How about a comprehensive search for a really good printer?
July 31, 2011 03:02PM
I'll add this to the wiki later. Where should I put it?
Let's go through absolutely all the options, starting from the top with all possible methods of heating, depositing materials etc. for a comprehensive search for better printers that can produce real world, useful goods from full strength materials.

Yes, biology might lead to molecular assemblers. But I'm not willing to wait that long, are you? There is still absolutely enormous potential for getting manufacturing capabilities into the hands of real people through a truly versatile printer that can make it easy to make real-world goods.

A good metal printer for instance could make practically anything a lathe, milling machine, forging press, casting, cold rolling mill, wire mill, etc. can, but be far cheaper than buying all those machines.

A good multimaterial printer (maybe three or four materials on a single workpiece, several microns accuracy, good surface finish, no stray particles, water soluble supports, would suffice?) could print motors, PCBs, sensors, gears, journal bearings, structural parts, screwdrivers, and combine them all into a single object in one print operation making robots, household appliances, light bulbs, stirling engines, welding guns, parts for industrial machinery, and who knows what else, certainly not anything, but it would be incredibly useful. It could nearly replace the functionality of a large amount of not just production equipment like lathes, but assembly equipment too.

Remember the methods may be combined if it were advantageous, with e.g. most of the heat deposited with one method and the rest deposited with a more precise method to acheive reasonable resolution. Sorting things in a comprehensive way will help with the attempt to avoid missing potential and promissing methods.

Also remember there are undoubtedly many options that include stuff that had no idea existed, like the plasma detection to determine melt pool temperature. Patents could be mined and also brainstorming from people who know physics would help a lot to fill in this listing of possibilities.

Where this is organized heirarchically - is a first level and -- is a second level in the heirarchy. Include things that are considered and rejected as well.

Heating methods to form a melt pool
Light (do calculations do find out what intensity will give what material build rate for what types of materials, then find out what the intensities the various sources can produce and if it is adequate. There may be something which can produce intense enough light which is likely to be cheaper/easier to make than a laser.)
-laser
-Thermally radiant: sun, halogen light, plasma, gas and/or other extremely hot objects maybe magnetically confined, like a peice of tungsten, molten, suspended in a vacuum and heated inductively... but the tungsten would evaporate though. Hm. Maybe there are materials less prone to evaporation.
-- melt probe, basically a tungsten halogen light bulb with a method to circulate the halogen to cool the glass, then highly transparent glass similar to fiber optic glass (maybe not needed), then the tungsten right up close to the surface of the glass. Could be used for bulk melting of material. Under a vacuum a melt probe could just be a piece of tungsten sans glass.

-synchrotron radiation?
-other?
-
- main issue is brightness and cost per watt of radiation, remember cost is up in the air and probably a lot lower than current market price if you can print the object.

Modulation or direction of light:
-galvo mirrors
-essentially a super bright projector i.e. a raster image bright enought to melt the material being printed, may have e.g. only one line of vertical resolution or similar
- mechanically moving the light source or a fiber optic head which emits the light (often used with fiber lasers on DMLS machines)
- move the workpiece instead of the light source
- materials which change refractive index when exposed to electric feild
- combo, could use motion for gross motion and galvo etc for fine control
- modulation of laser per se depends entirely on the type of laser usually and needs to built into it's design though an element could be added in between laser and workpiece to selectively reflect or absorb some light

Radio waves or microwaves
-probably not because the resolution would be low, although it could be used in combination with radiant heating maybe

Conductive
-A hot melt probe?
- a wire comes down, gets extremely hot by some means and promptly touches the surface, but this is sort of a convective method since it would melt.
- the bulk of the powder bed is often heated in laser sintering


Electrical direct ohmic
- have wire much like wire welding but with very small wire so can get decent resolution,

Electrical inductive
-magnetic induction (seems like it would be hard to get the precision, but maybe with multiple coils and areas where the feilds cancel out?)

Particle beam
-electron beam commonly used, currently known how to make low cost per watt of heating power to the melt pool:
-- magnetic fields produced around the melt pool might move the particle around a bit? Not much if any since it is low current
-- Might not be practical to print anything nonconductive due to the accumulation of charge that would occur, redistributing powder and causing deflection of the electron beam.
-- Requires high vacuum, but making good metal parts sort of requires vacuuum anyway maybe not as high. Oil diffusion pump is a low cost way to get high vacuum though so probably not a major problem.
-- stray electrons could be an issue? Make everything inside print chamber out of metal and ground it.
-- relatively easy to aim and modulate

-ion beam, probably no good because would deposit ions in the material

Friction
-see ultrasonic,
-Friction stir welding? Other rotating rod?

ultrasonics?
-ultrasonic welding, 2 pieces touch and friction welds them together, vibrating rod or wire touching surface?
-maybe just heating due to the expansion and compression of the material.

Convective (hot fluids)
-hot gas blown on the surface?
-hot plasma blown on surface
-hot liquid metal drizzled or sprayed on as droplets (there is a method of surface coating that uses sprayed droplets but apparently always leaves a porous bulk material)


chemical
-Small hydrogen flame or other flame, like welding
- decompostion of a chemical gas



Depositing the material
Gas
-vapor deposition (seems like it would be hard to get high res or accuracy, even with heating - or cooling maybe (by exposing to a cold object nearby so heat lost by radiation or convection or even conduction) some parts of the workpiece to deliberately increase the deposition rate while keeping it low in others, also seems limited to certain materials)


Liquid
-droplets
--heated droplets,
--electrospray, would be powder by the time it gets to the surface probably

Solid
Powder
-distribute in thin layer over the surface, then sinter
-- textured roller (common)
-- electrospray with molten metal
--powder gun with electrostatics, nozzle can be round or wide and flat, beam of charged powder particles could be steered maybe, (one problem maybe the different charge/mass ratio of the different particles, could be reduced in various ways like using sorted powder particles), ultrasonic atomization type thing to get the powder to jump off the surface of the reservoir bed if it is needed to overcome the particles sticking together, or maybe just charge it strongly enough it jumps off due to mutual repulsion (much like with electrospray).
--use a spinning impeller to simply throw the powder around in various ways, down a tube and onto the workpiece, or dispersed randomly over the surface, thrown at a plate so it spreads out into a sheet-like spray, then move the spray back and forth across the surface.

-fire directly into melt pool with powder gun of some sort (accuracy could be a problem) there is the LENS system, the company that makes it claims they can focus a particle stream entrained in gas (helium probably) to a 10 micron spot which is pretty good.

General points relating to powder:
Powder distribution could be messed up by nearby charges or magnetic feilds or gravity, vibration, etc. the uniformity of the layer and the thickness errors would add up without feedback and the ability to manipulate the powder bed after application

Manipulating powder after being deposited on surface:
-Intense pulse from laser or electron beam could cause rapid local heating at a spot, causing expansion, causing some powder to jump away from that area. Powder could be "herded" in that way maybe.
-magnetic feild from electron beam
-saw a paper once about moving objects around on a flat surface with a phased array of transducers, peizoceramic elements could be used and ultrasonic for finer control but will always be limited control presumably as stray vibrations will mess up powder distribution elsewhere. But it only has to be good in the are being sintered...
- ultrasonic or sonic lubrication could help to level the powder bed after application.
-electrical charges and electrostatics could be used in various ways, apply some charge in an area with an electron beam or use a charged probe to "herd" the powder, maybe combined with ultrasonic lubrication


very small Non spherical particles like powder:
-nasa preferred smal rods apparently for some reason instead of powder in an ebm for their use


Plasma:
-sputtering, heat some areas to prevent deposition while allowing in others (probably no good accuracy)


Removing powder
-The surface of the workpiece could be charged enough to get the powder to jump off by mutual repulsion. For nonconductive surfaces spraying it with an electron beam might be used to give the charge. But the residual charge may need to be removed to get a nice even powder layer layed down afterwards.

-Brushes etc. might be practical.

-Have the workpiece upside down or turn it upside down, then vibrate with ultrasonics etc. to remove any sticking powder.

-blow it or vacuum it off with gas
- attract neutral powder away from surface with electrostatics
- centrifugal force, probably not practical
-light pressure (photon pressure) ulikely to be practical but maybe
- other vibration
-- thermal expansion getting it to jump off, as metnioned above, just herd it over the edge of workpiece or to a disposal area


Feedback methods for the workpiece shape and powder layer thickness etc. on it.
In some cases they are specific to or dependent on specific printer approaches. Where this is the case, add some details in brackets after.

Shape (of workpiece, powder bed etc.):

-Scanning electon microscope, also other types of electron microscope (tunnelling, non scanning lensing type (like the first electron microscope? not common?) (under vacuum)

- cameras, normal cameras, pinhole cameras, light feild cameras, microlense array camera (microlense for each pixel eliminates the focus problem)
-- stereo cameras
-- the thing with the laser line generator and only a single camera to produce a 3d image (needs an xyz table)
- use a laser to scan the surface and a photodetectore of some type so it's like a scanning electron microscope but with light (good for laser sintering maybe) (main point is photosensor cheaper than camera)
- a single LED or laser, measuring resonant frequency to nearby objects by being part of a resonant circuit that resonates with the frequency corresponding to the optical path, then apply fourrier analysis not very accurate though. Have more than one emitter/reciever for 3d and maybe can interpolate or similar for higher res. Maybe too difficult computationally for any image area of reasonable size.

-radar presumed useless

-touch probe like AFM or with a much larger probe (too slow and disrupts the powder layer? could be used after powder is removed or along with powder bed manipulation methods)

-using resonant frequency measurement plus fourrier analysis and other computation to determine the shape of a workpiece surface probably only works practically with conductive workpiece, maybe not though, could work with sonics or ultrasonics, maybe multiple emitters/recievers makes computation easier. much the same as the led resonant circuit one and similar problems. Like an ultrasound microscope?

temperature of melt pool feedback:
-pyroelectric sensors, slow though? Maybe there are good ones available.
-electrical characteristics of a photodetector give information about the color of light striking it?
-Use refraction of diffraction to divide the wavelengths and them multiple photosensors, examples are a color camera, spectroscopes to get emission spectrum info
-saw a patent that used the plasma emitted by the melt pool heated by a laser, sensed by the current between 2 nearby electrodes to estimate melt pool temp (under vacuum I think) , mine patents more.
-ultrasonics to determine changes in propagation speed in the hot melt pool
-amount of laser light reflected from melt pool change with temp?
-modulate laser beam and listen to the sound produced
-what else can do with modulating the laser or electron beam? Modulate the beam while doing something else? Don't think of it as a steady state system.
-comprehensive information gathering with a complete model of the printer system and as much feedback as possible from the real printer for various parameters might reveal ways to infer the temperature of the melt pool etc.(see general) ( also dead-reckoning using computer simulation if there are in-between areas where sensing leaves blinds spots etc.)

-light reflected back from melt pool, and the shape of the light feild may reveal info about smoothness of melt pool etc. maybe smoother when molten.

- overall conductivity of path, how changes with time etc. (for electron beam heating based printer especially since already have vacuum and ebeam)

-modulate electron beam and watch the response, noises produced, net current flow, backscatter using the sensors for the SEM, etc. (for electron beam heating especially)

General:
-Remember the higher level possibility of combining all the characteristics of the system that can be manipulated - everything down to the current/voltage ratio of the electron beam in an electron beam printer and the ambient temperature of the print chamber for example - and all the things that can be sensed with whatever hardware is already being used or low cost additional hardware (for example, a microphone to detect vibrations that are being produced), then create a system that allows manipulation and sensing (for example, modulate the electron beam current and see what sort of vibrations are produced or form a graph of the voltage vs. current relationship. This information might be used to reveal information about the temperature of the melt pool. ) or even totally passive sensing to be combined with computation to infer what you want to know. In many cases there may be manipulatable values and easily sensible parameters or other information that we forget we can use.

Humans of course tend to be pretty good at doing this when using a machine manually because we pick up on clues. In this case we broaden our own sensing capabilities to include things like the voltage vs. current relationship of the electron beam, and do something similar. Knowing in detail how the printer works - idealy having a nearly complete computer simulation - would help a lot to interpret the signals available.

Another example of information from somewhere you might not expect, information from the SEM shape feedback mechanism might conceivably, for instance, give information about the melt pool temperature through the amount of electrons reflected from the melt pool, or the shape or smoothness of the pool surface or similar.

A genetic algorithm might help if it had a good computer simulation to work with. Digital prototyping tools in e.g. autocad may reduce the need for custom software for the simulation?


Level 2 in the design process hierarchy: Specific potential printers and points to consider:

- Selective inhibition sintering machine but with a brighter light source so it can sinter a wider range of materials practically. (question: the solid material must be more dense than the powder so presumably the powder layer top slowly get higher than the workpiece and may topple onto the workpiece? Never seen mention of this beign corrected for.) How good is the accuracy though?

-add full idea for metal printer

- Multimaterial printer with laser heating:
An array of lasers, say 5 by 5 or 10 by ten or whatever the photonics people indicate is appropriate, with galvo mirror(s) on each one. The focus is directed to the workpiece at a spot several microns across or whatever is a good melt pool size for the laser power that turns out to be convenient (or more for a co2 laser). The galvo mirrors in the adjacent array have scan areas that overlap slightly. The array is calibrated so they work in concert effectively. Their closeness to the surface allows high resolution without the need for insanely accurate or galvo mirrors and also reduces the demands on the flatness and shape of the optics a bit. That provides the precisely directed heating needed.

The lasers would be designed so that they can be produced with a machine which itself can be mostly printed.

The atmosphere is argon, like in the LENS system.

Then the capability to put a powder layer down is provided, probably textured roller as it's proven. Brownian motion helps to provide a uniform powder layer as the powder falls through the argon. Then you need some way to remove the powder highly effectively, like blowing it away with highly pressurized argon, maybe ultrasound to loosen any stuck particles, then vacuuming up the cloud of dust to reduce the mess and prevent it from settling elsewhere on the workpiece (metal and other dusts harmful if inhaled etc.). Apply a different powder. Repeat. Support structures as needed.

Bulk melting could be done with some other light source maybe, which was less precise than lasers but way cheaper per watt.

--It has to be able to print a vertical cliff face sort of thing somehow, might be a problem if powder falls off the rounded edge of the cliff face. Could be fired at the surface with enough force to allow slight sticking to the surface? Or maybe would stick naturally enough. Could be given a slight electric charge.
--Powder particles might remain on the workpiece and cause abrasion or otherwise shorten the life of bearings that were printed.
--Plastic next to metal plastic would burn at the melt pool temperature of the metal if you tried to add it after. As long as the high temperature material is printed first should be okay so maybe not a major problem. So during the print process the metal would protrude above the plastic layer at all times until the final layer of plastic.
--one of the materials would need to be a support material, ideally water soluble or similar for easy removal. (ideas anyone? Has to be something that can be sintered, not corrosive or too toxic either)

Multimaterial printing
- Lay powder down, print layer, then remove *all* the excess powder, lay a powder for a different material down, print, remove all excess, repeat. Needs supports since no surrounding powder bed.
- If could direct powder very carefully and precisely into the melt pool? Some stray powder probably inevitable though.

General


Printers seem almost invariably to use a single point to add material to i.e. a single melt pool. Having a large array of lasers or ebeams or whatever and therefore many melt pools might be better in a number of ways, allowing faster build times with finer detail and also eliminating the x and y axis motion requirements if galvo mirrors or similar were used. Might reduce the per watt cost of laser light too. If a large number of lasers were used the whole thing would be close enough to the print bed that you could eliminate some of the optical path components, but then would need to be able to lift it vertically as printing progressed which would be a source of innacuracy due to play in the mechanism but not much. An array that was high above the printer could use electrorefractive stuff instead of galvo mirrors and maybe be accurate enough without z axis motion.

In many cases ultrasonic lubrication may be useful to keep the powder moving through the reservoir or delivery channels or whatever.

- a lot of problems with controlling the temperature of the melt pool, if it is too high boiling or evaporation of the material results when under vacuum.
- in some cases the resolution vs. the size of the print bed may not be satisfactory because the angular resolution with which a laser or ebeam can be directed is too low. In that case, maybe using multiple printheads which are closer to the workpiece may be better.

- Speed is increased while adding material to the interior of the object by sacrificing accuracy etc. in many cases there are similar ways to improve performance greatly compared to e.g. what you would be stuck with if you used only a powder layer 4 microns deep and a melt pool 5 microns wide, which would give very fine detail but be very slow. But you only need detail at the surface of the object. If you print up a sort of wall where the outline of the object is that were say 40 microns high, the basin that is formed between the walls can be filled with powder and sintered relatively fast with a large melt pool.

- Other ways of increasing real world performance and reducing demands on e.g. laser modulation speed, by similarly recognizing the limitations on the sort of object we actually tend to want to print.


Laser cost:
One of the main problems with using the electron beam is that it would leave nonconductive objects charged, complicating powder deposition and beam aiming. Multimaterial printing therefore would probably be better done with light as the heat source, either laser or with a magnetically confined very hot plasma or other extremely bright light source. Lasers are proven to work already. The main problem is the cost per watt when purchased.

If the printer is sufficiently capable it is not unreasonable to expect it can be used to make e.g. a CO2 laser tube or a machine which can make a tube. It may be better to make an array of laser tubes each with their own galvo mirrors, to acheive the same net power output but without the difficulty of handling a lot of high intensity light with a single mirror/lense, like an array of 10 by 10 40 W tubes, each with their own galvo mirrors. You may have to calibrate them so they work together effectively, with adjacent printed areas being aligned. Since you could print most or all of the galvo mirrors the cost is probably not a major issue, though the first prototype might be expensive. You could simply use 2 tubes and galvo systems for the prototype, and scale up the size of the array later.

Another issue for the laser is the modulation of the laser, and the power supply, which is not all that cheap or easy. There will be a ton of waste heat too. Ultimately maybe the problem needs to be handed off to some photonics people and maybe they can find a way to produce a suitable system which can provide the light we need with a complete system that is low cost (after factoring in the ability to print it or a widget that can make it ourselves, so not talking about the market price cost).





Ebeam printer
Would it be possible to periodically remove some of the powder, so that the level of the powder bed remains slightly below that of the top surface being printed rather than above it? That could provide the benefits of the surrounding powder bed acting as a support structure, but also give the more desirable shiny finish rather than matte as particles from the surrouding bed would not stick to the outer surface as it were sintered.

Mutual repulsion of powder particles could maybe be used to get them to spray off the powder bed surface and transfer to another area.


Laser printer
Need a cheaper laser, that is the main thing, but direct laser sintering similarly suffers from matte finish due to the surrounding powder bed. A support material may be needed to avoid it, or like the metal printer reducing the level of the powder bed?

Examples of existing printers that can print in or have the potential to print in full strength materials:
[www.answers.com]
[www.answers.com]
The radiative selective inhibition sintering one, but only for low melting point materials
direct metal laser sintering, there are apparently quite a variety of such printers on offer in the marketplace which can print in full strength
ebeam printers that can print in full strength are similarly available from a variety of companies.

in a way the ability to print a support material is already a dual material printer?

Edited 1 time(s). Last edit at 07/31/2011 03:11PM by GreenAtol.
Re: How about a comprehensive search for a really good printer?
August 01, 2011 09:04PM
Please lurk more.
Re: How about a comprehensive search for a really good printer?
August 02, 2011 02:09PM
And what exactly is that supposed to mean? I am aware of things like reprapmetalica for instance if that is what you mean.
Re: How about a comprehensive search for a really good printer?
August 02, 2011 03:06PM
I think what germanicus is suggesting is that you hang out in the forum for a while, and get a feel for the place before posting. Take some time to gather your thoughts, and contribute where you can.

The sheer volume of words and topics in your post will almost certainly guarantee that no meaningful discussion will occur here. Instead, pick one of the topics that you've listed above, see if there is a particular sub-forum that is appropriate, and begin the discussion there.
Re: How about a comprehensive search for a really good printer?
August 02, 2011 06:41PM
Thank you jcabrer, those were my thoughts almost exactly. I was just being lazy.
Sorry, only registered users may post in this forum.

Click here to login