Waxuum Version 1.0 by mattmoses

Last crawled date: 3 years ago

The waxuum is sort of a reverse-extruder. The idea is that a heated hollow needle is used to remove material from a block of wax in a controlled manner, analogous to conventional machining using an endmill. A vacuum pump* pulls the molten wax through the needle, after which it is deposited in a reservoir where it can be recycled. The wax part can then be used directly, or more likely it can be used as a pattern for a mold. Below is a basic overview of how the process might work in a well-developed system. See video of a simple test at http://www.youtube.com/watch?v=rnKD9oIzcnM .

A heated basin is filled with wax, which is then allowed to cool. This big block of wax forms the working material for our little setup.


A waxuum mounted where the extruder usually goes on your 3D printer carves a master pattern (including containment walls) out of the wax block.


Elastomer resin is poured directly into negative pattern in the wax block.


When the elastomer cures, it is peeled off the wax master and used as a mold to crank out large numbers of parts.

The wax master is remelted within its heated basin. The removed wax in the reservoir is added back. The basin is cooled, and the wax is ready to use again for a new master pattern.
ADVANTAGES

The wax is melted instead of cut, so high forces are not required at the tool-tip. The low force requirement means that the XYZ positioner can be much more flexible (and cheaper and easier-to-make) than is normally required for conventional machining. Unlike conventional machining, there is no need for chip removal.


In many cases the surface finish on parts is better than that on filament-extruded parts, due to the smoothing effect of the hot needle moving over the wax. There are also fewer warping, delamination, and anisotropy problems.

You get a mold instead of a part: casting from a pattern can produce parts at a much faster rate than printing. You also have a greater choice of materials (plastics, metals, ceramics, and wax can all be cast in silicone molds).
DISADVANTAGES

You get a mold instead of a part: there are several additional steps and materials, including the manual work of pouring resins. Sometimes you really want to just print your parts and go.


Limited geometry: unless you make multi-part molds with cores and such, you are limited to relatively simple geometry. Hollow and concave parts are difficult.

The waxuum is relatively unproven compared to the many filament extruder designs currently in use.
RESULTS
The test showed it was feasible to use a tool of this design to make wax patterns. The most important thing to consider seems to be optimizing heat transfer from the needle to the wax, while minimizing heat loss due to movement of cool air through the needle. The thin-walled brass tubing is just barely acceptable for this purpose. The next version will use a material with higher thermal conductivity, such as thick-walled copper tubing. The heater should probably be located outside of the case. Possibly two heaters should be used - one for the needle and one to keep the wax molten inside the case.
*Update March 6 2010: See this cool article on converting an aquarium pump to a vacuum pump http://garage-shoppe.com/wordpress/?p=109