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3D printing is still relatively uncharted, and questions continue to abound regarding mechanical properties as we seek the most affordable, strong, and durable materials and parts. Now, researchers at the University of Toronto are investigating options with short fiber composites in SLA 3D printing. Their findings have been recently published in ‘Mechanical Analysis of Short Fiber Composites Manufactured by Inverted Stereolithography,’ authored by Chemical Engineering & Applied Chemistry thesis student Ignace (Joe) Brazda.

Brazda realizes that many 3D printed parts are not suitable for load-bearing applications due to a lack of strength in mechanical properties. To improve on this issue, he combined glass fibers with an acrylic resin for SLA printing. Brazda found success in increasing the elastic modulus, but challenges otherwise. He chose SLA 3D printing because there are so many benefits for making strong prototypes, despite other problems such as the amount of resin required to the fill the tank (with the build volume corresponding to the size of the tank), which can be cumbersome. Also inconvenient is the need to dump surrounding resin to get rid of partially cured material.

A conventional setup for a stereolithography system 1) Sweeper 2) Prototype 3) Resin 4)
Build Platform 5) Elevator 6) Resin Tank 7) Laser Beam 8) XY Mirror 9) Lenses 10) UV Laser

An ISLA system setup. 1) Prototype 2) Scaffolding and supports 3) Resin 4) Build platform 5) UV Laser 6) Mirror galvanometers 7) XY Scanning mirror 8) Transparent resin tank base 9) Resin tank

“To appeal to a greater number of consumers, an SLA machine with a small footprint and basic power voltage requirements is preferable,” states Brazda.

With inverted SLA, the system cures from the bottom. The parts are inverted on the build platform, and because there is no viscous resin, support structures must be printed so the sample does not shift. The Form 2 is a good example of an ISLA 3D printer allowing for smooth workflow.

Formlabs has developed a large material pipeline, with each resin having various colors, mechanical properties, and applications. While Rigid Resins does contain glass particles, the author states that it maintains isotropy while still limiting mechanical properties required.

“The Form 2 is not the only ISLA printer available,” states the author. “However, in comparison to other competitors (Nobel Series by XYZ Printing, Peopoly Moai, Asigo Pica 2), the Form 2 provides the highest XY resolution (140 µm) and is the only ISLA printer to include a wiping mechanism.”

In examining whether composites could be effective for SLA printing, the research focused on their intrinsic mechanical properties. Currently, these types of materials are used for creating parts in aeronautics, the medical field, sports, and more.

“The properties of a composite can be tailored to suit the applications,” states Brazda. “For example, fiberglass is a resin combined with glass fibers. Fiberglass will exhibit properties of both the fibers and the matrix resin. By varying the quantities of the constituents, the mechanical properties of the fiberglass can be tailored for a specific application. The orientation and length of the fibers also effect the mechanical behavior.”

Brazda chose short glass fibers for resin reinforcement with the Form 2 due to their high strength and modulus, along with their excellent capabilities for bonding. They are available in a range of sizes and can be coated by the user depending on adhesion requirements.

“Most importantly, the glass fibers will not interfere with the intensity of the UV laser,” states the author. “The laser is still able to pass through the fibers, allowing the surrounding resin to cure.”

Brazda’s goal was to create 3D printed samples with ‘superior mechanical qualities.’ He believes this type of research to be novel, with no previous attempts to use short glass fibers for such means. The samples were then analyzed regarding their performance in ISLA workflow. Flow of the fibers and print geometries were a focus.

While the fibers will able to be mixed into the resin tank successfully, Brazda discovered that flow gradients generally offered ‘non-ideal’ orientation of the fibers. This means that applications for such 3D prints could be limited:

“The resin accelerates towards the nearest boundary of the print, which will cause the fibers to align in the direction of the flow. This will generally be across the width a high aspect ratio member, and causes transverse fiber orientation, which will not significantly increase the elastic modulus of the specimen along the main axis of the member,” concluded Brazda.

“Future work with the ISLA should continue exploring flow induced orientation and conceptualizing new ideas to modify the movement of the resin. To obtain longitudinally aligned fibers, channel flow is desired. It is likely that using an ISLA printer with more open source capabilities is preferable.”

The topic of mechanical properties is a popular one, as researchers around the world consider how the benefits of 3D printing can be further integrated into manufacturing with materials like SLM 3D printed titanium, aluminum, and PLA. What do you think of this news? Let us know your thoughts! Join the discussion of this and other 3D printing topics at 3DPrintBoard.com.

Tensile testing setup of a short glass fiber reinforced composite

[Source / Images: Mechanical Analysis of Short Fiber Composites Manufactured by Inverted Stereolithography]
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