Solution of dynamic cutting mechanism of ultrasonic viration assisted micro drilling

本研究的目的是明确超声振动对微细钻削法向面和斜面孔入口处钻削行为的影响，以及法向深孔钻削时对切屑放电特性的影响。钻探行为是根据使用快速止动装置保存的钻孔的形状来推断的。在深孔加工中，观察了切屑的处理情况，考虑了切屑的形成机理，在微细钻削到法向平面时，超声振动阻止了入口处的钻头漂移运动，这是由于增大了凿边的有效前倾角而引起的径向力的减小，以及凿边的锤击运动，以及防止了微小的间歇切割引起的钻头位移的累积。从而提高了入口孔形状和大小的精度。振动时钻槽中切屑所占的面积比不振动时小。随着振动的增加，切屑流动角变大，侧旋曲率变小。这些特征可能是由于刀刃角侧和中心侧的切割速度差减小，以及振动改善了锯齿刃的切削性能而引起的径向切屑速度的增加所致。在振动辅助深孔加工中，切屑的平稳处理防止了因卡屑而造成的钻头破损，无需分步进给，提高了切割效率。减少了切屑摩擦引起的孔壁完整性劣化。在斜面钻削中，由于钻头中心位置的改善，振动时的不圆度比无振动时小，尽管径向力一直作用到全切削刃开始啮合。

The purpose of the present research is to make clear the effect of ultrasonic vibration on drill behavior at the hole entrance in micro drilling to the normal plane and the inclined plane, and the effect on chip discharge characteristics in deep drilling of normal plane. Drill behavior is deduced from the shape of the drilled hole preserved using a quick stop device. In deep drilling the chip disposal condition is observed and chip formation mechanism is considered.In micro drilling to the normal plane the ultrasonic vibration prevents the drill wandering motion at the entrance, which results from the decrease of radial force due to the increase of effective rake angle on chisel edge, the hammering motion of chisel edge and the prevention of accumulation of drill displacement due to infinitesimal intermittent cutting. As a result, the accuracies of hole shape and size at the entrance are improved. The area occupied by chip in drill flute becomes smaller with vibration than that without vibration. Chip fiow angle becomes larger and curvature of side curl becomes smaller with vibration. These features may be caused by the decrease of difference between cutting velocities at corner side and center side of a cutting edge and by the increase of radial chip fiow velocity due to the improvement of cutting performance at chisel edge with vibration. In vibration-assisted deep drilling smooth disposal of chip prevents drill breakage due to chip jamming, needs no step feed and improves cutting efficiency. The deterioration of hole wall integrity caused by the rubbing of chip is reduced.ln drilling to the inclined plane the out-of-roundness becomes smaller with vibration than without vibration due to the improvement of drill centering although radial force is acting until the start of engagement of full cutting edges.