SURFACE ROUGHNESS AND ROUNDNESS ERROR PREDICTION MODELS IN TURNING LOW CARBON STEEL

Abstract

Cutting tests were conducted to longitudinally turn low carbon steel using HSS tools with cutting fluid. The experimental design used was based on response surface methodology (RSM) using a central composite rotatable (CCD) design. The primary cutting tests confirmed the use of proper specimen design with length to diameter ratio (L/D) of 2 in the subsequent cutting tests of this research. Further cutting tests were carried out to turn low carbon steel with L/D=2 to determine the effect of using different cutting conditions on the surface roughness and roundness error (out of roundness) of the machined surfaces. At the end of each cutting test, the surface roughness and roundness error measurements were taken and analyzed using “DESIGN EXPERT 8” experimental design software. Mathematical models of responses (surface roughness and roundness error) as functions of the conditions (cutting speed, feed, and depth of cut) were obtained and studied. A quadratic predicted model for surface roughness showed that the feed, cutting speed and their squares and interactions were more effective than the depth of cut because of its little influence on the surface roughness. Also, the resultant two-factor interaction (2FI) model for roundness error exhibited that cutting speed, feed and the interaction of feed and speed were significant parameters, while the depth of cut had no effect. The predicted models indicated that at higher cutting speed and various feed levels, both responses decreased, resulting in a smooth machined surface with lower roundness error. But, both models exhibited that at lower cutting speed and higher feeds, the surface roughness and roundness error increased, producing a rough machined surface with higher out of roundness error.