Effects of geometric structure of twist drill bits and cutting condition on tool life in drilling 42CrMo ultrahigh-strength steel

To investigate the influence of the geometric structure of coated cemented carbide twist drills on the drill tool life, drilling experiments of 42CrMo steel were carried out at various cutting parameters. The geometric structure parameters of the specially manufactured drill bits were designed by the multifactor orthogonal experiment method. The effects of cutting edge preparation, drill point geometry, and flute geometry on the tool wear were investigated by the range analysis and variance analysis. And their effects on chip pattern were also studied. Then the influence of cutting parameters on the tool life was investigated. Based on these investigations and extending the tool life, the optimized geometric structure was the honed cutting edge with a radius of 0.06 mm and conventional conical flank, and the corresponding cutting parameters were 80 m/min and 0.18 mm/rev. At last, the tool wear characteristics were discussed and the main wear mechanisms were abrasive wear, adhesive wear, coating exfoliation, and tipping.