During the micro-drilling process of stainless steel, the wear, fracture, and breakage of the micro-drill easily occur. Micro-drill geometry parameters have significant influence on the drilling performance of the micro-drill. Nowadays, the helical point micro-drill is proposed and its improved drilling performance is validated by some researchers. In this study, to analyze the effect of geometry parameters of the helical point micro-drill on drilling performance, the mathematical models of the helical flank and ground flute are proposed, and the cutting lip shape, rake angle, and uncut chip thickness are calculated using MATLAB software. Then, based on the orthogonal tests, nine kinds of micro-drills with different point angles, web thicknesses, and helix angles are fabricated using a six-axis CNC tool grinder, and micro-drilling experiments on 1Cr18Ni9Ti stainless steel are carried out. The drilling force, the burr height, and the hole wall quality are measured and observed. The results show that the point angle is the main contributing factor for the thrust force and burr height, and the web thickness is the main contributing factor for the micro hole wall quality. The increased point angle offers a larger thrust force, but gives rise to a smaller exit burr. A larger web thickness leads to a larger thrust force and burr height, and results in a poor surface quality. With the helix angle increased, the thrust force and burr height decreases, and the surface quality of micro-hole improves. The geometry parameters with a point angle 70°, a point angle of 40°, and web thickness ratio of 0.2 can used to improve the drilling performance of the helical point micro-drill.
Keywords: drilling performance; geometry parameters; helical point; micro-drill; stainless steel.