Simulation And Experiment Research On Microdispensing Based On Piezoelectric Drive

Micro-dispensing technology plays an important role in the production andassembly of micro-assembly systems. With the rapid development of ultrasonicmachining, electron beam machining, laser machining, photolithography processing andother subtle processing methods, the size of the tiny components become smaller andsmaller, and the requirement for dispensing is also higher and higher. The volume ofexisting business dispenser is generally microliter, and some can reach nanoliter. As aresult of the viscosity of colloids, tiny nozzles, a large surface force and other factors,picoliter research on micro-dispensing technology is a hot spot and challenge.Micro-dispensing system based on piezoelectric drive was designed to achieve theprecision package of micropart. Microdispensing was realized by applying voltage tothe piezoelectric ceramic, selecting the suitable colloid and surface tension of viscosityand using micronozzle. Micro-dispenser need to come true the dispensing dropletdiameter of about20μm and volume of picoliter (pL).Firstly, the research status of dispensing technology was reviewed and the overallscheme design of dispensing system based on the piezoelectric principle and workingprinciple were described. The performance of piezoelectric ceramic and the colloidmovement in the capillary were analyzed. The affecting factors of the micro-dispensingprocess which mainly included colloid viscosity, surface tension, density, nozzlediameter, capillary length, the drive voltage parameters, etc. were obtained by buildingthe model of dispensing process and analyzing the dimensionless numbersin fluid dynamics.Secondly, the multi-physics coupling simulation model which consist of thepiezoelectric devices, fluid-structure interaction and the two-phase flow was establishedand then setting the boundary conditions and dividing the mesh. The relationshipbetween the deformation of capillary wall and the applied voltage amplitude was drawnby analyzing the deformation of capillary wall using piezoelectric devices. Therelationship between exit velocity and the pipe length, voltage amplitude, colloidviscosity and other parameters was obtained by analyzing exit velocity in thefluid-structure interaction model. The colloid extrusion process was demonstrated in thetwo-phase flow model and then the influencing factors of forming droplets whichcontained the nozzle diameter, colloid viscosity, surface tension, driving voltageamplitude and pulse width, etc. were simulated. When the nozzle inner diameter of20μm, about20pL droplet was dispensed by simulation, which provided the basis ofparameters to subsequent experiments.Finally, micro-dispensing experiment system based on piezoelectric principle was built to achieve microdispensing using teflon tube and replaceable dispensing head. Theparameters which included nozzle diameter, colloid viscosity, surface tension and thedriving voltage amplitude and pulse width had been studied through the experiments onthe dispensing volume of droplets. The experimental results show that it can dispenseabout8pL volume when the colloid viscosity is less than30mPa·s and realize about33pL volume when the colloid viscosity is100mPa·s, which validated the correctness oftheoretical analysis and simulation.