Development of a New Ultra-precision Finishing Process Applying the Cavitation Phenomena in Ultrasonic Vibration

本研究提出了一种利用超声振动引起的空化控制磨料在蒸馏水中运动的超精密精加工新工艺。磨料在超声振动的基础上积聚在工件表面，并通过空化作用表现出微观振动。这必须从工件表面去除材料。为实现上述原理，研制了由超声振荡器、电致伸缩振动器（频率18khz，输出400w）、振动放大喇叭和工具组成的实验装置。将SUS3O4不锈钢制成的工具安装在喇叭的尖端。工件被放置在一个容器中，蒸馏水和磨料在喇叭下。超声波振动垂直传递到工件的目标表面。利用所开发的机构对其加工特性进行了实验研究。采用C3604黄铜板（□20×5 mm）作为工件。喇叭尖端与工件目标表面的间隙在0.5-2.0 mm之间变化。实验结果表明：(1)在蒸馏水中加入磨料有助于工件表面的光滑，但同时也阻止了水中的空化现象。这导致了加工效率的降低。(2)刀尖与工件目标表面的间隙越小，由于空化增强产生的加工力越大，加工深度越深。(3)当间隙较小时，由于空化的集中，加工的几何形状更接近刀具的几何形状。这使得在刀具中心的加工更有效，在加工区域的中心产生比边缘更粗糙的表面。(4)该工艺不仅适用于微加工，也适用于微边缘精加工。

This research proposes a new ultra-precision finishing process in which the motion of the abrasive is controlled by cavitation caused by ultrasonic vibration in distilled water mixed with abrasive. The abrasive accumulates onto the surface of the workpiece and shows microscopic vibration by cavitation based on the ultrasonic vibration. This must remove the material from the surface the workpiece. To realize the above-mentioned principle, an experimental setup, which consists of an ultrasonic oscillator, electrostrictive vibrator (l8kHz frequency, 400 W output), vibration amplifying horn, and tool, was developed. The tool made of SUS3O4 stainless steel was mounted onto the tip of the horn. The workpiece was set into a container with distilled water and the abrasive under the horn. The ultrasonic vibration was imparted vertically to the target surface of the workpiece. The machining characteristics were experimentally investigated using the developed setup. A C3604 brass plate (□20×5 mm) was used as a workpiece. The clearance between the horn tip and the target surface of the workpiece was varied from 0.5-2.0 mm. Machining characteristics identified from the experimental results were summarized as follows : (1) Although abrasive mixed into the distilled water helped to smooth the surface of workpiece, it prevented cavitation in the water. This resulted in a decrease of the machining efficiency. (2) The smaller the clearance between the tool tip and the target surface of the workpiece, the deeper was the machined depth because of the higher machining force by the enhanced cavitation. (3) Because of the concentration of the cavitation when the clearance was smaller, the machined geometry more closely followed the tool's geometry. This caused more effective machining at the center of the tool, generating a rougher surface at the center of the machining area than at the edge. (4) This process is applicable not only for micro-machining but also micro-edge finishing.