Investigating The Geometry and Fluid Mechanics of 3-D Printing Defects via Under-Extrusion

Abstract

During additive manufacturing, filament is extruded through nozzles of various sizes onto a heated, movable bed. Often times, small variances in the amount of material extruded can have large effects on the structure and material properties of the desired object[1]. Usually, the required volume of extrudate is automatically calculated by a program responsible for machine code generation.[2] However, if one is to manually change extrudate volume, a host of new, exciting printer capabilities are unlocked. Though examples of over-extrusion, such as viscous buckling, coiling, and folding, have been studied in detail[3–5], far fewer attempts have been made to understand the fluid mechanics involved in under-extrusion in 3D-printers. Here we aim to deliver a more complete analysis than previous literature examining this phenomenon [6]. This includes classifying the characteristics of this instability for a far broader set of parameters, analyzing this phenomenon through a theoretical lens, and developing a computational model that generates the required printing parameter given a desired instability output. In doing so, we provide the framework needed to extend the use of 3D printers to reliably print bendable structures through under-extrusion, providing insight into future applications, which could include tissue engineering, filtration, and textile fabrication.