| 摘要 |
PURPOSE:To reduce thrust load and cutting torque to perform drilling with small exothermic reaction, vibration, etc. forming a crack extending axially in a material. CONSTITUTION:A through hole is provided along the axis of a billet 1 and sealed at both ends in the air tight condition by welds 2. And this billet 1 is hot extruded by the use of a dies 3. Both surfaces of such crack can slide along each other in the drilling so that the surface pressure of a chisel edge of the drill is substantially reduced. Also, chips are cut to pieces and easily discharged. Thus, thrust load and cutting torque are reduced so that the drilling can be performed with small exothermic reaction, vibration, etc. |
