive area of steels, and because of many differences between mechanical and physical properties of different kinds of stainless steels, it is still necessary to study this type of steels. The surface roughness has been regarded by many researchers since many years ago, because of its high importance in the efficiency of final product, and also because it is considered as a main parameter in examining machinability of metals. In this paper, the experimental reports about optimizing roughness of final surface in milling stainless steel X22 Cr MoV 12 1, has been carried out using multiple regression technique and ANN(Artificial Neural network). The second order mathematical model has been attained from input parameters of process including cutting speed; Feed rate, radial and axial depths of cut. Each of these inputs of the research has been studied in 3 levels and for this purpose totally 81 experiments have been performed. After measuring the surface roughness caused by milling, the obtained model has been used for scrutinizing the effects of different parameters, and also for predicting the optimal milling parameters in order to obtain ideal surface Roughness. KEYWORDS: Stainless Steel, Milling Parameters, Multiple Regression, Artificial Neural Network, Surface Roughness. The reason for choosing stainless steels in industry is usually their high strength and resistance against impact, and also unique capability of these steels in resistance against corrosion and heat. Machinability of different kinds of stainless steels varies diversely in different usages of them and this fact is a ground for machining these steels. Since physical and mechanical properties of each type of these steels differ with those of each other, so their machinability are different too Martensiticstainless steel X22 CrMoV 12 1 is a Ferromagnetic steel and belongs to the group of stainless steels resistant against heat and creep which is used in pressure pipes, boilers, airspaceequipment, manufacturing reactors, components of turbines, and also in screws and nuts which work in high temperatures. Because of high toughness, low heat transfer, and high degree of work hardening, stainless steels are known as hardlymachinable materials • Stainless steels have higher tensile strength and higher median between yield strength and failure strength, comparing with low and medium carbon steels. Hence the needed energy for machining stainless steels is more than that for cutting ordinary steels. • Austenitic stainless steels have high work hardening rate and low heat transfer. High hardening work rate results in increment of consumed energy in comparison with carbonic non-hardened steels, and also low heat transfer of these steels causes increasing the heat slope of chips, and increasing produced heat in the region of secondary transformation leads toincrement of temperature in common interface of chip and tools which consequently raises the rate of wear (wear is considerably function of temperature). • Some groups of high carbon stainless steels which contain remarkable amount of free particles of carbide are hardly machining, since because of existence these particles, the ground hardness increases and also results in rigorous wear of the cutting tool. Surface roughness of stainless steels 304 and 316 using two carbide tools coatedby Titanium Nitride and Aluminum Oxide has been studied (Ciftici, 2006). His report showed that in both cases by increasing cutting speed the surface roughness and machining force reach to a minimum measure and then by more increment of this speed they increase. The cause of decrement of surface roughness is that the built-up edge did not form, and the cause of decreasing the force is decrement of contact area and shear strain in the Flowing area as a result of raising temperature. Increasing in both roughness and force are caused by tool wearing. (Razfar,Zinati,2011) have studied the optimization of surface roughness resulted from process of turning and milling (facemilling) Martensitic stainless steel 420 (X20Cr13). Through performing 81 examinations, which were implemented for three levels of four input parameters __ insert edgeradius, cutting speed, Feed rate and cutting depth__, (Suresh et al) have predicted an