An Overview of Binder Jetting

Originally published on fastradius.com on March 7, 2020

What is binder jetting? In 1993, the Massachusetts Institute of Technology developed this Inkjet-in-powder-bed form of 3D printing to print complex parts out of a variety of materials. Today, there are binder jetting applications in several industries, and you can create everything from metal parts to large sand-casting cores to full-color prototypes. Binder jetting is fast and cost-effective, but many product teams are unfamiliar with this manufacturing process. Here’s what you need to know.

What is binder jetting?

While many other 3D printing methods use a single nozzle or laser to create parts layer by layer, binder jetting sprays liquid binder onto a bed of powder. In fact, the binder jetting 3D printing process is similar to how a 2D printer adds ink to paper. It’s mainly used to print metal, sands, and ceramics and is known for its speed, affordability, and ability to print large parts.

To begin the binder jetting process, you’ll need to create a digital model of your part, slice it, and send it to your manufacturing partner. They’ll then input it into the binder jetting printer. Then, a recoating blade or roller will spread a thin layer of powder over the build platform, and a carriage with Inkjet nozzles will pass over the powder bed, depositing drops of binding agent. If you’re creating a full-color part, the machine will also deposit colored ink during this step.

The build platform will then lower in accordance with your model’s layer thickness. Most full-color models have a layer height of 100 microns, most metal parts have a layer height of 50 microns, and most sand casting mold materials have a layer height between 200 and 400 microns. Next, the blade or roller will recoat the surface, and the process will repeat until your part is complete. Your engineer can then cure your part to increase its strength, gently free it from the loose powder on your powder bed, and clean it using a brush or pressurized air.

Parts that have just been created using binder jetting are in a green state and typically have high porosity and poor mechanical properties. As such, your engineer might add on a few post-processing steps after printing, which will vary depending on your part’s material. For example, a metal part might need to be sintered with a low-melting-temperature metal like bronze. If you have a full-color part, your engineer might infiltrate it with acrylic to improve its vibrancy. If you have a sand casting core or mold, no additional processing is required.

Common materials binder jetting materials

Binder jetting materials fall into three categories — powder, sand, and metal.

Sandstone and PMMA powder

Since binder jetting 3D printing machines often have secondary printheads that add color as the primary printhead adds the binding agent, it’s easy to create full-color models using sandstone or polymethyl methacrylate (PMMA) powders. However, the resulting parts will be very brittle — even after processing — and are best used as non-functional models like topographical maps or figurines.

Sand

Sand and silica sand are relatively affordable, so they’re great for creating one-time-use molds and cores. Not only will binder jetting sand enable you to create complex geometries that would be difficult or impossible to produce with traditional methods, but you’ll also be able to achieve a dimensional accuracy of ± 0.3 mm. Also, note that:

• You won’t need additional post-processing.
• Layer thicknesses for sand casting cores and molds usually fall between 200 and 400 μm.
• Build sizes can be as large as 2200 x 1200 x 600 mm.

Metal

Binder jetting is also a popular choice for 3D printing metal. It’s up to 10 times more economical than selective laser sintering (SLS) or selective laser melting (SLM) and offers relatively large build sizes of up to 800 x 500 x 400 mm. Binder jetting also allows for complex geometries, doesn’t require support structures, and has a dimensional accuracy of ± 0.2 mm.

Binder jetting is compatible with steel, titanium, chromite, copper, and more, but you’ll need to post-process your part to improve its strength no matter which metal you use. Post-processing options include:

• Infiltration: Infiltration involves placing a cured part in a hot furnace. After the binding agent has burned off, the part’s density will reduce to around 60%. Your engineer can then fill the voids left behind with bronze or another low-melting-temperature metal until it reaches at least 90% density. Infiltrated parts are relatively strong and have good mechanical properties, but they will be around 2% smaller after infiltration.
• Sintering: If you want even better mechanical properties, you can have your metal part sintered. Sintering involves heating a part in a furnace to bake out its binders and fuse its metal particles. Sintered parts have high corrosion resistance and 3% porosity, but the drawback is that they often shrink around 20% from their initial size. This shrinkage may not be uniform, which can cause post-printing inaccuracies, even if your design already accounted for 20% shrinkage.

Binder jetting advantages and disadvantages

When you choose binder jetting, you can:

• Achieve relatively high dimensional accuracy: Since binder jetting occurs at room temperature, you don’t need to worry about warp and your part will remain highly dimensionally accurate. If you’re binder jetting with metal, you also don’t need to worry about relieving residual stresses during secondary post-processing. However, you’ll likely notice shrinkage after sintering.
• Save money: Binder jetting a metal part is more than ten times more economical than using SLM or SLS. Not only is it more affordable, but it also uses less energy because it uses a liquid binding agent instead of a laser. Plus, binder jetting ceramic and metal powders are usually more affordable than powders for SLS and SLM. Similarly, you can produce a full-color prototype via binder jetting for a fraction of what it would normally cost to produce one via SLS, SLM, or material jetting.
• Forgo support structures: In binder jetting, the unbound powder provides all the support your part needs, eliminating the need for support structures and giving you more design freedom. This also means shorter post-processing times and less material consumption compared to other 3D printing technologies.
• Cut back on waste: 100% of unused powder can be reused for future prints, helping you save material and money. In comparison, only 50% of powder used by SLS 3D printers is reusable.
• Quickly produce a large part or several smaller parts simultaneously: Binder jetting machines have build volumes of up to 2200 x 1200 x 600 mm, which means you can produce large parts or simultaneously build several smaller ones.

However, there are a few disadvantages to consider when using binder jetting. Keep in mind that:

• Metal binder jetting parts will have lower mechanical properties than their SLS counterparts because of their higher porosity.
• Binder jetting offers a limited material selection compared to other 3D printing processes.
• Parts are brittle in their green state, which means you can only print rough details.
• Most binder jetted parts require post-processing, which can significantly lengthen production times and introduce inaccuracies.

3D printing with SyBridge

Binder jetting is a fast and affordable technology that’s great for large prints and full-color prototypes. Is binder jetting the best process for your next project? Working with an experienced manufacturing partner can help you make the right decision.

At SyBridge, our team of professionals has years of experience with the latest 3D printing technologies. We can help optimize your design for 3D printing, select a material and 3D printing method that suits your needs, and more. Contact us today to get started.