Metal FDM thread

martinprice2004 Wrote:
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> Hot Forging
>
> Another possible method of joining wire to your
> part would be not to melt but to form interatomic
> bonding. I used to work for a spark plug company
> and the ground electrodes on sparking plugs are
> not welded on but projection heated and forced
> together. The process is similar to a blacksmith
> forging two pieces of metal together, heated until
> soft then hammered or pressed together. The reason
> is that the ground electrode is a different metal
> than the threaded shell and often has a copper
> centre core so welding wouldn't work. The bond is
> very strong and when you slice the joint up for
> inspection you can see the two distinct parts and
> the joint line.
>
> Applying this to rapid prototyping, a wire pressed
> against a metal workpiece could be made to soften
> by passing a current between the two rather than
> sparking between a gap as in welding. It may be
> possible to do this and lay a wire on the part
> bonded to the surface and build your part up that
> way.
>
> Two questions that do arise are how do you start
> the first layer and how do you stop feeding the
> wire when moving to a separate area of the part.
>
> Perhaps JohnRPMs idea of the small metal balls may
> be more suitable for this proces than wire
> feeding.


Effectively a device to lay a track of wire and a spot welder to stick it to the layer below? I think this could produce a functional device!

However I think the difficulties in metal FDM are so large, that actually, something laser sintering based is actually simpler.

there is already a term for that technique - i can't remember what it is called though. Its like FDM metal forming, for some reason its too expensive.

Quote
konwiddak
Effectively a device to lay a track of wire and a spot welder to stick it to the layer below? I think this could produce a functional device!

Yes! A lot of folks seem to think that the metal has to melt.

The metal does not have to melt.

A process by which a wire feed is spot-welded at regular, close, spacing to a growing metal part seems entirely feasible. There was a great little DIY spot welder featured on hackaday recently. (C.L. Stong wrote about a similar machine almost 60 years ago in the Amateur Scientist*.)

It is not hard to imagine a wire-bonding toolhead made by combining a spoolhead and a simple spot welder. If you're worried about the choreography of this, imagine the spoolhead leading in front, with the spot welder able to steer behind as it follows. (Kind of like how the smoothing trowel follows the extruder in countour crafting).

Another possibility is to use some variant of diffusion welding. A small heater (at 50 to 70% of the working metal's melting temperature) could be used to heat a wire or strip, while mashing it onto a growing part. Depending on the metal, this may have to be done in an inert environment, and there would need to be some method for preparing the metal immediately prior to bonding (say by sanding) and a means for guiding the wire/strip around the part as it is placed.

Yet another variation (I believe VDX mentioned this in another thread) is to cut out metal layers and then press and bond a stack of layers. This requires a bigger press and higher forces than would bonding one tiny bit at a time, however.

Diffusion welding is called by other names, such as diffusion bonding. Somewhat related process are cold welding, vacuum welding, and ultrasonic welding. There is also ultrasonic consolidation, which involves a combination of ultrasonic strip welding and conventional machining.

Here are some videos:
Diffusion Bonding Process Illustrated
Ultrasonic Consolidation demonstration

* Two Devices for Electric Welding, One Using a Carbon Arc Torch and the Other a Rattrap
C.L. Stong, November 1966

How does a crystalline metal melt to itself if it isn't at or above melting temperature?

I humbly offer to you a quote from the wikipedia page on cold welding:

Quote
wikipedia
Cold or contact welding is a solid-state welding process in which joining takes place without fusion/heating at the interface of the two parts to be welded. Unlike in the fusion-welding processes, no liquid or molten phase is present in the joint.

Cold welding was first recognized as a general materials phenomenon in the 1940s. It was then discovered that two clean, flat surfaces of similar metal would strongly adhere if brought into contact under vacuum. Newly discovered micro- and nano-scale cold welding has already shown great potential in the latest nanofabrication processes.

People might also be interested in this paper. They do pressure welding of aluminum, copper, and nickel at room temperature:

Pressure Welding of Thin Sheet Metals: Experimental Investigations and Analytical Modeling
by Mahabunphachai et al
Journal of Manufacturing Science and Engineering, Aug 2009
link

Another search term to use when looking up these processes is "solid state bonding" or "solid state welding".

... I've done some experiments with a wire-bonder and wires of aluminium, gold and platinum.

The bonding was done with mechanical compression combined with moderate heating and ultrasonic 'activation' - the force was enough to squeeze the gold and aluminium wires to maybe 1/5 of the diameter!

Depending of the parameters the bonding was perfect or not sufficient, so the wire released with small pulling forces.

Bilding solid 3D-parts won't be practical with this methode, as the stacked body would be inhomogenous and the pressing force will either deform the lower layers or wouldn't be enough to bond.

Then I've changed to laser-welding/brazing, what's much better to control and resulted in perfect shapes and some more options for tweaking and combining of different materials and fabbing methodes ... but this is a complete different story

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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]

Quote

Bilding solid 3D-parts won't be practical with this methode

Well, I tried proposing something similar a few weeks ago* in the other other Metal Print thread but the idea was dismissed as impossible. So if the general consensus of the skeptics is changing from "not possible" to "not practical" then at least we are moving in the right direction!

But seriously, I think it may be possible to find the right set of materials and conditions so that temperature, pressure, deformation, and atmosphere were achievable, even with "kitchen equipment", no melting necessary.

And certainly the spot-welded-wire idea (which does not rely on diffusion bonding or anything fancy) seems very feasible to me.

At some point, of course, one has to wonder what advantages such a contraption would have over a conventional milling machine... But armchair engineering is fun, so what the heck.

*martinprice2004's post about using interatomic bonding predates this current discussion by a few years

I am humbled.

But - I offer this:
"if two metallic surfaces are brought together with only a few angstroms separation, there being 300 million angstroms to one centimetre, interaction between the free electrons and ionised atoms can occur. This will eliminate the potential barrier, allowing the electron cloud to become common. This, in turn, results in a bond and therefore a weld."

So, how can we overcome this ridiculous surface flatness/smoothness challenge, while repraps that are typically rougher than any plastic forming method ever... This make sense if you put together two sheets that are super smooth and just put pressure on the areas you want to bond, then remove the unwanted ares, then apply another sheet - a process so complex, you might as well CNC machine.

It turns out the heat is mainly to make the metal more ductile under pressure so it is flat.

Yes, if the idea is called impossible, then yes you are actually innovating! Awesome reframe isn't? In fact, that an entire field of "experts" will tell you something is impossible is a perfect reflection of their own natural barriers and group think - i.e., if they thought it were possible, they would have tried it, and the knowledge would have become part of the field, and it would not be "impossible..." we use this psychology all the time at Armanicreations.

... I've tried then to bond wires on top of previously bonded ones - this won't be possible with common weld-bonders, as the underlying wires didn't support the stiffness7rigidity for the bonding pressure ... but this was totally different with laser-brazing

What's 'possible', is changing the bonding process after the first 'layer' to weld the wires with a tweezer, that connects the wire to a 'loose' piece by compressing it horizontally ... but this is more a kind ow 'knitting', so a complete different process with a complex handling, what#s possible manually but really hard to realize for automatic 'knitting'

Spark-welding would be a real challenge too, when trying to bond more than 2 layers - the base current has to go through all the wires and connections, what could damage (burn) small structures with small effective conducting volume.

So for me the only viable methode is laser-welding --- or in combination with a paste-dispenser and wire-cutter: brazing with a laser or a common halogen spot-light with >100Watts on a spot of 3mm diameter (used for spot-welding, but most >5k€ in price )

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

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

There is a casio laser projector with 20 3 watt blue lasers inside... People De solder them and make deadly strong laser torches with them. I think it was $800 or so.

Edited 1 time(s). Last edit at 02/15/2013 11:16AM by Simba.

... they has 24 of blue 1W-diodes, that were powered with maybe 0.6 Watts max. -- but they aren't combined to a single spot (not possible with this setup), but to a maybe 10mm wide inhomogene beam.

I have some of this blue diodes for testing laser-engraving, 3D-scanning and light-curing ... and one of this casio-beamers with 6 of the diodes remaining, so it can project 'full colour', but not so bright as with all 24 in place ...

---

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

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

Just saw this thread in the LulzBot forum where someone is getting encouraging results printing with solder. It was on hackaday a a few weeks ago too so you might have seen it already.