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SLS and Material Jetting Unite

What Is Binder Jetting? – 3D Printing Simply Explained

Picture of Leo Gregurić
by Leo Gregurić
Apr 5, 2019
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Binder jetting is a 3D printing technology that combines principles of SLS and material jetting. Take a tour of this unique technique to discover how it works, its pros and cons, and its ideal applications.

Binder Jetting

What Is It?

A full-color object produced via binder jetting.
A full-color object produced via binder jetting. Source: 3D Hubs

Binder jetting (BJ) is a relatively new 3D printing technology. BJ 3D printers make use of powders, which are bound together with liquid binder agents to make solid parts. In this sense, you can think of BJ as a combination of SLS and material jetting.

The element of SLS that is clearly visible in BJ is, of course, the use of powder. The particles are bound together using binder droplets, which are jetted out of the print head, making BJ similar to material jetting.

In the rest of the article, we’ll take a look at how the technology works, the different kinds of BJ and their applications, and finally, the pros and cons of BJ.

Let’s dive right in!

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Binder Jetting

How Does It Work?

The various components of a BJ 3D printer.
The various components of a BJ 3D printer. Source: 3D Hubs

The main components of a BJ 3D printer are a powder bin, (multiple) print heads, a build platform, a material container, and a powder recoater.

Before the BJ 3D printing process begins, material must be loaded into the powder bin, just like in SLS. Unlike SLS, this powder is not heated. Throughout the entire process of BJ 3D printing, heat is not involved.

Printing begins with a single layer of powder being deposited onto the build platform. The print heads then sweep over the powder, selectively jetting droplets of the binder agent.

The best way to understand the binder agent is to think of it as a glue for powder particles. When droplets make contact with powder, the particles fuse together and form a solid. 

Once the entire first layer of the design has been fused with the binder agent, the build platform moves down one layer in height, a new layer of powder is deposited, and the process is repeated until the part is completed.

When finished, a part is entirely covered in powder.

What Happens After Printing?

After the printing process is finished, the parts are left covered in powder in order to provide the part or parts with structural support while they cure.

When the post-printing process is over, the parts are “dug out” of the powder using compressed air. Parts made via BJ can be post-processed using a number of techniques, which we’ll present later.

Materials for BJ

What makes BJ stand out from SLS is the fact that 100% of the powder can be recycled. Speaking of powder, let’s take a brief look at the materials BJ technology uses.

Parts are made using either sand or metal powders. Naturally, there are various powders available.

Deciding which powder to use is up to the user and highly depends on the part’s intended application. We’ll go into more detail about materials when discussing both metal and sand BJ.

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Binder Jetting

Metal Binder Jetting

A part made through metal binder jetting.
A part made through metal binder jetting. Source: ExOne

Apart from SLM and DMLS, metal 3D printing can also be done via metal BJ. The metal powder is utilized alongside the binder agent to produce metal parts. Since the nature of BJ is similar to metal powder bed fusion technologies, it’s possible to 3D print parts of extreme complexity.

Materials for Metal BJ

Various materials can be used for metal BJ. Bronze-infiltrated or sintered stainless steel as well as sintered inconel alloy are among the most popular.

Applications

Metal BJ is mostly used for the production of complex metal parts, at a lower price tag than SLM or DMLS. These can be end-use parts or high-end prototypes.

Post-Processing

Compared to SLM and DMLS, metal parts made via BJ have weaker mechanical properties. In order to enhance a part’s strength, post-printing processes are required. The two main techniques are infiltration and sintering, after which standard post-processing techniques may or may not be applied.

1) Infiltration

After the parts have been printed, they’re left for a few hours inside the powder so that the curing process can fully complete. Afterwards, parts are put into a furnace, where they are heated to remove the binder agent. Naturally, many voids are left in place of the binder.

In order to improve the mechanical properties of a part, metals with low melting points are usually poured into the voids using a capillary process. The result is an increase in the part’s density and strength. The most common metal used for infiltration is bronze.

2) Sintering

After the normal post-print curing process, parts are exposed to even higher temperatures in a furnace. This initiates sintering, which increases part density and strength.

3) Standard Metal Post-Processing

Next to infiltration and sintering, standard metal processing techniques can be applied to metal BJ parts, but only if the parts have gone through either infiltration or sintering.

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Binder Jetting

Sand Binder Jetting

A part made through sand binder jetting.
A part made through sand binder jetting. Source: Tongtai / YouTube

Sand BJ is an important 3D printing technology, as it enables the production of stunning, full-color models, but more importantly, sand molds. Sand BJ is a truly amazing production technique capable of making low-cost, complexly-shaped parts, especially molds.

In general, sand BJ 3D printing is considered cheaper than metal BJ.

Materials for Sand BJ

Alongside the liquid binder agent, sand BJ usually uses either sandstone or artificial sand, commonly referred to as silica sand. Apart from these two materials, “sand” BJ also works with PMMA powders based on sandstone. PMMA powders are mostly used for making visually stunning, full-color models.

Applications

Sand BJ is mostly used for the production of detailed molds and full-color models. The corresponding 3D printers typically contain a few extra print heads.

The binder and colors require separate print heads, which work hand-in-hand. First, the binder is jetted onto the build plate, where the powder is awaiting. Then, color droplets immediately follow.

Post-Processing

After the parts have been printed, they’re “dug out” of the sand and cleaned. Because no additional post-processing is required for parts made with sand BJ, the process represents an extremely cost-effective mold-making technique.

As previously mentioned, sand BJ is also utilized in full-color model production. Although post-processing of such parts is not required, it’s possible to enhance vibrancy using epoxy coatings.

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Binder Jetting

Pros & Cons

A batch of parts made with binder jetting.
A batch of parts made with binder jetting. Source: ExOne

As with any other 3D printing technology, MJ 3D printing has its pros and cons.

Pros

As discussed above, BJ is similar to SLS but doesn’t use a laser to sinter the powder. This means that there are no high temperatures involved in the printing process.

One of the biggest problems with almost every 3D printing technology is the heat-caused disorders that occur during printing, such as warping. Since there’s no heat involved in BJ, heat-caused disorders are not present.

This allows for printing bigger parts, as there’s no worry that the greater cross-sectional area will cause the print to fail. In fact, BJ 3D printers are known for their relatively large build volumes.

Materials for BJ are generally inexpensive, with sand-like materials being cheaper than metal powders. Still, even the latter are cheaper than SLM or DMLS powders.

The cost-effective production of complexly-shaped parts is possible thanks to BJ’s ability to work without support. As the parts are built inside the powder, the powder itself acts as the support material. This benefit is also present in SLS, as the two technologies share this similarity.

Another great benefit of BJ, which only adds to the cost-effectiveness, is that unused powder is 100% recyclable, which reduces waste and therefore each part’s production cost.

Cons

Poor mechanical properties of parts are the biggest limitation of BJ. In the case of full-color models, structural strength is not that important, as these models are mostly used as visual protoypes. Meanwhile, if your goal is to make functional parts via BJ, you’ll definitely need to invest in some post-processing to enhance the part’s strength.

The other limitation is the relatively minimal selection of materials. Although there are a few to choose from, other 3D printing technologies offer a wider range of materials when compared to BJ.

Feature image source: YouTube / Proxima 3D

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License: The text of "What Is Binder Jetting? – 3D Printing Simply Explained" by All3DP is licensed under a Creative Commons Attribution 4.0 International License.

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