压电式微滴按需喷射的过程控制和规律

微滴喷射增材制造技术中沉积微滴的大小与均匀性是影响成型件质量的关键因素.本文设计了一种用于生成均匀微滴的压电驱动式微滴喷射装置,通过压电材料带动柔性膜片振动,将液体从喷嘴中喷出生成微滴,采用数值模拟和实验相结合的方法,研究了不同控制参数下膜片振幅及其对生成微滴尺寸和均匀性的影响.研究结果表明:膜片振幅大小受到驱动电压和压电频率的共同影响,压电频率是导致膜片中心点振幅实验测量值小于理论计算值的主要原因,膜片振动会导致喷嘴内部压力发生变化从而影响微滴生成尺寸.在相同驱动电压条件下,压电频率为10 Hz时存在压电膜片振幅最大值.随着膜片振幅的增大,喷孔处液体速度和液柱长度增大到临界值时可以生成微滴,当喷孔处的液柱长度超过临界值时,会形成卫星液滴. 当膜片振幅区间在30 $\mu$m$\sim $42 $\mu $m可以稳定生成微滴,生成最小微滴尺寸为339.8$\mu$m,直径最大变化率为0.29%,相邻两微滴间距最大变化率为2.67%,生成微滴的尺寸及均匀性较好.研究结果有助于提高压电式微滴喷射装置的液滴生成质量. 

STUDY OF PROCESS CONTROL ON PIEZOELECTRIC DROP-ON-DEMAND EJECTION 1)

The size and uniformity of micro-droplets are key factors influencing the quality of the molded part by micro-droplet ejecting additive manufacturing technology. In this paper, a piezo-actuated micro-droplet ejection device for generating uniform micro-droplets is studied. The piezoelectric material drives the flexible diaphragm to vibrate and pushes the liquid out of the nozzle and produces micro-droplets. The amplitude of the diaphragm under different control parameters and its influence on the size and uniformity of the generated micro-droplets are investigated by numerical simulation and experiment. The results indicate that the amplitude of the diaphragm is affected by the driving voltage and the piezoelectric frequency and the experimental value of the diaphragm's center point amplitude is less than that of the theoretical calculation value which is mainly influenced by the piezoelectric frequency. The amplitude of the diaphragm will change the pressure inside the nozzle, which leads to the varied sizes of the micro-droplet. When the driving voltage is constant, the diaphragm has the maximum amplitude for the piezoelectric frequency at 10 Hz. As the amplitude of the diaphragm increases, droplets can be generated when the liquid velocity at the orifice and the length of the liquid column increase to a critical value. As the amplitude of the diaphragm continues to increase and the length of the liquid column at the orifice is beyond to a critical value, a satellite micro-droplet is formed. When the amplitude range of the membrane is between 30 $\mu $m and 42 $\mu $m, micro-droplets can be stably formed whose uniformity and size meet the demand well, and the minimum generating micro-droplets size is 339.8 $\mu $m. The maximum change rate of droplet diameter and adjacent two droplets are 0.29% and 2.67% respectively. Results are benefit to promote the uniformity of micro-droplets and will provide a reference for the development of piezoelectric droplet ejection devices.