Session: Research Posters

Paper Number: 120272

120272 - Multiphase Modeling of Droplet-Based 3d Printing: Predicting Printability, Resolution, and Shape Fidelity in Additive Manufacturing Processes 

Droplet impact dynamics and its spreading on a solid surface have been extensively studied with experiments and computational methods. When impinged on a solid substrate, the free surface of a droplet experiences several deformation stages, from spreading, recoiling, oscillations, rebound, and splashing. The present work focuses on studying the spreading and recoiling of a liquid droplet on a solid surface and its effect on the final spreading diameter. The deposition process is characterized by the ‘Spreading Factor,’ defined as the maximum spread diameter to the initial drop diameter during 3D printing process. The spreading, wetting of the droplet and other process parameters decide the quality of the final printed product. The low-volume deposition mechanism involves a complex physical phenomenon involving surface tension, gravity, contact angle forces, and other dissipative forces that determine the motion and shape of the droplet. Overall, the fluid properties (such as density, viscosity, and surface tension), droplet size, the initial velocity of the droplet, and surface topology characterize the 3D printing process via droplet deposition.

This present work uses the Volume of Fluid (VOF) multiphase modeling method to study the impact and spreading behavior of droplets with its application in additive manufacturing. The role of key material properties and processing conidtions is evaluated in exploring the spreading and recoiling behavior of the droplet to predict the final spread diameter. Through validation of the code with experimental data, a parametric study is done to evaluate the quality of printing and decide optimal parameters for the desired print quality. The models are used to correlate achievable resolutions with droplet size distribution in the additive manufacturing processes. 
The numerical model shows good agreement with the experimental data reported by Kim and Chun et al. (2006) by following the shape evolution of a water and ink droplet on a polycarbonate surface. The model illustrated different stages of spreading, recoiling, lamella formation, and wetting for droplet dynamics in printing, as reported in other experimental and numerical studies. A parametric study suggested that the initial velocity significantly influences spread diameter in the spreading phase; however, it did not affect the final deposition for the given range of velocities. The selected range of nozzle to substrate distance did not affect the spreading diameter or final deposition. Higher values of initial velocity and nozzle to substrate distance can cause splashing of droplets which are not desired in the printing process. It is also found that the contact angle significantly affects the spread diameter and final deposition. Other parameters like surface tension and temperature can be studied further with their implications on the final printing quality. The constant contact angle model fairly predicts the initial spreading behavior while overpredicts the recoiling behavior. However, the dynamic contact angle model performs better than the constant angle model for initial spreading and recoiling behavior. It also captures the post-recoiling oscillations better than the constant contact angle model. The computational model slightly overpredicts the equilibrium base diameter which is evident from the qualitative shape evolution analysis. Overall, the computations are effective for the analysis of spreading and recoiling behavior for the water droplet impinging on a polycarbonate surface. Many industrial materials like polymers, bioinks and other commercial printing inks can also be analyzed with parametric studies for better print quality and fidelity.

Presenting Author: Rauf Shah Joint School of Nanoscience and Nanoengineering

Presenting Author Biography: Rauf Shah is a Graduate Research Student at North Carolina A&T State University, Greensboro, NC. His research primarily focuses on the multiphase flow modeling of additive manufacturing processes. He is currently working on studying the spread and impact behavior of droplets in droplet-based additive manufacturing processes. He holds a Masters degree in Mechanical engineering with a specialization in Manufacturing processes.

Authors:

Rauf Shah Joint School of Nanoscience and Nanoengineering
Ram Mohan North Carolina A&T State University