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Machining with pressurized coolant is nowadays widely accepted technique in the manufacturing industry, especially in high performance machining conditions. The data on the effects of variation of high coolant pressure in drilling operation is limited. This paper presents the effect of high coolant pressures along with spindle speed, feed rate and peck depth on hole diameter accuracy. Experiments were performed on EN9 steel with TiAIN coated through coolant drill on CNC vertical machining center. Taguchi technique was employed for design of experiments and analysis of results. Results showed that the higher values of optimal coolant pressure and spindle speed were demanded for drilling at bottom of hole as compared to that for drilling at top of hole. The optimal values of feed rate and peck depth were same for both the cases of drilling at top and bottom of hole. Use of high coolant pressure in drilling permits higher peck depth for better hole diameter control which results in reduced cycle time and hence production cost.

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Purpose This paper aims to examine an investigation of high-pressure coolant (HPC) drilling process with regard to experimental models of output parameters, effect of input parameters on output parameters and simultaneous optimization of the output parameters. Design/methodology/approach Experimental plan was designed using response surface method and experiments were conducted on HPC drilling set up. Measurements for output parameters were carried out and mathematical models were obtained. Multi response optimization using a composite desirability function approach was used to obtain optimum values of input parameters for simultaneous optimization of output parameters. Findings Optimal value of input parameters for optimization of HPC drilling process were obtained as; coolant pressure: 21 bar, spindle speed: 3,970 rpm, feed rate: 0.084 mm/rev and peck depth: 5.50 mm. The composite desirability obtained is 0.9412, which indicates that the performance of HPC drilling process was significantly optimized. Developed mathematical models of the output parameters accurately represent the entire design space under investigation. Originality/value This is the first study that involves variation of higher coolant pressure and investigation of HPC drilling process using response surface methodology and multi response optimization technique with desirability function.