WHAT IS BINDER-JETTING? (DEFINITION, PROS, CONS AND APPLICATIONS)
As part of a broader family of additive manufacturing technologies and processes, binder inkjet, or 3D inkjet printing, is considered the fastest additive manufacturing process for mass-producing functional and high-density precision parts.
Inkjet printing uses powder materials—such as metals, composites, sand, and ceramics—that are scattered to create a thin layer of powder in a manner similar to that used in selective laser sintering (SLS). However, while SLS uses a laser to bond successive layers of powder, inkjet application uses an industrial printhead that selectively applies a liquid binder to the powder. Thus, layers of material are created from the CAD file until the required layer thickness is reached and the final 3D object is ready. Once formed, the part must be cured (if made of plastic) or sintered (if made of metal) for finishing.
Sometimes referred to as "jetting," jet bonding is a cost-effective, low-energy method for manufacturing parts from powdered materials. Consuming less energy than similar methods due to the absence of a laser in the process, binder blasting also allows the use of available materials, and the fast production time results in low operating costs per part produced, making it ideal for precise and scalable mass production of small but precise objects.
Content
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Story
How it works?
Print Options
materials
Advantages
Flaws
What is inkjet printing on a binder used for?
Is binder blasting environmentally friendly?
Is binderjetting the same as material blasting?
How accurate is binder blasting?
Conclusion
Story
The printing process was originally developed at the Institute of Technology (MIT) in the early 1990s to print complex parts from industrial grade materials.
In 1996, ExOne obtained an exclusive license for the additive manufacturing inkjet method, and in 1998 launched the first commercial inkjet metal 3D printer, the RTS-300. After releasing its first S15 sand 3D printer in 2002, ExOne was acquired by Desktop Metal in 2021.
How it works?
The following is a step by step guide to the binder blasting process:
Step 1:
First, the coating blade spreads a thin layer of powder material over the build platform.
Step 2:
A carriage of inkjet nozzles, similar to those used in desktop 2D printers, travels over the bed and selectively releases droplets of binder to bind the powder particles together. In full-color inkjet printing, color ink is also applied at this stage along with the binder. The diameter of each drop is about 80 µm, which makes it possible to achieve good resolution.
Step 3:
After the first layer is completed (based on the CAD design), the build platform is moved down and another layer of powder is applied to the surface.
Step 4:
Repeat steps two and three until the final piece is complete.
Step five:
Once assembly is complete, the part must be left to cure and cure, after which pressurized air can be used to remove excess powder.
Step six:
Some materials require post-processing to complete the part. Metal bond parts require heat treatment (eg sintering) or infiltration with a low melting point metal such as bronze. This step is due to the fact that some materials exit the printer in a so-called "green" state, which means that they have poor mechanical properties and can be brittle and highly porous. Sandcast parts usually do not need post-treatment, but full color parts are impregnated with acrylic to improve the vibrancy of the colors.
Print Options
Almost all technological parameters used in inkjet printing on a binder are pre-set by machine manufacturers. This automation makes the process easy to use, but typical layer heights vary depending on the material used.
For full color models, a layer height of 100 microns is typically used, while for metal parts as little as 50 microns. Sand casting materials typically use a much higher layer height of 200 to 400 microns.
materials
Metals and ceramics are widely used materials for inkjet application of the binder, although other powdered materials such as sand can also be used. In addition, polymers such as ABS or PLA can also be used in binder jetting operations.
Metal alloys, including titanium, stainless steel, and copper, are regularly used for their characteristics, which make it possible to produce parts that are strong yet lightweight.
Beyond industrial applications, binder inkjet processes have even found their way into baked goods, with companies like The Sugar Lab using 3D printing with sugar and water granules to create complex culinary structures.
Advantages
The main advantage of resin inkjet printing is that the process takes place at room temperature, which means that heat-related deformation of parts is not a problem. As a result, the build volume of bonded inkjet presses is one of the largest of any 3D printing technology. The largest machines (up to 2200 x 1200 x 600 mm) are usually used to produce sand casting molds. Metal binder inkjet systems are smaller (up to 800 x 500 x 400mm) but still larger than DMSL/SLM systems, allowing multiple parts to be produced at the same time.
Blasting the binder also does not require any support structures. Instead, the powder provides its own support as the structure grows. This not only eliminates the need for post-processing to remove supports, but also allows parts to be positioned to maximize assembly volume.
Binder blasting produces metal parts with low surface roughness (up to Ra 3 µm if a shot blasting step is used) compared to DMLS/SLM (Ra 12-16 µm). This low surface roughness is beneficial for parts with internal channels and geometries that are difficult to finish.
Binder jetting is also faster and more cost-effective than many other additive manufacturing technologies, as it allows you to quickly create multiple parts at the same time using multiple print head nozzles or holes.
Flaws
Despite the advantages of binder blasting, there are some problems associated with this process.
The main problems associated with inkjet bonding are accuracy and tolerances, which can be difficult to predict as a result of part shrinkage in post-processing steps. For example, metal parts due to infiltration can be reduced by 2% for small products and more than 3% for large products. Sintering can cause shrinkage by an average of 20% as well as buckling caused by friction between the furnace platen and the bottom surface of the part. The heat used in sintering can also soften the part and cause loose areas to deform under their own weight. If these problems can be compensated for during assembly, uneven shrinkage is more difficult to account for.
Bonded parts may also exhibit poor mechanical properties as a result of internal porosity. This porosity can be reduced by sintering (97% density parts) or infiltration (90% density parts), but it can leave voids that lead to cracking. As a result, fracture strength and fatigue can become a problem.
What is jet binder used for?
Considering the advantages and disadvantages of the binder blasting process, it is clear that it is more suitable for some applications than others.
Binder blasting is used to produce full color prototypes, low cost metal parts, and to make large cores and sand casting molds. Due to its low cost and fast production time, this process is even being used to make accessories for the film industry and is used by mobile printing systems to produce spare parts in the field for US Army personnel. Binder blasting is also used in jewelry manufacturing.
Is the binder blasting sustainable?
Sustainability spans a range of factors, but binder blasting certainly has some environmental benefits over other production methods.
First, because blasting uses a wide range of powder materials, they can be sourced locally, reducing logistics costs. Like all additive manufacturing methods, binder blasting has very low material waste and low energy consumption compared to conventional manufacturing methods. However, the speed and high production volumes possible with binder blasting further reduce the carbon footprint.
A less obvious area to consider is the descaling and cleaning methods used and the cleaning fluids that are used for these steps. Common binders for metal parts, such as carnauba, paraffin or special polyethylene wax, must be selectively removed from the part before sintering. This reduces sintering time and can now be achieved with modern, environmentally friendly debinding fluids. What's more, the use of these fluids in steam degreasing methods offers a number of additional environmental benefits, including a reduction in the amount of electricity or water needed for the process, without compromising productivity.
Is bond blasting the same as material blasting?
There is a similarity between binder blasting and material blasting in that they both deposit particles on a process plate to create a 3D object layer by layer. However, blasting materials involves applying droplets of photosensitive resin, which are then cured by exposure to ultraviolet light, while blasting bonding materials applies layers of powdered materials held together by a binder.
How accurate is binder blasting?
The accuracy of applying the binder depends on what materials are used for the process and whether the color is injected into the part.
In addition, those materials that require post-processing can shrink (see "disadvantages" above), although this shrinkage is often taken into account at the assembly stage.
For example, dimensional accuracy of metal, full color material or ceramic/sand:
Dimensional Accuracy:
Metal: ± 2% or 0.2 mm (up to ± 0.5% or ± 0.05).
Full color: ± 0.3 mm
Sand: ±0.3mm
Conclusion
Inkjet printing uses a binder applied to layers of powder. This substance acts like an adhesive, binding the powders together, after which more powder is added on top and bonded layer by layer to create the part.
This process does not require the use of support structures, but may require post-treatment, depending on the materials used. In addition, colored binders can be used to create full color parts or prototypes.
Compatible with different materials, so the exact production steps will vary accordingly. Metal parts will require sintering or annealing to properly bond the powder particles together, but sand molds created with binder blasting will be ready for use right away. Although, in any case, before completing the work, it will be necessary to remove excess powder.
The advantages of resin jet molding include less buckling because it occurs at room temperature, lower cost than many other methods, and high volume production.
However, parts typically only have moderate mechanical properties and high porosity, which means they may not meet all requirements.