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During the sintering step, AM parts are heated to temperatures near melting point to remove the remaining binder and fuse the metal particles together. The sintering atmosphere plays a key role in achieving the target final densities of between 96 and 99.8%. A reducing atmosphere is required to remove oxides, facilitate the bonding of powder metal particles and avoid oxidation during cooling. Hydrogen and bespoke mixtures with hydrogen are the most powerful gases for this purpose.
We offer a wide range of dedicated gas-enabled solutions and bespoke mixtures to support and optimize sintering processes such as metal fused deposition modeling (FDM) and binder jetting.
FDM in focus
Fused deposition modeling (FDM) technology is an additive manufacturing (AM) process ideal for the fabrication of 3D metallic structures and electronic components. Metal FDM builds 3D shapes using, for example, filaments of thermoplastic compound materials. It drives these filaments into a heated liquefier, from where they are extruded through a narrow nozzle onto a build platform.
Advantages of metal FDM include the fact that it does not require the expensive lasers used in sintering processes or the electron beam needed for the electron beam melting process. It also enables operators to use less expensive materials and systems. In addition, it is the only direct metal system to combine thermoplastics and metals within the same build. On the downside, however, it can be prone to oxidation during the build process if the atmosphere is not precisely controlled. This is where we can help.
The metal FDM process
Metal FDM is based on the widely known polymer FDM process. The key difference is that the feedstock (in the form of a filament, a rod or metal injection molding (MIM) granulate) combines a polymer binder and metal powder in an innovative compound. It is a multi-step process.
The feedstock is processed through a printhead which moves along the xy axis while the build platform moves along the z axis. The polymer component of the feedstock is melted and deposited layer by layer on the build platform until the part is completed.
Ensuring part integrity and strength during sintering with controlled atmospheres from Linde
In the third and final phase, the 3D-printed part is fed to a furnace for sintering. During this step, the other binder component (a second-level thermoplastic binder) is removed. Using near melting temperature, this densification results in the final metal part.
This sintering step plays a critical role in the structural integrity of the metal part. Precise control of atmospheric conditions is critical to ensure a high-quality, high-strength part. Without the right atmosphere, the part could oxidize, causing not only discoloration but also weakening the part’s integrity. We developed a bespoke gas mixture to overcome this challenge by delivering optimal atmospheric conditions in metal FDM sintering furnaces.
The binder jetting process
Binder jetting is a powder-based AM technology that combines inkjet technology with a binding agent. A liquid polymer binder phase is selectively deposited onto the powder bed joining the metal particles and forming a green body.
Once the printing process has been completed, the parts have to be removed from the “powder cake”, i.e. the surrounding loose but densified powder. To improve the removal of the excess powder from the green body, brushes or a blasting gun with air pressure are often used.
The green body has to be post-processed in a debinding and sintering process to create a dense metal part. The printed parts are placed in a high-temperature furnace for this, where the binder is burnt out and the remaining metal particles are sintered together. The sintering results in densification of the 3D-printed green body to levels as high as 98% or 99%.
Suited to high-volume, low-cost applications, binder jetting offers speed and cost advantages over some other AM processes. Like all AM processes, atmosphere control is a key success factor in the quality of the final printed part.
Linde solutions for FDM and binder jetting processes
- ADDvance® Sinter250 – bespoke argon/hydrogen mix specially created for metal fused deposition modeling
- Pure argon 5.0 gas supplies for parts made from metal alloy and tool steel powders
- Customized installation kits to accelerate deployment of 3D printing systems such as Desktop Metal’s Bound Metal Deposition™ process
- Design, provision and installation of gas supply system
- On-stream gas system technical and maintenance services
- Gas safety – equipment, safety checks and training