We have hijacked the thread on mother to daughter, daughter to granddaughter, etc loss of printing accuracy to pick up a much more interesting discussion on how current reprap can evolve to make parts other than thermoplastics.
> Slightly off topic has anyone discussed the
> fundamental stumbling block of extruding a part
> that will stand the temperature of extruding the
> same material. How are we ever going to make an
> extrusion nozzle?!
Well, single-material isn't a design goal. So - just extrude something that isn't a thermoplastic.
... that should be easy: - print a dispenser and then dispense ceramic slurry ... was mentioned several times spinning smiley sticking its tongue out
Viktor
We are also looking at adding milling and other subtractive technologies. But I guess then we end up with the problem of making new drill/mill bits.
As for harder materials from softer ones, many tools start off soft and become hardened by a secondary process, like tempering, case hardening, peening, work hardening. It may mean that our machines become complicated enough to heat treat and surface harden parts, and possibly cast parts as well. As mentioned above, ceramics can be extruded as a paste, baked until solid, filled with molten metal, then opened to release the part. Even metal can be melted by using electric current to localize the part that melts. MIG welding melts steel wire as it exits a copper tip, even though copper melts at a lower temperature than steel.
With the full range of techniques, additive and subtractive, thermoplastics, ceramics, and molten metal, tempering and surface hardening, it should be possible to make all the mechanical parts. Remember, a black smith shop is a self-replicating fabricator.
Mike
Foundry crucibles are sometimes made of a material with a material of a lower melting point than it's contents. They use water cooled plumbing to wick heat away from the crucible. Same concept as lighting a paper cup on fire.
We are also looking at adding milling and other subtractive technologies. But I guess then we end up with the problem of making new drill/mill bits.
Step 1: Bolt a dremel or large router on the machine.
Step 2: Worry about fabricating vitamins. smiling smiley
Ditto with laser tubes or laser diodes:
[reprap.org]
I'm not saying that I don't want us to design a cnc endmill grinder, (hypothetical) sodium silicate cement or epoxy-granite flycutter with carbide inserts, or printable diode laser in the wiki. grinning smiley
.. the most promising omnipotent technology is laser-sintering - here you haven't mechanical forces, so your mechanics can be lightweight, but have to be really accurate.
And you can make any shape from every material you can melt/sinter with the laser.
The only problem is the fabrication of the laser source, here only CO2-tubes with extrenal mirrors and a high-volt PS are in the DIY-range, all other systems need high precise/cleanroom-equipment ...
Viktor
As you have all suggested FDM would seem to require other processes like milling or paste extrusion in order to make a machine capable of total self replication. This makes the machine more and more complex and raises ever increasing difficulties (The technology pyramid is the wrong way up!).
I agree with Viktor that laser sintering would seem to be an easier route. I am surprised that this technology doesn't recieve much more attention than FDM. Perhaps this is natural as the Reprap Machine design has pointed people down the FDM route. The laser is a problem, but perhaps focussed light may be a possibility to overcome this.
A guiding philosophy of the reprap project was to make the machine capable of bieng built in a third world country, growing the raw materials. Dremels and milling cutters would be quite hard to source. Heat treatment of metals would however be possible in a simple forge.
By the way MIG welding doesn't melt metal wire near the copper tip but some distance away from the tip. This is also why TIG welding has to use a Tungsten tip.
... beside SLS there is another sintering technique called "Selective Mask-Sintering" - here you rise your powder-bed as with SLS but then you place an optical mask on the powder-surface and activate an areal IR-heater above the mask, so only the powder not covered by the mask melts.
I would atach the PDF-file, but it's 3MB, so i cant upload ... here the (maybe temporary) link to the (German) PDF ...
This masks can be made with the same process as in Skeinforge - essentially you can use the created SVG-file of the cuttings directly without any change spinning smiley sticking its tongue out
Viktor
There's another variation on the mask, where you use a print head to spray water or a cooling mix then bring a heater over the bed to fuse other areas.
... not water, it's called "Inhibition Sintering" and you print with a salt-water mixture - the water evaporates, the salt remains and "inhibits" the melting/sintering of the 'contaminated' area.
When heating the surface with an IR-heater, the clean powder melts and the salt crystals prevent the fusing in the printed lines ...
Viktor
I didn't understand how the mask is made? Does it mean that you can only make what are essentially extruded parts or do you have to remake the mask every layer as the section changes? What is the mask made out of.
Is it possible to focus infra red heat to a beam or through a small hole slot? Effectively producing a poor mans laser?
I did like the look of this process where the heat seems to be bounced off a reflective printed mask.
Sintermask
I liked this video also
Inhibition sintering video
These technologies to me seem to have much more going for them than FDM. Particularly the way they overcome the support material issue, have natural higher resolution and also would tend to shorten the time to produce parts.
Its finding a good source of black plastic powder that seems to be the first hurdle.
That inhibition sintering sounds good, you could print salt water using a conventional inkjet head without issue.
What about a reflective powder and you overprint a dark ink to change the infra red absortion where you need it. Or vica versa
Another thing that puts me off lasers is the inherent danger of losing ones eyesight whilst experimenting...am i just a coward!
.. inkjet printimg and areal sintering is much faster than fabbing with FDM or laserspot, but you are limited by possible materials and final stability.
Masks are made from heatresistant and/or reflective material and you have to cut every changing layer or combine single elements as in oldstyle Gerber photoplotters.
With laser you have much higher temperatures, so you can melt/fuse any material to solid, what's much more interesting with ceramics, metals and hard-alloys.
So you have to select your methode corresponding for your needs - my needs point me to micromechanical structures made fom resins, ceramics and metals ... sometimes even combined in interfusing 3D-structures spinning smiley sticking its tongue out
Viktor
Martin,
The sintering process, whether laser, mask, or inhibition, does have the advantage of support material so that any shape can be made. But it also has the problem of big piles of left over sintering material that must be cleaned out of the work area before the next piece can be started. This makes any degree of automation beyond single parts difficult, and the process in general rather messy. The inhibition process also wasted a great deal of material by fusing almost all of the negative space, too. This increases per-part costs. And the mask based sintering is fast, but requires a huge number of distinct masks to make a thick part. It is not clear if the masks are easy to generate and the material reusable. FDM and laser spot sintering are slower, but less wasteful.
Mike
... by the way - if you already have a cutting/sintering laser, you can combine the mask-sintering method by applying an IR-heater and cutting the masks with the laser.
But there are some really hard to realize preconditions: - for the masks you need a material which you can cut with the laser, that withstand the heat from the IR-source and is cheap enough for highcount masks per part.
For plastic powder you can use paper (dark coloured with diode- or SS-laser, any colour with CO2-lasers), as the ignition temperature of paper is much higher than melting temperature sof most plastics ... but for materials with higher melting temperatures you need 'green' ceramic sheets, what's really expensive (i have some blue-coloured samples from Dupont Chemical with 0.1 to 0.5mm thickness)
Viktor
ocket_scientist Wrote:
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> ...Remember, a black smith shop is a self-replicating fabricator.
That brings up a good question: Is the goal of this project to make a rapid prototyping machine that a human can use to make another rapid prototyping machine? That seems to be what the RepRap project is aiming for. I wasn't sure if articulated robot arms for assembly and so on were part of its scope.
... i think the idea behind RepRap was to create a system capable of building most (if not all) of its own parts with an affordable cost, so anyone interested in the technique could participate.
The idea is not unique (most CNC-routers can do the same), but it was based around FDM with DIY-plastic (PLA) for reducing the basic costs and an ecologic meaning ... but you need some 'vitamines' as electronics, motors, cables and bearings anyhow ...
With time there will (and have) evolved and forked other designs and technologies, but this is not a problem and will help to find better optimized solutions grinning smiley
Viktor
... i think the idea behind RepRap was to create a system capable of building most (if not all) of its own parts with an affordable cost, so anyone interested in the technique could participate.
The idea is not unique (most CNC-routers can do the same), but it was based around FDM with DIY-plastic (PLA) for reducing the basic costs and an ecologic meaning ... but you need some 'vitamines' as electronics, motors, cables and bearings anyhow ...
With time there will (and have) evolved and forked other designs and technologies, but this is not a problem and will help to find better optimized solutions grinning smiley
Viktor
That brings up a good question: Is the goal of this project to make a rapid prototyping machine that a human can use to make another rapid prototyping machine? That seems to be what the RepRap project is aiming for. I wasn't sure if articulated robot arms for assembly and so on were part of its scope.
They are. Everything is. grinning smiley
Self-assembly and daughter-assembly are separate and difficult challenges, and folk chose to go after machine-fabricated and human-assembled to begin with.
This is a good place to discuss it.
[[url=http://forums.reprap.org/read.php?132,30757,43136#msg-43136]forums.reprap.org[/url]]
VDX mentioned that he had done some work on a related subject, and might be up to putting it in the wiki.
Philosophically, RepRap is a guerrilla movement as opposed to a tightly choreographed formal army.
If you tack up a robot arm, a robot arm is part of RepRap.
If you tack up a vase, smiling smiley, a vase is part of RepRap:
[[url=http://reprap.org/wiki/Untested_vase]reprap.org[/url]]
And so on.
Remember that you are in charge, and decide what is the most fun to work on.
-Sebastien, RepRap.org librarian.
Hi Sebastien,
> VDX mentioned that he had done some work on a
> related subject, and might be up to putting it in
> the wiki.
... i'm really busy now, but
here is a related discussion and atached images with some of my then developed and used tools ... mabe helpfull?
Viktor
did think inhibition sintering sounds a little wasteful, which is why I suggested a possible inverted process whereby the part material is doped with something to enable it to take more heat energy. I am still a little curious as to why salt is needed rather than the water being enough to take energy from the surface for evaporation.
If you could avoid using salt solution and use water or maybe a magnetic medium there may be a way to dry or separate support powder for reuse.
Masking also sounds a little wasteful, but is there a way to use an LCD panel or something. A laptop screen would be a relatively cheap source of a reprap sized panel. I know there is electro photo reactive glass used in buildings to reflect heat, I was wondering if there is anything similar.
I still think this inhibition sintering sounds the forerunner so far for plastic parts, but I can see the limitations for metals. In the video I posted above the machine actually looks like something that a reprap enthusiast would have made. (I don't mean that in a negative way). Much of the technology used is available to the home builder.
... the water disperses nearly immediately in the powder and evaporates quickly if heated, so it's not enough for sintering-inhibition ... the salt crystalizes out, so a thin coating of nano-salt-crystals separates the wetted particles, even if they melt under the IR-heater ...
An LCD-mask is only usefull if the LCD isn't affected by the heat from the IR-source and don't block the radiation on the powdersurface - here i know only UV-cured epoxy what's masked with a LCD ...
Viktor
VDX Wrote:
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> ...UV-cured epoxy [is] masked with a LCD
It occurred to me the other day that one might be able to replace the OEM fluorescent bulbs in a standard LCD HDTV with tanning booth UV fluorescent bulbs for this purpose. Has this idea come up before at all?
A solution to the temperature sensitivity of an LCD panel (they are very temperature sensitive. Some LCD strips are printed with calibrated temperatures to be used as a stick on temperature gauge!) you can switch to a different current display technology, DLP. The micro mirrors of a digital light pipe, or more accurately a multi-mirror device, can withstand much more intense light and heat, and still spread the heat over the surface in a controlled way. With the very short time constants for changing the mirrors from on to off or back again, they could even be sliding down the work material shining a shifting pattern constantly to only illuminate the material to be sintered. (Hey, is this a patentable idea? If the but companies make them, I want my share!) With the ability to illuminate most or all of the work surface at once, this would be a very fast buildup technique. Current DLP panels are less than an inch across, in the 1 to 1.5cm range, so optics would still be needed to spread the light (heat) around to make a larger work area. And as for whether or not they can stand the heat, just consider how hot the light must be for a 10,000 lumen projector when the light intended to fill a 12 square meter screen is all focused onto one (or three) 2 square cm panels.
This idea sounds so good I am going to start a separate thread, which we should have done long ago for the methods beyond thermoplastic FDM 3D printing
Mike