Concept multimaterial laser printer

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After doing a lot of reading for the metal deposition head, there are a number of approaches that are interesting and could be used in conjuction with the multimaterial printer. But it is more clear than ever that laser deposition from a sheer performance (in terms of net capability for parts, excluding cost/performance ratio) standpoint, with a very small melt pool under argon is a highly interesting and capable approach.

Purpose

The ultimate goal here is basically to move towareds getting meaningful production capacity back in to the hands of real people. A start on that is to reduce the cost of the smallest indivisible unit of production means. For example a lathe is wonderful and might cost $10,000 but without some other equipment it is useless WRT making practical machines and goods. A multimaterial printer that could put a wide range of high performance materials into the right voxels would be able to produce useful goods right off the bat, and with the addition of a small amount more equipment what you can make rises even more sharply. The cost may be expected to be a small fraction of say a fab lab (which is $60k -- see RepLab) and also be able to make a wider range of important stuff with less manual intervention, though certainly the first generation machines at least are likely to be a lot slower per dollar of equipment.

This would also be a boon to innovation and open source hardware.

Overview

One problem is that with the multi head approach, you still cannot really print a bearing or other parts in situ. You still need to assemble them later. In the interest of achieving "type 3" replication as opposed to type 2 (complete automation vs. large labor input to assemble parts) I turn to thinking about other approaches.

So in considering what I might at this point consider the most interesting approach for a multimaterial printer, I'm of course not sure and this is all just thinking at this point. There are a lot of different ways and it's not really possible to tell at this stage which would turn out to be better, but this is my current favorite:

  • under argon, atmospheric
  • An array of lasers which can be modulated at suitably high speed. The power of each laser is whatever gives the degree of precision (with good melt pool control rather than trying to cram high build rates per melt pool in just have larger number of lower power pools) and resolution required (yet to be determined, see todo list). The resolution is determined largely by melt pool size. The smaller the melt pool the less thermal distortion too. But the smaller the melt pool, the smaller the laser which usually means higher cost per watt (at these power levels, which is a couple watts). More research and calculation is needed to determine the build rate for various laser powers, melt pools sizes and materials to make a good decision. Basically smaller melt pool means higher ratio of heat power lost to the bulk of the object vs. gone in to heating the new material so slower build rate per watt. So some compromises there.
  • array mounted on xyz bot
  • Deposit powder, heat to weld in place then vacuum it up, then really scrub or vibrate or gas-blast the workpiece to get the last bits of powder off. Then add a different powder for the other material.
    • shoudl include a plastic (probably have to be low viscosity so the particles will consolidate well without any pressure), a durable ceramic like silicon carbide, a support material so leaders can be printed (water soluble ceramic sounds good), and metal, maybe more than one metal - copper and steel.
  • proof of concept. Maybe only one laser but of the size that was determined appropriate for the laser array. Probably very small. The size of a hand or fist? Makes the high precision desired easier and cheaper - we know we can do it at a larger size for the right price so no need to make it large.
  • Hydrostatic bearings, maybe with ferrofluid. Air (argon) or pumped fluid if needed - woudl be expensive for the prototype but can tehmselves be printed so no problem for next gen.
  • extremely high precision/accuracy. Probably use encoders on linear bearings, maybe optical. could be a modified digital readout micrometer? Is no force so that helps.
    • hydrodynamic bearings avoid stiction and normal friction, only highly predicable fluid forces.
    • there must be hydrodynamic leadscrew mechanisms? The same principle can be applied easily and it would provide the desired precision. Otherwise ball screw maybe biassed.
    • Somebody in the forum mentioned that they were part of a project to do a positioning stage that got to 10 nm for microfabrication at low cost. Talk to them about precision positioning on a budget. As long as the encoders are fast enough and the laser can be modulated, the main thing is to get some force on the laser head that is stable and predictable and smooth.
    • maybe use the SEM but with light thing to image the object to some degree. Modulate the laser intensity down, move the laser up so that it is focussed right to a point on the print plane, and scan.
  • Would be extremely slow with only one laser most likely, but proof of concept. If laser moves at 1 meter per second and has a 10 micron melt pool and 2 micron layer thickness then 20 mil cubic microns per second, 1 cc is 10,000^3 or 10^12 cubic microns, so 2/10^6 CC per second, (3.6*2)/10^3 cc per hour for the outline of the boundaries between material/the outer boundary. However the bulk areas could be done much faster as no precision is needed. 100 micron melt pool, 20 micron layer thickness and 5 m/s speed, 10x10 array of lasers, (5*3.6*2)*10 =50 cc per hour. Pretty slow but enough for a proof of concept. More lasers still might be added or maybe parts could be made in parallel on different printers then consolidated ultrasonically after being precisely positioned over each other (they could have alignment pegs or cones built in to the top/bottom). Obvious problem is that 10x 10 array of lasers would be quite expensive, but the laser in a dvd writer can't cost more than a couple bucks and is a few watts (2 I think).
  • a central assumption is that a gas laser could be produced that was suitable to replace the diode laser that is used during prototyping, which would have a much lower cost per watt. The cavity per se without the end cap, including any and all electrodes in the gas chamber and conformal cooling channels, could be printed in a single glass block. The end caps and lenses could be printed roughly and then would be finished with standard mandrel polishing using a printable companion unit and maybe even printed mandrel. The lens form accuracy ultimately does not have to be perfect because we do not need to focus to a diffraction limited spot anyway, so 1 micron dimensional accuracy may suffice. If the experience with the stages allows higher accuracy still that would be good though.
    • ideally a TEA laser or something else with a wavelength that can use materials that are easy to obtain, not the zinc selenide used by CO2 lasers although ultimately maybe it is not that expensive, have to check. Zinc is cheap and selenium isn't that expensive.
      • problem with tea lasers is that they are pulsed. Either has to be qutie high frequency (like a MHz might be good if the melt pool is 10 microns and the speed of movement is 1 m/s) or CW.
    • maybe something like a CO2 laser but higher wavelength.
    • power supply for a gas laser will not be cheap as they are low efficiency, but the device should have little difficulty printing most of a vacuum tube (require removal of support material, sealing and evacuation as well as addition of a volatile material as charge carrier maybe).
  • use extremely fine powders, they are not that expensive. The powder needs to be vacuumed off the surface anyway as you print so it can be stored for re use and also does not need much or any cleaning after, should not escape the print chamber. Might need a mechanism to vacuum any stray powder from the print chamber and build tray to prevent escape and prevent mixing of powders (so powders that are vacuumed up do not need to be sorted before re use)
  • heating areas with a large depth to width ratio of valleys that laser can reach for heating. Because of the need for vertical separation between printing materials that could pyrolize or otherwise break down at temperatures required for deposition of other materials, if you wanted to print say a thin wall of wax between 2 metal walls the height of the metal walls could block laser light to an undesirable degree. Might put serious limits on the width of such wax (or other non temperature resistant material) walls. This is one argument in favor of longer stand off distances and smaller aperture numbers for the laser optics i.e. large rforcal length to lens diameter ratio, so the angle of the cone of light is small if you see what I mean.
    • What does that do to the precision that the optics need? With galvo mirrors or lenses the laser can come in from the side sometimes, bbut conversely it is forced to come from the side to some degree in most cases. A lot of laser energy might end up getting blocked one way or the other. Fortunately undesired heating of the materials blocking the light unlikely since they will be higher melting point materials due to the processing temp being higher the reason they protrude in the first place? Easy to identify during computer simulation of the build process.
  • a similar problem as the metal deposition head printer has when it comes to printing a horizontal or nearly horizontal ledge: the material underneath the ledge has to be resistant to the metal deposition temperatures. An argument in favor of temperature resistant support material. WRT the dimensioning accuracy, there is no machining here as there would be with the metal deposition head so form and surface finish accuracy would likely suffer little or none I think.
  • materials that need higher deposition temperatures should probably be deposited first to avoid melting or burning the base of a neighboring wall (burning (or rather pyrolizing or otherwise causing chemical decomposition since there is no oxygen) is an obvious no no, even if the more heat sensitive material is not chemically damaged distortion could occur as 2 liquids of different density in contact try to flow around each other, or diffuse within each other. Diffusion might not be so bad, depends if it causes an undesirable material in the diffusion zone i.e. excessively brittle or something. In most cases it would just glue the materials together I guess, which might be desirable for improved strength.)
  • might be good to print a lubricant, print chamber could be at sub zero temp so lubricant is solid, could be one of the support materials too maybe or different
  • have to be able to print thin walls of the void/support material and lubricant to achieve close separation between components when desired
  • alternative heating methods, rotating array that is mounted on x and z axis for motion, the galvo lenses or mirrors (scan areas shoudl overlap so not all lasers need to be operable)
  • ideally the laser array should be designed so that each area on the surface of the object can be heated by more than one laser so not all the lasers need to work
  • exolaind the lack of brighnesss from other light sources, maybe there is a plasma one but likely would be used already by commercial dmls units? Check to see if there are patents on. Also less coherent so focussing not as easy but ocudl use mirrors to avoid chromatic abberation.
  • explain how the gas laser and machine might go, might need liquid crystal modulation cell if the power output cannot otherwise be modulated at the desired speed.
  • the staircase problem: the layerwise deposition leaves staircase shaped profile but would prefer smooth. Mayb the staircase side can be tilted by careful control of the melt pool/ irradiation and positioning of focal area? move slightly towards the edge of the object to smear the top layer of the desired material. Could also print up a shallow wall of support material (with a support material that melts at a higher temperature than the desired material) more than one print slice tall above the plane where the desired material is, and the sufrace tension of the melt pool at the edge of the wall gives smoothness and roundness, or even if not could selectively melt the sides of the wall in the area between print slice thicknesses to smooth them out. When the desired material is deposited it takes on the form of the support material have to be sure no gas gets trapped in the area but probably would not
  • powder deposition done with precise deposition method. Can't really use imprecise method followed by knife edge or roller going over the surface (have to be very precisely made), ultrasonic lubrication to level it etc. because of the vertical height separation between materials that needs to be maintained during the build process. Powder would fill in the valleys.
    • maybe could use knife, roller etc. if could get the top level of thepowder bed to go down precisely after application, by spraying it off electrostaticaly or something. Spray the surface with high voltage electrons? Process would be different for different materials. Residual static charge has to be removed after each cycle though
    • could maybe do printing upside down? Spray the particles at the surface and maybe they will stick lightly in a very thin and reasonably uniform layer.
  • focus on precisely getting suitable material where it needs to be for good voxel control. Size of machine, etc is all optional, can be very small but preferrably done with a larger practical machine in mind. Proof of concept only. Could use the parts from a DVD or CD burner in various ways to keep costs down perhaps.
  • Need feedback of surface shape and preferrably melt pool temperature and video of it, at least for during the prototyping process so am not working in the dark as much.
    • small microscope on gantry should do? Mount on another xyz bot but does not have to be more precise than the viewing area. Should be able to focus though. Might need piezo actuator or similar. Maybe the lens focusing thing from a CD writer would do? Also the linear bearings and stepper motors. Small project of it's own. Also preferably it does not block the laser, so can look at the melt pool while it is going.
    • Scanning laser microscope thing much like electron microscope could maybe be used with 2 photosensors to scan in the surface. Focus laser do smallest spot can, scan, focusing done with movement in the z axis of the laser probably since have the precision xyz bot, collect light intensity signal and form image like a SEM. 2 sensors for stereo vision. The lasers can be modulated each at a different high frequency and the signal processed to use multiple lasers at once. Would be quite slow to scan in the whole surface, suppose 1 micron focal area, 1 m/s traversal, that would take 100 seconds per square centimeter (10,000 rows, 100 rows per second) per laser. An argument for a larger number of lasers (if the signal processing can handle it)?
      • could use larger number of photosensors if desired. They could be built into the laser array or just arranged around the periphery
      • make all surfaces black where can, done in the dark of course to reduce signal noise.
      • no video possible
      • can be used to align the overlap of the laser focal areas since the lasers scan over the surface of the same shape the offsets can be calculated easily.
      • another reason to use a laser with short wavelength
      • diffraction limited spot would require precise optics though. May not need to be that small though.
  • powder removal with vacuuming and gas jets, brushes, ultrasound or sonic vibes, whatever works - complicating factors include adhesion of particles of materials to like or unlike materials, thin films of lubricants or oxidesor adsorbed films of water , abrasion that may be caused by ceramic particles left behind (very fine powders might help as they would be a lot smaller than the lubricant film thickness),
  • list of complicating factors for the deposition material physics
    • crystal structure of metals deposited affects surface roughness, the roughness caused by it may be on the order of the print resolution in this case? Small melt pools might help compensate
    • gas bubbles especially argon trapped under the powder for viscous or low density materials. For metal bubbles would mostly float to the top. Probably have to use low viscosity materials.
    • surface tension (cohesion), wetting or lack of wetting (adhesion) of the melt pool material to the nearby material surfaces etc. all confounding factors but can be useful too (e.g. to reduce step profile as mentioned above), maybe do computer simulation to see how things happen at this size scale or can find info in ref materials. Microscope vision system will help too. Also viscosity of the melted material vs. time that heating is applied (especially with regards to plastics which may be much more viscous than molten metals).
    • adhesion of particles of materials to like or unlike materials, thin films of lubricants or oxides or adsorbed films of water or other substances, may be useful too though e.g. when spreading powder layer as mentioned above.
    • thermal expansion and distortion, small melt pools help.
    • phase transition distortion again small pools help
    • what else? probably quite a few things
  • melt pool temperature control done how? Open loop with suitable computed settings for the situations expected applied? With diode lasers could monitor electrical characteristics which will change with backscatter. Backscatter may change when surface melts and also with temperature as the reflectivity of the material changes? See methods on comprehensive search page. If large number of melt pools then might preclude some types of sensors.
    • during prototyping, the microscope might have a set of filters that could be changed to allow temperature sensing crudely.
  • support strategy
    • Requirements:
      • Support thing walls and shafts against any forces, probably not much but some during powder removal.
      • Act as a "void" voxel in the final part, i.e. provide spacing etc. between moving parts.
      • Might be nice if it could act as a lubricant after printing but there are no lubricants that can stand the temperatures of metal deposition. Maybe one of the materials in the dual material with different temperature compatibilities approach could be a lubricant.
      • be easy to remove somehow
        • melting, dissolution, sublimation, powderized with ultrasonics, pulverized by submersing in a bath of hard beads and vibrating (might not work or cause problems elsewhere)

Todo

  • Check out the the size, traversal rates and power inputs for various materials for good melt/fusion pools and decide on the right laser powers etc. for the array.
  • need to nail down the precision and accuracy and feature sizes/resolution needed to print hydrodynamic bearings, other journal bearings, leadscrews, and also maybe the parts for a laser and the optics production machine (so read up about spinning mandrel and other common optics production methods)
  • hydrodynamic or dynamic leadscrew and nut exist?
  • make a list of things want to be able to print, their material and resolution, tolerance (including surface finish) requirements to try and make things a little easier. So it is mostly a proof of concept even if it can't print everything (or even any complete objects).
    • a precision stepper motor with bearings of some sort included
    • Hydrostatic bearing surfaces including the hydrostatic journal bearings and the leadscrew and nut
    • Hydrodynamic bearing surfaces including air bearings and bearings that use water or oil as the fluid.
      • Okay, hydrodynamic bearings should be highly polished if bearing large loads, not sure if this can be accomplished with this printing method, might need to remove the parts and process them separately then. What if not bearing large loads? Also the purpose is to remove asperites
    • a precision leadscrew no might be too precise, [1] says 0.6 micron/mm tolerance of screw that might be average though, it could vary by more that but randomly and cancel out over long distances, [2] says 25 micron per foot. no info on surface polish but probably like other journal bearings are boundary lubricated but with nylon as one element so probably not need much polish.
    • the mandrel tool for a lens making process - bearing, drive coupling and the form thing to attach
    • the vacuum attach cup thing for the mandrel polishing machine
    • the blank pre lens thing before polishing
    • a PCB. Basically very low tolerance.
      • materials: copper and insulating material that can stand 200 C degrees at least over periods of some minutes, and 275 C during soldering, basically. Copper has to not delaminate from the substrate when soldered. Don't bother with other conductors, the metallurgy of soldering won't be as reliable so not commercial quality boards.
      • Could attach components and weld them onto the board right in the machine with a pick and place tool as long as the vertical height between the bottom of the laser array and the top of the print surface is okay. It might be nice to be able to print resistors, inductors which should be possible and practical. Printing capacitors of any size might be less practical but maybe... and small ones should be doable. Most of a vacuum tube would be printable too, though the sealing evacuation and addition of charge carriers would require post processing.
    • turbine blades for air turbine tools as expanders. main thing is the bearings, back of the envelope calcs indicate that balance is not the problem and should be fine. Aerodynamics probably not that critical wrt form or surface finish.
    • other expanders with suitable long lasting bearings, roots and gear, and piston expanders in particular. see bearings.
    • connectors, no strict requirements there on mechanical tolerances, materials should be good like nickel or gold plating on the surfaces, is stainless steel okay? I don't think so.
    • coils for inductors and motors, can do that if the print process is reliable enough i.e. no breaks in the wires
    • hydraulic pistons. not a problem, pistons are sealed with a rubber seal usually not metal to metal. Usually chrome plated but optional.
    • gearboxes and gears. precision not a problem, wear probably not, surface finish may well be a problem basically much like a ball or roller bearing the movinge surfaces past each other. IIRC 12 micron lubricant thickness was typical. for roller bearings
    • what gets really interesting is when even a few of these things can be combined in to a single object automatically inside the printer as the print process proceeds, especially bearings and gears and coils and populated pcbs
    • Industrial tools of all sorts, particularly important
      • dies and stamping tools - very high strength materials needed like tungsten carbide etc. precision depends on the part, but ultimately not need much since so much is lost anyway when stamping or extruding something.
      • casts for molding not a problem, only acheives 50 microns anyway with the best casting, so precision not demanding
      • the machines to make rolling element bearings, probably not a problem, see wikipedia on bearings and ball (bearing) the methods used compensate for lack of precision in the tooling to some degree - one of those methods of improving precision. (another one is the hydrodynamic bearings apparently only exhibit [3] rotational errors only 1/3 of bearing surface errors
      • Particularly interesting: equipment for chemical engineering processes. Often needs to be made of specific materials though for chemical compatibility like teflon or whatever. In cases where it is not possible to make with the material, make whatever equipment it takes to make with the material.
    • obviously structural components of all sorts, materials metals mostly precision pretty low but some areas should be precise for good alignment etc.
    • fasteners and fittings
      • might seem like no point because they tend to be cheap but they are often not that cheap, or are hard to obtain. Plus to print a machine that does not require assembly but can be maintained (i.e. not all welded together) you sort of need them.
      • tolerance for a bolt is like 50 microns not to strict at all.
      • can probably do without rivets.
      • motor couplers and machine screws etc.
    • every part in a car basically. Need some sort of meltable elastomer for the tires, seals of various sorts.
      • Hard wearing and durable materials for the inner part of the cylinder and piston
      • as mentioned high quality bearings important, the bearings in the piston head and crankshaft are subject to special polishing procedures that basically remove asperites. The thing is they are subject to huge loads (like 12,000 pounds peak) and the higher the load the more polished it has to be - the asperites have to not protrude through the lubricant layer basically, the lubricant layer is smaller at high loads so the asperities have to be smaller. Exactly what is the surface finish needed in Ra?
      • many things fall into the materials zone and fall outside of what such a printer could ever do.
      • many of the things like the differential, transmission, engine and valves, brake pads and hydraulics, door locks, are already covered by capabilities mentioned elsewhere the other things mentioned.
      • painting can be done by bonding a thermoplastic mix with pigment to metal like polypropylene with UV additives (basically is an anti rust method, previously mentioned).
      • durable electrical contacts. The contacts in a motor commutator are usually graphite copper composite that might be hard to deposit with melting. The other end of the commutator is just copper alloy though

for much of the above, a much wider range of materials would of course be needed to make a good one, than only 3 like tool steel, silicon carbide and polypropylene... but for the most part they seem to be melt processable so could fit into this scheme. Exceptions for mechanical parts alluded to or which are usually part of the above that can't be melt processed:

    • rubber obviously, but there are probably elastomers that can replace it and are melt processable. http://en.wikipedia.org/wiki/Thermoplastic_elastomer
    • maybe some things that require specific crystalline structures but none that I can think of except parts that require hardening will probably be a problem, but those may be replaceable with softer but stronger materials that are coated with ceramics or alloys that are very hard and tough without heat treatment, or maybe it would in fact be possible to control the processing to do heat treatment of a surface or bulk material during building, in situ though there would be limitations on nearby material layer's temperature compatibility etc., maybe not.
    • lubricants of course have to be added after probably, after support structures are removed. Also other liquids and fluids like battery electrolyte or hydraulic fluid.
    • natural materials like wood or cotton not usually involved in any of those things.

Okay, so some precision stuff http://www.minibearings.com.au/technical/precision/440/ tolerance of races for rolling element bearings http://en.wikipedia.org/wiki/Ball_%28bearing%29 on the balls

Could not find anything on hydrostatic hydrodynamic or even boundary lubricated bearings though looked pretty hard. IIRC film thickness in hydrodynamic bearing in an engine is roughly 8 microns or so so the tolerances will follow from that. Hydrostatic unknown but would be nice to know, don't have time to search any more though. Is on the order of microns for an airostatic bearing and presumably substantially more without. Found one doc [4] that seems to indicate it is more than 20 microns thickness. In IC engine between the piston ring and the cylinder wall varies during the stroke but, on the order of about 8 microns thick during the bulk of the motion (so probably similar for rotational hydrodynamic bearing) [5]. the surface finishes are also alluded to there, polishes in the half micron Ra seem to be workable.

  • desirable but probably not printable directly
    • already sharp drill and milling bits
    • ball bearings and other rolling element bearings, shafts and raceways for them, might be able to get form accuracy but would be a push (2.5 microns sphericity for balls needed) polishing probably needs special finishing as 0.125 is good I think (double check that document linked above)
    • objects which require certain chemically resistant materials
    • e.g. halogen light bulbs, how would you get the halogen in there without post processing? Still you could do most of the work.
    • optics of any sort. Could it not be conceivable that selective melting of a near net shape glass surface not lead to an optical quality surface? Would take special techniques to achieve extra precision but, basically it is conceivable that most of the hardware in this printer could be reused for a device for (slow) optics production. would require some sort of optical encoder that depends on Time of flight or something perhaps, or the capacity to scan in the optic and determine it's shape to a high degree, then keep machining in the places that need correction, and repeat. Some readingon optics production http://www.optics.arizona.edu/optomech/student%20reports/tutorials/Katie_Introduction%20to%20the%20Optics%20Manufacturing%20Process.pdf. also see wikipedia on aspheric lens. looks doable coudl use spinning fluid for the original form for hte molding one, or vacuum plate or maybe other methods.
    • I think you could make most of the parts for a gas laser, though you might have to have a special apparatus to help you assemble and align them by hand. There are a lot of people who make homemade lasers but they are maybe importing precision in the optics usually so that's not really proof of being able to make one from scratch....


  • interesting things you might be able to make or do, but not that important
    • microturbines
    • composite mesoscale antennas etc. for radio waves or sort of like optics for them.
    • clothes (out of synthetic fibers pretty much, cotton etc is out) The fibers are above the resolution of the printer mostly, though some may be only microns wide you could certainly make clothes of a sort that were functional. Might be really slow though as high res printing tends to be slower due to smaller melt pool. Probably better to just be extra sure you can print a machine that which can make the stuff
    • mesostructured materials. The high resolution that is needed for bearings also could be used to print interesting structures like microhoneycombs. Slow though
    • novel things like very small mechanical systems. Again slow.
    • repair worn or damaged objects by building up the appropriate areas. Laser focus area has to be able to reach though. Still the technology and software developed might even be adapted to robot arm based head that could basically print directly on another object, so the object is welded on and fully consolidated with the large part.
    • put ceramic coatings etc. on existing metal objects, plastic anti corrosion layers etc.
    • functionally graded or composite materials
    • weird or high performance things like a model helicopter blade made from ceramic.



  • given the issues and demands of the printing process above, identify suitable materials to print with given the things want to print, conductive, tough structural material, an insulator and a good support/void material.
  • put together a support structure strategy that lays out the required roles as did for the metal depot head can copy most of it
  • Find out about the surface tension etc. other complicating factors as applies to small scales
  • when advanced enough ask for comment etc. on forums.
  • random notes:

support materials

    • support materials
      • The problem is processing/deposit/melting temperature incompatibility . Sometimes you would want to print the support material on top of a low temperature material, and sometimes you need to deposit high temperature material on the support material. So either it melts at a low temperature to avoid melting the low temperature stuff, or it melts at a high temperature to not be melted. However it may be acceptable to have a limited amount of melting of the support material and/or the material on which is it deposited, as long as the melting is localized. It is less than ideal though because it messes up the interface between the two, either from diffusion or undesired flow of them.
        • undesired flow may be quite limited due to the small melt pool size and the surface tension and viscosity of the liquids subsequently overwhelming gravity.
          • Fundamental problem is getting the material from the main storage to the desired volume and only that volume/voxel as close as can, so a printing process again but with special requirements.
        • so options (given the other requirements of a support structure strategy):
          • 1) Could have 2 support materials. Low temperature melting but highly temperature resistant material (preferably insulating, reasonably strong (doesn't take much though since this is mostly force free, though there may be some forces during powder removal) and also otherwise compatible with any materials it touches, e.g. not a metal because it would dissolve other metals) and high temperature: print the low temp where needed and then print high temp on top, that undesirable melting would occur but only at an interface that does not matter (since both materials will be removed after printing anyway).
            • Problem: The combined thickness might be too much for some places in printed parts because want to print bearings. As mentioned in todo file need to find out bearing tolerances and resolution (which would tell the gap layer needs).
          • A material that can be deposited at low temperatures but stands high temperatures. How?
            • A solvent which was carrying the material, leaves deposit behind. Low resolution probably. Could use piezo inkjet head. Dilute solution could produce thin layer

What about a solvent that has very low adhesion, which carries a solute that makes a suitable support material? If suitably low adhesion it could be deposited as droplets without spreading out on the surface, and could be vacuumed up more easily.

            • something that cured thermally or due to the light. Anything that could possibly liquefy at low temperature once and then refuse to liquefy again until high temperatures.
            • some sort of treatment with a particular gas, support material reacts with the gas to produce a temperature resistant upper layer (all of which can still be easily removed and/or act as a lubricant). Probably something that can do this, CVD may be a good place to start looking for suitable substances.
            • some other treatment involving something other than temperature. UV, Pressure, vibration, solvents or solutions of chemicals. Solvents in particular sounds like there might be something that can be found that is both volatile and reacts with the support material, and does not contaminate the metal etc. in the chamber when it is time to melt that.
            • a Preceramic polymer or some other substance that when heated enough, converts into another substance that has the desired temperature resistant properties. The obvious problem is that it would melt during the transition, and if it was not the material that was lowermost during the build process it might slump or flow in undesired ways. It could be heated so fast there is not enough time to slump.
      • temperature incompatibilities will necessarily impose some limitations on exactly what can be built. Imagine the whole build process. Metal cannot be laid down on top of polymer because it would normally burn or otherwise decompose the polymer, leading to a fragile layer in between. You could roughly approximate it with a thermally insulating and tolerant material to lay on top of the polymer, or some other material that forms a durable bond layer like a preceramic polymer maybe. If such approximations were strong enough maybe you'd be okay and could print what you want essentially. In the case where you do not want the layers bonded that's not as much of a problem usually because that implies a bit of space between the two layers at least a few microns wide, which can be filled with support material which is similarly temperature resistant but does not have to provide a strong bond. If what you want is not a bond but sliding action over the plastic I'm not sure how you would get that. Even if you could print the plastic under the metal somehow it would stick to the metal due to the melting. There might be some way to get durable long lasting sliding with the right interface material though? Or you could just print support/void material and then fill the void with lubricant after the support material is dissolved out. but the support material has to provide the same termperature interfacing functionality, and with a very small thickness, while also being removeable entirely afterwards... nanoparticles of aerogel embedded in the material (ahead of time) , maybe even under vacuum ?
        • only way I can think of right now to get past the limitation on temperature is to do the welding with firing the particles at the target at extreme velocities or as an ion beam. Extremely small particles might help as they would need less mechanical distortion to come into adequate contact with the surface? question: what sort of speeds would be needed to achieve 100% bonding and near 100% density? Plasma spraying achieves 97 to 99 percent density, but I don't think the bonds are full strength. Plus the plasma impinges on the workpiece so it would produce temperature problems itself. In plasma spraying the particles are melted though - what about firing solid particles and just letting them deform plastically on impact so they form a bond like in explosive or electromagnetic pulse welding? Would need extreme speeds. Wikipedia says EM pulse welding involves 1 km per second speeds. We only need to accelerate small particles. How would you do it?
          • travelling wave inside a chamber, helium or h2, extremely high pressures, the particles ride the front of the wave.
          • Speed of sound in solids can be even higher, a tube with surface waves that are moving towards the front of the tube (then around the outside and back in maybe), accelerate particles by getting them to ride the crests.
          • even plastic and ceramic particles are slightly conductive, maybe possible to accelerate them with lorenze forces like in em pulse welding, and maybe repeatedly along a sort of EM gun? Might at least work for metal particles? From the list of things that want to make metal and plastic are the most important things, if metal can be codeposited with with plastic and to high precision with a support material that is the bulk of it even if ceramics are out.
      • Dissolving or otherwise removing support material from very narrow areas like between the surfaces of a bearing might be hard or take a long time. Ultimately brownian motion may help with dissolution so eventually you could get it out though. Reacting with a gas similarly. With melting it might be pretty much stuck in there though liquid or not.
  • interesting reading on techniques related to material deposition approaches taht might help overcome the temperature incmompatibility issue

shoudl double check what the thermal distrotion would be for metal deposition again, can't be more than the shape change of the actual melt pool? could actually need those papers http://www.springerlink.com/content/e2v47241l87053u8/ strength of copper

http://www.sciencedirect.com/science/article/pii/S0167577X03007705 bondinc in the layer http://www.sciencedirect.com/science/article/pii/S0924013608002112 attempt to reduce porosity in titanium http://www.springerlink.com/content/g432j6526768130l/ suitability of materials for cold spraying http://www.sciencedirect.com/science/article/pii/S1359645405005975 details of how to do cold spraying speed powder size http://www.sciencedirect.com/science/article/pii/S135964540300274X some about strengths of coatings http://www.sciencedirect.com/science/article/pii/0025541688901917 very intersesting heated though but plasma sprayy freeform fabrication

&maybe find out more about ultrasonicconsolidation maybe the bond is not that good in the end?

(go through and mark the most interesting pages in bold )

prototyping methods

add to prototypical mehtods sectino :

( more general stuff can be found on google scholar with "layered manufacturing")

http://www.sciencedirect.com/science/article/pii/S0924013699003921 deposition of ceramicas with inkjet printer

heat transfer

calc for heat transfer away fro mteh welding zone into the bulk material basic check for welding feasibility have it in another file somewhere the reflectivities

re

for heat lost from meltpool suppose it was a rod. left side is temp x right side is temp b what is conductivity of rod, problem is conductivity changes with temperature so just go for worse case scenario/general estimate

soppose hemisphere was uniforrm temp therefore cond, for iron was 300 W/m*k

temp dif is 1500 k , surface area is

Average cross sectional area between point and outer surface of spherical shell, integral of reciprocal of area of shell over radius . let's talk about heat lost per degree from just a point or maybe a spherical surface 1 micron in radius in th middle of a large metal block at equilibrium (therm conductivity goes up with temp so is worst case) to the surface of a spherical boundary maintained at a fixed temp say 10 mm radius, can divide by two later. thermal resistivity is additive and inversely proportional to area and proportional to the thickness, so the integral of the inverse of surface area over the radius of a sphere from the 1 micron radius to the 10 mm radius is the total resistance if it is the same throughout the material


1/(4pi*r^2) =1/a

0-1 all in meters

integral is -1/(4pi*r)

so if spot is 20 microns radius and hemisphere is 1 meter across then -1/(4pi*1)-(-1/(4pi*0.000020))= -0.079/m+ 15915/m

Note: seems to be something pretty wrong with the above does not mesh with the laser welding jwri doc figure 7 especially.

so if 1/300 m*K/W so 53 K/W so would need many watts 30 or so but absorptivity of surface silver is 0.02 so obviously this is a bit off and more detailed calcs are needed. which more or less meshes with the doc. at so would need much smaller melt pool 1.256/10^4 sq cm if the spot size was 20 micron radius (ignoring some details) so 3.6*10^5 watts per sq cm which is way more than the welding thing indicated but that was different. they say 9.2 kw/sq cm and 50 watts were tried so woudl be 0.0054 sq cm so 5.4*10*5 sq microns or 414 microns wide focal area which meshes with the pictures, in fig 6 so more detailed calcs are needed to determine the melt rate that could get from steel with a 1 watt laser with various focal area sizes.

but there was thta paper doing sintering with 800 micron diameter spot in bronze and iron alloys with 25 watt laser that cant be right. oh, checked again and the parts were only 50% dense which changes everything. Says 10^6 is okay for deep welding but thta might be in keyhole mode where higher absorption and probably not apply at small scales due to increased conduction, .

adsorptivity changes with temp, thermal conductivity goes up with temp, might become weird at high irradiances.


calculate max theoretical melt rate for different laser powers and spot sizes annd materials make tables check forums for it first

Some explanation for the above: http://www.welding-consultant.com/PulsedLaserWelding.pdf. OUPLING Metals and alloys are not transparent to laser light. Photons in the laser beam that hit a metal surface are either absorbed or reflected. Most metals/alloys are good reflectors of laser light at room temperature. Figure 2 shows a chart of room temperature absorptivity of typical metals as a function of laser frequency [1]. Consequently, majority the initial photons that hit the weld area are reflected from the surface. Energy from the select few photons that do get absorbed is converted to heat and raises the local temperature of the metal surface. As temperature increases, so does the absorptivity at the weld surface, and more of the photons that follow are absorbed. Increase in absorptivity with temperature leads to a chain reaction and in a very short time practically all the photons impinging on the weld are absorbed and the weld zone reaches melting point (Figure 3). This process of transitioning from initial photon reflection at room temperature to majority photon absorption in molten state is defined as coupling.

http://www.journalamme.org/papers_vol24_1/24101.pdf. 1 Selection of Absorbents With the interaction of the laser light and its movement over the surface, very rapid heating of metal workpieces can be achieved, and subsequent to that also very rapid cooling down or quenching. The cooling rate, which in conventional hardening defines quenching, has to ensure martensitic phase transformation. In laser hardening the martensitic transformation is achieved by self-cooling, which means that after the laser light interaction the heat has to be very quickly conducted into the workpiece interior. While it is quite easy to ensure the martensitic transformation by self-cooling, it is much more difficult to deal with the heating conditions. The amount of the disposable energy of the interacting laser beam is strongly dependent on the metal absorptivity. The absorptivity of the laser light with a wavelength of 10.6 µm ranges in the order of magnitude from 2 to 5 % whereas the remainder of the energy is reflected and represents the energy loss. By heating metal materials up to the melting point, a much higher absorptivity is achieved with an increase of up to 55 % whereas at vaporization temperature the absorptivity is increased even up to 90 % with respect to the power density of the interacting laser light. For this purpose, besides CO2-l

http://www.ne.anl.gov/facilities/lal/Publications/laser%20welding/Laser_Welding_Al.pdf

they also include some equations for laser welding power levels needed


specific integral is is 1/(3*pi)=

so resistivity*1/3*pi is the resistance from point in th imiddle to the outside

resistance is (1/300)m*k/W* 0.106=k/W for a 1 meter sphere no

resistivity*1/pi*r^2



coudl have sum which is the resistance

volume divided by radius

Rate of printing, assume that heat the melt pool up to melting and overcome the latent heat, then repeat

13.8 kJ mol-1 enthalpy of fusion for iron

prototyping methods

  • examples of small melt pool or focal areas or otherwise particularly detailed printing of full strength parts

http://www.eos.info/en/about-eos/technology/micro-laser-sintering-mls.html http://www.3d-micromac.com/microFORM-en.html might not be full strength https://www.lia.org/laserinsights/2011/05/20/laser-additive-manufacturing-of-turbine-components-precisely-and-repeatable/#more-1120 says precision but probably not https://www.lia.org/laserinsights/2010/05/06/high-density-laser-micro-sintering/ okay so not focal areas maybe also not full strength

http://www.fcubic.com/ not clear what this one is, says precision inkjet that can deposit metal http://www.wiley-vch.de/berlin/journals/ltj/07-01/LTJ0701_S26_S31.pdf looks good, micro laser sintering check that fully dense resolution 3 0 micron btu check precision http://www.wiley-vch.de/berlin/journals/ltj/07-01/LTJ0701_S26_S31.pdf building up parts with micro welding tool and microscope by hand not that interesting though says laser welding is expensive

so in conclusion more resear ch on thermal distortions, in particular if they add up as you build or are limited in size to the size of teh melt pool, and if they are reduced with smaller melt pool sizes.

conclusion on precision requirements: a reasonable okayish surface finish goal is half micron Ra. Dimensional accuracy check above but 2 microns or so preferrably for rolling element bearings of modest size or the races for a machine that coudl make them (over what distance? check the abec chart). Resolution less than 8 microns so the gap between the bearing surfaces can be printed. Materials: Should be able to print in any weldable powderizable material preferrably, to essentially full strength and greater than 95 percent dense. These methods of depositing metals from gas and so on may be adapted to a range of alloys though with the right gas mixes, similar for electrochemical deposition but the material properties of such materilas still need to be checked .

  • thermal stresses and distortion in melt deposition methods:

http://edge.rit.edu/content/P10551/public/SFF/SFF%202001%20Proceedings/2001%20SFF%20Papers/41-Pohl.pdf. Page 1 Thermal Stresses in Direct Metal Laser Sintering

  • Page 1

Melt Pool Size and Stress Control for Laser-Based Deposition Near a Free Edg http://utwired.utexas.edu/lff/symposium/proceedingsArchive/pubs/Manuscripts/2003/2003-18-Aggarangsi.pdf

Direct Metal Deposition Processes

in Laser-Based SFF Processes

  • http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.11.9017&rep=rep1&type=pdf good one
  • useful for both this mthod and for metal deposition too: coefficient of thermal expansion from wikipedia page o nthermal expansion is 10 ppm per degree or so for steel, so if steel is heated to melting point at 1500 deg c then cooled to 0 change of 15,000 ppm or 15 mm per meter. 15 microns per mm, so prretty large. how uniform is it though? so judging from the klingbell doc looks like the expansion is nowhere near additive within the printing plane i.e. the net stress/strain due to shrinkage when depositing metal bit bu bit is nowhere near as high as if you were to hypothetically take a sheet of metal and just heat it to melting, plonk it on the lower layer and let it cool? The figures indicate the plate warped vertically by about 0.003 inches over an inch square, which implies a far smaller shrinkage of the deposit layer. What we really want to know is how much, if you were printing say a circular pillar the material surface at a point various distances below the print plane would move, given different melt pool sizes and traversal rates of the melt pool and material addition rates (which implies the layer height basically since the width is a matter of hte melt pool size(width)). But it would certainly be a fraction of what the print planes are changing by? well no it could be larger, as onl layer is deposite, shrinks, compressing the layer below slightly, then the next layer deposited, shrinks and compresses the layer below it, so the lower layer shrinks again. so the pillar might take on an hourglass shape. However the melting of the second layer might relieve stress in the layer below due to the heat... Secondly it is really only the unpredictable changes that really matter because the milling step or deposition steps deposit/remove material in such a way that the resulting object after cooling is what you want. Ideally have a complete computer simulation, for a hybrid (deposition then subtraction) method this would be the ideal and could improve accuracy to the couple micron levels, by all appearances.
    • welding books say that most of the distortion is caused by the phase transition from liquid to solid, but could not find more about this. As mentioned previously, it depends on how and when the material acheives tensile strength during the solidification
      • However, phase transformation processes which are greatly dependent upon the carbon content account for large difference in the shrinkage behaviour between the various grades of steel and extremely high apparent TLEs are calculated for low carbon steels; for example the apparent TLE for a 0·05 wt-%C steel is calculated to be 111·81 ×10-6 K-1. http://cat.inist.fr/?aModele=afficheN&cpsidt=18635476 Tle is Thermal linear expansion coeff. So might be 10 times the above, presumably they are factoring in when it changes shape since with continuous casting any changes that occur while the material has no or very low tensile strenght is not really important? However it might be in effect smaller for us as the early contraction while the tensile strength is low may be counteraced by yeilding of the contracting material (flowing basically) since it is being braced very well by the nearby solid metal against contraction. So as it solidifies it shrinks, and so it exerts some forces on the metal around it and that sets up stresses in the surrounding metal but as the metal cools what would be it's stress free linear size in all dimensions continues to go down, and the difference between what size it wants to be and what size it is forced to be is what causes stress but he amount of stress in the material cannot be greater than the yeild strenght because it would just flow, and that would relieve the stress until it was equal to the yeild strength. So if you had a graph of (the diff between the linear size it wants to be and the linear size it is)* the stress/strain relationship vs temperature, that would tell you would be the stress v.s temperature in the material as it cools without flow (in a given situation which could be with it perfectly braced or with say the melt pool on the surface of a block of the same material of infinite size or whatever), then add a yeild strength (which is in the same units as stress) vs. temperature line to the graph, an it will intersect with the other line at some point and go below it. The stress in the material at any time if flow can occur at a given temperature is the lower of the points on the two curves. Normal thermal expansion (or stress increase if perfectly constrained) described by the thermal expansion coeff only occurs when yeild stress curve is not the one being followed. This is well known but the thing here is to expand the graph past the solidus temperature so we can see what is happening during melting, and secondly to see the graph for different constraint conditiones as mentioned, and thirdly how this affects distortion of the object being printed as the melt pool moves along depositing material.
        • it would seem that the contraction stress would be basically the same in all areas that were melted if you melted a very shallow area on a very large metal block, i.e. if you were printing with a relatively small melt pool and the stress coudl be determined by the method above. Then the next layer goes on and when the melted area passes over the lower area stress is relieved by thermal expansion but it comes back again to the same level or so after things cool, not counting the new stresses set up by the layer above(suppose they are somehow unconnected mechanically).
    • idea for support structure strategy with hybrid method: hae metal support structures be built out almost horizontally to the leader area, then print the leader on them. then machine the supports away, either just where they connect to the part or really all of the support material converted to chips (when it woudl be hard to remove otherwise)
    • also this microcasting thing is the dripping metal on the surface thing apparently blobs 1/4 to 1/8 of an inch. Could melt with arc like gtaw with detection of droplet size and fall, maybe with a way to shake the droplet off or otherwise just have size controlled by wire diameter.
    • next need to know thermal gradients to see what z axis separation would need to be maintained for what distortion.
      • add to support strategy for possibl ematerials: there are some materials that solidify at temperatures different than melting point (hysterisis) such amaterial might be useful fo r temperatur einterfacing if the temps involed were different engouht and high enough
    • ideas to improve plasma spraying md star method (described in a pdf above) (add to the ideas section): use laser cut foil or plate section for the leaders (bottom of cylinder described) coudl be machined toa shape, for the particles to bond to, and the support structures could be the mask layers: apply mask, spray, grind a small amount off the surface to remove the excess material, then apply and mask again. The fear of wasting material doesn't make much sense given the cost of steel, and that it can be recycled with a companion widget.
      • Idea that can also apply to metal and multimatieral printer. what about machining plates of material then precisely positioning them in place on a suitably shaped support structure so as to solve the problem of precision shaping of the bottom of leaders and overhangs?

Could forma printing method by itself, if plates could be made and ultrasonically welded or resistance or explosive welding adequately well together? could folllow with a milling step if desired.

Support structures could be built in the same way from another material. Basically moving towards more of a micro or millifactory approach then.

  • reconsider the need to make stuff that is already assembled. The most important thing is the capacity to make the parts to the extent that you can assemble them yourself with one or two people. That would require stong materials, wear resistant coatings, high temperature resistance, high precision, and so forth of the same types used in normal car parts etc. In some cases getting to the stage where things can be hand assembled will require multiple materials bonded to the workpeice though. However it eliminates the need to print to 8 micron resolution to do the gaps between bearings. May allow gaps between parts large enough to get a milling bit in there so a hybrid multimaterial approach could work. Parts could be removed and polished solving the polishing problem. Still have temperature incompatibility problem though except that metal parts could be made elsewhere and then lowered in, allowing sliding surfaces, or heated lightly to bond the plastic... but there would still be some situations where you want plastic underneath a metal or ceramic material and the metal or ceramic material cannot simply be lowered onto the plastic surface because of the geometry. To solve this basically there just has to be a way to get the plastic under the metal after the metal is in place.
    • to solve temperature incompatibility you could print thin sections of the object and then weld them together ultrasonicaly but that would never work very well probbably due to the weld quality being too low? Maybe it could work. The main reason you can print a very thin section even when there is metal that goes over plastic while also metal that goes under it (so you can't just print it upside down although I suppose you could print the high temperature part, then turn it upside down... that limits the size to thickness ratio though) in other areas, is the difficulty of depositing and machining a surface that is far from the upper print plane, just because you can't reach in there and maybe because if you had a ledge say or wanted to print a plate of metal at a slant it might be hard to print it withouth something for the slant to be built on top of. i.e can you build a metal plate or wall or shaft at a slant when it is only surrounded by gas? yes, this is often doen in larger scale FFF systems, presumably the physics of the melt pool allows it.
      • Comes down to being able to control the tilt, and to what angles. Saw one alticle ("welding discovery"one) that involved FFF using a welding ( cold dip welding I think, definitely cold something although it is not actually cold just particularly small melt pool) that trumpeted being able to print horizontal ledges without supports even. Probably just a matter of how close the bead is to the edge or even on the edge, you can make it so there is atiny lip of metal over the edge, or the bead of metal added does not go quite to the edge, allowing control over the rise to run. If using powder layed on the surface ahead of time a lip might still be done by melting to allow some flow to the area where you want a lip. Melt the edge of th elip, and a bit flows there from elsewhere in the melt pool, leaving the surface of metal slightly lower than the interior of the wall, then move the melt pool one melt pool diameter into the object, so more metal flows from the interior towards the edge, repeat. could take some time, longer than printing a surface which tilts into the interior of the object.
      • a lot of this comes down to the possible width of a wall of material between two that are incompatible and higher temperature, divided by the distance (usually vertical but in the case of a metal ledge with plastic under it horizontal) needed to separate incompatible materials, due to the difficulty of depositing and removing materials from narrow crevices from above, and secondly from the side (in the case of the metal ledge with plastic under) especially when there is material very close to the entry of the crevice so you can't get anything even to the opening with a line of sight to where you wnat to deposit or remove material. The material that is located at the entry to the crevice could be deposited after rather than before obviously, except... it might be hard to reach the deposit tools in there, or the object to be built might require 2 crevices right close to each other in a plane that is too close - can't do both crevices in that case ever if you had a 5 axis mill an ddeposition head that can deposit and remove in deep crevices.
        • so solutions already discussed else where, polymers that break down to form materials that are still strong, interface materials (small melt pools help reduce quantity of heat that needs to be kept away by an insulating layer of interface material), methods to deposit ceramics and metals without high heat etc.


    • a hybrid printer which can deposit multimaterial net shaped objects within tolerances that were concluded as needed and described elsewhere on this page, of any geometry of the sort that are seen in existing economically important products, however the problem to begin with is the high difficulty that is being encountered with how to print such net shape parts, and also which are also already all assembled. So basically the purpose of the other equipment here is to overcome that difficulty by:
        • objects with wear resistant or antifriction or other coatings of choice
        • a way to do hardenin gof th esurface, spot hardening (maybe doable with lasers in situ).
      • a way to heat treat objects of choice, like a wrench or similar which you wan t to have the bulk of heat treated
    • software to plan and ideally execute the entire process for any object that can be made
        • includes deposition of plastic, and ceramics for surface coatings etc.
        • ideally it woudl be as close to finished shape as possible to simplify assembly as assembly can quickly get complex and often involves joining of parts which involves getting at the mating surfaces which is hard or impossible or requires adhesives etc that have serious limitations - parts that nedd to be joined should instead be formed as a single part.
  • thermal stress in plasma looks good http://utwired.engr.utexas.edu/lff/symposium/proceedingsArchive/pubs/Manuscripts/1993/1993-01-Amon.pdf Material Issues in Layered Forming
    • to reduce stresses withouth heating the whole part can heat just the surface where depositing material, it expands, deposit material, it and the deposited layer contract but because it was thermally expanded before deposition the final stress would be way lower, could use radiant nichrome or tungsten or induction or hot gas or a combo, plus large heat affected zone might help I guess actually since is basically preheatin the surface in fron tof an aroung the melt pool, might be useful for metal head or mult with only ceramic .

prototyping methods

  • more for cold deposition note for other readers: there are a lot of prototypical printing methods right now that are not in the prototypical methods section, which shoudl also be rounded up and put into the main comprehensive search page
    • http://www.mem.drexel.edu/zhou2/Portals/0/PDF/CLD-fanl.PDF says CVD is like .1 to 1 micron per minute extremely slow, very interesting method, deposit liquid droplet, boils and i ngas phase reactions occur, metals deposit on surface. Wit hright reactants can deposit wide range of alloys and metals (probably all the good ones?). Clearly the methods of depositing materials and so forth have a problem space that is not normally visible to laypeople. Who would have guessed at this method working?. Therefore it is important to get the message out there and try to get people who have deep expertise to think up ways to do it. But we can probably still use the comprehensive method to spur thinking and to map the space to a good degree. so add to the method of dtansfer to surface: in a chmeical which will be decomposed. An absolute is that th molecules or atoms have to get to the surface and be rearranged( either due to sheer force or they have to be in a state that can flow more easily than solid or plastic, like gas or plasma or liquid, so can still us the sates of matter for organization?).
    • http://utwired.engr.utexas.edu/lff/symposium/proceedingsArchive/pubs/Manuscripts/2009/2009-29-Goel.pdf. more on not very interesting electrochemical
    • http://creativemachines.cornell.edu/papers/AIAASpace2006_Malone.pdf. kind of interestin gbut limited to polymers etc apparently some low performance actuators etc. for making robots etc. in space
    • http://utwired.utexas.edu/lff/symposium/proceedingsArchive/pubs/Manuscripts/1998/1998-16-Cohen.pdf. interesting idea:' use electrodeposition but have a large electron beam device and CRT but the front ofhte CRT replaced with a large number of metal rods with ceramic in between, so you can fire the electron beam at any desired rod. Problem is the voltage of electron gun usually pretty high and want low voltage high current, but maybe manageable with carbon nanotube or other electron source that emits electrons at lower voltages or thermionic emission, especially since focus area can be big. Could also make it out of glas and use lasers or even less intense heat sources probably and use thermal decomposition with chemicals mentioned in the drexler doc
      • still have not been able to determine the strenght of materials deposited with chemical reactions and decomposition or electrochemically, seem to recall that in leectroplating there are a lot of issues with stresses in some materials. Maybe pressure coudl be pressureized and the stuff done unde high pressure? Up to 550 for water migh thelp relieve stress but very high pressure. Maybe other solvents that are better. Support materials for use with these methods can use metals that can be selectively dissolved compared with the other metals nearby, with suitable solvents available there is probably a range of suitable solvent-metal pairs to go with any desired material. , more knowledge of chemistry would obviously help here. Have never seen anything with metals being deposited out of solution yet, must be at least some solvents that coudl work nitric acid is a volatile liquid and might work for instance. Need to keep this sort of thing in mind to keep options open Could also use depositio nof aprecursor material like a metal oxide and then reduce it with hot h2 on each layer maybe but has to form strong materials of the chosen types also high temperature anyway. Proably other better combos of precursor and converter gas
    • for metal head or metal and plastics conceivably the whole build chamber could be heated to a very high temperature to greatly reduce thermal stresses as done in SLS, any components in the chamber that cvant be heated could be water cooled, but there is a random component to the shape changes that occur with cooling, so depends how big that is, if it is too big then would nto be able to make precise parts anyway.
  • basically add to microfactory section that what want is a microfactory ultimately. are trying to get it out of a single machine which is a printer, but Might make more sense to define requirements, exactly what want out of it in more detail than have, then look at a system that takes from whateveer approaches there are because while it looks reasonably hopeful and certainly deserves a lot more research and though, making aprecision printer is not strictly necessary and it might be a shorter and more reliable development project to come up with a microfactory approach
    • http://www.me.gatech.edu/Lackey/djsff1999.pdf. another on laser chemical vapor deposition, look interesting but watch the build rate
    • maybe use deposition from gas to fill in the porosity of a sintered material or something? probably not because as porosity was filled wold shut off gas flow. What about co spraying of a precursor with plasma spraying or em deposition leading to better bonding and reduced porosity for full strength?

prototyping methods

ADAPTIVE HIGH-PRECISION EXTERIOR, HIGH-SPEED INTERIOR, LAYERED MANUFACTURING masters thesis FDM though

Process Planning and Automation for Additive-Subtractive Solid Freeform Fabrication

potential problem: one of the documents that was about a sintering sytem ("necking" some ways from fully dense parts made maybe a thermal stress one?) mentioned the diffiulty of getting the powder to become fully dense but that must have been below the melting point? since electron beam seems to have no problems making full strength parts

powder deposition

http://www.google.ca/patents/download/6063194_Dry_powder_deposition_apparatus.pdf?id=AWYDAAAAEBAJ&output=pdf&sig=ACfU3U0N_25Cp5pkr41Flq3WEWaTrip0dA interesting powder dispensation mechanisms for controlled powder deposition


Over ten RT methods have been proposed, and examples are 3D Systems’ Keltool, DTM’s RapidSteel, CEMCOM’s Nickel Ceramic Composite (NCC) Tooling, Dynamic Tooling’s PolySteel, ExpressTool’s Electroforming, and Extrudehone’s PROMETAL (Ashley, 1998). Each approach comes with a unique set of limitations, yet each promises to reduce the time it takes to produce metal tooling. None of the new RT approaches offer the choice of material

ways to combine metal and plastic in a single part

  • ideas: injection molding to deposit plastic underneath the metal. Basically the temperature incompatibility problem comes down to not being able to print the metal on top of the plastic and you can't print the plastic under the metal after the metal is on because you can't reach. However if you printed the metal part, and made sure support material was printed in such a way so that when the plastic is injected it takes on the right form in any areas that are not already walled off by the metal... Suppose you want to print a car wheel with the tire (using a thermoplastic elastomer). You woudl print the metal hub and while ti is printed the support material is also layed down at the same time in a way so that the material fills the volume where there is not supposed to be any plastic inside the tire, there is a void in between it and another volume of support material with the tread pattern printed on. When the hub is completed you keep printing support material so that you are above the top level of where the tire is supposed to be, and a void is left which plastic can be injected into. Obviously there are problems, as the support material has to have pillars to support the hub and other stuff during printing, which would have to pass through the volume where the tire is supposed to be. You could inject the tire plastic, remove those pillars then inject more where they were but that gets more complicated, have to have access to the pillars do that etc. (well they coudl be dissolved if 2 different support materials were used , one which allows you to print a channel through which you can pump solvent capable of not dissolving the channel but dissolving the other support material)
    • The Shaped Brick ultrasonic welding method for doing intermaterial layer interfaces or even whole objects. The goal is to solve the thermal distortion problem, the temperature incompatibility problem and maybe even the polish problem. That pretty much mops up the lot and could lead to a very good printer if only the bonds are good and the blocks precisely shaped enough.

Consists of this: You have a very small robotic pick and place tool with a built in sonotrode. It picks up very small bricks and puts them down in the right place, then welds them there. You could either print the (relatively large) bricks themselves as you go along in whatever desired shape you want that section of the object to be. Or theoretically they could all be just 1 micron cubes to achieve the right resolution, but that might be difficult and result in very slow printing. You could have cubes of varying sizes to reduce the number of pick and place operations greatly.

Or, you coudl use shapes other than cubes that might be superior in some ways. To be able to print all the things we want to print using larger blocks, you could use an approach that uses a larger variety of block shapes (shaped blocks - maybe we should call them tidbits because block implies rectangular prism whereas the shapes of the blocks will likely be in a shape similar to a pineapple tidbit.), each of which are a lot larger than a micron: consider that the outline of the parts are the problem here, the bulk of the parts can have the material added through other means or quite large blocks since the resolution doesn't matter much because we have no reason to print objects less than a few millimeters across (features like gear teeth and maybe air channels, but not objects) and the precision does not matter much as long as there are not many gaps or voids. The thing with this is that there woudl always be some space between blocks unless they were rectangular? maybe not.

So, to determine the set of block shapes that are required, you would look at all the different curves that you want to be able to print in the object, both in the xy plane and the vertical planes. To illustrate that a range of curves much larger than the number of block shapes there are can be made let's start in 2 dimensions. Consider a disk of radius r with a hole in it (with radius r-x). Now cut the disk with hole into wedges of equal size and shape - divide it in half, then half those halves, etc. maybe 4 times or so. So now you have abunch of segments, blocks with that shape can be used to print a curve or a peice of a curve with radius of curvature r. If you want to print a curve with a larger radius then you increase the distance between each segment and fill (or rather almost fill because there would still be some small spaces) the intervening space with segments of similar shape but much smaller, or rectangular blocks. Obviously the surface is not perfect but it doesn't have to be, even for a bearing it can vary by like 8 microns or something as mentioned above. Basically use a range of block sizes and shapes to drastically reduce the number of blocks that need to be placed.

Obviously since the range of curves you might want to print has an upper an lower bound but would ideally be infinitely variable in between no set of blocks will fit together perfectly to print anything in the range, but I think the amount of plastic deformation that occurs with the welding may be enough get blocks that fit reasonably closely bonded nearly 100% together for an approximaiton of any radius in the range and secondly there are presumably block sets that are much beter fitting than the ones described above.

A computer program could be used to determine the optimum block shapes. You could define the different shapes you want, probably in terms of just a collection of radii of curvatures, or a range. Then specify the allowable deviation the outer surfaces produced by the blocks may have from the ideal forms, for various radii and for different types of variation - over larger or smaller scales basically. That could be done by defining the acceptably amplitude differences in a fourier transform outputs bands performed on the surface the assembled blocks can produce vs. the real shape. The thing is while rectangular blocks might work okay they have sharp corners, which produces surfaces where the deviations from the ideal shape are these 90 degree triangles which are good at piercing lubricant layers and getting corroded. It would be better to have shapes that can be assembled with only rounded edges on the outside perimeter I think....

Having a set of bricks might make brick production a whole lot faster and simpler because you coudl use molds or something. But in the end maybe printing a small block a millimeter on a side or something in the desired shape would be better to reduce the number of welding operations and interfaces and increase the size of the arm to a more manageable level, and maybe there are not blocks that can produce shapes much better than cubical blocks anyway... The blocks can be printed with DMLS or high precision FDM. You may only need to print the higher temperature blocks though, and put the pastic on the workpeice directly.



      • important point: the sides of the blocks can be given a wavy pattern that interlocks. With this the ultrasonic bond does not have to be 100% strength in order for the connection between the blocks to be 100%! Because the bond layer over most of the surface is not being pulled on perpendicularly when you try to pull the blocks appart, but at an angle, and there is a large bond area. This wavyness would also greatly reduce the positioning accuracy that the hand needs to be able to acheive to very practical levels because the blocks self align when pressed together.
      • if used for whole objects might be a tad slow
      • can't be done unless the welding is good and the blocks are precise enough to have acceptably little discontinuities in teh surfaces where they meet etc.
  • more research

. Thus, ultra thick (5-50 mm) coatings can be produced without adhesion failure. The high energy-low temperature formation of coating leads to a wrought-like microstructure with near theoretical density values http://www.asbindustries.com/documents/int_status_report.pdf. has information of strenght of materials deposited with cold spray looks quite good, more than 75% of the theoretical strengths, in some case yeild strengths are actually higher

prototyping methods

prototyp metgod http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JMSEFK000122000003000484000001&idtype=cvips&gifs=yes&ref=no Enhanced Aluminum Properties by Means of Precise Droplet Deposition dripping of aluminum for structural net shape parts

the part is removed, and the part is air cooled to room temperature. Bead blasting with silicon carbide, aluminum oxide or other appropriate blast media removes any powder clinging to the part surface. At this point, the as-processed part has a textured surface that resembles a sand casting. If http://utwired.utexas.edu/lff/symposium/proceedingsArchive/pubs/Manuscripts/2003/2003-53-Cormier.pdf notes cracking

can be achieved, which is necessary for avoiding self-equilibrating stress (how big?). http://edge.rit.edu/content/P10551/public/SFF/SFF%202006%20Proceedings/Manuscripts/42-Sigl.pdf.


also ch eck out the possibility of high preheat temperatures to reduce stress levelss

  • EB-PVD electron beam chemical vapor depositio n? electron-beam physical ~a-

pour deposition (EB-PVD) http://ftp.rta.nato.int/public/PubFullText/AGARD/R/AGARD-R-823/09chap09.pdf.


  • look into extremely high deposition rate cvd x
  • more on hybrid (subrtactive pplus additive)

then is much like the block printer thing that mentioned with '

    • http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.11.6376&rep=rep1&type=pdf. planning and automation of hybrid
    • http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.12.475&rep=rep1&type=pdf. another process planning thing
    • http://utwired.utexas.edu/lff/symposium/proceedingsArchive/pubs/Manuscripts/2002/2002-54-Mizukami.pdf. not fully dense so almost didn't add it here, but the sintering might stillbe useful for something and this one might get around thermal stresses, basically just pressing the powder on there and then milling, could be useful for other things, coudl be done upside down to application of powder or something too d
      • powder application idea esp for fine nanoscale powder: have powder bed that has been fluidized and then leveled and then dip the part in it, and dust off the excess, only what sticks to the part? might not be even. Could also apply the part compresing powder where want it, then turn the part upside down and remove the plate the powder was on. could bemade of teflon or be charged with very slight charge that is the same as the powder to reduce sticking. Could also maybe have holes i nthe base from which a support rods were removed (wherever desired), then all excess powder blown out of the areas where you do not want it, then an indiscriminate heating method could be used to sinter the powder, followed by machining (hybrid). Maybe even have the plate do the heating by conduction? Or to prevent powder from sticking to surfaces that have been machined, print a support layer material over them.
        • generalization of indiscriminate metal depostion plus subtractive plus coating the finished surfaces with a material to protect them from further material addition, coudl work with plasma spray, PVD, liquid and gas CVD, electrolytic maybe and other methods, basically relaxes requirements on the material deposition method precision but not on stresses or materials
    • http://www.springerlink.com/content/77223n514722640x/ looks good, try to find free oneRetrofitment of a CNC machine for hybrid layered manufacturing

K. P. Karunakaran, S. Suryakumar, Vishal Pushpa and Sreenathbabu Akula Subtractive manufacturing [computer numerical controlled (CNC) machining] has high quality geometric and material properties but is slow, costly, and infeasible in some cases. On the contrary additive manufacturing (rapid prototyping) has total automation but compromises quality. A hybrid layered manufacturing process presented in this study combines the best features of both these approaches. It uses arc weld deposition for building near-net shapes, which are subsequently finish machined. Time and cost savings of this process can be attributed to reduction in NC programming effort and elimination of rough machining. It is envisioned as a low cost retrofitment to any existing CNC machine for making metallic objects without disturbing its original functionalities. Near-net shape building and finish machining happening at the same station is the unique feature of this process. A customized software generates the NC program for near-net shape building. The intricate details of integrating arc welding unit with a CNC milling machine are presented in this paper. l

    • Shape Deposition Manufacturing With Microcasting: Processing, Thermal and Mechanical Issues

SDM combines microcasting with other intermediate processing operations, such as CNC machining and shot peening, to create high quality metal parts. http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JMSEFK000120000003000656000001&idtype=cvips&gifs=yes&ref=no looks good try to get copy

      • Parametric thermal analysis of a single molten metal droplet as applied

to layered manufacturing http://eprints.utp.edu.my/5882/1/Heat_%26_Masss_Transfer_Paper.pdf

prototyping methods

SDM

material removal technques, as well as other inter- mediate processing operations. In this approach, the growing parts are built on pallets which are trans- ferred to different processing station using a robotic palletizing system. (Figure 3). The two primary sta- tions are for deposition and shaping. Individual layer segments are first deposited as near-net shapes and then machined to net-shape with a 5-axis CNC mill before depositing more material. Layer segments are formed such that undercut features need not be machined, but formed by previously shaped seg- ments. A complete layer is therefore made up sever- al segments. Building shapes with selective deposition and shap- ing also permits multi-material structures to be formed. A multi-material deposition station includes thermal deposition apparatus including weld-based systems and thermal spraying. for making metal structures, and epoxy and wax apparatus for making plastic structures. In thermal deposition, internal residual stresses build up as each new layer is deposit- ed due to differential contraction and thermal gra- dients between the freshly deposited molten materi- al and the previously solidified layer. Individual lay-

(SDM) is introduced. The process is based on the concept of layered manufacturing in SFF, but uses separate deposition and shaping steps to create a layer. Three dimensionally shaped layers are created using 5-axis CNC machining, to achieve the required geometric accuracy for fully functional shapes. Thermal deposition technologies (thermal spraying, welding) are used to achieve the required material properties. A novel, droplet based deposition process, microcasting, has been developed, to create well-bonded, high-strength material, while minimizing the heat input into previously shaped layers ers can be shot-peened at a peening station to con- trol the build up of stress. O

    • more on thermal stresses in SDM Thermal Stresses and Deposition Patterns in Layered

Manufacturing http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.11.9017&rep=rep1&type=pdf

  • there are probably other ways to relieve stress in the surface layers, what speed do the shot in shot peening move at, maybe a rotating set of balls on cables would be good but without getting shot everywhere.

electron beam

accuracy of±0.3 mm.

powder by electron beam selective melting prettyg good http://pep.metapress.com/index/LHJ44U88364N2868.pdf

    • if the surface finish is only as good as cast what exactly is the point? might as well just build the cast and fill it, no stress good metallurgy. Dimension variations are a lot better than 0.3 mm, see investiment casting process. But we want machined parts, and in order to machine any area you have to be able to reach it. That is the main benefit of building the metal part layer by layer, you can reach the areas in a much wider range of geometries, plus the machine tool may not need as many axis. Supposedly machine tools are uber hard to operate compared to layered mfrging but that sounds like bullshit, unless you wanted special tolerances or something.
    • if fast scanning reduces thermal stress then line processing or high speed array deposition with welding shoudl be good.
  • idea to reduce stresses in deposited layer when using powder, just don't deposit it sequentially, just deposit in an array of dots, with them becomming joined? Could really help? not seeing why it might help but then the different patterns for the scan patters shoudl not make much difference either so maybe it would anyway
  • need more info on how predictable the dimensional changes are when cooling from a high temperature, if the random component is too high then machining must be done at low temperatures.
  • important: when the liquid chemical deposition freeform fabricatiion people say the build rate is 1 micron per minute they might actually mean for the part as a whole, though probably not as that would not really make any sense if it is point deposition they mean. Even 1 micron per minute is enough to fill in sintered objects though, and there are ways to increase the deposition rate probably, plus it can be very high for some precursor and deposition combos (many hundreds microns) if that material is useful then could be useful I guess for something though is far from the gold medal.
  • cold spray followed by induction heating to return dictility wihtouth melting could provide low stress metal deposition of high strength for imprecise deposition (and maybe precise)

laser sintering

  • also search for ways to improve surface finish with laser sintering /melting
  • some stuff on shrunken small scale or high precision sintering (not always fully dense though):
    • maybe search for a sort of micro LENS process to do the outline of bulk mettal parts
    • In early 2003 Laserinstitut Mittelsachsen e.V.

announced a newly developed modification of SLS – mean-while referred to as “laser micro sintering” - that shifted the resolution of selective laser sintering below the limits commercial SLS devices had been confined to [1,2]. looks like they were using 1 micron or submicron powders accrodign to http://www.laser.hs-mittweida.de/3_forschung/21_mikrosintern/9_ver%F6ffentlichung/Advancements.pdf. (that doc describes 10 mcron powders though

FABRICATION WITH LASERS not clear what they mean by potential they seem to mean speed

LI Baoming(Shanghai University,Shanghai,China)QIU Fusheng LI Dichen LU Bingheng Three-Dimensional micro machinery is made be means of the technology of direct laser sintering of metal powers. Based on our sintering experience, the advantages and disadvantages of sintering process with different kinds of lasers are analyzed, and the influence of various technical parameters,including the power density of the laser, the scanning speed, the distance away from the focus ,on the sintering precision are summarized. The SEM micrographs of some sintering swatches and the integration of multi-materials are presented.The propose of making micron-scale three-dimensional machinery by electronic jet sintering of submicron powders is also put forward. thteresting cant get copy though

electron beam

  • for ebeam printing, what is the degree to which the beam diverges at various atmospheric pressures? Because the spot size is about a millimeter anyway. Also this approach MetalicaRap is taking doesn't look that promising as it will be hard(why?) to get the dimensional accuracy desired though maybe, there would be a lot of vaporizing to do. If it could be done under air then EDM would probably be a lot easier. Also cameras instead of an electron microscope for dimensional feedback during machining, though that is not strictly needed as normal EDM machines do not have it, they have other ways of compensating for electrode wear could also. Maybe could use moving wire, why not done? maybe other methods(what?) are more precise
  • mention to other readers the issue with diode lasers is the brightness maybe, but the laser in a dvd is focused to a diffraction limited spot size though, what brightness can the 1W IR diode lasers get? CO2 laser is already known though to work with DMLS like processes though IIRC.
  • for ebm might be able to get better accuracy if not in a powder bed per se. Also semi bonded powder makes good support material according to other sources. Submicron powder might be hard to use with EBM due to the physical forces involved. Maybe microfibers of metal though. not pack very densely probbaly, but could be formed in to a mat of uniform thickness! That's good. the paper just goes on and melt in the right places then that's it. solves powder dispersion. Could be a foil too maybe actually come to think of it. Surface wetting is annoying but as long as it is predicatble it can be compensated for . Or a sintered sheet from particles maybe

for the machined plate one electron beam welding in keyhole mode could be used to bong the sheets together but woudl damage the interface machining

  • search "microsintering"
  • so at this point it looks like if you could solve these problems, that would be clearing away the main barriers to precise full strength multimaterial or metal printing:
    • Thermal stress when depositing bulk material, could allow precision hybrid metal printer (withouth solving the machining the bottom of some or most leaders thing though, could be potentially be soled with other mthods mentioned elsewhere on this page though)
      • Cold deposition of at least some sort? for metals and ceramics onto plastics they are deposited on.
      • see the thermal stress reduction stuff on the metal deposition head page
    • surface finish problem, but thermal stress/distortion problem has to be solved first really, could lead to good bearings. Is not needed for serviceable bearings though as existing processes like LENS acheive enough surface finish just by melting the surface and allowing it to set, so we could too probably in most cases that involve surface melting or CVD, or in hybrid the mill leaves good enough finish to be serviceable.
    • ability to deposit metal and preferrably ceramics on top of plastics, ideally materials of your choice but the could be just a couple of select ones, and elastomer, a tough metal, a tough ceramic like silicon carbide and then a high performance plastic like PEEK or some high temp polyamides or something
    • control of bonding between layers maybe would be nice but ultimately any parts that are meant to not be bonded are usually meant to move past each other which means they are pretty much bearings (without load maybe not technically the same but there is always some load probably).


Chapter 4 proposes a molecular assembly line based on wavelength selective 9 Page 10 Introduction: Overview photocleavage of carbonyl compounds

    • electrostatic acceleration of nanoparticles? nano because they have higher charge to mass ratio at a give voltage
    • 5746844 patent is droplet deposition so like microcasting but with an annealing thing apparently, check how long it says it takes to anneal
    • idea: the machined layers thing with double sided machining, idea could be used for multimaterial too, make the layer with the high temp materials on top and then bond together. Problem is bonding together, alignment of the layers (can be solved with alignment pegs though) and there are still limits on the nature of the layers, if the layer thickness needdd to get the desired features with this apporach are too thin then they could not be handled. If the object is layered in the x and y axis too then it becomes the block building method that I mentioned basically.

pattern language

  • would realy need to know exactly what are going to make maybe lookup pattern language of industrial machines or something so can extend the listing above so it is closer to complete

reducing internal stress

  • other ideas for metal deposition, even if cant deposit any metal alloy desired, mostly to either deposit a stress free material or to at least do it cold?
    • infiltrate sintered objects, the ability to produce accurate sintered forms is already proven, there are methods aready discribed electrochemical and liquid and electroless plating (deposit form solution) methods, maybe gas phase methods CVD could be used as althought e surface growth rate is slow that is okay because massive surface area involved,
      • sinve the precursor has to flow in there the metal has to be deposited in such a way that it does not block precursor untill nearly full density is reached
      • may e could get good surface plish too with these methods
      • could be relatively low temp?
      • maybe coudl use something like elctron beam building (that one with SEM taht was super slow) or ion beam building but with the ions penetrating the bulk of the sinterd object so they induce pladint throughout the bulk of the object, one problem is that there woudl be more plating on the surface which might be a problem
      • wha tabout Xrays or other penetrating radiation? ANything that will ionize gas or send electrons spraying around should work for the cvd methodso that may well work! the ionizing radiation might interfere with plastics etc in multimaterial but in metal only printing could be good
      • could leave channels in the part to get gas or liquid to flow through there, maybe even inject it into the center of the part or suck it out from there
      • is probably some docs about CVD being used to infiltrate sintered objects
      • could use PVD plasma, sputtering, any of those ones, or evaporative deposition, lots of options there from the microfabrication(mems) industry and semiconductor industry
    • look into vacuum deposition atomically again, can deposit something stress free with sputtering or evaporative deposition? Basically get the stuff over there as individual atoms,
    • look into ion bem plating again with firing metal and other ions at a surface, another atomic depo method
    • what about using dpray deposition at velocities enough or something sothat the impact produces enough compressive stress in the layer below that it counteracts the tensile stress that was produced due to thermal deposition? Maybe use large particles that would do the stres relief mixed in with the smaller particles, have to get the small particles under the other ones, or maybe they could flow there plastically, might need multi axis spraying so the particles end up with enough small particles under it? or fire it hard enough that a sphere would embed at least halfway so only the hole it leaves behind needs to be filled in.
      • firing metal or ceramic particles or rods into the surface of the metal maybe another way to releive stress in the metal layer?
    • think I said before EM pulsees and lenz/s law could be just like a shot peen hammer but more easily controllable and stuff?
    • even higher velocities with an EM pulse gun? what happens at ultra high velocities?
    • Ionizing radiation and neutrons probably has no effect? Neutrons coudl be embedded but migth make stuff radioactive, maybe to a manageable degree though.
    • proton beam again ion beam basically
    • what woudl very high voltage electrons do? Could produce a region that was strongly charged breifly so enough force to force the material appart a bit?
    • What would very low temperatures do? Crack it probably so no help, unless the cracks were filled in again with material but woudl probably be too numerous and small
    • fundamentally have to increase the density of atoms in the layer in order to releive stress. Annealing does it by plastic flow/creep, ion beams by embedding ions, shot peening by compression etc., they want to hav their density increased so may be a lot of ways to do it
    • what if could deposit the metal in a supercooled state, before it crystallizes? probably not doable though
      • what happens if metal is cooled extremely fast? still shrinks as much as ever I think, there was one paper abstract in the stress relief area ( amd coming back and adding this during editing) that mentions cooling the metal fast enough that it stays in it's high temperature state but that may not be what they mean as it was senodn language english japanese paper.
    • could heat and cool the powder so fast there is no time for it to expand to begin with, but then maybe not enough time for a bond to form
      • in other words have it compressed during a melting step to depposit it, compressed by it's own inertia in thi scase. probably not practical to compress it in some other way, but e.g. hold the nozzle against the surface real hard like a diamond pressure cell and deposit some liquid metal under those conditions, the compressive strength of the metal is lower when it is hot presumably (check) so it might be possible to do so without causing any permanent stress in the metal layer below. Obvious problem is impracticality of depositing a layer of metal in that way for various reasons like sealing the pressure cell against the previous deposit.
    • the em thing looks the most interesting, could be used with microcasting like process, for each drop of metal you would give it a whack with the EM hammer so to speak, doesn't have to be an EM hammer though actually a physical one might do to, but EM is probably more convenient as the whack strenght and timing can be precisely controlledand the depth below the surface at which the force is exerted could also be controlled to some degree perhaps through varying pulse shape. Has to not heat the substrate up again too much though at least not to melting point. Could have an array of such hammers.
      • actually I wonder if it might be possible to do surface shaping with an array of such hammers... might be lower force method than milling when only a little bit of shaping needed? probably not very useful but see if it exists
      • search for methods to relieve stress in deposited layers right after deposition
    • with the machined then bonded layer thing theoretically with thin enough layers you could still do any shape withing the 2d limits of the mill (unless it had feature sizes or precisions you can't do). What sort of features are there that oculd not be done with reasonably thick plates? Ultimately in normal manufacturing there are a large variety fo different ways of making stuff so it might not be a good idea to assume that can make most of the stuff using any given method without a reasonably detailed and completish view of what needs to be made. However that is not practically doable for this project so have to make do with deciding what stuff we want at least as completely as can, and that is important to do in enough detail, more than has been done in order to ensure that the results of the project are highly meaningful and relevant. Can be used for other full strenght material printers too.
  • more on sintering or diffusion bonding as an intermediate step:
    • have not yet ben able to find any examples of precise laser melting/sinterng to full density or anywhere near.
    • sintered powder or fiber mats might be used instead of a powder layer to transfer material to the surface, and has many advantages:
      • the piston in a cylinder thing used for laser sintering probably has issues with friction between the powder and the edge of the piston distorting the powder layer there. With sintered mats you don't need a piston, just stack the mats up.
      • it could be relatively easy to remove a single layer of powder which may be valuable esp. for multimaterial printing, or at least handy as the mats protrude above the powder level.
        • not if themats stick together too much though so maybe not
        • a device to pick up single layers under vacuum could be made with small fingers, protruding at an angle from a surface and which can be retracted. Press the surface against the mat and extend the fingers, then they stick into the powder mat so ti ccan be lifted. Under an atmosphere obviously a vacuum pickup tool would be easier.
        • it might be desirable to remove some fo the powder around the edges of the part surfaces to get at them for remelting to improve accuracy or surface finish, or even to machine them.
      • could maybe even be done upside down which might be useful if eg. shot peening were done the shot would fall down away from the work area maybe bt more likely it sould get imbedded in th mat layers though... if machining were used the chips would fall away from the workpeice better, under a vacuum blowing them away not practical so might be useful
      • the method to level the powder bed in laser sintering entials some forces on the sintered parts, including leaders, but that has appartently been solved though with slihtly sintering the surrounding powder so maybe not
      • could reduce the ongiong problems with powder shifting around during printing especially with ebeam (magnetic and electrostatic forces see document above on transient physical effects), when the bed is wetted by the bead for instance, which would reduce the variations in the bead width which would reduce the random errors in th esurface,
        • may allow much thinner layer thickness and smaller powders for electron beam printing due to overcoming the physical forces which could increase precision a great deal
      • very reliable layer thickness coudl be achieved
    • could also put powder down, then laser sinter with a low power diode laser as described in the docs above laser diodes can be adequate for sintering, and secondly we already know that sintering can be highly precise as shown by the microsintering papers.
      • after the powder was sintered in the right places the other powder could be blown away or otherwise removed, with the roller type powder levelling method normally used after for the next print layer
      • also works as a support structure, but th eareas supported by the powder would be poor surface finissh and have to be sintered, cant be fully melted because it woudl probbaly melt the support too. So that could be a problem... However the object being printed could, through a powder removal step protrude above the surroundign powder bed and so have smooth sides without any powder stuck to them or powder getting wetted in from the sides.
      • The heating step could then be relatively imprecise and still get good precision in the end.
    • maybe not related to this per se, but what about turnign the object being printed upside down, dipping it in a shallow pan of powder, and then pick it up and vibrating it to get almost all the powder off but with a thin layer sticking to it, then doing the EBM. The powder particles would have been pressed against the surface during the application, so they might not be susceptibel to columb forces since they would be better grounded.
    • with hybrid microcasting machine what sort of unpredictable change would there be due to thermal fluctuations with varisou amounts of prcomputation using finite element analysis or other simulation approaches
    • nother form of microcasting, print a layer of cast, put metal in, machine away whatever you need to of the cast layer so yo ucan get at and machine the surface of the metal layer, then print cast material back onto the surface of the area that has been machined, plus up into the next print layer, machine the cast material again (might require dipping into the previous layer a bit) and repeat.
      • maybe if coudl deposit the casting material resonably precisely you could do without machining it, but you still have to remove any of the cast material that spread out over the surface where it was not supposed to be if it does.
      • still needs suitable cast material the is temp resistant, thermal expanision similar to the metal, and easily removed at the end of printing, and preferrably strong enough to ac tas support matieral too although another support material could be used too which was stronger or more rigid, with just a protective insulating layer of cast material on top of it.
      • the problem of the machining area being close to the high temperature deposition zone is probably worse with this method, than with just printing up the near net shape of the metal part and then machining below the deposition layer since it woudl be directly under it. A combo approach with the machining plane well below the deposition plane could be done and might save the day if the metal deposition method had problems with printing free vertical faces or something but don't think it would, welding or microcasting should be fine, the metal cools pretty fast and is fairly viscous so would not run down edges anyway. A combo approach might require entail thatmore casting material be added and then machined away at each step, if it at each print layer round (like per metal layer deposited) it filled in the void that the mill needed to clear away to reach the machining layer. Maybe the casting material could be viscous engouh that it doesn't too that, depends on the size of the void the mill needs, which could be pretty big .
      • might still want 5 axis machining so that the tips of millning bits can be used for tight radius of curvature areas like a sharp inner corner
      • with hybrid microcasting, the deposition of the mechanical suppor tmatieral to brace against milling forces would need to be deposited basically in the machining layer, so the deposition mechanism shoudl eb able to reach wherever the mill can but that's probably not a big problem, coudl be an FDM sort of deal or something, the deposition tool coudl be a tool for the milling thing maybe somehow maybe less practical than dedicated tool, could use the axis of the milling machine, rotatle it 180 an dget the FDM tool instead of the milling bit, FDM tool would stick out in the direction opposite to the milliing bit, or actually having it on the ame rotating peice but rotated at an axis ofset from the milling bit might be better. so basically 5 axis milling device with different tools, one of which is the millng head and another the other the fdm head and maybe another for the metal depot ead
      • if can't mill hte bottom of some part then couldn't mill it with normal milling anyway so might be relatively unlikely that need it.
      • can print various rigs etc with a hybrid machine that can make use of a hybrid machine in other ways, so e.g. if wnated to print a bearing ball coudl make a device that holds and turns the rough ball as it is being machined by the mill. Move the ball 180 degrees along the right axis so yo ucan mill hte place where the holder thing was attached or clamped on, mill and then you have a ball that is machined to nearly the percision which the mill can do.
    • many printers are scalable, have a larger faster one for rougher work, then attach the smaller one to the xyz gantry and bring it in to do smaller or more precise areas of the object being built, with it bracing against the object itself. The absolute coordinates within the build could be determined with optical sensors of some type detecting the location of the small printer to get high absolute location accuracy for the print head of the second printer, but you would not usually need much anyway. Probably not needed. And of course they can be used in lines or arrays too as mentioned on the comprehensive search page.
    • could use electron beam printing instead of microcasting to avoid stress in metal layer if EM or other peening turns out not to be practical since already know it works at least serviceably, could be combined with peening or something too, could use the powder sintered or even fully built as the support material, just have a second support material that can be added on top of the metal support for insulation and to avoid sticking, then machine the top of that material layer, then deposit metal onto it. Suggest this to the metallicarap people, and also maybe that the SEM should be mounted not on the gantry but on the ceiling so ot speak, electrons that backscatter from the side walls probably pretty small amount, and secondly they could be sheilded from the photosensors with a shroud that moves with servos so it only allows veiwing of the area you want to image. Could also make a good scanner except there are a lot of areas that would be blocked from veiw.
      • MetalicaRap has the same problem of not being able to machine the undersides of leaders or ledges that are too steep or flat bottomed, unless you accept a staircase profile which could be acceptable I guess actually if the layers were mere microns thick.
      • the slightly sintered powder bed could be ground up again after to reuse the material
      • also point out to MetalicaRap people the importance of checking if the electron gun can operate acceptably with a plasma window or a micron sized hole type thing remember that effect that the gas cannot move faster than the speed of sound anyway through sucha hole and calculate the requierments of the vacuum pump to use this basic method remember only the beam generatin gpart has to be under high vacuum, not the deflector coils. Could make thigs a great deal cheaper and easier to make all things considered because the vacuum chamber does not ned to be high vacuum anymore only low or even atmospheric. Ulitmately the electron gun can be brought close to the surface although it is pretty big. The melting in a normal EBM is all bulk low resolution anyway, so precision is not a concern, though scanning rate is....coudl use the rotating thing like for the lasers
        • for the electron melting thing the 1m/s thing is probably about righ tactually since the power needed to weld is in the range for that and no more really , so tig wor another welding method could aveive that traversal speed easily especially with dual arc and so get the low stress, also can handle the preheat temps no prob
        • would really be a better idea to make a mini one first as there are a lot of issues and uncertainties and the cost is just too high for the big one
        • need to check again why exactly the EBM can deposit relatively low stress layers, is it the preheat temperature of the bed or the scan speed that is the fundamental difference? Because the high preheat temp could be done with DMLS and other methods too is probably the high scan speed but need to knwo for sure
        • look into atmospheric eletron beam welding and see if there are metallurgical issues due to embeddin ions or the ionization of nearby argon and it doing somthin gto the metal, probably not though
        • if nothing else could connect the oil diffusino pump to the electron gun so that ougassing of stuff was a lot less of a problem, might be able to do 10^-3 torr for instance, calclulate to see if that is so, the oil diffusion pump along the micron wide hole (laser drilled should be cheap) not after it, maybe use diverter like thing similar to the one way aerodynamic valve wannabe thing tesla invented - what sort of pumping for what sort of differential pressure isneeded, and what sort ofp pressure in the print chamber would be causecx by using normal equipment like servos cameras etc?
      • maybe the mat thing can be used for the water soluble support material deposition probably no point can use fdm etc
      • powder layer is not critical with the subtractive capability so maybe eliminate the piston and the other stuff for special powder and just spray or fling the powder, the powder coluld be kept in place by sintering the walls around the powder bed too or maybe all of the powder could be lightly sintered, and then ground up after for reuse? grinding would change it's properties a bit but again the process here is just bulk metal layer deposition, so precision not important anyway just have to make surre things like th ebead breaking up don't happen as they did in that paper with the water powder
      • maybe the second, high temperature resistant but low temperature deposition material can be dispensed with by using sintered powder instead of it. As long as the welding bead does not go through the sintered metal bed and the insulation qualities are reasonable (might have to go slow tih the printing), then after the first bit of the leader is printed, mill just a bit all the way under the leader, then deposit the primary support material with a nozzle in the hole left by the mill. Repeat all the way around the leader, then it is fairly well stuck to the material below. One problem is that the sintered powder has to support it against much movement during this process. Then, now that is is fixed in place go back and mill away the primary support material just left in some places and do the finish milling, all the while redepositing support material as soon as are done milling an area. Still some pretty severe limitations on the process though. Could print the upside down of a leader bottom and then machine it in place then release it somehow, turn it upside down and put it in place, which is like already said with producing the leader separately. There is still the problem of attaching the bit of the leader precisely in the right place so it is aligned with the rest of the part which is to be printed. For some leaders could print the whole hook and the rest of the object up to th eplane where it attaches to the main object, then machine alignment pins into the face of the main objec tand the leader, then weld them together with the metal deposition, or just allow the leader to rest in place in a machined out hollow of support material. Or maybe could do something similar but in a lower plane and then keep printing some, but do not mill the leader for a few print layers, and unlike usual print some support material around it as soon as you can due to the temperatues involved. When it has been printed up a bit, and is attached well enough by the support material, then mill away the material in one small area , do the final finish milling, then fill it back in with support material, and repeat all the way around.
        • another way might be to deliberately weld it to another gantry on the xyz system or a separate system, and hold it i nplace that way but then depositing powder might be a rpoblem.
        • might be something that could be used to glue it down to the hollow in the support material.
  • exactly what kind of forces are there in precision milling? a grinding bit might be better though poorer surface finish?
      • if electron beam printing can be done with mats and under atmosphere then could be converted into a free space deposition methods using a mat, moves in front of the egun, fresh mat is dispensed and presed against the surface, gun draws on the surface to consolidate. Or maybe cold spray method, anything that gets particles to stick to the surface of the metal in a cake of sorts so they can be welded on, has to be a layer or line not point deposition though so can get the high scan speeds.
      • could use shaped block building but with an encapsulation layer on the outside of the object and then isostatic pressure to consolidate might give better bonds, might cange shape a bit though. Also what bout ultrasonic uner vacuum? might improve bonding. Ultimately as mentioned the wavy surface thing can overcome imperfect bonds though, just a matter if ultrasonic wwelding wavy surfaces can work then.
  • remember seeing marketing material for probably dmls or maybe ebeam that advertied stress free parts with their remelting of previous beads, try googling again also low stress and stress relieved or reduced
  • if can heat the area directly below where put th e liquid and it expands as far as it can then would be no stress between the upper and immedidately lower layer theoretically maybe could so somethign like this inductive heating? Still have the problem of high themal gradients causing stresses elsewhere though, and/or also doing such preheating would entail dumping a large amount of energy into the object by conduction. Basically want to know what the maximum thermal gradient to not cause permanent deformation in the machining layer would be, and then deposit the preheat energy in a way to get just below that gradient, then deposit metal, and also keep gradient acceptable during cooling. Even with low gradients it coudl still cause distortion under some circumstances with some geometries though. Still it's all a compromise, something else could be done for those geometries.

for block production of rhte block thing could also press and ultraound powder works for metal to full density

    • to do preheating maybe could do large number of microcast droplets on the surface all at once or in a short time over a relatively large area, energy is then dumped effectively into the upper layer of the metal object to heat it before the solidification.
      • could just print support material around everything except the area and volume (print a wall up around it) which the metal is to be deposited in, then coudl deposit metal en mass in a single go, could eliminate the need for a dropper (microcasting) array in which the dropers can be contro;led individually, and be even better wrt the stress issue since the whole upper surface of the metal is heated at once during depostion, then since a whole plate of metal was depoisited mill around the areas of the part you want then remove the scrap plates and they can be recycled later, then mill away the support matierial to get at the miliing layer, maybe after cooling the whole thing down or at least for the final machining, actualy might wear the bit less to do rough machining while hot
        • could have the chmaber under pressure to speed cooling befor the machining, if it is helpful for precision to machine while cold, but cooling it before the machining step and the reheating it every deposition step migth cause problems
    • look into multi satge casting etc co casting find what it is called. Are doing something similar if you print a sort of mini cast (of thin thickness, only for that layer of the part, or even that layer of metal just as a thin rectangular block) on the metal part below and then pour the metal in, as menthioned above.


    • how do they do the reuseable casting material in investment casting? could make a good support material. has similar thermal expansion to the metals, can be reused apparently, probably sets as quickly as they can make it. Might not stick to the metal very well and might not be easy to remove though.


    • if the thickness of the deposited layer could be very small then maybe to get over the inability to machine some leaders in a hybrid machine (among the other methods mentioned such as printing the tip of the leader separately and then picking and placing it in the right area) you could use a micro DMLS like process, (which couldn't find evidence of anyone trying though) with very thin layers, printed on top of a support material or onto a support that consists of sintered material with the same powdered but only lightly sintered, can be weaker since no ned to stand the milling forces I guess.
  • maybe think of tools that can be used manually and how you would make the objeccts in the desired object list using manual methods with a very small number of tools or something, and if those methods coudl be automated or not

A method and apparatus for the accurate formation of a three-dimensional article comprises providing a supply of substantially uniform size droplets of a desired material wherein each droplet has a positive or negative charge. The supply of droplets is focused or aligned into a narrow stream by passing the droplets through or adjacent an alignment means which repels each droplet toward an axis extending through the alignment means. The droplets are deposited in a predetermined pattern at a predetermined rate onto a target to form the three-dimensional article without the use of a mold of the shape of the three-dimensional article. A means for reducing stress anneals portions of the deposited droplets which form a newly formed surface of the three-dimensional article.

METAL DEPOSITION PROCESS

powder
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