Delta robot - Printing metal? - Calling all 3d print gurus!

[Xantos]

So..... I actually registered just for this post, so hi everyone ! Longtime hackaday fan from Denmark, who happens to work as a special effects guy... !

Anywho...I have a question for you guys, as I haven't delved into the murky waters of 3dprinting yet, but I was wondering....

Say you had the perfect heating element that could heat up to 1200 C or more continuously and stable, and that the heating element had a hole in the middle which could heat up thin aluminum wire running through.... would it be possible to just pressurize it, put a nozzle at the end, and mount it on the delta ? The main problem seems to be, how to deposit the materials quickly enough, but what if the molten aluminum was cooled instantaneously... would that work ?

And to those who didn't see the post about the delta robot....

http://hackaday.com/2012/07/13/3d-print ... he-concept

And hi again

[Colecago]

I really don't think you could do this. Pouring metal is dangerous and difficult and I don't think you could control a small stream for a pirinter, maybe, maybe, commercial level, but nothing close to hobby.

The best thing you could do, is print something out of plastic, pack it in sand, then pour your metal into it. The plastic will evaporate through the sand and metal will take its place.

Also, I think some printers print some type of metal powder and glue to make a somewhat metal product, then they do some other processes to infuse metal into it, see
http://www.ponoko.com/make-and-sell/sho ... less-steel

They pour aluminum at my hackerspace, and they say any moisture the metal will pop
http://www.youtube.com/watch?v=A796N_YZTm8

[Osgeld]

http://hackaday.com/2012/01/31/3d-print ... -in-metal/

[Xantos]

Hmmm okay I can see that this requires a bit more convincing...

The heating element I have in mind is the line of "crystal" igniters from http://www.crystaltechnica.com/.... They are pretty much magical and I use them in all our special effects project... You can get them in whatever voltage you vant, and it can stay heated / energized for at least 3 hours non-stop without any thermal damage to the igniter itself....

I am on good relations with these people and was wondering...What if you could get them to mold a heating element that was hollow ? That could enable the molten metal to be directly deposited where needed....

We are a company specializing in movie special effects, and work with real weapons, nitrogen systems, explosives and pyrotechnics almost daily... We do nothing but hack and make dangerous stuff all day long, so I am quite comfortable with the the safety aspects of above - Please see this in the kindest possible of ways - I am in no way downplaying safety !

IF you could make a system that was safe..... Would it be possible to say build a low-res 3d printer that just printed a continuous stream ? Let's not care about the resolution for now....

http://utwired.engr.utexas.edu/lff/symp ... Priest.pdf

All papers i'm reading right now says yes.... What if you mechanically pushed the aluminium through the heating element ?

[Techartisan]

Im not here to discourage....just want to point a few technical issues you may have to overcome to find success in your endeavor.

1. oxidation....youll need to build your printer in a controlled atmosphere (argon, helium, vacuum etc) or youll never get layers to bond to eachother.
2. layer to layer bonding....if layer 1 is sufficiently cooled layer two will not melt into it but rather solidify on top of it....so youll likely need some way to preheat the "deposition target"
3. The delta advantage is speed....however high speed requires low inertial mass or high drive force....Youll likely have to build a pretty beefy delta.

a different potential path of pursuit to consider...certainly not as cheap as your heating element but worth consideration....
what about using a delta platform to path a wirefed welder instead? While there are other models out there....Hobarts 190 is available with their spoolrunner wirefeed gun for under $900 online.

[k-ww]

what about usings "wood's metal" as the metal - melts around the boiling point of water?

I remember joke teaspoons made of it being sold - they would disolve in your coffee

[Xantos]

Good to see the discussion kicking off ! The thought of woods metal actually crossed my mind... While reading through the pdf I posted above, i noted there has been a lot of leg work done with low melting point metals..... I think a cheaper starting point could be solder, as it comes in the perfect form already....

I have done very little work with stuff like liquid nitrogen, but would it be possible to have the whole printerhead running in liquid nitrogen or just above it ? That would help with the initial problem of bonding ? Vacuum would probaly result in a lot nicer uniform structure..... That wouldn't be impossible to build something for a prototype.....

And Techartisan... The welding idea is good but was your idea to use it as deposit mechanism or just to have a Delta Welder ? (sounds kinda cool !)

If we go back to the nitride elements for a bit.... Would the idea of having a heated white-hot cartridge tip or reservoir which could then be fed some kind of wire - let's choose solder for now.... Would it work or am i missing something basic ? I'm thinking either pneumatic pressure pushing on the wire, controlled through a solenoid, or maybe simply pushing it through..... hmmmm.....

The delta robot sure is awesome though..... My plan regarding strength would be to initially build a direct copy from the blueprints, and then when makerslide and openrail becomes available, i'll start scaling it up.... We would probaly end up building a quite large one (thinking two meter rods) as the scale of being able to build something larger than a 2 liter coke bottle would be quite interesting.... Furthermore, what's to stop us from mounting our plasmacutter or a 3d scanner to it.... oooh... 3dprinter robot scanning 3d scans using the arms.... That would be the ultimate first gen replicator ! Just switch out the heads and you're ready to go.....

And wow.... Sorry for rambling

[Techartisan]

No liquid nitrogen would do the exact opposite of help layer adhesion. The issue isnt getting the hot material cold its getting the already deposited material hot enough that the new material being added causes a "skin melt" for bonding.

While Vacuum would be superior....a proper vacuum chamber and pump is a bit pricey to test a concept.....Argon or helium would be better choices....Helium youd just have to put the printer in an inverted box, run a tube, and crack open a balloon tank from any party store....Myself Id go argon....being heavier than air its really easy to contain, maintain, and control the atmosphere....and its terribly easy to comeby. Shielding would be a less significant issue in materials less prone to oxidation than aluminium.

The wire fed welder idea was being pitched as a form of deposition though it could serve the dual purpose of robotic welding.

Okay so assuming heating elements are your final choice of attempt....my take on how to go about it.....
The duty cycle on the nitride elements you cited appear insufficient for 3d printing.
you could perhaps machine a steel "pen" tip with a body wide enough to accommodate cartridge heaters.....
if you are only using solder than you can likely use a reprap style feed with a few modifications....all metal of course and you may need some spring tension to maintain proper pressure on the solder. The hobart spool runner is only a couple of hundred without the welding supply....so if you decide to go aluminum it might be worth hacking the spoolrunner gun as it already feeds aluminum wire from a spool....just a thought.

Now when it comes to eutectic alloys Id avoid woods metal....so much lead. There are plenty of lead free alloys to choose from.

Ultimately if the properties of these metals are acceptable to your intended applications....Id sooner print in plastic, refine and polish by hand, make a silicone mold, and cast as many of them as I could ever want. That is after all the great advantage to these alloys... their temperature is too low to require using sacrificial patterns and investment material...they can be cast repeatedly in rubber or silicone molds.

Ill not comment on the build detail of your delta as its still far to theoretical to have a known robustness requirements. Ive used a delta 3d scanner...one of these http://youtu.be/KA-oEvmXlfk?t=14s from the point of novel utilization of an existing structure (in the case of your printer doing double duty) its a great idea....but they are very slow in comparison to structured light or photogrametry....and they (deltas) are unsuitable for capturing some geometry.

I would say that a dlp photopolymer printer capable of directing the projector to a second scanning chamber using structured light would come closer to your Ultimate first gen replicator than what youve described....but that is just my take on the subject.

and as for your "rambling"...no need to apologize this is your thread....ramble on..

[martinmunk]

Warning: Off topic!

May i ask where ind Denmark you're from? And for whom you do special effects?

In 9'th grade i where an intern at Denmarks Radio for a few weeks doing special effects.

[Annirak]

A disclaimer: I think you should consider some of the costs involved. Heating metal to the point of plasticity takes a LOT of energy. The electrical costs and safety hazards involved in 3D printing metal may not be worth the effort. E.g. if it costs 3x the price to build up a metal piece than it costs to mill it down, why not just mill it? It might be simpler or cheaper to build a wax 3D printer and cast your metal parts with lost-wax casting.

With that out of the way, here are some thoughts:
Instead of cartridge heaters, have you considered using an inductive heater? You magnetically couple energy straight into the metal you're working and use its own resistance to heat it. This should be far more reliable than a cartridge heater. I know there are some electric forges out there, but the majority of that kind of equipment is gas-powered.

There are a few ways to deposit metal:

If you want to go for the strict reprap-like method, you'll need a method to heat the metal to the point of plasticity without allowing it to melt. Obviously, some metals will work better than others if you want them to stay plastic. E.g. you have to keep Aluminum under 660C but hot enough to deform easily, much like forging. As has been mentioned before, heating any metal will cause it to oxidize (Aluminum, in particular will actually burn before it melts), so you'll need an inert gas atmosphere. One way to fix layer adhesion would be to retrace prints with a TIG welding head. The electrical discharges would weld each layer to the previous one, but would cause some loss of resolution--essentially smudging each layer. How much smudging probably depends on how fast you move the head.

You could deposit small quantities of liquid metal. This would be very slow, since you can't allow the metal to pool enough for surface tension to take over. Again, an inert gas atmosphere is a requirement.

You could deposit metal powder and sinter it. You might be able to do this with a TIG welding head, but you probably need a laser to be able to control the depth. However, I wouldn't recommend taking the laser route unless you've taken laser safety training and are willing to spend a lot of money on laser equipment.

You could use a modified MIG welder. This could take two forms: first, you could set the welder so that it spatters metal onto your substrate. Or, you could turn it up high enough to get continuous ion transfer. Either way, your construction material is welding wire.