Fusionreprap

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Fusion Reprap

Release status: Experimental

Fusionreprap.jpeg
Description
Metal Printing Reprap
License
GPL
Author
Contributors
Based-on
Categories
CAD Models
External Link


The FusionReprap

The proposed Fusion Reprap uses common metals to fabricate objects. The printer relies on fusion welds (also called forge welds) to deposit layers of metal atop one another. To facilitate this welding process, the printed object is fabricated inside a vacuum.

The vacuum is achievable with an amateur set-up. A high vacuum is not necessary for this process. Currently, the theory is that good parts in aluminium should be able to be produced in a chamber at equal to or less than 30 Torr. The necessity is for nitrogen, water, and oxygen to be sufficiently rare in the environment of the chamber. Removing oxidation from the metal is also necessary for high quality welding. Melting the metal prior to welding should remove (or at least mobilize) oxidation.

Materials

Aluminum is the test metal. Other materials could become feasible in time.

Construction

The set-up consists of:

  • An amateur-quality vacuum chamber (complete with pump, gauge, and tubing).
  • A smaller version of a Rostock robot
  • A heater for the extruder capable of melting aluminum.
  • A wire feed system for the extruder (which may include a bubbler for liquid metal).
  • Typical reprap electronics and software (like the Sanguinololu).
  • Modifications of various materials and designs of existing systems (like the Rostock and an extruder) to handle high temperature, low pressure, and fit in a small area.
  • A heated Build Plate.
  • The Bubbler, a molten metal purification/feeding system.

Vacuum Chamber

The current theory is using two giant canning pressure cookers, open-side to open-side, with a sheet of thick mylar in between them, allowing us to pump the air out, and run cabling into the chamber.

Modified Rostock

Other than the modifications required for fitting in the limited space, the folowing modifications are going to be made:

  • Screw drives instead of belts. this does not need to go fast.
  • Tiny nozzle. metal parts that are low precision will likely not be in high demand.

Build Plate

The build plate will be nichrome wire in direct contact with a steel sheet. atop that plate will be a sheet of aluminium (for the item to stick to).

The build plate will use ceramic insulation to connect to the bottom bed of the printer. It will also have the option of liquid cooling (through a high heat resistance subject), to pull the heat away from the printed object.

The Bubbler

Metalbubblersketch.JPG

Currently, a bubbler is under consideration for providing metal to the wire feed system. Printing large objects requires a large volume of metal. Stocking the chamber with an adequate amount of metal in the form of wire becomes less practice the larger the printed object becomes. For small prints, a small spool of wire provides sufficient raw material. For large prints, an adequately sized spool of wire may not or cannot fit in the chamber. Restocking the printer during a print requires opening the chamber. This exposure will oxidize the metal already printed, and present difficulties to printing new layers. A metal bubbler provides a solution to these problems.

The bubbler system works by continuously casting aluminum from an outside reservoir of liquid aluminum. The outside reservoir heats aluminum to a liquid state. A narrow tube (viz. a ceramic straw) is lowered into the reservoir, so that the tip is beneath the level of the liquid. The tube is open to the vacuum within the chamber. Liquid metal is pushed into the tube by atmospheric pressure, similar to a barometer. As the liquid ascends the tube, it cools and solidifies. The cooled aluminum forms a plug, preventing more liquid from rising. This plug occurs where atmospheric pressure and the weight of the liquid are close to equilibrium. (Finding this point is a matter of fine calculation and experimentation.) A motor mechanically pulls the solid aluminum from the column. The pulled metal is pushed into a wire guide (such as a bicycle brake cable). The wire is then received on the other end of the wire guide, melted, and extruded. By keeping the tube narrow, large demands on cooling can be avoided. Simply put, we're only concerned with a small amount of aluminum. A passive system could provide all the cooling necessary for creating thin, solid aluminum wire from a molten pool.

The advantage of the bubbler system is providing--ideally--all the aluminum necessary for a print without restocking the interior of the vacuum chamber. However, stocking the interior with a spool of wire should be very simple.

Cooling

For cooling the motors (and possibly the build plate), we're going to use parts from a PC watercooling system, with mineral oil running through them. this is going to be an open system, with mineral oil pooling on the bottom of the chamber. to allow the heat to escape, the chamber's bottom few inches will be submerged in water, that will be cooled outside of the chamber.

Material Delivery

The extruder is going to be near the top of the printer, delivering material down a tube consisting of a steel coil (bicycle brake cable?). to heat the material, we will be using nichrome wire, wrapped around the carrying tube. a final heating chamber(forge) will be carried on the carriage of the printer.

Developers