This is the final episode of a three-part mini-series on making things with low-melting-temperature-alloy. The collection of things here form a hot material transfer system that can be used to extrude (sort of) molten metal or wax. This is inspired by earlier work done by Dr. Sells and Prof. Bowyer reprap.org/bin/view/Main/AutomaticDepositionOfMoltenAlloyInt oACastingChannelToCreateAVerySimple Electro-mechanicalComponent .
As usual, remember that low-melt alloys are toxic and hot enough to cause burns and fires, so only use this material if you are experienced in a lab environment. On the plus side, this system can also be used to make things out of wax, which is much safer to use, although you still have to watch out for burns and fires! Possible uses for a wax-handling system include: 1) automated wax casting; 2) use of wax as a support material.
If you omit the heaters, you can probably use the nozzle and syringe pump to deposit slurries or liquids.
The idea of operation is that a standard RepRap prints a layer of plastic (HDPE, ABS, etc). Then the toolheads are switched, and the metal/wax toolhead deposits molten material in the channels or cavities formed by the plastic. If necessary, the process can be repeated for constructing thicker and more complex parts.
We have had good success using the nozzle as a hand-held tool for transferring metal. For example, we used it to make this thing: thingiverse.com/thing:802 .
We have had somewhat less success using it when mounted to a RepRap, as seen in the pictures. The main problem is poor control of flow-rate (see photo of pattern on hot plate). With some modification (such as a smaller nozzle hole diameter) and tuning of parameters (feed rate, height of nozzle above plate, etc) it might work much better. We RepRapped a simple test piece, manually filled it with metal while it was still on the hotplate, then let it cool (see photo of widget with 25-cent piece). This yielded fairly good results, indicating that an automated system may be able to produce usable parts.
The main components of the system are
1) Heated cup - this is a heated reservoir that contains the molten work material.
2) Heated copper nozzle - the nozzle slurps up material from the cup, then moves to a desired location and deposits the material.
3) Syringe pump - a motor-driven syringe controls air flow in and out of the nozzle, which in turn causes the nozzle to slurp or deposit material.
4) Heated plate - this keeps the work hot to improve the flow of the heated material. It also melts the base of the deposited part, creating a good seal between part and plate, so that molten material does not leak under the part. In general, the heated plate seems to help avoid warping, but the downside is that the bottom of the part starts to ooze outwards after a while.