Investigation of lubricant condition and machining parameters while turning of AISI 4340

Abstract

Metal cutting fluids change performance of machining operations because of their lubrication, cooling, and chip flushing functions. But the use of cutting fluid has become more problematic in terms of both employee health and environmental pollution. The minimization of cutting fluid also leads to economical benefits by way of saving lubricant costs and workpiece/tool/machine cleaning cycle time. Hence, the concept of minimum quantity lubrications (MQL) has been proposed a decade ago to solve problems of environmental intrusiveness and occupational hazards associated with the airborne cutting fluid particles on factory shop floors. The present work contains an experimental investigation to study the effect of various lubrication and machining parameters on tool wear and surface roughness in turning of AISI 4340. Firstly, 12 exploratory experiments have been carried out under 3 different machining regimes and 4 strategies of lubrication namely dry (without any lubricant), air cool (with gaseous lubricant), wet (with pure liquid lubricant), and MQL (mixture of air and liquid). The results indicated that in all cases, the MQL strategy ensures lowest surface roughness and tool wear. Hence, it was selected as the main cooling strategy for the next stage of experiments. In the second stage of experiments, 27 experiments have been designed based on L27 orthogonal arrays to investigate the influences of feed rate, spindle speed, depth of cut, cutting angle, and mist inlet pressure on surface roughness and tool wear (R a and V B). Then, analysis of variances (ANOVA) has been performed to study the influence of each factor on R a and V B. In order to correlate the relationship between turning parameters and responses, an adaptive neuro-fuzzy system (ANFIS) has been employed. In order to select the optimal solutions for simultaneous minimization of R a and V B, a Grey relational analysis has been applied. The results indicated that cutting speed and feed rate are the most important factors which have major effect on the tool wear and surface roughness. Also, increasing in mist inlet pressure leads to lower surface roughness and tool wear due to cooling and flushing of damaging chips from cutting zone. Also, feed rate of 0.2 mm/rev, spindle speed of 250 RPM, depth of cut of 0.5 mm, cutting angle of 90°, and mist pressure of 3 bar are the optimal combination of turning factors which cause lowest R a and V B, simultaneously. This result has been experimentally verified to prove the effectiveness of the proposed method.