Session: 17-15-01: Society-Wide Micro/Nano Poster Forum

Paper Number: 99942

99942 - Computational Studies on Optimization of Printing Process Parameters via Multiphase Modeling of Droplet-Based Additive Manufacturing 

Additive manufacturing is considered pioneering technology in the progress of fields like manufacturing, medicine, construction, and education. Out of existing technologies, droplet-based printing yields better control and final resolution due to controlled deposition of the material on the substrate. Experimental studies show that the final quality of the printing depends on the impact, recoiling, and spreading behavior of the droplet during deposition. This phenomenon is dictated by body forces (Surface Tension, gravity), contact angle forces, dissipative forces due to motion, and fluid properties. Computational studies give an insight into the overall process performance and final quality with respect to fluid properties, initial droplet size, impact velocity, and traverse speed of the printing. This helps in determining optimal process parameters for the desired quality and resolution of the droplet-based printing.

Droplet dynamics and its role in printing has been studied extensively using experiments, and analytical and computational methods in the last decade. Computational approaches involve the use of multiphase models to study droplet dynamics and their relevance to additive manufacturing. This paper uses the volume of fluid (VOF) method to capture the impact, spreading, and recoiling of the droplet during deposition on a solid surface. It involves solving basic Navier-Stokes and continuity equations for an incompressible flow with two or more immiscible phases on a finite volume grid. An indicator function is used to keep track of the interfaces and calculate surface tension forces. In this work, we study the droplet evolution on a fixed grid using an open-source code, OpenFOAM (interfoam multiphase solver) after specifying velocity field, pressure, contact angle, and phase fraction as boundary conditions in the computational domain. A dynamic contact angle model (Kistler’s correlation) is used to capture droplet shape and its interactions with the surface and surrounding fluid.

A test case is validated with a comparison to experimental results from Kim et al (2001) for a water and ink droplet deposition on a polycarbonate surface. This showed good agreement with the experiments. The code also showed good convergence for grid independence and was used further for parametric studies of the printing process. A parametric study is conducted for different printing materials and varied process conditions. The different print materials are accommodated in the computations by modifying fluid properties like viscosities, density, and surface tension while the process parameters are chosen for a range of impact velocities, nozzle-to-base distance, and traverse speed. The coalescence of droplets is studied to predict the final resolution of the printed strand with traverse speed for simultaneous deposition of two droplets. It is found that the contact angle has the most significant effect on the droplet dynamics while the traverse speed dictates the final resolution predominantly.  Overall, this computational study gives an insight into the droplet dynamics involved in additive manufacturing and predicts optimal parameters for the desired quality of the printing.

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 Master's 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