Grinding process of helical micro-drill using a six-axis CNC grinding machine and its fundamental drilling performance

Helical drill point is characterized by a continuous helical flank surface and an S-shape chisel edge, and its special geometry contributes to a superior drilling performance and a better grinding efficiency. However, the existing grinding processes are complicated and hard to be reproduced in practice, and it is difficult to meet the accuracy requirements as the drill diameter becomes smaller. Thus, it is crucial to research further grinding method of helical micro-drill and its drilling performance. In this paper, a grinding method of helical drill flank using a six-axis CNC grinding machine is proposed based on the mathematical model of generatrix of the helical surface. Then, this grinding process is simulated using the 3D CAD software and is validated by experimentally fabricating the helical micro-drill. The results show that this method is feasible for obtaining the micro-drill with high dimensional accuracy. For the comparison with helical micro-drill, the planar and conical micro-drills with the same geometry parameters are produced as well. The drilling experiments on 1Cr18Ni9Ti austenitic stainless steel with the planar, conical, and helical micro-drills are conducted, and the drilling force, tool wear, and hole quality are measured and analyzed. The experiment results show that the increasing rate of the radial force of helical micro-drills at the beginning of the drilling process is smaller than those of planar and conical micro-drills, the thrust force and wear of helical drill point are also smaller, and the quality of micro-holes by helical drill point is better as well. It is confirmed that the proposed grinding process is effective to fabricate the helical micro-drill with good drilling performance.