Deep hole drilling of AISI 1045 via high-speed steel twist drills: evaluation of tool wear and hole quality

Review of the available literature has revealed that limited data has been reported on tool wear pattern of twist drills and hole quality for the case of deep hole drilling of AISI 1045. Considering that AISI 1045 has widespread applications as mould material, this paper presents the findings of an experimental investigation on the performance of high-speed steel twist drills of 10-mm diameter for drilling deep holes with L/D >10 in AISI 1045. It is found that the combination of the lowest spindle speed (200 rpm), feed rate (10 mm/min) and peck depth (3 mm) results in better tool life producing 32 holes. Maintaining the lowest spindle speed and feed rate and an increase in peck depth from 3 to 5 mm deteriorated tool life by ~18% due to restricted cooling during the cut. All variable factors were found to be significant with feed rate showing the highest percentage contribution (PCR) of ~50%. Evaluation of the cutting tool indicated fracture at the chisel edge and built-up edge (BUE) formation in all trials. As for the hole quality, it is seen that test performed at 5-mm peck depth outperforms the test conducted at 3 mm producing better surface finish and less errors associated with diameter, roundness and cylindricity. This can be attributed to lesser numbers of times the tool re-engages with workpiece for the case of higher peck depth to reach desired depth thus translating into better stability and reduced errors. A strain hardened layer extending up to the depth of 300 μm was observed irrespective of peck depth and number of holes drilled. Approximately, 30% higher hardness on average was observed in close vicinity of the machined surface (within 30 μm).