High surface quality and/or dimensional accuracy of the products produced by machining plays an important role in the part performance. The use of polymer materials is gradually replacing that of metallic materials. Due to their anisotropy and non-homogeneity, their machining behavior differs greatly from that of normal metallic materials. Because the phenomena responsible for material removal while cutting fiber reinforced plastic composite materials and those of typical metals and their alloys differ fundamentally, particular attention must be paid to the choice of the proper tool and machining conditions. The present study examines various turning process parameters, including cutting speed, feed rate, depth of cut, and their significance in determining the surface roughness and material removal rate of glass fiber reinforced polyester (GFRP) tubes. The experimental work is carried out on a CNC lathe. After turning the external diameter of the workpiece according to predetermined turning conditions, average surface roughness (Ra) was measured, and material removal rate (MRR) was calculated. The study utilizes the methodology of Grey Relational Analysis (GRA) and Analysis of Variance (ANOVA) to determine the optimal parametric combination giving the smallest values of Ra and the highest values of MRR.

GRA and ANOVA of gray relational grade revealed that the spindle speed has the greatest impact on both Ra and MRR with a contribution percentage of 47.88%, followed by depth of cut with a contribution percentage of 22.03 %, and lastly feed rate with a contribution percentage of 16.86%.