Micro-injection Dispensing Simulation And Nozzle Structure Design Based On Fluid Dynamics

Spray dispensing is a dispensing technology developed gradually in the production and assembly process of electronic products,which is an important technological innovation to change the traditional contact dispensing method to non-contact dispensing method.In the spray dispensing process,the volume of a single glue drop seriously affects the dispensing quality.The volume of a single drop and the consistency of the shape of the glue point on the substrate are affected by many factors.Most of the spray dispensing fluids belong to high viscosity non-Newtonian fluids,and the dispensing process involves the coupling of fluid-solidheat multiple physical fields.Therefore,numerical simulation analysis of micro-jet dispensing can be performed by using computational fluid dynamics to study the main factors affecting the glue speed,the volume of individual drops,and to achieve stable dispensing by micro-jet while ensuring the consistency of the drops,so that the structure of the spray valve nozzle can be optimized.Firstly,the working principle of jet dispensing is analyzed,and based on the theory of fluid mechanics,the rheological characteristics of the fluid and the dimensionless number characterizing the injection state are analyzed,and the critical injection speed and stable injection conditions that control the dropping of jet dispensing are derived,which are Reynolds number,Weber number and Ohnesorge numbers.Since the volume size of a single droplet in micro-spray dispensing is considered in this paper,the formation mechanism of spraying droplets is analyzed,the spraying process of individual droplets is analyzed,and the mathematical model of the spraying speed and spray volume of a single droplet is established,which provides theoretical basis for simulation analysis.Combined with the microjet dispensing injection conditions,the continuity equation,momentum conservation equation and energy conservation equation under laminar flow in the fluid flow state,based on the VOF model,Fluent is used to simulate and analyze the flow state of the internal fluid of the nozzle,and the jet dispensing simulation model is established,because the nozzle striker belongs to the geometric symmetry model,and the physical boundary conditions also meet the symmetry distribution,so a two-dimensional axisymmetric model is established,and the nozzle cone angle,nozzle diameter,nozzle length,striker radius,pressure cavity diameter are studied through simulation,the length of the pressure chamber,fluid viscosity,striker speed,glue supply pressure,impact distance on the fluid injection speed and the volume of a single droplet influence law,which provided guidance for improving ejection performance and controlling single-point glue volume.Secondly,based on the mathematical model of single droplet velocity and volume and the results of single factor simulation analysis,the parametric modeling of nozzle structure was carried out,the orthogonal test was designed,and the range and variance analysis was carried out,the importance and significance of the factors affecting the single droplet volume were obtained,and the single droplet volume regression model was established and validated.Since the orthogonal test did not take into account the interaction between the factors,according to the response surface,the significant factors were selected to establish a prediction model for individual drops.The interactive effects of nozzle diameter,cone Angle and firing pin radius affecting the volume of a single glue drop were solved,which provided the basis for selecting the appropriate combination of nozzle parameters.Because the surface quality of the inner runner of the nozzle affects the flow resistance,the micro-morphology of the inner runner of the nozzle was observed and analyzed by SEM.A micro-dispensing experiment platform was set up,and a high-speed camera was used to observe the dispensing process.The process capability of micro-injection dispensing was analyzed,and the solution of CPK=2.33,CPK≥1.67 was obtained by Minitab software,which indicated that the micro-injection dispensing was stable.The influence of the working parameters of glue supply pressure,driving voltage,heating temperature and impact time on single-point glue output was studied.The experiment of micro-injection dispensing height was designed,and the cause of the formation of dispensing point under different injection height was analyzed.Finally,the experiment of micro-injection dispensing was designed,and the minimum dispensing amount was 1.57nL.The maximum relative error of the model and experiment was 10.93%,and the minimum relative error was 1.21%,the correctness of the simulation and model is verified.