Tools:Laser
From Fab @ Home
I seem to recall an early rapid prototyping machine using a laser to solidify liquid plastic, then the model was lowered down into the plastic, one layer at a time. Has this been experimented with with the Fab@Home, or is it an outmoded method that would require too much time/effort to be truly practicable?
I will do some research, as it seems that the deposition tool/material is the real sticking point for the whole program. (At least to my eyes)
Stepper motor technology is mature, and well understood, as CNC machining is actually coming to the home market. Check out 5Bears, a guy who actually made his own CNC mill. But deposition, aye, there's the rub.
Great stuff here. Von Neumann, anyone?
JoshuaViktor@gmail.com
JoshuaViktor
Laser prototyping can enhance the capabilities in the rapid prototyping (RP) arena, by allowing a greater range of materials to be used. It can even facilitate the RP of metalic objects. The approach is to heat a layer of metallic powder to near melting point and to trace a laser over areas to be fused. The extra energy that the laser adds is just enough to melt the material and fuses it to the object. Once the layer has been fused a new layer of powder is laid down and the process is repeated.
Laser engraver for sintering?
Ran across this and thought perhaps it might be adaptable for laser sintering non-metals... It's a small computer driven laser engraver... If it can engrave something, it oughta be able to sinter it, right? If you could drive the mechanism directly, all you'd need to add would be vertical travel on the tray, and a roller/grader to push a new layer of powder over the workpiece... Or maybe just mount the laser on the fab case and a couple of mirrors on the axis travel mechanism to point the laser down where the syringe would be... Just random thoughts, this isn't really my area of expertise. Yet. Anyway, here's the link...
http://www.iehk.net/Products/IE300.html
Kent
It seems that the cheapest that you can get a second-hand CO2 laser in the 30-40W range is about $1000. Despite my initial feeling that "it's just a couple of of mirrors, some low pressure CO2 and a bulb" it seems that they are not easy to build (but I'm keeping an open mind, I feel that when your needs are specific there is usually a fudge/hack/shortcut that will get you there). Also delivering the beam from a CO2 laser is not easy. Unlike solid-state lasers, I don't think the price scales rapidly with power. I have been wondering how narrow we could focus a beam and how much power we would need. Clearly the rate of incoming energy / outgoing energy is a complicated thing, certainly not just a matter of x Watts per square meter. This all depends on grain size, material, focus, temperature etc. The only real solution is experimentation. But we need a plausible design to work with first. Otherwise using a focussed and screened bulb or array thereof may be more suited to home-building. Again such an array is not easily mounted and it would be necessary to come up with a clever system for beam delivery.
Casper
Here's what seems to be a very detailed FAQ on CO2 laser DYI -- http://www.repairfaq.org/sam/lasercc2.htm -- and from the looks of it, building a laser is more expensive than buying a used one ("save your money and look for a used laser" draws my attention). But isn't the chassis of the Model 1 laser-cut plastic? Wouldn't it be nice if the laser were a tool included in the basic design? I still like the idea of the self-assembling machine shop.
Michael
It ocours to me that you are all working too hard, and driving up the cost unnecessarily. A CO2 laser is expencive, and just provides heat. Why not just create an upgraded soldering iron? It still provides heat to a tiny area, you can controll resolution by changing points, and you will end up spending several thousand dollars less. The laser is higher quality, I will not dispute that, but the main objetive was to create a 3-D printer everyone could afford. Not everyone will be able to afford, or maintain the laser model.
Richard
You don't need to get too fussy with power rating using the laser as a fusing element. In the old days before laser printers were as common as dirt, we used electrostatic platemakers. The polymer toner was deposited on a charged plate, and touched-up by hand with a small magnet on a stick. Then the plate was carefully removed to a separate fuser, which was nothing more than a halogen bulb and a drum that rotated the plate under the bulb. Rotation speed controlled the fusing. This suggests two paths, at least: Your CO2 laser will have to move very quickly or it will vaporize the polymer; or use your positioning stage to deposit powder in the desired pattern and heat the entire area with a halogen bulb. Or synthesize the two and use a focusing device to project the heat of an IR or halogen bulb onto the powder in the desired pattern. I have worked with units that use fiber-optics to do this very trick, although the heat was in the solder/weld realm. So maybe the amateurs can cobble up a lower-power unit suitable for plastic. Think of all those powder-coating colors out there! Those with the budget can buy a commercial IR unit or laser and sinter metal.
MDIM
The laser to use would be a laser diode, and the power output doesn't need to be that high, A few watts would be sufficient (you want it focused to a small point for precision) and they are available in the $100 range. The way most of the commercial rapid prototypers I have seen work is by depositing a thin layer of a thermoplastic powder covering the whole surface inside a container and then only fusing it where the part is supposed to exist with a laser tool, when done you remove your part from the powder. One of the biggest advantages of this method is that the unfused powder supports the structure during fabrication so that overhangs etc can be built. I am working on a simple machine to produce uniformly atomized paraffin wax (and similar thermoplastics) which would significantly reduce material costs and allow easy recycling of parts. My eventual plan is to use the wax parts for investment metal casting for finished parts, but the recyclable nature of the wax parts will allow many more print/modify iterations to refine a design. The technique could potentially work with any thermoplastic material or even possibly some metals. The part of this design I haven't put much into is the tool to deposit a uniform thin layer of the powder. I have considered that a vacuum system might be ideal to help compress the powder slightly for more uniformity (i.e. a vacuum sucks air from the bottom of the container through a fine cloth filter or something similar to help up the powder density).
Oh, for the liquid deposition tools, has anyone experimented with a peristaltic pump mechanism ??
In fact you sometimes can get 30-50W laser diode bars on eBay. There are a couple on auction at ebay America at the moment (its the 22.09.09). I would have already bought one, but sadly the seller only sells and ships to america.
Erik
