Effect of high-speed steel screw drill geometry on cutting performance when machining austenitic stainless steel

Drilling into the solid material is one of the basic technological operations, which creates a cylindrical hole in an appropriate time with required quality. Drilling operation demands a favourable removal of chips from the cutting area because a creation of an undesirable shape of chips can impart a lower quality of the drilled hole corresponding with the generation of excess heat due to the intense contact of the chip with drill. The solution for a proper machining is a suitable modification of the drill geometry i.e., point and clearance angles as presented in current study. The tested drills are made of M35 high-speed steel characterized by a very thin core at the point of the drill. An interesting feature of the drills is the use of cutting speed higher than 30 m min(-1), with the feed of 0.2 mm per revolution. The surface roughness (Ra and Rz lower than 1 mu m and 6 mu m respectively), cylindricity (0.045 mm), roundness (0.025 mm), perpendicularity of the hole axis (0.025 mm), diameters and position of the individual holes were achieved for a drill with point angle 138.32 degrees and clearance angle 6.92 respectively. The increase of the drill point angle by 6 degrees resulted in the decrease in the feed force of more than 150 N. In addition, an increase of the clearance angle by 1 degrees resulted with a decrease in the feed force of 70 N. The results of the experiment showed that with the correct geometry of the tool the effective machining without using internal cooling can be realised.