Binder Jetting

Introduction to Binder Jetting 3D Printing

Binder jetting refers to a category of additive manufacturing techniques. Binder Jetting is a process in which a binder is randomly deposited onto the powder bed, bonding these areas together one layer at a time to form a solid component. Metals, sand, and granular ceramics are some of the most popular materials used in Binder Jetting.

 

 

Binder Jetting is used in a variety of uses, including full-color designs (such as figurines), massive sand casting cores and molds, and the manufacturing of low-cost 3D printed metal pieces. For so many uses, it’s critical for a designer who wants to make the most of Binder Jetting’s capability to consider the process’s basic dynamics and how they relate to its core benefits and limitations.

 

 

 

 

How does Binder Jetting work?

The Binder Jetting procedure is as follows:

A recoating blade applies a thin film of powder to the build platform first.

A carriage with inkjet nozzles (similar to those used in desktop 2D printers) then travels over the bed, depositing droplets with a binding agent (glue) that binds the powder particles together.The colored ink is also deposited during this process in full-color Binder Jetting. Since each decline is around 80 meters in diameter, decent resolution can be obtained.

When the coating is finished, the build platform descends and the blade re-coats the board. The operation is then repeated before the whole portion is completed.IV. 

The component is encapsulated in the powder after printing and permitted to cure and gain strength. The component is then removed from the powder bin and washed with pressurized air to clear any unbound, excess powder.

A post-processing phase is normally expected, depending on the content. Metal Binder Jetting pieces, for example, must be sintered (or otherwise heat treated) or infiltrated with a metal with a low melting point (typically bronze). To increase the vibrancy of colors, full-color samples are also infiltrated with acrylic and coated. After 3D printing, sand casting cores and molds are usually ready to use.

This is due to the fact that the pieces are “green” as they leave the printer. Binder Jetting components have low mechanical properties (they are very brittle) and a high porosity in their green state.

Binder Jetting

Characteristics of Binder Jetting

Printer Parameters

Almost all process parameters in Binder Jetting are set by the system manufacturer.

The average layer height varies depending on the material: 100 microns for full color versions, 50 microns for metal pieces, and 200-400 microns for sand casting mold materials.

Binder Jetting has a significant benefit over other 3D printing technologies in that bonding takes place at room temperature.This ensures that dimensional distortions caused by thermal effects (such as warping in FDM, SLS, DMSL/SLM, or curling in SLA/DLP) are not an issue when using Binder Jetting.

As a result, when opposed to other 3D printing systems, Binder Jetting machines have one of the highest build volumes (up to 2200 x 1200 x 600 mm). The majority of these big devices are used to make sand casting molds.Metal Binder Jetting systems usually have greater build volumes (up to 800 x 500 x 400 mm)

than DMSL/SLM systems, allowing for parallel manufacture of many parts at the same time. Because of the post-processing stage, the overall component size is limited to a recommended length of up to 50 mm.

Furthermore, Binder Jetting does not need any support systems since the surrounding powder provides all of the required support to the component (similar to SLS). This is a significant distinction between metal Binder Jetting and other metal 3D printing techniques, which often involve elaborate support systems, which allows for the construction of freeform metal structures with few geometric constraints.Geometric inaccuracies in metal Binder Jetting are primarily due to post-processing steps, which will be discussed later.

Binder Jetting allows the entire construction volume to be used so the pieces do not need to be connected to the build platform. Binder Jetting is therefore appropriate for small-to-medium batch processing.To fully use the capability of Binder Jetting, it is critical to understand how to fill the machine’s entire build volume effectively (bin packing).

 

Full Color Binder Jetting

Binder Jetting, like Material Jetting, may create full color 3D printed pieces. Because of its low cost, it is commonly used to 3D print figurines and topographical charts.

Sandstone powder or PMMA powder was used to print full-color versions. The binding agent is jetted first by the primary printhead, followed by colored ink by a secondary printhead. In a similar manner to a 2D inkjet printer, various colored inks can be mixed to create a wide range of colors.

 

Following printing, the pieces are coated with cyanoacrylate (super glue) or another infiltrant to increase component strength and color vibrancy. A secondary epoxy coating may then be applied to increase the strength and color appearance even more. Full-color Binder Jetting pieces are highly fragile, even with these extra steps, and are not recommended for practical applications. A CAD model with color details must be given to make full-color prints. Color can be added to CAD models in one of two ways: per face or as a texture map. While applying color to each individual face is fast and simple, using a texture map allows for more flexibility and detail. Relevant instructions can be found in your native CAD applications.

A full color print printed in sandstone with Binder Jetting - Photo Credits : 3D HUBS

Sand Casting Cores and Molds

One of the most popular applications for Binder Jetting is the development of massive sand casting patterns. The process’s low cost and speed make it an ideal alternative for complex pattern designs that would be difficult or impossible to construct using conventional methods. Sand or silica is commonly used to print the cores and molds. Molds are usually ready for casting right after they are printed. After casting, the casted metal part is normally removed by breaking the mold. And if these molds are only used once, they save a lot of time and resources as opposed to conventional production.

 

Metal Binder Jetting

Metal Binder Jetting is up to ten times more cost-effective than other metal 3D printing systems (DMSL/SLM). Furthermore, Binder Jetting has a broad build size and the created parts do not need any support structures during printing, allowing for the production of complex geometries. Metal Binder Jetting is therefore a very attractive technology for low-to-medium metal processing.

Metal Binder Jetting components have a number of technical flaws that make them unsuitable for high-end applications. Nonetheless, the material properties of the produced parts are comparable to metal parts manufactured using Metal Injection Molding, one of the most commonly used manufacturing processes for mass production of metal parts.

Infiltration & Sintering

Since metal binder jetting pieces are simply metal particles bound together with a polymer adhesive, they involve a secondary process like infiltration or sintering after printing to achieve their strong mechanical properties.

Infiltration: The component is inserted in a furnace after printing, where the binder is burned out, leaving voids. Approximately 60% of the component is porous at this stage. 

The voids are then filled with bronze through capillary action, resulting in parts with a low porosity and high strength.

Sintering: After printing, the pieces are put in a high-temperature furnace, where the binder is burned out and the remaining metal particles are sintered (bonded), resulting in parts with very low porosity.

Characteristics of metal Binder Jetting

Accuracy and tolerance varies a lot depending on the model, and they’re difficult to estimate because they’re so dependent on geometry. Parts with a range of 25 to 75 mm, for example, shrink between 0.8 and 2% after penetration, whereas larger parts shrink by 3 percent on average. The component shrinkage during sintering is approximately 20%.The system’s program compensates for shrinkage in the parts’ lengths, but non-uniform shrinkage may be a problem that must be addressed during the design stage in coordination with the Binder Jetting machine operator.

Inaccuracies may also be added during the post-processing stage. The component is heated to a high temperature and becomes smoother during sintering, for example. Unsupported areas can deform under their own weight in this softer state. Furthermore, as the component shrinks during sintering, friction develops between the furnace plate and the lower surface of the part, which may result in warping. Again, contact with the user of the Binder Jetting system is crucial to obtaining the best performance.

 

Internal porosity can be present in sintered or infiltrated Binder Jetting metal pieces (sintering produces 97 percent dense parts, while infiltration approximately 90 percent ). This has an effect on the mechanical properties of metal Binder Jetting pieces since voids can cause cracking. Internal porosity has the greatest impact on material properties such as fatigue and fracturing strength, as well as elongation at separation. Advanced metallurgical methods (such as Hot isostatic pressing, or HIP) can be used to make pieces with almost no internal porosity. However, DMLS or SLM are preferred for applications where mechanical efficiency is critical.
The surface roughness of the manufactured pieces is an advantage of metal Binder Jetting over DMLS/SLM. After post-processing, metal Binder Jetted pieces usually have a surface roughness of Ra 6 m, which can be lowered to Ra 3 m if a bead-blasting stage is used. DMLS/SLM pieces, on the other hand, have a surface roughness of around Ra 12-16 m as-printed. This is particularly useful for sections with complicated internal geometries, such as internal channels, where post-processing is challenging.