Influence of chisel edge axial rake angle on the drilling performance of helical point micro-drill

The chisel-edge axial rake angle has an important effect on the processing performance of helical point micro-drills. In this research, the mathematical modeling for the spiral groove, helical flank, and cross-shaped chisel edge are conducted, and then three types of helical point micro-drills, each having a thinned chisel edge with an unequal axial rake angle, are designed and fabricated. Then, the finite element simulations and processing experiments of micro-drilling are performed separately, and the thrust force, torque, chip morphology, tool wear, and micro-hole machining quality are measured and evaluated. With the rise of the axial rake angle of the chisel edge, the curling degree of the chips and the thrust force were found to decrease owing to the increase of the rake angle along the inner cutting edge. The angle between the tool axis and chip axis was found to gradually decrease due to the reduction of the rake angle gradient along the cutting edge. Additionally, the thickness and width of the uncut chip of the inner cutting edge were found to increase, bringing about the rise in the torque. The wear degree of the micro-drills with a 0° axial rake angle (Type II) was the smallest due to their medium thrust force and torque, and a better micro-hole entrance morphology and minimum roundness were obtained. When drilling to the 30th hole, compared with the micro-drills with a − 10° axial rake angle (Type I) and 10° axial rake angle (Type III), the chisel edge maximum wear width of Type II (δ = 0°) was respectively reduced by 82.43% and 19.69%, and the micro-hole roundness respectively decreased by 26.7% and 11.33%. The thrust force of Type I (δ = − 10°) was the largest, so it caused greater tool wear and poorer micro-hole quality. The larger torque and lower rigidity of the inner cutting edge of Type III (δ = 10°) led to poorer drilling performance. Thus, helical point micro-drills having the 0° chisel edge axial rake angle are suitable for drilling 304 austenitic stainless steel.