Metal Binder Jetting _ 3D metal printing

Metal Binder Jetting (MBJ) is a metal additive manufacturing technology also known as metal 3D printing.

Metal Binder Jetting (MBJ) is a metal additive manufacturing technology also known as metal 3D printing. MBJ involves working with loose metal powder on which a binder is deposited. The name BMJ comes from Metal Binder Jetting (MBJ) is a metal additive manufacturing technology also known as metal 3D printing. MBJ involves working with free metal powder on which an adhesive-type binder is deposited. The name BMJ comes from "binder jet" to assemble the metal particles, which differs from other processes that work by melting the metal powder.

As with all additive manufacturing technologies, the 3D printing of the part is done from a 3D file compatible with metal printing software.

The process:
As with all additive manufacturing technologies, the 3D part is printed from a 3D file compatible with metal printing software.

Operationally, the manufacturing of a metal part by Metal Binder Jetting is done by successive steps of powder deposition on the surface of the printing plate, followed by binder deposition and then powder deposition again... until the number of passes necessary to produce the part is obtained. The binder is deposited by the print head in drops of about 50 microns in diameter.
The unbonded powder residues are blown off and recovered for the next print. After the residual metal powder has been removed, the shape of the object is created. It is also possible to colour the binder to obtain colour variations and aesthetics of parts with MBJ.
At this stage of the design process, the structure is still fragile, but it is now time to deepen it. At the end of the printing process, the material is in the green state. It is therefore necessary to deepen the structure by a post treatment step.


Two options are available for post-processing to solidify the parts. It is possible to inject a liquid metal at low temperature which will be lodged within the structure obtained (this is often bronze). The density obtained following infiltration by injection reaches 90%. The second and most frequently used possibility is to sinter the powder by heating in an oven. In this case the glue melts and the heated particles fuse together giving the part its full rigidity. Sintering gives a material density of 97%. Regardless of the post-treatment applied to a part manufactured by binder jet; a porosity remains.

Compatible materials:
Binderjet 3D printing is compatible with stainless steel, inconel, copper, titanium and tungsten carbide. In the near future it should be possible to use this technology with thermoplastics as well.

Surface finish:
The accuracy and finish of the part depends on many factors such as the height of the layers, the size of the metal particles and the size of the binder drops.
The roughness of a part surface when leaving binder jetting is of the order of 6µm in the green state and of the order of 3µm when leaving post treatment.

Deformation:
In Metal binder Jetting technology, the parts undergo deformation at the time of post treatment. It is therefore important to anticipate this at the design stage. For injection moulding post-processing, the parts can undergo an average shrinkage of 3% of their overall size. When sintering is used as an after treatment the shrinkage can reach 10% of the overall size of the part. On the other hand, it is important to note that the deformation is not necessarily homogeneous.

Mechanical properties:
The intrinsic porosity of parts made with MBJ makes their strength weaker than parts made by material removal. Indeed, there is a greater risk of crack initiation in the porosities. Fatigue resistance at breakage should be considered when choosing a manufacturing technology.

DMLS or SLM metal additive manufacturing technologies have better mechanical strengths. The advantage of MBJ lies in the surface finish of the part, which is much better than for DMLS or SLM. Metal binder jetting offers the possibility to produce relatively large parts quickly and without support, which reduces the cost of manufacturing parts compared to other metal 3D printing technologies. Finally, this technology lends itself well to the production of small and medium-sized series.

Example of uses:
MBJ can be used in the foundry industry for the production of mould cores, it is also used in the luxury industry for jewellery or luggage accessories as the mechanical properties are not decisive for this type of part.

More surprisingly, the binder jet technology can be used with sand instead of metal - this is called "Sand Mold Jetting" (SMJ). In this case the advantage is that there is no need for post treatment. Working with sand is suitable for foundry moulding because it can be removed after the casting stage.

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