Concept multimaterial laser printer

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.

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 hinking 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, probably without galvo mirrors for now. 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. The resolution is determined 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)