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

本研究提出了一种新的超精密光整加工工艺，通过超声振动在混合磨料的蒸馏水中产生空化来控制磨料的运动。磨料堆积在工件表面，在超声振动的基础上，通过空化表现出微观振动。这必须从工件表面去除材料.为了实现上述原理，研制了一套由超声振荡器、电致伸缩振子(频率18 kHz，输出功率400W)、放振喇叭和工具组成的实验装置。该工具由SUS3O4不锈钢制成，安装在喇叭的尖端。工件被放入一个容器中，容器中装有蒸馏水和喇叭下的磨料。超声振动垂直于工件的目标表面。利用所研制的加工装置对其加工特性进行了实验研究。采用C3604黄铜板(-20×5 mm)作为试件。角尖与靶面之间的间隙在0.5~2.0 mm之间变化。实验结果表明：(1)虽然在蒸馏水中掺入磨料有助于使工件表面光滑，但它防止了水中的气蚀。这导致了加工效率的降低。(2)刀尖与工件靶面的间隙越小，由于气蚀增强所产生的加工力越大，加工深度越深。(3)当间隙较小时，由于气蚀的集中，加工的几何形状更接近刀具的几何形状。这导致在刀具中心进行更有效的加工，在加工区域的中心处生成比在边缘处更粗糙的表面。(4)该工艺不仅适用于微细加工，也适用于微细刃磨削。

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.