| Piezoelectric inkjet 3D printing is an additive manufacturing technology that generates high-precision structural and functional components by depositing the microdroplets injected on demand layer by layer on the substrate.With the advantage of no touch,digitization and high flexibility,the technology has a broad prospect in the fields of structural and functional components manufacturing.The way to ensure the high machining precision and high producing efficiency of piezoelectric inkjet 3D printing is to reduce satellite droplets during single micro-droplet ejection and suppress residual oscillations between micro-droplet ejection processes.Nevertheless,the structural and functional materials used in piezoelectric inkjet 3D printing are generally power-law fluids containing high molecular polymer.Viscosity is a measure of energy loss and the shear-thinning characteristic of the power-law fluid makes its micro-droplet ejection and formation different from that of Newtonian fluid.It is difficult to obtain the uniform and stable micro-droplet of power-law fluid rapidly by the control methodology used for micro-droplet ejection of Newtonian fluid.With the great demand of integrated forming and manufacturing of structural and functional parts,the realization of high efficiency and high precision jet deposition of power law fluid has become an urgent problem to be solved.Theoretical analysis and experimental research are carried out on the power-law fluid micro-droplet ejection and formation process in piezoelectric inkjet 3D printing.Based on the power-law fluid micro-droplet ejection mechanism,the flow rate at the inkjet printhead outlet is controlled by adjusting the drive parameters to improve power-law fluid microdroplet formation,which raised the printing frequency and precision of power-law fluid micro-droplet ejection.The main work is as follows:A dynamic model is established to describe power-law fluid flow process inside the inkjet pipe.According to the quasi-one-dimensional theory,Navier-Stokes equation and continuity equation are simplified to obtain the dynamic equations that are appropriate for power-law fluid inkjet pipe flow.Through principle of acoustic and electrical analogy,an equivalent circuit construction method is proposed to describe power-law fluid flow inside the inkjet pipe,which includes the equivalent circuit branch division according to fluid flow states and the expressions of components in the equivalent circuit.By applying the energy attenuation law of Stokes vibrating plate,an expression form is presented for the thickness of boundary layer between the flowing power-law fluid and inkjet pipe wall.By combining the power-law constitutive equation,an expression form is presented for the relationship between frictional resistance and velocity of power-law fluid flowing inside inkjet pipe.Through the joint between Kirchhoff’s law,the equivalent circuit branch division and equivalent circuit parameter expressions,a dynamic model is established,which is used to describe power-law fluid inkjet pipe flow.The flow rates at inkjet printhead outlet are obtained through solving the dynamic model of power-law fluid ejection by iterative algorithm.Through comparison between the calculation results of dynamic model and the simulation results of CFD,the dynamic model is verified to describe the power-law fluid flow at inkjet printhead outlet during ejection accurately,which lays the foundation for establishing correspondence between the drive parameters and the flow rates at inkjet printhead outlet and realizing the precise control of power-law fluid ejection.A solving method is presented for the fluid flow rates corresponding to fine power-law fluid ejection effect.Through qualitative analysis of power-law fluid micro-droplet formation at inkjet printhead outlet,we obtain the relationship between fluid flow rates and power-law fluid micro-droplet formation.The flow rate waveform is adjusted according to the law of mass conservation to retrieve the fluid ligament.According to the law of energy conservation,the relationship between the flow rates at inkjet printhead outlet and microdroplet fracture morphology is established to obtain the critical amplitudes of flow rates corresponding to micro-droplet generation and satellite droplet generation.Finally,a solving method is presented for the fluid flow rates corresponding to fine power-law fluid ejection effect.Through comparison between the calculation results of dynamic model and the simulation results of CFD,the flow rates obtained by this method corresponds to the power-law fluid ejection without residual oscillations and satellite droplets,which lays the foundation for the improvement of inkjet frequency and the production of high-quality micro-droplet.A control method is presented for the power-law fluid flow rates at inkjet printhead outlet.According to the law of mass conservation,the deformation of piezoelectric ceramic pipe caused by driving voltage waves is transformed into the power-law fluid flow inside the piezoelectric ceramic pipe.The modifications have been made to the equivalent circuit construction method and the dynamic model,thereby the correspondence between the driving voltage waves and the flow rates at inkjet printhead outlet is established.On this basis,the driving voltage waveform is optimized by combining with the iterative algorithm with strict convergence and a control method is presented for the power-law fluid flow rates at inkjet printhead outlet.Meanwhile,the optimal control scheme of power-law fluid droplet ejection is obtained by combing the equivalent circuit model of power-law fluid ejection process and the solving method of fluid flow rates corresponding to fine powerlaw fluid ejection effect.Through the verification of microdroplet ejection experiment,this method could adjust the flow rates at inkjet printhead outlet according to the rheological properties of power-law fluids,the printhead structure and the inkjet demand,which provides guarantees for the quick and accurate piezoelectric inkjet 3D printing. |
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