The Virtual Foundry (TVF) sinters bound metal Filamet™ parts in an ordinary open-atmosphere kiln. All you need is a kiln, a crucible, refractory ballast and Sintering Carbon. The protective atmosphere is made inside the crucible, right next to the part, by a layer of Sintering Carbon and supported by refractory ballast. This guide explains how that works, which kiln temperatures to use, and how to size your CAD model so the sintered part comes out at the right dimensions.
The short version
- Atmosphere: open-atmosphere kiln, in-crucible sintering.
- Reducing agent: carbon monoxide (CO) generated locally by a top layer of Sintering Carbon getter.
- Support: refractory ballast holds the part's shape while the binder leaves and the metal densifies.
- Peak temperatures: 1232°C (2250°F) for 316L, 17-4 PH, Inconel® 718 and Tool Steel H13; 1052°C (1925°F) for copper.
- Sizing: Oversize Factor OF = 1 / (1 − S).
Why in-crucible chemistry works
Metal powder is covered in thin surface oxide films. Those films block the particle-to-particle diffusion that turns a printed, debound part into solid metal. A sintering atmosphere has to remove the oxide and keep fresh oxide from forming.
TVF does this with a carbon getter layer placed on top of the crucible contents. As the kiln heats, the carbon consumes the oxygen trapped in the crucible and produces carbon monoxide:
2C + O2 → 2CO
Carbon monoxide is a strong reducing agent. It diffuses through the packing around the part and strips oxygen from metal oxide on the particle surfaces:
MO + CO → M + CO2
The carbon bed keeps the cycle going, because carbon dioxide reacting with hot carbon regenerates carbon monoxide:
CO2 + C → 2CO
The result is a small, self-sustaining reducing atmosphere that exists only inside the crucible. Everything the process needs is already in the crucible.
The crucible, layer by layer
- Refractory ballast surrounds the part. It supports overhangs and thin features as the binder burns out, and it lets CO reach the part.
- Sintering Carbon getter sits as the top layer. It is the source of the CO atmosphere.
- A loosely fitted lid lets binder vapor escape while the carbon layer protects the contents.
Follow the packing depths and firing schedule published with your Filamet material. Browse the materials on the Filamet collection.
TVF kiln temperatures
These are TVF kiln schedules for the in-crucible process. They are not the temperatures quoted for industrial metal injection molding (MIM) furnaces.
| Material | Peak sintering temperature |
|---|---|
| Stainless Steel 316L | 1232°C (2250°F) |
| Stainless Steel 17-4 PH | 1232°C (2250°F) |
| Inconel® 718 | 1232°C (2250°F) |
| Tool Steel H13 | 1232°C (2250°F) |
| Copper | 1052°C (1925°F) |
1232°C (2250°F) is the maximum for the high-temperature alloys above.
The math: Oversize Factor
Sintered parts shrink. To end up at the dimension you want, print larger by the Oversize Factor:
OF = 1 / (1 − S)
S is the linear shrinkage as a fraction. Use the shrinkage figure published for your specific material and print orientation.
Worked example. If S = 0.20 (20% linear shrinkage), then OF = 1 / (1 − 0.20) = 1.25. Scale the model to 125%. A 50 mm finished part needs a 62.5 mm green part.
Common mistake. Adding the shrinkage percentage (scaling to 120%) leaves the part undersized. A 100 mm target becomes 96 mm after shrinking 20%, because 100 × 1.20 × 0.80 = 96.
OF is linear. It applies to each axis. Volume scales by OF cubed, so a 1.25 oversize factor means the green part has about 1.95 times the volume of the sintered part.
Backed by a growing body of independent research
Independent, peer-reviewed research on bound-metal filament sintering, including work on Filamet, continues to be published. New papers appear regularly, and reported applications span aerospace (for example thrusters), medical (radiation shielding) and thermal management (for example gyroid heat exchangers). We track this literature so our guidance keeps pace with it.
Frequently asked questions
What equipment do I need to sinter Filamet?
A standard open-atmosphere kiln, a crucible, refractory ballast and Sintering Carbon. The Sintering Carbon getter creates the reducing carbon monoxide environment inside the crucible.
What is the maximum sintering temperature for 316L, 17-4 PH, Inconel 718 and H13?
1232°C (2250°F).
What is the sintering temperature for copper Filamet?
1052°C (1925°F).
What does the Sintering Carbon layer do?
It reacts with trapped oxygen to form carbon monoxide, which reduces surface oxides on the metal particles and protects the part during the firing cycle.
How do I calculate how much larger to print my part?
Use OF = 1 / (1 − S), where S is the material's linear shrinkage as a fraction, and scale each axis by OF.
Ready to try it? Start with the Filamet metal filaments or the 316L stainless Filamet.