Introduction: Silica sand is an attractive powder material that can be easily processed using a binder jet additive manufacturing (BJAM) process due to its low coefficient of thermal expansion (CTE) and low cost, making it particularly suitable for making tools andmold. However, the mechanical defects of green parts have always been a major bottleneck, and the low strength of the green body after molding is difficult to support subsequent operations, which also hinders the widespread use of BJAM silica sand in molds. Therefore, the development of a binder that can bond silica sand materials and provide good strength to the green body is a topic that scientists have been exploring.
On November 14, 2021, researchers at Oak Ridge National Laboratory (ORNL) have developed a new polymer binder to bind and strengthen silica sand for use in additive manufacturing.At present, the main application direction of this new polymer is adhesive jet manufacturing, which is an industrial process for prototyping and part production.3D printingmethod.
The printing sand structure bonded by this polymer has complex geometry and high mechanical strength. In addition, it has a remarkable feature – it is soluble in water, which greatly facilitates the printing of models.
post-processing
Process. The study was published in the journal Nature Communications.
Links to related papers:https://www.nature.com/articles/s41467-021-25463-0
DOI: 10.1038/s41467-021-25463-0
△Figure: Binder-Jet Additive Manufacturing (BJAM) process and representative prints. BJAM printer and curing process. The powder on the feed side of the printer, labeled “sand”, is moved to the build side by the counter-rotating printer. The powder in the printer labeled “Sand” is moved to the build side by counter-rotating rollers. After each layer of adhesive has been deposited, the build side will be lowered. After deposition, the build side will drop. The printed parts were cured at 180°C. The powder bed during printing, showing the binding of the binder to the silica sand powder bed, which makes the powder bed darker. c Complex free-standing sand features produced with BJAM. Complex free-standing sand features produced with BJAM showing leaf structure in (left) panel a and (right) panel b. The leaf structure pictured here, and (right) a castle with intricate features printed on a batch of sand, with intricate features printed on a sand blank.
The paper also shows a 6.5 cm long3D printingThe sand bridge can carry 300 times its weight, a feat similar to the 12 Empire State Buildings built over the Brooklyn Bridge.
△3D printingSand Bridge; Credit: Dustin Gilmer/University of Tennessee
Binder jetting
The binder jet printing process is cheaper and faster than other 3D printing methods used in industry, and allows the creation of 3D structures from a variety of powder materials, offering cost and scalability advantages. The concept stems from inkjet printing, but instead of using ink, the printhead jets a liquid polymer to bind powdered materials, such as sand, to build a 3D design layer by layer.
The team used polymer expertise to design a polyethylene or PEI binder that imparts strength to the printing sand by binding the polymer. This adhesive doubles the strength of sandblasted parts compared to traditional adhesives.
Parts printed by binder jetting are initially porous when removed from the print bed. The design can be reinforced by filling the gaps with an additional superglue called cyanoacrylate.The second step is eight times stronger than the first, making the polymer sand composite more powerful than any otherarchitectureMaterials and any known building materials (including masonry) are stronger.
“There are very few polymers that are suitable as binders for sand printing,” said ORNL’s Tomonori Saito, lead researcher on the project. “We have also been looking for binders with certain properties, such as solubility, that would give We bring the best results. At the moment, our main discovery is the unique molecular structure of PEI media. Traditional bonding materials generally use penetrating materials such as super glue to make parts, which are denser in structure, but none of them reach A level close to PEI’s adhesive performance. PEI’s impressive strength stems from the way the polymer reacts with the cyanoacrylate during processing.”
The discovery of new polymers is3D printingSand provides exceptional strength
One potential application for ultra-high-strength sand is the development of tools for making composite materials.Silica sand has historically been an inexpensive and readily available material that has been used incarandaviationThe potential of the field to produce composite parts has been of interest.
△TomonoriSaito at ORNLenergyThe Department of Manufacturing Demonstration Facility showcases a3D printingsand castle.Image credit: Oak Ridge National Laboratory
Dustin Gilmer, a college student at the Predison Center in Tennessee and lead author of the studymedicine“A 3D-printed sand core or ‘tool’ is wrapped around a lightweight material such as carbon fibre or glass fibre and heat treated,” said Dr. Silica sand has excellent properties during this process because it does not change when heated Its size, and it has a unique advantage in washable tools. In composite applications, the use of water-soluble binders to make sand tools is important because it allows a simple washing step with water to remove the sand, leaving a hollow Composite form.”
Existing sand casting molds have been limited in industrial use, primarily because the heat and pressure applied during cleaning, like those traditional commercial methods, can cause parts to crack or fail on the first try. Therefore, stronger molds are needed to support mass manufacturing and enable rapid part production.
Gilmer said that the new high-strength polymer is well equipped for this forming and strengthening function, increasing the complexity of adhesive jet manufacturing of parts, allowing for more complex geometries and expanding manufacturing, Tools and construction applications.
In addition, this new binder has won the annual R&D Top 100 Award in 2019 and has received industry partnersExOneresearch license.
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