Friday, 11 May 2012

Brain Storm session

Hello everyone,

This is the result of our first brainstorm session. This time, we investigate two possible options for 3D metal printing. The first option is Direct Metal Sintering, or should we say Localized Metal Melting, using a LASER. The second one is metal paste (also called metal clay) extrusion.

Localized Metal Melting
The idea is to design a machine that will be able to guide a LASER beam aimed at metal powder. The machine will also have to evenly spread metal powder over a bed.
  • The process is rather simple ( No complicated manipulations)
  • The process does not require post treatment other than cleaning, polishing and annealing if required.
  • The parts comes out to scale.
  • The porosity can be very low.
  • The time of processing can be quick with a powerful laser.
  • The support  is ensured by the powder and is easy to remove.
  • The machine can easily be transformed into a laser cutter.

  • High power laser is required. Simple calculations tells that a 10 to 20 watt laser would be required to process 1 mm³ of metal per second. 
  • High power laser cost a lot. Even the cheap laser diode option is not very cheap. One also need to get optics and mirrors.
  • Laser are dangerous. Especially the high power ones. And any security mechanism (filter glass, safety switches, googles...) are not strong enough against the curiosity of a DIY user. 
  • Melting metal can produce hazardous gases that need to be vented.
  • To reduce metal oxidation, the atmosphere in the machine should be controlled (vacuum, nitrogen, hydrogen, argon ...)
  • The machine need a lot of powder to fill the bed, even if the printed part is small. Also, not all the loose powder can be recuperated.
  • Due to the need of a bed and hermetic enclosure, this process cannot be integrated directly into an existing low cost open 3D printer.
Metal paste extrusion
This process is very similar to the fab@home system. A metal paste is placed in an extruder device, such as a motorized or pneumatic syringe. This paste is extruded on a building platform to the desired shape. The metal paste can be made from very fine metal powder mixed with water and other chemicals. Once the piece is completed, it is left to dry. Then the part is heated to around 500°C in an oxidizing atmosphere to burn the remaining chemicals. The part is then sintered in a reducing atmosphere to the temperature required for the used metal. These high temperature steps can be done very cheaply using a propane/butane torch or, more controlled using a kiln.

  • Existing open 3D printer can be easily used to print the part.
  • No significant waste of material. (Unless you break the part in the process)
  • Low setup cost possible. If using the 'propane/butane' torch method.
  • Porosity can be moderate. Useful to save on metal when the part does not require high strength.
  • Metal properties can be controlled using different temperature profiles in a kiln.
  • For good quality parts, a kiln is a must. This considerably raise the setup cost and time of the process.
  • The parts shrink from 10% to 30% according to many parameters (metal paste recipe, sintering time and temperature ...)
  • Many 'post printing' operations are required (drying, burning, sintering, finishing)
  • The sintering and burning process produce a lot of gases and should be vented.
  • A high temperature kiln is not a safe thing to have on a desk at home. 

As you can see, no solutions are perfect. Although the metal paste extrusion + propane torch sintering offer a very low cost alternative, anyone that look for anything better will be required to buy/build a 300 to 1200 USD kiln or a 2000-3000 USD laser machine. Both solution require a controlled atmosphere to prevent metal oxidation. This means having to find a nitrogen/argon gas bottle supplier or having to make an hydrogen generator.

Because of the danger and high cost of the laser concept, we preferred to turn to the metal extrusion method for now. The Laser option will probably be investigated further in the far future. Some tests are under way to check the ability to extrude metal paste from a syringe. We hope to be able to post some results soon. 


  1. Could you achieve a higher density and possibly not require a kiln by placing the 3d printer in a pressurized enclosure.

    1. I see two ways to "pressurize" the part. One way, usually used in sintering, is to apply pressure using a press inside a negative mold of the part. The pressure crushes the particles and forces the air between the particles out of the part. This can effectively increase the density of the part. However, in the case of a 3D printed part, one doesn't have a negative mold of the part and applying such pressure will most likely result in crushing the part.

      The other idea is to pressurize the whole enclosure. To be able to crush metal particles to the point of welding them together, we are talking of 10 to 100's of atmospheres (1000's of PSI). The other thing is that the pressurized fluid inside the chamber is very likely to infiltrate in the part by the fine channels between the grains thus balancing the pressure all around the grains. This results in no net force on the grains and therefore no forces to crush the grains against each other.

      I believe that the best way to get a full part is to soak the finished part with another lower melting point metal. Like a sponge, the spaces between the original metal particles will wick the molten metal, filling those spaces.

  2. Hi Etienne,

    I find your project super interesting - I am also looking for a safe and affordable method for 3D printing with metal and am curious to know if you have made any progress with your research.



  3. We have made some experiments with the metal paste extrusion process. But the problem that we found is that the paste must be liquid enough when extruded, but hard enough, when released, to hold it's shape. Sadly those two properties doesn't match. Copper powder mixed with water actually behaves the opposite way (like corn starch) it solidifies when pressed but liquify when released. This can be attenuated by adding a small amount of Carboxymethyl cellulose (a non toxic chemical normally use to thicken cream). The stuff burns when heated in the kiln. Putting too much trap the water inside the paste and the evaporating water make the structure grow a bit like popcorn.

    Right now the project is on standby since the original team dissolved. I joined a new maker space recently, so the project might get back on track soon.