Incision Effect in Ultrasonic Vibratory Cutting of Wood

Abstract

切削中, 切込量が直線的に増加する二次元勾配切削を用いて, 木材の超音波振動切削における切込促進効果 (工具が被削材に切込み易くなる効果) を検討し, 次の結論を得た。振動切削においては切込促進効果が存在する。この効果は振幅a, 切削速度V_O, 被削材の傾斜角θ (切削方向と被削材原表面のなす角) によって影響される (振動数fは17. 6kHzで一定)。一般に切込促進効果は振幅の増大とともに良くなり, 高切削速度, 小傾斜角において顕著である (Fig. 3)。また切込促進効果と切削速度比αν (=V_o/2πaf) の間には一次的な関係は存在せず, α_νのある変化域で切込効果が最良になる (Fig. 4)。切込促進効果は切削面の性状においても現われる。振動切削における切込みは円滑で, 切削面の粗さは相当減少し, また木口切削における繊維方向の割れも顕著に減少する (Fig. 5, 7)。本実験においては加工精度向上効果が認められた。この効果は切削速度よりもむしろ振幅によって大きく左右される (Fig. 8)。

Using an inclined cutting in which original work surface inclines by a given angle toward the cutting direction and the depth of cut increases linearly during cutting, incision effect (i. e., promotion effect of the penetration of cutting edge into work material) in ultrasonic vibratory cutting of wood was examined. The application of ultrasonic vibration to cutting edge resulted in the appearance of incision effect under every set of conditions. This effect was affected by vibration amplitude, cutting speed and inclination angle between original work surface and the cutting direction. In general, the incision effect increased with increasing amplitude and was conspicuous at a higher cutting speed and a lower inclination angle (Fig. 3). Furthermore, there was a non-linear relation between the incision effect and cutting speed ratio αv (Fig. 4). This relation indicates that the most beneficial incision effect can be obtained under a certain limited range of αv. The incision effect resulted in the improvement of the quality of machined surface; the penetration of cutting edge into wood went on smoothly, and the roughness of machined surface decreased considerably (Figs. 5 and 7). Furthermore, the wood split at right angles to the machined surface and parallel to the grain was much reduced (Fig. 7). On the other hand, in the present study an effect to elevate the machining accuracy was recognized (Fig. 8). This effect was greatly affected by vibration amplitude rather than by cutting speed.