A team of researchers from the Department of Nano Engineering at the University of California, San Diego, has developed an expanded foam resin that can be used in SLA 3D printers.
The resin can be thermally induced to expand after UV curing and can produce parts much larger than the printer's print size. For example, if you print a big bear in 3D, it will become big bear·······
The 3D printed resin sphere expands gradually after being heated. The photo is provided by the University of California, San Diego
Geometric constraints
Parts produced using modern manufacturing techniques (including additive and reducing materials) are usually limited by the working space or manufacturing area of the machine. For this reason, large mechanical systems need to be made up of smaller parts that are fastened, welded or glued together.
The researchers aim to break the constraints of these geometric size constraints and list potential applications in areas with high technical requirements, such as architecture, aerospace, energy and biomedicine.
3D printing expandable resin
The first stage of the study focuses on the selection of a monomer as a component of polymer resin. The monomer must be UV curable for a relatively short curing time and show the ideal mechanical properties for high stress applications. After testing three potential monomers, the team finally identified 2-hydroxyethyl methacrylate (we call it HEMA).
After the monomer was locked, the researchers began to find the best concentration of photoinitiator and the right matching of foaming agent and HEMA. The researchers tested two photoinitiators to test their curing ability under standard 405 nm UV light, which is common in most SLA systems. The photoinitiator was mixed in the ratio of 1:1 and 5% by weight to obtain the best effect. Foaming agent - used to promote the expansion of HEMA cell structure, so as to produce "foaming" - is difficult to find. Many of the tested foaming agents are insoluble in water or difficult to stabilize, but the team eventually identified a non-traditional foaming agent, which is commonly used in polystyrene polymers.
The complex mixture of ingredients was used to make the final photopolymer resin, and the team started 3D printing some less complex CAD designs. The models were 3D printed on an anyc ubic device and heated at 200 ℃ for up to 10 minutes. The heat decomposes the foaming agent, activates the foaming effect of the resin, and enlarges the size of the model. After comparing the dimensions before and after expansion, the researchers calculated a volume expansion rate of up to 4000% (40 times), which made the 3D printing model break through the size limit of the photon building board. Because the density of the expanded material is very low, the researchers think that this technology can be used in lightweight applications, such as air floating membrane or buoyancy assistant.
3D printing model before and after heat treatment, photos provided by the University of California, San Diego.
Source: 3D printing of Antarctic bear