3D Printing process: Selective Powder Deposition (SPD)
Build volume of Model C: about 279x274x110 mm
Build volume of Model G: about 610x610x310 mm
Pourer diameter: 0.9 mm and 1.9 mm
Layer height: 0.1 to 1 mm (user configurable in GUI)
Min width of a detail: one pourer diameter
Min height of a detail: one layer height
Model C cost: $8,000 + shipping
Model G cost: $35,000 + shipping
The printer itself is material agnostic, and can pour any powder that flows through a small hole. SPD can work with any metal combinations where the infill metal has lower melting temperature than the powder and the final alloy. Though, different metals require different baking temperatures and atmospheres.
Carbon oxide atmosphere is easy to produce by placing coke into the crucible, but it adversely affects the infill process and the resulting alloy. Hydrogen-argon atmosphere is harder to produce, but it would work much better. The Ellingham Diagram shows that non-reactive metals, such as iron, copper, nickel, tin, lead, bismuth, molybdenum, cobalt, tungsten, palladium, cadmium, silver, gold, and platinum are easy to reduce, even with a relatively wet hydrogen. Other metals would require a dry hydrogen.
Also, for metals with low melting temperature, such as tin, lead, and bismuth - a soldering paste or brazing flux can be used.
SPD can be used to print not just metals, but also glass, ceramics, and composites. For glass and glass-ceramic composites, a recycled glass can be used, which is very cheap. We have also looked into infilling ceramic powders with aluminum and other metals, and found many good artiles which confirm the feasibility of this method and provide process parameters. Though more research is needed.
When using the infill method - there is no shrinkage, because the metal powder is not sintered, but infused with infill metal. There is a very small distortion due to uneven thermal expansion of different powders. But overall, the size and shape are well preserved.
When using the sintering - there is shrinkage and consequently shape distortion. But this method is still useful in some cases. For example when printing glass, if the precision is not required. The shrinkage can be controlled by choosing baking temperature, and by mixing non-meltable particles, such as quartz, aka sand, into the glass powder.
SPD itself doesn't reduce the strength in any way. The microstructure of the printed parts is similar to the cast ones. The strength of the printed object is determined by the metal composition, cooling rate, and the atmosphere. Note that carbon oxide atmosphere deposits soot onto the powder, which interferes with the infill process, and increases carbon content in the print. So, for the best results, a hydrogen-argon atmosphere is recommended.
Print time very much depends on the size and complexity of the object. Rough average would be about 24 hours.
Yes. After the printer fills the crucible with the powders - you need to add the infill metal, and bake it in a kiln or furnace.
The baking temperature must be above the melting temperature of the infill metal, but below the melting temperature of the build powder and the final alloy.
The hold time should be sufficient for the heat to get to the middle of the crucible and melt the infill metal. The minimum hold time depends on the size and thermal conductivity of the crucible, the mass, and the difference between the melting temperature of the infill metal and the temperature in the kiln. Usually 2 or 3 hours is sufficient.
For copper infill metal, your kiln should be able to go above the copper melting temperature, which is 1084°C, so most pottery kilns would work. A kiln with a programmable digital controller is preferred, because it can be programmed to warm up slowly, to avoid cracking the crucible. A new pottery kiln might cost you about $1000. A used one you might find for a few hundred dollars on Craig's List, if you look for a while. Hydrogen furnaces are more expensive, but they would provide much better results and would work for a larger variety of metals.
You can buy the consumables from 3rd parties. In general, for the powder to flow good, the hole size should be at least 5-10 times larger than the particle size. So, for example, 200 microns powder would flow well thru 2 mm hole (or larger). And 40 microns powder would flow well thru 0.5 mm hole (or larger). Powders smaller than 40 microns are not recommended, because they tend to cake, and also they get airborne easier, which would present a health hazard. So, the ideal particle size is 100 microns for the 0.9 mm hole, and 200 microns for the 1.9 mm hole. The powders and the infill metal shouldn't have too many impurities. For example, reactive metals, especially in the powder, might oxidize and prevent infilling. Crucibles for baking with coke should be non-porous and have a tight lid. Crucibles for baking with a hydrogen-argon atmosphere can be porous and don't need any lid. Most of the things you can buy from atomwell.com
Infill metals you can buy from MetalShipper and RotoMetals.
Stainless steel crucibles, sand, and iron powder from TriDPrinting.com.