考虑热影响的超声振动珩磨下单空化泡运动过程分析

发布时间：2018-09-01 13:38

【摘要】：超声振动珩磨技术是一种难加工材料的有效处理方法,磨削液在超声作用下会产生空化现象。空化泡的振动过程、溃灭瞬间的高温高压物理环境以及随之产生的微射流和冲击波都会对材料表面产生不可忽略的影响。本论文针对磨削区的单空化泡,结合空化泡动力学相关理论,采用理论建模、数值仿真和试验分析等方式,研究了单空化泡运动过程中各参量的变化情况,并探究了多种因素对单空化泡运动的影响。主要的研究内容和结论如下:1.在前人研究基础上,考虑煤油蒸气的冷凝与蒸发和珩磨加工环境的特点,建立了超声振动珩磨磨削区单空化泡的动力学模型,运用Matlab软件对空化泡运动过程中的气泡半径、泡内温度、泡内压强和煤油蒸气分子数进行了数值模拟,结果表明煤油蒸气的冷凝与蒸发能够有助于解释泡内温度和泡内压强的变化过程。2.通过比较传统超声与超声振动珩磨两种环境、不同初始半径下磨削区空化泡状态参量的变化情况,发现由于珩磨压力的存在,超声振动珩磨下的空化泡运动幅值受到较大抑制,但运动变化频率却加快,泡内压强与温度的最小值较大,同时泡内煤油蒸气分子数较少;随着空化泡初始半径的增大,气泡半径快速膨胀的时刻提前,最大膨胀倍数减小,压缩溃灭时间也相应缩短,泡内压力和温度的最大值变大,泡内煤油蒸气分子数增多。3.研究超声珩磨和外界环境因素对空化泡运动过程的作用,结果表明珩磨压力、煤油液粘性和超声频率有较大影响,而珩磨头的回转和往复速度几乎没有影响。珩磨压力的增大会显著减小空化泡的最大半径,还可能将空化泡直接压溃;煤油粘性系数越大,空化泡膨胀的阻力越大,半径的变化越小;超声波频率越高,超声作用时间越短,空化泡越难以充分生长,半径将变小。4.探讨不同外界声场激励下空化泡的运动状态,与单频激励(正弦信号)相比,发现多频激励下的空化泡会经历更为平缓的生长过程,半径变大;不同的多频激励相位差组合,会随机地改变空化泡的运动过程;三角波的功率较小,输入的声场能量也较少,致使空化泡半径略小,而方波正好与三角波相反。5.采用水听器法测量了超声珩磨磨削区的空化声场,结果表明随着水听器探头与变幅杆距离的不断增大,测得的空化声压值逐渐减小;增大超声波发生器的功率,声压值明显升高。利用铝箔腐蚀法研究了空化效应对材料表面的空蚀作用,铝箔表面会出现许多大小不一的空蚀坑;增大功率,减小铝箔与变幅杆的横向距离,空蚀坑变密集,声压值越大的地方,空化效应越剧烈。
[Abstract]:Ultrasonic vibration honing is an effective method for the treatment of refractory materials. The grinding fluid can produce cavitation under the action of ultrasonic. The vibration process of cavitation bubble, the instantaneous physical environment of high temperature and high pressure, and the resulting micro-jet and shock wave can not be ignored. Based on the theory of cavitation dynamics and theoretical modeling, numerical simulation and experimental analysis, the variation of parameters in the process of single cavitation bubble is studied in this paper. The influence of various factors on the motion of cavitation bubble is also discussed. The main contents and conclusions are as follows: 1. On the basis of previous studies, considering the characteristics of condensing, evaporation and honing environment of kerosene vapor, a dynamic model of single cavitation bubble in ultrasonic vibration honing grinding area is established. The bubble radius in the process of cavitation bubble motion is calculated by using Matlab software. The results show that condensation and evaporation of kerosene vapor can help to explain the change process of temperature and pressure in the bubble. By comparing the variation of cavitation bubble state parameters in different initial radius between traditional ultrasonic honing environment and ultrasonic vibration honing environment, it is found that the amplitude of cavitation bubble motion under ultrasonic vibration honing is greatly restrained due to the existence of honing pressure. However, with the increase of the initial radius of the cavitation bubble, the rapid expansion of the bubble radius is advanced, and the maximum expansion multiple decreases, with the increase of the initial radius of the cavitation bubble, the minimum value of the pressure and temperature in the bubble is larger, and the number of kerosene vapor molecules in the bubble is less. The compression collapse time was also shortened, the maximum pressure and temperature in the bubble increased, and the molecular number of kerosene vapor in the bubble increased by .3. The effects of ultrasonic honing and external environmental factors on cavitation bubble movement are studied. The results show that honing pressure, kerosene viscosity and ultrasonic frequency are greatly affected, while the rotary and reciprocating velocity of honing head have little effect. As the honing pressure increases, the maximum radius of cavitation bubble will be significantly reduced, and the cavitation bubble may be crushed directly. The larger the viscosity coefficient of kerosene, the greater the resistance of cavitation bubble expansion, the smaller the change of radius, and the higher the ultrasonic frequency. The shorter the ultrasonic action time, the more difficult the cavitation bubble is to grow fully, and the radius will become smaller. 4. The moving state of cavitation bubble under different external acoustic field excitation is discussed. Compared with single frequency excitation (sinusoidal signal), it is found that the cavitation bubble under multi-frequency excitation will experience a more smooth growth process and a larger radius, and different combinations of multi-frequency excitation phase difference, The moving process of cavitation bubble will be changed randomly, the power of triangle wave is smaller and the input energy of sound field is less, so the radius of cavitation bubble is slightly smaller, and the square wave is just opposite to triangle wave. The cavitation sound field in the grinding area of ultrasonic honing is measured by hydrophone method. The results show that with the increasing of the distance between the hydrophone probe and the horn, the measured sound pressure decreases gradually, and the power of the ultrasonic generator increases. The sound pressure increased obviously. The cavitation effect of the cavitation effect on the surface of the material is studied by using the aluminum foil corrosion method. Many cavitation pits of different sizes will appear on the surface of the aluminum foil, increasing the power, reducing the transverse distance between the aluminum foil and the amplitude lever, and the cavitation pit becoming denser. The greater the sound pressure, the more intense the cavitation effect is.
【学位授予单位】：中北大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG663;TG580.67

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