The binder jetting process consists of a print head that selectively deposits a liquid binder onto a powder bed. The particles in contact with the binder solidify, creating a layer of the final object. All of the layers that are binded together form the final object. For this reason, the choice of the binder is fundamental for the correct application of this technology. Today we are talking about the different types of CONCR3DE binders and their applications.
Firstly it is important to consider the printhead. Different printheads exist for diffent applications and different types of binder. In the standard configuration of our printers you will find a highly versatile industrial piezoelectric printhead that is suitable for a range of different types of fluid and a large range of rheological properties. The printhead allows for nanoparticles, UV curing agents, solvents and aqueous solutions to pass through. It is even heatable, meaning a large range of viscosities can be jetted on the powder substrate.
Our standard printhead allows for relatively low viscosity binders that are typically aqueous. For highly viscous binders a different printhead, the Xaar Aquinox, can be used in the Armadillo White.
Water-based binders are the preferred binder of use in our company. This is because they are environmentally friendly, safe and easy to handle. Several kinds of aqueous binders are available, each for a different purpose.
1.1 BS1001 Mineral Binder
The principal Water-based Binder produced by CONCR3DE is our BS1001 Mineral Binder. It is meant for Armadillo White and Armadillo Grey users and is developed to work with stone-like and cementitious powders. One of the main advantages of this binder is its low ecologic footprint. Since this mineral binder contains only non-toxic substances, it is biodegradable and environmentally friendly. The binder is slightly alkaline, making it extremely suitable for the minerals that are found in our stone-like powders. This binder can also be used in cases where additional binding agents are introduced in the powder itself, as the binder itself does not work like a glue but is purely an aqueous agent to start the curing process. This binder is also the binder of choice in our calcium alumina refractory material.
This binder works incredibly well if coupled with the Armadillo Green, our latest machine development, which was specially engineered for printing biobased materials. Soon available materials will be sawdust, coffee grounds, and seaweed. This biobinder provides immediate green strength to any powder based material that is inserted in the printer. This powder does not require any additives – sawdust for example can directly be put in the machine. The Bio-binder works by using a sustainble biopolymer to bond powders and is therefore fully biodegradeable. Parts printed with sawdust are post processed after using bio binder to obtain their green strength and can be used in product design, automotive, furniture, packaging, interior architecture and other applications. Another application for this binder is tooling. When printed on sand a water soluble part is achieved that can be used as a core or mold for tooling purposes. A green shape can be printed and after its use as a pattern, the binder can be flushed out into regular sewage. The sand used to make the pattern can then be used again to print.
The BC1002 Alu Binderis also water-based ink, but with a twist. It is specifically designed to print dense alumina ceramics. It is able to make these dense parts because the binder is a suspension of nanoparticles that are printed as a slurry on an alumina substrate. This binder solves the low-density issue of alumina parts printed through binder jetting, as the nanoparticles fill the gaps between the grains in the powder. The consequence is a lower porosity and a higher density, therefore making the object less prone to be shattered and enhancing the material's properties. The binder also provides green strength to the alumina parts, making them easy to depowder and gives the user the ability to create highly complex ceramic geometries. When using the alu binder, it is necessary to follow a standard alumina sintering process, where printed parts are debinded and then brought to high temperature, going from a green state to the final object. This unique particle filled ink binder was developed together with WZR in Germany.
This binder is another aqueous binder specifically designed for silicon carbide parts, to be used with PC1001 SiC powder. Because it is aqueous it is especially safe to handle and environmentally friendly. This binder is also developed in collaboration with known ceramic development institute WZR in Germany.
There are cases where an aqueous binder might not be the best solution. An example is metal printing, where solvent based binders are essential to prevent oxidation of the powders. For this application a solvent-binder is developed.
2.1 BM1001 Metal Binder
At CONCR3DE we call our solvent binder BM1001 Metal Binder. It is mainly used for ceramics and metal powders, as it provides good adhesion in the printing stage. A polymer is introduced in the solvent that, when printed, hardens the substrate without requiring any reactive agents in the powder. This means that the M-binder can potentially be used for any powder compatible with the Armadillo printers and with a higher sintering temperature than the binder. It is essential to remember that debinding (removing the binding agents through heat) and sintering (forming a solid mass of material through heat and pressure) are obligatory steps of post-processing parts printed with M-binder. Another advantage of this binder is that it evaporates faster than aqueous-based binders, allowing quicker drying times.
And finally our printers also work with known binders typically found in the metal casting industry. We use one of the most versatile printheads in the market, making our systems highly versatile as well. Available binders are inorganic and phenolic in nature.
Our preferred binder for metal casting is a silicate based binder called . Silicate, or waterglass, based binders are common in the foundry industry because of their high strength and high refractoriness (SK33 – up to 1730 degrees celsius).. There is also a sustainability benefit: the sand used in a mold when printed with this material is reclaimable and toxic gases emitted when casting are minimized.
Lastly a phenolic binder is possible. Phenolics are a type of resin that are very common in the casting industry. The resin is printed on foundry sand mixed with an activator which is cured after printing. Parts printed with this binder have excellent refractoriness (again SK33), dimensional stability and are easy to demold. The process is suitable for casting ferrous and non-ferrous material and compatible with existing foundry processes. There is also an application for this binder with silicon carbide, as parts printed with phenolic resin will have residual carbon in them after sintering as the phenolic is burnt out. This residual carbon can be used in the silicon infiltration process to create more silicon carbide.
Other types of binder are always in development. In the future we will expand this article to include them in it. Do you have a specific requirement for a binder for your company or research project? Feel free to contact us for a feasibility study, compatibility check, custom binder development or waveform development.
Would you like to know more? Contact our team today!