Direct Droplet Writing – A Novel Droplet-punching Capillary-splitting 3D Printing Method for Highly Viscous Materials

Abstract

The drop-on-demand (DOD) based three-dimensional (3D) printing methods can fabricate an object with a high level of accuracy and shape complexity using multiple materials. However, a key limitation of the DOD approaches such as ink jetting is only the inks with low viscosity can be used. Such low-viscosity restriction severely limits the material options for the DOD-based 3D printing methods. To address the viscosity issue, we have developed a novel drop-on-demand 3D printing method called direct droplet writing (DDW) for highly viscous material. One main idea of the DDW process is to use direct droplet-punching to enable the printing of materials that may have a viscosity over 190,000 mPa·s; and another main idea of the DDW process is to use capillary-splitting to avoid common issues of various ink-jetting approaches, including splashing, droplet deflection, and satellite droplets. The DDW process can reliably fabricate 3D structures using a wide range of materials that are challenging for the jetting-based and extrusion-based methods. Analytical models to characterize the DDW process are presented. A set of test cases have been conducted using the in-house developed prototype system to characterize the relationship between droplet size and process parameters such as droplet punching speed and dispensing gap. Various materials, including high-loading photocurable tricalcium phosphate (TCP) ink and polyurethane (PU) leather ink, were successfully used in the DDW process. In addition to a much broader range of 3D printable materials, the DDW process is robust, without ink clogging or leaking, and can achieve consistent printing results using digitally controlled droplets.