Methods for Enhancing Stereo- Lithography 3D Printing

Introduction:

My Undergraduate Research Opportunity Project sponsored by the University of Minnesota Duluth, looked into the feasibility of compositing-coiled carbon Nano- tubes with UV curable resin commonly used in SLA 3D printers. SLA 3D printers are one the first types of 3D printers and uses roughly 150mW laser to cure the resin. This process produces very high-resolution parts but the downside is the resin is generally brittle. By adding carbon Nano-tubes to the resin it was viewed to lower the ultimate tensile strength of the resin but marginally increased the toughness of it.


Process:

WaterShedTM 1120 UV curable resin was donated for use in the project. Various types of carbon Nano-tubes were looked at for the project. The limited budget of the project only allowed for one type of Nano-tube to be tested in the resin. It was chosen to use coiled-CNT from nanoarmor.com because it has been suggested by a journal article that it would be an ideal additive. The reason is you do not have to worry about functionalizing the CNT nor having outer layers of the CNT separate because of the interlocking coil shape. Based off of this information it was chosen for the project because of the highest probability of success.

To disperse the CNT, a combination of shear and bath sonication was used to disperse the CNT homogeneously in the resin. A scanning electron microscope, or SEM, showed a good dispersion of coiled CNT with minimal agglomerates seen. Various weight percent’s of CNT were tested in the resin for hardness after a one-hour cure time. It was seen that higher weight percent of CNT in resin would reduce the surface hardness of the test sample. A quarter weight percent was chosen because of the most minimal impact on surface hardness and most likely to be used in a SLA printer successfully by not affecting the cure time as significantly as higher weight percent CNT.

ASTM D638 number 5 tensile test sample specifications were used to produce the tensile test samples for evaluating the strength of the resin in comparison to unmodified resin. The molds were made 3mm thick in accordance to molded test samples and they molds were made on a 3 axis CNC machine out of HDPE. The composite test liquid and neat liquid were poured into the molds and cured with the 3D systems UV oven that is used for post cure of SLA printed parts. The samples were then evaluated on a MTS tensile testing machine with the results of the .25% by weight coiled-CNT show below.