Assessment of Chip Shape and Hole Quality in Drilling of AISI 304 Stainless Steel Under Flood and HPC Conditions

Stainless steels are widely used in industry due to their favorable functional properties; however, their machining poses a significant technological challenge. This study analyzed chip shape, chip thickness ratio (Kh), hole dimensional accuracy, and surface topography of AISI 304 stainless steel during drilling as a function of cooling conditions and cutting parameters. Two values of cutting speed and feed rate were applied based on a 22 Full Factorial Design (FFD). The experiments were conducted under flood and high-pressure cooling (HPC) conditions. The results showed that at a high feed rate, both flood cooling and the HPC method resulted in short arc-shaped and conical helical chips. Compared with flood cooling, the HPC method reduced Kh by approximately 60% for a specific combination of cutting parameters. Analysis of chip morphology revealed qualitative differences in the occurrence of plastic deformation bands on the chip surfaces under HPC conditions compared with flood cooling. Compared with the HPC method, flood cooling resulted in a 0.09 mm larger hole diameter under lower cutting conditions, whereas under higher cutting conditions, the HPC method resulted in a 0.08 mm larger hole diameter. The application of the HPC method reduced the Ra and Rz surface roughness parameters by approximately 45% for f = 0.12 mm/rev and v = 40 m/min and by approximately 60% for f = 0.06 mm/rev and v = 80 m/min. Moreover, the HPC method provided a more regular surface texture, whereas furrows and hills were observed on the machined surfaces under flood cooling, depending on the cutting parameters. Overall, the application of HPC led to differences in chip morphology and hole quality compared with flood cooling, with the observed effects varying depending on the applied combination of feed rate and cutting speed.