Multi-Material Extrusion-Based Additive Manufacturing: Refinement and Vertical Stacking in a Dual-Silicone DIW System

Abstract

This thesis advances previous research in multi-material extrusion-based additive manufacturing using Direct Ink Writing (DIW) to develop a more controlled, vertically capable printing process. Building on a dual-material pneumatic extrusion system created at the University of Oklahoma, this work focuses on refining material flow, optimizing print parameters, and exploring early-stage stacking behavior with silicone elastomers.After replicating the original dual-material setup using EcoFlex 00-30 silicone with and without THI-VEX additive, print inconsistency and overspreading highlighted the need for systematic control. A nine-line matrix was developed to isolate the effects of pneumatic pressure and print speed. Results identified 5 psi and 200 mm/min as optimal for consistent, single-layer deposition. Two-pass stacking trials then tested three THI-VEX concentrations (15%, 20%, and 25%) to assess Z-axis behavior. Dimensional analysis showed the 20% formulation provided the most stable stacking, balancing stiffness with print reliability. Though time constraints and dimensional limitations prevented multilayer stacking, this work establishes a repeatable framework for future Z-axis development in dual-silicone DIW systems. The findings transition this project from exploratory replication to process refinement, providing a validated path forward for additive manufacturing of soft, multi-material structures.