Metal Binder Jetting : the future of metal 3D printing ?
What is metal binder jetting ?
Metal binder jetting is an additive manufacturing process from metal powder. This process is mainly carried out in two steps, a first shaping step by 3D printing followed by consolidation by sintering.
step 1 : 3D Printing
This first step makes it possible to obtain the pieces to green. It takes place in 3 distinct phases.
It is based on the same principle as the widely used office printers. Printing heads on a bed of metal powder deposit a liquid binder
The printer spreads a metal powder layer via a roller and selectively deposits the binder there, defining the geometry of the printed parts. A succession of powder layer and binder deposit then takes place until the entire construction volume is filled.
Once the printing is complete, the production volume is heated to a certain temperature in order to polymerize, that is to say to make solid, the binder. The grains of metal powders are then linked together by the polymer, which makes it possible to obtain the green parts.
The unbound powder is then removed from the parts by suction or blowing in a powder station. All of the powder is recovered to be recycled via a sieving system.
Step 2: Consolidation by sintering
The principle is to subject the green parts to a thermal cycle in a controlled atmosphere. The green parts from the first stage are placed in a sintering furnace (eg ECM technologies furnaces). At the exit, the product will have the desired mechanical resistance.
The thermal cycle has two main phases:
Debinding consists of evacuating or eliminating the residual polymer in the green parts. The challenge of this process is to avoid the formation of defects such as cracks or deformations during the removal of the primary binder.
The parts are maintained at a temperature just above the boiling point of the binder until the binder is completely vaporized. After debinding, the porosities, that is to say the space between the powder grains, are free of polymer.
Sintering is a process in which the metal powder is subjected to a high temperature without exceeding the melting point in order to create atomic diffusion. Thus, the atoms of each grain of powder diffuse with the atoms of neighboring neighbouring grains, creating bond bridges between the grains of powder, which makes it possible to give a mechanical strength to the part.
During sintering, the porosities between the grains gradually disappear, resulting in dimensional shrinkage. Controlling this shrinkage is essential to ensure the correct correlation between the CAD and the final part.
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