Determination of the Optimum Cutting Parameters on Surface Roughness in Turning AISI 4340 Steel

Abstract

This study investigates the effects of fundamental machining parameters including insert types on the surface roughness (Ra) obtained during finish turning of AISI 4340 steel. External turning experiments were conducted on a Spinner TC65 CNC turning centre using a Taguchi L9 orthogonal array. Three different inserts like uncoated carbide, coated carbide, and CBN, respectively, were used to find out optimal conditions. Analysis of variance was carried out and the multiple linear regression equation was established. The results indicated that measured Ra values ranged from 0.361 to 2.411 μm. Feed rate was the dominant factor affecting on Ra, followed by cutting speed/insert type, and depth of cut. The optimal conditions based on the S/N response were determined as a cutting speed of 230 m/min, a feed rate of 0.08 mm/rev, a depth of cut of 1.2 mm, and the CBN insert. The regression model explained the Ra response with R-sq = 98.05%, R-sq(adj) = 96.10%, and R-sq (pred) = 90.09%. Moreover, ANOVA results revealed that feed rate was statistically significant (p < 0.001) by indicating the highest contribution to the variation of Ra values. Cutting speed was also statistically significant (p = 0.029), while the insert type and depth of cut were not statistically significant at the 0.05 level.