Low Temp Metal Extruder Design

I would like feedback on building an extruder for depositing low-temperature metal. This type of material melts in boiling water or even cooler. Fields Metal melts at 144 deg F and is not toxic. If a dual-extruder can be set up to dispense this low-temp metal and the typical plastic extrusion, overhangs and other de-couplings can be enabled without requiring cut-away and post-processing. It might even improve the surface quality of the resultant plastic part.

Removal of the metal merely requires heating the part back to 150 deg F and letting it drain out. I'm sure a device can be easily designed to heat and slowly spin the part to allow all material to flow out without distorting the plastic. The metal-material can then be re-used for the next part.

The challenges that I see are:
1. Re-molding the used material back into a shape that can be re-used by the machine (pellets? bars? ingot, then extrude it into wire?)
2. Managing/compensating for differing expansion rates of the plastic and metal
3. The nozzle design will have to be tuned to optimize the output for this material
4. The layer thickness may not be consistent between the metal and plastic
5. Outgassing of the metal may cause health issues despite it being non-toxic in solid form
6. The plastic may melt the adjacent metal, causing loss of integrity
7. Plastic extruded onto a surface of this low-temp material may immediately melt it and it would loose its connection, thereby sliding. (Software could be tuned to lift the nozzle above the surface to drop it onto that area instead of smearing it)

Any other issues to consider?
Has this been tried before?

--Joe

The build material needs to bond with the support material if you want to support anything other than simple bridges. I.e. it needs the same attributes as a bed surface. I doubt ABS will stick to low melting point metal.

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[www.hydraraptor.blogspot.com]

... 'Fields metal' IS toxic!

It contains Cadmium, what's highly toxic and should be avoided by any means for private use.

To reduce the toxicity and remain the 'low temp melting' there was creates 'Roses metal', where Cadmium was replaced by Bismut with rising the melting temperature to aroung 98°C ... but 50% lead is something, you should handle carefully too ...

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Viktor
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Aufruf zum Projekt "Müll-freie Meere" - [reprap.org] -- Deutsche Facebook-Gruppe - [www.facebook.com]

Call for the project "garbage-free seas" - [reprap.org]

I think you are confusing it with Wood's. Field's doesn't have cadmium or lead: [en.wikipedia.org]

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[www.hydraraptor.blogspot.com]

Chris, you're right!

When tinkered with the different LT-alloys some years ago I've got the feeling, Fields metal were nearly the same as Wood's.

With Galinstan it's another interesting aspect, as it stays fluid at room-temp and has a good adhesion to plastics (in difference to Mercury), so this could be an interesting field for exploring the adhesion to ABS or PLA ...

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Viktor
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Aufruf zum Projekt "Müll-freie Meere" - [reprap.org] -- Deutsche Facebook-Gruppe - [www.facebook.com]

Call for the project "garbage-free seas" - [reprap.org]

I understand that ABS will probably not conveniently adhere to the metal. But, could that first layer of ABS on the metal be applied using a different technique? Or, could a third extruder or other application mechanism be used to apply an interim coating that adheres to both materials? Sort of like a primer paint layer.

Another approach might be to increase the ABS extruder temp as high as possible at low speed to allow the material to flow more freely from the extruder while traversing the metal surface. Also, the metal surface might also be extruded with low density spacing in order to provide more ridges to catch the ABS.

This is starting to look like semiconductor manufacturing where the big challenge is in getting the dissimilar materials to adhere to each other.

Another idea: Formulate a new, more optimal LT metal or other substance. Any chemists out there? Can you formulate a "sticky" material that liquefies above room temp but below the temp where ABS or PLA softens, and can be precisely extruded?

At the moment I'm formulating standard machining wax for use in my CNC router projects. Paraffin and LDPE are the ingredients. That's going to be too hot for this purpose. But, there is probably another material that hits this temp window (what is the range?) and provides the surface characteristics for ABS and PLA adhesion at their melting points.

--Joe