A novel electric field-assisted material extrusion process for clean additive manufacturing

Abstract

Material extrusion (MEX) is a type of additive manufacturing technique that is widely used in a variety of applications. However, the issue of reduced quality of printed parts caused by degraded polymer debris accumulation on the nozzle surface during the MEX process has received very limited attention. This work presents a novel electric field-assisted MEX (E-MEX) method to solve the quality issue by significantly reducing the accumulations of polymer debris on the nozzle. By applying a high-voltage power source between the nozzle and the build plate, an electrostatic force was generated to overcome the which showed great potential to reduce the accumulation of molten thermoplastic material on the nozzles. Both the E-MEX and conventional MEX methods were used to print test specimens for specific amounts of time to confirm the efficacy of the E-MEX method. 3D scanning was used to quantify the volumes of debris that had accumulated on the nozzle. Compared to the conventional MEX method, the E-MEX printing reduced debris accumulation by 47 % after about 5 h and over 80 % after about 15 h of the printing process. The changes in electric field intensity over orienting height were analyzed using numerical simulations. The relationship between electric field intensity and time spent by the nozzle during the printing process at a specific height was established. The polymer accumulation in the E-MEX process was found to be dependent on the electric field intensity and the continuous time spent by the nozzle in the weaker electric field enhanced polymer debris accumulations on the nozzle surfaces. The presented study integrates experimental observations with simulation results, revealing the mechanism of debris accumulation on the nozzle when the electric field decreased to a certain level during printing process. A numerical simulation model was developed to understand the traveling of accumulated polymer debris from the nozzle's outer surface to the printing layer under the influence of electrostatic force. The simulation results showed that the dragging of polymer debris towards the build plate occurs when the electric force acting in the tangential and normal direction is sufficient to overcome the viscous force and normal force in the polymer debris. The simulation results also showed some part of the debris remained in the crease area of the nozzle surface due to the viscous and surface tension forces prevailing over the electric force.