Microdroplet Jetting Forming Mechanism And Electromechanical Co-Control Method

Piezoelectric droplet deposition technology has a micron-level material deposition accuracy and a wide range of applicable physical properties.Therefore,it has been widely used in the field of single-material 3D printing.With the increasing demand for the manufacturing of functional parts composed of multiple materials and multiple structures,Multi-material jetting in multi-material 3D printing technology has become a key technology that needs urgent breakthrough.However,due to the complicated coupling relationship between the print-head structure,material physical properties,drive waveforms and droplet characteristics,and the interaction mechanism is unknown,the precise control mechanism of the multi-material jetting process has not been established,it is difficult to quickly realize the material with different physical properties High-speed,high-precision jetting.In response to this problem,this dissertation systematically studied the modeling,analysis and control of the droplet jetting process of the piezoelectric print-head.The main work is as follows: 1.Established a micro-channel dynamic model for material jetting process control.Starting from the conservation of momentum and mass conservation equations in fluid mechanics,an equivalent circuit construction method suitable for any print-head structure and material is proposed.By introducing the energy attenuation characteristics of the Stokes vibration plate,the calculation method of the thickness of the boundary layer in the micro-channel is proposed.Based on this calculation method,the parameter mapping relationship of equivalent circuit components is established,and combined with Kirchhoff's law,a microchannel dynamic model suitable for the control of the transient jetting process of materials is established.CFD simulation and experimental results show that the relative error between the analysis results of the model and the measured results are less than 7.42%.Compared with CFD simulation,the analysis time is reduced from tens of hours to several milliseconds,which lays the foundation for the precise control of the transient process of material jetting.2.Establish a droplet morphology prediction model suitable for droplet morphology control.For the complex fluid rupture rule in the droplet forming process,a similar flow principle is introduced to describe the process form fluid rupture to forming a droplet.On this basis,the distribution equation corresponding to the dimensionless number of the specific flow pattern is derived,and the equation is used to propose two critical conditions corresponding to jet good droplet morphology.Therefore,the droplet morphology prediction problem is converted into critical condition judgment problem,and finally,a droplet morphology prediction model for droplet morphology control is established.CFD simulation and experimental results show that the relative error of the model and CFD simulation results is less than 4.85%,the predicted droplet morphology is highly consistent with the measured droplet morphology,thus laying a foundation for the precision droplet ejection of multiple materials.3.A droplet jetting control method for improving the adaptability of multi-materials and controlling droplet morphology is proposed.By intercepting the jetting part of the traditional material jetting volume flow rate and discarding the residual vibration part,the droplet morphology prediction model is integrated into the intercepted jetting volume flow rate.On this basis,a method that design the desired jetting volume flow rate according to the physical properties of the material and the nozzle size is proposed,and the desired jetting volume flow rate is used as the optimal control target,and the drive waveform is used as the optimized object.Combined with the micro-channel dynamics model,an iterative optimization algorithm is proposed.Based on this,to control different material jetting process,the iterative optimization method of the drive waveform is proposed.The experimental results show that the method can not only effectively suppress the residual pressure oscillation,increase the jetting frequency,and adjust the droplet diameter according to the material characteristics and nozzle size,but also can jet good morphology droplets for different materials.Therefore,for functional parts with different materials and different structures,this method provides guarantee for accurate deposition of multi-materials.4.An active control method to suppress the residual vibration of the piezoelectric print head structure is proposed.Using the self-sensing principle of piezoelectric materials,the vibration characteristics of the composite structure of the piezoelectric material and the micro-channel wall are measured,and a lumped parameter dynamic model that accurately describe the vibration characteristics of the piezoelectric print-head structure is established and identified.Based on this,combining this dynamic model with the aforementioned iterative algorithm,a method to suppress the vibration of the piezoelectric print-head structure is proposed.The experimental results show that the optimized drive waveform reduces the vibration energy of the piezoelectric print-head structure.Compared to the original drive waveform,the vibration energy of the structure decreased by 87.3%,thereby further improving the control accuracy of the drive waveform to the material jetting process.5.Developed a droplet watch device.A piezoelectric active reflector device is proposed.By embedding it in the architecture of a traditional droplet watch system,The device can record the shape of a single droplet at different times into a single image,and the improved droplet watch device not only retains all functions of the traditional droplet observation device,and it can also record the formation process of a single droplet.Therefore,it overcomes the defect that the traditional droplet watch device cannot record the formation process of a single droplet.The experimental results show that the improved droplet watch device can achieve an equivalent frame rate of up to 1 MFPS,and can visualize the droplet formation process with a time resolution of 1?s,which provides a foundation for verifying the models and methods in this dissertation.