Abstract: Non-coaxial helical flank micro-drill has a significant advantage in the tool grinding efficiency and drilling performance compared with the plane flank drill. A slight change in the geometry structure of micro-drill causes a significant change in drilling performance. The mathematical models of non-coaxial helical flank and helical groove are proposed, and the cutting lip shape, rake angle and uncut chip thickness are calculated. The micro-drilling finite element simulation models of stainless steel are established to optimize the geometric structure of non-coaxial helical flank micro-drill, and the effects of helix angle, web thickness and point angle on drilling force, temperature and chip morphology are investigated. The results show that the thrust force increases with the increase in point angle within a certain range of geometric parameters. On the contrary, the torque and temperature decrease with the increase in point angle. The drilling force and temperature decrease with the increase in helix angle. The geometry of chip is continuous chip when the helix angle arrives to 40°, which is easily blocked lead to tool breaking. With the increase in web thickness, the drilling force and temperature increase simultaneously, but the width of chip reduces. The optimized micro-drilling geometric parameters are obtained based on the variation of drilling force, drilling temperature, and chip morphology during the micro-drilling of stainless steel. The non-coaxial helical flank micro-drill is fabricated based on six-axis CNC tool grinder and the mathematical model. The measured results show that the geometrical parameters are basically the same as the designed values. And the experimental results show that the micro-drill with the optimized geometric structure has good drilling performance.Key

Key words: non-coaxialhelicalflankmicro-drill, geometry, drilling, cuttergrinding, stainlesssteel