Response Surface Optimisation of Material Removal Rate during Wet Lathe Drilling of ASTM A36 Mild Steel Using Central Composite Design

Abstract

Optimization of the material removal rate (MRR) in wet lathe drilling can improve machining efficiency, while keeping the process parameters under controlled conditions for structural steel applications. Previous studies have explored machinability of ASTM A36 using Taguchi analysis, ANOVA analysis, process-capability analysis, and numerical optimization; however, limited attention has been given to the linear, interaction and quadratic influence of spindle speed, feed rate, and drilling length on MRR under continuous wet lathe drilling conditions with experimental verification. A quadratic model for the MRR was developed and validated and the significant factor effects were established; the optimum conditions for MRR maximization within the design space were determined.; the predictions obtained from the model were verified by experimental trials. For process optimization, 27 experiments were conducted in a randomised central composite design, involving a face-centred arrangement with two replicates for each experimental condition, with rotation included as the fifth factor within defined ranges: spindle speed from 255 to 385 rev/min, feed from 0.177 to 0.303 mm/rev and length of drilling from 44.9 to 60.1 mm. Based on the ANOVA results and prediction error, we developed regression models, using response surface Methodology and Bounded Numerical Optimization method. Fifteen additional runs were subsequently performed independently. The quadratic model was significant. F (9, 17) = 51.95 p < 0.0001 R² = 0.9649 Adjusted R² = 0.9463 and predicted R² = 0.8246. Spindle speed, drill length, each of the two- factor interactions and the quadratic terms of spindle speed and drilling length were also significant. The numerical optimum occurred at 385 rpm, 0.177 mm /rev, and 56. 040 mm and predicted an MRR of 119.076 mm/s. At the independent verification point, the observed mean was 114.489 ±1.098 mm /s compared with the predicted value of 114. 551 mm /s with a mean percentage prediction error of 0.055 %. The validated response surface provides a practical basis for selecting productive wet lathe-drilling conditions for ASTM A36 mild steel within the investigated factor ranges.